PROBLEMS OF ROUGHNESS MEASUREMENTS USING STM

Scanning tunneling microscopy (STM) seems to be the ideal tool for measurements of surface roughness on a nanometer scale. However, especially in the nanometer size range the extension and form of the tunneling tip comes into play. As an example for the problems arising in investigations of the surface topography a study of indium tin oxide (ITO) films is presented. Roughness measurements are performed using various methods. Several examples of pictures are discussed in which only multiple images of the tunneling tip are seen. A convolution of the substrate and of the STM tip topography occurs. Roughness parameters determined on the basis of such images reflect also the form of the tunneling tip. Reliable data for the surface can be obtained only with very fine tips. All etching techniques tested turned out to be not very reliable. However, in a few cases very sharp tips have been produced by electrochemical etching techniques, leading to the first images of an ITO surface with an ordered domain structure.