Abstract
This paper describes three advanced detection techniques in glow discharge optical emission spectrometry: (a) an applied voltage modulation method for a d.c.-powered glow discharge emission source, (b) a bias-current introduction method and (c) an amplitude modulation method for an r.f.-powered glow discharge emission source. In the applied voltage modulation method, an alternating component superimposed on a d.c. bias voltage is applied to the excitation source. Only the emission component corresponding to the alternating frequency can be selectively detected at very low noise levels with a lock-in amplifier, thus contributing to an improvement in the signal-to-noise ratio. In the bias-current introduction method, a d.c. current driven by the self-bias voltage is conducted through the plasma body by connecting a low-pass filter circuit and a load resistor with the glow discharge lamp. The electrons introduced into the plasma can cause various excitation processes more actively and, as a result, the emission intensities increase, which yields a better detection limit in the quantitative analysis. In the amplitude modulation of an r.f. voltage, the emission detection with a lock-in amplifier enables the measurement to be performed with a better signal-to-noise ratio, whereas the sputtering rate and the sampling amount are reduced. This method can be successfully applied to determine depth elemental composition of nm-order thin films.
Original language | English |
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Pages (from-to) | 393-403 |
Number of pages | 11 |
Journal | BUNSEKI KAGAKU |
Volume | 52 |
Issue number | 6 |
DOIs | |
Publication status | Published - 2003 Jun |
Keywords
- Amplitude modulation
- Atomic emission spectrometry
- Bias current
- Detection limit
- Glow discharge plasma
- Lock-in amplifier
- Signal-to-background ratio
- Signal-to-noise ratio
- Voltage modulation
ASJC Scopus subject areas
- Analytical Chemistry