Analysis of thin electroplated layers by the bias-current controlled RF glow discharge optical emission spectrometry

In radio-frequency glow discharge optical emission spectrometry (r.f. GD-OES), a bias-current conduction technique has been successfully applied to the analytical application with higher detection sensitivity. The d.c. bias current can introduce a great many electrons into the plasma, thus leading to an enhancement in the emission intensities through the collisional excitations, whereas the sputtering rate is reduced due to the decreased d.c. bias voltages. This feature can be utilized to improve the information depth in depth profiling by r.f. GD-OES, because of the lower sampling rate as well as the better sensitivity. When nickel electroplated steel sheets were analyzed, the integrated intensities increased by a factor of 30 or more. The information depth in the coating weight analysis could be reduced about 20-fold, compared to that obtained with the conventional measurement.