We investigate and assign the pressure-induced structural transformations in crystalline diborane (B 2 H 6 ) observed spectroscopically by Song and co-workers (J.

Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic band gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the band gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the band gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 - m monolayers of ZnS. The predicted band gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.

Recent theoretical investigations of high-pressure structures of diborane have yielded many intriguing predictions which have so far remained untested due to challenges of acquiring experimental data at extreme pressures. Here we report new pressure-induced polymorphic transformations of crystalline diborane observed between 36 and 88 GPa by in situ Raman spectroscopy and interpreted using electronic structure calculations. Two previously unknown phase transitions are identified near 42 and 57 GPa, as evidenced by significant changes in the Raman profiles. The corresponding new phases, labeled IV and V, consist of B2H6 molecules and have triclinic unit cells (P), as deduced through evolutionary structure search and comparison of experimental and simulated Raman spectra. Density-functional calculations suggest that, at pressures above 110 GPa, phase V will form new molecular structures consisting of one-dimensional (BH3)n chains and will become metallic near 138 GPa. Our findings make a significant contribution to the elucidation of the structures and properties of diborane in the near-megabar pressure region.

A quasi-analytical methodology was developed to model combined conductionradiation heat transfer through the thickness of a re ective multi-layer insulator. This methodology was validated based on the experimental result. It can be applied to the initial design of high-temperature multi-layer insulators. Traditionally, radiation thermal conductivity approximation was employed for the initial stages of design. Despite the acceptable accuracy of this approach in steady state cases, it yields some unacceptable errors when thermal load is transient. It was shown that the older version of this methodology could not predict maximum temperature and time of occurrences by acceptable margins. The developed model originated from the radiation thermal conductivity approximation. Unlike the primitive one, the developed model shows acceptable performance in transient cases. This model was developed with emphasis on thermal emittance through the thickness of the insulator. It can predict the maximum temperature of a structure and its occurrence time with an error less than 4%.