Scanning Tunneling and Atomic Force Microscopies

Abstract

The scanning tunneling microscope (STM) developed by Binnig and Rohrert^(1–3) at the IBM Zürich research laboratory in the early 1980s was the first example of a new family of instruments based on a concept radically different from that of the optical and electron microscopes. The basic idea is to examine a surface at very close range (near field) with a scanning probe, the position of which can be perfectly controlled in three dimensions to within ± 0.1 nm. The signal generated on each point of the surface by the interaction between the probe and the surface atoms is translated electronically into an image of the surface. The resolution depends essentially on the probe size and on the accuracy of its positioning. There are potentially a wide variety of probes and signals which can be used to image a surface. We will focus our attention on the scanning tunneling microscope (STM) based on the tunneling current generated between the extremity of a metal tip and the surface atoms of a conducting material at a different potential. We will also examine the atomic force microscope (AFM) based on the repulsive force between the atoms of a diamond tip and surface atoms. The AFM, developed more recently,^(4,5) has a potentially wider application range since it does not require conducting materials. Finally a few other scanning probe microscopes will be mentioned. They do not give atomic resolution but do not require a high surface flatness. So far applications in surface science have been carried out mainly with the STM.