Comparison of fundamental characteristics between radio-frequency and direct current powering of a single glow discharge atomic emission spectroscopy source

Abstract

A comparison between radiofrequency (rf) and direct current (dc) powering of a single glow discharge atomic emission spectroscopy (GD-AES) source has been conducted. A NIST SRM 1252 Phosphorized Copper alloy was used as the cathode sample for a series of measurements. With each powering mode, the analyte emission, sputtering, and charged particle characteristics were investigated under its own optimized operating conditions. Comparison of the results indicates that the rf mode has higher analyte S/B values although the dc mode shows higher signal intensities. Rf-powered plasmas yield much shorter stabilization times and less variation over extended periods of operation. These two factors result in the general trend of the rf mode having lower detection limits for the suite of analytes. With the use of the S/B value as the quantitative measure, similar sample-to-sample reproducibility (5–10% RSD) can be achieved for both modes. The measurement of sputtered crater depths illustrates that the dc mode has a much higher sputtering rate. Finally, Langmuir probe measurements indicate that the rf mode has much higher electron energies and thus higher excitation efficiency.