ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
When scanning steeply sloped features which are near micron size or taller, scanning tunneling microscopes with conventional feedback control loops exhibit slower response on downhill slopes than on uphill slopes. This effect is caused by the exponential dependence of the tunneling current on the tip-sample distance. A gap smaller than the setpoint produces a sizable error signal, whereas a gap larger than the setpoint gives only a weak error signal. As the scan rate is increased, the tip begins "flying'' well above the surface on steep downhill regions. We have developed a modification of the conventional integral feedback system which eliminates this problem. This circuit makes the error signal growth with increasing distance between the tip and sample similar to the usual exponential growth when the tip-sample distance decreases. This modification allows an increase in scan rates by a factor of 5–10 with no reduction in image quality. The modification can be dialed in or out of circuit as needed, such as when switching between large scale images and atomic scale images, and can easily be installed in any existing scanning tunneling microscope that uses an analog feedback circuit.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1143263
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