Gold Nanowires and Their Chemical Modifications

Abstract

Equilibrium structure, local densities of states, and electronic transport in a gold nanowire made of a four-atom chain supported by two gold electrodes, which has been imaged recently by high-resolution electron microscopy, and chemical modification of the wire via the adsorption of a methylthiol molecule, are investigated with ab-initio local density functional simulations. In the bare wire at the imaged geometry the middle two atoms dimerize, and the structure is strongly modified by the adsorption of the molecule with an accompanying increase of the ballistic conductance through the wire. PACS: 73.40.Jn, 85.30.Vw Generation of wires of atomic scale dimensions in the process of formation and/or elongation of interfacial contacts has been predicted through early molecular dynamics simulations using many-body potentials [1,2], and in the face of fundamental interest and technological considerations driven by the relentless miniaturization of electronic and mechanical devices such wires have been the subject of intensive experimental and theoretical research endeavors [3]. Indeed, nanometer-scale wires (nanowires, NWs) have been created and their structural, mechanical, and transport characteristics were studied using a variety of techniques [3], including most recently combined scanning tunneling microscopy (STM) and direct imaging with the use of high-resolution transmission electron microscopy (HRTEM) [4][5][6].We report here on ab-initio local-density functional (LDA) investigations [7] of the atomic structure, electronic spectrum and conductance of a gold NW consisting of a four-atom chain connected to gold electrodes, which is the smallest NW imaged by HRTEM [6,8]. Our study reveals dimerization of the gold atoms in the middle of the chain [8] akin to a Peierls transition in (extended) one-dimensional systems. Furthermore, we explore structural and electronic spectral modifications resulting from adsorption of a molecule (methylthiol, SCH 3 ) to the wire [9], demonstrating the sensitivity of these properties to such chemical interactions, as well as their effect on the electronic conductance of the wire which we find to increase upon adsorption. These results provide a new interpretation of the measured HRTEM image of the atomic gold wire [6,8] and suggest a new strategy for formation of organo-metallic NWs, as well as the use of NWs as monitoring and chemical sensing devices.In light of the aforementioned STM/HRTEM observations [6,8] we start our simulation from a 4-atom Au wire consisting of two tip-atoms (t) located at the apexes of two opposing tip-electrodes distanced initially by d (0) tt =8.9Å, and of two internal Au atoms (i) located in the gap between the two electrodes with initial uniform distances dii =2.967Å between neighboring atoms of the wire; the tip-electrodes consist each of 29 gold atoms arranged in a pyramidal shape made of facecentered-cubic stacked (110) layers and exposing (100) and (111) facets, with the tip atoms (as well as the internal wire atoms) and the atoms of the und...

Electron transport through monovalent atomic wires

“…[13][14][15] These works show that the chains have a tendency to dimerize upon strong elongation in accord with the Peierls mechanism. However, the conductance as a function of the chain length has not been studied consistently.…”

First-principles study of electron transport through monatomic Al and Na wires

“…55,56 From a theoretical viewpoint the concept of eigenchannels 57 has been utilized for model potentials, [58][59][60] in tight binding model calculations, [61][62][63] and for the potentials derived from the selfconsistent potentials obtained in electronic structure calculations. 64,65 In this paper, we present first-principles calculations of electron transport, in particular, the conduction channels through Al and Na atom wires, using the eigenchannel decomposition ͑ECD͒ combined with the first-principles recursion-transfer matrix ͑RTM͒ method. 66 The electronic states are calculated using the first-principles RTM method, 67 and conductance, local density of states ͑LDOS͒, and current density 68 are decomposed into eigenchannels.…”

Communication: Theoretical exploration of Au++H2, D2, and HD reactive collisions

“…6 Reactivity is intimately connected to the electronic structure and geometry of the cluster, and gold nanoparticles present a very interesting variety of forms, 7 such as nanowires, 8,9 planar (2d) clusters, [10][11][12] and cages. 13,14 The peculiar reactivity of gold is attributed to important relativistic effects, which makes the 6s and 5d orbitals become closer in energy than in other coinage atoms allowing efficient sd hybridization.…”