AN ADAPTIVE SCAN GENERATOR FOR A SCANNING TUNNELING MICROSCOPE

A novel scan generator for a scanning tunneling microscope (STM) has b een developed. The instrument compares tunneling current with three th resholds values, to generate an x-scanner signal with a dynamically ch angeable step size for adaptation to sharp topographical changes. It h as two advantages compared to conventional STM scan generators (i) a b etter protection from a tip crash and (ii) minimization of the image a cquisition time. The implementation is made with a digital signal proc essor (DSP) DSP32C from AT&T, mounted on a commercially available PC A T-compatible plug-in card. Test images of extremely rough surfaces con firm the usefulness of our novel scan generator. The concept could als o be used for different scanning probe microscopes.