A schematic STM setup. When a tip is brought several angstroms away from a sample and a voltage are applied between them, a very small current flows—of order 10−10 amperes—between the last atom of the tip and the sample. For comparison, a typical light bulb usually has a flowing current of order 1 ampere. Our tunneling current is roughly 10 billion times smaller. As we scan the tip over the surface, the rise and fall of the atomic landscape comprising the sample surface leads to changes in the current and hence to the STM’s ability to image the surface.
