Analytical Application

Introduction

Glow Discharge Spectroscopy (GDS) finds its application in direct elemental analysis of solid samples. Although bulk analysis is perfectly possible it's most interesting application is Content Depth Profiling analysis of solid layered materials. Both the substrates and the layers can be metals, polymers, glasses and ceramics. A Glow Discharge Optical Emission Spectrometer (GD-OES) is build of a glow discharge source and one or more optical spectrometers, including detectors, either Photomultiplier tubes or solid state detectors, usually CCD's. A schematic layout is given to the above. The spectrometer displayed here uses a concalve grating in the Rowland circle or Paschen-Runge configuration and photomultiplier tubes for the light detection.

The use of solid state detetectors, CCD's and photo diode array's have become a common alternative for PM tubes. These detectors allow the acquisition of the entire spectrum, or at least a large portion of it, but are usually slower then PM tubes and therefore not suitable for very short acquisition times used in thin film analysis.

The principle of operation is fairly easy to understand. In a glow discharge, cathodic sputtering is used to remove material layer by layer from the sample surface. The atoms removed from the migrate into the plasma where they are excited through collisions with electrons or metastable carrier gas atoms. The characteristic spectrum emitted by this excited atoms is measured by the spectrometer.