By means of a hybrid density functional, we comprehensively investigate the energetic, electronic, optical properties, and band edge alignments of two-dimensional (2D) CdS/g-C ${}_3$ N ${}_4$ heterostructures by considering the effect of biaxial strain and pH value, so as to improve the photocatalytic activity. The results reveal that a CdS monolayer weakly contacts with g-C ${}_3$ N ${}_4$ , forming a type II van der Waals (vdW) heterostructure. The narrow bandgap makes CdS/g-C ${}_3$ N ${}_4$ suitable for absorbing visible light and the induced built-in electric field between the interface promotes the effective separation of photogenerated carriers. Through applying the biaxial strain, the interface adhesion energy, bandgap, and band edge positions, in contrast with water, redox levels of CdS/g-C ${}_3$ N ${}_4$ can be obviously adjusted. Especially, the pH of electrolyte also significantly influences the photocatalytic performance of CdS/g-C ${}_3$ N ${}_4$ . When pH is smaller than 6.5, the band edge alignments of CdS/g-C ${}_3$ N ${}_4$ are thermodynamically beneficial for oxygen and hydrogen generation. Our findings offer a theoretical basis to develop g-C ${}_3$ N ${}_4$ -based water-splitting photocatalysts.

In this work, graphene-like ZnO (g-ZnO)-based two-dimensional (2D) heterostructures (ZnO/WS₂ and ZnO/WSe₂) were designed as water-splitting photocatalysts based on the hybrid density functional. The dependence of photocatalytic properties on the rotation angles and biaxial strains were investigated. The bandgaps of ZnO/WS₂ and ZnO/WSe₂ are not obviously affected by rotation angles but by strains. The ZnO/WS₂ heterostructures with appropriate rotation angles and strains are promising visible water-splitting photocatalysts due to their appropriate bandgap for visible absorption, proper band edge alignment, and effective separation of carriers, while the water oxygen process of the ZnO/WSe₂ heterostructures is limited by their band edge positions. The findings pave the way to efficient g-ZnO-based 2D visible water-splitting materials.

Based on the analysis of the evanescent wave from total internal reflection, a light-emitting diode (LED) structure with a plasmonic Ag nanostructure and indium tin oxide (ITO) grating was proposed to enhance the extraction efficiency. The two-dimensional finite-difference time-domain method was used to study the spectral properties of the hybrid structure and the effects of structure parameters on extraction enhancement. The results demonstrate that the plasmonic Ag nanostructure can couple the evanescent wave to a propagation wave around the GaN/ITO interface, and then the photons are scattered out of the LED chips by the ITO grating with high extraction efficiency. Under the optimal parameters, the light extraction efficiency can reach approximately three times the original value at a relatively longer wavelength.

Its outstanding mechanical and thermodynamic characteristics make SrAl₂O₄ a highly desirable ceramic material for high-temperature applications. However, the effects of elevated pressure on the structural and other properties of SrAl₂O₄ are still poorly understood. This study encompassed structural, elastic, electronic, dynamic, and thermal characteristics. Band structure calculations indicate that the direct band gap of SrAl₂O₄ is 4.54 eV. In addition, the Cauchy pressures provide evidence of the brittle characteristics of SrAl₂O₄. The mechanical and dynamic stability of SrAl₂O₄ is evident from the accurate determination of its elastic constants and phonon dispersion relations. In addition, a comprehensive analysis was conducted of the relationship between specific heat and entropy concerning temperature variations.