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Use of Gratings to Detect Small Quantities of Materials by Raman

IP.com Disclosure Number: IPCOM000052044D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Gordon, JG: AUTHOR [+2]

Abstract

The sensitivity of Raman spectroscopy can be improved by a factor of 10 by depositing the sample to be analyzed on a grating especially designed for efficient excitation of surface plasmons at the frequency of the exciting laser light. The angle of incidence of the laser beam onto the grating is also adjusted for maximum surface plasmon excitation. By this technique we have been able to detect layers of polymer 100 angstroms thick and 6 monolayers of cadmium arachidate. We have extended the measurements to layers one monolayer thick.

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Use of Gratings to Detect Small Quantities of Materials by Raman

The sensitivity of Raman spectroscopy can be improved by a factor of 10 by depositing the sample to be analyzed on a grating especially designed for efficient excitation of surface plasmons at the frequency of the exciting laser light. The angle of incidence of the laser beam onto the grating is also adjusted for maximum surface plasmon excitation. By this technique we have been able to detect layers of polymer 100 angstroms thick and 6 monolayers of cadmium arachidate. We have extended the measurements to layers one monolayer thick.

In previous work the samples were deposited on the bare unprotected surface of the metal grating. This is not satisfactory for an analytical device because it cannot be used repetitively. Instead, we use a grating coated with a very thin continuous SiO(2) overlayer to protect the metal from corrosion. Other transparent protective materials, such as S(3)N(4), could also be used.

For quantitative analytical purposes it would be useful to have an internal Raman standard so that relative intensity measurements could be made, since it is very difficult to make absolute Raman intensity measurements. Making the protective film a polymer would provide such an internal standard. The only requirements are that the polymer Raman lines not overlap those of the sample. Particularly suitable materials would be plasma polymerized hydrocarbons and fluorocarbon films since thin, impervi...