Positron lifetime studies were made of films of hydrogenated amorphous material prepared using the glow-discharge method. Films which had been deposited and thermally annealed at various temperatures were investigated in order to determine microstructural parameters such as the contents of H, micro-voids, and vacancies. The appearance of a long-lifetime (more than 3ns) component in the lifetime spectrum, together with a narrow peak in the two-dimensional angular correlation of positron-annihilation radiation, confirmed the existence of large micro-voids in the films. Variations in the intensity of the long-lifetime component, as a function of the deposition and annealing temperatures, was studied in detail. This clearly showed that molecular H existed at high pressures in the micro-voids and effused out at high temperatures, to leave behind empty micro-voids in the film. Two stages of H effusion at 275 and 600C were clearly identified in films deposited at 25C. Films deposited at 300C exhibited only the high-temperature effusion stage and indicated that the low-temperature stage was related to trapped molecular H, while the high-temperature (600C) one was related to bonded H. The positronium lifetime increased with annealing temperature, reflecting micro-void growth, and was attributed to the onset of an agglomeration process in parallel with H effusion. Information concerning the presence of quadri-vacancies and penta-vacancies in the films and their response to heat-treatment was also deduced from the intensity and lifetime corresponding to the trapped positron state. An attempt was made to correlate the positronium component with electron spin resonance results.

V.G.Bhide, R.O.Dusane, S.V.Rajarshi, A.D.Shaligram, S.K.David: Journal of Applied Physics, 1987, 62[1], 108-16