Ultrathin resonant cantilevers are promising for ultrasensitive detection. A technique is developed for high-yield fabrication of single-crystalline-silicon cantilevers as thin as 12 nm. The formed cantilever resonators are characterized by resonance testing in high vacuum. Significant specimen size effect on Young’s modulus of ultrathin (12–170 nm) silicon is detected. The Young’s modulus decreases monotonously as the cantilevers become thinner. The size effect is consistent with the published simulation results of direct-atomistic model, in which surface effects are taken into consideration.

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 (4.8×10−17 N) at 300 K is also expected with these cantilevers.

Ultrathin single-crystalline silicon cantilevers with a thickness of 170 nm as a resonating sensor are applied to mass sensing. The hydrogen storage capacity of a small amount of carbon nanotubes (CNTs), which were mounted on an ultrathin resonator by a manipulator, is measured from the resonant frequency change. The resonator is annealed in ultrahigh vacuum to clean the surface and increase the quality factor, and exposed to oxygen gas to oxidize the surface for long-term stability. The resonator can be electrostatically actuated, and the vibration is measured by a laser Doppler vibrometer in ultrahigh vacuum. The mass of the CNTs is determined by the difference of resonant frequencies before and after mounting the CNTs, and the hydrogen storage capacity is determined from the frequency change after exposure to high-pressure hydrogen as well. The obtained hydrogen storage capacitance is 1.6%–6.0%. The available mass resolution and the achieved stability of the resonance of the 170-nm-thick resonator are below 10−18 g and 5 Hz/days, respectively.

Very weak light emission due to micro-discharges in the micro-gap of an electrostatic actuator under a high electric field can be imaged using a highly sensitive CCD camera. In this paper, we focus, in particular, on the relation between the micro-discharge and the electric field breakdown. Micro-discharges attributed to local breakdown is observed even if the electric field strength is below the breakdown threshold. The observations of the micro-discharge give important information on the irregularity and inhomogeneity of the electric field. It is found that irregular instability and inhomogeneous distribution of the electric field develop micro-discharges. The micro-discharge evaporates the electrode material, which results in increasing pressure in the gap, and finally grows to the breakdown. This effect seems to be remarkable, especially in narrow gaps. Furthermore, the electric breakdown threshold depends on the electrode material. A silicon-to-silicon gap configuration shows a higher breakdown threshold as well as the prebreakdown threshold in comparison to a silicon-to-metal gap.

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