The effect of low power plasmas on carbon fibre surfaces

The effect of a variety of low power plasma treatments (e.g., NH3, N2, air and Ar) on low modulus carbon fibre surfaces have been examined using X-ray photoelectron spectroscopy. Grazing angle techniques have been used to probe only the first 12–15A of the fibre surface. Plasma treatments were carried out in an in situ plasma cell which was attached to a PHI 5400 X-ray photoelectron spectrometer. This enabled the immediate effects of the plasma to be studied before the treated surface was exposed to air. Air plasmas introduced both alcohol and carboxyl groups onto the fibre surfaces. Nitrogen plasmas gave very similar results to ammonia plasmas with the formation of three nitrogen containing species on the fibre surface. The signal at 398.9eV was assigned to a combination of aromatic amines (-NH2), and -CNH groups. Its relative intensity, as expected was greater for fibres treated in ammonia plasmas. Air exposure of these activated surfaces results in a strongly bound -O-H layer. Significant etching or pitting was not observed in the scanning electron micrographs of these treated fibres. Comparing XPS spectra of the immediate surface with those taken at bulk sensitive angles, it can be concluded that chemical change only occurred in the first few atomic layers.