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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
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
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 )
Today
Ultrathin Single Crystalline Au Nanowires
- Mechanism of Growth
- Structure
- Properties and Applications - Electrical transport - Sensing- Catalysis
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
https://en.wikipedia.org/wiki/Amorphous_silicon
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
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}
Prediction of pathways forshape control of nanostructures
J. Phys. Chem. C 2009
Fact 1: Au is a high symmetry (cubic) metal and will not grow as a wire
http://www.snowcrystals.com/science/science.html
External shape related to ‘shape’ of building block
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!!
July 2007
HAuCl4 + Oleylamine AuCl Au (particles) Wires
Au nanoparticles Au Nanowires
{100} & {111} Facets
Amine-CappedNanoparticles111
100
Adv. Mater. 2007
Ultrathin Single Crystalline Nanowires
Adv. Mater. 2007
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/
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
Fact 2: Au has an FCC structure
Fraction of surface atoms increases dramatically
https://en.wikibooks.org/wiki Introduction_to_Inorganic_Chemistry/Basic_Science_of_Nanomaterials
Atoms on the surface are ‘unhappy’ less neighbours
Atoms are social creatures!Like to be surrounded by their kind
butane.chem.uiuc.edu
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
ChemPhysChem 2012, 13, 2443 – 2454
Lattice Parameter Changes in Small Particles
Density Functional Theory
+
Electron Microscopy
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
- 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
Internal ‘Wrinkling’ of Close-packed Planes
Ultrathin Au Nanowires grown on a graphene support - Minimize complications in interpretation due to substrate
Aberration-corrected microscopy to study modulations
Experimental Image Calculated Image (STEMsim)
With Knut Muller and Andreas Rosenauer
Molecular Dynamics Simulations
Displacement localized at surface
Fact 3: Au is a good metal and is an excellent electrical conductor
ACS Nano (2011)
Metallic wire??!!
Fact 4: Au is very ‘noble’ and unlikely to be a good catalyst
2010
Summary
Ultrathin single crystalline Au nanowires
Conventional wisdom fails!!
Thank You