Graphene resonant sensors have shown strong competitiveness with respect to sensitivity and size. To advance the applications of graphene resonant sensors, the damage behaviors of graphene harmonic oscillators after thermal annealing and laser irradiation were investigated by morphology analysis and frequency domain vibration characteristics. The interface stress was proven to be the key factor that directly affected the yield of resonators. The resulting phenomenon could be improved by appropriately controlling the annealing temperature and size of resonators, thereby achieving membrane intactness of up to 96.4%. However, micro-cracks were found on the graphene sheets when continuous wave (CW) laser power was more than 4 mW. Moreover, the fluctuating light energy would also cause mechanical fatigue in addition to the photothermal effect, and the threshold damage power for the sinusoidally modulated laser was merely 2 mW. In this way, based on the amplitude-frequency surface morphology of the graphene resonator, the thermal time constant of the order of a few microseconds was confirmed to evaluate the damage of the graphene oscillator in situ and in real time, which could be further extended for those resonators using other 2D materials.

A miniature high-sensitivity Fabry-Perot (F-P) resonant pressure sensor was developed by transferring multilayer graphene (MLG) onto a copper mesh with a bore diameter of 20 μm. The resonance of graphene membrane suspended and clamped on the copper mesh was opto-thermally excited and detected via optical fiber F-P interference. The measured resonant behaviors showed that the sensor achieved a maximum resonant frequency of 1.11 MHz with a good sensitivity of 10.4 kHz/kPa in the tested range of 0.01 to 50 kPa, which is much higher than that of common silicon resonant pressure sensor with a normal sensitivity of 0.1-0.4 kHz/kPa. Also, the output stability within 4200 seconds demonstrated an extremely low frequency deviation of 0.18% at 6 mW of optical power and 0.16% at 5 mW of optical power, thereby verifying a great potential in highly sensitive pressure measurement.

Nanomechanical resonators made of suspended MXene-sensitive membranes can be used to characterize thermodynamic properties. A highly sensitive MXene Fabry-Perot resonant pressure sensor was developed by transferring Ti3C2Tx MXene onto a Transmission electron microscope (TEM) grid with an aperture of 20 μm. The MXene membrane was suspended and clamped on a TEM grid, and its resonance was detected by optical fiber photothermal excitation. To determine the elastic properties of the MXene resonator, the relationship between the resonance response and Young's modulus was analyzed theoretically based on experimental data, and Young's modulus of the MXene-sensitive membrane of the resonator was calculated to be 18 GPa. Subsequently, the measured resonance behavior showed that the sensor reached a maximum resonance frequency of 4.31 MHz over the test range from 0.005 to 100 kPa. It also has a sensitivity of 24.2 kHz/kPa, which is higher than that of common silicon/graphene resonant pressure sensors with sensitivities ranging from 0.1 to 6.9 kHz/kPa. Moreover, the maximum frequency shifts of the resonator at 5 mW, 6 mW, and 7 mW optical power compared to the average frequency of 4.322 MHz, 4.344 MHz, and 4.367 MHz are 0.03%, 0.03%, and 0.04%, with a standard deviation of 1.2 kHz, 1.4 kHz, and 2.1 kHz, respectively. The sensor structure proposed in this paper offers a promising solution for miniaturization and characterization of the elastic properties of pressure sensors using two-dimensional materials as sensitive membranes.

Photothermal graphene resonant sensors hold significant promise for micromechanical sensing due to their superior mechanical and thermal properties. This study investigates the resonant and thermal behaviors of graphene resonators under varying optical power and temperature conditions. We measured the thermal time constants of five-layer (5L), eight-layer (8L), ten-layer (10L) graphene resonators, observing increases by 71, 74, and 57 ns, respectively, as optical power increased from 1 to 5 mW, alongside temperature rises in the graphene films. Additionally, the corresponding thermal and mechanical properties were further examined across different ambient temperatures. Results show that the resonant frequency increases with temperature-induced surface tension, while increased tension enhances Umklapp scattering among phonons, reducing thermal conductivity. This work lays the groundwork for utilizing photothermal graphene resonators in mechanical sensing applications.