High-bandwidth intermittent-contact mode scanning probe microscopy using electrostatically-actuated microcantilevers

Abstract

A critical issue in scanning probe microscopy (SPM) in the intermittent-contact (IC) mode is the achievable bandwidth, which is limited because of the high quality factor of the cantilevers. Cantilevers for IC-mode SPM must have high stiffness for stable operation, which necessitates high quality factors for high force sensitivity, and thus results in a slow response time. Here we present an IC SPM method that achieves high bandwidth by using electrostatically-actuated cantilevers with low stiffness and low quality factor. Reliable IC operation is achieved by shaping the input signal applied to the cantilever for electrostatic actuation. By keeping the oscillation amplitude small, high-frequency operation is possible and the tipsample interaction force is reduced, which in turn prolongs the lifetime of tip and sample. For high-bandwidth imaging, the cantilever deflection signal is sampled directly at each oscillation cycle using input-based triggering. Our experimental results demonstrate the efficacy of the proposed scheme. In particular, in long-term scanning experiments, the tip diameter was maintained over a remarkable 140 m of tip travel. Moreover, as no demodulation electronics are needed, compact SPM devices using this method could be developed, including devices that employ large arrays of cantilevers in parallel operation for high throughput. © 2011 Springer-Verlag Berlin Heidelberg.