Scanning tunneling microscopy tip shape imaging by “shadowing”: Monitoring of in situ tip preparation

Abstract

The shape of the scanning tunneling microscope (STM) tip was imaged with nanometer resolution using “shadow images.” When a Ge molecular beam is evaporated from the side onto a Si sample while the STM tip is stationary in tunneling 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 monitor the tip shape after in situ tip preparation processes, like sputtering and heating of the tip.