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<jats:p>A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors (HEMTs). For GaN channel HEMTs with gate–drain spacing <jats:italic>L</jats:italic> <jats:sub>GD</jats:sub> = 2.5 μm, the breakdown voltage <jats:italic>V</jats:italic> <jats:sub>BR</jats:sub> increases from 518 V to 582 V by increasing gate metal height <jats:italic>h</jats:italic> from 0.2 μm to 0.4 μm. For GaN channel HEMTs with <jats:italic>L</jats:italic> <jats:sub>GD</jats:sub> = 7 μm, <jats:italic>V</jats:italic> <jats:sub>BR</jats:sub> increases from 953 V to 1310 V by increasing <jats:italic>h</jats:italic> from 0.8 μm to 1.6 μm. The breakdown voltage enhancement results from the increase of the gate sidewall capacitance and depletion region extension. For Al<jats:sub>0.4</jats:sub>Ga<jats:sub>0.6</jats:sub>N channel HEMT with <jats:italic>L</jats:italic> <jats:sub>GD</jats:sub> = 7 μm, <jats:italic>V</jats:italic> <jats:sub>BR</jats:sub> increases from 1535 V to 1763 V by increasing <jats:italic>h</jats:italic> from 0.8 μm to 1.6 μm, resulting in a high average breakdown electric field of 2.51 MV/cm. Simulation and analysis indicate that the high gate metal height is an effective method to enhance breakdown voltage in GaN-based HEMTs, and this method can be utilized in all the lateral semiconductor devices.</jats:p>

<jats:p>As the combination of surface plasmon polariton and femtosecond laser pulse, femtosecond surface plasmon polariton has both nanoscale spatial resolution and femtosecond temporal resolution, and thus provides promising methods for light field manipulation and light–matter interaction in extreme small spatiotemporal scales. Nowadays, the research on femtosecond surface plasmon polariton is mainly concentrated on two aspects: one is investigation and characterization of excitation, propagation, and dispersion properties of femtosecond surface plasmon polariton in different structures or materials; the other one is developing new applications based on its unique properties in the fields of nonlinear enhancement, pulse shaping, spatiotemporal super-resolved imaging, and others. Here, we introduce the research progress of properties and applications of femtosecond surface plasmon polariton, and prospect its future research trends. With the further development of femtosecond surface plasmon polariton research, it will have a profound impact on nano-optoelectronics, molecular dynamics, biomedicine and other fields.</jats:p>

<jats:p>Time-dependent damage to fused silica induced by high frequency ultraviolet laser is investigated. Photothermal spectroscopy (PTS) and optical microscopy (OM) are utilized to characterize the evolution of damage pits with irradiation time. Experimental results describe that in the pre-damage stage of fused silica sample irradiated by 355-nm laser, the photothermal spectrum signal undergoes a process from scratch to metamorphism due to the absorption of laser energy by defects. During the visible damage stage of fused silica sample, the photothermal spectrum signal decreases gradually from the maximum value because of the aggravation of the damage and the splashing of the material. This method can be used to estimate the operation lifetime of optical elements in engineering.</jats:p>

<jats:p>A multi-coating technique of reduced graphene oxide (RGO) was proposed to increase the sensitivity of paper-based pressure sensors. The maximum sensitivity of 17.6 kPa<jats:sup>−1</jats:sup> under the 1.4 kPa was achieved. The electrical sensing mechanism is attributed to the percolation effect. Such paper pressure sensors were applied to monitor the motor vibration, which indicates the potential of mechanical flaw detection by analyzing the waveform difference.</jats:p>

<jats:p>Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model. In the model, the phase transition, melt flows, and heat transfer are coupled and mathematically described by using the lattice Boltzmann (LB) scheme. The anisotropic streaming-relaxation operation fitting into the LB framework is implemented to model interface advancing with various preferred orientations. Crystal pattern evolutions are then numerically investigated in the conditions of with and without melt flows. It is found that melt flows can significantly influence heat transfer, crystal growth behavior, and phase distributions. The crystal morphological transition from dendrite, seaweed to cauliflower-like patterns occurs with the increase of undercoolings. The interface normal angles and curvature distributions are proposed to quantitatively characterize crystal patterns. The results demonstrate that the distributions are corresponding to crystal morphological features, and they can be therefore used to describe the evolution of crystal patterns in a quantitative way.</jats:p>

<jats:p>The effects of buried oxide (BOX) layer on the capacitance of SiGe heterojunction photo-transistor (HPT), including the collector–substrate capacitance, the base–collector capacitance, and the base–emitter capacitance, are studied by using a silicon-on-insulator (SOI) substrate as compared with the devices on native Si substrates. By introducing the BOX layer into Si-based SiGe HPT, the maximum photo-characteristic frequency <jats:italic>f</jats:italic> <jats:sub>t,opt</jats:sub> of SOI-based SiGe HPT reaches up to 24.51 GHz, which is 1.5 times higher than the value obtained from Si-based SiGe HPT. In addition, the maximum optical cut-off frequency <jats:italic>f</jats:italic> <jats:sub> <jats:italic>β</jats:italic>,opt</jats:sub>, namely its 3-dB bandwidth, reaches up to 1.13 GHz, improved by 1.18 times. However, with the increase of optical power or collector current, this improvement on the frequency characteristic from BOX layer becomes less dominant as confirmed by reducing the 3-dB bandwidth of SOI-based SiGe HPT which approaches to the 3-dB bandwidth of Si-based SiGe HPT at higher injection conditions.</jats:p>

<jats:p>The structure–activity relationship of functional materials is an everlasting and desirable research question for material science researchers, where characterization and calculation tools are the keys to deciphering this intricate relationship. Here, we choose rechargeable battery materials as an example and introduce the most representative advanced characterization and calculation methods in four different scales: real space, energy, momentum space, and time. Current research methods to study battery material structure, energy level transition, dispersion relations of phonons and electrons, and time-resolved evolution are reviewed. From different views, various expression forms of structure and electronic structure are presented to understand the reaction processes and electrochemical mechanisms comprehensively in battery systems. According to the summary of the present battery research, the challenges and perspectives of advanced characterization and calculation techniques for the field of rechargeable batteries are further discussed.</jats:p>

<jats:p>Battery materials are of vital importance in powering a clean and sustainable society. Improving their performance relies on a clear and fundamental understanding of their properties, in particular, structural properties. Pair distribution function (PDF) analysis, which takes into account both Bragg scattering and diffuse scattering, can probe structures of both crystalline and amorphous phases in battery materials. This review first introduces the principle of PDF, followed by its application in battery materials. It shows that PDF is an effective tool in studying a series of key scientific topics in battery materials. They range from local ordering, nano-phase quantification, anion redox reaction, to lithium storage mechanism, and so on.</jats:p>

<jats:p>Although the efficiency of CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub> has been refreshed to 25.2%, stability and toxicity remain the main challenges for its applications. The search for novel solar-cell absorbers that are highly stable, non-toxic, inexpensive, and highly efficient is now a viable research focus. In this review, we summarize our recent research into the high-throughput screening and materials design of solar-cell absorbers, including single perovskites, double perovskites, and materials beyond perovskites. BaZrS<jats:sub>3</jats:sub> (single perovskite), Ba<jats:sub>2</jats:sub>BiNbS<jats:sub>6</jats:sub> (double perovskite), HgAl<jats:sub>2</jats:sub>Se<jats:sub>4</jats:sub> (spinel), and IrSb<jats:sub>3</jats:sub> (skutterudite) were discovered to be potential candidates in terms of their high stabilities, appropriate bandgaps, small carrier effective masses, and strong optical absorption.</jats:p>

<jats:p>The (3+1)-dimensional Burgers equation, which describes nonlinear waves in turbulence and the interface dynamics, is considered. Two types of semi-rational solutions, namely, the lump–kink solution and the lump–two kinks solution, are constructed from the quadratic function ansatz. Some interesting features of interactions between lumps and other solitons are revealed analytically and shown graphically, such as fusion and fission processes.</jats:p>