Zero Bias Anomalies in Electrochemically Fabricated Atomic-Scale Metal Junctions
L. H. Yu and D. Natelson
Rice University Dept. of Physics and Astronomy, US
Keywords: nanowire, metal point contact, electronic transport, nanoelectrodes
Metallic nanojunctions (MNJ) are unique tools for examining electronic transport, correlations, quantum coherence, and disorder at the atomic scale. Extensive progress has been made in understanding clean MNJs fabricated in ultrahigh vacuum (UHV) by the break junction method. MNJs have also been prepared using electrochemistry, and electrochemically grown nanoscale electrodes have been proposed for use in molecular electronic devices. Unlike clean MNJs made in UHV, MNJs made in solution may be highly disordered by grain boundaries, incorporation of ionic impurities, or adsorption of impurities onto surfaces. Low temperature transport properties of these systems have not been previously reported.
We describe an electrochemical nanojunction fabrication protocol that streamlines elements from previously published methods. We report new low temperature electronic transport measurements of atomic-scale electrochemically grown nanojunctions. We find zero bias anomalies (ZBAs), suppressions of the dc conductance near zero bias, at low temperatures. In junctions made with alkaline buffer solution and having room temperature conductances < ~2e2/h, we observe zero bias conductance suppression approaching 100%. Much smaller ZBA are observed in junctions made with an HCl-based technique. We present evidence that the large ZBAs in atomic-scale nanojunctions are caused by nonperturbative corrections to the local density of states of the disordered metal leads. Such effects imply that nanoscale electrodes fabricated by certain electrochemical procedures may be poorly suited for use in molecular electronic devices.
NSTI Nanotech 2003 Conference Technical Program Abstract