Mechanical and electrical coupling at nanoscale metallic contacts was investigated using a conducting-probe atomic force microscope (AFM). The current-voltage responses were non-Ohmic, symmetric about zero bias, with conductance values smaller than the quantum conductance limit, which indicate electron tunneling through an insulating layer. Using a self-consistent contact mechanics model and a parabolic tunneling model for thin insulating layers, we determined the contact area, barrier height, and barrier thickness as a function of applied contact load. The results suggest the presence of two insulating layers: an oxide layer on the AFM tip and an organic contaminant layer on the metallic surface.
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