Raman spectroscopy

• US 20100067000A1
• Filed: 09/07/2005
• Published: 03/18/2010
• Est. Priority Date: 09/10/2004
• Status: Abandoned Application

• Current Assignee: University of Southampton
• Original Assignee: University of Southampton
• Inventors: Pelfrey, Suzanne, Bartlett, Phillip N., Sugawara, Yoshihiro, Baumberg, Jeremy J., Russell, Andrea, Abdelsalam, Mamdouh
• Application Number:
  US11/575,043
• Publication Number:
  US 20100067000A1
• Time in Patent Office: Days
• US Class Current: 356/301
• CPC Class Codes: G01N 21/658 enhancement Raman, e.g. surface plasmons

Abstract

It has been discovered that specially structured metallic films containing voids can deliver a hugely enhanced surface enhanced Raman spectroscopy (SERS) effect. By selecting a particular size and geometry for the voids, metallic films can be provided which have an enhanced photon-to-plasmon conversion efficiency for incident radiation of a predetermined wavelength. Controllable surface-enhanced absorption and emission characteristics may thus be provided, which are useful for SERS and potentially also other optical spectrometry and filtering applications. With such a large Raman signal, the invention enables fast, compact and inexpensive Raman spectrometers to be provided opening up many new application possibilities.

Claims

1. A spectrometer for obtaining a Raman spectrum from a sample material, the spectrometer comprising:

an optical source for generating optical radiation;

a substrate for receiving the optical radiation, the substrate comprising a metallic film incorporating a plurality of voids of a predetermined size for confining surface plasmons, wherein the surface plasmons are for coupling energy from the optical radiation to a sample material when located proximal the substrate and for converting scattered energy emitted from the sample material into Raman scattered radiation; and

a spectral analyser for analysing the Raman scattered radiation emerging from the substrate.

2. The spectrometer of claim 1, wherein the voids have the shape of a truncated sphere.

3. The spectrometer of claim 2, wherein the voids have a diameter from about 50 nm to about 10,000 nm.

4. The spectrometer of claim 1, wherein the substrate is generally planar in shape and the voids are uniformly spaced over at least part of a planar surface of the substrate.

5. The spectrometer of claim 1, wherein the substrate further comprises a waveguide structure for coupling the optical radiation to a sample material through the metallic film.

6. The spectrometer of claim 5, wherein the spectral analyser is further configured to collect Raman scattered radiation that emerges from the waveguide.

7. The spectrometer of claim 1, wherein the spectral analyser comprises input channel optics for collecting the Raman scattered radiation emerging from the substrate.

8. The spectrometer of claim 7, wherein the input channel optics has a numerical aperture less than 0.4.

9. The spectrometer of claim 7, wherein the input channel optics comprises a fibre optic input channel oriented towards the substrate.

10. The spectrometer of claim 1, wherein optical source comprises a laser diode array.

11. A method of obtaining a Raman spectrum from sample material, the method comprising:

providing a Raman spectrometer comprising;

an optical source for generating optical radiation;

a substrate for receiving the optical radiation, the substrate comprising a metallic film incorporating a plurality of voids of a predetermined size for confining surface plasmons, wherein the surface plasmons are for coupling energy from the optical radiation to a sample material when located proximal the substrate and for converting scattered energy emitted from the sample material into Raman scattered radiation; and

a spectral analyser for analysing the Raman scattered radiation emerging from the substrate;

introducing sample material into the spectrometer proximal to the substrate;

activating the optical source; and

operating the spectral analyser to provide the Raman spectrum of the sample material.

12. The method of claim 11, wherein the step of introducing sample material comprises flowing a fluid containing the sample material across the substrate in a region illuminated by the optical radiation.

13. The method of claim 11, further comprising varying the electric potential of the metallic film of the substrate.

14. A method of making a substrate having an enhanced efficiency of coupling optical energy to surface plasmons at a predetermined wavelength of optical radiation incident upon the substrate, the method comprising:

determining the size and shape of voids which when formed in a metallic film efficiently couple optical energy at the predetermined wavelength to surface plasmons that form in the voids; and

forming a substrate comprising a metallic film that includes a plurality of voids of the determined size and shape.

15. The method of claim 14, comprising forming voids in the metallic film that are uniformly spaced over a surface of the substrate.

16. The method of claim 14, further comprising forming a waveguide structure in the substrate for coupling optical radiation from the substrate through the metallic film.

17. The method of claim 14, wherein determining the size and shape of the voids comprises determining the size and shape of a truncated spherical void.

18. The method of claim 17, wherein the diameter of the truncated spherical void is chosen to be of the same order of magnitude as the predetermined wavelength of optical radiation.

19. The method of claim 18, wherein voids have a diameter from about 50 nm to about 10,000 nm.

20. The method of claim 17, wherein the thickness of the voids is chosen so as to couple optical energy at the predetermined wavelength to zero-dimensional plasmons that form in the voids.

21. The method of claim 14, wherein the step of forming a substrate comprises:

depositing a template of ordered spherical particles on a substrate surface; and

passing a predetermined amount of charge though a metallic ion containing solution that surrounds the template so as to deposit the metallic film on the substrate surface.

22. A substrate made according to the method of claim 14.

23. The substrate of claim 22, wherein the metallic film comprises one or more of the following materials:

gold, platinum, silver, copper, palladium, cobalt and nickel.

24. The substrate of claim 22, further comprising a sample material for analysis provided in the voids of the metallic film.

25. The substrate of claim 24, wherein the sample material is an organic material that selectively binds to a specific target molecule.

26. An optical device incorporating the substrate according to claim 22.

27. (canceled)