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An excellent infrared window material should have both high transmittance and good mechanical strength to adapt to applications in harsh environments. In this report, we use first-principles calculations to investigate the effect of oxygen alloying on the mechanical and optical properties of the well-used infrared window material ZnS. We have found that with increasing oxygen content, the mechanical properties including elastic constants, bulk modulus, shear modulus, Young’s modulus of ZnS1−xOx compounds are improved compared to the pristine phase. Meanwhile, the infrared optical transmittance of the system is retained with changing oxygen compositions. We have also considered the influence of oxygen/sulfur vacancy defects in the system. We have observed that the optical transmittance of the system is degraded upon induction of vacancies. These results have revealed that the mechanical properties of optical materials can be effectively enhanced with appropriate alloying, but there are also challenges in practice due to the presence of defects. Our investigations can guide the design of these infrared optical materials in special applications such as aircraft and space systems.

Motivated by the fascinating properties of both two-dimensional transition metal dichalcogenide quantum dots (TMD QDs) and Janus TMD monolayers, we theoretically explore the equilibrium structures of free-standing Janus MoSSe QDs in which atomic asymmetry of chalcogen is introduced. Two distinct types of spontaneous curling are observed by molecular dynamics simulations, and the curling behavior depends on the size of QD. The bowl-like (tube-like) curling occurs in relatively small (large) MoSSe QDs with different shapes (hexagon and triangle) and edge types (zigzag and armchair). The transition between these two curling types occurs at the sizes of around 10 nm and 13 nm for hexagonal and triangular shapes, respectively. By applying equivalent misfit strains into two adjacent sublayers, finite element analysis reproduces similar curling behavior. This confirms the relaxation of intrinsic strain in Janus structure acting as the predominant driving force of spontaneous curling. In addition, the curvatures of Janus TMD QDs increase from MoSSe to MoSeTe to MoSTe, indicating the positive correlation between the curling and misfit.