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Deposition pressure is an important process parameter for coating preparation. To study its influence on the microstructure, mechanical properties and high-temperature oxidation resistance of AlCrTiSiN nanocomposite coatings, two types of AlCrTiSiN nanocomposite coatings were prepared using RF magnetron sputtering and pulse DC magnetron sputtering composite technologies at different deposition pressures(0.6, 0.8 Pa). Comparative analyses of the structure and properties of two types of coatings were performed using X-ray diffractometer(XRD), scanning electron microscope(SEM) equipped with an energy dispersive spectrometer(EDS) and nanoindenter. Results showed that the phase structure of the coatings prepared under two kinds of deposition pressures was fcc-(Al, Cr, Ti) N, which grew preferentially along the(111) crystal plane. However, the larger(111) texture coefficient of the coating prepared at 0.8 Pa indicated that the preferred orientation was more pronounced. Compared to the coating prepared at the deposition pressure of 0.8 Pa, the coating prepared at 0.6 Pa was characterized by finer surface particles, a denser coating and better mechanical properties, including better resistance to elastic and plastic deformation, as well as better adhesion between film and substrate. This was partly because the deposited particles reached the substrate with greater energy at the lower deposition pressure. On the other hand, a thicker and softer Si3N4 phase might have been present in the coating prepared at 0.8 Pa. After oxidation at 900 ℃ for 6 h, a continuous and dense Al2O3 mixed oxide film had formed on the surface of the coating, effectively preventing the diffusion of oxygen into the coating and protecting the coating under the oxide film. With the increase in deposition pressure from 0.6 to 0.8 Pa, the oxide particles increased, the thickness of the oxide film increased, and the high-temperature oxidation resistance decreased.

Understanding the microscopic mechanism of photoinduced sp2-to-sp3 structural transformation in graphite is a scientific challenge with great importance. Here, the ultrafast dynamics and characteristics of laser-induced structural transformation in graphite are revealed by non-adiabatic quantum dynamic simulations. Under laser irradiation, graphite undergoes an interlayer compression and sliding stage, followed by a key period of intralayer buckling and interlayer bonding to form an intermediate sp2-sp3 hybrid structure, before completing the full transformation to hexagonal diamond. The process is driven by the cooperation of charge carrier multiplication and selective phonon excitations through electron-phonon interactions, in which photoexcited hot electrons scattered into unoccupied high-energy conduction bands play a key role in the introduction of in-plane instability in graphite. This work identifies a photoinduced non-adiabatic transition pathway from graphite to diamond and shows far-reaching implications for designing optically controlled structural phase transition in materials. [ABSTRACT FROM AUTHOR]

Understanding hot carrier dynamics between plasmonic nanomaterials and its adsorbate is of great importance for plasmon‐enhanced photoelectronic processes such as photocatalysis, optical sensing and spectroscopic analysis. However, it is often challenging to identify specific dominant mechanisms for a given process because of the complex pathways and ultrafast interactive dynamics of the photoelectrons. Here, using CO2 reduction as an example, the underlying mechanisms of plasmon‐driven catalysis at the single‐molecule level using time‐dependent density functional theory calculations is clearly probed. The CO2 molecule adsorbed on two typical nanoclusters, Ag20 and Ag147, is photoreduced by optically excited plasmon, accompanied by the excitation of asymmetric stretching and bending modes of CO2. A nonlinear relationship has been identified between laser intensity and reaction rate, demonstrating a synergic interplay and transition from indirect hot‐electron transfer to direct charge transfer, enacted by strong localized surface plasmons. These findings offer new insights for CO2 photoreduction and for the design of effective pathways toward highly efficient plasmon‐mediated photocatalysis. [ABSTRACT FROM AUTHOR]

The microscopic arrangement of atoms and molecules is the determining factor in how materials behave and perform; i.e. , the structure determines the property, a traditional paradigm in materials science. Photoexcitation-driven manipulation of the crystal structure and associated electronic properties in quantum materials provides opportunities for the exploration of exotic physics and practical applications; however, a generalized mechanism for such symmetry engineering is absent. Here, by ultrafast electron diffraction, structure factor calculation, and TDDFT-MD simulations, we report the photoinduced concurrent intralayer and interlayer structural transitions in the Td and 1T' phases of XTe 2 (X = Mo, W). We discuss the modification of multiple quantum electronic states associated with the intralayer and interlayer structural transitions, such as the topological band inversion and the higher-order topological state. The twin structures and the stacking faults in XTe 2 are also identified by ultrafast structural responses. The comprehensive study of the ultrafast structural response in XTe 2 suggests the traversal of all double-well potential energy surfaces (DWPES) by laser excitation, which is expected to be an intrinsic mechanism in the field of photoexcitation-driven global/local symmetry engineering and also a critical ingredient inducing the exotic properties in the non-equilibrium state in a large number of material systems.

Understanding hot carrier dynamics between plasmonic nanomaterials and its adsorbate is of great importance for plasmon-enhanced photoelectronic processes such as photocatalysis, optical sensing and spectroscopic analysis. However, it is often challenging to identify specific dominant mechanisms for a given process because of the complex pathways and ultrafast interactive dynamics of the photoelectrons. Here, using CO 2 reduction as an example, the underlying mechanisms of plasmon-driven catalysis at the single-molecule level using time-dependent density functional theory calculations is clearly probed. The CO 2 molecule adsorbed on two typical nanoclusters, Ag 20 and Ag 147 , is photoreduced by optically excited plasmon, accompanied by the excitation of asymmetric stretching and bending modes of CO 2 . A nonlinear relationship has been identified between laser intensity and reaction rate, demonstrating a synergic interplay and transition from indirect hot-electron transfer to direct charge transfer, enacted by strong localized surface plasmons. These findings offer new insights for CO 2 photoreduction and for the design of effective pathways toward highly efficient plasmon-mediated photocatalysis., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)