COMPARATIVE IN-SITU TOF-SIMS/XPS STUDY OF POLYSTYRENE MODIFIED BY ARGON, OXYGEN AND NITROGEN PLASMAS

The on-line combination of time-of-flight secondary ion mass spectrometry (ToF-SIMS) and monochromatized photoelectron spectroscopy is a valuable analytical tool for the characterization of chemically modified surfaces. By an in situ combination of these techniques with a plasma modification chamber, we have investigated polystyrene surfaces modified by various kinds of microwave plasmas (argon, oxygen and nitrogen). The modified surfaces are widely different with respect to the incorporation of elements originating from the plasma, the degree of chemical changes caused by the plasma and the plasma-induced etching rate. Significant formation of new functional groups specific for the plasma gas is only observed for nitrogen and oxygen. As compared to nitrogen and argon, treatment with the oxygen plasma leads to a high etching rate, but only moderate changes of the chemical state of the polymer surface. In all cases, severe degradation of the aromatic system occurs. Exposure to air after plasma treatment leads to the uptake of considerable amounts of oxygen. In the case of the oxygen and argon plasma, the high mass resolution of ToF-SIMS allows the identification and distinction of clusters that are specific for the oxygen incorporated during plasma treatment and those appearing during exposure to the atmosphere.