A comprehensive study was made of C-rich films of amorphous hydrogenated material by using optical absorption, Fourier-transform infra-red spectroscopy, thermal desorption, atomic force microscopic, positron lifetime and Doppler-broadening techniques. The results suggested that open volumes formed in the films due to incomplete breaking of the source molecule during film deposition. These open volumes were interconnected and could trap ambient gases during film growth, or afterwards. With increasing temperature, the gases were desorbed from the internal surfaces of these open volumes and were released from the sample. This then increased the areal density of the defects, and was detected via positronium formation and the annihilation of positrons with surface electrons. At sufficiently high temperatures, thermal rupture of Si-H and C-H bonds occurred and resulted in irreversible structural changes, and film densification, due to new C-C bond formation.

T.Friessnegg, M.Boudreau, P.Mascher, A.Knights, P.J.Simpson, W.Puff: Journal of Applied Physics, 1998, 84[2], 786-95