Theoretical Investigation of Ballistic Electron Transport in Au and Ag Nanoribbons

Sushil Kumar and R.K. Moudgil

Abstract. We have systematically investigated the ballistic electron transport in gold and silver nanoribbons using first principle methods. The electronic structure calculation is carried out using the “density functional theory” (DFT) within the “SIESTA” code. While the electronic transport is studied using the “non-equilibrium Green’s function” (NEGF) method combined with the “Landauer-Buttiker” (LB) approach. We have explored the transport along both the armchair (AC) and zigzag (ZZ) directions. Interestingly, both elements turn semiconducting in the AC-configuration, and their band gap oscillates with increasing width of the nanoribbon. On the other hand, nanoribbons retain metallic character in the ZZ-configuration, with a quantized electrical conductance 4G0 for sufficiently small width and temperatures as high as nearly 200 K; G0=2e2/h, is the elementary quanta of electrical conductance. At zero bias, electronic thermal conductance in each system increases non-linearly with temperature. More is the width of nanoribbons, more is the electronic contribution to heat transport. Further, to assess the utility of nanoribbons in thermoelectric devices, we have calculated the room-temperature Seebeck coefficient S. It is found to evince an oscillatory structure as a function of electrochemical potential μ of electrodes, with pronounced peaks (nearly -118 μV/K in the narrowest gold nanoribbon considered) in the AC-configuration. The maximum S achieved is seen to be comparable to the atomic chains of these elements in linear, ladder and zigzag topologies, suggesting practical importance of nanoribbons as thermoelectric sensors in nanoelectronic devices.

Keywords
Electron Transport, Nanoribbons, DFT, NEGF, Thermoelectric

Published online 3/25/2022, 7 pages
Copyright © 2022 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA

Citation: Sushil Kumar and R.K. Moudgil, Theoretical Investigation of Ballistic Electron Transport in Au and Ag Nanoribbons, Materials Research Proceedings, Vol. 22, pp 28-34, 2022

DOI: https://doi.org/10.21741/9781644901878-5

The article was published as article 5 of the book Functional Materials and Applied Physics

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

References
[1] L. Yang, C.-H. Park, Y.-W. Son, M. L. Cohen, S. G. Louie, Quasiparticle energies and band
gaps in graphene nanoribbons, Phys. Rev. Lett., 99 (2007) 186801.
[2] M. Y. Han, B. Özyilmaz, Y. Zhang, P. Kim, Energy band-gap engineering of graphene nanoribbons, Phys. Rev. Lett., 98, (2007) 206805. https://doi.org/10.1103/PhysRevLett.98.206805
[3] E. Unsal, R. Senger, H. Sevinçli, Enhancement of thermoelectric efficiency of T – HfSe2 via nanostructuring, Physical Review B, 103 (2021) 014104. https://doi.org/10.1103/PhysRevB.103.014104
[4] P. Kapoor, A. Kumar, P. K. Ahluwalia, Size-dependent electronic, mechanical and optical properties of noble metal nanoribbons, Materials Science and Engineering B: Solid-State Materials for Advanced Technology, 262 (2020) 114786. https://doi.org/10.1016/j.mseb.2020.114786
[5] G. Singh, K. Kumar, R. K. Moudgil, Coherent phonon thermal transport in nanoribbons of gold and silver, in AIP conference proceedings, 2115 (2019) 030373. https://doi.org/10.1063/1.5113212
[6] M. Büttiker, Y. Imry, R. Landauer, S. Pinhas, Generalized many-channel conductance formula with application to small rings, Phys. Rev. B, 31 (1985) 6207–6215. https://doi.org/10.1103/PhysRevB.31.6207
[7] P. N. Butcher, Thermal and electrical transport formalism for electronic microstructures with many terminals, J. Phys. Condens. Matter, 2 (1990) 4869. https://doi.org/10.1088/0953-8984/2/22/008
[8] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, The SIESTA method for ab initio order-N materials simulation, Journal of Physics: Condensed Matter, 14 (2002) 2745. https://doi.org/10.1088/0953-8984/14/11/302
[9] D. R. Hamann, M. Schlüter, C. Chiang, Norm-conserving pseudopotentials, Phys. Rev. Lett., 43 (1979) 1494. https://doi.org/10.1103/PhysRevLett.43.1494
[10] N. Troullier, J. L. Martins, Efficient pseudopotentials for plane-wave calculations, Phys. Rev. B, 43 (1991) 1993. https://doi.org/10.1103/PhysRevB.43.1993
[11] J. P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett., 77 (1996) 3865. https://doi.org/10.1103/PhysRevLett.77.3865
[12] J. Moreno, J. M. Soler, Optimal meshes for integrals in real- and reciprocal-space unit cells, Phys. Rev. B, 45 (1992) 13891. https://doi.org/10.1103/PhysRevB.45.13891
[13] M. Brandbyge, J.-L. Mozos, P. Ordejón, J. Taylor, K. Stokbro, Density-functional method for nonequilibrium electron transport, Phys. Rev. B, 65 (2002) 165401. https://doi.org/10.1103/PhysRevB.65.165401
[14] N. Papior, N. Lorente, T. Frederiksen, A. García, M. Brandbyge, Improvements on non-equilibrium and transport Green function techniques: The next-generation transiesta, Computer Physics Communications, 212 (2017) 8. https://doi.org/10.1016/j.cpc.2016.09.022
[15] S. Datta, Electronic Transport in Mesoscopic Systems, Cambridge university press, 1997.
[16] N. Papior, Sisl: v.0.10.0, 2020.
[17] G. Singh, K. Kumar, R. K. Moudgil, On topology-tuned thermoelectric properties of noble metal atomic wires, Physica E: Low-dimensional Systems and Nanostructures, 109 (2019) 114. https://doi.org/10.1016/j.physe.2019.01.007
[18] G. Singh, K. Kumar, R. K. Moudgil, Alloying-induced spin Seebeck effect and spin figure of merit in Pt-based bimetallic atomic wires of noble metals, Phys. Chem. Chem. Phys., 21 (2019) 20965. https://doi.org/10.1039/C9CP01671F