N. RavishankarMaterials Research Centre Indian Institute of Science Bangalore 560012 India

nravi@mrc.iisc.ernet.in

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