title: 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.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Shi
authors.forename: Paul W
authors.initials: PW
authors.lastname: Bohn
mesh_terms: D003300:Copper / Q000737:chemistry; D004563:Electrochemistry; D004566:Electrodes; D004573:Electrolytes / Q000737:chemistry; D006046:Gold / Q000737:chemistry; D019216:Metals, Heavy / Q000737:chemistry*; D012834:Silver / Q000737:chemistry; D013696:Temperature
chemical_list: D004573:Electrolytes; D019216:Metals, Heavy; D012834:Silver; D006046:Gold; D003300:Copper