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

Plasma modification of polymer surfaces is a well-established techniqu e for many technological applications. The control of the surface comp osition after plasma treatment requires in situ characterization by ad equate surface analytical techniques. As an example, we investigated p olystyrene modified by a microwave (2.45 GHz) nitrogen plasma by using an on-line combination of time-of-flight secondary ion mass spectrome try and monochromatized photoelectron spectroscopy. Plasma treatment w ithout 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 se em to be stable against organic solvents. A particular feature is the formation of a graphite-like C ls state after prolonged plasma treatme nt. The polystyrene surface after plasma treatment is very reactive, p articularly the graphite-like carbon state. Exposure to the atmosphere leads to the disappearance of this state, to considerable uptake of o xygen and to the formation of carbon-nitrogen-oxygen bonds, as evidenc ed by the CNO- secondary ion cluster and the amide binding state in th e C 1s line.