intriguing structure and transport behaviour of …...n. ravishankar materials research centre...
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N. RavishankarMaterials Research Centre Indian Institute of Science Bangalore 560012 India
82nd IAS Meeting, 6 Nov 2016, IISER Bhopal
Intriguing Structure and Transport Behaviour of Ultrathin, Single Crystalline Gold Nanowires
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Collaborators
Aditi Halder- Au Nanowire Growth Paromita, Chandni, Arindam Ghosh- Electrical Transport Ahin Roy, Abhishek Singh - DFT Studies Aditi Halder, Subhajit Kundu – Synthesis of Au nanowires Paromita Kundu, Van Tendeloo (EMAT) Microscopy Knut Muller, Andreas Rosenauer (Bremen)– AC-TEM Saransh, Prita, Gururajan (IITB)– Molecular Dynamics Joerg Weissmuller (Hamburg)– Continuum Analysis Praveen Kumar – Finite Element ModellingAveek Bid- Sensors, Noise
Facilities:Materials Research Centre, IISc Advanced Facility for Microscopy and Microanalysis, IISc
Acknowledgments
Funding: Swarnajayanti Fellowship, TUE - DST NanoMission, SERB-DST
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Wet Chemical Methods for Nanostructure Growth Understanding Mechanisms Functional Nanostructures
What we do .
Nanoscale Hybrids Understanding heterogeneous nucleation Microwave-assisted methods
(Nanolett. 2014, Angew.Chem 2014, Small 2014, ACS Nano 2014, Adv.Mater 2013, Nanoscale 2013, Particle 2013, ACS Nano 2011(a,b,c); Adv. Mater 2007; Biomater 2008; J. Phys. Chem. 2006, 2009; Nanotech. 2008; J. Coll. Interf. Sci. 2008; Langmuir 2009; J. Mat. Chem. 2010,2011; J. Am. Chem. Soc 2010, 2011; Nanoscale 2010, 2011, Nanotechnology 2007; Scripta Mater 2007)
(JACS 2014; Dalton Trans 2013; RSC Adv 2013; PCCP 2013; Nanoscale 2013; ACS Nano 2011; J. Mater. Chem. 2011; Chem Mater 2011; Dalton Trans 2012; Nanoscale 2011, 2012; PCCP 2011)
Porous Structures by Aggregation Controlling Nanoparticle Interactions Controlling the Composition Stability of Porous Structures
(ACS Nano 2011; Nanoscale 2013, 2011, 2010; Particle 2013; J. Mater. Chem. 2011; Langmuir 2009 )
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Today
Ultrathin Single Crystalline Au Nanowires
- Mechanism of Growth
- Structure
- Properties and Applications - Electrical transport - Sensing- Catalysis
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http://course1.winona.edu/kbates/bio241/images/figure-11-06.jpg 2 nm
Diameterof Au wire
~ 2 nm 5-6 atoms thick
~ 2 m long
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https://en.wikipedia.org/wiki/Amorphous_silicon
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Synthesis of building blocks Wet Chemical Method for Metal Nanoparticles
Mn+ + Reducing Agent + Capping Agent Capped M0
Size Control Shape Control
C.J. Murphy Group Mirkin Group
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Equilibrium Morphology Growth Morphology - Depends on anisotropy of growth rates
Pyrite
- Reflects point-group symmetry - Initial stages of nucleation
Cuprite
{100}
{111}
NaCl
Au
Heyraud and Metois
FCC
{111}
{100}
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Prediction of pathways forshape control of nanostructures
J. Phys. Chem. C 2009
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Fact 1: Au is a high symmetry (cubic) metal and will not grow as a wire
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http://www.snowcrystals.com/science/science.html
External shape related to ‘shape’ of building block
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No unique axis for a‘cubic’ system
Will not ‘normally’ like to grow as a wire
Presence of a unique axis
Can grow as a wire
Symmetry breaking!!
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July 2007
HAuCl4 + Oleylamine AuCl Au (particles) Wires
Au nanoparticles Au Nanowires
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{100} & {111} Facets
Amine-CappedNanoparticles111
100
Adv. Mater. 2007
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Ultrathin Single Crystalline Nanowires
Adv. Mater. 2007
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Coalescence of droplets
Regions of Different Chemical Potential
Diffusion from convex to concave regions
Neck Growth during Sintering of Particles
Adv. Mater. 2007
http://mntl.apps01.yorku.ca/index.php/research/
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Ωσ svCwD
RTrrx
t
46)(
Neck Growth by Surface Diffusion
32
)1)(3(ρ
πηkT
rt
Average time between Collision of Brownian Particles
Adv. Mater. 2007
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Fact 2: Au has an FCC structure
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Fraction of surface atoms increases dramatically
https://en.wikibooks.org/wiki Introduction_to_Inorganic_Chemistry/Basic_Science_of_Nanomaterials
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Atoms on the surface are ‘unhappy’ less neighbours
Atoms are social creatures!Like to be surrounded by their kind
butane.chem.uiuc.edu
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Origin of Surface Stress
Weissmuller, in Electrocatalysis: Theoretical Foundations and Model Experiments, I ed
Tendency of surface atoms to come closer (positive surface stress)
Leads to stress within the ‘bulk’ of the material
Stresses linked by the generalized capillary equation
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ChemPhysChem 2012, 13, 2443 – 2454
Lattice Parameter Changes in Small Particles
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Density Functional Theory
+
Electron Microscopy
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Density Functional Theory Results
Au Nanowires – Hexagonal prism morphology [111] wire axis bounded by {110} ‘prism’ planes
ABC stacking and periodic boundary conditions
Displacements of the order of 20 pm about the mean position
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- Atomic defects - strain
Wires on C-film: Titan 120 kV, dose 20-25 e/Å2
TITAN3
Atomic Structure of Au Wires
In collaboration with EMAT, Antwerp
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Internal ‘Wrinkling’ of Close-packed Planes
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Ultrathin Au Nanowires grown on a graphene support - Minimize complications in interpretation due to substrate
Aberration-corrected microscopy to study modulations
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Experimental Image Calculated Image (STEMsim)
With Knut Muller and Andreas Rosenauer
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Molecular Dynamics Simulations
Displacement localized at surface
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Fact 3: Au is a good metal and is an excellent electrical conductor
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ACS Nano (2011)
Metallic wire??!!
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Fact 4: Au is very ‘noble’ and unlikely to be a good catalyst
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2010
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Summary
Ultrathin single crystalline Au nanowires
Conventional wisdom fails!!
Thank You