A simple approach is developed to identify the layer number of 2D MoS₂ sheets. By using an optical imaging method combined with image analysis software, a high-contrast image of the MoS₂ sheets can be extracted from the red (R) channel of the color optical microscopy image. The value of the intensity difference in the grayscale image of the R channel between MoS₂ sheets (1-3 layers) and the SiO₂ substrate can be used to identify the layer number of the sheet.

Theoretical and experimental investigations of diacetylene-linked COFs with remarkable charge-transport properties.

Optimal band gap and average effective mass of two-dimensional channels for high-performance tunneling transistors.

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The whale optimization algorithm (WOA) is a powerful swarm intelligence method which has been widely used in various fields such as parameter identification of solar cells and PV modules. In order to better balance the exploration and exploitation of WOA, we propose a novel modified WOA (MWOA) in which both the mutation strategy based on Levy flight and a local search mechanism of pattern search are introduced. On the one hand, Levy flight can make the algorithm get rid of the local optimum and avoid stagnation; thus, it is able to prevent the algorithm from losing diversity and to increase the global search capability. On the other hand, pattern search, a direct search method, has not only high convergence rate but also good stability, which can boost the local optimization ability of the WOA. Therefore, the combination of these two mechanisms can greatly improve the capability of WOA to obtain the best solution. In addition, MWOA may be employed to estimate parameters in single diode model (SDM), double diode model (DDM), and PV modules and to identify unknown parameters of two different types of PV modules under diverse light irradiance and temperature conditions. The analytical results demonstrate the validity and the practicality of MWOA for estimating parameters of solar cells and PV modules.

In this article, we establish a space-time continuous finite element (STCFE) method for viscoelastic wave equation. The existence, uniqueness, and stability of the STCFE solutions are proved, and the optimal rates of convergence of STCFE solutions are obtained without any time and space mesh size restrictions. Two numerical examples on unstructured meshes are employed to verify the efficiency and feasibility of the STCFE method and to check the correctness of theoretical conclusions. MSC: 74S10; 65M15; 35Q35

Monolayer hexagonal arsenene, antimonene, and bismuthene are emerging two-dimensional (2D) semiconductors. We explore the possibility of their applications on 10 nm gate long tunneling field effect transistors (TFETs) from the ab initio quantum transport simulation. We predict that the ML bismuthene TFET has the largest on-state current I on (1153 μA μm −1 ) among the three checked hexagonal group V-enes ones for high-performance (HP) application. We further propose a prototype negative capacitance TFET, where a ferroelectric dielectric is adopted in the TFET to improve the device performance. The resulting I on is dramatically elevated to 1868 μA μm −1 , which has met the requirement of International Technology Roadmap for Semiconductors for HP devices (1450 μA μm −1 ). Therefore, the combination of 2D semiconductor channel and negative capacitance technique breaks the bottleneck of a very low on-state current of conventional TFETs.