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High-temperature differential scanning calorimetry was used to understand the thermal properties of Si-rich metal–silicon alloys. Insoluble metals (A and B) were found to produce an alloy with discrete ASi2 and BSi2 dispersed phases. In contrast, metals that form a solid solution result in a dispersed phase that has a composition of AxB1−xSi2, where x varies continuously across each inclusion. This complex composition distribution is putatively caused by differences in the solidification temperatures of ASi2 versus BSi2. Though this behavior was observed for several different combinations of metals, we focus here specifically on the Cr/V/Si system. To better understand the range and most probable element concentrations in the dispersed silicide domains, a method was devised to generate histograms of their Cr and V concentrations from energy-dispersive X-ray spectroscopy hyperspectral images. Varying the Cr/V/Si ratio was found to change the shape of the element histograms, indicating that the distribution of silicide compositions that form is controlled by the input composition. Adding aluminum was found to result in dispersed phases that had a single composition rather than a range of Cr and V concentrations. This demonstrates that aluminum can be an effective additive for altering solidification kinetics in silicon alloys.
Polycrystalline diamond films were synthesized using an oxy-acetylene flame in the open atmosphere and in an enclosed chamber. In the present work, we have shown that the 2.16eV defect band seen in the photoluminescence spectra from the central portion of the films grown in the open atmosphere show a dependence on the growth temperature. Films grown in the open atmosphere all exhibit a decrease in the crystalline quality when moving to the outside edge most likely due to the entrainment of nitrogen into the films.
The present study was done in the enclosed chamber using an oxygen atmosphere via an oxygen flow around the torch. Films have been grown in the enclosed chamber that show only trace amounts of the 2.16eV band. Both the Raman and the photoluminescence spectra show that the films grown in the enclosed chamber are very uniform over the deposition area, which suggests that the degradation of the outer portion of the open atmosphere films may be the result of room air entrainment, and not a temperature variation across the substrate. In addition, when either lower purity oxygen is used or lower growth temperatures, we easily observe the 2.16eV band which may be the result of nitrogen impurities in the source gases.
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