| Nanoelectromechanical Systems (NEMS) are electromechanical systems with critical dimensions in the sub-micron range. NEMS are often operated in their fundamental resonant modes at high frequencies. As such, their active masses and intrinsic dissipation levels are usually very small. Resultantly, NEMS devices are rapidly being developed for a variety of sensing applications, high frequency electromechanical signal processing and time-keeping tasks.; Most high-impact sensing applications require NEMS operation in fluids, where undesirable fluidic effects degrade device performance. Overcoming the challenges in operating NEMS devices in fluids requires a new understanding of fluid dynamics at high frequencies. Newtonian fluid dynamics, which has been used to describe similar problems in larger scale devices such as MEMS, requires characteristic length and time scales of the flow to be significantly larger than the mean free path and relaxation time of the fluid, respectively. Both assumptions fail for NEMS devices in gaseous environments. In fact, NEMS resonators provide a unique opportunity to study this previously inaccessible flow regime.; In an effort to understand this novel flow regime, doubly-clamped nanomechanical beam resonators spanning a wide range of size and resonance frequencies were fabricated. The resonant behavior of these devices was studied as a function of surrounding gas pressure in an optical interferometer, which was developed for characterizing sub-wavelength devices. Through analysis of resonance parameters, fluidic dissipation and inertial loading effects were extracted. The combination of varying gas pressure and resonator dimensions allowed for the exploration of a large parameter space.; The experimental data were compared to various formulations of fluid dynamics developed for resonant structures. The observed transitions in fluidic dissipation as a function of frequency and gas pressure agreed closely with a recently developed non-Newtonian theory of fluid dynamics at high frequencies. The possibility of increasingly elastic response, and thus reduced fluidic dissipation, at high resonance frequencies may result in exciting opportunities for next-generation NEMS operating in fluids. |
