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Proximal Probe Techniques

Surfaces

  1. Roland Wiesendanger

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a2503m

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Wiesendanger, R. 2006. Proximal Probe Techniques. Encyclopedia of Analytical Chemistry. .

Author Information

  1. University of Hamburg, Germany

Publication History

  1. Published Online: 15 SEP 2006

Abstract

Proximal probe techniques are based on sharp tips which are brought within a small distance of a sample to be investigated by means of a stepper motor. The various interactions of these probe tips with the sample, which might be of mechanical, electrical, magnetic, optical or thermal origin, can be used to probe the sample's properties locally and to control the separation between tip and sample surface.

If the distance dependence of a particular type of interaction is strong, the distance control based on that interaction is very sensitive to small changes in tip–sample separation. By scanning the probe tip over the sample surface while keeping the interaction strength constant using a feedback loop, the surface contours can be followed by the tip with high accuracy. By monitoring the vertical position of the tip as a function of the lateral position, a three-dimensional image of the sample surface is obtained. The motion of the tip both laterally and vertically with respect to the sample surface can be realized with subatomic accuracy by means of piezoelectric drives.

In contrast to electron microscopy and vacuum-based surface analytical methods, proximal probe techniques can be operated in air and in liquids in addition to in vacuum. Therefore, proximal probe techniques offer great potential for investigations of solid–liquid interfaces or for in vivo investigations of biological specimens. Furthermore, proximal probe techniques can be operated in a wide temperature range (from millikelvin up to more than a 1000 K) and under extreme conditions (e.g. in high magnetic fields or high-pressure conditions). The most attractive feature of proximal probe techniques is, however, that they combine ultrahigh spatial resolution (down to the atomic scale) with high-resolution spectroscopic measurements so that detailed information about the physical, chemical or biological state of the sample can be extracted. Limiting factors are the finite size and often ill-defined state of the probe tips and the limited information depth of proximal probe techniques. It has also found to be difficult to identify elemental species based solely on proximal probe measurements although chemical-selective imaging even down to the atomic scale is nowadays routinely achieved.