Nanomechanical spectroscopy (NMS) is a recently developed approach to determine optical absorption spectra of nanoscale materials via mechanical measurements. It is based on measuring changes in the resonance frequency of a membrane resonator vs. the photon energy of incoming light. This method is a direct measurement of absorption, which has practical advantages compared to common optical spectroscopy approaches. In the case of two-dimensional (2D) materials, NMS overcomes limitations inherent to conventional optical methods, such as the complications associated with measurements at high magnetic fields and low temperatures. In this work, we develop a protocol for NMS of 2D materials that yields two orders of magnitude improved sensitivity compared to previous approaches, while being simpler to use. To this end, we use mechanical sample actuation, which simplifies the experiment and provides a reliable calibration for greater accuracy. Additionally, the use of low-stress silicon nitride membranes as our substrate reduces the noise-equivalent power to NEP = 890 fW H z − 1 , comparable to commercial semiconductor photodetectors. We use our approach to spectroscopically characterize a 2D transition metal dichalcogenide (WS₂), a layered magnetic semiconductor (CrPS₄), and a plasmonic super-crystal consisting of gold nanoparticles.

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There are many uncertainties regarding the future level of natural gas consumption in China. In order to obtain a clear idea of what factors drive fuel consumption choices, we focus on three regions of China: Beijing, Guangdong, and Shanghai. Using an economic optimization model (MARKAL), we consider drivers including the level of sulfur dioxide emissions constraints set by the government, the cost of capital, the price and available supply of natural gas, and the rate of penetration of advanced technology on both supply and demand sides. The results from the model show that setting strict rules for SO 2 emissions will be instrumental in encouraging the use of natural gas, and may also cause some reduction in CO 2 emissions. The currently differentiated cost of capital for various sectors within the Chinese economy, on the other hand, artificially boosts the economics of capitalintensive coal relative to natural gas. This suggests that financial reform could be a lever for encouraging increased gas use.@en