INVESTIGATIONS ON THE LATERAL DISTRIBUTION OF THE EMISSION-LINE INTENSITIES IN THE PLASMA OF A GRIMM-TYPE GLOW-DISCHARGE SOURCE

The distribution of emitting species in the plasma of a GRIMM-type glow discharge source for optical emission spectroscopy (GD-OES) has been investigated by line intensity measurements in parts of the plasma separately imaged onto the entrance slit of the spectral apparatus. Whereas the species of chemically homogeneous sample surfaces are distributed in the plasma parabolicly with the maximum at the centre of the sputtering crater, the species of a coarse inclusion-adjusted at different distances from the crater centre and thus simulating sample inhomogeneity-form a cone the apex, of which corresponds to the position of the inclusion on the sample surface in each case. Contrary to this behaviour of sputtered species, the species of the sputtering gas and its impurities show a constant distribution over nearly the whole excitation area, thus indicating a position-independent constant excitation. These results should be used for improving the reliability and detection limits of GD-OES bulk analysis by better adaptation of slit illumination to the actual analytical task. Moreover, the information obtained on the excitation and the distribution of the emitting species is important for modelling calculations in connection with the quantification of GD-OES depth profiling. Finally, the distribution of the species in the plasma must be considered for plasma diagnostic measurements of spectral line intensities.