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• The nanocrystalline coatings were designed and prepared by magnetron sputtering. • In-situ Al 2 O 3 nanoparticles were found in the SNO coatings. • The diffusion of Ta throughout the coating is retarded by reactive sputtering with o. • The oxidation resistance of the SNO coatings is significantly improved. The presence of excess Ta in high-temperature protective coatings can compromise the integrity of the Al 2 O 3 scale on the surface, which has a negative impact on the oxidation behavior and reduces the service life. The effects of oxygen doping on the isothermal oxidation of three sputtered nanocrystalline coatings were investigated at 1100 °C. The results indicated that oxygen doping inhibited the diffusion of Ta from the coating to the oxide scale, which was primarily attributed to the preferential oxidation of the Al in the coating. However, excess oxygen doping decreased the amount of Al available for the formation of the Al 2 O 3 scale on the coating, thus reducing the inhibitory effect on Ta oxidation. Moreover, doping with excess O caused spalling of the oxide scale. Therefore, the right balance in O doping is crucial for suppressing Ta oxidation while maintaining the integrity of the oxide scale. [Display omitted] [ABSTRACT FROM AUTHOR]

• Oxygen (O) element is introduced in the bulk graphitic carbon nitride (CN) for the first time through a precursor pretreatment by ultraviolet (UV) light irradiation. • The doped O non-metal photocatalyst of CN increased visible light absorption and enhanced carrier density. • The optimized sample has lower charge recombination and suppressed electron deep trapping. • The optimized sample shows enhanced photoreduction activity of CO 2 to CH 4. While photoreduction of CO 2 to CH 4 is an effective means of producing value-added fuels, common photocatalysts have poor activity and low selectivity in photocatalytic CO 2 -reduction processes. Even though creating defects is an effective photocatalyst fabrication route to improve photocatalytic activity, there are some challenges with the facile photocatalyst synthesis method. In this work, an O element is introduced into a graphitic carbon nitride (CN) skeleton through a precursory ultraviolet light irradiation pretreatment to increase the visible light absorption and enhance the carrier density of this modified non-metal CN photocatalyst; the charge transfer dynamics thereof are also studied through electrochemical tests, photoluminescence spectroscopy, and nanosecond transient absorption. We verify that the optimized sample exhibits lower charge recombination and a suppressed 84 ns electron-trapping lifetime, compared to the 103 ns electron-trapping lifetime of the CN counterpart, and thereby contributes to robust detrapping and a fast transfer of active electrons. Through density functional theory calculations, we find that the improved light absorption and increased electron density are ascribed to O-element doping, which enhances the CO 2 adsorption energy and improves the CO 2 -to-CH 4 photoreduction activity; it becomes 17 times higher than that of the bare CN, and the selectivity is 3.8 times higher than that of CN. Moreover, the optimized sample demonstrates excellent cyclic stability in a 24-hour cycle test. [ABSTRACT FROM AUTHOR]

The strategy of a reliable transition temperature control of vanadium dioxide (VO 2) is reported. Rectangular VO 2 nanobeams were synthesized by a thermal chemical vapor deposition (TCVD) system. The metal-insulator transition (MIT) temperature increases to above 380 K when the TiO 2 ratio of the source is 5 at.%, although the Ti source is not physically doped into VO 2 nanobeams. The XPS spectra of the V 2p orbital reveal the excessive oxidation of V after the TCVD processes with a higher TiO 2 ratio, indicating that the TiO 2 precursor is important in the O-doping of the surface V O bonds when forming volatile Ti-O gas species. Thus, TiO 2 reactants can be used as a VO 2 surface chemical modifier to manipulate the MIT transition temperature and maintain a homogenous VO 2 phase, which is useful for a Mott device application with a record on/off switching ratio > 104 and Mott transition temperature > 380 K. [ABSTRACT FROM AUTHOR]