Evanescent field optical readout of graphene mechanical motion at room temperature

TL;DR

This paper demonstrates a room-temperature evanescent optical readout method for graphene mechanical resonators, achieving high sensitivity and bandwidth without cryogenic cooling, enabling practical sensing applications.

Contribution

First demonstration of cryogen-free evanescent optical readout of graphene motion with enhanced sensitivity and bandwidth at room temperature.

Findings

Achieved a transduction sensitivity of 2.6×10^{-13} m/Hz^{1/2}.

Force sensitivity limited by thermal noise at 1.5×10^{-16} N/Hz^{1/2}.

Resolved the first three thermally driven resonances of graphene drums.

Abstract

Graphene mechanical resonators have recently attracted considerable attention for use in precision force and mass sensing applications. To date, readout of their oscillatory motion has typically required cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the first demonstration of evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilise a high $Q$ microsphere to enable evanescent readout of a 70 $\mu$m diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of $S_{N}^{1/2} = $ 2.6 $\times 10^{-13}$ m $\mathrm{Hz}^{-1/2}$. The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of $F_{min} = 1.5 \times 10^{-16}$ N ${\mathrm{Hz}}^{-1/2}$ with a bandwidth of 35 kHz at room temperature (T = 300 K). Measurements on a 30 $\mu$m graphene drum had sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances.