Dynamics of photothermally driven VO2-coated microcantilevers

The dynamic response of VO2-coated silicon microcantilevers thermally driven over the film's insulator-to-metal transition was studied using laser light pulses directly incident on the cantilevers. The measured photothermal response revealed very high curvature changes of approximately 2500m(-1) up to pulse frequencies greater than 100 Hz and readily observable vibrations up to frequencies of a few kHz with no amplitude degradation after tens of thousands of pulses. Maximum tip amplitudes for 300-mu m-long, 1-mu m-thick cantilevers used in these experiments were nearly 120 mu m and correspondingly less for 2-mu m-thick cantilevers. The main mechanism limiting oscillation amplitude was found to be heat transport response during heating and cooling, which depends mainly on thermal conduction through the cantilever itself to the massive anchor and chip body, which acted as a heat sink at room temperature. For the laser-driven oscillations studied, damping by the surrounding air is unimportant in the range of frequencies probed. Large-curvature response is expected to extend to higher pulse frequencies for cantilevers with smaller dimensions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658776]