Imaging cos( s, z): A method to separate the geometric and compositional contributions on STM barrier height profiles

Abstract

We have developed a new method to separate the geometric and compositional contributions on STM barrier height profiles. The cosine of the angle formed by the local gradient vector and the modulation direction (cos( s, z)) has been numerically calculated from several topographic data and then, compared to their corresponding barrier height images measured in two different vacuum environments. Two kind of images have been found in both situations. In some cases, a very good agreement between the cos( s, z) image and the barrier height image has been interpreted as areas with constant work function. In other zones, the difference between these images was atributed to real changes in chemical composition. Sometimes, anomalously low barrier height values have been observed and are discussed in the text.