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Exploiting irregular MoS2 nanostructures for very high frequency (VHF) nanomechanical resonators with mode shape engineering and frequency control

Vibrating nanoelectromechanical systems (NEMS) made of atomically-thin two-dimensional (2D) crystalline nanostructures have demonstrated attractive potential for making new actuators and sensors. Nanoscale devices in new types of 2D materials are generally first obtained by mechanical exfoliation, which can often lead to irregular and asymmetric geometries. Here we investigate irregular molybdenum disulfide (MoS2) nanoflakes and ultrathin 2D nanomechanical resonators at high & very high frequencies (HF/VHF). We explore the effects of irregularities and imperfections, such as incomplete drumhead structures partially covering microtrenches, upon the device characteristics. We observe that such irregular and seemingly nonideal boundary conditions with free edges do not compromise device performance. Instead, they provide an additional geometrical degree of freedom which allows novel engineering of the device vibrations, such as controlling the mode shape and mode index, and tuning the frequency ratios between different resonant modes. This capability may be interesting for designing multimode resonators in nanomechanical circuits.