Abstract
We demonstrated a miniature and in situ ~13-layer graphene nanomechanical resonator by utilizing a simple optical fiber Fabry-Perot (F-P) interferometric excitation and detection scheme. The graphene film was transferred onto the endface of a ferrule with a 125-μm inner diameter. In contrast to the pre-tension induced in membrane that increased quality (Q) factor to ~18.5 from ~3.23 at room temperature and normal pressure, the limited effects of air damping on resonance behaviors at 10−2 and 105 Pa were demonstrated by characterizing graphene F-P resonators with open and micro-air-gap cavities. Then in terms of optomechanical behaviors of the resonator with an air micro-cavity configuration using a polished ferrule substrate, measured resonance frequencies were increased to the range of 509–542 kHz from several kHz with a maximum Q factor of 16.6 despite the lower Knudsen number ranging from 0.0002 to 0.0006 in damping air over a relative pressure range of 0–199 kPa. However, there was the little dependence of Q on resonance frequency. Note that compared with the inferior F-P cavity length response to applied pressures due to interfacial air leakage, the developed F-P resonator exhibited a consistent fitted pressure sensitivity of 1.18 × 105 kHz3/kPa with a good linearity error of 5.16% in the tested range. These measurements shed light on the pre-stress-dominated pressure-sensitive mechanisms behind air damping in in situ F-P resonant sensors using graphene or other 2D nanomaterials.
Highlights
Nanomechanical resonators have been widely used to measure force [1], mass [2], charge [3], and displacement [4] with high sensitivity
It can be clearly observed from this table that the measured resonance frequency and Q factor values are by far less than most of the results reported in previous literatures
Miniature, and in situ mechanical F-P resonators with open and sealed cavities were fabricated to characterize the resonance behaviors of a nanothick graphene diaphragm suspended onto a large-area 125-μm inner diameter ferrule endface by using simple optical interference excitation and detection
Summary
Nanomechanical resonators have been widely used to measure force [1], mass [2], charge [3], and displacement [4] with high sensitivity. Preliminary studies under vacuum (low damping) conditions conducted by Bunch et al on electromechanical resonators from mechanically-exfoliating graphene sheets over trenches in SiO2 have found that the tension resulting from the fabrication process could increase the resonant frequency [10], graphene typically has higher energy loss [26], especially in air damping owing to a lower thickness per unit layer and mass density. This suggests that the overall effects of the tension in membrane and viscous air damping on resonance characteristics should be estimated for improving the clamping at the suspended graphene-substrate interface. The results validated the developed F-P resonator and the measured resonance frequencies in contrast to Q factors revealed the more strongly dependence upon the stress tensor in nanomembranes [27], in comparison to viscous damping or free molecule flow damping previously reported in [28]
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