The evolution of interfacial reactions during the deposition of Pt and Pd on epitaxial Si1−xGex alloys was studied using x-ray photoelectron spectroscopy (XPS) for metal coverage up to 10 Å. Auger electron depth profiling was performed on a thicker metal overlayer before and after in vacuo annealing to study the redistribution of composition in the reactions. We have found that Pt and Pd react mainly with Si to form silicides at 350 °C, leaving some Ge to segregate at the surface. These results were correlated with Schottky barrier height measurements. We found that the Schottky barrier heights of Pt/n-Si0.8Ge0.2 and Pd/n-Si0.8Ge0.2 are about the same, pinned at 0.68 eV, which is much smaller than those of n-Si. These barrier heights are quite stable up to 550 °C.

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Oils from soybeans with high or low contents of furanoid fatty acids were evaluated during storage for flavor intensity of soybean oil (SBO) off‐flavor, but no significant differences were found. In addition, the compound 3‐methylnonane‐2,4‐dione (MND), a breakdown product of furanoid fatty acids suggested by other researchers to contribute to reversion flavor of SBO, was evaluated for its contribution to off‐flavor. The compound was synthesized in the laboratory and purified by gas chromatography (GC) on a Silar 10 C column. GC analysis of the purified MND on a nonpolar SPB‐1 column showed two well‐separated main peaks that have been suggested to represent keto and enol forms. Between these two peaks, a bridge of poorly resolved compounds may have represented various possible enol forms or an equilibration among these forms during the GC separation. MND had an intense straw‐like and frulty odor when evaluated at the outlet of a gas chromatograph. Sensory evaluation of MND in a mineral oil/water emulsion system showed that its flavor intensity increased almost imperceptibly with increased concentration (from 0.09 to 2.56 ppm). An explanation for this unusual flavor response may be that, when molecularly dispersed in air, MND has an intense odor, but when placed in a mineral oil or soybean oil emulsion, MND may exist in a form with relatively low flavor intensity, or it may be bound by the media. The concentrations of MND in SBO at various peroxide values were measured at 0 to 0.804 ppb, which were far less than concentrations tested in mineral oil/water emulsions during sensory evaluation and below published odor threshold values for MND in oil. Therefore, these results do not support the theory that furanoid fatty acids or MND contribute strongly to the reversion flavor of SBO.

Carbon quantum dots (CQDs) have attracted more and more attention as the representative of a new generation of photoluminescence (PL) and photodetecting materials due to their unique optoelectrical properties. However, the formation mechanism of the CQDs as well as the origin of the PL from the CQDs are still open questions to be issued. Here, we report our recent progress on the synthesis of the nitrogen-doped carbon quantum dots (N-CQDs) with a high photoluminescence quantum yield (PLQY) of 97.4% by adjusting the hydrothermal synthesis parameters with citric acid (CA) and ethylenediamine (EDA) as the precursors. The detailed structure and properties indicate that N-CQDs are synthesized by dehydration, condensation, and carbonization, and the PL is attributed to the synergistic effect of the carbogenic core and the surface/molecule state. With the above progress, an all-carbon-based ultraviolet (UV) photodetector is fabricated based on the N-CQDs/graphene hybrid composites, which exhibits a significant negative photoconductivity phenomenon. A maximal negative responsivity up to 2.5 × 104 AW–1 in the UV region has been observed, which was attributed to the two competing mechanisms. One is the oxygen adsorption and photodesorption induced negative photoresponse, while the other is the surface defects in N-CQDs related positive photoconducting. Our work reveals the mechanisms driving force behind the positive and the negative photoconductance phenomenon of photodetectors based on CQDs, which not only contributes to further understanding of the fluorescent and photoresponse mechanisms of CQDs, but also promotes the application potential of CQDs in the field of photodetection and nano-optoelectronic sensors.