IR and UV-VIS optical spectroscopy have been used to study the transformations of the properties of diamondlike carbon films following isothermal anneals from T a ϭ300 to 650°C. Several processes due to the annealing have been observed: ͑1͒ the increase of the absorption due to vibrations of unsaturated bonds of C͑sp 2 ͒ atoms at ϳ1600 cm Ϫ1 for T a у350°C, ͑2͒ the decrease of the absorption due to C͑sp 3 ͒-H bonds at T a у350°C, and ͑3͒ the reduction of the optical energy gap. Analysis of the kinetics has shown that the dehydrogenation of the alloys and the formation of unsaturated bonds may proceed independently. The reduction of the energy gap is related to the formation of C͑sp 2 ͒ atoms with unsaturated bonding which occurs mostly in hydrogen-free regions. Intensive graphitization of the films occurs above T a ϭ650°C. Transformations of C-H bonds are proposed to occur via fast rearrangement in stressed regions leading to formation of new C͑sp 2 ͒-H bonds and formation of methane molecules as the most important product of the anneals inside the polymeric highly hydrogenated regions in the alloys. It appears that both bond removal and reordering have taken place as a result of annealing.
The chemical vapor deposition of pyrolytic boron nitride from borazine (the B3N3H6–N2 system) in the temperature range of 1300–1800 °C and chamber pressures of 1–10 Torr has been studied using a cold-wall reactor. The density, phase composition and B/N ratio of the samples (0.2–0.8 mm thick) have been measured. The deposition process from borazine is controlled by diffusion and produces stoichiometric boron nitride with a high fraction of the hexagonal phase of boron nitride in the samples. Employing borazine as a precursor reduces the temperature of formation of h-BN in comparison with the well-known BCl3–NH3–N2 system.
The free energy model previously developed for the prediction of the bonding in amorphous Si-based alloys is extended here to amorphous carbon alloys, a-CxH1−x, containing carbon atoms with sp3 and sp2 hybridization. Predictions have been made for the bonds present in the alloys, with the case of ‘‘chemical’’ ordering at T=0 K corresponding to phase separation into separate C (sp3) and C(sp2) regions. For T≳0 K phase separation is eliminated and there is no evidence for the clustering of graphitic carbon, indicating the importance of the configurational entropy in influencing the bonding in the alloys. Hydrogen atoms are predicted to bond preferentially to C (sp3) atoms for all T. The sp3/sp2 ratio is predicted to increase with increasing H content, as observed experimentally, and also with increasing T due to entropy effects. Predictions have been made for the distribution of bonds in tetrahedral C(sp3)- and planar C(sp2)=C(sp2)-centered units. It is found that essentially no aromatic or graphitic structures are present in typical alloys. The a-CxH1−x alloys have been proposed to consist of five amorphous components: diamondlike, graphitic, polymeric, olefinic, and mixed diamond–graphitic (d–g) components. It is predicted that the polymeric and mixed d–g components dominate in typical plasma-deposited alloy films while the mixed d–g component dominates in hydrogen-free a-C films.
A model for the infrared radiation emitted by a film/substrate system has been developed which includes both the effects of interference in the growing film and of scattering from its rough growth surface. Predictions of the model for the time-dependence of the apparent temperature Tapp of the film/substrate system measured in-situ by both one-color and two-color infrared pyrometers are presented for the case of diamond growth on Si. Using this model, the following information can be obtained from in-situ pyrometric results in real time: the true temperature of the film/substrate system, the instantaneous film growth rate, and the rms surface roughness σ of the film.
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