Feedback Electromigration Assisted by Alternative Voltage Operation for the Fabrication of Facet-Edge Nanogap Electrodes

Electron transport experiments for molecular devices have been evaluated by using single-molecule bridging nano- and/or sub-nanoscale junctions between two metallic electrodes. Thus, although several techniques have been developed to make the junctions, many of the actual junction surfaces structure cannot be defined. Ideally, it is better to use a well-defined single-metal surface to simplify transport characterization in the simple structure modeling. If the clear crystal surface with well-defined crystal orientation can be used for the single-molecule characteristics, more rapid scientific progress can be expected. Then, a molecular-scale space “nanogap” deformed with two facet-edge Au crystals is the ideal tool for a metal–molecule junction to realize molecular electronics devices. For fabricating such a molecular-scale space nanogap, we developed a feedback-controlled electromigration (FBEM) combined with alternate polarity voltage operation (inversed-FBEM: iFBEM). The nanogaps fabricated via iFBEM under low temperature and an H2 atmosphere were confirmed as two single-domain Au crystals in direct observation via field-emission scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. It can be expected that distributions of molecular angles adsorbed on the electrode surface and the variability of molecular devices are both suppressed.