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Load-displacement response of Co–Cr AFM tip brought into contact with an Au surface. The arrows indicate loads at which electrical conductance measurements were performed. The tip-surface contact areas at these loads are indicated at the top of the plot.
Current density–voltage responses for Cr–Au contacts at the contact loads indicated. Symbols represent measurements for a single voltage sweep. Solid lines represent best fits to the data using a parabolic-barrier tunneling model. The inset is a schematic diagram of the electrical circuit used to obtain the data, showing positive sample bias.
Schematic diagram of the electron energy levels in metal-insulator-metal structure in which the insulator forms a parabolic barrier for electron tunneling between the metals. The dotted lines indicate the levels in the unbiased state; the solid lines indicate the levels in a biased case (positive if the sample of Fig. 2 is taken on the right).
The variations in tunneling barrier thickness (left) and barrier height (right, in terms of peak energy level above the metal Fermi levels) with contact area of Cr-insulator-Au contacts. The schematic diagram depicts the likely bilayer form of the insulating layer.
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