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Bilayer graphene (BLG) grown via chemical vapor deposition (CVD) tends to exhibit twisted stacking. The twist angle θ t in twisted BLG (tBLG) provides a new degree of freedom for engineering its electronic and optical properties. In this paper, we investigate the θ t-dependent optical absorption in tBLG and deeply understand the electronic structure-optical properties correlations. New absorption peaks, whose wavelengths are modified by θ t, are observed on the feature of optical contrast (OC) in tBLG. Under the corresponding energy excitation, the Raman G mode in tBLG exhibits a significant enhancement. Furthermore, the results of θ t obtained by OC absorption peak are verified to be consistent with those by the Raman R mode. All these properties are proved to be related to the energy difference between low-energy Van Hove singularities (E VHS) in the density of states of tBLGs. This work builds a relation between optical absorption and twist angle, providing a viable method to identifying twist angles in tBLGs.

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer. [ABSTRACT FROM AUTHOR]

Abstract: A solid superacid catalyst was evaluated for the production of fatty acid methyl esters (FAMEs) from acid oil containing about 60wt.% free fatty acids. It was demonstrated that /ZrO2–TiO2/La3+ was an effective catalyst for simultaneous transesterification and esterification. The optimization of reaction parameters was performed, showing that maximum yield of above 90% could be obtained under the conditions that molar ratio of alcohol/oil was 15:1, catalyst amount was 5wt.%, temperature was 200°C and duration was 2h. The catalyst was finally recycled and utilized for five times repeatedly with little loss in activity. The final products purified by molecular distillation were detected by GC–MS. The content of FAMEs reached 96.24%. [Copyright &y& Elsevier]