Real-Time Monitoring of AFM Probes
BOULDER, Colo., April 5, 2011 — A new way to measure the degradation of ultrasmall probes in situ and as it is happening promises to dramatically speed up and improve the accuracy of atomic force microscopy (AFM).
If you are trying to measure the contours of a surface with a ruler that is crumbling away as you work, then you at least need to know how fast and to what extent it is being worn away during the measurement. This has been the challenge for researchers and manufacturers trying to create images of the surfaces of nanomaterials and nanostructures. Taking a photo is impossible at such small scales, so researchers use atomic force microscopes. However, the AFM probe tips are so small that they tend to wear down as they traverse the surface being measured.
As an atomic force microscope’s tip degrades, the change in its size and shape affects its resonant frequency, and that can be used to accurately measure, in real time, the change in its shape. (Image: J. Killgore, NIST)
Today, most researchers stop the measurement to “take a picture” of the tip with an electron microscope, a time-consuming method prone to inaccuracies.
Led by Jason Killgore, scientists at the National Institute of Standards and Technology (NIST) have developed a method for measuring in real time the extent to which AFM tips wear down. Killgore measures the resonant frequency of the AFM sensor tip while the instrument is in use. Because changes to the size and shape of the tip affect its resonant frequency, he can measure the size of the AFM’s tip as it works — in increments of 0.1 nm. The technique, called contact resonance force microscopy, is described in a paper published March 15, 2011, in the journal Small.
The potential impact of this development is considerable. Thousands of AFMs are in use at universities, manufacturing plants, and research and development facilities worldwide. Improving their ability to measure and image nanosize devices will improve the quality and effectiveness of those devices. Another benefit is that developing new measurement tips — and studying the properties of new materials used in those tips — will be much easier and faster, given the immediate feedback about wear rates.
For more information, visit: www.nist.gov
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