GDOES made its first appearance in 1968 and was designed primarily for bulk spectrochemical analysis of various metals and their alloys. Since its introduction, this method has been steadily developed and has excelled in the areas of surface and coating analysis as well. Compared with conventional excitation techniques, the striking feature of Glow Discharge Technology is the ability to discern defined surface layers of the material being examined and analyze their chemical composition. In the field of metal analysis GDOES is ideal for concentration profile analysis and surface analysis. All kinds of surface treatment processes as well as surface coating processes can be monitored by analyzing the surface and near-surface areas the treated material. Coating thickness and chemical composition can be accurately measured using the technique of depth profile analysis. GDOES is the preferred method of analysis for materials that were previously impossible to analyze by traditional methods, and it is one of the fastest methods available.
A stream of argon ions mill material from the sample surface. The sputtered material is then excited in a low pressure plasma discharge and resulting light emission is used to characterize and quantify the sample's composition. Glow Discharge offers an improved excitation source for fast, economical, accurate, and reliable sample turnaround. This source ultimately removes material from the sample surface which reduces the effects of metallurgical and chemical history inherent in all samples.
A Glow Discharge Optical Emission Spectrometer (GD-OES) is built 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 using a concave grating in the Rowland circle or Paschen-Runge configuration and photomultiplier tubes for the light detection.
The use of solid state detectors, CCD's and photo diode array's have become a common alternative to Photomultiplier tubes. These detectors allow the acquisition of the entire spectrum, or at least a large portion of it, but are usually slower than Photomultiplier 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 atom is measured by the spectrometer.
GDOES can be used in many industries such as :
- Automotive industry and its suppliers.
- Metalworking industry.
- Iron and steel industry.
- Aerospace industry.
- Electronics industry.
- Glass and ceramics industry.
- Surface technology.
- Galvanizing industry.
- Photovoltaic industry.
- Scientific institutes.
Advantages of GDOES
- Limited matrix effect.
- Linear working curves.
- Minimal spectral interferences.
- Excellent precision.
- Analysis of difficult materials (as-cast iron, low melting point alloys).
- Automatic cleaning between samples.
- Low reference material and gas consumption.