Femtosecond visualization of oxygen vacancies in metal oxides.

Oxygen vacancies often determine the electronic structure of metal oxides, but existing techniques cannot distinguish the oxygen-vacancy sites in the crystal structure. We report here that time-resolved optical spectroscopy can solve this challenge and determine the spatial locations of oxygen vacancies. Using tungsten oxides as examples, we identified the true oxygen-vacancy sites in WO2.9 and WO2.72, typical derivatives of WO3 and determined their fingerprint optoelectronic features. We find that a metastable band with a three-stage evolution dynamics of the excited states is present in WO2.9 but is absent in WO2.72. By comparison with model bandstructure calculations, this enables determination of the most closely neighbored oxygen-vacancy pairs in the crystal structure of WO2.72, for which two oxygen vacancies are ortho-positioned to a single W atom as a sole configuration among all O─W bonds. These findings verify the existence of preference rules of oxygen vacancies in metal oxides

Water vapor isotopic data of heavy rainfall events in Nanjing

<p>Water vapor isotopic data of heavy rainfall events in Nanjing</p&gt

Global abnormal precipitation 18O depletion during late/post monsoon season

Previous studies found depletion of precipitation 18O (18Op) during the late or post Asian monsoon season when precipitation amount is much lower. This is inconsistent with the amount effect of precipitation isotopes commonly found in tropical regions. It is still unclear whether this late/post season abnormal 18Op depletion also occurs in other monsoon regions, and what are the possible underlying mechanisms. In this paper, we examined seasonal variations of observed and modeled isotopic composition in precipitation (δ18Op) across the global monsoon regions, and their relationship with atmospheric circulations. We found that this abnormal 18Op depletion occurs in all monsoon regions globally, and it is largely caused by strong rainout along the global trade wind moisture transport pathway. The finding suggests that tropical cyclones are not the only mechanism to deplete 18Op during the late or post monsoon seasons, as suggested by previous studies. We should interpret such low δ18O values in the high-resolution paleoclimate records with more caution