Glow Discharge Spectroscopy (GDS) is a spectroscopic technique designed for use with solid samples, primarily metals. One advantage of GDS is that it enables depth profiling of a sample. In a GDS system, a solid sample absorbs energy from a plasma of argon ions, causing atom to sputter from the sample’s surface. As the electrons return to their ground state, they release energy absorbed from the plasma in the form of light. The spectrometer separates the light into its component wavelengths for the benefit of the detectors.

Although traditional GDS instruments typically used photomultiplier tubes as detectors, the technique has followed the path of other atomic spectroscopy techniques, and solid-state area detectors are now much more common. For either type of detector, the characteristic frequencies of a particular element allow the identification and quantification of the sample’s elements.

GDS is destructive, in that a sample’s atoms are physically removed, leaving behind a circular sputter spot. Continued analysis of the sample sputters more deeply into the sample, so that inner layers of the sample are sequentially analyzed. This allows researchers to build up a full depth profile of the material, which is important for measuring coating thickness and quality, or other chemical effects on samples. Such depth profiling distinguishes GDS from bulk material atomic spectroscopy methods like X-ray fluorescence or arc-spark, while still remaining less expensive than more complicated surface science techniques like secondary ion MS.

Further refinements of GDS include pulsed modes and radio frequency oscillations of the plasma current. These refinements reduce background interferences and provide better analysis of non-conductive samples or nonconductive surface layers.

The total market for glow discharge spectroscopy was about $22 million in 2008. Due to weakness in the global economy and the metals sector in particular, the market is forecast to contract slightly in 2009, but should see a return to slight growth in the long term. Helped by its strong focus on the metals industry, LECO holds the leading position in the GDS market. The Jobin Yvon (JY) division of Horiba is the next largest competitor in this market. JY Horiba’s GD Profiler line of instruments includes the GD Profiler HTP, which was introduced at the beginning of this year (see IBO 3/31/09). This instrument is a turnkey solution for analyzing and evaluating heat treatment processes in metallurgical processes such as the tempering of steel. Spectruma is a German company focused entirely on the GDS market. This might put the company at a disadvantage with respect to its larger competitors, except that the company has a strong association with Spectro Analytical (AMETEK), which has had a controlling interest in Spectruma since 1999.

Glow Discharge Spectroscopy

at a Glance:

Leading Suppliers

• LECO

• Horiba

• Spectruma

Largest Markets

• Metals

• Semiconductors

• Coatings and Films

Instrument Cost

• $100,000–$300,000