Near field scanning optical and force microscope including cantilever and optical waveguide

• US 5,354,985 A
• Filed: 06/03/1993
• Issued: 10/11/1994
• Est. Priority Date: 06/03/1993
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Stanford University
• Inventors: Quate, Calvin F.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): LE, QUE TAN
• Application Number:
  US08/072,286
• Time in Patent Office: 495 Days
• Field of Search: 250/234, 250/235, 250/306, 250/307, 250/216, 385/12
• US Class Current: 250/234
• 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: G01Q 20/04 Self-detecting probes, i.e. wherein the probe itself generates a signal representative of its position, e.g. piezoelectric gauge
• CPC Class Codes: G01Q 60/06 SNOM [Scanning Near-field Optical Microscopy] combined with AFM [Atomic Force Microscopy]
• CPC Class Codes: G01Q 60/22 Probes, their manufacture, or their related instrumentation, e.g. holders
• CPC Class Codes: G01Q 60/38 Probes, their manufacture, or their related instrumentation, e.g. holders
• CPC Class Codes: Y10S 977/862 Near-field probe
• CPC Class Codes: Y10S 977/863 Atomic force probe
• CPC Class Codes: Y10S 977/868 with optical means
• CPC Class Codes: Y10S 977/873 Tip holder

Abstract

A near field scanning optical microscope (NSOM) includes a cantilever which is aligned generally parallel to the surface of a sample. An optical waveguide extends along the cantilever to a tip which protrudes downward from the cantilever. A small aperture at the apex of the tip allows light radiation flowing through the waveguide to be directed toward the sample. The cantilever is vibrated, and variations in its resonant frequency are detected and delivered to a feedback control system to maintain a constant separation between the tip and the sample. The NSOM can also be operated as an atomic force microscope in either a contact or non-contact mode.

Claims

1. A cantilever for use in a near field optical scanning microscope, the cantilever comprising:

a flexible cantilever member having a free end and a fixed end,

a tip formed near the free end of the cantilever member, the tip extending from the cantilever member in a direction substantially perpendicular to a longitudinal axis of the cantilever member;

an optical waveguide positioned along the cantilever member and extending to an apex of the tip, an aperture for allowing light to escape from the waveguide being formed near the apex of the tip.

2. The cantilever of claim 1 wherein the optical waveguide has a first surface and a second surface, the first and second surfaces of the waveguide being substantially planar and parallel to each other.

3. The cantilever of claim 2 wherein the optical waveguide comprises a channel region, the thickness of the waveguide in the channel region being greater than the thickness of the waveguide in regions outside the channel region.

4. The cantilever of claim 2 comprising a buffer layer adjacent the second surface of the waveguide, the buffer layer having a ridge region, the thickness of the buffer layer in the ridge region being greater than the thickness of the buffer layer in regions outside the ridge region.

5. The cantilever of claim 2 wherein the waveguide comprises a means of focusing a beam of light at the tip.

6. The cantilever of claim 5 wherein the means of focusing comprises a convex lens.

7. The cantilever of claim 5 wherein the means of focusing comprises a concave lens.

8. The cantilever of claim 5 wherein the means of focusing comprises a Fresnel zone plate.

9. The cantilever of claim 1 wherein the tip is conical in shape.

10. The cantilever of claim 1 wherein the tip is tetrahedral in shape.

11. The cantilever of claim 1 wherein the cantilever comprises a piezoresistor for detecting bending of the cantilever.

12. The cantilever of claim 11 wherein the piezoresistor comprises doped silicon.

13. A near field scanning optical microscope (NSOM) comprising:

the cantilever of claim 1;

a scanner for scanning the cantilever with respect to a sample positioned in the NSOM;

a light source;

a means for directing a beam of light from the light source into the optical waveguide of the cantilever; and

a means of detecting the beam of light after it strikes the sample.

14. The NSOM of claim 13 further comprising:

a detection means for detecting the deflection of the cantilever;

a feedback control system connected to receive the output of the detection means; and

a means for altering the distance between the cantilever and the sample in response to an output from the feedback control system.

15. The NSOM of claim 14 wherein the detection means comprises a piezoresistor.

16. The cantilever of claim 1 wherein the optical waveguide is capable of carrying light in at least one of the transverse electric (TE) mode and the transverse magnetic (TM) mode.

17. The cantilever of claim 1 wherein the optical waveguide comprises Si₃ N₄.

18. The cantilever of claim 1 wherein the optical waveguide comprises one of a channel waveguide and a film waveguide.

19. The cantilever of claim 1 further comprising optical energy passing through the waveguide, the waveguide having a thickness approximately equal to one wavelength of said optical energy.

20. The cantilever of claim 1 further comprising a capacitive plate positioned adjacent said cantilever member.

21. The cantilever of claim 20 wherein a DC voltage applied to the capacitive plate displaces the cantilever member from a neutral position.

22. The cantilever of claim 20 wherein an AC voltage applied to the capacitive plate excites a mechanical resonance of the cantilever member.

23. The cantilever of claim 1 comprising a structure for focusing light at the tip.

24. The cantilever of claim 1 further comprising a structure for channeling light toward a centerline of the waveguide.

25. The cantilever of claim 1 wherein the tip is sharpened by an oxidation sharpening process.

26. The cantilever of claim 11 wherein the piezoresistor is U-shaped.

27. The cantilever of claim 26 wherein the cantilever member comprises arms extending on opposite sides of an open space, the optical waveguide being formed along a centerline of the cantilever member.

28. The NSOM of claim 14 wherein the cantilever deflects in response to an attractive force such as van der Waals force.

29. The NSOM of claim 14 further comprising a capacitive plate positioned adjacent said cantilever.

30. The NSOM of claim 29 wherein a DC voltage applied to the capacitive plate displaces the cantilever from a neutral position.

31. The NSOM of claim 29 wherein an AC voltage applied to the capacitive plate excites a mechanical resonance of the cantilever.

32. The NSOM of claim 14 wherein the detection means comprises a capacitive plate.

33. The NSOM of claim 32 wherein a DC voltage is applied to the capacitive plate to displace the cantilever from a neutral position.

34. The NSOM of claim 32 wherein an AC voltage applied to the capacitive plate excites a mechanical resonance of the cantilever.