Conductivity of Si(111)-(7×7): the role of a single atomic step.

While it is known that the Si-(7×7) is a conducting surface, measured conductivity values differ by 7 orders of magnitude. Here we report a combined STM and transport method capable of surface conductivity measurement of step-free or single-step containing surface regions and having minimal interaction with the sample, and by which we quantitatively determine the intrinsic conductivity of the Si-(7×7) surface. We found that a single step has a conductivity per unit length about 50 times smaller than the flat surface. Our first principles quantum transport calculations confirm and lend insight into the experimental observation.