INVESTIGATION OF SCANNING-TUNNELING-MICROSCOPY TUNNELING BARRIER SIGNALS IN AIR AND WATER

In an atmospheric environment and in water, the tunneling barrier sign als are usually very low compared with those measured in the ultrahigh vacuum. The tunneling barrier data presented in this paper show that the barriers in air and in distilled water have a statistical characte r. The barrier mean value depends not only on the tip and specimen, bu t also on the medium in the tunneling gap. By repeated scannings of sp ecimen surfaces, it is found that the barrier heights connected to ind ividual specimen locations are reproducible. This is illustrated by re peated scans on a (TiN on W)/water interface obtained with a tungsten tip. The areas of TiN and W are clearly distinguished. Measurements of tunneling barrier heights are therefore suited for nucleation studies of surface coatings and for the detection of different material compo nents in a specimen.