A STM point-probe method for measuring sheet resistance of ultrathin metallic films on semiconducting silicon

We report a novel approach for distinguishing surface, bulk and space-charge layer conductivities of metalized semiconductor surfaces. The method employs current injection from the tip of a scanning tunneling microscope and a spring-contact electrode placed on the surface in situ in UHV. The current-voltage behavior is sensitive to polarity in a way that distinguishes the surface contribution. The method is illustrated for the Si(1 1 1) 7 × 7 metallized surface and dependence of the conductivity with changing thickness of silver overlayers.