Slippage and Boundary Layer Probed in an Almost Ideal Gas by a Nanomechanical Oscillator

Abstract

We measure the interaction between ⁴He gas at 4.2 K and a high-quality nanoelectromechanical string device for its first three symmetric modes (resonating at 2.2, 6.7, and 11 MHz with quality factor Q>0.1×10⁶) over almost 6 orders of magnitude in pressure. This fluid can be viewed as the best experimental implementation of an almost ideal monoatomic and inert gas of which properties are tabulated. The experiment ranges from high pressure where the flow is of laminar Stokes-type presenting slippage down to very low pressures where the flow is molecular. In the molecular regime, when the mean-free path is of the order of the distance between the suspended nanomechanical probe and the bottom of the trench, we resolve for the first time the signature of the boundary (Knudsen) layer onto the measured dissipation. Our results are discussed in the framework of the most recent theories investigating boundary effects in fluids (both analytic approaches and direct simulation Monte Carlo methods).

Lifetime of a Nanodroplet: Kinetic Effects and Regime Transitions

“…Rarefaction manifests itself through a temperature jump and kinetic boundary (Knudsen) layer, which have been observed experimentally [9][10][11] and predicted theoretically [12,13]. Notably, even at Kn ≈ 10 −3 -where the d-squared scaling is still seen-the NSF equations with classical boundary conditions are unable to give a good quantitative prediction of the total evaporation time of micrometer size droplets [9].…”

Operating Nanobeams in a Quantum Fluid

“…In this paper we address the efforts to develop new MEMS and NEMS devices, or to adapt those already available, for use in liquids at cryogenic temperatures [7][8][9][10][11] . There are two very major aims here.…”

Nanomechanical Resonators for Cryogenic Research

“…The agreement with theory is reasonable, considering that the gap distance d and the value of the diffusion time τ are not known accurately since the geometry determined from microphotographs at room temperature may change as there are stress induced changes in the device shape as it is cooled down to 4.2 K temperature. The damping has also been reported to decrease, when the mean free path of gas is close to the gap distance d [18]. From the elastic part of the squeeze film force, we would expect an increase in the resonance frequency.…”