Inductively coupled, radiofrequency-induced plasmas of propenoic ('acrylic') acid and propanoic acid, operated at a low electrical power (1-10 W), have been investigated using a combination of mass spectrometry (MS) and deposition-rate measurements. Thin films of plasma polymers of both compounds were deposited onto silicon substrates and analysed by X-ray photoelectron spectroscopy (XPS). The positive-ion MS data obtained from both compounds indicate the presence of species of the form (M + H)+, (2M + H)+ and (3M + H)', where M represents the molecular weight of the starting material. No neutral oligomeric species were detected. XPS analysis reveals an inverse relationship between the electrical power supplied to the plasma and the degree of retention of the carboxylic acid functionality in the solid product. Comparison of the MS and XPS results suggests that the above cationic species are responsible for the carboxylic-acid functionalisation of the plasmapolymer product, whereas fragmentation processes lead to the introduction of other functional groups such as alcohol and ketone. The thin film which featured the highest degree of retention of carboxylic acid (65%) was obtained from a plasma of propanoic acid operated at 1 W, and was deposited at the lowest rate (0.90 ng s-').

Plasma polymers of acrylic (propenoic) acid and propanoic acid were prepared from inductively coupled, radio-frequency-induced plasmas excited in vapors of the starting materials. The plasma polymers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and static secondary-ion mass spectrometry (SIMS). Detailed interpretation of the spectra allows determination of the distribution of chemical functionalites at the surface of the product and of the influence of unsaturation and plasma power on this distribution. The results are discussed in the context of previously proposed mechanisms of plasma polymerization of the compounds under investigation.

Ion Ñux, mass spectral and mass deposition rate measurements have been made in radiofrequency-induced continuous-wave plasmas of acrylic acid. At 1 W input power, an ion Ñux of 0.05 ^0.1 ] 1018 ions m~2 s~1 was measured for acrylic acid. At this power, ions corresponding to (2M ] H)`and (3M ] H)`were prominent in the positive-ion mass spectrum. When this spectrum was corrected for the transmission function of the quadrupole mass spectrometer (conservatively taken as intensity P m~1), it was evident that the cationic portion of plasma contained many ions of high m/z, as opposed to small fragments of acrylic acid. The m/z of the " average Ï ion was calculated as 115. The mass of ions arriving at a solid surface in the centre of the plasma was then calculated by multiplying the Ñux by the average mass to give 9.6 lg m~2 s~1. This value represents a signiÐcant fraction of the total mass deposited, determined by means of a quartz crystal mass balance (45.5 lg m~2 s~1). Repeating the calculation for a 5 W plasma yields an ion mass Ñux of 39.6 lg m~2 s~1 (measured mass deposition of 57.3 lg m~2 s~1). At 15 W, the calculated mass deposited (based on ion Ñux) exceeds that measured by the quartz mass balance. The " average Ï ion mass decreased as plasma input power increased.Based on these data, and XPS measurements of the solid-phase deposit we make a Ðrst attempt at describing semi-quantitatively the possible role of ions in deposit formation.

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