High resolution scanning raman microscope

• US 6,002,471 A
• Filed: 11/04/1997
• Issued: 12/14/1999
• Est. Priority Date: 11/04/1996
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Quake, Stephen R.
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US08/964,295
• Time in Patent Office: 770 Days
• Field of Search: 356/301, 356/317, 356/318, 356/73, 356/376, 250/458.1, 250/459.1, 250/461.1, 250/461.2
• US Class Current: 356/73
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: B82Y 5/00 Nanobiotechnology or nanomedicine, e.g. protein engineering or drug delivery
• CPC Class Codes: G01N 2021/656 Raman microprobe
• CPC Class Codes: G01N 21/648 using evanescent coupling or surface plasmon coupling for the excitation of fluorescence
• CPC Class Codes: G01N 21/658 enhancement Raman, e.g. surface plasmons
• CPC Class Codes: G01Q 60/06 SNOM [Scanning Near-field Optical Microscopy] combined with AFM [Atomic Force Microscopy]
• CPC Class Codes: Y10S 977/87 Optical lever arm for reflecting light

Abstract

A method of obtaining high-resolution spectroscopic information from a scanning microscope. An optical beam is directed at a sample and light emitted from the sample (e.g., from Raman scattering or fluorescence) is collected. Resolution is improved by supporting a tiny conductive element (e.g., a silver particle) from a probe located within the optical beam area. The conductive element enhances the light emitted from molecules in the vicinity of the probe. The invention provides the high spatial resolution of microscopes such as the AFM with the high chemical detection sensitivity of surface enhanced Raman spectroscopy. This combination allows the isolation and differentiation of single molecules on surfaces of nanostructures.

Claims

1. A scanning microscope for obtaining high-resolution spectroscopic information, the microscope comprising:

a support stage, having surfaces for supporting a sample;

a first optical apparatus for directing an optical beam at the sample;

a second optical apparatus for collecting light emitted from the sample to reduce the background noise;

a spectral dissociating apparatus coupled to said second optical apparatus to dissociate light emitted from the sample for analysis;

a probe supporting a conductive element at a location within the optical beam area, the conductive element being configured to enhance emission of light from molecules in the vicinity of the conductive element; and

a probe height detection apparatus operatively connected with said probe to generate detection signals representing surface topography, said probe height detection apparatus detecting a change in surface profile by differencing a reference beam from a reflected signal of the reference beam.

2. The scanning microscope of claim 1, wherein the second optical apparatus is a spectrometer.

3. The scanning microscope of claim 1, wherein the emitted light is Raman scattered light.

4. The scanning microscope of claim 1, wherein the emitted light is fluorescence.

5. The scanning microscope of claim 3 or 4, wherein the area illuminated by the optical beam is greater than the area in which enhancement occurs in the vicinity of the conductive element.

6. The scanning microscope of claim 3 or 4, wherein the area illuminated by the optical beam is at least ten times greater than the area in which enhancement occurs in the vicinity of the conductive element.

7. The scanning microscope of claim 1, wherein the distance between the conductive element and the surface of the sample is controlled.

8. The scanning microscope of claim 7, wherein the probe is an atomic force microscope probe.

9. The scanning microscope of claim 1, wherein the support stage has a three dimensional scanning capability.

10. The scanning microscope of claim 1, wherein the surface of the conductive element has a curvature of less than or equal to 20 nm.

11. The scanning microscope of claim 1, wherein the probe comprises carbon nanotubes with a radius of curvature of less or equal to 5 nm.

12. The scanning microscope of claim 1, wherein the probe has pyramidal geometry.

13. The scanning microscope of claim 1, wherein the probe comprises silicon nitride.

14. The scanning microscope of claim 1, wherein the the conductive element comprises a conductive layer.

15. The scanning microscope of claim 14, wherein the conductive layer comprises a conductive particle.

16. The scanning microscope of claim 15, wherein the conductive particle is a sphere.

17. The scanning microscope of claim 15, wherein the conductive particle is an ellipsoid.

18. The scanning microscope of claim 15, wherein the conductive particle is a silver particle.

19. The scanning microscope of claim 1, wherein a photon counting avalanche photodiode is used to detect the optical signal.

20. The scanning microscope of claim 2, wherein the spectrometer comprises a diffraction grating and an image intensified charged coupled device (CCD) camera.

21. The scanning microscope of claim 1, wherein the probe oscillates in a tapping frequency which is used to modulate the detection signals generated by said probe height detection apparatus, such that the modulation increases probe sensitivity and operates to generate enhanced-quality surface topography.

22. The scanning microscope of claim 20, wherein the CCD camera is cooled.

23. The scanning microscope of claim 14, wherein the conductive element comprises a colloidal silver particle attached by surface adhesion forces.

24. The scanning microscope of claim 14, wherein the conductive element comprises metal particles selected from the group consisting of silver, gold, platinum, copper, and aluminum.

25. The scanning microscope of claim 14, wherein the conductive element comprises multiple metallic layers.

26. The scanning microscope of claim 1, wherein the probe comprises single crystalline silicon.

27. The scanning microscope of claim 1, wherein the probe comprises carbon.

28. The scanning microscope of claim 1, further comprising:

a detection system coupled to said spectral dissociating apparatus, said detection system receiving spectroscopic information of the dissociated light and generating optical image of the sample.

29. The scanning microscope of claim 1, wherein said second optical apparatus includes filters, pinholes, lenses, and mirrors.

30. A method of obtaining high-resolution spectroscopic and surface topographic information of a sample, the method comprising:

supporting the sample on a support stage;

directing an optical beam at the sample;

collecting light emitted from the sample through a series of filtering mechanisms to reduce the background noise;

spectrally dissociating light emitted from the sample;

supporting a conductive element from a probe at a location within the optical beam area, the conductive element being configured to enhance the light emitted from molecules in the vicinity of the conductive element;

generating a reference beam using a laser and coupling the reference beam to the probe;

receiving perturbations of the reference beam caused by the surface of the sample from the probe and transmitting the perturbations as a reflected signal; and

generating surface topography by differencing the reference beam from the reflected signal.

31. The method of claim 30, wherein the light emitted from the sample is Raman scattering.

32. The method of claim 30, wherein the light emitted from the sample is fluorescence.

33. The method of claim 30, wherein the area illuminated by the optical beam is greater than the area in which enhancement occurs in the vicinity of the conductive element.

34. The method of claim 30, wherein the area illuminated by the optical beam is at least ten times greater than the area in which enhancement occurs in the vicinity of the conductive element.

35. The method of claim 30, wherein the distance between the conductive element and the surface of the sample is controlled.

36. The method of claim 30, wherein the probe is an atomic force microscope probe.

37. The method of claim 30, wherein the support stage has a three dimensional scanning capability.

38. The method of claim 30, wherein the surface of the conductive element has a curvature of less than or equal to 20 nm.

39. The method of claim 30, wherein the probe comprises carbon nanotubes with a radius of curvature of less or equal to 5 nm.

40. The method of claim 30, wherein the probe has pyramidal geometry.

41. The method of claim 30, wherein the probe comprises silicon nitride.

42. The method of claim 30, wherein the the conductive element comprises a conductive layer.

43. The method of claim 42, wherein the conductive layer comprises a conductive particle.

44. The method of claim 43, wherein the conductive particle is a sphere.

45. The method of claim 43, wherein the conductive particle is an ellipsoid.

46. The method of claim 43, wherein the conductive particle is a silver particle.

47. The method of claim 30, wherein a photon counting avalanche photodiode is used to detect the optical signal.

48. The method of claim 30, wherein a spectrometer directs the optical beam and the spectrometer comprises a diffraction grating and an image intensified charged coupled device (CCD) camera.

49. The method of claim 30 applied to sequencing DNA by obtaining surface enhanced Raman scattering images of the four individual DNA bases.

50. The method of claim 31 applied to performing in situ diagnostic quality control of nanostructural electronic devices by scanning the probe over the surface of the nanostructures and obtaining surface enhanced Raman scattering spectra.

51. The method of claim 31 applied to detecting ultra-low level chemical components in a mixture by obtaining surface enhanced Raman scattering spectra.

52. The method of claim 30, further comprising:

generating optical image of the sample by using spectroscopic information of the dissociated light.