Scanning tunneling microscopy

Scanning Tunneling Microscopy (STM) is a new method for studying surface phenomena in semiconductors and metals on an atomic scale. A metal tip is scanned over the surface at such a small distance that a tunneling current in the nanoamp range flows under application of a voltage between tip and sample. Surface areas are scanned by moving the tip in a prescribed pattern with subangstrom accuracy, employing piezoelectric positioners. The tip position is controlled to a fixed distance from the sample. The tunneling current is very sensitive to the tip-surface distance. Maintaining a constant tunnel current while scanning over the surface, the tip generally traces a topographic contour of the surface. Near-atomic resolution is achieved depending on the charge distribution at the surface. Outstanding properties of the STM are the low voltage operation, the high spatial resolution and the local sensing capability. Spectroscopic information can be obtained via the local current-voltage characteristic. STM is likely to supplement usual surface-analysis techniques which rely on (diffraction-limited) beam techniques. The STM technique will be discussed, and results presented from previous studies as well as from recent work on materials important in semiconductor technology. © 1986.