Improved carrier transport in Mn:ZnSe quantum dots sensitized La-doped nano-TiO2 thin film

Mn:ZnSe/ZnS/L-Cys core-shell quantum dots(QDs)sensitized La-doped nano-TiO2 thin film(QDSTF)was prepared.X-ray photoelectron spectroscopy(XPS),nanosecond transient photovoltaic(TPV),and steady state surface photovoltaic(SPV)technologies were used for probing the photoelectron behaviors in the Mn-doped QDSTF.The results revealed that the Mn-doped QDSTF had a p-type TPV characteristic.The bottom of the conduction band of the QDs as a sensitizer was just 0.86 eV above that of the La-doped nano-TiO2 thin film,while the acceptor level of the doped Mn2+ions was located at about 0.39 eV below and near the bottom of the conduction band of the QDs.The intensity of the SPV response of the Mn-doped QDSTF at a specific wavelength was ~2.1 times higher than that of the undoped QDSTF.The region of the SPV response of the Mn-doped QDSTF was extended by 191 nm to almost the whole visible region as compared with the undoped QDSTF one.And the region of the TPV response of the Mn-doped QDSTF was also obviously wider than that of the undoped QDSTF.These PV characteristics of the Mn-doped QDSTF may be due to the prolonged lifetime and extended diffusion length of photogenerated free charge carriers injected into the sensitized La-doped nano-TiO2 thin film.

Grain boundary boosting the thermal stability of Pt/CeO_(2)thin films

Understanding how defect chemistry of oxide material influences the thermal stability of noble metal dopant ions plays an important role in designing high-performance heterogeneous catalytic systems.Here we use in-situ ambient-pressure X-ray photoemission spectroscopy(APXPS)to experimentally determine the role of grain boundary in the thermal stability of platinum doped cerium oxide(Pt/CeO_(2)).The grain boundaries were introduced in Pt/CeO_(2)thin films by pulsed laser deposition without significantly change of the surface microstructure.The defect level was tuned by the strain field obtained using a highly/low mismatched substrate.The Pt/CeO_(2)thin film models having well defined crystallographic properties but different grain boundary structural defect levels provide an ideal platform for exploring the evolution of Pt–O–Ce bond with changing the temperature in reducing conditions.We have direct demonstration and explanation of the role of Ce^(3+)induced by grain boundaries in enhancing Pt2+stability.We observe that the Pt^(2+)–O–Ce^(3+)bond provides an ideal coordinated site for anchoring of Pt^(2+)ions and limits the further formation of oxygen vacancies during the reduction with H_(2).Our findings demonstrate the importance of grain boundary in the atomic-scale design of thermally stable catalytic active sites.