Surface effects and high quality factors in ultrathin single-crystal silicon cantilevers

Surface effects in ultrathin single-crystal silicon cantilevers of 170 nm thickness, which are optically actuated mainly by the light pressure effect, are investigated under ultrahigh vacuum (UHV) condition. Annealing the cantilevers at 1000°C for 30 s in UHV results in an over 1 order of magnitude increase of the quality factor (Q factor), up to about 2.5×10⁵ for cantilevers of 30-90 μm in length. The improvement of Q factor was found to be associated with the deoxidization of the surface, as determined by x-ray photoelectron spectroscopy. These results suggest that the surface effects in the ultrathin cantilevers dominate their mechanical behavior. With the promising mechanical behavior, the cantilever can be easily actuated by a laser beam (beam size: about 300 × 100 μm²) with power down to less than 40 μW at a wavelength of 680 nm, corresponding to 480 nW, i.e., 1.64×10¹² photons/s, irradiated on the cantilever surface (60×6 μm²). This provides a rather simple way to operate the ultrathin cantilevers dynamically in UHV. Atomic scale force resolution (4.8×10^-7 N) at 300 K is also expected with these cantilevers.