Applied Physics

Fidget-Free Microscopy

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Science  27 Mar 2009:
Vol. 323, Issue 5922, pp. 1647
DOI: 10.1126/science.323.5922.1647a

Many people find it hard to sit still for extended periods without fidgeting and shifting about. A similar problem plagues the widely used technique of atomic force microscopy: Though the probing tip can resolve individual atoms, it is fundamentally a mechanical device and so inevitably drifts in space over time. As a result, the period available for signal-averaging to improve data quality is limited; moreover, it is often impossible to deliberately shift the tip to a different portion of the sample and then return to precisely the same starting position during the course of an imaging session (for example, to monitor slow rearrangements in two or more distinct domains of a protein). King et al. address this shortcoming using a laser-based feedback scheme for tip stabilization. Specifically, they detect backscattered laser light from the tip as well as a reference marker (a silicon disk) on the sample. The tip is then adjusted to remain in a fixed position relative to the marker. Studies of gold nanospheres in room-temperature air demonstrate a lateral drift rate limited to just 5 pm/min over the course of more than an hour. The method is optimized for transparent substrates, due to the backscattering detection geometry, but could potentially be extended by incorporating the reference marker into the instrument's cantilever assembly. — JSY

Nano Lett. 9, 10.1021/nl803298q (2009).

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