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Glow discharge optical emission spectroscopy (GDOES) is a quantitative, chemical analytical technique used to study the elemental composition of solids. It is particularly well suited for analysis on thin- and thick-film samples, or for depth-profiling of multilayer film stacks.
To increase the wear protection, carbon is introduced into steel. The layer thicknesses of such carbon layers may be up to 1 mm. Since the maximum layer thickness detectable by GDOES amounts to approx. 200 µm, these layers cannot be measured in a single step. Instead, several measurements are performed on the same sample.After the first measurement the sample is grinded a little bit in such a way, that the first burning spot is still visible. The next measurement is performed on the grinded area as near as possible to the old spot. The recorded spectra are stringed together to a single profile. This procedure can be repeated until the desired depth is reached. The figure shows a depth profile combined of several measurements. Only the elements iron and carbon are displayed.
Aluminum cladded materials are used in the automotive industry for cooling fins and radiators etc. They consist of two different aluminum alloys glued by heat and pressure. The control over the thickness of the cladding as well as the purity of the layers and the surface is of great importance. As can be seen in the figure on the left, the alloy on the surface contains silicon while the alloy beneath contains manganese, magnesium and copper. The turning point of a curve (black framed area in the diagram) defines the end of a layer. In this case, the layer thickness of the Si-containing alloy amounts to 34 µm. (as described in This Application Note).
In contrast to microscopic methods GDOES does not require a laborious and time consuming sample preparation. Samples must meet only four criteria:
| Criteria | Reason |
|---|---|
| 1.) Under standard conditions: flat sample surface required. | 1. ) The sample surface must seal the glow discharge source tightly. So a proper vacuum can be generated and no contaminations from the atmosphere can get into the sample chamber. |
| 2.) Minimum sample size: 20 mm for the 8-mm-anode, 15 mm for the 4-mm-anode and 6 mm for the 2.5-mm-anode. | 2. ) The sample surface must seal the glow discharge source tightly. So a proper vacuum can be generated and no contaminations from the atmosphere can get into the sample chamber. |
| 3.) Surface must be dry and free of oil and dirt. | 3.) Even small traces of oil and dirt are detected and can falsify the analytical results. |
| 4.) The distance between the anode and the reamer is 45 mm. Samples exceeding this size must be cut. | 4.) Otherwise samples do not fit into the sample compartment. |
| Feature | GDOES | GDMS |
|---|---|---|
| Principle | Optical emission of excited atoms/ions | Mass spectrometry of ionized atoms/ions |
| Detection Method | Photons (light intensity at wavelengths) | Ions (mass-to-charge ratio, m/z) |
| Primary Use | Depth profiling (surface to bulk) | Ultra-trace bulk analysis (ppb-ppt) |
| Speed | Very fast (µm/min depth resolution) | Slow (minutes to hours per sample) |
| Depth Resolution | Excellent (1–10 nm) | Poor (bulk analysis, no depth resolution) |
| Detection Limits | ppm to % (major/minor elements) | ppt to ppb (trace/ultra-trace) |
| Isotope Sensitivity | No | Yes (resolves isotopes) |
| Sample Conductivity | Requires conductive samples (or RF mode for non-conductors) | Handles conductors and non-conductors better |
| Quantitative Analysis | Semi-quantitative (standards needed) | Highly quantitative (standardless possible) |
Glow Discharge Optical Emission Spectroscopy (GD-OES) is an analytical technique used for elemental analysis of solid conductive materials. It operates by generating a glow discharge plasma in a low-pressure gas environment (typically argon) within a vacuum chamber. The excited atoms in the sample emit light at characteristic wavelengths, which is then analyzed to determine the elemental composition and concentration of the sample.