The analytical impact of power control in a radio frequency glow discharge optical emission plasma

Abstract

Direct current (dc) and radio frequency (rf) glow discharge power control requirements, and limitations are described. The differences between dc and rf power control are explored. The various difficulties faced with rf power regulation are listed and explained. In light of these challenges, the appropriate design goals for an rf glow discharge power supply and control system are outlined. The design and implementation of such a new rf design is then detailed. The ability of this new design to deal with the various rf difficulties is discussed. This design is evaluated and experimental evidence that it functions as anticipated is collected, presented, and discussed. This new rf power supply design is shown to have significant new capabilities.

Electrical measurements at radio frequency glow discharges for spectroscopy

“…But with a discharge the ripple factor becomes worse. Marshall et al [14] reported a harmonic distortion of up to 6%.…”

“…Marshall et al developed a working mode where the matchbox is not adjusted during a depth profile measurement [14]. The tuning capacitors C m1 and C m2 are locked down.…”

The effects of traces of molecular gases (H2, N2& O2) in glow discharges in noble gases

“…In the original design, the diameter of the anode tube was 8 mm; typical operating conditions were 800 V, 80 mA, with an argon pressure of~500 Pa. The source proved very convenient for routine analysis of bulk metallic samples; in all cases, calibration with samples of known 4 To whom correspondence should be addressed The gaps between the outside of the anode tube and the cathode block, and between the end of the anode tube and the sample are each~0.2 mm, and are evacuated by pump 1, so that when a discharge is initiated, it is restricted to an area of the sample equal to the cross-sectional area of the anode tube and no discharge occurs on the outside of the anode tube.…”

Radiofrequency glow-discharge devices for direct solid analysis

“…When current-voltage characteristics for different conducting and insulator sample materials, pressures, and voltages were presented for such a system, estimated errors in voltage, current, and power measurement were smaller than 8% [29]. Interest in, and the feasibility of, using a control mode based on constant "effective power-voltage" to operate the rf-GD-OES has been evaluated [30]. This control mode provides the requested power to the plasma by compensating for power losses occurring during delivery to the discharge.…”

“…Studies investigating the influence of three rf-GD modes of operation (constant "forward power and pressure", constant "dc bias voltage and pressure", and constant "forward power and dc bias voltage") on the analysis of several conductive samples (Zn layers) have obtained satisfactory results for depth-profile quantification using any of the three operational modes [45,46,47]. However, it has to be emphasised that problems have been reported with use of multimatrix calibration curves when the matrices have significantly different electrical properties (the so-called "family effect") if a control based on constant forward power and pressure is used [30].…”