In this study, thin-film deposition in a pulsed rf polymerizing discharge (13.56MHz) struck in acrylic acid has been investigated by mass spectrometry, x-ray photoelectron spectroscopy, and quartz crystal microbalance techniques. The experiment was conducted at a fixed acrylic acid pressure of 1.3Pa and “on” pulse duration of 0.1ms, whereas the “off” time was varied between 0 and 20ms. The rf input power in the “on” time and gas flow rate were varied between 10 and 50W and 1.5 and 4.8sccm (sccm denotes cubic centimeter per minute at STP), respectively. These changes of the discharge conditions resulted in large-scale progressive variations in film and gas-phase plasma composition. In particular, the –COOH functionality of the monomer was increasingly retained in the plasma-generated thin films as the duty cycle was lowered (i.e., with lowered time-averaged powers). The monomer retention reached its maximum value of 66% for “off” times exceeding 5ms, when the discharge was operating in the power-deficient regime. The results show that the film deposition rate is a strong function of the monomer flow rate, whereas –COOH retention is correlated to the amount of unfragmented monomer in the plasma, controlled by the applied power.

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