grantor:
University of TorontoA series of hydrogenated amorphous carbon (a-C:H) semiconducting thin films was deposited using the dc saddle field glow discharge deposition technique. The ion energy during the deposition was varied to achieve films ranging from soft to hard a-C:H. In order to study the structure and the properties of a-C:H films, ultraviolet, visible, infrared, photoluminescence, and X-ray Auger electron spectroscopies, scanning electron microscopy, and mass density measurements, were used as diagnostic techniques to extract information on growth rate, mass density, sp2/sp3 ratio, hydrogen concentration, Tauc gap, photoluminescence, concentration of non-radiative recombination centers, and the degree of cross-linking of the carbon network. Based on these results, the films studied in the present research are found to consist of sp2carbon clusters of which the size increases with increasing mean ion energy during the deposition, resulting in a lower Tauc gap; this is explained in terms of the Robertson model. The growth rate of the films increases due to an increase in the concentration of unsaturated bond sites which act as chemisorption centers for radicals on the growing film surface. The increased hydrogen evolution from the film at higher ion energies results in increases in the sp2 fraction, the degree of cross-linking of the C-C network, and the mass density of a-C:H films. Atmospheric aging of soft a-C:H films reveals a decrease in the concentration of C-H bonds in a-C:H. The proposed reaction paths for the hydrolysis and oxidation of C:H films indicate that the films mainly react with water. Thermal annealing of a-C:H films in vacuum greatly influences the soft a-C:H films, in which the chemical bonds in the hydrocarbon network are restructured due to the evolution of hydrogen, which results in a graphitic structure.Ph.D
