Investigation of electromigration induced by field emission current flowing through Au nanogaps in ambient air

Abstract

We developed a simple and controllable nanogap fabrication method called “activation.” In the activation technique, electromigration is induced by a field emission current passing through the nanogaps. Activation enables the electrical properties of Ni nanogaps in a vacuum to be controlled and is expected to be applicable to Au nanogaps even in ambient air. In this study, we investigated the activation properties of Au nanogaps in ambient air from a practical point of view. When activation was performed in ambient air, the tunnel resistance of the Au nanogaps decreased from over 100 TΩ to 3.7 MΩ as the preset current increased from 1 nA to 1.5 μA. Moreover, after activation in ambient air with a preset current of 500 nA, the barrier widths and heights of the Au nanogaps were estimated using the Simmons model to be approximately 0.5 nm and 3.3 eV, respectively. The extracted barrier height is smaller than that of 4.6 eV resulting from activation in a vacuum and much lower than the work function of bulk Au. This difference implies the presence of atmospherically derived moisture or contamination adsorbed on the nanogaps. These results suggest that activation can be utilized for Au nanogap fabrication even in ambient air.