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 $\text{1000\hspace{0.05em}°}\mathrm{C}$ for 30 s in UHV results in an over 1 order of magnitude increase of the quality factor $\mathrm{(Q}$ factor), up to about ${\text{2.5×10}}^5$ 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 $\text{300×100\hspace{0.05em}μ}{\mathrm{m}}^{\mathrm{2}})$ with power down to less than 40 μW at a wavelength of 680 nm, corresponding to 480 nW, i.e., ${\text{1.64×10}}^{12} \mathrm{photons/s},$ irradiated on the cantilever surface $\text{(60×6\hspace{0.05em}μ}{\mathrm{m}}^{\mathrm{2}}\mathrm{).}$ This provides a rather simple way to operate the ultrathin cantilevers dynamically in UHV. Atomic scale force resolution ${\text{(4.8×10}}^{\text{−17}} \mathrm{N})$ at 300 K is also expected with these cantilevers.