In 1987, Richard Passetemps at Renault successfully modified the JY-Grimm source to allow operation with radio frequency (RF). In the Renault source the cathode block is ceramic and the RF voltage is applied to the back of the sample. In all other aspects it is close to the original Grimm design. Ken Marcus at Clemson University, developed at the same time a different version of a radio frequency power glow discharge source.
The principle is based on the measurement of the luminous emission that accompanies the passage of an electric current in a gas under low pressure, the glow dischare
The sample to be analyzed is placed in front of an enclosure under argon, at a pressure of several hPa. The ionized argon (Ar+) under potential difference of -400 to -2000 V bombards the surface of the cathode sample and and caused cathodic sputtering of the sample surface. The atoms thus freed are then excited by secondary impacts with the energitic Ar atoms, ions and plama electrons: during the de-excitation process they emit electromagnetic radiation, light, with a characteristic energy spectrum. The light intensity is proportional to the element concentration in the sample, or more precisely in the plasma. The light emittession and the line intensities are continuously monitored by a spectrometer.
The ion bombarding previously described leads to a plane and regular erosion, when the dischare pararmeters are well chosen. These flate craters make the continuous examination of the layers deposited on the surface of a material possible
However, when using a DC discharge this process of analysis is limited to samples that are conductive or of low resistivity, to nonconductive layers of very small thickness (less than 2 microns), and to plane samples with a diameter greater than 20 mm.
The rf source developed by R. Passetemps has the objective to overcome these limitations and it applies especially, although not exclusively, to the automobile field.
The automobile body sheet metal pieces are successively provided with layers of phosphates, cataphoretic intermediate deposits, sealer, lacquer and varnish. In the ever-growing quest for quality of anticorrosion protective coatings, it has become necessary to check qualitatively and quantitatively the presence of the various constitutive elements of the protective layers. It is also very important to check the absence of undesirable products in this structure.
Only the quality of the coating of phosphates can be checked by DC-GDOES, before depositing of the following layers, because all other layers are non-conductive.
This the application of power makes the continuous study of all the above layers possible. It is possible to determine their thickness, the distribution of the elements that constitute these layers. The presence or absence of undesirable compounds or the possible migration of atoms between the layers can be checked tested as well.
In the same way, the process of analysis of the invention makes it possible to study products of synthetic material, such as vehicle shields coated with lacquers and thus to find the homogeneity and thickness of the latter.
It is also possible to apply the Renault source to the control of the quality of glued windshields, particularly by checking the property of the glass support at its edge its thickness and the nature of the bond resulting from the depositing of enamels and adhesive to its surface.
Although the Renault source has been developed in the context of the automotive industry it can be applied tackle different analytical questions. Particularly in the field of printed circuits, the possibility of determining content depth profiles of non conductive materials is crucial. Question that can be answer include layer thicknesses, inks deposited, the presence of unwanted oxides, etc.
- W Grimm, Naturwiss. 54, 586 (1967).
- M Chevrier and R Passetemps, European Patent No. 0 296 920 A1 (1988).
First published on the web: 15 May 2000.
Author: Thomas Nelis; The text is based on Richard Passetemps patent as found on the web.