Time-domain response of atomically thin $\mathrm{MoS_2}$ nanomechanical resonators

TL;DR

This study uses time-domain ring-down measurements to determine that the spectral line-width of atomically thin MoS2 nanomechanical resonators at room temperature is primarily limited by dissipation, not frequency fluctuations.

Contribution

It provides the first direct quantification of energy dissipation in MoS2 nanomechanical resonators using time-domain methods, clarifying the origin of spectral broadening.

Findings

Q-factor from ring-down matches spectral measurements, indicating dissipation dominates.

Frequency fluctuations contribute negligibly to spectral line-width.

Dissipation limits the resonance quality at room temperature.

Abstract

We measure the energy relaxation rate of single- and few-layer molybdenum disulphide ($\mathrm{MoS_2}$) nanomechanical resonators by detecting the resonator ring-down. Recent experiments on these devices show a remarkably low quality (Q)-factor when taking spectrum measurements at room temperature. The origin of the low spectral Q-factor is an open question, and it has been proposed that besides dissipative processes, frequency fluctuations contribute significantly to the resonance line-width. The spectral measurements performed thus far however, do not allow one to distinguish these two processes. Here, we use time-domain measurements to quantify the dissipation. We compare the Q-factor obtained from the ring-down measurements to those obtained from the thermal noise spectrum and from the frequency response of the driven device. In few-layer and single-layer $\mathrm{MoS_2}$ resonators the two are in close agreement, which demonstrates that the spectral line-width in $\mathrm{MoS_2}$ membranes at room temperature is limited by dissipation, and that excess spectral broadening plays a negligible role.