Mass sensing with resonating ultra-thin silicon beams detected by a double-beam laser Doppler vibrometer

This paper reports on mass sensing with 33 nm thick single-crystalline cantilevers by a double-beam laser Doppler vibrometer. The resonant frequency of an oscillating thin cantilever beam is very sensitive to a loaded mass. However, the drift of the resonance, due to gas adsorption and mechanical instability, limits the minimum detectable mass in general. Two cantilevers for sensing and its reference will compensate their influences. Two cantilevers were made to self-oscillate by electrostatic actuation at different resonant frequencies. A 10 pg sample (a particle of organosilicon monomer) was mounted at the end of one cantilever, and thermogravimetry of the sample using the two cantilevers was demonstrated. The cantilevers were heated up by a heater in vacuum, and the change in mass was detected from the change in resonant frequency. The exact temperature change can be estimated from the change in resonant frequency of one cantilever as a reference. The derivative of the frequency change, corresponding to desorbed mass, clearly shows a peak of mass desorption at about 270 °C.