An extensive survey of the Raman spectral activity of a wide variety of carbon materials has produced experimental evidence for at least five structure‐sensitive lines or bands. In addition to the well‐known, always present 1580 cm−1 graphite line and the 1360 cm−1 disordered carbon line, there is a disorder line at ∼1620 cm−1 that is responsible for the apparent blue‐shift of the graphite line in very disordered carbons; and there are lines at ∼2700 and ∼2735 cm−1 that are strong in graphite and annealed carbons but absent in very disordered carbons. These additional lines increase the capability of Raman spectroscopy to characterize carbon materials.
Oxidation of {111} single‐crystal silicon and dense, chemically‐vapor‐deposited silicon nitride was done in clean silica tubes at temperatures of 1000° to woo°C. The oxidation rates of silicon nitride under various atmospheres (dry O2, wet O2, wet inert gas, and steam) were several orders of magnitude slower than those of silicon under the identical conditions. The activation energy for the oxidation of silicon nitride decreased from 330 to 259 kJ/mol in going from dry O2 to steam while that for Si decreased from 120 to 94 kJ/mol. The parabolic rate constant for Si increased linearly as the water vapor pressure increased. However, the parabolic rate constant for silicon nitride showed nonlinear dependency on the water vapor pressure in the presence of oxygen. The oxidation kinetics of silicon nitride is explained by the formation of nitrogen compounds (NO and NH3) at the reaction interface and the counterpermeation of these reaction products.
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