A shadow-edge contact for epitaxial nanostructures on silicon

We have developed a method to apply a thin (5 nm) metal film with a sharp edge (100 nm) onto the surface of a silicon sample in ultrahigh vacuum, to provide a counter-electrode for the study of electrical properties of epitaxial nanostructures. Film sheet resistance, Rs, is monitored continuously during deposition, to identify ``electrical closure'' of small grains. Film roughness, $\sigma $, is measured ex situ using Atomic Force Microscopy and in situ using Scanning Tunneling Microscopy. We find that Pt is more suitable than Au, attaining $Rs\approx 300\Omega /sq$ and $\sigma \approx 10nm$ versus $Rs\approx 1000\Omega /sq$ and $\sigma \approx 50nm$ for Au.