Fabrication of ultra-thin free-standing chromium foils supported by a Si3N4 membrane-structure with search pattern

A microfabrication process is described to produce samples with a search pattern that enables finding a small area of interest with Scanning Tunnelling Microscopy (STM). This area is a 100 mu m square membrane, containing 0.6 - 3 mu m square windows with 5 - 8 nm thick free-standing Cr foils. All three components - search pattern, membranes and the small windows - are patterned on the sample and aligned with respect to each other with Electron Beam Lithography. For subsequent material removal both wet etches and dry plasma etches are used. With E-gun evaporation a Cr layer is deposited on the front side, to obtain a conducting surface, and on the backside for the free-standing foils. Search pattern and foils are tested successfully with STM.