PRACTICAL APPLICATIONS OF SCANNING TUNNELING MICROSCOPY

Scanning tunneling microscopy has recently been introduced as a promising tool for analyzing surface atomic structure. It allows the analysis of surface structure with sizes that range down to one ångström (0.1 nm). In addition, it has the capability to readily store the data digitally for further processing. Its extremely high resolution and its ability for imaging in ambient atmosphere make it an attractive technique for a variety of materials which can achieve atomic resolution in favorable cases. A number of examples will be presented from molecular scale objects on up through at least three orders of magnitude in scale. When the high-resolution capability of scanning tunneling microscopy is coupled with digital data acquisition, it is possible to get quantitative information on surface texture. This has been used for surface roughness measurement, and in searching for fractal behavior. The peak altitude method of measurement of surface roughness is illustrated for evaporated gold films and the dependence of roughness on deposition temperature and annealing time is described. By using algorithms for scale-dependent measurement of surface area, the existence of fractal morphology of metal and epoxy resin fracture surfaces are investigated. Some limitations of STM for roughness measurement are discussed, and the need to develop practical routes to spectroscopic analysis of the surfaces to improve image interpretation are emphasized. © 1990.