Resonance frequency behavior of silicon nitride cantilevers as a function of pressure in different gas environments

We present experimental data on resonant behavior of the first flexural mode of a silicon nitride cantilever in noble gas ambients of He, Ar, and Xe. To this aim thermal noise spectra have been measured with an optical setup. Overall resonance frequency and the quality factor of the first flexural mode vs. pressure are in good agreement with the existing theories for the molecular and viscous pressure regimes. Prior to the viscous regime we observe a small anomalous increase in the resonance frequency which is most pronounced in the He environment. The increase points to a slight stiffening of the cantilever. Surprisingly temperature increase from laser irradiation shows a further increase in the stiffening. Diffusion of gas in the near-surface region of the amorphous cantilever material may lead to stiffening and so account for the small frequency increase.