Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1997-12-03
1999-11-02
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
25033906, 2504581, 250244, G01N 2100, G01N 2101
Patent
active
059775459
DESCRIPTION:
BRIEF SUMMARY
Subject matter of the invention are sample carriers for use in infrared transmission spectroscopy that have a sample zone alternatively referred to as a sample platform and a holder for holding said sample zone. Moreover, the layer thickness of the sample zone is less than one quarter of the shortest wavelength of the radiation used within the material of said zone.
Also disclosed is the application of sample carriers in quantitative infrared transmission spectroscopy, and a method and a system for performing transmission spectroscopy using said sample carriers. A further embodiment concerns sample carriers for use in IR transmission spectroscopy that have at least two sample zones on a common holder, and in which these (at least) two sample zones are made from materials that do not have any common absorbance bands with an absorbance greater than 0.1 in the infrared range used.
Sample carriers for use in infrared spectroscopy are known in the prior art that are shaped like a plane-parallel plate made from materials that are as permeable to infrared radiation as possible. German patent DE 4030699 describes such sample carriers as the prior art and proposes an improvement to said carriers in which the sample carrier is designed as a converging lens. The sample carrier materials disclosed in the prior art are potassium bromide, zinc selenide, sodium chloride and other materials that are permeable to infrared radiation. The materials used in the prior art have a thickness of many millimeters to ensure sufficient mechanical stability.
Also known from the prior art are infrared sample carriers from 3M called "disposable IR cards". These sample carriers consist of a cardboard strip with an opening. The opening in the cardboard is closed with a sample zone made from either polyethylene or PTFE (poly-tetrafluoro-ethylene). The 3M sample carriers have the disadvantage that the absorption bands of polyethylene and PTFE may overlap the absorptions of the sample material to be tested. In particular, each of the materials used in the sample zone has relatively strong bands that usually cannot be eliminated, even using differential measurement. Such sample carriers can therefore usually not be used to perform quantitative analysis.
The object of the present invention was to propose easy-to-use sample carriers that, due to their characteristics in the infrared range, make it possible to perform quantitative infrared spectroscopy. The object is solved by the sample carriers according to the invention that have a holder to hold a sample zone, and a sample zone with a layer thickness less than one quarter of the shortest wavelength of the radiation used within the sample material. In developing suitable sample carriers, the first attempt was to improve the sample carriers known in the prior art by decreasing the layer thickness. Experiments using sample carriers with a layer thickness in the range of 20 .mu.m did not yield convincing results. It was not possible to quantitatively reproduce spectra that were absorbed by semiconductive materials with this layer thickness. It was shown that interference phenomena appear that strongly depend on the thickness of the material, so that even relatively small deviations in the thickness of the sample zone due to manufacture lead to fluctuations in intensity. Moreover, wavelength-dependent fluctuations in intensity appear in thicknesses of many micrometers that overlap the spectrum of the sample, making it very difficult or impossible to perform a quantitative evaluation. Surprisingly, quantitatively reproducible spectra can only be absorbed in an area that is less than 1000 nm thick. It has been shown that the sample zone should have a layer thickness that is less than one quarter of the wavelength of the shortest measurement wavelength within the material of said zone. The upper limit of thickness for the sample zone depends on the material from which it is made, due to the known fact that the wavelength depends on the refractive index of the material in which the wavelength propaga
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"Optical Characterization of Diamond Synthesized Using CH.sub.4 -CO.sub.2 gas mixtures without supplying hydrogen gas", Chen et al, Thin Solid Films 253, ElSevier, 1994, pp. 162-167.
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Haar Hans-Peter
Werner Gerhard
Hannaher Constantine
Israel Andrew
Roche Diagnostics GmbH
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