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<jats:p>Based on the rough surface topography with fractal parameters and the Monte–Carlo simulation method for secondary electron emission properties, we analyze the secondary electron yield (SEY) of a metal with rough surface topography. The results show that when the characteristic length scale of the surface, <jats:italic>G</jats:italic>, is larger than 1 × 10<jats:sup>−7</jats:sup>, the surface roughness increases with the increasing fractal dimension <jats:italic>D</jats:italic>. When the surface roughness becomes larger, it is difficult for entered electrons to escape surface. As a result, more electrons are collected and then SEY decreases. When <jats:italic>G</jats:italic> is less than 1 × 10<jats:sup>−7</jats:sup>, the effect of the surface topography can be ignored, and the SEY almost has no change as the dimension <jats:italic>D</jats:italic> increases. Then, the multipactor thresholds of a C-band rectangular impedance transfer and an ultrahigh-frequency-band coaxial impedance transfer are predicted by the relationship between the SEY and the fractal parameters. It is verified that for practical microwave devices, the larger the parameter <jats:italic>G</jats:italic> is, the higher the multipactor threshold is. Also, the larger the value of <jats:italic>D</jats:italic>, the higher the multipactor threshold.</jats:p>

<jats:p>Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature <jats:italic>T</jats:italic> <jats:sub>0</jats:sub>. However, the <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high <jats:italic>T</jats:italic> <jats:sub>0</jats:sub>. In Ti<jats:sub>50</jats:sub>Au<jats:sub>50−<jats:italic>x</jats:italic> </jats:sub>Cr<jats:sub> <jats:italic>x</jats:italic> </jats:sub> alloys, the strain glass appears at <jats:italic>x</jats:italic> = 25, and exhibits a <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> of 251 K, while in Ti<jats:sub>50</jats:sub>Pt<jats:sub>50−<jats:italic>y</jats:italic> </jats:sub>Fe<jats:sub> <jats:italic>y</jats:italic> </jats:sub> alloys, the strain glass takes place at <jats:italic>y</jats:italic> = 30, and shows a <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> of 272 K. Both of them are comparable with the highest <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> of the strain glass is limited. This work may help to design new strain glass systems with higher <jats:italic>T</jats:italic> <jats:sub>0</jats:sub> above ambient temperature.</jats:p>

<jats:p>A facile method of combining the defect engineering with the dielectric-screening effect is proposed to improve the electrical performance of MoS<jats:sub>2</jats:sub> transistors. It is found that the carrier mobility of the transistor after the sulfur treatment on the MoS<jats:sub>2</jats:sub> channel is greatly enhanced due to the reduction of the sulfur vacancies during vulcanization of MoS<jats:sub>2</jats:sub>. Furthermore, as compared to those transistors with HfO<jats:sub>2</jats:sub> and SiO<jats:sub>2</jats:sub> as the gate dielectric, the Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>-gate dielectric MoS<jats:sub>2</jats:sub> FET shows a better electrical performance after the sulfur treatment, with a lowered subthreshold swing of 179.4 mV/dec, an increased on/off ratio of 2.11×10<jats:sup>6</jats:sup>, and an enhanced carrier mobility of 64.74 cm<jats:sup>2</jats:sup>/V⋅s (about twice increase relative to the non-treated MoS<jats:sub>2</jats:sub> transistor with SiO<jats:sub>2</jats:sub> as the gate dielectric). These are mainly attributed to the fact that a suitable <jats:italic>k</jats:italic>-value gate dielectric can produce a dominant dielectric-screening effect overwhelming the phonon scattering, increasing the carrier mobility, while a larger <jats:italic>k</jats:italic>-value gate dielectric will enhance the phonon scattering to counteract the dielectric-screening effect, reducing the carrier mobility.</jats:p>

<jats:p>We propose a metal organic vapor phase epitaxy (MOVPE) method of pre-introducing TMIn during the growth of u-GaN to improve the subsequent growth of InGaN and discuss the impact of this method in detail. Monitoring the MOVPE by the interference curve generated by the laser incident on the film surface, we found that this method avoided the problem of the excessive InGaN growth rate. Further x-ray diffraction (XRD), photoluminescence (PL), and atomic force microscope (AFM) tests showed that the quality of InGaN is improved. It is inferred that by introducing TMIn in advance, the indium atom can replace the gallium atom in the reactor walls, delivery pipes, and other corners. Hence the auto-incorporation of gallium can be reduced when InGaN is grown, so as to improve the material quality.</jats:p>

<jats:p>High-speed laser cladding technology, a kind of surface technology to improve the wear-resistance and corrosion-resistance of mechanical parts, has the characterizations of fast scan speed, high powder utilization rate, and high cladding efficiency. However, its thermal-stress evolution process is very complex, which has a great influence on the residual stress and deformation. In the paper, the numerical models for the high-speed laser cladding coatings with overlap ratios of 10%, 30%, and 50% are developed to investigate the influence rules of overlap ratio on the thermal-stress evolution, as well as the residual stresses and deformations. Results show that the heat accumulation can reheat and preheat the adjacent track coating and substrate, resulting in stress release of the previous track coating and decreased longitudinal stress peak of the next track coating. With the overlap ratio increasing, the heat accumulation and the corresponding maximum residual stress position tend to locate in the center of the cladding coating, where the coating has a high crack susceptibility. For a small overlap ratio of 10%, there are abrupt stress changes from tensile stress to compressive stress at the lap joint, due to insufficient input energy in the position. Increasing the overlap ratio can alleviate the abrupt stress change and reduce the residual deformation but increase the average residual stress and enlarge the hardening depth. This study reveals the mechanism of thermal-stress evolution, and provides a theoretical basis for improving the coating quality.</jats:p>

<jats:p>By using scanning tunneling microscope/microscopy (STM/STS), we reveal the detailed electronic structures around the sharp edges and strained terraces of lateral monolayer-bilayer Pd<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> heterostructures. We find that the edges of such heterostructures are well-defined zigzag type. Band bending and alignment are observed across the zigzag edge, forming a monolayer-bilayer heterojunction. In addition, an n-type band bending is induced by strain on a confined bilayer Pd<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> terrace. These results provide effective toolsets to tune the band structures in Pd<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub>-based heterostructures and devices.</jats:p>

<jats:p>We demonstrate high-performance broadband tunable external-cavity lasers (ECLs) with the metal-organic chemical vapor deposition (MOCVD) grown InAs/InP quantum dots (QDs) structures. Without cavity facet coatings, the 3-dB spectral bandwidth of the Fabry–Perot (FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm. Combined with the anti-reflection (AR) / high-reflection (HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 kA/cm<jats:sup>2</jats:sup>. The maximum output power of 6.5 mW was achieved under a 500 mA injection current. All achievements mentioned above were obtained under continuous-wave (CW) mode at room temperature (RT).</jats:p>

<jats:p>A multi-phase-field model is implemented to investigate the peritectic solidification of Fe-C alloy. The nucleation mode of austenite is based on the local driving force, and two different thicknesses of the primary austenite on the surface of the ferrite equiaxed crystal grain are used as the initial conditions. The simulation shows the multiple interactions of ferrite, austenite, and liquid phases, and the effects of carbon diffusion, which presents the non-equilibrium dynamic process during Fe-C peritectic solidification at the mesoscopic scale. This work not only reveals the influence of the austenite nucleation position, but also clarifies the formation mechanism of liquid phase channels and molten pools. Therefore, the present study contributes to the understanding of the micro-morphology and micro-segregation evolution mechanisms of Fe-C alloy during peritectic solidification.</jats:p>

<jats:p>We prepare stretchable elastic electromagnetic interference (EMI) shielding and stretchable antenna for wireless strain sensing using an elastic composite comprising commercial steel wool as a conducting element. The prepared elastic conductor shows anisotropic electrical properties in response to the external force. In the stretchable range, the electrical resistance abnormally decreases with the increase of tensile deformation. The EMI shielding effectiveness of the elastic conductor can reach above –30 dB under 80% tensile strain. The resonance frequency of the dipole antenna prepared by the elastic conductor is linearly correlated with the tensile strain, which can be used as a wireless strain sensor. The transmission efficiency is stable at about –15 dB when stretched to 50% strain, with attenuation less than 5%. The current research provides an effective solution for stretchable EMI shielding and wireless strain sensing integrated with signal transmission by an antenna.</jats:p>

<jats:p>The T-gate stem height of InAlAs/InGaAs InP-based high electron mobility transistor (HEMT) is increased from 165 nm to 250 nm. The influences of increasing the gate stem height on the direct current (DC) and radio frequency (RF) performances of device are investigated. A 120-nm-long gate, 250-nm-high gate stem device exhibits a higher threshold voltage (<jats:italic>V</jats:italic> <jats:sub>th</jats:sub>) of 60 mV than a 120-nm-long gate devices with a short gate stem, caused by more Pt distributions on the gate foot edges of the high Ti/Pt/Au gate. The Pt distribution in Schottky contact metal is found to increase with the gate stem height or the gate length increasing, and thus enhancing the Schottky barrier height and expanding the gate length, which can be due to the increased internal tensile stress of Pt. The more Pt distributions for the high gate stem device also lead to more obvious Pt sinking, which reduces the distance between the gate and the InGaAs channel so that the transconductance (<jats:italic>g</jats:italic> <jats:sub>m</jats:sub>) of the high gate stem device is 70 mS/mm larger than that of the short stem device. As for the RF performances, the gate extrinsic parasitic capacitance decreases and the intrinsic transconductance increases after the gate stem height has been increased, so the RF performances of device are obviously improved. The high gate stem device yields a maximum <jats:italic>f</jats:italic> <jats:sub>t</jats:sub> of 270 GHz and <jats:italic>f</jats:italic> <jats:sub>max</jats:sub> of 460 GHz, while the short gate stem device has a maximum <jats:italic>f</jats:italic> <jats:sub>t</jats:sub> of 240 GHz and the <jats:italic>f</jats:italic> <jats:sub>max</jats:sub> of 370 GHz.</jats:p>