Glow Discharge Optical Emission Spectrometer (GD-OES)
The LECO GDS-750A optical emission spectrometer utilizes the principle of an electric discharge in a low-pressure argon atmosphere, with atoms continuously being sputtered (eroded) from the sample’s surface by the bombardment of argon ions (discharge plasma). Ultra-pure carrier grade (99.9993%) bottled argon gas is used for the sputtering process.
Glow discharge spectroscopy (GDS) is also known as glow discharge lamp (GDL); glow discharge lamp spectroscopy (GDLS); glow discharge optical spectroscopy (GDOS); glow discharge optical emission spectroscopy (GDOES); or glow discharge atomic emission spectroscopy (GDAES). The techniques are essentially the same if they use the classic GRIMM lamp technology. If the spectrometer is equipped only with a radio frequency (RF) source (lamp), it may be referred to as RF-GDS. GDS (DC source) is primarily used for analysis of conductive material and RF-GDS is used for the analysis of conductive and non-conductive material. The spectrometer is designed to remove material layer-by-layer allowing for elemental Quantitative Depth Profile analyses. Bulk content analysis is also possible with this technique.
The excitation mechanism for GDS is as follows: Positively charged argon (Ar+) ions, which are generated by the electric field of the source, are accelerated (in a vacuum) across the cathodic (negative potential) sample surface. These ions continuously bombard the sample and cause atoms to be ejected toward the anode. They are subsequently excited or ionized in the negative glow of the plasma gas mainly by collisions with electrons, emitting energy in the form of characteristic light emission. The light emitted by the sample passes into the spectrometer to photomulitiplier tubes that simultaneously quantify the intensity of the spectral lines (wavelengths) in the emitted light. Each individual element in the sample has its own characteristic spectrum and its own unique wavelength or fingerprint.
The following are features of the GD-OES spectrometer:
- Analysis on any solid conductive materials that a plasma can be initiated and maintained on.
- Detection limits: ppm sensitivity, bulk mode.
- Minimal spectral and metallurgical interference.
- Complex multi-matrix algorithms correct for sputter rate variations in different materials, allowing for Quantitative Depth Profiling.
- Determine the thickness and composition of surface layers and coatings.
- The sputter produces an analysis area that is a 4-mm diameter flat bottom crater.
