The Development of Atomic Force Microscopes

In 1981 researchers at IBM were able to utilize the methods first demonstrated by Young to create the scanning tunneling microscope⁶ (STM). Binnig and Rohrer demonstrated that by controlling the vibrations of an instrument very similar to Young's Topographiner, it was possible to monitor the electron tunneling current between a sharp probe and a sample. Since electron tunneling is much more sensitive than field emissions, the probe could be used to scan very close to the surface. The results were astounding; Binnig and Rohrer were able to see individual silicon atoms on a surface. Although the STM was considered a fundamental advancement for scientific research, it had limited applications, because it worked only on electrically conductive samples.

A major advancement in profilers occurred in 1986 when Binnig and Quate⁷ demonstrated the Atomic Force Microscope. Using an ultra-small probe tip at the end of a cantilever, the atomic force microscope could achieve extremely high resolutions. Initially, the motion of the cantilever was monitored with an STM tip. However, it was soon realized that a light-lever, similar to the technique first used by Schmalz, could be used for measuring the motion of the cantilever. In their paper, Binnig and Quate proposed that the AFM could be improved by vibrating the cantilever above the surface.

The first practical demonstration of the vibrating cantilever technique in an atomic force microscope was made by Wickramsinghe⁸ in 1987 with an optical interferometer to measure the amplitude of a cantilever's vibration.

Using this optical technique, oscillation amplitudes of between .3 nm and 100 nm were achieved. Because the probe comes into close contact with the surface upon each oscillation, Wickramsinghe was able to sense the materials on a surface. The differences between photo-resist and silicon were readily observed.