Electrochromic switching devices have elicited considerable attention because these thin films are among the most promising materials for energy-saving applications. The vanadium oxide system is simple and inexpensive because only a single-layer film of this material is sufficient for coloration. Vanadium dioxide thin films are fabricated by electrochemical deposition and cyclic voltammetry. Chronoamperometric analyses have indicated that the thin V2O5 film demonstrates faster intercalation and deintercalation of lithium ions than those of the thick V2O5 film, benefiting the coloration rate. Despite substantial research on the synthesis of vanadium oxides, the monitoring of electronic and atomic structures during growth and coloration of such material has not been thoroughly examined. In the present study, in situ X-ray absorption spectroscopy (XAS) is employed to determine the electronic and atomic structures of V2O5 thin films during electrochemical growth and then electrochromic coloration. In situ XAS results demonstrate the growth mechanism of the electrodeposited V2O5 thin film and suggest that its electrochromic performance strongly depends on the local atomic structure. This study improves our understanding of the electronic and atomic properties of the vanadium oxide system grown by electrochemical deposition and enhances the design of electrochromic materials for potential energy-saving applications.

Two-dimensional (2D) layered GaSe films were grown on GaAs (001), GaN/Sapphire, and Mica substrates by molecular beam epitaxy (MBE). The in situ reflective high-energy electron diffraction monitoring reveals randomly in-plane orientations of nucleated GaSe layers grown on hexagonal GaN/Sapphire and Mica substrates, whereas single-orientation GaSe domain is predominant in the GaSe/GaAs (001) sample. Strong red-shifts in the frequency of in-plane $${E}_{2g}^{2}$$E2g2 vibration modes and bound exciton emissions observed from Raman scattering and photoluminescence spectra in all samples are attributed to the unintentionally biaxial in-plane tensile strains, induced by the dissimilarity of symmetrical surface structure between the 2D-GaSe layers and the substrates during the epitaxial growth. The results in this study provide an important understanding of the MBE-growth process of 2D-GaSe on 2D/3D hybrid-heterostructures and pave the way in strain engineering and optical manipulation of 2D layered GaSe materials for novel optoelectronic integrated technologies.

Regardless of the dissimilarity in the crystal symmetry, the two-dimensional GaSe materials grown on GaAs(001) substrates by molecular beam epitaxy reveal a screw-dislocation-driven growth mechanism. The spiral-pyramidal structure of GaSe multi-layers was typically observed with the majority in ε-phase. Comprehensive investigations on temperature-dependent photoluminescence, Raman scattering, and X-ray diffraction indicated that the structure has been suffered an amount of strain, resulted from the screw-dislocation-driven growth mechanism as well as the stacking disorders between monolayer at the boundaries of the GaSe nanoflakes. In addition, Raman spectra under various wavelength laser excitations explored that the common ε-phase of 2D GaSe grown directly on GaAs can be transformed into the β-phase by introducing a Se-pretreatment period at the initial growth process. This work provides an understanding of molecular beam epitaxy growth of 2D materials on three-dimensional substrates and paves the way to realize future electronic and optoelectronic heterogeneous integrated technology as well as second harmonic generation applications.

Kohlrausch’s stretched exponential law correlates well with the photoluminescence (PL) decay profiles of $\mathrm{Zn}{\mathrm{Se}}_{1-x}{\mathrm{Te}}_x$ . As the Te concentration increases, the stretching exponent $\beta$ initially declines and then monotonically increases. This result can be understood using the hopping-transport and energy transfer model. The increase in the number of isoelectronic Te localized traps can reduce the PL decay rate and increase the linewidth, whereas the hybridization of the Te localized states with the valence-band edge states causes a reduction in both the lifetime and linewidth.