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<jats:p>The p-type doping efficiency of 4H silicon carbide (4H-SiC) is rather low due to the large ionization energies of p-type dopants. Such an issue impedes the exploration of the full advantage of 4H-SiC for semiconductor devices. In this study, we show that co-doping group-IVB elements effectively decreases the ionization energy of the most widely used p-type dopant, i.e., aluminum (Al), through the defect-level repulsion between the energy levels of group-IVB elements and that of Al in 4H-SiC. Among group-IVB elements Ti has the most prominent effectiveness. Ti decreases the ionization energy of Al by nearly 50%, leading to a value as low as ∼ 0.13 eV. As a result, the ionization rate of Al with Ti co-doping is up to ∼ 5 times larger than that without co-doping at room temperature when the doping concentration is up to 10<jats:sup>18</jats:sup> cm<jats:sup>−3</jats:sup>. This work may encourage the experimental co-doping of group-IVB elements such as Ti and Al to significantly improve the p-type doping efficiency of 4H-SiC.</jats:p>

<jats:p>Two-phase <jats:italic>γ</jats:italic>-TiAl/<jats:italic>α</jats:italic> <jats:sub>2</jats:sub>-Ti<jats:sub>3</jats:sub>Al lamellar intermetallics have attracted considerable attention because of their excellent strength and plasticity. However, the exact deformation mechanisms remain to be investigated. In this paper, a solidified lamellar Ti–Al alloy with lamellar orientation at 0°, 17°, and 73° with respect to the loading direction was stretched by utilizing molecular dynamics (MD) simulations. The results show that the mechanical properties of the sample are considerably influenced by solidified defects and tensile directions. The structure deformation and fracture were primarily attributed to an intrinsic stacking fault (ISF) accompanied by the nucleated Shockley dislocation, and the adjacent extrinsic stacking fault (ESF) and ISF formed by solidification tend to form large HCP structures during the tensile process loading at 73°. Moreover, cleavage cracking easily occurs on the <jats:italic>γ</jats:italic>/<jats:italic>α</jats:italic> <jats:sub>2</jats:sub> interface under tensile deformation. The fracture loading mechanism at 17° is grain boundary slide whereas, at 73° and 0°, the dislocation piles up to form a dislocation junction.</jats:p>

<jats:p>L1<jats:sub>0</jats:sub>-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe<jats:sub>42</jats:sub>Ni<jats:sub>41.3</jats:sub>Si<jats:sub>8</jats:sub>B<jats:sub>4</jats:sub>P<jats:sub>4</jats:sub>Cu<jats:sub>0.7</jats:sub> amorphous alloy, and the L1<jats:sub>0</jats:sub>-FeNi formation mechanism has been studied. It is found the L1<jats:sub>0</jats:sub>-FeNi in annealed samples at 400 °C mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 °C lower than the measured onset temperature of the second stage with a 5 °C/min heating rate. Annealing at 400 °C after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1<jats:sub>0</jats:sub> phase, or the removal of B from L1<jats:sub>0</jats:sub> lattice and improvement of the ordering quality of L1<jats:sub>0</jats:sub> phase due to the reduced temperature from 520 °C to 400 °C. The first stage of crystallization has hardly direct contribution to L1<jats:sub>0</jats:sub>-FeNi formation. <jats:italic>Ab initio</jats:italic> simulations show that the addition of Si or Co in L1<jats:sub>0</jats:sub>-FeNi has the effect of enhancing the thermal stability of L1<jats:sub>0</jats:sub> phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L1<jats:sub>0</jats:sub>-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.</jats:p>

<jats:p>The degradation mechanism of the all-inorganic perovskite solar cells in the ambient environment remains unclear. In this paper, water and oxygen molecule adsorptions on the all-inorganic perovskite (CsPbBr<jats:sub>3</jats:sub>) surface are studied by density-functional theory calculations. In terms of the adsorption energy, the water molecules are more susceptible than the oxygen molecules to be adsorbed on the CsPbBr<jats:sub>3</jats:sub> surface. The water molecules can be adsorbed on both the CsBr- and PbBr-terminated surfaces, but the oxygen molecules tend to be selectively adsorbed on the CsBr-terminated surface instead of the PbBr-terminated one due to the significant adsorption energy difference. While the adsorbed water molecules only contribute deep states, the oxygen molecules introduce interfacial states inside the bandgap of the perovskite, which would significantly impact the chemical and transport properties of the perovskite. Therefore, special attention should be paid to reduce the oxygen concentration in the environment during the device fabrication process so as to improve the stability and performance of the CsPbBr<jats:sub>3</jats:sub>-based devices.</jats:p>

<jats:p>Exploring new abnormal thermal expansion materials is important to understand the nature of thermal expansion. Metal–organic framework (MOF) with unique structure flexibility is an ideal material to study the thermal expansion. This work adopts the high-resolution variable-temperature powder x-ray diffraction to investigate the structure and intrinsic thermal expansion in Sr-MOF ([Sr(DMPhH<jats:sub>2</jats:sub>IDC)<jats:sub>2</jats:sub>]<jats:sub> <jats:italic>n</jats:italic> </jats:sub>). It has the unique honeycomb structure with one-dimensional (1D) channels along the <jats:italic>c</jats:italic>-axis direction, the <jats:italic>a</jats:italic>–<jats:italic>b</jats:italic> plane displays layer structure. The thermal expansion behavior has strong relationship with the structure, ZTE appears in the <jats:italic>a</jats:italic>–<jats:italic>b</jats:italic> plane and large PTE along the <jats:italic>c</jats:italic>-axis direction. The possible mechanism is that the <jats:italic>a</jats:italic>/<jats:italic>b</jats:italic> layers have enough space for the transverse thermal vibration of polydentate ligands, while along the <jats:italic>c</jats:italic>-axis direction is not. This work not only reports one interesting zero thermal expansion material, but also provides new understanding for thermal expansion mechanism from the perspective of the structural model.</jats:p>

<jats:p>We report a new type of near-zero thermal expansion material <jats:italic>β</jats:italic>-CuZnV2O7 in a large temperature range from 173 K to 673 K. It belongs to a monoclinic structure (C2/c space group) in the whole temperature range. No structural phase transition is observed at atmospheric pressure based on the x-ray diffraction and Raman experiment. The high-pressure Raman experiment demonstrates that two structural phase transitions exist at 0.94 GPa and 6.53 GPa, respectively. The mechanism of negative thermal expansion in <jats:italic>β</jats:italic>-CuZnV2O7 is interpreted by the variations of the angles between atoms intuitively and the phonon anharmonicity intrinsically resorting to the negative Grüneisen parameter.</jats:p>

<jats:p>The impact of droplets on the liquid film is widely involved in industrial and agricultural fields. In recent years, plenty of works are limited to dry walls or stationary liquid films, and the research of multi-droplet impact dynamic films is not sufficient. Based on this, this paper employs a coupled level set and volume of fluid (CLSVOF) method to numerically simulate two-droplet impingement on a dynamic liquid film. In our work, the dynamic film thickness, horizontal central distance between the droplets, droplets’ initial impact speed, and simultaneously the flow velocity of the moving film are analyzed. The evolution phenomenon and mechanism caused by the collision are analyzed in detail. We find that within a certain period of time, the droplet spacing does not affect the peripheral crown height; when the droplet spacing decreases or the initial impact velocity increases, the height of the peripheral crown increases at the beginning, and then, because the crown splashed under Rayleigh–Plateau instability, this results in the reduction of the crown height. At the same time, it is found that when the initial impact velocity increases, the angle between the upstream peripheral jet and the dynamic film becomes larger. The more obvious the horizontal movement characteristics, the more restrained the crown height; the spread length increases with the increase of the dynamic film speed, droplet spacing and the initial impact velocity. When the liquid film is thicker, more fluid enters the crown, due to the crown being unstable, the surface tension is not enough to overcome the weight of the rim at the end of the crown, resulting in droplets falling off.</jats:p>

<jats:p>Lithium-sulfur batteries have attracted attention because of their high energy density. However, the “shuttle effect” caused by the dissolving of polysulfide in the electrolyte has greatly hindered the widespread commercial use of lithium-sulfur batteries. In this paper, a novel two-dimensional TiS<jats:sub>2</jats:sub>/graphene heterostructure is theoretically designed as the anchoring material for lithium-sulfur batteries to suppress the shuttle effect. This heterostructure formed by the stacking of graphene and TiS<jats:sub>2</jats:sub> monolayer is the van der Waals type, which retains the intrinsic metallic electronic structure of graphene and TiS<jats:sub>2</jats:sub> monolayer. Graphene improves the electronic conductivity of the sulfur cathode, and the transferred electrons from graphene enhance the polarity of the TiS<jats:sub>2</jats:sub> monolayer. Simulations of the polysulfide adsorption show that the TiS<jats:sub>2</jats:sub>/graphene heterostructure can maintain good metallic properties and the appropriate adsorption energies of 0.98–3.72 eV, which can effectively anchor polysulfides. Charge transfer analysis suggests that further enhancement of polarity is beneficial to reduce the high proportion of van der Waals (vdW) force in the adsorption energy, thereby further enhancing the anchoring ability. Low Li<jats:sub>2</jats:sub>S decomposition barrier and Li-ion migration barrier imply that the heterostructure has the ability to catalyze fast electrochemical kinetic processes. Therefore, TiS<jats:sub>2</jats:sub>/graphene heterostructure could be an important candidate for ideal anchoring materials of lithium-sulfur batteries.</jats:p>

<jats:p>The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs), and GaN polarization superjunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.</jats:p>

<jats:p>Doublet luminescence from hybrid metal trihalide perovskite semiconductors is observed along with materials processing when high-quality single crystals are obtainable. Yet, the underlying physical mechanism remains poorly understood. Here, we report controllable solution-processed crystallization that affords high-quality CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbBr<jats:sub>3</jats:sub> single crystals with atomically flat pristine surfaces. Front-face photoluminescence (PL) shows doublet luminescence components with variable relative intensities depending on the crystal surface conditions. We further find that the low-energy PL component with asymmetric spectral line-shape becomes predominant when the atomically flat crystal surfaces are passivated in the ion-abundant saturated solutions, while poor-quality single crystal with visually rough surface only gives the high-energy PL with symmetric line-shape. The asymmetric spectral line-shape of the low-energy PL matches perfectly with the simulated bandedge emission. Therefore, the low-energy PL component is attributable to the intrinsic bandedge emission from the crystal bulk while the high-energy one to surface-specific emission. Elliott fitting to the absorption data and multi-exponential fitting to the time-resolved photoluminescence traces jointly indicate the coexistence of excitons and electron–hole plasmas in optically excited CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbBr<jats:sub>3</jats:sub> single crystals, thereby catching the physical merit that leads to the occurrence of doublet luminescence.</jats:p>