Overview
We develop spatial mapping techniques to visualize the vibrational resonances of micro- and nanoscale mechanical devices by combining Fabry–Pérot (F-P) interferometry with network analysis. This approach enables direct measurement of both the amplitude and phase of mechanical motion with high spatial resolution.
In our system, the mechanical resonator and the substrate form a Fabry–Pérot cavity. Mechanical motion modulates the cavity length, which in turn changes the intensity of the reflected optical signal. The device is driven using an external excitation, and the optical response is analyzed using a network analyzer to obtain the full frequency-dependent transfer function, including both resonance amplitude and phase.
To reconstruct the spatial distribution of resonances, the device is mounted on a precision translation stage and scanned relative to the fixed optical probe. At each spatial position, the network analyzer records the resonance spectrum. By extracting the resonance amplitude and phase at selected frequencies, we build two-dimensional maps that directly visualize the mechanical mode shapes across the entire structure.
Featured Publications:
Spatial mapping of multimode Brownian motions in high-frequency silicon carbide microdisk resonators
Using ultra-sensitive scanning laser interferometry, we directly measured and spatially mapped undriven thermomechanical (Brownian) vibrations up to the ninth flexural mode in SiC microdisks—achieving displacement sensitivities of 7-14 fm/√Hz. The multimode mapping capability enables new modalities for sensing and reveals rich physics of high-order Brownian motions, with implications for quantum-limited measurements
Temperature Compensated Graphene Nanomechanical Resonators
Our spatially resolved quantitative mapping of thermomechanical noise resonant motions on bilayer-graphene devices allows us to unambiguously determine the resonance characteristics of the graphene devices. Our temperature compensation techniques in 2D NEMS provide an efficient and practical approach to significantly enhancing the frequency stability of these 2D NEMS resonators when exposed to varying environmental temperatures.
We performed ultrasensitive optical interrogation of the motions of drumhead-structured MoS2 resonators. With careful measurements and displacement-domain calibration from Brownian motion thermomechanical noise to well beyond the onset of Duffing nonlinearity, we are able to observe and deterministically quantify the intrinsic dynamic ranges of these 2D NEMS resonators.
References:
- +Wang ZH, +Lee JS, Feng PXL*, “Spatial mapping of multimode Brownian motions in high-frequency silicon carbide microdisk resonators”, Nature Communications 5, Art. No. 5158 (2014). [This article has been featured by R&D Magazine’s ‘Feature Story’ and ‘Editor’s Pick’. It has also been featured in German, by pro-physik.de. This work has also been featured in Science Daily, Physics & Matter News, Nanowrek, Space Daily, Science Newsline, Phys.Org, EurekAlert!, Nanotechnology Now, London the News, Chicago Chronicle, etc., and other tech/public media] DOI: https://doi.org/10.1038/ncomms6158
- +Lee JS, +Wang ZH, He KL, Yang R, Shan J, Feng PXL*, “Electrically Tunable Single- and Few-Layer MoS2 Nanoelectromechanical Systems with Broad Dynamic Range”, Science Advances 4, eaao6653 (2018). [This article has been featured by many science and technology magazines and news outlets, including IEEE Spectrum, Mechanical Engineering, featured in various languages too]. DOI: https://doi.org/10.1126/sciadv.aao6653
- Lee J, Zhao L, Chiu HY, Shan J, Feng PXL*, “Temperature Compensation of Graphene Nanomechanical Resonators”, Advanced Functional Materials 35, 2415708 (2025). DOI: https://doi.org/10.1002/adfm.202415708