Nanomechanical Measurement of the Brownian Force Noise in a Viscous Liquid

We study the frequency spectrum of the thermal force giving rise to Brownian motion of a nanomechanical beam resonator in a viscous liquid. In the first set of experiments, we measure the power spectral density (PSD) of the position fluctuations of the resonator around its fundamental mode at its center. Then, we measure the frequency-dependent linear response of the resonator, again at its center, by driving it with a harmonic force that couples well to the fundamental mode. These two measurements allow us to determine the PSD of the Brownian force noise acting on the structure in its fundamental mode. The PSD of the force noise from multiple resonators spanning a broad frequency range displays a colored spectrum and follows the dissipation of a blade oscillating in a viscous liquid-by virtue of the fluctuation-dissipation theorem of statistical mechanics.

Automated summary

In this study, the spectral characteristics of the thermal force causing Brownian motion in a nanomechanical beam resonator in a viscous liquid are investigated. The measured power spectral density and linear response of the resonator help determine the colored spectrum of the Brownian force noise at different frequencies, following the fluctuation-dissipation theorem of statistical mechanics.