Micromachined Scanning Tunneling Microscopes and Nanoprobes

Abstract

The magnitude of a tunneling current that passes across a vacuum gap changes by about one decade as the gap changes by 0.1 nm. The very high sensitivity of electron tunneling with respect to the gap distance can be used to sense very small changes in the gap distance. An STM (scanning tunneling microscope) [1] is a distinctive application of this very high sensitivity of electron tunneling. The STM has been utilized as a powerful and convenient tool for observing and manipulating individual atoms and molecules on the nanoscopic scale. However, a conventional STM has dimensions over 10⁸ times larger than the positioning accuracy required of it, and this means that STMs encounter the following problems:

• they are liable to be affected by vibrations due to the heavy weight and large size of the actuator, so that very good anti-vibration equipment is needed;

• they are relatively expensive due to the cost of components and the need for precise assembly and anti-vibration equipment;

• it is difficult to reduce their size due to the small deformation limit (< 0.01%) of the piezoelectric material, and a minimum size of several mm is necessary;

• they are subject to instability and nonlinearity due to creep and hysteresis in the piezoelectric actuator.