Applications of raman spectroscopy

Raman spectroscopy and its applications in various field with the help of raman spectrometer

1. APPLICATIONS OF RAMAN SPECTROSCOPY Submitted by, KAAVYA B Holy Cross College, Trichy 2

2. Resonance Raman Scattering Raman microscopy Surface Enhanced Raman scattering CARS Applications In a) Medical b) Forensic c) Inspection of products d) Art e)Geology f) Nanotechnology Conclusion 2 OUTLINE

3. Many substances, especially colored ones, may absorb laser beam energy and generate strong fluorescence, which contaminates Raman spectrum. It was discovered that instead of fluorescence some type of colored molecules could produce strong Raman scattering at certain condition.This effect is Resonance Raman . 3 Resonance Raman Spectroscopy

4. In RRS the λ of incoming laser is selected to coincide with an electronic transition of the molecule or material. Raman signal is amplified for about 10 6 magnitude orders. Extensively used for biological molecules. Detection of dilution solution possible (concentration—10 -3 M) All kinds of samples are analyzed . 4

5. It can be used to measure the atomic displacement between ground state & excited state. It can be used in the analysis of air pollutants,aerosol particles etc., 5

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7. Highly monochromatic tunable lasers are used. Glass can be used for windows, lenses, and other optical components . When resonance Raman spectra are recorded, however, sample heating and photo-bleaching can cause damage and a change to the Raman spectrum obtained 7 Instrumentation

8. Although scattered light leaves the sample in all directions the collection of the scattered light is achieved only over a relatively small solid angle by a lens and directed to the spectrograph and CCD detector. The laser beam can be at any angle with respect to the optical axis used to collect Raman scattering. 8

9. The collected scattered radiation is focused into a spectrograph, in which the light is first collimated and then dispersed by a diffraction grating and refocused onto a CCD camera 9

10. It consists of optical microscope, and adds an excitation laser, laser rejection filters, a spectrometer or monochromator , and an optical sensitive detector such as a charge-coupled device (CCD ) It uses 2 lasers---- one of them produces RR spectrum & other monitors the position of the objective over the sample through CCD. 10 Raman Microscope

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12. The optical microscope uses light to magnify and identify samples while the Raman spectrometer scatters light and measures the excitation vibration. The back scattered radiation from the sample is imagined on to the entrance slit of a monochromator . The data by the computer gives details regarding the sample at the position monitored by the CCD camera. 12

13. Raman microscopy of inorganic specimens such as rocks and ceramics can use a broader range of excitation wavelengths. Optical microscope + Raman spectrometer = high resolution images of small samples. It is useful in studying phase transition in molecular crystals. 13

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15. It is an ideal tool for trace analysis Better to study highly diluted solutions Raman signal can be amplified by the adsorption of molecules in certain metallic surfaces--- surface enhanced raman scattering. It permits the study of surface interactions, adsoption process, electrode reactions, single molecule detection. 15 Surface Enhanced Raman Spectroscopy

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17. 2 mechanisms— A.Electromagnetic model : interactions among the incident EM radiations with the surfaces. B.Charge transfer/chemical model : interactions between adsorbed molecules with the metallic atoms involved in adsorption. Greatest enhancement --when excitation λ is near plasma frequency of metal. 17

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19. Output is not linearly proportional to its input. It can effectively reduce the influence of fluorescence. Hyper Raman Spectroscopy, Coherent anti stokes Raman Spectroscopy, Coherent stokes Raman spectroscopy, Stimulated Raman gain and inverse raman spectroscopy. 19 Nonlinear Raman spectroscopy

20. When tunable lasers generate frequency which equals the anti stokes scattering frequency , there is a signal enhancement. And the vibrational transitions equals the energy difference between the two light sources. CARS signal is anti stokes region. It is useful for molecules with high fluorescence effect. 20

21. Bio molecules are highly raman active due to their non polar molecular structure, the abundance of water do not interfere with the spectra due to the extreme polarity of water molecules. This dichotomy between the scattering cross section of biological macromolecules and water is what allows raman to be used on both tissues. 21 Medical

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26. Quality control of crystalline silicon are tested. Orientation of silicon molecular structure will affect raman spectra. For pure crystalline silicon , there is only one allowed molecular vibration peak 521cm -1 If wafer undergoes any stress or strain correspondingly the peak will reduce. 26 Silicon Wafer Testing

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28. Laser can be focused through optically transparent packaging allowing the content to be analyzed without opening it Ava spec mini weighs 175 grams and of dimensions 95mm x65mm x20mm 28 Inspection of products

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30. Raman data can be obtained from almost  any surface , allowing minute traces  of explosives  or a firearm’s discharge to be  detected  without attempting to lift samples  from evidence. Raman spectroscopy is highly sensitive to  minute  chemical  differences between inks. 30 Forensic

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33. Identification of individual pigments and their degradation product leads to insight into the working method of artist. It also gives information about the original state of painting. 33 ART

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35. It helps us to know whether the sample is polarizable or not.– Raman scattering occur after a dipole is induced in a molecule by the incident radiation. It also indicates the compostion,structure,stability & vibrational levels within the sample Concentration of the scatter is found. 35 Conclusion

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