16 September, 2016

Venue Silver Jubilee Hall

S. N. Bose National Centre for Basic Sciences, Kolkata

YOUNG SCIENTIST’S COLLOQUIUM YSC 2016

ABSTRACT BOOKLET

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ORAL PRESENTATION

Sl. Title / Speaker / Affiliation Page No.

01

Determination of the electronic structure of the elusive metastable state in chemically exfoliated MoS2 layers Banabir Pal, Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru

5

02 Robust local and nonlocal transport in the topological Kondo insulator SmB6 in the presence of a high magnetic field. Sangram Biswas, Department of Physics, Indian Institute of Science, Bangalore

6

03

Colloidal CsPbX3 Perovskite Nanocrystals: Excellent Luminescence and Photovoltaic Cell Abhishek Swarnkar, Department of Chemistry, Indian Institute of Science Education and Research (IISER) Pune

6

04

Influence of measurement protocol on the magnetocaloric properties in Mn-Ni-Sn-Si off-stoichiometric Heusler alloy Arup Ghosh Department of Physics, Indian Institute of Science Education and Research, Pune

7

05

Magnetic and magnetocaloric properties of rare earth intermetallic compounds RCoNi (R = Gd, Tb, Dy and Ho) and HoCo2-xNix (0 ≤ x ≤ 2) Rajib Mondal, Department of Physics, Indian Institute of Technology Madras, Chennai

9

06 High Performance Supercapacitor Device based on Polyaniline Nanostructures Sanjoy Mondal, Polymer Science Unit, Indian Association for the Cultivation of Science, Jadavpur, Kolkata

10

07

Charge and Energy Transfer Dynamics of Chlorophyll-a reinforced nanohybrid Materials Debmallya Das, Dept. of Metallurgical and Material Engineering, Jadavpur University, Kolkata

11

08

Cooperative J-aggregation and impact on photophysical properties and excited state dynamics of core- substituted naphthalene diimides (cNDI) Haridas Kar, Polymer Science Unit, Indian Association for the Cultivation of Science, Kolkata

13

09

Synthesis of n-type and p-type doped carbon dots: Their influence on electron/hole transfer process Monoj Kumar Barman, Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata

13

10

Supramolecular Assembly of Organic Luminogens into One-dimensional Structure at Air-water Interface Subrata Maji, Centre for advanced materials (CAM), Indian Association for the Cultivation of Science, Kolkata

14

11 Design of Nanoprobe for the Imaging of Mitochondria and Golgi apparatus Atanu Chakraborty, Centre for Advanced Materials, Indian Association for the Cultivation of Science, Kolkata

15

12

Extremely robust zirconia based superhydrophobic coating on cotton fabrics for diverse applications Indranee Das, Nano-Structured Materials Division, CSIR-Central Glass and Ceramic Research Institute, Kolkata

16

13 Synthesis of nanotubes from bio-waste Eichhornia Crassipes: A novel approach to develop oxygen separation membrane Quazi Arif Islam, CSIR-Central Glass and Ceramic Research Institute, Kolkata

18

14 Big Atoms and their Compounds Rekha Mahadevu, Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore

19

15 Evaluation of Semi-metallic Fe3O4 Nanocavities using Terahertz Waves R. Rakshit, Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Kolkata

20

16 Single molecule DNA sequencing using graphene nanopore device Sourav Kundu, Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Kolkata

21

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POSTER PRESENTATION

SL. Title / Presenter / Affiliation Page No.

P1

Spin-orbital liquid state assisted by singlet-triplet excitation in J = 0 ground state of Ba3ZnIr2O9 Abhishek Nag Department of Material Science, Indian Association for the Cultivation of Sciences, Kolkata

22

P2

Synthesis and biocompatibility study of nano crystalline hydroxyapatite from Mercenaria clam shells Anindya Pal Indian Institute of Engineering Science and Technology, Shibpur, Howrah

24

P3

The Structural Properties Based On WO3/SiO2/p-Si Sensing Element and the Effects of Annealing Temperatures Anup Dey Jadavpur University, Kolkata

26

P4

Nano-heterostructures: Interface as a Quantum Device Arup Chakraborty Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata

27

P5 Multiferroic studies on geometrically frustrated “114” cobaltites C. Dhanasekhar Department of Physics, Indian Institute of Technology, Kharagpur

30

P6

Electrochemical Behavior and Mechanical Integrity of Few Layers Graphene upon Lithiation / Delithiation Farjana J. Sonia Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology (IIT) Bombay

31

P7

Composite of Colloidal Graphene - Titanium nitride Nanocrystals for Plasmonic, Electrical conductivity and Elctrocatalytic Applications G. Shiva Shanker Department of Chemistry, IISER - Pune

32

P8 Observation of transient superconductivity at LaAlO3/SrTiO3 interface Gopi Nath Daptary Department of Physics, Indian Institute of Science, Bangalore

33

P9 Colloidal, Ligand-free semiconductor nanocrystals for optoelectronics Metikoti Jagadeeswararao Department of Chemistry, IISER-Pune

34

P10

Strength-toughness optimization by incorporating functionalized metal oxides within jute polyester composites Jaideep Adhikari Indian Institute of Engineering Science and

34

P11

Theoretical and experimental investigations on surface plasmon resonance assisted interferometric fringe modulation under both radial and lateral shearing environment with application in sensing Jayeta Banerjee University of Calcutta, Kolkata

36

P12

Defect mediated n-type behaviour of unintentionally doped ZnO nanorods: correlating defects, emission spectra, morphology and conductivity K. Bandopadhyay Indian Institute of Science Education and Research, Thiruvananthapuram

38

P13

Tuning of Edge and Surface Energy of TiO2 Nanotubes via Partial Rupture by Controlling Anodization Voltage for Gas Sensor Device Applications Koushik Dutta Indian Institute of Engineering Science and Technology, Shibpur, Howrah

40

P14

Functionalized Nanocomposite Cathode to Enhance the Stability of Solid Oxide Fuel Cell Performance Koyel Banerjee (Ghosh) CSIR-Central Glass and Ceramic Research Institute, Kolkata

42

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P15

A study of inorganic metal halide perovskites and their application in opto-electronic devices Lekha Peedikakkandy Centre for Research in Nanotechnology and Science, IIT Bombay

44

P16

Low field magnetoresistance of polycrystalline Gadolinium for different spatial dimensions (Bulk, Film and Nanowire) Manotosh Chakravorty S. N. Bose National Centre for Basic Sciences, Kolkata

45

P17

Visible Light Activity and Thermoelectric Performance of Aluminium Doped Zinc Oxide / Polyaniline (AZP) Hybrid Mousumi Mitra Department of Physics, Indian Institute of Engineering Science and Technology, Shibpur, Howrah

46

P18

First-principles Design of 2D Nanostructures for Efficient Storage of Hydrogen and Fuel Cell Catalysis Paramita Banerjee Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata

48

P19 Artificial Leaf as Future Energy Harvesting Tool Priyam Mitra Dept. of Chemical Engineering, Haldia Institute of Technology, Purba Medinipur

50

P20

Protein induced structural modulation in phospholipid model membranes: An x-ray scattering study R P Giri Saha Institute of Nuclear Physics, Kolkata

51

P21 Pd/RGO/TiO2 Nanotube Ternary Hybrid Structure as a Novel Gas Sensor Device Sanghamitra Ghosal Indian Institute of Engineering Science and Technology, Howrah

53

P22 Reduced Band-gap Ferroelectric Materials for Photovoltaic Application Shyamashis Das Indian Institute of Science, Bangalore

55

P23

Photo-voltaic and catalytic Performance of Anatase TiO2 Nanocubes with Coexposed {101} and {001} facets Soumita Mukhopadhyay CSIR-Central Glass and Ceramic Research Institute, Kolkata

56

P24 Low Threshold Quantum Dot Lasers Veena Hariharan Iyer Indian Institute of Science, Bangalore

57

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Determination of the electronic structure of the elusive metastable state in chemically exfoliated MoS2 layers

Banabir Pal,1 Anjali Singh,2 Sharada. G,1 Pratibha Mahale,1 Abhinav Kumar,1 S. Thirupathaiah,1 H.

Sezen,3 M. Amati,3 Luca Gregoratti,3 Umesh V. Waghmare,2 and D. D. Sarma1*

1 Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru 560012, India

2 Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru 560064, India

3 Elettra - Sincrotrone Trieste S.C.p.A., SS14 - km 163,5 in AREA Science Park, 34149 Basovizza, Trieste, Italy

Abstract: 2D transition metal di-chalcogenides have emerged as promising platform in the field of electronic switching1 and optoelectronics2 with several intriguing properties and potential applicability, as an alternative to graphene. Specifically, Molybdenum di-sulphide (MoS2), due to its finite bandgap and excellent electrostatic gate coupling properties in lower dimensions, is undoubtedly the preeminent member in the metal chalcogenides family, for applications in the field of transparent and flexible electronics.3-5

While most of these properties are related to the major crystallographic hexagonal 2H phase of MoS2, it is well known that MoS2 exhibits a number of polymorphic forms6,7. Other polymorphic forms of MoS2, variously denoted as 1T, 1T (2a×a superstructure) and 1T (a×a superstructure), are all characterized by a trigonal distortion of the hexagonal structure of the 2H form. All these metastable phases can be kinetically stabilized as small patches embedded in the majority hexagonal 2H MoS2 phase in chemically exfoliated system which is an attractive and easily scalable route to obtain one or few layer MoS2 in large amounts. This chemically exfoliated system containing distorted trigonal phase have also shown several novel beneficial device properties.

The stable hexagonal 2H form is extensively studied and its electronic properties are well understood as a semiconductor with a large band gap. Unfortunately, the electronic structure of the elusive trigonal phase is little understood in absence of any direct experimental data and conflicting claims from several theoretical calculations ranging from being metallic (1T phase) to normal insulator 8 (for 1T phase) or even ferroelectric insulator 9 (1T phase). We have addressed this issue by investigating the electronic structure of chemically exfoliated MoS2 few layer systems using highly spatially resolved (~120 nm) X-ray photoemission spectroscopy and Raman spectroscopy in conjunction with state-of-art electronic structure calculations and establish that the ground state of this phase is a small gap (90 meV) semiconductor in contrast to most claims in the literature; we also identify the specific trigonal structure it has among many suggested distorted ones. References:

G. Fiori, F. Bonaccorso, G. Iannaccone, T. Palacios, D. Neumaier, A. Seabaugh, S. K. Banerjee, and L. Colombo, Nat. Nanotech. 9, 768 (2014).

K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Phys. Rev. Lett. 105, 136805 (2010). A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C.-Y. Chim, G. Galli, and F. Wang, Nano Lett. 10,

1271 (2010). B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, and A. Kis, Nat. Nanotech. 6, 147 (2011). Q. H. Wang, K. Kalantar-Zadeh, A. Kis, J. N. Coleman, and M. S. Strano, Nat. Nanotech. 7, 699

(2012). R. G. Dickinson and L. Pauling, J. Am. Chem. Soc. 45, 1466 (1923). F. E. Wickman and D. K. Smith, American Minerologist 55, 1843 (1970). Matteo Calandra Phys. Rev. B 88, 245428 (2013). S. N. Shirodkar and U. V. Waghmare. Phys. Rev. Lett. 112, 157601 (2014).

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Robust local and nonlocal transport in the topological Kondo insulator SmB6 in the presence of a high magnetic field.

Sangram Biswas1, Ramya Nagarajan1, Suman Sarkar1, Kazi Rafsanjani Amin1, M. Ciomaga Hatnean2,

S. Tewari3, G. Balakrishnan2 and Aveek Bid1, 1Department of Physics, Indian Institute of Science, Bangalore 560012, India

2Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom

3Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634, USA Abstract: SmB6 has been predicted to be a Kondo topological insulator with topologically protected conducting surface states. We have studied quantitatively the electrical transport through surface states in high-quality single crystals of SmB6. We observe a large nonlocal surface signal at temperatures lower than the bulk Kondo gap scale. Measurements and finite-element simulations allow us to distinguish unambiguously between the contributions from different transport channels. In contrast to general expectations, the electrical transport properties of the surface channels were found to be insensitive to high magnetic fields. We propose possible scenarios that might explain this unexpected finding. Robust topologically protected spin helical states can exist even under the conditions of broken time-reversal symmetry. This magnetic field insensitivity of topological surface states in two-dimensional topological insulators has been ascribed to a spin-chern topological invariant. We note that the conduction through the surface states of time-reversal invariant topological insulators is also expected to be insensitive to time-reversal (TR) symmetry-breaking perturbations if the Fermi energy of the surface Dirac cones is not too close to the zero energy. Low field magneto conductivity measurement shows clear presence of weak anti localization. Local and nonlocal magneto resistance measurements allowed us to identify possible signatures of helical spin states and strong interband scattering at the surface. References:

D. J. Kim, S. Thomas, T. Grant, J. Botimer, Z. Fisk, and J. Xia, Sci. Rep. 3, 3150 (2013). D.-J. Kim, J. Xia, and Z. Fisk, Nat. Mater. 13, 466 (2014). S. Hikami, A. I. Larkin, and Y. Nagaoka, Prog. Theor. Phys. 63, 707 (1980). L. Du, I. Knez, G. Sullivan, and R.-R. Du, Phys. Rev. Lett. 114, 096802 (2015).

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Colloidal CsPbX3 Perovskite Nanocrystals: Excellent Luminescence and Photovoltaic Cell

Abhishek Swarnkar1,2, Vikash Kumar Ravi1, Ashley R. Marshall2,3, Joseph M. Luther2* and

Angshuman Nag1* Corresponding author. E-mail : angshuman@iiserpune.ac.in, joey.luther@nrel.gov.

1Department of Chemistry, Indian Institute of Science Education and Research (IISER) Pune, Pashan, Pune 411008 India

2Chemical and Materials Science, National Renewable Energy Laboratory, Golden, CO 80401 USA

3Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 USA Abstract: Traditional CdSe based colloidal quantum dots (cQDs) have captured the attention over the past many years with their extensive optoelectronic properties. In this presentation, I will discuss about a new class of luminescent nanocrystal (NC), namely colloidal CsPbX3 (where X=halide) NCs, that has high photoluminescence (PL)quantum yield (QY) (~90% in case of CsPbBr3 NCs and ~55% in case of CsPbI3 NCs) along with exceptionally narrow (FWHM = 85 meV) spectral width. Interestingly, in case of ~11 nm CsPbBr3 NCs the spectral widths of a single-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Consequently, luminescence from films of ~11 nm CsPbBr3

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NCs does not suffer from the vexing problems of self-absorption and Förster resonance energy transfer (FRET). Also, ~11 nm colloidal CsPbBr3 NCs show no change in the PL peak position with variation of temperature from 25 oC to 100 oC unlike the traditional CdSe based cQDs where PL peaks get red-shifted with increase in temperature. Although the weak confinement can inhibit size-dependent tuning of emission color towards the blue (<500 nm) region and smaller (<7 nm) CsPbBr3 nanocubes have a tendency to form nanoplatelets and nanorods, eventually yielding inhomogeneity in the shape and size of blue-emitting NCs.

On the other side CsPbI3 is an all-inorganic analogue to the hybrid organic cation halide perovskites. However, the cubic phase of bulk CsPbI3 (α-CsPbI3, the variant with desirable bandgap) is only stable at high temperature, preventing its adoption within the community. I will describe formation of α-CsPbI3 QD films, phase stable for months in ambient air, with long-range electronic transport, leading to the fabrication of the first colloidal perovskite QD solar cells with an open-circuit voltage of 1.23 V and power conversion efficiency of 10.77 %. These devices also function as light emitting diodes (LEDs) with low turn-on voltage and tunable emission. The synthesis of normally unstable material phases stabilized through colloidal QD synthesis provides another mechanism for materials design for photovoltaics, LEDs, and other applications. All these PL behaviors of CsPbX3 perovskite NCs are advantageous over those of traditional CdSe based cQDs, and therefore, CsPbX3 NCs are better candidates for optoelectronics. References:

A. Swarnkar et al., Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots. Angew. Chem.-Int. Edit.54, 15424 (Dec, 2015)

A. Swarnkar et al.,Excellent green but less impressive blue luminescence from CsPbBr3 perovskite nanocubes and nanoplatelets. Nanotechnology, 27, 325708 (2016)

A. Swarnkar et al., Quantum dot-induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. In Press

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Influence of measurement protocol on the magnetocaloric properties in Mn-Ni-Sn-Si off-stoichiometric Heusler alloy

Arup Ghosh 1*, Pintu Sen 2 and Kalyan Mandal 3

1Department of Physics, Indian Institute of Science Education and Research Pune, Dr. Homi Bhabha Road, Pashan, Pune 411 008, India

2Physics Group, Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata 700064, India 3Magnetism Laboratory, Department of Condensed Matter Physics and Material Sciences,

S.N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098, India *E-mail address: arup.1729@gmail.com and arup@iiserpune.ac.in

Abstract: This work reports the magnetocaloric properties in a Si-doped, Mn-rich Mn46Ni39.5Sn10Si4.5 alloy in the aspects of different measurement protocols across its martensitic and reverse transition. A good agreeable value of the magnetic entropy changes (∆SM ~ 20 J/kg K due to a ∆H = 50 kOe) along with large refrigerant capacity (RC ~ 110 J/kg) has been obtained from the high field M-T measurements, which can be a very handy tool for magnetocaloric study. We have analyzed the field dependent magnetization data during heating and cooling near the structural transition for different field changes and fitted them universally using a Lorentz function. The isothermal measurement by ramping the temperature discontinuously during cooling is found to be one of the most convenient and energy efficient ways to minimize the field induced losses, which helps to achieve a very high RC in similar materials exhibiting first order phase transition.

1. Introduction Magnetocaloric effect (MCE) has a large influence in the modern society due to its promising

applications in room temperature magnetic refrigerators for environment friendly and energy saving cooling

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[1]. During the last decade, the materials with first order magnetic and magneto-structural transition have drawn immense attention as these materials are expected to show large MCE [2]. Ni-Mn based Ni-Mn-Sn off-stoichiometric Heusler alloys are found to be very effective in this context as they can exhibit interesting and valuable multifunctional properties like MCE [3], magnetoresistance (MR) [4] and exchange bias (EB) [5]. They show a structural phase transition from the cubic austenite to a tetragonal martensite phase on cooling which accompanies an enormous change in the magnetic and transport properties also. Recently, Mn-rich (Mn ~50 at%) Mn-Ni-Sn alloys have drawn special attention due to its stronger magnetic correlations and large variation of the same with the change of structural phases, which shows significant enhancement in the magnetocaloric properties also [6-8].

Calculation of MCE is generally done from the isothermal M-H curves taken across any phase transition involving changes in magnetic properties by using the Maxwell’s relations [2]. Although, it is found to be a good treatment for the materials having second order magnetic transition (SOMT), the first order magneto-structural transition (FOMST) suffers due to the overestimation problem, which questions about the validity of calculated results [9]. This turns out as a debate if the Maxwell’s relation is valid for estimating the ∆SM in the materials exhibiting FOMST.

In this work, we have prepared a Mn-rich Si-doped Mn46Ni39.5Sn10Si4.5 alloy and studied its MCE. The isothermal M-H curves across the martensitic transition have been taken in both the discontinuous heating and cooling mode. Cooling mode is found to be more effective for getting better and error free MCE value. 2. Results and discussion

Mn-rich Mn46Ni39.5Sn10Si4.5 alloy was prepared by conventional arc melting technique and annealed in vacuum for 24 h which was followed by an ice-water quenching. The sample is found to be in cubic austenite phase at room temperature (300 K) and undergoes a SOMT below 250 K. The sample also undergoes a FOMST from FM austenite parent phase to a weakly magnetic or paramagnetic (PM) like martensite phase (near 200 K) on decreasing the temperature.

The isofield and isothermal magnetic study show the existence of large MCE in Mn46Ni39.5Sn10Si4.5 alloy across its FOMST. Moreover, the isothermal measurements during discontinuous heating show an overestimated and field sweeping dependent MCE, while the measurements under discontinuous cooling is found to be independent of the mode of applied magnetic field (increasing or decreasing). We have carried out a phenomenological universal curve fitting of the temperature dependent MCE data and the best fitting has been achieved only for the cooling mode. Unlike heating, cooling mode does not suffer from any field induced hysteresis and metamagnetic effect which are responsible for the nonlinearity in the saturated region of the isothermal field dependent magnetization data that result in unwanted spikes in the temperature dependent MCE curves. The advantage of measuring MCE in the cooling mode is also reflected in the net refrigerant capacity values [10]. 3. Conclusion

In summary, the discontinuous heating protocol can overestimate the entropy change values in the high field region and decrease the cooling power of the material due to the metamagnetic transition. In the case of discontinuous cooling protocol, the changes in magnetic entropy are more stable and consistent. Along with this, it’s almost negligible field induced hysteresis results in a very large net value of the refrigerant capacity. The universal phenomenological curve fitting of the normalized entropy has converged only under the cooling protocol during both the times of increasing and decreasing the magnetic field. All these results collectively indicate that the use of discontinuous cooling protocol to study the MCE in materials with first order magneto-structural phase transition (like Heusler alloys) can provide a better and more accurate result.

References [1] K. A. Gschneidner Jr., V. K. Pecharsky and A. O. Tsokol, Rep. Prog. Phys. 68, 1479 (2005) [2] V. D. Buchelnikov and V. V. Sokolovskiy, Phys. Met. Metallog. 112, 633 (2011) [3] A. Planes, L. Manosa and M. Acet, J. Phys.: Condens. Matter 21, 233201 (2009) [4] H. C. Xuan, Y. Deng, D. H. Wang, C. L. Zhang, Z. D. Han and Y. W. Du, J. Phys. D: Appl. Phys. 41,

215002 (2008) [5] M. Wang, Y. Liu, B. Xia, P. Ren and L. Wang, J. Appl. Phys. 111, 043912 (2012) [6] L. Ma, S. Q. Wang, Y. Z. Li, C. M. Zhen, D. L. Hou, W. H. Wang, J. L. Chen and G. H. Wu, J. Appl.

Phys. 112, 083902 (2012) [7] A. Ghosh and K. Mandal, J. Phys. D: Appl. Phys. 46, 435001 (2013)

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[8] A. Ghosh and K. Mandal, J. Appl. Phys. 117, 093909 (2015) [9] N. A. de Oliveira and P. J. von Ranke, Phys. Rev. B 77, 214439 (2008). [10] Ghosh, P. Sen and K. Mandal, J. Appl. Phys. 119, 183902 (2016)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Magnetic and magnetocaloric properties of rare earth intermetallic compounds RCoNi

(R = Gd, Tb, Dy and Ho) and HoCo2-xNix (0 ≤ x ≤ 2)

Rajib Mondal Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India

Abstract: Investigations on magnetic refrigeration based on magnetocaloric effect (MCE) have attracted considerable attention in the recent times due to the environment friendliness and energy efficiency of magnetic refrigeration over the conventional vapor-cycle refrigeration. The magnetocaloric effect is an intrinsic property of the magnetic materials in which a reversible temperature change and magnetic entropy change is caused by the application or removal of magnetic field under adiabatic and isothermal conditions, respectively [1]. Rare earth based intermetallic compounds and alloys are the obvious choices for the magnetic refrigeration owing to the large molar entropy and large magnetic moment associated with the heavy rare earth elements. It has been evidenced that the order of the magnetic transition also influences greatly the MCE of a material. An ample investigation on MCE of various materials offers magnetic cooling over a wide range of temperature ranging from liquid-He temperature to near room temperature. The discovery of giant MCE in compound Gd5(Si2Ge2) opens up the door for the rapid search of magnetocaloric materials [2]. The rare earth and transition metal based compounds, RT2 (R = Dy, Ho, Er and T = Co, Ni) also exhibit large MCE near transition. While RCo2 (R = Dy, Ho and Er) compounds display large MCE

caused by the first order metamagnetic transition near the ferrimagnetic ordering (TC), RNi2 (R = Dy, Ho and Er) compounds display large MCE near their second order ferromagnetic transition. Crystalline electric field anisotropy is known to influence greatly the magnetic and magnetocaloric properties of RNi2 compounds [3-4]. The partial substitution of Ni at Co-site of RCo2 affects the d-state near Fermi level of RCo2 compounds and hence it is expected to alter the associated magnetic and magnetocaloric properties. The research work hence focuses to study the influence of Ni substitution at Co-site of RCo2 compounds on the magnetic and magnetocaloric properties. Substitution of Ni by 50 at. wt. % at Co-site of RCo2 (R = Gd, Tb, Dy and Ho) compounds leads

to the ferromagnetic ordering at TC unlike the parent RCo2 (R = Gd, Tb, Dy and Ho) compounds which are ferrimagnetic in nature. The TC of RCoNi (R = Gd, Tb, Dy and Ho) compounds are almost one-half of the parent RCo2 compounds confirming the d-band filling effect. RCoNi (R = Gd, Tb, Dy and Ho) compounds exhibit large value of maximum isothermal magnetic entropy change (ΔSm

max) with large broadening in MCE curves leading to large relative cooling power (RCP) near the second order magnetic transition. While HoCo2 exhibits first order transition at TC, HoCoNi exhibits a second order magnetic transition. An additional transition is observed below the ferromagnetic transition temperature at 11 K (TSR) which could be due to spin reorientation. A significant value of ΔSm of ~ - 2.8 J/kg-K is observed for ΔH = 20 kOe around this TSR. The ΔSm

max value at TSR shifts towards higher temperatures with increasing ΔH thereby leading to broaden the ΔSm vs T curves for this compound. It is to be noted that HoCo2 possesses first order magneto-structural transition at TC while a second order magnetic transition at TC is exhibited by HoNi2.

0.0 0.5 1.0 1.5 2.00

20

40

60

80 TC (K)

Smmax for H = 50 kOe

Ni Concentration

T C (K

)

HoCo2-xNix

Figure 1: Magnetic phase diagram of the rare earth intermetallic compounds HoCo2-xNix (0 x 2)

12

16

20

24

28

S mm

ax (J

/kg-

K)

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Hence the change in MCE due to the change in the order of magnetic transition can be tracked and a magnetic phase diagram of the compounds HoCo2-xNix (0 ≤ x ≤ 2) has been constructed [Figure 1]. The observation of large drop of TC for small amount of Ni substitution is attributed to the d-band filling effect and reduction of 3d-4f exchange interaction and the further small decrement of TC with Ni substitution can be understood from the dominant RKKY-type exchange interaction in HoCo2-xNix (0 ≤ x ≤ 2) compounds. All the compounds possess large MCE around TC and the broadening of MCE curves increases with increasing Ni concentration leading to large RCP. Among them, the compound HoCo0.25Ni1.75 displays large ΔSm

max value with wide temperature span of cooling around its TC of 22 K and large RCP which make HoCo0.25Ni1.75 a potential magnetic refrigerant for low temperature applications such as hydrogen liquefaction. The order of the magnetic transition at TC of the compounds has been determined from the magnetization data using three different models, namely, (1) Arrott plots, (2) Inoue-Shimizu model and (3) Universal scaling of temperature dependent isothermal magnetic entropy changes which reveal that HoCo2 compound exhibits first order transition at TC and all other compounds exhibit a second order magnetic transition at TC. Large RCP with minimal thermal hysteresis loss due to second order magnetic transition at TC makes the Ni substituted RCo2 compounds potential magnetic refrigerants at low temperatures [5-8]. References: [1] V. K. Pecharsky and K. A. Gschneidner Jr., Int. J. Refrig. 29, 1239 (2006) [2] V. K. Pecharsky and K. A. Gschneidner Jr., Phys. Rev. Lett. 78, 4494 (1997) [3] N. H. Duc and P. E. Brommer, Handbook of Magnetic Materials, edited by K. H. J. Buschow (North-Holland, Amsterdam), Vol. 12, Chap. 3, p. 259 (1999) [4] P. J. von Ranke, Daniel F. Grangeia, A. Caldas, and N. A. de Oliveira, J. Appl. Phys. 93, 4055 (2003) [5] Rajib Mondal et al., AIP Conference Proceedings 1447, 1115 (2012) [6] Rajib Mondal et al., J. Appl. Phys. 113, 17A930 (2013) [7] Rajib Mondal et al., Physica B 448, 9 (2014) [8] Rajib Mondal et al., J. Magn. Magn. Mater. 393, 376 (2015) and some unpublished results ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

High Performance Supercapacitor Device based on Polyaniline Nanostructures

Sanjoy Mondal and Sudip Malik* Polymer Science Unit, Indian Association for the Cultivation of Science, Jadavpur,

Kolkata-700032, India E-mail: psusm@iacs.res.in

Abstract: A new technology, the supercapacitor, has emerged the portable very powerful energy storage. Supercapacitors are working as conventional capacitors, but utilize higher surface area electrodes and thinner dielectrics to achieve greater capacitances. This allows for energy densities greater than those of conventional capacitors and power densities greater than those of batteries. They combine the advantages of dielectric capacitors and rechargeable batteries to achieve high power density, long durability, fast charge/discharge rate and operational safety. This brief overview focuses on the different types of supercapacitors.

Figure 1

(a) FESEM image of PANI nanotubes (chemical structure of PANI) (b) and (b) PANI based supercapacitor device.

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Recently many materials like carbon materials (CNT or graphene), metal oxides, composite materials and conducting polymers have been used as supercapacitor electrode materials. In the conducting polymers family polyaniline (PANI) is most familiar due to easy synthesis, low production cost; long range of conductivity, doping/dedoping nature, good environmental as well as thermal stability and so on. Owing to these advantages PANI based composites used as supercapacitor materials now a day in research field. In the conventional liquid electrolyte based energy storage devices grow the safety issue thus researchers are trying to develop an encapsulation technique for high-standard safety. Therefore replacement of liquid electrolyte part with a solid counterpart electrolyte or separator in the energy storage devices is thus very beneficial for developing many advantages such as lightweight, high safety, thin device, flexibility etc. Finally, thin all-solid state supercapacitor could be integrated with micro sensor, microelectronic devices easily as a dominant power source. References [1] Mondal, Sanjoy; Rana Utpal; Malik, Sudip, Chem. Commun., 2015, 51, 12365. [2] Winter, Brodd, Ralph, J., Chem. Rev., 2004, 104, 4245. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Charge and Energy Transfer Dynamics of Chlorophyll

- a reinforced nanohybrid Materials

Debmallya Das Dept. of Metallurgical and Material Engineering, Jadavpur University, Kolkata

Abstract: Recent years have seen unprecedented motivation for the emergence of new solar energy technologies as an alternative of the rapid decline of fossil fuels and other energy resources, which is economically scalable and sustainable. Along with the fast growing infrastructure, with increased per capita income the energy demand in third world countries especially in India is expected to grow up to 95% by 2030.The three challenges to achieve this goal are developing new solar technologies, integrating solar materials at large scale into existing electric systems and designing efficient policies to support solar technology deployment. We aim to address the first one, to develop new material which can be leveraged into a cost effective sustainable solution to achieve economic Photovoltaic cell deployment. Inherent limitations of current silicon technologies, including high processing complexity and silicon’s inherently poor light absorption, drive the need for sustained R&D in advanced silicon and alternative technologies. Thus we hold the innovation opportunity in designing more robust materials and cell architectures and decreasing reliance on rare elements by developing new materials with similar ease of processing. Artificial photosynthesis turning the energy of the sun into hydrogen and oxygen—could prove to be the ultimate in green, clean energy and can address the long-term battle against human-induced climate change as well as can be the answer of eventual dearth of energy resources. In nature, chlorophylls are often self-organized into nanoscale superstructures to funnel sunlight through light-harvesting complexes comprising ≈200 molecules, through which the photoexcited exciton can be delocalized as coherent excited states in regularly arranged porphyrin arrays and energy is transferred via a sequence of quantum mechanical energy transfer processes across a total distance of 20−100 nm with near-unit quantum efficiency [1] coupled to the perfect stacking pattern of chromophores toward a reaction centre. Thus, systems containing porphyrin arrays with specifically coupled geometry are very likely to mimic the antenna function for its long-range association of π-network and can afford favourable excitonic migration for photovoltaic and organic electronic application.

Inspired by this concept exploiation of Chlrophyll-a (CHL-a) has been given rise to different structured-nanohybrid systems with respect to their functionalities. For example CHL-a conducting polyaniline nanohybrid has been successfully prepared with more than 70% energy-transfer efficiency from polymer to CHL-a.[3] We have also studied excitonic interactions of a CHL-a supramolecular assembly [spherical and polymeric] within different polypyrrole nanostructures [nanosphere, nanorod] and shown the

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excitonic delocalization, which is an essential phenomenon in natural light-harvesting systems, can be regulated, couple with different coordination strengths.[2] We extended our research towards the development of a graphene/CHL-a nanohybrid where the CHL-a molecules are used as a driving agent to produce single layer graphene by exfoliation of graphite in agitation dependent bi-solvent environment. The extended interface formed via the Langmuir Blodgett method by exploiting CHL-a amphiphilicity can create synergistic effects resulting in unique properties and superior performance with regard to photovoltaic and advanced electronics applications. In CHL-a exfoliated graphene/CHL-a nanohybrid the reduced lifetime of excited-state CHL-a molecules, evident from time-resolved fluorescence decay (TCSPS) data, is accounted for the effect of two phenomena that are intermolecular exciton migration through packed chlorophyll-a molecules [radiative] and electron transfer from CHL-a to the graphene surface [nonradiative]. The G band in the Raman spectra gradually shifts to lower frequency with decreasing layer numbers; implying electron transfer from porphyrin to graphene is prominent due to the doping induced change of the equilibrium lattice parameter along with nonadiabatic removal of the Kohn anomaly.[4] The lattice relaxation effect is also evident from the decrease in symmetric 2D band intensity with increased electron concentration over the graphene surface. The specific correlation between the chlorophyll-a modification scheme of the graphene and their novel tuneable material properties is evaluated through scanning tunneling spectroscopy, which shows increased electron density and reduced Fermi velocity, revealing that CHL-a can effectively tune the graphene density of state by introducing corrugation through π-stacking, leading to the appearance of the Van Hove singularity. This graphene/ CHL-a nanohybrid can be highly functional in advanced molecular electronics and next generation photovoltaics. Then we attempted to expand the horizons of graphene oxide (GO) reduction methods using CHL-a, which is inclined to react favourably with GO by virtue of photo-excited electron transfer from the singlet excited CHL-a LUMO (-0.7 V) to GO (-0.4 V) in aqueous media assisted by the interactive affinity between CHL-a and reduced graphene oxide (RGO), which is ensured through π–π interaction between the CHL-a macro-cycle and the GO surface. This results in the formation of a CHL-a+ radical which might favour the oxidation of water with oxygen evolution. The formation of RGO after photo-exposure can also be confirmed via TEM and Raman spectroscopy. Gradual restoration of sp2 hybridisation in the GO framework with increasing CHL-a concentration can be correlated with the enhanced contribution of the conformation in which electron transfer is efficient from CHL-a to GO (also supported by XPS and XRD data). This fact corroborates the faster component augmentation with increasing CHL-a concentration towards overall excited state lifetime. The applicability of this RGO/CHL-a nano-hybrid as a possible electro-catalyst, to be used for oxygen reduction in energy conversion systems such as fuel cells, has also been explored through cyclic voltammetry.[5] All these results cumulatively highlight the effective, environment-friendly mechanism of the photo-excited CHL-a assisted deoxygenation of GO in aqueous media, which eventually gives rise to a RGO/CHL-a nanohybrid as a potential electro-catalyst in next generation bio-fuel cells. Finally we tried to develop a photovoltaic prototype and used this graphene/CHL-a nanohybrid as a transparent electrode which gives rise Incident photon to current conversion ratio 8%, greater than conventional ITO electrode. References: (1) Scholes, G. J. Phys. Chem. Lett. 2010, 1, 2−8. (2) Sarkar Manna, J.; Das, D.; Mitra, M. K. J. Phys. Chem. C 2014, 118, 6558−6564. (3) Sarkar Manna, J.; Das, D.; Mitra, M. K. J. Phys. Chem. C 2013, 117, 9573−9580. (4) Das, D.;Sarkar Manna, J.; Mitra, M. K. J. Phys. Chem. C 2015, 119, 6939−6946. (5) Das, D.;Sarkar Manna, J.; Mitra, M. K. RSC Advance 2015, 5, 65487. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Cooperative J-aggregation and impact on photophysical properties and excited state dynamics of core- substituted naphthalene diimides (cNDI)

Haridas Kar and Suhrit Ghosh*

Polymer Science Unit, Indian Association for the Cultivation of Science, Kolkata -700032 Email: psuhk@iacs.res.in

Supramolecular designing skills that can dictate intermolecular interaction and macroscopic structures of π-conjugated chromophores are closely related in different organic optoelectronic applications. In this context, core-substituted naphthalene-diimide (cNDI)-derivatives are promising owing to their wide range of light absorption spanning over almost the entire visible range, fluorescence, variable π-acidity and tunable electrochemical properties (both di-cation and di-anion formation are possible) and photo-induced charge-separation. Nevertheless, in contrast to extensive literature on self-assembly of core-unsubstituted NDIs, such examples on cNDI are scarce likely due to lack of suitable synthetic methods for their structural diversification until recent past. In the recent past we have demonstrated designs for suitable cNDI building blocks based on ring substitution by amine1 or sulfur atom2 which, by virtue of directional H-bonding, exhibit highly cooperative J-aggregation and macroscopic gelation in nonpolar aliphatic hydrocarbon solvents. Among various cNDIs, sulfur-substituted derivatives are particularly exciting in wide-ranging application owing to their low lying LUMO energy level. We have disclosed the first report on supramolecular assembly of a sulfur-substituted NDI derivative leading to the formation of very strong (Tg> 90C) organogel in methyl-cyclohexane(MCH) due to synergistic effect of H-bonding, aromatic and van der Waals interaction. Photophysical studies show explicit features of J-aggregation in aliphatic hydrocarbon solvents which restrains the non-radiative fluorescence rate constant significantly and thus results in remarkable fluorescence enhancement (ΦPL enhances from 1% to 30 %). Such high ΦPL is unprecedented in the entire NDI family which rarely exhibit fluorescence due to fast inter system crossing (ISC). While sulfur substituted cNDI shows promising fluorescence, its amine substituted cousins are considered to be the simplest synthetic mimic of chlorophyll. Inspired by their rich photophysical and redox properties, we have recently examined the self-assembly of an amine substitute donor-acceptor-donor type cNDI which shows H-bonding promoted supramolecular polymerization following macroscopic assembly by cooperative J-aggregation and crystallization of alkyl chains resulting in formation of discrete nanotubes. Effective confinement of the J-aggregated dye molecules in the multilayer walls of the tubes makes strong impact on their excited state photophysical properties showing unprecedented stabilization of the charge-separated excited state as indicated by the remarkably prolonged lifetime extending beyond 100 μs. References: 1. H. Kar, D. W. Gehrig, N. K. Allampally, G. Fernández, F. Laquai, S. Ghosh, Chem. Sci., 2016, 7, 1115-1120. 2. H. Kar, S. Ghosh, Chem. Commun., 2016, 52, 8818-8821. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Synthesis of n-type and p-type doped carbon dots: Their influence

on electron/hole transfer process

Monoj Kumar Barman and AmitavaPatra Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata, 700 032, India

Abstract Doping is the major renowned pathway to control the properties of nanoscale materials. It is well established that n-type (extra electron) and p-type (extra hole) doping in semiconductor cause significant change in electronic structure of the materials which lead to change the optical and electrical properties and make them suitable for potential devices. Nowadays, research on fluorescent carbon dots have been paid great attention due to their promising applications in various fields like bio-imaging, photo-catalysis, photovoltaic, sensing,

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LED and lasers.1-4 Recently, continuous efforts have been made to fabricate hetero atom doped carbon nanomaterials which exhibit good tunable optical and electrochemical properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorous co-doped nitrogen containing carbon dots [C-dots (N, P)] and born co-doped nitrogen containing carbon dots [C-dots (N, B)] and detail elemental analysis has been unveiled by X-ray Photoelectron Spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady state and time resolved spectroscopy. Nitrogen containing carbon dots has quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the non-radiative electron-hole recombination pathways due to incorporation of excess hole, as a result QY, radiative rate and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached Nickel (II) phthalocyanine on the surface of C-dots. It is seen that, phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs. References:

Baker, S. N.; Baker, G. A., Luminescent Carbon Nanodots: Emergent Nanolights. Angew. Chem. Int. Ed. 2010, 49, 6726-6744.

Barman, M. K.; Bhattacharyya, S.; and Patra, A., Steady State and Time Resolved Spectroscopic Study of C-Dots - MEH-PPV Polymer Nanoparticles Composites. Phys. Chem. Chem. Phys., 2013, 15, 16834-16840

Barman, M. K.; Jana, B.; Bhattacharyya, S. and Patra, A., Photophysical Properties of Doped Carbon Dots (N, P and B) and Their Influence on Electron/Hole Transfer in Carbon Dots- Nickel (II) Phthalocyanine Conjugates. J. Phys. Chem. C 2014, 118, 20034−20041

Barman, M. K.; Paramanik, B.; Bain, D. and Patra, A.,Light Harvesting and White-Light Generation in a Composite of Carbon Dots and Dye-Encapsulated BSA-Protein-Capped Gold Nanoclusters. Chem. Eur. J 2016, 22, 11699-11705.

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Supramolecular Assembly of Organic Luminogens into One-dimensional Structure

at Air-water Interface

Subrata Maji and Somobrata Acharya Centre for advanced materials (CAM), Indian association for the cultivation of science, Jadavpur, Kolkata-

700 032, India Abstract: Organic luminogens are in the centre of attraction owing to their potential applications in the field of optoelectronics. In this regard, aggregation-induced emission (AIE) luminogens are important materials since luminescence can be realized in solid state. This phenomenon is in opposed of well-known aggregation-induced quenching effect of the organic luminogens. In AIE, the non-radiative relaxation pathways are blocked by the effective restriction of bond movements that controls the excited-state photophysical processes. Therefore, control of long-range molecular order is the central issue for designing to obtain efficient optoelectronic features from AIE active luminogens. Chromophoric building blocks spontaneously self assemble to form aggregates by various non-covalent forces such as π-π interaction, hydrogen bonding, van der Waals or electrostatic interactions. This is particularly true for π-gelators, which spontaneously self-assemble into entangled network fibers where the chromophoric part getting oriented in perpendicular to the long axis is relatively easy to achieve. Thus, designing ordered structure of organic chromophoric building blocks is not only fundamentally challenging but also may help in the modulation of

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inter-chromophoric interactions and consequently the photo-physical properties by precisely tailoring molecular orientations within an aggregated assembly. In this regard Langmuir-Blodgett (LB) technique is well-known for tailoring the molecular level interactions at the air-water interface by controlling packing, orientation and spatial arrangement of molecules with precise control. We have used LB technique to assemble these organic luminogens and AIE luminogens into one dimensional (1D) nanorods and nanowires at air-water interface. Oligo(p-phenylenevinylene)-derived π-gelator forms aligned nanorods at air-water interface, in which the gelator molecules are reoriented parallel to the long axis of the rods.1 The orientation change of the molecules results in distinct excited-state properties upon local photo excitation, as measured using near-field scanning optical microscopy (NSOM). Another π-gelator dialkoxynaphthalene derivative (DAN-U) forms micrometers long nanowires at air-water interface. This conformation is different from entangle fiber formation upon dropcust.2 Critical gelation concentration (CGC) for DAN-U can be lowered significantly at the air-water interface with the aid of 2D surface pressure to reinforce gelation into uniform ordered nanowires. A further increase in the surface pressure uniquely merges the ordered wires in a side-by-side fashion forming two dimensional molecular sheets. AIE luminogens mono-cyclometalated Ir(III) complex can form supramolecular molecular aggregate at air-water interface to form 1D nanowires which is different form irregular bulk form aggregation.3 This Ir(III) complex shows in-plane J-aggregation at the air-water interface due to the restriction of intramolecular vibration of bidentate phenylpyridinato and intramolecular rotations monodentate triphenylphosphine ligands at air-water interface. As a consequence, a large enhancement of luminescence comparable to the solid state is obtained from the monolayers of supramolecular wires. This unique feature is utilized for the fabrication of light emitting diodes with low threshold voltage using supramolecular wires as active layer. These findings emphasis the superiority of LB technique for ordered supramolecular assemblies at the air-water interface. References: 1. K. Sakakibara, P. Chithra, B. Das, T. Mori, M. Akada, J. Labuta, T. Tsuruoka, S. Maji, S. Furumi, L. K. Shrestha, J. P. Hill, S. Acharya, K. Ariga and A. Ajayaghosh, J. Am. Chem. Soc. 2014, 136, 8548-8551. 2. S. Maji, A. Das, P. K. Sarkar, A. Metya, S. Ghosh and S. Acharya, RSC Adv. 2014, 4, 44650-44653. 3. S. Maji, P. Alam, S. Biswas, P. K. Sarkar, G. S. Kumar, B. Das, I. Rehman, B. B. Das, N. R. Jana, I. R. Laskar and S. Acharya, Angrew Chemie (under revision). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Design of Nanoprobe for the Imaging of Mitochondria and Golgi aparatus

Atanu Chakraborty1, Nikhil R Jana2*

1(Centre for Advanced Materials, Indian Association for the Cultivation of Science)

2(Centre for Advanced Materials, Indian Association for the Cultivation of Science)

Abstract: The rapid improvement of the nanotechnology in the field of bioimaging, biosensing, drug delivery, phototherapy now requires more focus on cell nanoparticle interaction and subcellular localization for their better biomedical performance. Although nanoparticle based cellular imaging probes are reported, the development of subcellular imaging probe is challenging. Various molecular dyes are commercially available for this purpose but they can get easily bleached under strong light exposure. In contrast nanoparticle can retain their emission for longer time. The main challenge for the development of subcellular nanoprobe is the endosomal entrapment which restricts subcellular localization such as mitochondria, golgi, nucleus etc. So bypassing of endosomal pathway should be the criteria for subcellular localization. Endocytosis uptake mechanism and subcellular localization is highly dependent on the cell nanoparticle interaction and nanoparticle surface chemistry. Here we have synthesized a series of nanoparticles with optimized surface chemistry. We found out that the cationic QD interacts with the cell membrane strongly and induce clathrin mediated endocytosis where zwitterionic-lipophilic QD interacts with the lipid raft domains of the cell membrane and induce lipid raft/caveolae mediated endocytosis. Clathrin mediated endocytosis traffics the particle to the endososme/lysosomes but the caveolae or lipid raft

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endocytosis traffics the particle to the golgi, endoplasmic reticulum, mitochondria. This approach can be extended to other particles, targeted drug delivery and efficient photothermal therapy applications. References: 1) Duan, H. W.; Nie, S. M. J. Am. Chem. Soc. 2007, 129, 3333−3338. 2) Anas, A.; Okuda, T.; Kawashima, N.; Nakayama, K.; Itoh, T.; Ishikawa, M.; Biju, V. ACS Nano 2009, 3, 2419−2429. 3) Chakraborty, A.; Jana, N. R. J. Phys. Chem. C, 2015, 119, 2888−2895. 4) Chakraborty, A.; Jana, N. R. J. Phys. Chem. Lett. 2015, 6, 3688−3697. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Extremely robust zirconia based superhydrophobic coating

on cotton fabrics for diverse applications

Indranee Das Nano-Structured Materials Division, CSIR-Central Glass and Ceramic Research Institute

196, Raja S. C. Mullick Road, Kolkata 700 032 Abstract: It is observed that various superhydrophobic coating materials (silica and polymer based) lose their hydrophobicity due to either poor mechanical/adhesion quality or prone to degradation when come in contact with strong acid/alkali and organic solvents. Therefore, chemically inert and mechanically robust ZrO2 functionalized with a very minor fraction of fluorinated methyl silyl was synthesized to fabricate an extremely durable superhydrophobic coating on cotton fabrics applying simple immersion technique. The self-cleanable fabric surfaces possessed high water contact angle ≈163 ± 1°, low hysteresis ≈3.5° and superoleophilicity. These fabrics were also effective to separate oil/water mixture with a high separation efficiency of 98.8 wt% through ordinary filtering. Presence of highly stable superhydrophobic zirconia covalently bonded with cellulose promotes such excellent water repelling durability under harsh environment conditions like high temperature, strong acidic/alkaline solutions, different organic solvents and mechanical forces including extensive washings. Moreover, these coated fabrics retained their original superhydrophobicy as well as high separation efficiency even after several launderings and abrasions cycles. Therefore, such robust superhydrophobic/superoleophilic fabrics have strong potential for versatile industrial productions and long-term uses.

Recently, development of special wettability in textiles have attracted increasing interest for the industries concerned with cloths/paper or oil-water separation as well as to resolve the problem takes place from oil spill accidents. However, such superhydrophobic materials (silica based and other types) on fabrics have certain limitations due to the time-consuming chemical preparation, low chemical-mechanical stability, poor selectivity and reusability, and limited large scale fabrication. ZrO2 is well known for its strong covalent

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Tea drop

20 timesabraded fabric

After 30 d immersion

pH = 2

Cotton

Oil/waterseparation

Hexane

fsZr fabric

Water

Zr

O OH

O

OO

O

pH = 12

1200 1000 800 600 400

ZrOH

CF2

C=O

+ C

=C

CH

ZrOZr

Abs

orba

nce

(arb

. uni

t)

Wavenumber (cm -1)

Control(without fs)

fsZr

(C)

10 µm

(b)

100 µm

(a)

character, excellent mechanical strength with a very high bond dissociation energy, thermal stability as well as strong alkali/acid resistant property compared to other ceramic materials. On the other hand, fluorinated methyl silyl (fs) groups are less reactive and possess lower surface energy than the normal hydrophobic –CH3 groups.

Considering these issues, we have fabricated sol-gel derived fluorinated methyl silyl functionalized zirconia (fsZr) on fabrics maintaining very low proportion of fs (~3 mol%) by simple immersion technique without deteriorating the original flexibility and color of the fabric.1 Strong bonding between the fabric and functionalized zirconia, and robustness were facilitated by condensation after systematic thermal treatment. The FESEM image (Fig. 1a) and its magnified view (Fig. 1b) exhibit the clusters of homogeneously distributed coating material and microstructure on the fabric’s surface, respectively. FTIR studies of fsZr coating material and control (ZrO2 without fs) were conducted to understand the nature of bonding formed due to functionalization (Fig. 1c). FTIR confirms the presence of characteristic –CF2 peaks (near 1240–1150 cm–1) attached with ZrO2 in fsZr. Consequently, the superhydrophobic character of this fabric can be explained through the existence of these –CF2 groups as well as Cassie- Baxter

Fig. 1 (a) FESEM image of fsZr coated cotton fabric and (b) the corresponding higher magnification image showing the surface microstructure of the coating. (c) FTIR spectra revealing functionalization of ZrO2 in fsZr coating material compared to control. model where the water droplets form spheres and reside on the top of such dense rough fabric’s surface without filling up the nanogrooves.2

The existence of chemically inert and mechanically durable fluorinated silyl functionalized ZrO2 bonded with cellulose makes the superhydrophobicity of coating material sustainable under severe environment conditions such as high temperature, corrosive solutions, various organic solvents, and mechanical forces including washings for longer period of time (Fig. 2). Furthermore, the prepared fabric was repeatedly used for the rapid separation of oil/water mixtures with a high water separation efficiency of 98.8 wt% and showed appreciable superhydrophobicity (WCA ≈162 ± 1° and CAH ≈3.8°) even after several cycles of treatments (Fig. 2).

Fig. 2 Photographs show different functions of the fsZr coated superhydrophobic/superoleophilic cotton fabric.

Due to these outstanding features, the fsZr coated superhydrophobic/superoleophilic fabrics could be employed to manufacture oil/water separation apparatus, military suits, lab coats, medical clothing and daily garments. Thus this newly designed fsZr coating has immense potential to fetch revolution in the field of technical textiles with various functionalities for the benefit of humanity.

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Acknowledgement: ID acknowledges CSIR, India for providing fellowship. Reference: [1] I. Das and G. De, Sci. Rep., 2015, 5, 18503, doi: 10.1038/srep18503. [2] I. Das, M. K. Mishra, S. K. Medda and G De, RSC Adv., 2014, 4, 54989-54997. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Synthesis of nanotubes from bio-waste Eichhornia Crassipes: A novel approach

to develop oxygen separation membrane

Quazi Arif Islam CSIR-Central Glass and Ceramic Research Institute, India

Email: arif.chem007@gmail.com Abstract:

Exploration of green energy is now become a global agenda to avert the climate change impacts arising from greenhouse gas emissions. A process that is rapidly becoming attractive is oxy-fuel combustion, burning coal with pure O2 or O2/CO2 mixtures instead of conventional air combustion. In this process, almost pure CO2 is produced for subsequent transportation and geological storage. Currently, large scale O2 separation from air is carried out by cryogenics, a complex and energy intensive process which upon integration with a coal power plant has the potential to reduce power generation efficiencies from current best practice of around 40% down to 30%.1 Dense ceramic membranes are identified as the replacement of cryogenics and projected to reduce O2 production costs by ~35% or more.1 These oxygen transport membranes are generally known as mixed ionic and electronic conducting (MIEC) ceramic materials, which normally allow the transport of both electrons and oxygen ions simultaneously.1

Much effort is devoted to explore more advanced membrane materials with inherent high oxygen permeation flux and stability; however, it is still difficult to and one single compositional membrane with ideal performance in both areas. The review of recent literatures clearly indicates that the oxygen permeation flux of the perovskite membranes can be significantly improved either by changing different doping elements or by improving synthesis methodologies.2,3

Mimicking of microstructure from natural or synthetic sources is now becoming emerging research area for the development of multifunctional materials. A large number of studies indicate that engineered materials derived by exo or endo templating results in an enhanced physio-chemical properties than the conventionally synthesize materials. Moreover, the material property can be successfully tuned by selection of proper template. A template is a textured architect that provides a path for synthesis. After removal of such sacrificial template, a material is obtained with controlled morphology which mimics the textural pattern of the exo-template.4 Particle size ranging from nanometer to micrometer with high crystallinity can be tailor-made depending upon the choice of the template.

Fig. 1. Schematic representation of confined space synthesis and membrane development process

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The present study aims to develop a bio-templating process of synthesizing BaBi0.2Co0.35Fe0.45O3-δ

(BBCF) perovskite type oxygen separation membrane mimicking the interior of water hyacinth’s (Eichhornia Crassipes) petioles. In Indian sub-continent water hyacinth is considered as one of the worst aquatic weed whose removal is necessary from natural water reservoir to save aquatic environment. The idea of using such water pollutant to produce engineered microstructure for improving material’s functionality is the philosophy behind the present study. The exo-templating of water hyacinth results in interesting microstructure and enhanced the physical properties of BBCF membrane in terms of oxygen permeation flux. The novel, simple method may be extended to produce any multifunctional advanced material with a spectacular microstructure and unique properties.

The morphology of BBCF powder calcined at 950oC in air atmosphere reveals a 3D architecture of nano rod arrays. The rods like structure are almost uniform in diameter (50-80 nm) throughout the length with a quite smooth surface as observed. The origin of such type of morphology can be explained in terms of ‘confined space’ template assisted synthesis.4 By use of the confined space, it is possible to make unique structures depending on the interior and the space available with the templates. In the present study, the hollow channels of the petioles are likely to be considered as confined space utilized for synthesis. The stoichiometric low viscous BBCF gel is slowly loaded in the channels/pores during gel-impregnation process. On controlled heat treatment, the particulates of the product powder (BBCF) are formed inside the hollow path. Inside the channels, these particulates come closer and the grain boundary between two successive particles coalesces together to form a rod like morphology. During heat treatment, the further growth of the particles is restricted till the whole template is sacrificed at high temperature of 950oC. A proposed scheme and the overall membrane preparation process is shown in Fig. 1. The highest oxygen flux of 1.33 ml/min/cm2 is obtained at 900oC for the pellet synthesized by water hyacinth templating method. On the other hand, the BBCF membrane synthesized by soft chemical method exhibits lower oxygen permeation flux of 0.77 ml/min/cm2 at 900oC.

References: 1. J. Sunarso, S. Liu, Y. S. Lin and J. C. Diniz da Costa, Energy Environ. Sci., 2011, 4, 2516- 2529. 2. P. Zeng, Z. Shao, S. Liu and Z. Xu, Sep. Purif. Technol., 2009, 67, 304-311. 3. X. Shao, D. Dong, G. Parkinson and C. Z. Li, J. Mater. Chem. A, 2013, 1, 9641-9644. 4. X. Wang, H. Wang, Y. Zhou, Y. Liu, B. Li, X. Zhou and H. Shen, Nat. Sci. Rep., 2015, 5, 1-7.

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Big Atoms and their Compounds

Rekha Mahadevu and Anshu Pandey

Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 Abstract: Semiconductor quantum dots (QDs) resembles atoms because of their discrete energy levels. Since their physical dimension is larges that atoms they can be called as big atoms. Semiconductors are used as light harvesting materials in photovoltaic devices. Materials used for this purpose should satisfy two major optical requirements: absorb the maximum amount of sunlight while having long exciton decay kinetics. Type II nanocrystals (NCs) have anomalously long exciton lifetimes due to spatial separation of electron and hole wave functions. It is believed that this spatial separation of carriers should also cause these materials to absorb poorly at the band edge. Here we discuss this popular misunderstanding. We synthesize ZnTe/CdS type II NCs. Their absorption properties are examined and interpreted. We find that these materials can indeed exhibit absorption cross sections as large as or larger than type I NCs, while still having very weak transition dipole moments. An explanation for these curious observations is provided. Quantum Dot Assemblies: QDs can also form bonds between them, in general the properties of materials arise are derived from the properties of their building blocks-atoms. Since the properties of atoms are intrinsic and non-

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tunable, conventional materials design becomes an exercise in permuting and combining atoms in various ratios. Quantum dots exhibit tunable properties thereby offering a route to break this paradigm. Materials design with quantum dots however requires the demonstration of chemistry or chemical like behavior with these species. We report the design of quantum dots that can react with each other in the same fashion as atoms. These dot-dot reactions are shown to lead to stoichiometric end-products where quantum dots completely take on the role of atoms. The chemical bonds that hold these materials together are shown to be an order of magnitude longer and stronger than conventional chemical bonds. We further analyze the counterintuitive physical properties of these materials. In particular, we discuss the reasons why these materials exhibit a stoichiometry even though the physical characteristics of their building blocks limit the role of quantum mechanics in determining their properties. The potential of using these reactions for a middle-up route to materials design will be discussed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Evaluation of Semi-metallic Fe3O4 Nanocavities using Terahertz Waves

R. Rakshit1, K. Serita2, M. Tonouchi2, and K. Mandal1,

1Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences

2Institute of Laser Engineering, Osaka University

Abstract: Ferrites such as Fe3O4 are the best materials for high frequency applications and electromagnetic wave

absorption due to moderate magnetization, high electric permittivity and magnetic permeability and non-reciprocal behavior. Furthermore, it has been found that their nanostructures show unexpected enhancement of physical phenomena [1], therefore it is important to understand their physical behaviour to accelerate the research. On the other hand, Terahertz (THz) wave which lies 0.3 - 30 THz in electromagnetic wave frequency presents challenges for unexplored science and new industrial application; X ray-alternative security system, identification of biological molecules, ultrafast wireless communications and so on [2]. Since its unique abilities to evaluate various kinds of materials, it is attractive to measure and analyze such nanostructured Fe3O4.

Variable sized magnetite Fe3O4 NPs and NHSs were prepared by a solvothermal method [3]. Figure 1 shows THz absorption spectra of Fe3O4 nanoparticle (NP) and its hollow configuration (NHSs: nano-hollow spheres) having diameter 100, 185, 250, 350, 725 nm. It is clearly observed that the NPs are optically transparent to THz EM radiation, whereas NHSs perform as an excellent opaque object in the frequency of 0.4 - 2.0 THz. Meticulous analyses suggest that they follow Polaron Model instead of Drude-Smith Model due to phonon vibration upon THz excitation. Furthermore, in comparison to the solid configuration, the presence of nano-cavity has provided the drastic enhancement of THz absorption, e.g. two consecutive resonance peaks (0.97 and 1.08; 1.21 and 1.32; 1.45 and 1.55 THz) for NHS-100nm instead of corresponding single peak (1.05, 1.28 and 1.56 THz) as obtained in case of NP of same material. These results indicate that THz wave has potentials to provide the nanostructured information and its physical behaviors. [1] G. Sun et al., Chem. Mater. 23, 1587 (2011). [2] M. Tonouchi, Nat. Photon. 1, 97 (2007). [3] D. Sarkar et al., J. Appl. Phys. 112, 064318 (2012). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Single molecule DNA sequencing using graphene nanopore device

Sourav Kundu* and S. N. Karmakar Condensed Matter Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar,

Kolkata- 700064, India. Abstract: We report a tight-binding model based theoretical study of two terminal graphene nanopore baseddevice for sequential determination of DNA bases. Using Green's function approach we calculate conductance spectra, I-V response and also the changes in local density of states (LDOS) profile as four different nucleobases inserted one by one into the pore embedded in the zigzag graphene nanoribbon (ZGNR). We find distinct features in LDOS profile for different nucleotides and the same is also present in conductance and I-V response. We propose an efficient working principle of the device, by setting the bias across the pore to a fixed voltage (this voltage gives maximum discrimination between characteristic currents of the four nucleotides) and translocating the ss-DNA through the nanopore using a transverse electric field while recording the characteristic current of the nucleotides. Not only the typical current output is much larger than previous results, but the separation between them for different bases is also definite. Our investigation provides high accuracy and significant amount of distinction between different nucleotides.

Figure: In clockwise direction: i) Transmission probability T(E) with energy (E) of an electron passing through the nanopore while four different nucleotides are trapped in the pore, ii) LDOS of four nucleotides trapped at nanopore, iii) Current-Voltage characteristics of the nanopore device with four nitrogen bases situated at the nanopore, iv) Current output of the of a single-stranded DNA chain translocating through the nanopore. Characteristic currents are marked with A, T, G, C letters in the figure representing four different nitrogen bases of DNA. [2] References: [1] F. Sanger, S. Nicklen, A. R. Coulson, Proc. Natl. Acad. Sci. USA 74, 5463 (1977). [2] Sourav Kundu and S. N. Karmakar, arXiv: 1506:07361 (2015). Email : sourav.kunduphy@gmail.com

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Spin-orbital liquid state assisted by singlet-triplet excitation in J = 0 ground state of Ba3ZnIr2O9

Abhishek Nag1 and Sugata Ray1,2

Department of Material Science1, Centre of Advanced Materials2, Indian Association for the Cultivation of Sciences

Abstract: Strong spin-orbit coupling (SOC) effects of heavy d-orbital elements have long been neglected in describing the ground states of their compounds thereby overlooking a variety of fascinating and yet unexplored magnetic and electronic states, until recently. In oxides containing these heavy transition metals, the SOC becomes comparable to their on-site Coulomb (U) and crystal field interactions (ΔCFE) [1]. Complete understanding of the unusual behaviour of spin-orbit entangled electrons belonging to the multiplet J-states obtained in j-j coupling limit[2] for such compounds where the total angular momentum quantum number MJ becomes the only valid quantum number, needs exhaustive theoretical and experimental analysis. The unusual insulating state of the layered tetravalent iridates (Ir4+; 5d5), designated as novel Jeff = 1/2 Mott insulators, has recently been explained within single particle theories assuming splitting of t2g bands into a fully-filled Jeff = 3/2 quartet bands and half-filled narrow Jeff = 1/2 doublet bands due to finite SOC, which further splits into a fully occupied lower Hubbard and empty upper Hubbard bands in the presence of relatively small Hubbard U [3].

For a d4 system, due to presence of strong SOC, all the spin-orbital entangled electrons should get confined to a non- magnetic singlet ground state of J=0. Excitation of electrons may occur from these J=0 states to higher magnetic triplet states and give rise to Van-Vleck type of magnetism [4]. However, stabilization of such an unusual electronic state won’t be trivial as this J = 0 ground state at moderate λ′ could be exceptionally fragile to minute external perturbation and enhanced magnetic responses may appear with rather small variations in magnetic fields or IrO6 octahedral distortions giving rise to non-cubic crystal field effects [4].

We have synthesised Ba3ZnIr2O9, which stabilises in a P63/mmc space group within a 6H hexagonal structure. The IrO6 octadehra share faces and form Ir2O9 dimers which are in turn arranged in a triangular lattice on the ab-plane. While Ir ions within each structural Ir2O9 dimer prefer to form spin-orbit singlet state (SOS) with no net moment, substantial interdimer exchange interactions from a frustrated triangular lattice ensure quantum fluctuations till the lowest measured temperatures indicating formation of a spin-orbital liquid phase. Ba3ZnIr2O9 till date comes closest to the realisation of the elusive J = 0 state and a small magnetic moment is generated in this system as a result of comparable energy scales of singlet-triplet splitting and super-exchange interaction promoted via hopping between the Ir ions.

We have performed Rietveld refinement of neutron powder diffraction to obtain the structural parameters of Ba3ZnIr2O9. Negligibly small Zn/Ir site-disorder (<5%) is obtained from the NPD as well as XAFS experiments performed on the Zn K- and Ir L3- edges to probe any local chemical disorder [5].

We obtain a gapped electronic structure for the system both from the four probe electrical resistivity measurements and valence band spectra from X-ray photoelectron spectroscopy. This strange insulating behaviour for Ir5+ (valence state confirmed by XPS of Ir 4f core level) containing system was then investigated theoretically within single particle mean field framework using Density Functional Theory within Generalised Gradient Approximation and projector augmented wave calculations by systematically including Hubbard U and SOC. The eg states lie higher in energy as the octahedral crystal field is strong,

resulting in quite large (∼3.5eV) t2g- eg crystal field splitting. The metallic DOS without SOC, upon

inclusion of SOC and a Hubbard U (U-J= 2.5 eV) becomes insulating with a gap of 10meV. The t2g states split into two-fold degenerate Γ7 and four-fold degenerate Γ8 states. Since four electrons are available per Ir, all the Γ8 states are occupied and the system is insulating as seen experimentally. However, we find that local moments are spontaneously generated in the magnetic phase due to hybridisation between the occupied

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Γ8 and Γ7 pseudo-spin states, indicatin gapless spin excitations. Also, it is observed that the magnetic configuration with antiferromagnetic intradimer coupling is energetically favourable in the presence of SOC, emphasizing its importance in the realization of SOS states in Ba3ZnIr2O9. We also find that the intradimer interactions are not strong enough compared to the interdimer interactions, leading to a frustrated behaviour instead of a SOS-like long-range order.

NPD also showed no ordered moment down to 1.5K within the detection limit of 0.5μB and no structural transition till this temperature. To unravel the nature of the ground state stabilised in this compound we studied muon spin relaxation experiments in zerofield, a technique perfectly suited to detect weak and/or partial freezing of local magnetic moments till 0.1K. We didn’t observe any spontaneous oscillations or emergenceof a “1/3rd” tail that would signal a magnetic transition to a frozen state. The presence of the spin relaxation till the lowest measured temperature, to the application of a longitudinal field at base temperature also supports its dynamical origin. The prediction of a special QSOL state in Ba3ZnIr2O9 is further confirmed by analysis of heat capacity with a minute release of magnetic entropy generated due to excitations from non-magnetic singlet to triplet states. DC magnetic susceptibility also confirms the absence of magnetic ordering in this system along with substantial frustration present.

In conclusion, Ba3ZnIr2O9 is a J = 0 insulator where minute moments are generated from superexchange induced spin excitations [4]. The Ir moments within the Ir2O9 dimer interact antiferromagnetically resulting in spin-orbital singlets. The interdimer hoppings in the ab-plane induce quantum fluctuations and a long range magnetic order is suppressed due to geometric frustration, resulting in a quantum spin-orbital liquid state. References: [1] W. Witczak-Krempa,G. Chen,Y. B. Kim, and L. Balents, Annu. Rev. Condens. Matter Phys. 5, 57 (2014). [2] J. Rublo, and J. Perez, J. Chem. Education 63, 476(1986). [3] B. J. Kim et. al., Phys. Rev. Lett.101, 076402 (2008). [4] G. Khaliullin, Phys. Rev. Lett.111, 197201 (2013). [5] S. Middey et. al., Phys. Rev. B 83, 144419 (2011). This work has been published in Phys. Rev. Lett. 116, 097205 –3 March 2016. The full list of authors are: Abhishek Nag, S. Middey, Sayantika Bhowal, S. K. Panda, Roland Mathieu, J. C. Orain, F. Bert, P. Mendels, P. G. Freeman, M. Mansson, H. M. Ronnow, M. Telling, P. K. Biswas, D. Sheptyakov, S. D. Kaushik, Vasudeva Siruguri, Carlo Meneghini, D. D. Sarma, Indra Dasgupta, and Sugata Ray. ----------------------------------------------------------------------------------------------------------------------------------

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Synthesis and biocompatibility study of nano crystalline hydroxyapatite from Mercenaria clam shells

Anindya Pala, Shubhadeep Maityb, Sumit Chabric, Supriya Berab, Amit Roy Chowdhuryd, Mitun Dase,

Arijit Sinhaa,* 1Dr. M.N.Dastur School of Materials Science and Engineering,

Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India. 2Department of Metallurgical and Materials Engineering.

National Institute of Technology, Durgapur -713209, India. 3Department of Metallurgy and Materials Engineering.

Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India. 4Department of Aerospace Engineering and Applied Mechanics, Indian

Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India. Email: *arijit@matsc.iiests.ac.in

Key words: Mechanochemical synthesis; X-ray diffraction; Sea shell; X-ray diffraction; Hydroxyapatite;

Biocompatibity; MTT assay. Abstract The aim of the present study is to synthesis of nano-crystalline hydroxyapatite by a mechanochemical method using clam seashells and phosphoric and to explore in vitro biocompatibility. The CaO and H3PO4 acid at different wt.% ratios i.e. 1:0.75, 1:1.0, 1:1.25, 1:1.5 and 1:1.75, were ball milled and then heat treated at 1000 °C for 3 hr to complete reactions. The synthesized powders were characterized using X-ray diffraction, FTIR spectroscopy, scanning electron microscope and high resolution transmission electron microscopy. X-ray diffraction results showed that the average crystallite size of the powder varies from 53 nm to 67 nm and crystallinity of powder found to be in the range of 88% and 96%. In vitro biocompatibility studies carried out using osteoblast (MG63) and fibroblast cells (NIH3T3) demonstrated non-toxic nature of the sea shell derived HAp powder. Introduction Hydroxyapatite [HAp, (Ca10(PO4)6(OH)2)] is a popular bioactive ceramic having composition and crystal structure similar to the mineral component of natural bones and teeth. Due to its structural similarity with bone minerals, HAp exhibits excellent biocompatibility and osteoconductive properties [1]. Thus, HAp has been widely used in the form of powders, coatings, porous scaffolds and hybrid composites for orthopaedic, dental and cranio-maxillofacial reconstruction applications. In general, HAp can be prepared from synthetic calcium as well as different biogenic materials. However, it has been observed that response of HAp prepared from synthetic calcium is different from the bone mineral . HAp was successfully synthesized from different biogenic materials like coral, seashell, and eggshell using chemical synthetic routes. Synthesis technique such as solid state reactions, chemical precipitation, hydrothermal reactions, sol-gel and mechanochemical methods are used most widely for preparation of apatite from natural resources [1, 2]. In the present study, nano-crystalline HAp was synthesized by mechanochemical method from sea shells and phosphoric acid as precursors. The effect of phosphoric acid in different mixing ratios to seashell derived precursor powder on synthesize powders were extensively investigated. Further, cytotoxicity of the synthesized powder from sea shell was evaluated in vitro. Results In present investigation, Mercenaria calm shells were collected and washed properly with detergent

followed by calcinations at 1000⁰C for 3 hours. The structural and morphological analyses were done using

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X-Ray diffraction technique, scanning electron microscope, transmitted electron microscope. During the first 30 minutes most of the organic materials were burnt out, and then the seashell were converted to calcium oxide (CaO) as visualize from the XRD pattern. The calcined shells were crushed and milled in high energy ball mill with phosphoric acid are in ratio of 1:0.75, 1:1.0, 1:1.25, 1:1.5 and 1:1.75 respectively for

20 hours at 300 rpm. The ball milled powder were further heat treated at 1000⁰C for 3 hours. The ball

milled and heat treated powders were further subjected to structural and morphological analyses.

Fig.2 (a) XRD patterns of the raw seashell, (b) calcined seashell (at 1000°C for 3 hours)

The XRD patterns of the sea shell obtained after 3 hours calcination. CaO and Ca(OH)2 was observed in the calcined seashell. X-ray patterns of the powder samples of 1:1.25 and 1:1.5. Powders produced by ball milling (SB) contained Ca(OH)2. After heating at 1000°C for 3 hours Hap appeared in 1:0.75, 1:1.0, 1:1.25, 1:1.5 and 1:1.75 samples. The biocompatibility of the HAp powders synthesized from hard clam seashell (Mercenaria mercenaria) was assayed and compared with commercially available HAp powders using cell materials interaction. In vitro cytotoxicity behavior of HAp4 (CaO:H3PO4 wt% ratio of 1:1.5) powder synthesized from seashell was evaluated using human osteoblast-like cells (MG63) and mouse embryonic fibroblast cells line (NIH3T3). The primary in vitro assessment of biocompatibility was carried out using MTT [3-(4,5-dimethylthiazol-2-yl) -2,5-diphenyl tetrazolium bromide] assay. The compositional analysis from EDX showed the presence of calcium, phosphorus and oxygen and Ca/P in the synthesized powder were close to 1.6. Acknowledgement The authors wish to thank the financial support of the COE. The authors whole heartedly thank the help rendered by the Dr. M.N.Dastur School of Materials Science and Engineering (MNDSMSE), Shibpur. References [1] Sergey V. Dorozhkin, Bioceramics of calcium orthophosphates, Biomaterials 31 (2010) 1465–1485. [2] M. Akram, R. Ahmed, I. Shakir, W. A. W. Ibrahim, R. Hussain, Extracting hydroxyapatite and its precursors from natural resources, J Mater Sci 49 (2014) 1461–1475.

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The Structural Properties Based On WO3/SiO2/p-Si Sensing Element and the Effects of Annealing Temperatures

*Anup Dey and Subir Kumar Sarkar Jadavpur University, Kolkata, West Bengal, 700032, India

Email id: *anupetce@gmail.com

Abstract:

The paper presents Tungsten trioxide (WO3) thin film sensor on Silicon-di-Oxide (SiO2) deposited layer using sol-gel deposition technique for detection of gas sensing element. The structure of fabricated thin film is analyzed by the method of Scanning Electron Microscopy (SEM). The characterization of WO3 thin film sensor is observed at different working temperatures (1000C to 3000C).The WO3/SiO2/P-Si sensing element are annealed at the temperature range of 3500C -5500C. It is observed that Tungsten trioxide thin film with 550 °C has sharper grain image and smaller grain size (48nm) compared to the other annealed temperatures. It is also investigate that the sensing element (WO3/SiO2/P-Si) is suitable at the operating temperature 1500C. Introduction: A metal-oxide type semiconductor such as WO3, TiO2, SnO2, ZnO etc can use to detect many gases. Some of metal oxide utilized as sensor materials due to their high surface to volume ratio, high mobility of electrons and good chemicals and thermal stability under different operating condition and annealing temperatures. The sol-gel [1] is the simple and low cost deposition technique is used to deposit the nanostructure film. Metal oxide based thin film gas sensors generally activate in the temperature range of 1000C-3000C. Thin film gas sensors generally detect different gases (NH3, CH4, H2 and SO2) in their operating temperature [2]. Gas sensors can be used as fire detectors, leakage detectors. So that the sensing element is necessary to detect any kind of gas under at certain temperature condition. The sensor operates on the principle of catalytic combustion. Surface Morphology and Discussion: The WO3 thin film has been prepared by sol-gel process by using WCl6 and isopropanol at the ratio of 5gm/100ml. The structure of device is shown in fig. 1 and the characteristically measured by SEM of the WO3 thin films with different annealing temperature (350,450 and 650 °C) are shown in Figs. 2, 3 and 4. SEM images suggest that sol–gel grown metal oxide thin films have typical polycrystalline structure with different grain size. Typical SEM characteristics are also found that WO3 thin film with annealing temperature of 550°C have sharper grain image and smaller grain size compare to the other annealed temperatures.

Fig.1. Device structure.

Fig. 2-4: SEM image of WO3 thin film sensor at annealing temperature of 350°C, 450°C and 550°C.

Conclusion: WO3/SiO2/P-Si thin film sensor is fabricated using sol-gel technique for detection of gas sensing element. Scanning Electron Microscopy (SEM) is the useful technique to analyze the detailed structure of fabricated WO3 thin film with different annealing temperatures (3500C to 5500C). The performance of WO3 thin film sensor is analyzed at different working temperatures (1000C to 3000C). It is found that this WO3 thin film sensing element is suitable at the operating temperature range of 1500C. It is

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also observed that this sensing element with annealing temperature 5500C has smaller grain size (48nm) and sharper image compared to other annealing temperatures. Acknowledgement: Author thankfully acknowledges the financial support for this research work obtained from UGC-UPE Phase II sponsored project.

Reference: [1] Maosong, T., Guorui, D., and Dingsan, G., 2001, “WO3 thin film sensor prepared by sol-gel technique and its low-temperature sensing properties to tri methylamine,” Materials Chemistry and Physics, 69, pp. 176-179 [2] Tsai, T. H., Chen, H. I., Lin, K. W., Hung, C. W., Hsu, C. H., Chen, L.Y., 2008, “Comprehensive study on hydrogen sensing properties of a Pd–AlGaN based Schottky diode,” International Journal of Hydrogen Energy, 33, pp. 2986–2992 ----------------------------------------------------------------------------------------------------------------------------------

Nano-heterostructures: Interface as a Quantum Device

Arup Chakraborty and I. Dasgupta Department of Solid State Physics, Indian Association for the Cultivation of Science

Jadavpur, Kolkata – 700032, India Abstract: We have studied the electronic structure of two different heterostructures at nanoscale namely CdSe-ZnSe coupled quantum dot (CQD) and heterostructure of InAs polytype nanowires (NW). We have shown the heterostructure of CdSe-ZnSe CQD with similar size of its components is of quasi type-II with no offset for the highest occupied molecular orbital (HOMO) state. However varying the size of the ZnSe component it can be tailored to type-II which may be useful for photovoltaic devices. Interfaces at nano-scale consisting of polytypes of III-V semiconductors also offer an opportunity to tune band offsets primarily utilizing the strain at the interface. We have shown that there is no band offset in InAs wurtzite/zinc-blende NW heterostructure having 80% wurtzite fraction due to the presence of large interfacial compressive strain in agreement with resonance Raman measurement. 1. Introduction: Recently one of the challenges for material scientist is to find a more efficient photovoltaic device where the separation of photo-generated exciton into free electron and hole is mandatory. Nanomaterials are found to be suitable to get efficient exciton dissociation as they show interesting properties compared to bulk systems due to presence of quantum confinement and large surface to volume ratio. The combination of two or more nanomaterials basically the heterostructures at nanoscale offer better tunability of the properties compared to individual nanomaterials due to the combined effect of its components. Type-II semiconductor heterostructures are most suitable for photovoltaic devices because electron-hole are located in two different components and therefore paves the way for easy separation. It was shown that in CdS-ZnSe CQD the band-offsets can be tuned by tailoring the size of its components and it can be used in photovoltaic devices. [1,2] In the heterostructures at nanoscale not only the effect of quantum confinement (QC) but also interfacial strain due to lattice mismatch plays an important role to dictate the properties in these nano-heterostructures. In a recent experiment [3] it was shown that there is no band-offset in InAs ploytype NW heterostructure due to presence of strain. In this paper we present our results on electronic structure of CdSe-ZnSe CQD and illustrate changing size of one of the components offer an unique possibility to engineer the band-offset which may find application in a photovoltaic device. Further we study the impact of strain on band alignment of InAs polytype NW heterostructures. 2. Computational Details: The electronic structure calculation reported here are based on ab-initio density functional theory (DFT) with the generalized gradient approximation (GGA) as implemented in the Vienna ab-initio Simulation Package (VASP)[4]. Projector augmented wave (PAW) method along with plane wave basis set are used for our

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calculations. The band offsets are calculated using the energy resolved charge density (ERCD), a method proposed by N. Ganguli et. al. in [1]. 3. Results & Discussions: To begin with we have calculated the electronic structure of CdSe-ZnSe CQD of similar size (1.6 nm in diameter) where Cd terminated (0001) facet of wurtzite(WZ) CdSe dot is attached with Se terminated (111) facet of zinc-blende(ZB) ZnSe dot (see Fig.1(a)). In order to understand the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and to estimate the offset at the interface we have calculated ERCD suggested in Ref.[1]. Our calculation revealed that at the interface is of quasi type-II with no HOMO offset and LUMO offset of 0.5 eV and LUMO is localized in CdSe part (see Fig. 1(b)). Using the advantage of quantum confinement of quantum dot, we have shown that by varying the size of the ZnSe component to 2 nm (see Fig. 1(c)) that CdSe-ZnSe CQD can be transformed to type-II heterostructures (see Fig 1(d)) where HOMO and LUMO are localized in ZnSe and CdSe part respectively. Apart from CQD, we have also explored the band alignment and band offset at the interface of InAs polytype (WZ/ZB) nanowire heterostructure that are investigated recently by resonance Raman measurement [3]. In that resonance Raman experiment [3], it is found that at the interface of nanowire (NW) sample having 99% WZ fraction band alignment is of type-II and in another sample with 80% WZ fraction suggests that there is no band offset. In order to obtain insight on the nature of band alignment for the WZ/ZB NW heterostructure with 80% WZ fraction and 20% ZB fraction we have calculated ERCD for our model NW heterostructure. We have constructed a model of coupled WZ/ZB NW heterostructure having diameter of 1.4 nm and periodic (ZB/WZ/ZB/WZ..) along its length and surface atoms are passivated with pseudohydrogen (see Fig. 2(a)) as we did for the case of coupled dot. ERCD (Fig. 2(b)) and iso-surface of charge density (Fig. 2(a)) reveal absence of band offsets in valance band maximum and conduction band minimum. To trace the origin of absence of band offset at the interface we have calculated the volumetric strain for this NW heterostructure as proposed in Ref.[1]. The calculated strain (see Fig. 2(c)) for cationic plane and anionic plane are compressive and tensile respectively and at the interface strain has large value and far from the interface it decreases. The average strain is compressive in nature and is in good agreement with the experimental finding from phonon line width [3]. So the impact of large value of strain on the band alignment leads to the absence of band offset from our calculations.

Fig. 1.(a) and (d) are the model of CdSe-ZnSe CQD of similar size (1.6 nm) and with bigger size (2 nm) of ZnSe. (c) ERCD for structure at (a), (d) ERCD for structure at (d).

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Fig.2 (a) Iso-surface of charge density for VBM and CBM of WZ/ZB InAs NW with 80% WZ. . (b) ERCD for the mentioned structure, (c) Strain profile for it. 4. Conclusions: We have investigated the electronic structure of CdSe-ZnSe CQD and WZ/ZB InAs NW heterostructure using DFT. We find the band alignment at the CdSe-ZnSe CQD is of quasi type-II for similar size of the components and it can be transformed into type-II by changing the size of ZnSe component. Our calculations reveal that the tailoring of the band-offset is possible due to the effect of quantum confinement and the nature of chemical bonding at the interface. Further we have shown the strain dictates the absence band offset at the InAs polytype NW heterostructure having 80% WZ fraction and 20% ZB fraction in agreement with resonance Raman measurement. In conclusion, quantum confinement and impact of interfacial strain are essential ingredients that modulate the band alignment at the interface of the semiconductor heterostructures at nanoscale. References: 1. N. Ganguli, S. Acharya, I. Dasgupta, Phys. Rev. B (2014), 89, 245423. 2. A. Dalui, A. Chakraborty, U. Thupakula, A. H. Khan, T. Ghosh, B. Satpaty, I. Dasgupta, D. D. Sarma, S. Acharya, J. Phys. Chem., C (2016) 116, 10118. 3. J. K. Panda, A. Roy, A. Chakraborty, I. Dasgupta, E. Hasanu, D. Ercolani, L. Sorba, M. Gemmi, Phys. Rev. B (2015), 92, 205302. 4. G. Kresse et. al., Phys. Rev. B (1993), 47, 558; Phys. Rev. B (1996), 54, 11169.

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Multiferroic studies on geometrically frustrated “114” cobaltites

C. Dhanasekhar1,3, Ripandeep Singh2, A. Das2, A. K Das1 and A.Venimadhav3, 1,4Department of physics, Indian Institute of Technology, Kharagpur -721302, India

2Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India 3Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur -721302, India

Email: dsekhar21iitkgp@gmail.com Abstract: Multiferroics are materials that exhibit both magnetic and ferroelectric order parameters. Strong coupling of these order parameters inside a material can lead to novel physics as well as device applications [1]. In this aspect geometrically frustrated 114 cobaltite materials, which having a general formula of RBaCo4O7 (R= Ca, Y and Rare earth) seems fruit full candidates. The crystal structure of these 114 cobaltites is build with a Co triangular and kagome lattices, which are basics building blocks for the geometrical frustration [2]. In this family of materials, it is reported that CaBaCo4O7 (CBCO) shows a giant magneto electric (ME) coupling and switching of electric polarization is unclear due to its Noncentrosymmetric nature of the structure [3-4]. Further, the coupling between the magnetic and dipolar properties of these materials is not well understood.

The Noncentrosymmetric crystal nature and the magnetic triangular and kagome layers of Co sub lattice motivated us to study the multiferroic properties of these 114 cobaltites. We have chosen non magnetic (Ca, Y) and magnetic (Dy) elements for “R” site of these families and studied the multiferroic properties. We have investigated structural, magnetic and polarization properties of the geometrically frustrated “114” RBaCo4O7 (R= Ca, Y and Dy) cobaltites. We observed that the coupling between the magnetic and ferroelectric behaviours are strongly depends on the R site element. In case of CaBaCo4O7 we have seen non collinear ferrimagnetic-pyroelectric behaviour and there exist a strong coupling between spin and charge degree of freedom. While neutron diffraction of YBaCo4O7 showed antiferromagnetic ordering and DyBaCo4O7 surprises with no long range magnetic ordering down to 6 K. Our study suggests that excepting CaBaCo4O7 case, evaluating dipolar ordering in rare earth samples is not trivial. In this family only CaBaCo4O7 is pyroelectric and there is no report of ferroelectric ordering.

We have investigated Ni, Mn and Zn doping in CaBaCo4O7 and explored the effect on frustration and dipolar ordering. And our study has revealed Kagome lattice as the main ground to alter the dipolar ordering and by replacing a small amount of Co (5 %) can induce ferrroelectricty. References

• Sang-Wook Cheong and Maxim Mostovoy C, Nature Materials 6, 13 - 20 (2007). • V. Caignaert , V. Pralong , V. Hardy , C. Ritter , B. Raveau , Phys. Rev. B 81, 094417 (2010). • V. Caignaert, A. Maignan, K. Singh, C. Simon, V. Pralong, B. Raveau, J. F. Mitchell, H. Zheng, A.

Huq, and L. C. Chapon, Phys. Rev. B 88, 174403 (2013). • R.D.Johson, K.Cao, F.Giustino and P.G.Radaelli, Phys. Rev. B 90, 045129 (2014).

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Electrochemical Behavior and Mechanical Integrity of Few Layers Graphene upon Lithiation/Delithiation

Farjana J. Soniaa,p, Manoj K. Jangida, B. Ananthojub,c, Ravi Kalia, M. Aslamc, Priya Joharid, Amartya Mukhopadhyaya,*

a High Temperature and Energy materials Laboratory, Department of Metallurgical Engineering and Materials Science

b IITB-Monash Research Academy c Nanomaterials Laboratory, Department of Physics

, Powai, Mumbai 400076 d Department of Physics, School of Natural Sciences, Shiv Nadar University, Uttar Pradesh, India

p Presenting author: e-mail: farjana.jas@iitb.ac.in; Phone: +91 22 25764619 * Corresponding author: e-mail: amartya_mukhopadhyay@iitb.ac.in; Phone: +91 2225767612

Abstract Even though graphitic carbon is the most commonly used anode material for Li-ion battery, it possesses low gravimetric capacity and rate capability; which has stimulated research towards alternative anode materials. Recent investigations have indicated that graphene, the two dimensional building block of graphitic carbon, may possess enhanced Li-storage capacity, along with improved rate capability. However, the mechanism of reversible Li-storage and mechanical/structural integrity of graphene upon repeated Li-insertion/removal are yet to be understood. Therefore, using fairly well-ordered CVD-grown few layers graphene (FLG) film as model material and performing extensive structural/electrochemical investigations, as well as innovative in-situ studies, we have been able to develop better understanding of the inter-related phenomena concerning lithiation/delithiation mechanisms leading to higher Li-capacity, stress developments at different state of charges and mechanical integrity upon lithiation/delithiation. The electrochemical cycling of FLG (~7 layers) in the potential window of 2 to 0.001 V against Li/Li+ leads to the reversible specific capacity of ~4000 mAh/g, which is approximately an order of magnitude greater than that (i.e., ~380 mAh/g) attained with similarly grown thicker (~450 nm) bulk graphite film (TBG) and cycled in the same range of potential. Interestingly, similar to TBG, the chronopotentiograms as well as cyclic voltammograms, obtained with FLG, indicate presence of distinct features corresponding to the formation of Li-intercalated graphite compounds below 0.25 V against Li/Li+; which implies that the Li-intercalation/de-intercalation in the interlayer spaces takes place even for such reduced dimensions of graphitic carbon. Furthermore, the capacity obtained for FLG within just the same lower potential window, i.e., ~1650 mAh/g, is still ~4 times greater than the overall specific capacity obtained with the TBG. Analysis based on the electrochemical response indicated that this excess capacity (or Li-storage in FLG below 0.25 V) had contributions from both the surface as well as diffusion controlled processes of Li-storage. In this contest, simulation based on density functional theory indicated that the excess Li-capacity of graphene (beyond formation of the final Li-intercalated graphite compound i.e. LiC6) is associated with additional stable Li-storage on the surface in the form of multiple Li-layers (but different from Li-plating) and segregation of Li close to the stepped edges of few layers graphene. Even though the FLG possess higher specific capacity as well as improved rate capability with respect to TBG (as above), the cyclic stability of FLG over the full range of lithiation/delithiation (i.e., between 2 and 0.001 V against Li/Li+) was observed to be inferior w.r.t. TBG. However, the cyclic stability, when compared with respect to the capacities obtained just within the lower potential window (i.e., between 0.25 and 0.001 V vs. Li/Li+), was not inferior to that for TBG. In order to gain further insight into this, the in-plane stress developments in the FLG was monitored in-situ during galvanostatic cycling. The net in-plane stress development upon full range of lithiation in FLG matches reasonably well with the stress magnitude expected for the case of classical Li-intercalation in the inter-layer gallery of the graphene film (i.e., up to LiC6 formation). This tends to additionally indicate that the mechanisms of excess Li-storage (i.e., other than Li-intercalation in interlayer spaces of FLG) leads to comparatively much lesser in-plane dimensional changes. Another interesting phenomenon observed in the stress profile of FLG was the ‘stress release’ just within the potential window of 0.5-0.25 V (against Li/Li+), where pristine graphene, dilute stages I and IV co-exist. Based on the evidences obtained from the structural characterizations and geometrical modelling, such stress release is believed to be associated with the mechanical degradation taking place during the

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initial stages of lithiation and later stages of delithiation as a result of possible stretching of individual graphene layers due to Li-insertion at such states of charges beyond fracture strain [1]. Such phenomenon of stress release was not distinctly observed for thicker graphitic carbon films as was shown in ref [2]. Interestingly, the observed ‘stress release’ and expected mechanical/structural degradation for the case of FLG, in just the concerned potential window above 0.25 V, tends to agree well with the fading of overall capacity of FLG w.r.t. TBG, but comparable retention of capacity obtained below 0.25 V (against Li/Li+). These observations thus indicate that the possible reasons for the usually observed inferior cyclic stability of graphenic carbon, in comparison to bulk graphite, lie in the phenomena occurring at such higher potentials. References

• Farjana J. Sonia, Balakrishna Ananthoju, Manoj K. Jangid, Ravi Kali, M. Aslam and Amartya Mukhopadhyay; Carbon 88 (2015) 206.

• Amartya Mukhopadhyay, Anton Tokranov, Kevin Sena, Xingcheng Xiao, Brian W. Sheldon; Carbon 49 (2011) 2742.

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Composite of Colloidal Graphene - Titanium nitride Nanocrystals for Plasmonic,

Electrical conductivity and Elctrocatalytic Applications

G. Shiva Shanker, Metikoti Jagadeeswararao, Ganesh B. markad and Angshuman Nag* Department of chemistry, IISER - Pune - 411008, India.

Abstract: Graphene is one of the attractive material for nano material research due to its two dimensional structure, large surface area and faster charge transport that makes it an attractive building block for multiple applications in combination with nanomaterials1. In this context, graphene has been used as supporting material with different type of nanoparticles thus advancing the relevant performance and expand range of applications2. Metal nitride nanocrystals /graphene composite materials show wide range of applications in the different fields such as optical, electrical, electrocatalysis and so on2 .However, very few report exist on synthesis of titanium nitride nanocrystals /graphene composite4 and moreover there are no reports in the literature of colloidal solution of titanium nitride/graphene composite. Till date, this is an open challenge to make colloidal solution of composite that can open up low cost and easy processible method to study the different solution based properties include thin films, optoelectronic devices, photo catalytic, electrochemical and biological applications. Here, we developed colloidal solution of graphene/titanium nitride composite for the first time. In this presentation, I will discuss the (a) optical properties of composite which includes tuning of plasmon band maximum (700, 740 and 785 nm) with varying the size of titanium nitride nanocrystals on graphene and BET surface area of composite calculated 270 m2/g which is larger than the reported composites4. (b) electrical conductivity of composite (3 S/cm) and its possible mechanism , carrier density (_2.0* 1021 cm-3) and mobility (1.24 cm2 g-1 s-1) are studied. (c) electrocatalytic activity of composite in the presence of triiodide electrolyte is determined the result is comparable to conventional Pt electrode and finally we also studied electrochemical hydrogen evolution of composite. Further, looking into forward we are interested to study plasmon assisted dye sensitized solar cells and water splitting. References: 1. X. Du , I. Skachko, A. Barker, E. Y. Andrei , Nat. Nanotechnol.,2008, 3, 491. 2. X. Chen, G. Wu, J. Chen, X. Chen, Z. Xie , X. Wang , J. Am. Chem. Soc., 2011, 133, 3693. 3. M.M. Ottakam Thotiyl , T. R. Kumar , S. Sampath , J. Phys. Chem. C., 2010, 114 , 17934. 4. P. Han, Y. Yue, X. Wang, S. Dong, K. Zhang, C. Zhang, G.Cui, J. Mater.Chem., 2012, 22, 24918.

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Observation of transient superconductivity at LaAlO3/SrTiO3 interface

1, Shelender Kumar1, Pramod Kumar2, Anjana Dogra2, Dushyant Kumar3, N. Mohanta4, A. Taraphder4, R. C. Budhani2, and Aveek Bid1

1Department of Physics, Indian Institute of Science, Bangalore 560012, India 2National Physical Laboratory, New Delhi 110012, India

3Condensed Matter-Low Dimensional Systems Laboratory, Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016, India

4Department of Physics, Indian Institute of Technology Kharagpur, W.B. 721302, India Abstract: We observed a novel magnetic field assisted transient superconducting state in the two dimensional electron gas existing at the interface of LaAlO3/SrTiO3 heterostructures. The observed transient superconductivity appears upon the application of a time dependent magnetic field at a temperature significantly higher than the normal superconducting TC reported previously in this material. Superconductivity and magnetism are considered to be antagonistic to each other. Hence the observation of the co-existence of these two phases in the oxide heterostructures has thrown up many interesting and as yet unanswered questions. This metastable state depends critically on the doping density in the parent compound. It appears concomitantly with a Lifshitz transition as a consequence of the interplay between ferromagnetism and superconductivity and the finite relaxation time of the in-plane magnetization. Our results clearly demonstrate the inherently metastable nature of the superconducting state competing with a magnetic order in these systems. The co-existence of superconductivity and ferromagnetism in the conducting electronic layer formed at the interface of insulating oxides has thrown up several intriguing and as yet unanswered questions. An open question in this field is the energetics of the interplay between these two competing orders and the present observation goes a long way in understanding the underlying mechanism. References: [1] Ohtomo, A. & Hwang, H. A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface. Nature 427, 423–426 (2004). [2] Reyren, N. et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007). [3] Caviglia, A. et al. Electric field control of the LaAlO3/SrTiO3 interface ground state. Nature 456, 624–627 (2008). [4] Bert, J. A. et al. Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface. Nature physics 7, 767–771 (2011). [5] Li, L., Richter, C., Mannhart, J. & Ashoori, R. Coexistence of magnetic order and two-dimensional superconductivity at LaAlO3/SrTiO3 interfaces. Nature Physics 7, 762–766 (2011). [6] Dikin, D. et al. Coexistence of superconductivity and ferromagnetism in two dimensions. Physical Review Letters 107, 056802 (2011). [7] Joshua, A., Pecker, S., Ruhman, J., Altman, E. & Ilani, S. A universal critical density underlying the physics of electrons at the LaAlO3/SrTiO3 interface. Nature communications 3, 1129 (2012).

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Colloidal, Ligand-free semiconductor nanocrystals for optoelectronics

Metikoti Jagadeeswararao†, Kiran P. Kadla†, Padmashri Patil§, Shouvik Datta§ and Angshuman Nag†,* †Department of Chemistry, §Department of Physics, IISER-Pune, Pune 411008, India

Abstract: Colloidal inorganic nanocrystals are generally capped with organic ligands. While the property of the individual nanocrystal is determined by the inorganic core, its interaction with surroundings is governed by organic ligands. These organic capping ligands are typically insulating in nature, and thus, such organic capped inorganic nanocrystals are not suitable for integration in electronic and optoelectronic devices.1 In this presentation, I will present our results on synthesis of ligand-free metal sulphide nanocrystals.2 These ligand-free nanocrystals have excess sulfide ions on the surface, resulting in a negatively charged surface. Negatively charged nanocrystals repel each other providing colloidal stability in a polar solvent. Ligand-free nanocrystals of undoped and Mn-doped ZnxCd1-xS, AgInS2 and (ZnS)0.4(AgInS2)0.6 have been prepared. Similarly positively charged Sn-doped In2O3 NCs also been prepared for transparent conductors. Unlike organic capped nanocrystals, preliminary results suggest that the ligand-free nanocrystals are electronically coupled to each other in their close packed film. Ligand-free AgInS2 nanocrystal sensitized solar cell shows power conversion efficiency close to 1%, with open circuit voltage ~0.5 V.3 S2-capped (ZnS)0.4(AgInS2)0.6 NCs show 5 mmol g-1 h-1 of H2 photocatalytic activity and which is significantly higher than their bulk counterpart (1.1 mmol g-1 h-1).4 Ligand-free 10 % Sn-doped In2O3 (ITO) NCs exhibit one order magnitude less resistivity (35 mΩ.cm) than oleylamine capped ITO NCs maintaining strong absorption peaks due to localized surface plasmon resonance at ~ 1950 nm.5 References: 1. D. V. Talapin, J. S. Lee, M. V. Kovalenko, E. V. Shevchenko, Chem. Rev. 2010, 110, 389. 2. M. J. Rao, K. P. Kadlag, A. Nag, J. Phys. Chem. Lett. 2013, 4, 1676. 3. K. P. Kadlag, P. Patil, M. J. Rao, S. Datta, A. Nag, CrystEngComm 2014, 16, 3605-3612 4. M. Jagadeeswararao, S. Dey, S. A. Nag, C.N.R. Rao, J. Mater.Chem. A 2015, 3, 8276. 5. M. Jagadeeswararao, S. Pal, A. Nag, D. D. Sarma, ChemPhysChem 2016, 17, 710. ----------------------------------------------------------------------------------------------------------------------------------

Strength-toughness optimization by incorporating functionalized metal oxides within

jute polyester composites

Jaideep Adhikari1, Bhabatosh Biswasi1, Nil Ratan Bandyapadhyay1 Bhairab Chandra Mitra1, Prosenjit Saha1, Arijit Sinha1*

1Dr. M.N.Dastur School of Materials Science and Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India.

* Email: arijitsinha2@yahoo.co.in

Abstract Unsaturated polyester resin is relatively cheap and is easily curable at room temperature, although it ends up with reducing its toughness. So, enhancement in toughness was achieved by incorporating Al2O3 and ZrO2 particles within the matrix. Overall 20 wt. % filler content (18 wt. % fiber and 2 wt. % metal oxide particles) was selected as the optimized composition. 5 % NaOH treated fibers were used for better compatibility with matrix whereas the particles were treated with trimethoxymethyl silane for better adherence with the same. Microhardness, tensile, flexural and impact tests were carried out on the composites. Microstructural observations have also been performed on the fractured surfaces of the composites for an elucidation of toughening mechanism and to assess the effect of metal oxides on mechanical properties.

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Introduction Higher degree of cross-linking exerts thermoset matrices to be brittle in nature. Plastic deformation of the material gets constrained with the increase of cross-link density and thus toughness values decrease [1]. Stress risers’ assists as sites for crack initiation and which in term leads to the spontaneous failure of materials. Traditional toughening agents’ viz., rubber particles, glass beads, core-shell particles, thermoplastic materials etc. increases the toughness values while compromising with the other mechanical properties. So, rigid metal oxides particles viz. Al2O3 was tried for the enhancement of toughness by the researchers. Several theories explains the toughening mechanism, such as crack pinning, crack deflection, particle-matrix debonding, void formation around the particle etc. [2-3]. Along with the particles natural fiber is amalgamated in the matrices for strengthening of composites and prevention from catastrophic failure of the material. Materials and Methods The composites were fabricated using hand lay-up method. Methyl ethyl ketone peroxide (MEKP) as catalyst and cobalt naphthenate as accelerator were used for the room temperature curing of unsaturated polyester (UP) resin. 30 % styrene on the weight of UP resin was used as diluent. Alkali treatment on the fiber and silane treatment on the particles were also performed. Overall 3.5- 4 cm fiber length was maintained for composite fabrication. Results and Discussions In this work, a comparative study has been performed on the basis of mechanical properties of different jute composites viz. UP/Jute, UP/Jute/Al2O3 and UP/Jute/ZrO2. Vickers Hardness test was conducted using LECO LM 100 Micro Vickers Hardness Tester. From Fig. 1(a), it was observed that with incorporation of fiber microhardness values increases and reaches its maximum at 20 wt. % filler content. Further addition of fiber decreases hardness values as difficulty rises in mixing of fibers within the matrix with a high fiber loading. So, in this experiment composites were fabricated with 20 weight % filler content (18 wt. % fiber and 2 wt. % metal oxide particles). Enhancement in microhardness values was observed with the incorporation of metal oxides which can be seen in Fig. 1: (b).

Fig.1: (a) Miocrohardness variation with fiber loading of UP/Jute composites (b) Microhardness of different Jute composites with optimized filler loading.

Tensile tests were carried out according to ASTM D 3039 standards; Flexural tests and Impact tests were conducted according to ASTM D 790 and ASTM D 4812 standards. From Fig.2 it was clearly vivid that metal oxide dispersed composites have superior mechanical properties. ZrO2 added composites were found to be the best over Al2O3 added and blank jute composites. Impact strength was significantly enhanced with the addition of ZrO2 particles.

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Fig.2: (a) Tensile (b) Flexural (c) Impact properties of different composites.

Summary Metal oxide particles enhance mechanical properties in all aspects. Hindrance by the hard and rigid particles in the path of a propagating crack may be the reason of higher toughens values. From comparative study ZrO2 particles were found to be superior over Al2O3 added particles. The crude hand lay-up method displays moderate strength which can be used for low technical applications such as in the packaging field. But, from the results it can be assumed that modification in the fabrication technique viz. compression moulding may lead to a material with superior mechanical properties which can be used as a structural material. References

1. R.P. Singh, M. Zhang, D. Chan, J. Mater. Sci.,37 {2002} 2. B Wetzel , P Rosso, F Haupert, K Friedrich, Eng. Fracture Mechanics, 73 (2006) 3. B.B. Johnsen, A.J. Kinloch, R.D. Mohammed, A.C. Taylor, S. Sprenger, Polym. 48 (2007)

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Theoretical and experimental investigations on surface plasmon resonance assisted interferometric fringe modulation under both radial and lateral shearing environment

with application in sensing

Jayeta Banerjee 1*, Mahua Bera 2, Mina Ray3 1,2,3 Department of Applied Optics & Photonics

University of Calcutta, JD-2, Salt Lake, Sec-III, Kolkata – 700106, India E-mail: 1j.banerjee87@yahoo.com,

2beramahua@gmail.com, 3mraphy@caluniv.ac.in

*Corresponding Author Abstract: The superposition of two periodic or quasi-periodic patterns in optics produces the moiré patterns. In moiré, a new set of secondary fringe can be generated by combining two sets of fringes [1]. Apart from the sensing of stress, strain moiré fringes can be used to demonstrate the filtering effect of surface plasmons (SPs). Surface plasmon resonance (SPR) occurs for TM-polarization under the attenuated total reflection (ATR) coupler mode satisfying the wave vector matching condition. SPR technique can precisely measure small change in refractive index of the sensing medium. Thus it makes useful in chemical and biological sensing [2]. SPR measurement using phase detection based interferometric technique can improve the resolution of the device over conventional intensity measurement. SPR modulated radially sheared interference imaging has been demonstrated using a birefringent lens (BL) for the two substrates as well as for the two analytes [3]. Further a novel SPR mediated moiré fringe generation is theoretically and experimentally investigated using a BL and a Wollaston prism (WP) under dual shearing (lateral as well as radial) environment [4]. BL provides radial shear between two orthogonal polarizations whereas a WP provides the lateral shear. SPR configurations are the well known three/four layer SPR structure, and their uses depend on the application. Different SPR structures are analyzed based on different resonance parameters such as reflectance, phase, field enhancement, complex amplitude reflectance Argand diagram (CARAD) [5]. Moreover, multi spectral sensing has been demonstrated theoretically by us with multi spectral multi thickness (MSMT) structure [6].

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The schematic diagram of experimental set-up for Fresnel zone like moiré pattern (FZMP) generation is shown in Fig 1(a). A circularly polarized beam is generated from collimated beam after passing through a combination of polarizer and quarter wave plate. Collimated circularly polarized beam is focused and incident on WP in order to laterally separate two orthogonally polarized components. These laterally shifted beams are incident on BL having two longitudinally shifted foci, one corresponds to ordinary and other to extraordinary vibrations. BL produces radially sheared Fresnel zone-like pattern (FZP) having bright and dark centre for ±45° transmission axis of analyzer. The generated moiré pattern will be incoherent or coherent depending on absence or presence of the analyzer.

Different types of moiré patterns are shown in Fig 1(b). If the lateral shear is less than diameter of central zone of FZP, then broad straight equi-spaced straight moiré fringes are generated. Moreover, if the amount of lateral shear is greater than diameter of central zone of FZP, then FZMP will be appeared. This FZMP is incident on uncoated and 40 nm Al coated BK7 glass prism for demonstration of SPs excitation. As SPs couples to p-polarization, the p-polarization component of FZPs gets modulated and bright centre changes to dark centre as shown in Fig 1(c) whereas, the s-polarization component remains unaffected. Selection of the incident angle and metal thickness are very crucial for efficient SPs excitation [7].

Contour map of E-field enhancement for SPR structure with Al coated BK7 prism and air as analyte with simultaneous angular and wavelength interrogation for optimized 40 nm metal thickness is shown in Fig 2(a). Aluminum is selected as it provides maximum e-field enhancement among Ag, Au and Al as shown in inset of Fig 2(a) and moreover, it is cost effective. Fig 2(b) shows the phase curves for different concentration of oxygenated hemoglobin of human blood. Binary output of ‘00’ or ‘11’ and ‘01’ or ‘10’ due to SPR assisted moiré interferometry for Al coated and uncoated areas are shown in Fig 2(c). This binary representation can be further utilized in non contact testing of surface profilometry as proposed by us [8]. Acknowledgement: Jayeta Banerjee would like to acknowledge Department of Science & Technology, Government of India for financial support vide reference No Ref.No.SR/WOS-A/PM-1015/2015(G) dated 11/07/2016) under Women Scientist Scheme. References: [1] O. Bryngdahl, J. Opt. Soc. Am. 66, 87-94, 1976

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[2] J. Homola, Chemical Review, 108, 462-493, 2008. [3] M. Bera, J. Banerjee, M. Ray, Appl. Phys. Lett., 104(25), 251104-1-5, 2014. [4] M. Bera, J. Banerjee, Mina. Ray, Optics Letters, 40 (8), 1857-1860, 2015. [5] M. Bera, J. Banerjee, M. Ray, J. Mod. Opt., 61, 182, 2014. [6] J. Banerjee, M. Bera, M. Ray, Journal of Appl. Physics, 117, 113102, 1-13, 2015. [7] M. Bera, J. Banerjee, M. Ray, Journal of the Optical Society of America B, 32(5), 961-970, 2015. [8] J. Banerjee, M. Bera, M. Ray, Journal of the Optical Society of America B, 33(7), 1462 -1469, 2016

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Defect mediated n-type behaviour of unintentionally doped ZnO nanorods: correlating

defects, emission spectra, morphology and conductivity.

K. Bandopadhyay and J. Mitra School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram, 695016, India Abstract:

Electrically active native point defects (NPD) often, directly or indirectly control the optical and electrical properties of oxide semiconductors1. The reduced dimensionality of their nanostructured forms further influencing the defect density and abundance, especially at the surfaces. Controlling NPD abundance and understanding the consequential physical properties have become quite important, not only for the performance characteristics but often offer novel applications, hitherto unknown. ZnO nanostructures (ZoNS) possessing rather unique electrical and optical properties (band gap ~ 3.3 eV) is one such promising candidate for developing novel opto-electronic devices. Interestingly, most forms of nominally undoped ZnO exhibits n-type character while preparing its p-type counterpart remains a challenge. The origin of this unintentional n-type nature is thus a matter of intense debate. The complexity of the origin has been further exacerbated because the potential culprits harbouring excess electrons require processes that are energetically disfavoured. For example, while oxygen vacancies (VO) forms donor bands deep within the band gap, the formation energy of interstitial zinc (IZn), which forms a shallow donor band, are enthalpically too costly (≥ 4 eV). The photoluminescence (PL) investigations2, on ZoNS with varying concentrations of Zn, indicate that high incidence of both these NPDs results in shallower donor states, with evidence of defect states lying even within the conduction band (i.e. above the ZnO Fermi level), which would thus spontaneously dope the system. Our experimental findings provide the first evidence of theoretical investigations, which predict that complexes of the deep level VO and the shallow IZn NPDs forms hybridized3 defect states which are responsible for the n-type, electron rich character of ZoNS. When conducted with variable excitation energies the system displays a rich array of colours from violet, green, orange to red. The colours not only indicate the presence of the various shallow and deep level NPD states2 but their evolution provides crucial information regarding the transition processes in this oxide. Photoluminescence excitation (PLE) studies on the differentially Zn doped ZnO further evidences the above excitation energy dependence of emission and elucidates novel correlations in their electronic transitions. Additionally, the PLE spectra also indicate the presence of defect states within the conduction band itself only in a Zn rich environment, with strong correlation with emission in the visible. As mentioned earlier these results provides experimental verification of theoretically predicted mechanism for the n-type character of ZnO, giving rise to a more complete energy band diagram.

If understanding the physics of NPDs has been difficult, their control and engineering has been even more challenging. Broadly, their control has been successfully achieved by engineering the morphology of the ZoNS, i.e. by tailoring the growth techniques4 and conditions5. And, understanding the correlation of morphology with optoelectronic transport has become central to optimizing the device properties.

It has been well documented that in ZnO the highly mobile oxygen or rather its vaccancies play a major role in deciding the overall conductivity of the system. The large surface area afforded to ZoNS then very strongly couples its electrical response to the NPDs, especially important at the surfaces. The coupling has lead to some intriguing physical phenomenon and several important applications. In the next part of our study a conductive atomic force microscope (CAFM) has been used to study the spatially resolved

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photoresponse properties on individual ZnO nanorods, with the aim of correlating surface morphology and thus defect distribution via the spatial variation in photoresponse. The CAFM measurements, supplemented with differential conductance (dI/dV) maps (CMAP)6, were conducted on the hexagonal top facets of IZn rich ZnO nanorods. The results show the variation of surface conductivity and crucially its correlation with topography. The simultaneously recorded topography and dark CMAPs, on the hexagonal top facets exhibit a broad grain size distribution, ranging from 30 – 150 nm. The relevance of the distribution assumes significance since the current and CMAPs show that (i) the smaller grains carry much larger current than the bigger ones and (ii) the smaller grains show significantly enhanced conductivity and photoconductivity (to super bandgap excitations) compared to the larger grains. Thus the high current and conductivity is strongly correlated with the small grains i.e. regions with higher incidence of NPDs7, which though counterintuitive in general, is perhaps comforting in the context of ZnO.

Even though the deep level defect band(s) (originating from VO) has always shown green emissions (in the PL spectrum), it has been rather absent in absorption studies. Interestingly, we find that even though the bare nanostructures show no optical absoprtion in the green it does display discernable photoresponse to the same. The spatially resolved photoresponse data recorded for two wave-lengths 355 nm and 532 nm, corresponding to super- and sub- bandgap energies, respectively. The results not only provide direct evidence of correlation between surface morphology and photoresponse, but also discriminates between the photoactive regions in terms of the excitation energies. While the 355 nm excitation localises high conductivity and photoconductivity onto the smaller grains, the green excitation localises them not only to the smaller grains but importantly to the smaller grain boundaries than the grain centers. The high spatial resolution (~ 2nm) of the CMAPs and the energy discrimination thus helps us correlate the surface photoactivity in this colourful oxide. The spatially resolved data is also supplemented by detailed point current voltage characterisation to investigate the physics of charge transport in the CAFM tip-sample nanocontact, varying from thermionic emission to field assisted tunnelling.

Finally, our investigations have drawn a direct relationship between the NPDs, morphology, electrical conductivity and photoresponse in ZnO nanostructures, along with a demonstration of the capability of using illuminated surface conductivity (dI/dV) mapping AFM as a tool to characterize spatially resolved photoresponse of semiconductor nanostructures. References: 1. L. J. Brillson, et al., J. Vac. Sci. Technol. B: Microelectronics and Nanometer Structures 30 (5), 050801-050811 (2012). 2. K. Bandopadhyay and J. Mitra, RSC Advances 5 (30), 23540-23547 (2015). 3. Y.-S. Kim and C. H. Park, Phys. Rev. Lett. 102 (8), 086403 (2009). 4. D. Gedamu, et al., Adv. Mater. 26 (10), 1541-1550 (2014). 5. M. R. Alenezi, et al., Sci Rep 5, 8516 (2015). 6. K. Bandopadhyay and J. Mitra, Scientific Reports 6, 28468 (2016). 7. K. Vanheusden, et al., J. Appl. Phys. 79 (10), 7983-7990 (1996).

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Tuning of Edge and Surface Energy of TiO2 Nanotubes via Partial Rupture by Controlling Anodization Voltage for Gas Sensor Device Applications

1,*, Partha Protim Chattopadhyay2 and Partha Bhattacharyya1, * 1Department of Electronics and Telecommunication Engineering, Indian Institute of Engineering Science

and Technology, Shibpur, Howrah-711103, India 2Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and

Technology, Shibpur, Howrah-711103, India *Tel: +91 9163080083, e-mail: koushikdutta71187@gmail.com

Tel: +913326684561261 (Extn. 544), e-mail: pb_etc_besu@yahoo.com

Abstract

Sensing performance of metal oxide based gas sensor is predominantly governed by the adsorption-desorption kinetics at the adsorption sites which is a function of the truncation of the surface of nanoarchitechtured metal oxide [1]. The adsorption phenomenon, due to its endothermic nature, requires activation energy which is normally supplied either by external heating or photo energy (like ultra violet irradiation) [1]. On the other hand, nanostructured material supplies the Gibbs free energy which in turn reduces the requirement of external energy supply [2]. In this relation, the edges (termination of two surfaces) and the corners (meeting of two or more edges) of the nanostructured material plays a vital role as the atoms, residing at these sites, have lower saturation state due to which they exhibit higher catalytic activity than that of which resides at the surface [3]. Mathematically, the rate of adsorption can be represented as;

(1)

Where, R is the universal gas constant, T is the absolute temperature, Epo is the required energy for adsorption, P is the partial pressure, m is the molecular mass of adsorbate, k is the Boltzman’s constant and f(t) is the isotherm function. Eps, Epe and Epc are the free energies proportional to surface area, edge length and number of corners, respectively. From the application point of view, for the detection purpose of carcinogenic benzene, toluene and xylene (BTX) high operating temperature is required due to their higher dissociation energy [1]. In this connection, room temperature BTX sensor can possibly be achieved through increasing the amount of corner and edges in a nanoarchitechtured material.

In the present endeavor, titanium dioxide (TiO2) is considered due to its efficient sensing capabilities and catalytic effect. High voltage anodization (> 50 V) is a reliable route to partially split (bamboo-splitting) a selected portion of TiO2 nanotube [4]. But room temperature anodization results in covering on grown nanotubes [4]. To circumvent this, a bath temperature of 37°C was used for anodization of Ti foil for 12 hours applying 60 V potential with ethylene glycol based ammonium fluoride solution with 2 vol% water (T60). Also for comparison, another sample (T20) was prepared where the conventional 20 V anodization was performed keeping all the other parameters same. The FESEM images of both samples (annealed) are shown in Fig. 1(a-b) where the rupturing is evident only for T60. Moreover XPS study (Fig. 1(c-d)) authenticates that the T20 contains higher amount of oxygen vacancy than of T60.

Fig. 1. FESEM images of (a) T20 and (b) T60 with respective cross-sectional view in inset and XPS pattern O (1s) peak for (c) T20 and (d) T60

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To fabricate vertical device Pd, as the top electrode, was deposited via e-beam evaporation technique whereas Ti substrate served as the bottom electrode, for both the cases. Device schematic with dimension is shown in Fig. 2 (a). Each of the devices was exposed to 1-100 ppm of BTX at room temperature (~27°C). The dependence of response magnitude with concentration (Fig. 2 (b)) shows almost linear relation for both the samples. The transient characteristics are shown in Fig. 2 (c) and (d). It was observed that, the ruptured nanotubes (T60) were more sensitive than pristine one (T20).

Fig.2. (a) Device Schematic with dimensions (not to scale). (b) Variation of response magnitude with concentration for both samples and transient charateristics for (c) T20 and (d) T60 based device.

To establish the correlation with, a simple geometrical model (Fig. 3) of single nanotube was considered for pristine (un-ruptured) and ruptured one where the cotribution due to annular ring was neglected due to their smaller dimension. Also it was assumed that the ruptured section was of equilateral tringle shape in horizontal direction of side a. The vertical equilateral triangle with side y was in such a way that y = ma where m numbered section was ruptured due to high electric field during anodization. Simple calculations allows to infer that the there will be loss in surface area (if it is considered the rupturing was started from an un-ruptured nanotube) with the benefit of gain in edge length and introduction of corners at naotube morphology. They may be quanified as Egain and Crupt shown in Eq. 2.

and (2)

Fig. 3. Schematic of (a) un-ruptured nanotube and (b) ruptured nanotube. Magnified cross sectional view is shown as inset.

Hence, the significant increase in edge and corner increases the effective free energy which is responsible for such superior sensing performance of ruptured nanotubes (T60) at room temperature. The corresponding reduction (due to rupturing) in surface area/energy was proved to be insignificant and was dominated by the increment in edge/corner energy as demonstrated by a simple geometrical model.

References

[1] K. Dutta, P.P. Chattopadhyay, C-W. Lu, M-S. Ho and P. Bhattacharyya, Applied Surface Science 354 (2015) 353–361.

[2] G. Erana, Taylor and Francis, Boca Raton (2012) ISBN: 13:978-1-4398-6341-1. [3] E. Roduner, Chemical Society Reviews 35 (2006) 583–592. [4] J. H. Lim and J. Choi, Small 3 (2007) 1504–1507.

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Functionalized Nanocomposite Cathode to Enhance the Stability of Solid Oxide Fuel Cell Performance

Koyel Banerjee (Ghosh)

Fuel Cell and Battery Division CSIR-Central Glass and Ceramic Research Institute

Kolkata 700032, India Abstract

The electrochemical performance of Sr-doped lanthanum iron ferrite and cobaltite (LSFC) -based mixed ionic and electronic conducting material supersedes the conventional Sr-doped manganite (LSM) cathode in terms of oxygen reduction reaction (ORR) at a temperature <800 oC . In order to counter the major problem of demixing of Sr for LSFC-based cathodes, several approaches have been attempted to decrease the surface segregation of Sr.1-3 Because of the high solid solubility of SrO in ceria, the present work emphasises on a novel approach towards synthesizing nanocomposite cathode material La0.54Sr0.40Fe0.20Co0.80O3- (LSFC)@Co0.01Ce0.79Gd0.20O2- (CoCGO) where doped ceria and LSFC serve as the inner and outer layers respectively. Such synthesized particulates of patterned orientation of phases are aimed to restrict the Sr diffusion from LSFC within the particulates itself. The double stage autocombustion technique involves use of phase pure CoCGO particles, synthesized by soft chemical route, as a seeding agent in the precursor of LSFC for synthesizing LSFC@CoCGO functional material which is schematically shown in Figure 1.

Figure 1: Schematic representation of the synthesis procedure of LSFC@CoCGO.

XRD patterns of LSFC@CoCGO nanocomposite exhibiting all the characteristic diffraction peaks belonging to the crystalline CoCGO and LSFC reveal the formation of LSFC and CoCGO materials as a composite. UV absorption spectra reveal that the band gap for the synthesized LSFC@CoCGO is 4.09 eV whereas the same is found 4.88 eV and 4.99 eV for single phase CoCGO and LSFC respectively. Shifting of the band gaps towards lower eV confirms the formation of a hetero junction preferably at the interface of the synthesized LSFC@CoCGO materials. Raman Spectra obtained from the sintered LSFC@CoCGO shows a slight red shift of the CoCGO peak (446 cm-1) compared to Raman peak at 460 cm-1 (corresponding F2g mode) observed in single phase pure CoCGO materials. The spectrum from nanocomposite is confirmatory to the formation of direct interfaces between LSFC and CoCGO crystalline phases. TEM image of the calcined LSFC@CoCGO powder samples shows the average particulate sizes in the range of 20-30 nm. A contrast in the peripheral region compared to the central portion of the nanoparticulates suggesting presence of LSFC phase onto CoCGO. Elemental analysis of the LSFC@CoCGO sintered bulk using high angle annular dark field scanning transmission microscope (HAADF-STEM) exhibits a mutually interpenetrating continuous network.

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Electrical characterization of the sintered bulk samples LSFC@CoCGO results in higher electrical conductivity (~260 S cm-1 at 800 °C) over the conventionally synthesized admixtures of the individual components (~30 S cm-1 at 800 °C) confirming the presence of ohmic contacts between higher conducting LSFC phases surrounding CoCGO. Electrode and ohmic polarizations of the cathode in symmetric cell configuration are found to be 0.05 cm2 and 4.05 cm2 at 800 oC in static air. The single cell performance of this novel cathode material evaluated in the form an anode supported single cell of configuration Ni-YSZ||YSZ||CoCGO|LSFC@CoCGO results in the current densities (C.D.) as high as 2.88 A cm-2 at 0.7 V and 800 °C using hydrogen as fuel and oxygen as the oxidant. The C.D. of single cell with such cathode is found to be 2.33 A cm-2 under similar condition. The long term endurability study shows the voltage degradation of 0.7 % and 1.22 % per 240 h with a constant current load of 0.5 A cm-2 and 1.0 A cm-2

respectively. The lower cell voltage deterioration is preferably for the dissolution of SrO in the synthesized functional LSFC@CoCGO particulates, however, the increase in voltage degradation to 3.8 % and 4 % is observed under the similar condition in the span of 240-600 h. The probable mechanism for stabilizing nanocomposite cathode is schematically elucidated in Figure 4.

Figure 4: Schematic of cathode stabilization mechanism for LSFC@CoCGO

References

• A. Mai, V.A.C. Haanappel, F. Tietz, D. Stover, Solid State Ionics 177 (2006) 2103-2107. • Koyel Banerjee, J. Mukhopadhyay, R.N. Basu, International Journal of Hydrogen Energy 39 (2014)

15754-15759. • Koyel Banerjee Ghosh, J. Mukhopadhyay, R.N. Basu, Journal of Power Sources 328 (2016) 15-27. •

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A study of inorganic metal halide perovskites and their application in opto-electronic

devices

Lekha Peedikakkandy1 and Parag Bhargava2 1Centre for Research in Nanotechnology and Science, IIT Bombay, Powai, Mumbai-400076.

2Department of Metallurgical Engineering and Materials Science, IIT Bombay , Powai, Mumbai-400076. E-mail: Lekha@iitb.ac.in, pbhargava@iitb.ac.in.

Abstract:

Advent of a new class of conducting perovskites with ABX3(A=Cs, CH3NH3PbI3 B=Sn,Pb and X=Cl, Br, I) composition has generated a lot of interest among researchers in the field of opto-electronic devices. Organic-inorganic hybrid perovskites (eg: A=CH3NH3PbI3, CH3NH3SnI3) are well studied and reported. These hybrid perovskites show strong absorption in visible region and high charge transport properties and has been used as absorbers in perovskite solar cells with efficiencies up to 21%, but these organic-inorganic hybrid structures suffer from inherent stability issues. In contrast, inorganic perovskites remain less explored, there has been only very few reports on detailed study of structure, different phases and optical properties of this class of materials.

Cesium tin halides show strong PL at room temperature, with its excellent optical properties, tin halide perovskites are extremely promising materials which can be for application in light emitting devices or photo-detectors. This article reports the composition dependent structural and optical properties of varying compositions of CsSnX3 (X=Br, Cl, I).

Figure1:(a) Photoluminescence spectra for different compositions of CsSnX3 (b) Photoluminescence spectra for CsSnI3 with different cations (CH3NH3+ and Pb2+).

The optical band gap shows a ~54% blue shift in the absorption spectra for composition ranging from CsSnI3 to CsSnCl3 as shown in figure 1(a). It was observed that as the anionic composition of the CsSnX3 perovskite is varied from Cl to Br to I the optical band gap estimated from PL emission decreases from 2.8 to 1.3eV. The effect of cation substitution on the band gap was also studied by replacing Cs+ with organic cation CH3NH3+ and Sn2+ with Pb2+. The shift in optical band gap (figure 1(b)) was not as prominent as in the case of anion substitution.

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Figure 2 (a) SEM image and elemental mapping of cross section of DSSC prepared with CsSnI3as the HTM showing penetration of CsSnI3 HTM into the mesoporous network of photoanode. (b) J-V characteristics of SnF2 doped CsSnI3ss-DSSC with varying doping concentrations.

After a detailed study on the synthesis, structural and opto-electronic properties of different compositions of cesium tin halides. Application of cesium tin iodide as a hole transport material in DSSC with N3 dye was investigated. Figure 2(a) shows the cross-sectional SEM micrograph and elemental analysis of CsSnI3 HTM based ss-DSSC. Elemental analysis studies through the thickness of titania photo-anode confirm penetration of CsSnI3 through the mesoporous network of titania photo-anode. Figure 2(b) compares the J-V characteristics of ss-DSSCs with varying doping concentrations.

For higher doping concentration it was found that the Jsc of the cell reduced drastically from 10mA/cm2 for 5wt % SnF2 doping to 7.8mA/cm2 for 8% SnF2 doping. This was identified due to the corrosive nature of Fluoride (F-) ions. As the fluoride content in the HTM solution increases, fluoride ions de-nature the dye molecules reducing the photo-current of the cell.

References: [1] I. Chung, J.H. Song, J. Im, J. Androulakis, C. D. Malliakas, H. Li, A. J. Freeman, J. T. Kenney and M. G. Kanatzidis, J. Am. Chem. Soc. (2012), 134, 8579.

[2] P. Lekha and P. Bhargava, Mater. Sci. Semicond. Process, (2015), 33, 103.

[3] D. E. Scaife, P.F. Weller, W.G. Fisher, J. Solid State Chem. (1974), 9, 308.

[4] P. Lekha and P. Bhargava, RSC Adv. (2016), 6, 19857. ----------------------------------------------------------------------------------------------------------------------------------

Low field magnetoresistance of polycrystalline Gadolinium for different spatial

dimensions (Bulk, Film and Nanowire)

Manotosh Chakravorty S. N. Bose National Centre for Basic Sciences, Kolkata

Abstract: Magnetism in Gadolinium (Gd) is fast re-emerging as an actively researched area [1,2]. The magnetism, spin structure, and magnetocrystalline anisotropy in Gd (a 4f metal) is qualitatively different from those found in more conventional ferromagnetic 3d metals like Fe, Co, and Ni. Strongly localized magnetic moment of Gd ions without orbital contribution, rather low and temperature dependent magnetocrystalline anisotropy energy (MAE), makes Gd a special ferromagnetic metal. In recent years, there is renewal of interest in magnetism of Gd, particularly nanocrystalline Gd [1,2]. The spin reorientation (SR) transition in Gd occurs at a well defined temperature TSR~235K which is very unique because the magnetocrystalline anisotropy ~ 0 at TSR [3]. This feature is not seen in most (if not no other) ferromagnetic materials. Very recent neutron scattering studies [1] on nanocrystalline Gd powders found that while the angle θ in

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polycrystalline samples with large grains (size (D)>few μm) follows the temperature dependence as seen in single crystals, for samples with a characteristic grain size (DC) < 38 nm, θ has a temperature independent value ~ 500. In this work we study the evolution of low field (μ0H<0.2T) magnetoresistance (MR) of Gd as the grain size in the sample is changed from few microns (~ 4 μm) to the nanoscopic regime (~ 35 nm). The low field MR has a clear effect on varying grain size. In large grain sample (few μm), the magnetic domains are controlled by local anisotropy field determined mainly by the magnetocrystalline anisotropy. The low field MR clearly reflects the temperature dependence of the magnetocrystalline anisotropy. For decreasing gain size, the contribution of spin disorder at the grain boundary increases and enhances the local anisotropy field. Here we also study the low field MR of a single Gd nanowire (NW) patterned from a nano-structured film (average grain size ~ 35 nm) by focused ion beam. The results are compared by the polycrystalline sample with large crystallographic grains (~ 4 μm). It is observed that in the low field region the MR of NW is due to the motion of magnetic domains. The MR in the large grained sample shows a close relation to the characteristic temperature dependent magnetocrystalline anisotropy including a sharp rise in MR at the spin reorientation transition at 235K. In stark contrast, in the nanowire, the MR shows complete suppression of the above behaviours and it shows predominance of the grain boundary and spin disorder controlling the domain response. The spin disorder at the grain boundaries and pinning by disorder become important. A larger pinning potential for the domains reduces the MR in the films. This suppresses the features associated with the intrinsic magnetocrystalline anisotropy. The evolution of the MR with grain size shows clear cross over from an intrinsic magnetocrystalline anisotropy dominated regime to a grain boundary spin disorder dominated regime. Though the micro-structure of the NW is similar to a bulk nanocrystal film, MR seems to be governed by the shape anisotropy and disorder. Bibliography:

1. F. Dobrich, J. Kohlbrecher, M. Sharp, H. Eckerlebe, R. Birringer, and A. Michels, Phys. Rev. B 85, 094411 (2012).

2. D. H. Ryan, A. Michels, F. Dobrich, R. Birringer, Z. Yamani, and J. M. Cadogan, Phys. Rev. B 87, 064408 (2013).

3. C. D. Graham, Jr., J. Appl. Phys. 34, 1341 (1963).

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Visible Light Activity and Thermoelectric Performance of Aluminium Doped Zinc Oxide/Polyaniline (AZP) Hybrid

Mousumi Mitra, Dipali Banerjee*

Department of Physics, Indian Institute of Engineering Science and Technology, Shibpur-711103 *Corresponding Author Email: dipalibanerjeebesu@gmail.com

Abstract The appearance of organic-inorganic photo active materials has led to a noticeable growth in the heterogeneous visible-light photo catalysts [1]. Recently, metal oxide-conducting polymer composites are also used as assuring candidates for lightweight, cost-effective and nonpoisonous thermoelectric applications [2]. In the present work, AlZnO/PANI (AZP) hybrid was synthesized employing in situ oxidative polymerization of polyaniline (PANI) in presence of aluminium doped zinc oxide (AlZnO) nanorods, prepared via sol-gel route, acting as a template.

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Even after repeated use, AZP hybrid shows better photo catalytic action through aluminium (Al) doping in comparison with its components for the degradation of methyl orange (MO) and rose bengal (RB) dyes under visible-light irradiation. The superiority of the photo catalytic process was decided by the rate constant, 1.77 X 10-2 min-1 and 2.61 X 10-2 min-1 for MO and RB dyes. The role of active species played in the photo catalytic processes were discussed in the proposed mechanism section through scavenger test. Electrochemical impedance spectroscopy and linear scan voltammetry under dark and visible-light illumination also established the visible-light activity of the AZP hybrid due to decrease in the electron transfer resistance results in an enhancement in photocurrent. The significant enhancement of photo degradation may be assigned to the efficiency of charge separation, induced by synergistic effect between an organic conductor (PANI) and an inorganic semiconductor (AlZnO). Table 1. Rate constant values (min-1) of AlZnO, PANI, AZP hybrid (at room temperature)

The photoluminescence intensity decreases in the order of AlZnO > PANI > AZP, indicating that the existence of PANI diminishes the possibility of electron–hole pairs recombination. This can be attributed to the fact that the photo generated electrons at the conduction band (CB) of PANI move rapidly to the CB of AlZnO, while a few photo generated holes are excited from the valence band (VB) to the conduction band on the AlZnO surface and then moved to the PANI due to proper interface (hetero structure) potential, avoiding their direct recombination with electrons. Photo induced current density data of the prepared samples supports the separation efficiency of the photo generated carriers. The variations of the photo induced current densities of AlZnO (inset), PANI and AZP hybrid. It is observed that the hybrid creates higher photo induced current densities compared to both the constituents. This reveals that separation efficiency of the photo generated e-/h+ pairs, and the migration ability of the photo generated e-s of AlZnO are effectively increased due to addition of PANI in the hybrid. This hybrid can also be used as thermoelectric material. The thermoelectric properties of the AZP hybrid are measured at room temperature. Our results indicate that the Seebeck coefficient of the hybrid is increased nearly by three times with addition of AlZnO to PANI. The figure of merit ZT at room temperature for this hybrid (3.5 X 10-3) is enhanced than its constituents.

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References [1] Ansari, M. O.; Khan, M. M.; Ansari, S. A.; Lee, J.; Cho, M. H. RSC Advances 2014, 4, 23713. [2] Zheng, B.; Liu, Y.; Zhan, B.; Lin, Y.; Lan, J.; Yang, X. J. Electron. Mater. 2014, 43 (9), 3695. (c)

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First-principles Design of 2D Nanostructures for Efficient Storage of Hydrogen and Fuel Cell Catalysis

Paramita Banerjee Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-

700032 Email: mspb@iacs.res.in

Abstract: Hydrogen economy is arguably the most promising alternative to the current hydrocarbon based economy, towards providing clean and sustainable energy. Primarily, it is due to the fact that hydrogen is an ideal, environment friendly and renewable carrier of energy which contains the highest energy density per unit mass(120 MJ kg-1). It is mandatory to store hydrogen in such a way, that it could be recovered whenever needed and the stored energy can be converted into electrical energy via oxygen reduction reaction (ORR)in low temperature fuel cell.

First principles density functional theory (DFT) is a viable approach to investigate the binding energy and adsorption-desorption kinetics for hydrogen storage as well as, to study the reaction kinetics and evaluate the over potential values of different catalysts used to accelerate the kinetics of ORR. In this article, I report the results of our DFT simulations, using localized or plane-wave basis set (depending on the system under consideration),the hydrogen storage capability of two novel materials doped with light alkali and alkaline earth metal atoms: (a) carbon nanohorns and (b) hydrogenated h-BN nanosheet. Finally, I shall discuss(c) the catalytic efficiency of S and P doped graphene quantum dot (GQD) in ORR. The salient features of these three case studies are as follows :

Case-study (a):‘Nanohorn’ is a new type of carbon allotropes discovered by Iijima et al1 in 1998. Pristine single walled carbon nanohorns (SWCNH) are chemically too inert to be used for the technological applications like hydrogen storage. We have doped different alkali and alkaline earth metal atoms (e.g. Na, Ca and Li) on different sites of the SWCNH and investigated2 the hydrogen adsorption (Fig. 1) and desorption efficiency of these metal decorated carbon nanohorns. We found that Li doped carbon nanohorns can adsorb a maximum of 7 wt % hydrogen (Table 1) with an average binding energy ~ 0.14 eV/H2

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molecule, which satisfy the criteria set by the U.S. department of energy (DOE) for efficient hydrogen storage.

Case-study (b): Two dimensional h-BN sheet is a chemically inert insulating material (Eg ~ 5.0 eV). After full hydrogenation, this nanosheet (BHNH) becomes slightly corrugated with a reduction of band gap. Using Bader charge analysis, we ascertain that Li becomes cationic on the BHNH surface and acts as a binding site to adsorb hydrogen molecules (Fig.2 and Table 2). The binding energy (~ 0.18-0.3 eV/H2 molecule) and gravimetric density (~ 6 wt%) (upto~200 K) of the hydrogen molecules fall in the desirable energy window. Ab-initio molecular dynamics simulation indicates complete dehydrogenation from this system occurs at ~ 400K. Thus from the point of view of gravimetric efficiency as well as desorption kinetics, this nanostructure system3 is a prospective candidate for efficient hydrogen storage.

Fig3. ORR on S doped GQD in alkali medium

Case study (c): In order to design a new, cost-effective and metal free catalyst to increase the speed of ORR in fuel cell, we have performed a systematic study on pristine as well as P- and S- doped graphene quantum dot (GQD). We vary the position of doped S and P atoms, from the edge of the GQD to the centre and investigate the changes in the values of the over potential and reaction kinetics. Our preliminary results indicate that S- and P-doped GQD(Fig. 3) can be used as potential ORR catalyst with very high efficiency4

Conclusions: DFT based first principles approach provides a powerful tool that can be gainfully utilized to investigate some novel nanostructures viz. (i) doped nanohorns and BHNH sheet as hydrogen storage materials with optimum adsorption/desorption characteristics and (ii) doped GQD designed for ORR catalyst in a low temperature fuel cell. These are suggestive of some meaningful route towards hydrogen economy.

Acknowledgment: The author would like to thank Dr. R. Thapa, Dr. B. Pathak, Dr. K.R.S. Chandrakumar and Prof. G.P. Das for fruitful collaboration, guidance and support.

References:

1. S. Iijima, M. Yudasaka, R. Yamada, S. Bandow, K. Suenaga, F. Kokai and K. Takahashi, Chemical Physics Letters 309, 165, 1999.

2. Paramita Banerjee, K.R.S. Chandrakumar and G.P. Das (To be communicated), 2016.

3. Paramita Banerjee, Biswarup Pathak, Rajeev Ahuja and G.P. Das, International Journal of hydrogen energy 41, 14437, 2016.

4. Paramita Banerjee, Ranjit Thapa and G.P. Das, (To be communicated), 2016.

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Artificial Leaf as Future Energy Harvesting Tool

Priyam Mitra, Plabani Basu and Rabindranath Jana* Dept. of Chemical Engineering, Haldia Institute of Technology,

ICARE Complex, Haldia-721657, Purba Medinipur, West Bengal, India *Corresponding Author: Dr. Rabindranath Jana, Associate Professor

E-mail: rabindrajana@yahoo.com, Mobile: +91-9475501042 Abstract: An artificial leaf is a light harvesting tool that attempts to capture sunlight and preserve it into a valuable enrgy source for our futur use. It maximizes the efficiency in gathering solar power by mimicking the process of photosynthesis. It is a device that can harness sunlight by splitting water into Hydrogen and Oxygen. It operates under simple conditions with different catalytic materials bonded onto the two sides of the leaf, e.g., silicon layer coated with cobalt based catalyst can releases oxygen. The other side of the silicon sheet if coated with nickel molybdenum zinc alloy it may release hydrogen from water molecules. However, the main challenges are to efficiently convert water into hydrogen and oxygen. Hydrogen is generally produced from water by its electrolysis and stored in its molecular level by some metal hydrides; though these hydrides require a sophisticated storage system [1]. As hydrogen has the potential to be a clean, sustainable and abundant energy source, many scientist are engaged to work on it [2-4]. Inspired by natural photosynthesis, artificial leaf is designed to capture solar energy for water-splitting. Recent developments based on molecular and/or nanostructure designs have led to advances in our understanding of light-induced charge separation and subsequent catalytic water oxidation and reduction. Automakers have started introducing hydrogen fuel cell vehicles, which only emit water when driven. Producing hydrogen at low cost from water using the clean energy from the sun would be a great challenge. We have fabricated an artificial leaf from TiO2 nanoparticle and Multiwalled Carbon Nanotubes (MWNTs) on different substrates e.g, cast iron, ITO coated glass, etc and tested its performance (Fig. 1). We have selected MWNTs due to its special structures and unique electronic properties, MWNTs have the potential to extend the photo response range of TiO2 to visible-light region by modification of band gap and/or sensitization and increase the photo-activity of TiO2 by contribution to high surface area and inhibition of electron-hole recombination [5]. MWNTs-TiO2 nano-composite with visible-light-driven photo-activity has been successfully synthesized via direct growth of TiO2 nano-particles on the surface of the functionalized MWNTs by the hydrothermal treatment. MWNTs have shown a synergy effect on enhancing photo-activity for H2 evolution over a mixture of MWNTs and TiO2 (Fig 1 (e)). However, the effects of MWNTs pretreatment, MWNTs content and synthetic conditions of MWNTs-TiO2 nano-composite on its photo-catalytic hydrogen evolution efficiency and quantum efficiency under monochromatic light irradiation are to be investigated in details. If the use of the artificial leaf becomes as successful as predicted, it could have numerous applications and benefits. Because the leaf gives us access to hydrogen as a fuel, we most certainly solve the ominous challenge of finding a renewable energy resource to benefit communities worldwide. This creates opportunities to use this extracted hydrogen as a fuel source for nearly anything. This fuel could potentially go towards cars or electricity, solving major problems associated with such areas. Also, using hydrogen as fuel would reduce air pollutants by eliminating the need to use fossil fuels as power sources. Also, if hydrogen became a plentiful fuel source because of the artificial leaf, this fuel and energy could be used to solve other engineering challenges.

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References [1] M.V. Lototskyy, M.W. Davids, I. Tolj, Y.V. Klochko, B.S. Sekhar, S. Chidziva, F. Smith, D. Swanepoel,

B.G. Pollet, Metal hydride systems for hydrogen storage and supply for stationary and automotive low temperature PEM fuel cell power modules, Intl. J. Hydrogen Energy, 40 (35): 11491-97, 2015.

[2] B.L. Salvi, K.A. Subramanian, Sustainable development of road transportation sector using hydrogen energy system, Renew. Sust. Energy Rev., 5 1: 1132-55, 2015.

[3] M. Larsson, F. Mohseni, C. Wallmark, S.Grönkvist, P. Alvfors, Energy system analysis of the implications of hydrogen fuel cell vehicles in the Swedish road transport system, Intl. J. Hydrogen Energy, 40 (35):11722-29, 2015.

[4] T. Tang, K. Li, Z. Shen, T. Sun, Y. Wang, J. Jia, An appealing photo-powered multi-functional energy system for the poly-generation of hydrogen and electricity, J. Power Sources, 294: 59-66, 2015.

[5] B. Lu, N. Ma, Y. Wang, Y. Qiu, H. Hu, J. Zhao, D. Liang, S. Xu, X. Li, Z. Zhu, C. Cui, Visible-light-driven TiO2/Ag3PO4/GO heterostructure photocatalyst with dual-channel for photo-generated charges separation, J. Alloys and Comp., 630:163-171, 2015.

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Protein induced structural modulation in phospholipid model membranes: An x-ray

scattering study

Rajendra Prasad Giri, Mrinmay K Mukhopadhyay, Abhijit Chakrabarti and Milan K Sanyal Saha Institute of Nuclear Physics, Kolkata- 700064

Abstract: Peripheral membrane protein like spectrin as well as cholesterol and hemin are considered as the integral part of the erythrocyte membrane. As they all are associated with various complex mechanisms, our understanding about the interaction of phospholipids with the skeletal proteins and their cooperative mechanism in controlling important cellular events is very limited and needs detailed research in this field. Head-group specificity of adsorption of spectrin, a major membrane cytoskeletal protein, to phospholipid monolayer at air-water interface and supported phospholipid bilayer model membranes have been investigated using x-ray reflectivity, fluorescence spectroscopy and Langmuir monolayer isotherm measurements. Model bilayers of phosphocholine (PC) and phosphoethanolamine (PE) head-group containing lipids have been prepared on polymer cushion supported silicon substrates and the x-ray reflectivity measurement has been carried out from the bilayers immersed in a water bath using high energy x-ray. Further, lateral organization of cholesterol and its effect on regulating the physicochemical properties

(a) (b) (c) (d) (e)

Fig.1 Artificial Leaf developed (a) MWNTs & TiO2 drop casted on ITO, (b) Artificial leaf producing H2, (c) Working Module, (d) Working principal of artificial leaf, (e) Volume of H2 produced (in 30 min).

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of zwitterionic phospholipid model membrane has been revealed using Langmuir monolayer isotherm study, atomic force microscopy and x-ray reflectivity (XRR) measurement. Existing explanatory mechanical models [1] including the Umbrella Model, the Superlattice Model and the Condensed Complex Model explain the molecular mechanism behind the phospholipid-cholesterol interaction. Still our notion to visualize spatial arrangement of the cholesterol molecules inside the molecular layer at different lipid phases is very limited. In this work we present a systematic experimental study on both Langmuir monolayer and soft polymer cushion supported lipid bilayer model membrane to gain insight into cholesterol interaction with the model membrane. This work further focuses on the intercalation of hemin molecules in the 1, 2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC), zwitterionic phospholipid monolayer, at different phases and concentration of hemin in the lipid monolayer using x-ray reflectivity and Langmuir monolayer isotherm studies. Monolayer and bilayer formation and the molecular packing of physiologically relevant phospholipids at air-water interface as well as supported model membranes and their interactions with variant water soluble and insoluble proteins are intriguing issue in basic research in the field of protein interaction with phospholipid model membranes over past few decades [2, 3]. The major constituent, namely spectrin forms the cytoskeleton network through interaction with other membrane skeletal proteins such as actin, ankyrin, dematin, adducin and band 4.1 etc. Human erythrocyte contains almost 30-40 molar% of cholesterol. The fluid mosaic model [4] that treats the biomembranes as a homogeneous mixture of cellular components is seen to be no longer crudely valid in the eukaryotic cell membranes. The modern concept of structure of the cell membrane envisions the presence of ordered structure of cholesterol-enriched micro-domain assemblies, namely lipid rafts, in a relatively disordered phospholipid sea [5]. These assemblies are involved in plenty of cellular processes including drug delivery, protein sorting, signal transduction etc. Hemoglobin is the most abundant protein of the red blood cells, well known to carry oxygen and carbon dioxides to living cells and organisms. However, the hemin molecules show significant toxicity to cell membrane after its dissociation from the hemoglobin, under normal and diseased conditions. Thus the distinct morphologies, structure, dynamics and phase behavior of the zwitterionic phospholipids in presence of proteins like spectrin and hemin as well as cholesterol are the subject of intense research. Our experimental observation suggests a clearly different mechanism of spectrin adsorption to the PC and PE membrane although the lipids under consideration only differ by their head group size. In case of the bilayer containing PC head groups, the spectrin chains form a uniform layer on top of the bilayer with their long chains lying on the membrane surface while in the bilayer containing PE head groups, spectrin chains are attached only through few possible binding sites with the other parts projected out over the membrane surface. Moreover, the reflectivity profiles reveal penetration of spectrin chains through the underlying lipid bilayer membrane depending on the phospholipid head-group and bilayer phase. A physical semi-quantitative model based on salt ion mediated protein interaction with the purely zwitterionic lipid membrane has also been proposed here to explain the observed results. Experimental observation further demonstrates that there is a critical molar concentration of the cholesterol molecules up to which the lipid-cholesterol miscibility gradually increases and beyond this concentration mixture becomes inhomogeneous that can lead to the formation of lipid rafts. The critical concentration has been seen to depend on the subphase temperature or the nominal phase transition temperature of the phospholipids. Cholesterol costs a significant decrease in the possibility of trans-gauche rotations in the lipid acyl chains, thus imposing a conformational restriction on the hydrocarbon chains. X-ray scattering study from monolayer suggests cholesterol concentration dependent arrangements of the constituents that can be described by the existing physical models. Although we add hemin molecules in the water subphase, they are self-assembled in the lipid monolayer as hemin monomer up to certain concentration of hemin, called the critical concentration. Beyond that concentration, reorientation and efflux of the hemin molecules takes place that drives the system towards lower free energy even in presence of unfavourable intermolecular electrostatic repulsion between the hemin molecules. In addition, our experimental findings infer the hemin molecule to interdigitate into lipid membrane more favorably in the phospholipid head-group region rather than intercalating in the hydrophobic part of the monolayer. In conclusion, our study suggests a favorable adsorption of spectrin chains as a whole to the PC head groups than to PE because of their differences in monovalent salt ion adsorption to the head groups originating from the electrostatic screening effect. We further propose from the experimental evidence that all the existing

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models appear together with different weightage at different molar percentage of cholesterol that can explain the observed phenomena. At low concentration, the Umbrella Model along with the cholesterol condensing effect quite successfully explains the lipid condensation. It helps preventing the cholesterol molecules to come in contact with water as it is energetically unfavorable. But it cannot explain the raft formation at relatively higher cholesterol concentration. The Superlattice Model correctly describes a picture of cholesterol/PC mixing. Cholesterol molecules tend to keep a distance from each other in a PC bilayer. The model also predicts many highly symmetrical regular distribution patterns (super-lattices) at some well-defined lipid compositions, specifically at 25 molar% of cholesterol below the lipid chain melting transition temperature (Tm = 230C) and at nearly 55 molar% above Tm that are in line with the earlier studies [9]. This study also provides a clear representation of the configurations of lipid-hemin mixed system at different surface pressure and hemin concentration. Hemin uptake and efflux from the monolayer has also been addressed. References:

• Md Rejwan Ali, Kwan Hon Cheng, and Juyang Huang, PNAS 104, 5372 (2007) • V. M. Kaganer, H. Mohwald and P. Dutta, Rev. Mod. Phys. 71, 779 (1999) • M. Tanaka, E. Sackmann, Nature 437, 656 (2005) • N Mohandas and E Evans, Annu. Rev. Biophys. Biomol. Struct. 23, 787 (1994) • Kai Simons and Elina Ikonen, Functional rafts in cell membranes, Nature 387, 569 (1997)

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Pd/RGO/TiO2 Nanotube Ternary Hybrid Structure as a Novel Gas Sensor Device

Sanghamitra Ghosal1,* and Partha Bhattacharyya2, * 1School of VLSI Technology, -711103, India

2Department of Electronics and Telecommunication Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, India

*Tel: +91 9433428698, e-mail: sanghamitra.ju87@gmail.com Tel: +91 33 26684561/62/63 (Extn. 544), e-mail: pb_etc_besu@yahoo.com

Abstract TiO2 nanostructures, with the different shapes, have received extensive attention in the field of gas sensor research due to their unique physical, chemical and electronic properties. Graphene, a relatively new inclusion in the sensor element family, has recently become popular as sensing materials due to its extremely high specific surface area, high mobility and low electrical noise [1]. Nobel metals like silver, palladium and platinum are extensively used as the electrode or as the surface modifier of the semiconducting oxide nanoforms, with an aim to improve the gas sensor performance owing to the catalytic activity of such metals facilitating gas adsorption/dissociation via chemical of electronic sensitization [2].

In the present work, fabrication, characterizations and gas sensing performance of a novel ternary hybrid junction device based on Pd nanoparticles, Reduced Graphene Oxide (RGO) and TiO2 nanotubes is reported. Electrochemically derived TiO2 nanotubes were partially covered by uniformly distributed RGO islands, on top of which Pd nanoparticles were dispersed uniformly. After detailed structural, morphological and optical characterizations, gas sensing potentiality of such ternary hybrid device was tested for detection of ethanol and methanol vapors. Methanol showed relatively better sensing performance than that of Ethanol. Underlying mechanistic framework for gas sensing by such ternary junctions was explained incorporating the corresponding energy band diagram.

Fabrication of the ternary hybrid device structure employing TiO2 nanotubes, RGO and Pd consists of three steps, (i) TiO2 NT array synthesis by electrochemical anodization method (ii) electro-deposition of RGO on TiO2 NTs in the form of transparent layer (iii) Dispersion of Pd nanoparticle on RGO - TiO2 binary hybrid structure. GO is prepared by the standard Hummers method [1]. Then the RGO layer was deposited on top of the TiO2 NTs, with 0.5 mg / ml aqueous graphene oxide solution as the electrolyte. After, electro-

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deposition for 80 minutes with 15 V bias, the samples were dried in N2 jet and then heated at 60°C in an oven. The samples were then dipped into 0.05M PdCl2 solution for 10 seconds dried at room temperature and then was annealed at 150°C for 90 minutes. After detailed structural, morphological and optical characterizations, gas sensing potentiality of such ternary hybrid device was tested for the detection of ethanol and methanol vapors. The FESEM (Fig. 1(b)) image revealed the morphological features of the ternary hybrid structure. Raman ((Fig. 1(c)) spectra authenticated the presence of D, G and 2D peak of RGO [1]. XPS (Fig. 1(d)) analysis confirmed the existence of Pd peak over the ternary hybrid structure [3]. Variation of the response magnitude over the temperature range of 50°C to 150°C is shown in Fig. 2(a). At 150 °C temperature, in case of methanol the sensor offered the response magnitude of 93% and in case of ethanol the sensor depicts the response magnitude of 64%. Inset of Fig. 2(a) depicts that the sensor offered response time and recovery time of 14/27 sec and 20/46 sec at 150°C for 2000 ppm of methanol and ethanol, respectively. From Fig. 2(a) inset two types of adsorption-desorption kinetics is elucidated, the fast adsorption-desorption kinetics (fast carrier transport) occurs due to SP2 bonded RGO and relatively slow carrier transport occurs due to TiO2 nanotubes. Pd acts as active catalyst, which significantly increases the active sites for gas adsorption-desorption kinetics. Due to the existence of Pd nanoparticles on RGO-TiO2 matrix, activation energy requirement for gas adsorption decreases significantly. The Arrhenius equation states: f Ea decreases, the reaction rate (K) will increase, which eventually implies a reduction in the response time of the gas sensing device apart from the improvement in sensor response magnitude. From the band diagram (Fig. 2(b)), ɸM (Pd) > ɸM (RGO), the band bending (work function difference) will be from Pd to RGO (Fig. 2(b)).ΔVTiO2-RGO = 0.51 eV and ΔVRGO-Pd = 0.53 eV. As a result, at the TiO2 – RGO interface, the band bending qVS is lower in the gas, as compared to the band bending qVS in air, thereby signifying a higher conductivity in the gas, as compared to that in air. Considering the advantageous contribution of each element in the ternary hybrid structure, the sensor offered very promising response in case of alcohol vapour sensing performance.

Fig 1(a) A schematic representation of the ternary hybrid device structure (b) FESEM image of the top view of the hybrid structure (c) Raman Shift and (d) XPS analysis (Pd and PdO peak) of the ternary hybrid

structure

Fig.2(a) Variation of Response magnitude towards ethanol and methanol (2000 ppm) as a function of temperatures (50-150 °C); inset shows the transient response for a single pulse (2000 ppm at 150 °C) (b) Band diagram of TiO2 NTs-RGO-Pd ternary hybrid structure

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REFERENCES

• D. Acharyya and P. Bhattacharyya, IEEE Electron Device Letters, Vol. 37, Issue 5, pp. 656-659, May 2016. DOI:10.1109/LED.2016.2544954

• E. Karacsonyi , L. Baia, A. Dombi , V. Danciuc, K. Mogyorosi , L.C. Popb, G. Kovacs , V. Cos¸ oveanuc, A. Vulpoi , S. Simonb, Zs. Papa, ELSEVIER, vol. 208, pp. 19-27, September 2012. DOI: 10.1016/j.cattod.2012.09.038

• Wenyao Zhang, Huajie Huang, Feng Li, Kaiming Deng and Xin Wang, Journal of Materials Chemistry A, vol.2, pp.19084-19094, 2014. DOI: 10.1039/C4TA03326D

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Reduced Band-gap Ferroelectric Materials for Photovoltaic Application

Shyamashis Das1, Somnath Ghara2, A. Sundaresan2, Priya Mahadevan3, J. Gopalakrishnan1, D. D. Sarma1

1Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012

2Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064

3S.N. Bose National Centre for Basic Sciences, Salt lake, Kolkata 700098, India

Abstract:

Reduced band gap ferroelectric materials are highly sought after in the field of solar energy conversion [1-4]. The reason being the efficient polarization driven charge carrier separation as well as generation of higher than band gap photovoltage upon photoexcitation and hence in principle these materials can overcome maximum theoretical limit of photoconversion efficiency of commercially available heterojunction Si solar cells. Design and synthesis of reduced band gap ferroelectric transition metal oxides without compromising their interesting physical properties however is a long standing challenge. Doping of transition metal ions to any ferroelectric material in order to reduce its band gap almost invariably decreases its inherent polarization and in most cases leads to non-ferroelectric state. In this work, we explore the possibility of introducing transition metal ions to the well-known ferroelectric material BaTiO3 (BTO) to reduce its band gap from ultraviolet energy range to deep in the visible range while retaining its polarization to a large extent.

Substitution at Ti4+ site of BTO with homovalent transition metal ions like Mn4+ leads to stabilization of non-polar 6H perovskite phase [5]. But simultaneous substitution at two Ti4+ sites with a lower valence acceptor ion and a higher valence donor ion is known to retain the tetragonal symmetry of BTO [6] and this coupled substitution of d0 Ti4+ ions with two different transition metal ions containing finite d-electrons can reduce the band gap of BTO significantly. We exploit this strategy to synthesize BTO based reduced band gap ferroelectric material and prepared a series of hybrid doped BTO ceramics having a general composition BaTi1-x(TM11/2TM21/2)xO3 with TM1 being Mn or Fe and TM2 being Nb. Thus we obtained two separate series of co-doped BTO compositions, namely Mn-Nb co-doped and Fe-Nb co-doped series.

We found the hybrid doping strategy is extremely useful in reducing the band gap while retaining the polarization of parent material to large extent. We have performed first principle density functional theory calculation and found Mn-Nb co-doped compositions have larger ferroelectric stabilization energy than Fe-Nb co-doped sample. Dielectric and polarization measurement on these samples confirms presence of ferroelectricity and we found magnitude of polarization is more in Mn-Nb co-doped compositions in compare to Fe-Nb co-doped compositions. Moreover, Mn-Nb co-doped sample also possess lower band gap than corresponding Fe-Nb co-doped composition. Thus, the present material under investigation are expected to be potential in the use of ferroelectric materials as solar absorber layers and carrier separators in practical photovoltaics devices.

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References:

• T. Choi, S. Lee, Y. J. Choi, V. Kiryukhin, and S.-W. Cheong, Science 324, 63 (2009)

• S. Y. Yang, J. Seidel, S. J. Byrnes, P. Shafer, C. -H. Yang, M. D. Rossel, P. Yu, Y. -H. Chu, J. F. Scott, J. W. Ager, III, L. W. Martin, and R. Ramesh Nat. Nanotechnol. 5, 143 (2010).

• Illya Grinberg, D. Vincent West, Maria Torres, Gaoyng Gou, David M. Stein, Liyan Wu, Gunnan Chen, Eric M. Gallo, Andrew R. Akbashev, Peter K. Davies, Jonathan E. Spanier, and Andrew M. Rappe, Nature 503, 509 (2013)

• R. Nechache, C. Harnagea, S. Li, L. Cardenas, W. Huang, J. Chakrabartty, and F. Fosei, Nat. Photonics 9, 61 (2015)

• S.-F.Wang, Y.-C.Wu, Y.-C. Hsu, J. P. Chu, and C.-H.Wu, Jpn. J. Appl. Phys. 46, 2978 (2007).

• W. Liu, W. Chen, L. Yang, L. Zhang, Y. Wang, C. Zhou, S. Li, and X. Ren, App. Phys. Lett. 89, 172908 (2006).

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Photo-voltaic and catalytic Performance of AnataseTiO2 Nanocubes with Coexposed {101} and {001} facets

Soumita Mukhopadhyay and P. Sujatha Devi Sensor and Actuator Division, CSIR-Central Glass and Ceramic Research Institute, Jadavpur

Kolkata 700032, India

Abstract: Titanium dioxide (TiO2) is one of the most extensively investigated semiconducting metal oxides specially in energy induced environmental applications such as photoanode in DSSC, , photocatalyst in solar water splitting and photocatalytic dye removal. But all these applications extensively depend upon the morphology, surface structures and crystalline phase with exposed low index facets. Very recently many researchers have devoted their attention towards the fabrication of coexposed facets. Tailoring of cofacets leads to the formation of surface heterojunction where one facet acts as oxidative site and the other as reductive site. Consequently, the photogenerated charge carriers get spontaneous separation within a single component reducing their charge recombination and exert superior performanceas compared to the single faceted TiO2 either in energy related or in environmental applications where charge transfer dynamics is the basic principle. Herein, we report a facile hydrothermal synthesis of anatase TiO2 nanocube and its superior performance in Dye Sensitized Solar Cells (DSSC) as compared to its nanoparticles like counterpart. A photoconversion efficiency of 4.53% was observed under AM 1.5 solar irradiation using N719 dye as photosensitizer.The superior performance of the nanocubes was attributed to the coexistence of {101} and {001} high energy facets as compared to the regular {101} faceted nanoparticles. In environmental aspects, it is a well-accepted fact that carbonaceous materials like graphene, carbon nanotubes, fullerenes etc. are excellent candidates for water pollutant adsorption from the textile industrial effluents possessing п-п stacking interactions with the aromatic dyes. Hence, prior to employing these nanocubes as photocatalyst for the dye degradation, they were coupled with graphene oxide (GO) under hydrothermal treatment.Interestingly, it was observed that hydrothermal treatment at optimized condition resulted in the shape transition of anatase nanocubes to anatase nanospindles with enhanced {001} high energy facet% embedded on reduced graphene oxide (rGO) platform extending its optical response towards visible region. The underlying factors governing the shape transition from 3D cubes to pseudo 1D nanospindle keeping same crystalline phase on rGO platform were thoroughly optimized. Employing these nanocomposites as photocatalyst for the degradation of malachite green (MG) dye as a target water pollutant under simulated solar irradiation, it was observed that TiO2 spindle@rGOcomposite exerted ~6 fold enhanced efficiency over native TiO2 cubes.This significantly enhanced performance was ascribed to the

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synergistic effect of surface heterojunction formed by enhanced high energy {001} facet% within pseudo 1D spindle like anatase TiO2 and close interfacial contact with rGO platform.

Figure.1. Photo-voltaic and catalytic Performance of anataseTiO2. References

• Q. Guo, C. Zhou, Z. Ma, Z. Ren, H. Fan, X. Yang (2016), Chem. Soc. Rev., 45, 3701. • S. Mukhopadhyay, Partha P. Das, S. Maity, P. Ghosh and P. Sujatha Devi, (2015), Applied

Catalysis B. EnV. 65, 128. • P. P Das, S. A. Agarkar, S. Mukhopadhyay, U. Manju, S. B. Ogaleand P. Sujatha Devi (2014)

Inorg. Chem., 53(8), 3961. • S. Mukhopadhyay, I. Mondal, U. Pal and P. Sujatha Devi, (2015) Phys.Chem.Chem.Phys., 17,

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Low Threshold Quantum Dot Lasers

Veena Hariharan Iyer and Anshu Pandey Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore- 560012

Abstract Quantum dots have broadband absorption cross-section and tunable emission wavelengths. Today, most of the optically pumped lasers require other lasers as pump source owing to their narrow absorption band. A gain medium with broad band absorption could enable the use of polychromatic sources as pump. This may help in fabricating cheaper laser devices. The tunability of the gain medium is an added advantage since one can get desired output wavelength by varying the size of the quantum dot. This renders quantum dots to be an attractive choice for gain media. It has been observed from previous studies that quantum dots are capable of exhibiting gain when pumped with pulsed lasers1 2 3. A novel route to develop low threshold quantum dot lasers is discussed here. Rate equations for three and four level systems show spontaneous life-time to be the deciding factor (among others) of threshold fluence 4. On comparison with conventional solid state lasers, quantum dots with optimum lifetime can exhibit very low threshold fluence enabling use of continuous wave polychromatic pump sources. This is also experimentally proved in core/ shell/ shell heterostructure quantum dots in which electrons and holes are spatially separated5. Quantum dots show broad band absorption and tunability of emission wavelength and spontaneous lifetime. When enclosed in a resonator and pumped with 405nm continuous wave laser diode, the emission consists of multiple modes.

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On further characterization, these modes show spatial and temporal coherence and a distinct threshold. The lowest lasing threshold for these quantum dots less than 80 mW/cm2. References: (1) Klimov, V. I.; Mikhailovsky, A. A.; Xu, S.; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H. J.; Bawendi, M. G., Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots. Science 2000, 290, 314-317. (2) Klimov, V. I.; Ivanov, S. A.; Nanda, J.; Achermann, M.; Bezel, I.; McGuire, J. A.; Piryatinski, A., Single-Exciton Optical Gain in Semiconductor Nanocrystals. Nature 2007, 447, 441-446. (3) Dang, C.; Lee, J.; Breen, C.; Steckel, J. S.; Coe-Sullivan, S.; Nurmikko, A., Red, Green and Blue Lasing Enabled by Single-Exciton Gain in Colloidal Quantum Dot Films. Nat. Nano. 2012, 7, 335-339. (4) Iyer, V. H.; Pandey, A., Impact of Lifetime Control on the Threshold of Quantum Dot Lasers. Phys. Chem. Chem. Phys. 2015, 17, 29374-29379. (5) Iyer, V. H.; Mahadevu, R.; Pandey, A., Low Threshold Quantum Dot Lasers. J. Phys. Chem. Lett. 2016, 7, 1244-1248.