Measurements of the flow of thick 3He films over a highly polished silver surface, using a high precision torsional oscillator, have found unexpectedly long momentum relaxation times (Casey et al., Phys. Rev. Lett. 92, 255301, 2004). This results in a decoupling of the normal state helium film from the oscillator motion at low temperatures. In the ballistic regime the relaxation rate varies linearly with temperature.

We demonstrate piezoresistive transduction of mechanical motion from out-of-plane flexural micromechanical resonators made from stacked thin films. The resonators are fabricated from two highly doped polycrystalline silicon layers separated by an interlayer dielectric. We examine two interlayer materials: thermal silicon dioxide and stoichiometric silicon nitride. We show that via one-time dielectric breakdown, the film stack functions as a vertical piezoresistor effectively transducing the motion of the resonators.

We report on a method to produce free-standing graphene sheets from epitaxial graphene on silicon carbide (SiC) substrate. Doubly clamped nanomechanical resonators with lengths up to 20 μm were patterned using this technique and their resonant motion was actuated and detected optically. Resonance frequencies of the order of tens of megahertz were measured for most devices, indicating that the resonators are much stiffer than expected for beams under no tension.

High-stress silicon nitride microresonators exhibit a remarkable room temperature Q factor that even exceeds that of single crystal silicon. A study of the temperature dependent variation of the Q of a 255μm×255μ m×30nm thick high-stress Si3N4 membrane reveals that the dissipation Q-1 decreases with lower temperatures and is □ 3 orders of magnitude smaller than the universal behavior. Stress-relieved cantilevers fabricated from the same material show a Q that is more consistent with typical disordered materials.

We examine the relationship between squeeze film effects and resonance frequency in drum-type resonators. We find that the resonance frequency increases linearly with pressure as a result of the additional restoring force contribution from compression of gas within the drum cavity. We demonstrate trapping of the gas by squeeze film effects and geometry. The pressure sensitivity is shown to scale inversely with cavity height and sound radiation is found to be the predominant loss mechanism near and above atmospheric pressure.

We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the world's thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick. © 2008 American Chemical Society.

We examine size and frequency dependent gas damping of nanobeam resonators. We find an optimal beam width that maximizes the quality factor at atmospheric pressure, balancing the dissipation that scales with surface-to-volume ratio and dominates at small widths, against the interaction with the underlying substrate via the air that dominates the behavior of the wider devices. This latter interaction is found to affect the Knudsen number corresponding to a transition out of the molecular damping regime.

We have made reliable measurements of the sound velocity δv/v0 and internal friction Q-1 in vitreous silica at 1.03, 3.74, and 14.0 kHz between 1mK and 0.5K. In contrast with earlier studies that did not span as wide a temperature and frequency range, our measurements of Q-1 reveal a crossover (as T decreases) only near 10mK from the T3 dependence predicted by the standard tunneling model to a T dependence predicted if interactions are accounted for.

We present experimental observations of the suppressed superfluid transition temperature, T ca, superfluid fraction, Ï s/Ï and Leggett frequency of 3He-B in aerogel, Ω Ba. We determine T ca from mass decoupling and the vanishing of the frequency shift away from the Larmor frequency in our different samples and different laboratories.

We demonstrate the fabrication and operation of high aspect ratio tensile stressed silicon nitride string resonators. We explore the parameter space of small cross sections, on the order of 100 nm, and long lengths up to 325 μm, demonstrating that such high aspect ratio resonators can be made with standard wet release processing using a material with internal tensile stress. Room temperature quality factors exceed one million at frequencies above 1 MHz.