Investigation on the Emission Characteristics of Copper Atomic and Ionic Lines in Reduced-pressure Argon Spark Discharge Plasma Based on Time-resolved Measurement

Abstract

Time-resolved signals of several atomic and ionic copper lines from argon spark discharge plasmas were measured when the pressure of argon was varied at evacuated atmospheres. The time profiles of these emission lines were quite different. The profile width of the atomic resonance line, Cu I 324.75 nm, was broader than that of an ionic line, Cu II 213.60 nm. In the case of Cu I 324.75 nm, the overall lifetime of the signal was almost constant independent of the argon pressures, and the profile comprised an initial peak and a subsequent large tail which was more predominant at larger pressures of argon. In the case of Cu II 213.60 nm, the overall lifetime of the signal was a little varied at different argon pressures, and the profile comprised an initial peak and a subsequent small tail. These effects could be explained from the difference in the excitation process between the atomic and the ionic lines, which was changed temporally within a single spark shot.KEY WORDS: reduced-pressure argon spark discharge plasma; atomic emission spectrometry; copper emission line; time-resolved measurement; excitation mechanism.ISIJ International, Vol. 46 (2006), No. 11, pp. 1668No. 11, pp. -1673 sures, indicating that the signal-to-background ratios for analytical emission lines increase with reducing the Ar pressure. 8) In this paper, we report on the behaviour of copper emission lines emitted from reduced-pressure argon spark discharge plasmas by analysing transient response of their emission signals with the progress of the spark discharge. Copper atomic or ionic lines having various excitation energies were observed at various pressures of argon employed as the surrounding gas. The temporal variation of their emission intensities is different among these emission lines and strongly depends on the argon pressure, which gives important information on their excitations in the spark discharge plasma. The excitation mechanism of the copper lines is suggested from these experiments. Experimental Temporal Changes of Spark Discharge PlasmaA spark discharge is caused by discontinuous destruction in gas isolation between two electrodes, which is usually regulated by a charge/discharge cycle of a capacitor with an ignitor in a spark discharge instrument.7) The spark channel originates from a flow of electrons having large kinetic energies that can be provided by the charge voltage between the electrodes. Sample atoms, which are evaporated from the cathode surface (cathode spot) through heating by electron ejection, are excited and/or ionized in the plasma and then de-excited with a characteristic radiation. This radiation is detected and analysed in SD-OES. The spark discharge plasma results from various collisions between fast electrons and surrounding gas species; therefore, the excitation characteristics of the plasma would be dependent on the pressure of the plasma gas. Because the spark is a discontinuous discharge followed by a sudden decrease in the charge voltage, the resulting atomic emission from the plasma also gives a p...