The influence of operational modes on sputtering rates and emission processes for different sample matrices in rf-GD-OES

Abstract

A study was carried out to select the most convenient pair of the three key interdependent plasma operating parameters in a radiofrequency glow discharge (rf-GD) (generator output power, dc-bias developed in the sample surface and pressure) to be fixed in order to measure intensities by optical emission spectrometry (OES) or sputtering rates with adequate precision. The best operating conditions in order to obtain values of emission yields unaffected by the nature of the sample matrix are also given. Three different modes of rf-GD-OES operation were studied and emission intensities of selected elements (Fe, Ni, Zn, Cu) in eight different matrices were measured. Results showed that a mode in which generator output power and dc-bias voltage are fixed while pressure is allowed to vary provided the worst relative standard deviations (RSDs) for the emission intensities measured (higher than 15%). The other two approaches studied (either generator output power and pressure fixed with the dc-bias varied or pressure and dc-bias voltage fixed with the generator output power varied) provided better performance (lower than 4%) in both cases. Concerning the sputtering rates, the two modes, working either with variable dc-bias or with variable power, gave good precision for three replicates. Finally, these two modes seemed also to provide reliable values for the emission yields of each analyte emission line under study in the different reference samples investigated. Comparison of results observed by keeping constant the pressure in a rf-GD and those achieved by dc-GD in its usual mode of operation (variable pressure, maintaining fixed the voltage and current) shows similar behaviour for both sources when comparing the trends followed by the emission yields when modifying the matrix.