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<jats:p>Cs<jats:sub>2</jats:sub>TiBr<jats:sub>6</jats:sub> nanocrystals (NCs) are a type of promising optoelectronic materials, owing to their high photoelectric properties and non-toxicity. Here, we synthesize the colloidal Cs<jats:sub>2</jats:sub>TiBr<jats:sub>6</jats:sub> NCs using a hot-injection approach. The temperature-dependent absorption data shows that its energy band changes about 30 meV with temperature, reflecting that its energy band structure is much stable. The excitation intensity-dependent transient absorption data confirms its linear absorption cross-sections and carrier recombination rate constants, involving monomolecular and bimolecular recombination, which are all superior to those of conventional perovskite bromide counterparts. In addition, its nonlinear absorption cross-sections are also measured based on femtosecond <jats:italic>Z</jats:italic>-scan. Our results suggest that Cs<jats:sub>2</jats:sub>TiBr<jats:sub>6</jats:sub> NCs can be extensively applied in the field of optoelectronics, owing to its excellent carrier dynamics and nonlinear optical properties.</jats:p>

<jats:p>In the towed line array sonar system, the tow ship noise is the main factor that affects the sonar performance. Conventional noise cancelling methods assume that the noise is towards the endfire direction of the array. An acoustic experiment employing a towed line array is conducted in the western Pacific Ocean, and a strange bearing-splitting phenomenon of the tow ship noise is observed in the array. The tow ship noise is split into multiple noise signals whose bearings are distributed between 10° and 90° deviating from the endfire direction. The multiple interferences increase the difficulty in recognizing the target for the sonar operator and noise cancellation. Therefore, making the mechanism clear and putting forward the tow ship noise splitting bearing estimation method are imperative. In this paper, the acoustic multi-path structure of the tow ship in deep water is analyzed. Then it is pointed out that the bearing-splitting phenomenon is caused by the main lobe of direct rays and bottom-reflected rays, as well as several side lobes of direct rays. Meanwhile, the indistinguishability between the elevation angle and the bearing angle due to the axial symmetry of a strict horizontal line array causes the bearing to deviate from the endfire direction. Based on the theory above, a method of estimating bearing of the tow ship noise in deep water is proposed. The theoretical analysis results accord with the experimental results, which helps to identify the target and provide correct initial bearing guidance for noise cancelation methods.</jats:p>

<jats:p>The anoxia of coastal water has already been a serious problem all over the word. Nanobubbles are proved to have great applications in water remediation because they could effectively increase the oxygen content and degrade organic matters in water. But the existing methods to produce nanobubbles are complicated and high cost to operate, especially in deep sea. In this paper, we presented a low-cost method, hydraulic air compression (HAC), to produce a large number of nanobubbles and proved that nanoscale gas bubbles could be produced by HAC for the first time. Nanoparticle tracking analysis was used to measure the size and concentration of produced nanobubbles. It indicated that the concentration of nanobubbles would increase as the downpipe height increases. Degassed measurements proved that produced “nanoparticles” are gas nanobubbles indeed. More dissolved oxygen in water would provide the source for larger number of nanobubble formation. Those results are expected to be very helpful for water remediation in ocean in the future.</jats:p>

<jats:p>To integrate a terahertz pump into an ultrafast electron diffraction (UED) experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly. However, the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample, impeding it from recording structural information afterwards. In this article, we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe, and came up with several possible schemes to reduce such effect. As a result, a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized. We also found that MeV UED was more suitable for such terahertz pump experiment.</jats:p>

<jats:p>The layered van der Waals antiferromagnetic FePS<jats:sub>3</jats:sub> has received considerable attention because long range magnetic ordering can remain with single atoms layer, which offers potential applications in future ultrathin devices. Here, we perform Raman spectroscopy to systematically explore the variations of lattice vibration and crystal structure under pressure up to 18.9 GPa. We observe two structural phase transitions at approximately 4 GPa and 13 GPa, respectively. Moreover, by monitoring spin-related Raman modes, we demonstrate a pressure-induced magnetic structure transition above 2 GPa. These modes disappear accompanying the second structural phase transition and insulator-to-metal transition (IMT), indicating the suppression of long-range magnetic ordering, in agreement with earlier neutron powder diffraction experiments.</jats:p>

<jats:p>Pressure is an effective and clean way to modify the electronic structures of materials, cause structural phase transitions and even induce the emergence of superconductivity. Here, we predicted several new phases of the Zr<jats:italic>XY</jats:italic> family at high pressures using the crystal structures search method together with first-principle calculations. In particular, the ZrGeS compound undergoes an isosymmetric phase transition from <jats:italic>P</jats:italic>4/<jats:italic>nmm</jats:italic>-I to <jats:italic>P</jats:italic>4/<jats:italic>nmm</jats:italic>-II at approximately 82 GPa. Electronic band structures show that all the high-pressure phases are metallic. Among these new structures, <jats:italic>P</jats:italic>4/<jats:italic>nmm</jats:italic>-II ZrGeS and <jats:italic>P</jats:italic>4/<jats:italic>mmm</jats:italic> ZrGeSe can be quenched to ambient pressure with superconducting critical temperatures of approximately 8.1 K and 8.0 K, respectively. Our study provides a way to tune the structure, electronic properties, and superconducting behavior of topological materials through pressure.</jats:p>

<jats:p>With the rapid development of artificial intelligence and machine learning (ML) methods, materials science is rapidly entering the era of data-driven materials informatics. ML models serve as the most crucial component, closely bridging material structure and material properties. There is a considerable difference in the prediction performance of different ML methods for material systems. Herein, we evaluated three categories (linear, kernel, and nonlinear methods) of models, with twelve ML algorithms commonly used in the materials field. In addition, halide perovskite was chosen as an example to evaluate the fitting performance of different models. We constructed a total dataset of 540 halide perovskites and 72 features, with formation energy and bandgap as target properties. We found that different categories of ML models show similar trends for different target properties. Among them, the difference between the models is enormous for the formation energy, with the coefficient of determination (<jats:italic>R</jats:italic> <jats:sup>2</jats:sup>) range 0.69–0.953. The fitting performance between the models is closer for bandgap, with the <jats:italic>R</jats:italic> <jats:sup>2</jats:sup> range 0.941–0.997. The nonlinear-ensemble model shows the best fitting performance for both the formation energy and the bandgap. It shows that the nonlinear-ensemble model, constructed by combining multiple weak learners, effectively describes the nonlinear relationship between material features and target property. In addition, the extreme gradient boosting decision tree model shows the most superior results among all the models and searches for two new descriptors that are crucial for formation energy and bandgap. Our work provides useful guidance for the selection of effective machine learning methods in the data-mining studies of specific material systems. The dataset that supported the findings of this study is available in Science Data Bank, with the link <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://www.doi.org/10.11922/sciencedb.01611" xlink:type="simple">https://www.doi.org/10.11922/sciencedb.01611</jats:ext-link>.</jats:p>

<jats:p>Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry. Electric control is widely used to modify interfacial water, where the influence of surface charges is inevitable. Here we obtain positively and negatively charged surfaces using LiTaO<jats:sub>3</jats:sub> crystals and observe that a large net surface charge up to 0.1 C/m<jats:sup>2</jats:sup> can nominally change the contact angles of pure water droplets comparing to the same uncharged surface. However, even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols. Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet, while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface. Our results not only provide a fundamental understanding of the interactions between charged surfaces and water, but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.</jats:p>

<jats:p>Low-energy proton irradiation effects on the optical properties and the molecular structure of phenyl-C<jats:sub>61</jats:sub>-butyric acid methyl ester (PCBM) are studied in this work. The PCBM films are irradiated by 100-keV proton beams with fluences of 5 × 10<jats:sup>12</jats:sup> p/cm<jats:sup>2</jats:sup>, 5 × 10<jats:sup>13</jats:sup> p/cm<jats:sup>2</jats:sup>, and 5 × 10<jats:sup>14</jats:sup> p/cm<jats:sup>2</jats:sup>, respectively. The photoluminescence (PL) peaks of the post-irradiated PCBM films show a progressive decrease in the peak intensity as the proton fluences increase, which can be attributed to the deep defect levels induced by proton irradiation. Additionally, a slight blue-shift in the PL spectrum is also observed at a proton fluence of 5 × 10<jats:sup>14</jats:sup> p/cm<jats:sup>2</jats:sup>. The underlying mechanism can be traced back to the lift of the lowest unoccupied molecular orbital (LUMO) level, which is caused by the attachment of methoxy radicals on ortho position of the phenyl ring in the post-irradiated PCBM structure. This work is of significance in understanding the radiation hardness and the damage mechanism of the PCBM film in radiation environments, which is essential before it is put into practical application in space.</jats:p>

<jats:p>Due to non-saturating magnetoresistance (MR) and the special compensation mechanism, the Weyl semimetal TaAs single crystal has attracted considerable attention in condensed matter physics. Herein, we use maximum entropy mobility spectrum analysis (MEMSA) to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of TaAs. The carrier types and the number of bands are obtained without any hypothesis. Study of the temperature dependence shows details of carrier property evolution. Our quantitative results explain the non-saturated magnetoresistance and Hall sign change phenomena of TaAs.</jats:p>