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The thermal stability and relaxation processes in hydrogen free diamond-like-carbon films with different sp3 fractions (40%, 60%, and 80%) are comparatively studied for the first time by visible Raman spectroscopy. The 80% sp3 film is very stable under annealing in the entire temperature region investigated (300–1270 K) and shows only a minor change of the optical transmission, most likely due to a mild sp2 clustering, but no graphitization. This is very important for practical applications requiring a high thermal stability. The films with lower sp3 fraction show a thermal stability which decreases with the decreasing sp3. Graphitization starts at 700 K for the 40% sp3 film.

Micro-Raman scattering from single crystal GaN films, both free-standing and attached to Al2O3 substrates, was performed over the temperature range from 78 to 800 K. These measurements reveal that the Raman phonon frequency decreases and the linewidth broadens with increasing temperature. This temperature dependence is well described by an empirical relationship which has proved to be effective for other semiconductors. The experiments also demonstrate that the strain from Al2O3 substrates compresses the epitaxial GaN in the c-axis direction.

The bonding in a series of unhydrogenated amorphous carbon films has been analyzed quantitatively using Raman spectroscopy excited by laser light in both the visible and ultraviolet regions of the spectrum. The asymmetry of the peak near 1550 cm−1 in the visible Raman spectra is correlated with the percentage of sp3 bonding in the films. The ultraviolet Raman spectra exhibit two broad Raman peaks at 1650 and 1100 cm−1, due to sp2 and sp3 vibrational modes, respectively. The former is a resonance feature associated with a large proportion of paired sp2 sites, while the latter is a weighted phonon density-of-states for the distorted random network of sp3 sites. The position and relative intensity of the two peaks are shown to be strongly correlated with the percentage of sp3 sites in the films, providing a reliable measure of sp3 bonding which is both semiquantitative and nondestructive.

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