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The effect of growth pressure on the properties of β-Ga2 O3 thin films epitaxial on c-plane sapphire substrate with 6° oblique cut angle by plasma-assisted molecular beam epitaxy were systematically studied. All of the epitaxial films present (201) orientated single-crystalline structure with smooth surface morphology. In addition, the crystalline quality and growth rate increase gradually with the increase of the growth pressure, as demonstrated by X-ray diffraction and scanning electron microscopy characterizations. According to the X-ray photoelectron spectroscopy measurement results, the percentage of oxygen vacancy and Ga3+ oxidation states decrease and increase, respectively, with increasing growth pressure, resulting in the increment of atomic ratio of O to Ga. Moreover, through the calculation of Tauc formula and Urbach tail model, the results show that the optical band gap of the films increase from 4.94 eV to 5.00 eV, while Urbach energy decreases from 0.47 eV to 0.32 eV. These results suggest that the crystal quality and optical property of β-Ga2O3 were improved by increasing the growth pressure. [ABSTRACT FROM AUTHOR]

Combustion is the main energy source in the world, and plays an important role in the fields of transportation, industrial production, aerospace, etc. The combustion process is accompanied by the production of pollutants, which lead to serious environmental problems. In order to improve combustion efficiency and reduce pollutant emissions, it is necessary to understand and control combustion. As intermediates are the chain nodes of combustion reaction network, qualitative and quantitative measurements of key intermediates are essential not only for understanding combustion, but also for developing and verifying combustion reaction kinetic models. On the other hand, the preparation of various chemicals and fuels involves catalytic processes. The detection of catalytic reaction intermediates can further reveal the catalytic reaction mechanism, regulate the catalytic reactions and improve the conversion of target products. The detection of these key intermediates, especially active intermediates, has always been challenging. In recent years, the synchrotron radiation vacuum ultraviolet photoionization mass spectrometry (SVUV PIMS) combined with molecular beam sampling, can detect the key intermediates in the process of combustion and catalytic reaction, such as enols, hydroperoxides, free radicals, etc. Herein, SVUV PIMS and its application in combustion and catalysis were summarized in detail, and the future development direction was prospected. [ABSTRACT FROM AUTHOR]