Plasma sampling mass spectrometry (PSMS) has been carried out to study the fragmentation kinetics of hexamethyldisiloxane (HMDSO) in a low-pressure, axially asymmetric argon rf discharge designed for the growth of nanocomposite thin films through a hybrid PVD/PECVD method. Experiments have been conducted with a pulsed injection of HMDSO over a 5-s period. Plasma conditions have been chosen to favor formation and disappearance of dust occurring in cycles of a few hundred seconds. The dissociation degree of HMDSO and the relative intensities of HMDSO-related fragments are reported and analyzed regarding these two specific time-scales. PSMS showed that formation of dust increases HMDSO dissociation. The same result can be deduced from the particle balance equation of HMDSO using the electron density and temperature obtained from optical emission spectroscopy as the only input parameters. For HMDSO, electron-impact dissociation is the dominant loss pathway over diffusion and recombination on the reactor walls. Small C x H y compounds and H 2 are mostly generated from surface recombination mechanisms and lost by electron-impact dissociation. K E Y W O R D S organosilicon precursors, physical vapor deposition, plasma diagnostics, plasma-enhanced chemical vapor deposition 2 of 12 | GAROFANO ET AL. F I G U R E 7 Temporal variation of the fragment-to-parent molecule PSMS ratios (m/z 2-133 / m/z 147) during the formation and disappearance of the dust cloud. Standard conditions. PSMS, plasma sampling mass spectrometry GAROFANO ET AL.