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Chemical vapor deposition (CVD) with hydrogen is an interesting technique to grow graphene on silicon carbide (SiC) with excellent electronic properties. However, unanswered questions remain concerning whether the growth mechanism is similar or different to the graphene growth by silicon (Si) sublimation from SiC. In this paper, we emphasize the differences between these two methods based on thermodynamic simulations in an attempt to better understand the different contributors to the graphene formation in both cases. Our calculations prove that our growth technique, i.e. CVD with hydrogen, operates in a completely different thermodynamic system compared to the Si sublimation technique due to the presence of hydrogen. Finally, we complete our simulations with experimental graphene growth attempts which confirm the necessity of an external carbon source to grow graphene under a hydrogen atmosphere in a CVD reactor, unlike the Si sublimation technique. [ABSTRACT FROM AUTHOR]

AlN thin films, grown on (0001) sapphire substrates by molecular beam epitaxy (MBE), were annealed at high temperature (up to 1650 °C) in flowing N 2 . X-ray diffraction (XRD) studies, combined with Williamson-Hall and Srikant plots, have shown that annealing leads to a strong reduction of both edge and mixed threading dislocation densities, as confirmed by transmission electron microscopy (TEM) images, up to 75%. Moreover, it is found that annealing at high temperatures allows the relaxation of the tensile strain in the AlN film due to the growth process. In addition, the morphological properties of the films were determined by atomic force microscopy (AFM) and show that the annealing conditions have a strong impact on the surface morphology and roughness. Finally, an annealing at 1550 °C for 20 min appears as an ideal tradeoff to enhance the structural properties while preserving the initial AlN surface morphology. [ABSTRACT FROM AUTHOR]