As an atomic force microscope’s tip degrades, the change in tip size and shape affects its resonant frequency and that can be used to accurately measure, in real time, the change in the tip’s shape, thereby resulting in more accurate measurements and images at nanometer size scales. Credit: Jason Killgore, NIST
Scientists at the National Institute of Standards and Technology (NIST) have developed a way to measure the wear and degradation of the microscopic probes used to study nanoscale structures in situ and as it’s happening. Their technique can both dramatically speed up and improve the accuracy of the most precise and delicate nanoscale measurements done with atomic force microscopy (AFM).
NIST materials engineer Jason Killgore has 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, a natural vibration rate like that of a tuning fork, while the instrument is in use. Because changes to the size and shape of the tip affect its resonant frequency, he is able to measure the size of the AFM’s tip as it works—in increments of a tenth of a nanometer, essentially atomic scale resolution.
The potential impact of this development is considerable. Thousands of AFMs are in use at universities, manufacturing plants and research and development facilities around the world. Improving their ability to measure and image nanosized 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.
Contact resonance force microscopy is used during AFM scanning to resolve instantaneous and progressive nanometer-scale changes in the contact radius between an AFM tip and a silicon substrate. High-resolution quantitative measurements of contact radius reveal real-time information on wear rate, fracture, and tip-symmetry.
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