Radiant energy – Electron energy analysis
Patent
1988-01-27
1989-08-15
Berman, Jack I.
Radiant energy
Electron energy analysis
250306, 378 45, 378143, 378147, H01J 37256, G01N 23227
Patent
active
048577308
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus and a method for local chemical analyses at the surface of solid materials by X ray photoelectron spectroscopy.
X ray photoelectron spectroscopy (XPS) involves irradiating a sample located in an ultra high vacuum enclosure with x-ray photons photons and analyzing the photoelectrons emitted by the sample. The energy spectrum of the photoelectrons is used to discover the chemical composition of the surface as well as the nature of the chemical bonds found in the surface layers of atoms and molecules. Sources of x-ray photons include an x-ray tube of the:
type used in radiography or radiocrystallography, which is essentially composed of an anode bombarded by an electron beam,
synchrotron radiation provided by some particle accelerators
and the source recommended by the J. CAZAUX method from Universite de REIMS wherein the sample or the sample support acts as an anode. In the CAZAUX method, one of the faces is bombarded by an electron beam and, if the sample and its support are thin enough, photoelectrons are generated on the opposite face.
Using one of the above mentioned x-ray sources typically results in an area of examination of approximately 10 mm.sup.2.
Various techniques are known for reducing the area analyzed with these x-ray sources.
One technique involves collimating the x-ray source, wherein the irradiated area is reduced. However the flux of x-ray photons is correspondingly decreased and the signal-to-noise ratio of the detected signals suffers.
Another method is to reduces the analyzed area by placing a device at the analyzer input or otherwise reducing the field of observation. Once again the signal-to-noise ratio is reduced.
Reduction has been achieved by focusing the X rays with a grating. However, this reduction is also achieved at the expense of a significant loss of the signal-to-noise ratio, thus requiring the use of a multicollecting detector,
When using the CAZAUX method of generating x ray photons in a thin anode a focused electron beam reduces the area, however the thin sample must be integral with the anode.
At the present time, the CAZAUX method gives the best resolution, i.e. some microns, but it only applies to thin samples, thus considerably restricting its range of application. The CAZAUX method requires samples of the order of 0,1 to 1 micron, and, it is obvious to those skilled in the art that serious problems arise with samples of such a size. First, such samples are difficult to obtain additionally, the technique of surface analysis is extremely difficult to control with such thin sample surfaces, the analyzed thickness of which may sometimes be of the order of some atomic monolayers. It is also essential to clean the sample, which of course causes problems in itself.
When X rays are to be focused by a grating, the cost of the x-ray source and the monochromator is greater than 1,000,000 francs ($165,000).
The price of a conventional x-ray source with its supply is of the order of 300,000 to 500,000 francs ($50,000 to $85,000).
The present invention provides an apparatus and a method for local chemical analyses at the surface of solid materials by X ray photoelectron spectroscopy. Furthermore, there are no strict limitations due to the sample size which may range in size greatly and analyses can be carried out on a surface, the diameter of which may vary from about 100 microns to 1 millimeter, at relatively little expense.
The apparatus of the present invention enables local chemical analyses at the surface of solid materials by X ray photoelectron spectroscopy and the simultaneous observation of the analyzed area of the sample by scanning electron microscopy. This allows for noting the presence of anomalous surface features that may affect the analysis.
More specifically, the present invention is an apparatus for local chemical analyses at the surface of solid materials by X-ray photoelectron spectroscopy that utilizes:
an ultra high vacuum analysis chamber housing the sample to be analyzed. The sample is connected to a manipulato
REFERENCES:
patent: 3963922 (1976-06-01), Zulliger et al.
Berman Jack I.
Instruments S.A.
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