Sampling and Analytical Characteristics of an Electrically Vaporized Thin-Film Plasma in an External Magnetic Field

Abstract

A magnetic field of a few kilogauss oriented normal to the electric field in the plasma generated by a capacitive discharge through a thin silver film is used to obtain an ExB drift motion of the plasma. The plasma current is used to generate the magnetic field in a coil surrounding the plasma. The plasma drift motion is used to confine the plasma to the region near the surface of the plastic substrate which originally supported the thin film and the powder or solution residue sample. The result is greater interaction of the plasma with the sample, as illustrated by more rapid vaporization of the sample, reduced effects of particle size on analyte radiation intensity, and significantly improved shot-to-shot reproducibility. While analyte line intensities frequently are lower in the ExB plasma, line-to-background intensity ratios may be greater if an optical mask is used to block radiation near the substrate surface.

Preliminary characterization of a graphite vapor plasma in a theta-pinch magnetic field

“…Several recent studies have shown that external magnetic fields can be very effective in altering plasma properties for microwave-induced plasmas (3), high-current capacitive discharge plasmas (4)(5)(6)(7)(8), and glow-discharge plasmas with currents in the millampere range (9)(10)(11). The presence of the magnetic field causes ions and electrons to precess in circular paths in the plane normal to the field direction.…”

“…If the plasma contains a macroscopic electric field with a component normal to the external magnetic field, charged particles undergo a drift motion in the direction normal to the plane containing the electric and magnetic field vectors (12,13). This E X B drift motion has been used to alter the properties of highcurrent capacitive discharge plasmas (4, 5) and improve their analytical performance (6,7). Recently, this type of plasma drift motion also has been used to alter the properties of arc and glow discharge plasmas (11).…”

“…The plasma device is quite simple and convenient to use since it is designed for atmospheric pressure operation and a single power supply generates both the plasma and the magnetic field. The design of the plasma device and a preliminary spectral and electrical characterization are found in a companion report (6). In the present paper, some qualitative and quantitative analytical features of the plasma are presented.…”