IN-SITU TOF-SIMS XPS INVESTIGATION OF NITROGEN PLASMA-MODIFIED POLYSTYRENE SURFACES

Plasma modification of polymer surfaces is a well-established technique for many technological applications. The control of the surface composition after plasma treatment requires in situ characterization by adequate surface analytical techniques. As an example, we investigated polystyrene modified by a microwave (2.45 GHz) nitrogen plasma by using an on-line combination of time-of-flight secondary ion mass spectrometry and monochromatized photoelectron spectroscopy. Plasma treatment without subsequent air contact leads to the incorporation of nitrogen, the formation of amine, imine and nitrile bonds as evidenced by the C 1s and N 1s photoelectron lines, and the appearance of predominant C(x)N(y) clusters in the negative secondary ion spectra. These changes seem to be stable against organic solvents. A particular feature is the formation of a graphite-like C ls state after prolonged plasma treatment. The polystyrene surface after plasma treatment is very reactive, particularly the graphite-like carbon state. Exposure to the atmosphere leads to the disappearance of this state, to considerable uptake of oxygen and to the formation of carbon-nitrogen-oxygen bonds, as evidenced by the CNO- secondary ion cluster and the amide binding state in the C 1s line.