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A finite difference numerical model, which can correctly consider dispersion effect of waves over a slowly varying water depth, is developed for the simulation of tsunami propagation. The present model employs a linear Boussinesq-type wave equation that can be solved more easily than typical Boussinesq equations. In the present model numerical dispersion is minimized by controlling the dispersion-correction parameter determined by the time step, grid size and local water depth. In order to examine the applicability of the present model to dispersive waves, the propagation of tsunamis is simulated for an initial water surface displacement of Gaussian shape for the cases of several constant water depths and a submerged circular shoal. The numerical results are compared with analytical solutions or numerical solutions of linearized Boussinesq equations. The comparisons show that satisfactory agreement is obtained.

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We propose a hybrid gate structure for ion gel dielectrics using an ultra-thin Al2O3 passivation layer for realizing high-performance devices based on electric-double-layer capacitors. Electric-double-layer transistors can be applied to practical devices with flexibility and transparency as well as research on the fundamental physical properties of channel materials; however, they suffer from inherent unwanted leakage currents between electrodes, especially for channel materials with low off-currents. Therefore, the Al2O3 passivation layer was introduced between the metal electrodes and ion gel film as a leakage current barrier; this simple approach effectively reduced the leakage current without capacitance degradation. In addition, we confirmed that a monolayer MoS2 transistor fabricated with the proposed hybrid gate dielectric exhibited remarkably enhanced device properties compared to a transistor using a normal ion gel gate dielectric. Our findings on a simple method to improve the leakage current properties of ion gels could be applied extensively to realize high-performance electric-double-layer transistors utilizing various channel materials.

Bismuth telluride (Bi 2 Te 3 ) has recently attracted significant attention owing to its unique physical properties as a three-dimensional topological insulator and excellent properties as a thermoelectric material. Meanwhile, it is important to develop a synthesis process yielding high-quality single crystals over a large area to study the inherent physical properties and device applications of twodimensional materials. However, the maturity of Bi 2 Te 3 vapor-phase synthesis is not good, compared to those of other semiconductor twodimensional crystals. In this study, therefore, we report the synthesis of relatively large-area Bi 2 Te 3 crystals by vapor transport method, and we investigated the key process parameters for a synthesis of relatively thin and large-area Bi 2 Te 3 crystals. The most important factor determining the crystal synthesis was the temperature of the substrate. A Bi 2 Te 3 device exhibited a considerable photocurrent when the laser was irradiated inside the electrode area. This indicated that the photo-thermoelectric effect was the main mechanism of generation of photocurrent. The estimated Seebeck coefficient of the device was ∼196 μV/K, which is comparable to the previously reported high Seebeck coefficient of Bi 2 Te 3 . This synthesis method can guide the development and applications of various types of layered crystals with the space group of R3̅ m.

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