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.
In‐plane anisotropy in 2D rhenium disulfide (ReS2) offers intriguing opportunities for designing future electronic and optical devices, and toward such applications, it is crucial to identify the crystal orientation in such 2D anisotropic materials. Existing spectroscopy or electron microscopy methods for determining the crystalline orientation often require complicated sample preparing procedures and specialized equipment, which could sometimes limit their application. In this work, a dichromatic polarized reflectance method is demonstrated, which can quickly and accurately resolve the crystal orientation (Re–Re chain) in 2D ReS2 crystals with different thicknesses. Furthermore, it can be readily extended to multi‐chromatic schemes to achieve greater measurement capability and can be easily tailored to work for different 2D materials. The method offers a simple and effective approach for studying anisotropy in 2D materials.
We have studied the interference pattern of multiple reflections from a. uniaxial, optically active and non-absorbing plane parallel plate under normal incidence. Due to birefringence, a beam of polarized light splits into an ordinary and an extraordinary component. Because of optical activity, the number of beams is doubled after each reflection. During crossing of the plate the phase difference between beams is increased by fixed amounts. The calculated results show that the interference pattern of the transmitted light is more complex than that of an isotropic parallel plate. It consists of strong fringes at large phase intewals and weak doublets in between, at neatly the same phase intewals as in the isotropic plate.
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