Electrochemical Control of Stability and Restructuring Dynamics in Au−Ag−Au and Au−Cu−Au Bimetallic Atom-Scale Junctions

Abstract

Metallic atom-scale junctions (ASJs) are interesting fundamentally because they support ballistic transport, characterized by conduction quantized in units of G(0) = 2e(2)/h. They are also of potential practical interest since ASJ conductance is extraordinarily sensitive to molecular adsorption. Monometallic Au ASJs were previously fabricated electrochemically using an I(-)/I(3)(-) medium and a unique open working electrode configuration to produce slow electrodeposition or electrodissolution, resulting in reproducible ASJs with limiting conductance <5 G(0). Here, bimetallic Au-Cu-Au and Au-Ag-Au ASJ structures are obtained by electrochemical deposition/dissolution of Cu and Ag in K(2)SO(4) supporting electrolyte. The ASJs are fabricated in Si(3)N(4)-protected Au nanogaps obtained by focused ion beam milling, a protocol which yields repeatable and reproducible Au-Cu-Au or Au-Ag-Au ASJs without damaging the Au nanogap substrates. While Au-Ag-Au ASJs are relatively stable (hours) at open circuit potential in the supporting electrolyte, Au-Cu-Au ASJs exhibit spontaneous restructuring dynamics, characterized by monotonic, stepwise decreases in conductance under the same conditions. However, the Au-Cu-Au ASJs can be stabilized by applying sufficiently negative potentials. Hydrogen adsorption and shifts in the Fermi level are possible reasons for the enhanced stability of Au-Cu-Au structures at large negative overpotentials. In light of these observations, it is possible to integrate ASJs in microfluidic devices as renewable, nanostructured sensing elements for chemical detection.

Effect of Molecular Adsorption on the Electrical Conductance of Single Au Nanowires Fabricated by Electron‐Beam Lithography and Focused Ion Beam Etching

“…Tao et al were able to detect a small number of molecules by using metallic quantum wires, or so‐called atom‐scale junctions 4–6. Motivated by the exciting possibilities embodied in these nanoscale objects, we have recently focused on fabricating ultrathin metallic nanowires, including atom‐scale junctions, and investigating their applications as highly sensitive chemical and biomolecular sensors 6–8…”

Study of the surface structure of Fe quantum wire prepared by electrochemical method in solution

“…When the size of the materials and device is reduced to nanometer scale, many novel quantum phenomena will appear, which will bring many new and important applications [1][2][3]. A typical case is the quantum conductance behavior of the atomically thin metal junction, which has been verified with a large number of theoretical and experimental studies in the past decades [4][5][6]. If the width of a metal wire reaches its Fermi wavelength scale, the conductance will not change continuously with the diameter, and it will be quantized by G = G 0 n i=1 T i where G 0 = 2 e 2 /h (e and h represent, respectively, the electron charge and Planck's constant, so G 0 ≈1/12.9 kΩ), and T i represents the transmission coefficient for each quantum mode.…”

First-principles simulations on suspended coinage-metal nanotubes composed of different atomic species

“…1 These nanowires have displayed conductance quantization in units of 2e 2 /h and ultimate nanowires are one atom thick. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Two experimental techniques have been commonly used for obtaining metal nanowires and nanotubes, one is the mechanically controllable break junctions, and the other is in situ highresolution transmission electron microscopy (HRTEM). The former is more appropriate for conductance experiments and the latter allows real-time visualization, providing a better evaluation of the dynamical atomistic aspects of nanowire elongation.…”