Electrically Tunable MXene Nanomechanical Resonators Vibrating at Very High Frequencies

As an emerging class of two-dimensional (2D) layered nanomaterial, MXene exhibits a number of intriguing properties, such as good electrical conductivity and high elastic modulus, and has witnessed continued growth in related device research. However, nanoscale MXene devices which leverage both the intrinsic electrical and mechanical properties of these 2D crystals have not been experimentally studied. Here we demonstrate nanoelectromechanical resonators based on 2D MXene crystals, where Ti₃C₂T_x drumheads with a wide range of thickness, from more than 50 layers all the way down to a monolayer, exhibit robust nanomechanical vibrations with fundamental-mode frequency f₀ up to >70 MHz in the very high frequency (VHF) band, a displacement noise density down to 52 fm/Hz^1/2, and a fundamental-mode frequency-quality factor product up to f₀ × Q ≈ 6.85 × 10⁹ Hz. By combining experimental results with theoretical calculations, we independently derive the Young's modulus of 2D Ti₃C₂T_x crystals to be 270-360 GPa, in excellent agreement with nanoindentation measurements, based on which we elucidate frequency scaling pathways toward microwave frequencies. We further demonstrate electrical tuning of resonance frequency in MXene resonators and frequency-shift-based MXene vacuum gauges with responsivity of 736%/Torr and detection range down to 10^-4 Torr. Our study can lead to the design and creation of nanoscale vibratory devices that exploit the intrinsic electrical and mechanical properties in 2D MXene crystals.

Frequency Scaling, Elastic Transition, and Broad-Range Frequency Tuning in WSe2 Nanomechanical Resonators

Nanomechanical resonators based on atomic layers of tungsten diselenide (WSe₂) offer intriguing prospects for enabling novel sensing and signal processing functions. The frequency scaling law of such resonant devices is critical for designing and realizing these high-frequency circuit components. Here, we elucidate the frequency scaling law for WSe₂ nanomechanical resonators by studying devices of one-, two-, three-, to more than 100-layer thicknesses and different diameters. We observe resonant responses in both mechanical limits and clear elastic transition in between, revealing intrinsic material properties and devices parameters such as Young's modulus and pretension. We further demonstrate a broad frequency tuning range (up to 230%) with a high tuning efficiency (up to 23% V^-1). Such tuning efficiency is among the highest in resonators based on two-dimensional (2D) layered materials. Our findings can offer important guidelines for designing high-frequency WSe₂ resonant devices.