The effect of nitrogen on the microstructure and the luminescence properties of a-C:H thin films

In this paper, a comparative study of a-C:H films and low N content a-C:H:N films is performed by infrared, photoluminescence, and ultraviolet, visible, near-infrared spectra. Comparing the properties of as deposited samples with those after annealing cycles at increasing temperature, it is found that nitrogen weakens some C-H bonds, as confirmed by differential scanning calorimetric results. From the analysis of the IR peaks line-width, it is shown that the presence of nitrogen leads to a stress release. Moreover, we found experimental evidence for the weakening of C-H bonds due to the presence of nitrogen. In particular, a large scale rearrangement of the sp(3) carbon network: (probably a conversion from sp(3) to sp(2)) consequent to. the dehydrogenation of the sp(3) carbon sites, takes place. The effect of the stress in the sp(3) network upon sp(2) regions is evidenced by the change in the photoluminescence properties and in the line-width of infrared peaks. Copyright (C) 1996 Elsevier Science Ltd.