Sulfur and Silicon Doping in Ag₃PO₄

Silver orthophosphate (Ag₃PO₄) is known as a highly active visible-light sensitized photocatalyst, yet its doping effects on electric properties have not been well understood. Using hybrid density-functional calculations, we study possibilities for <i>n</i>-type and <i>p</i>-type doping in Ag₃PO₄. It is found that a sulfur substituted for phosphorus (S_P) has a relatively low formation energy (high solubility) and acts as a shallow donor in any growth conditions examined. Whereas, a substitutional silicon at phosphorus site (Si_P) is a deep acceptor and its solubility is low, indicating that <i>p</i>-type conductivity is unlikely to occur by Si doping. Our results suggest that sulfur doping is a promising approach for the realization of <i>n</i>-type Ag₃PO₄

Evidence for Native-Defect Donors in n-Type ZnO

Recent theory has found that native defects such as the O vacancy VO and Zn interstitial ZnI have high formation energies in n-type ZnO and, thus, are not important donors, especially in comparison to impurities such as H. In contrast, we use both theory and experiment to show that, under N ambient, the complex ZnI-NO is a stronger candidate than H or any other known impurity for a 30 meV donor commonly found in bulk ZnO grown from the vapor phase. Since the Zn vacancy is also the dominant acceptor in such material, we must conclude that native defects are important donors and acceptors in ZnO

Evidence for Native-Defect Donors in n-Type ZnO

Recent theory has found that native defects such as the O vacancy VO and Zn interstitial ZnI have high formation energies in n-type ZnO and, thus, are not important donors, especially in comparison to impurities such as H. In contrast, we use both theory and experiment to show that, under N ambient, the complex ZnI-NO is a stronger candidate than H or any other known impurity for a 30 meV donor commonly found in bulk ZnO grown from the vapor phase. Since the Zn vacancy is also the dominant acceptor in such material, we must conclude that native defects are important donors and acceptors in ZnO

Anatase TiO₂ Single Crystals Exposed with High-Reactive {111} Facets Toward Efficient H₂ Evolution

In this study, for the first time, {111} facet exposed anatase TiO₂ single crystals are prepared via both F^– and ammonia as the capping reagents. In comparison with the most investigated {001}, {010}, and {101} facets for anatase TiO₂, the density functional theory (DFT) calculations predict that {111} facet owns a much higher surface energy of 1.61 J/m², which is partially attributed to the large percentage of undercoordinated Ti atoms and O atoms existed on the {111} surface. These undercoordinated atoms can act as active sites in the photoreaction. Experimentally, it is revealed that this material exhibits the superior electronic band structure which can produce more reductive electrons in the photocatalytic reaction than those of the TiO₂ samples exposed with majority {010}, {101}, and {001} facets. More importantly, we demonstrate that this material is an excellent photocatalyst with much higher photocatalytic activity (405.2 μmol h^–1), about 5, 9, and 13 times that of the TiO₂ sample exposed with dominant {010}, {101}, and {001} facets, respectively. Both the superior surface atomic structure and electronic band structure significantly contribute to the enhanced photocatalytic activity. This work exemplifies that the surface engineering of semiconductors is one of the most effective strategies to achieve advanced and excellent performance over photofunctional materials for solar energy conversion