Scanning tunneling microscopy tip shape imaging by "shadowing": Monitoringof in situ tip preparation

The shape:of the scanning tunneling microscope (STM) tip was imaged with na nometer resolution using ''shadow images.'' When a Ge molecular beam is eva porated from the side onto a Si sample while the STM tip is stationary in t unneling position close to the sample,surface, the tip shades part of, the sample surface. Subsequent imaging of this shadow area with the STM results In contrast between areas on the sample where Ge was evaporated, and areas where the Ge flux was impeded by the tip, This method was applied to monit or the tip shape after in situ tip preparation processes, like sputtering a nd heating of the tip. (C) 1999 American Vacuum Society. [S0734-211X(99)012 02-0].