Coherent evanescent wave imaging

• US 6,980,716 B1
• Filed: 03/29/2002
• Issued: 12/27/2005
• Est. Priority Date: 03/30/2001
• Status: Expired due to Fees

• Current Assignee: Arizona Board of Regents (University of Arizona)
• Original Assignee: Arizona Board of Regents (University of Arizona)
• Inventors: Wagner, Michael, Menendez, Jose, Diaz, Rodolfo E., Panchanathan, Sethuraman, Booksh, Karl S., Tseng, Ampere A.
• Primary Examiner(s): Williams, Joseph
• Assistant Examiner(s): MACCHIAROLO, PETER J
• Application Number:
  US10/112,006
• Time in Patent Office: 1,369 Days
• Field of Search: 385/129, 385/141, 385130-131, 385/14, 356/445, 359/296
• US Class Current: 385/30
• 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: G01N 21/453 Holographic interferometry for dimensional measurements G01B9/021 - G01B9/029
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G02B 6/1226 involving surface plasmon interaction

Abstract

Methods and apparatus for gathering image information from nanostructures includes a composite waveguide of conductive nanoparticles in a dielectric medium. The waveguide is irradiated with preferably coherent blue light to form a slow surface wave. The evanescent wave that is the “tail” of the surface wave exists outside the waveguide contiguous to its surface. The nanostructures are located to encounter the evanescent wave. The slowing of the wave that occurs in the waveguide reduces the wave'"'"'s speed and wavelength sufficiently such that nanostructures can be imaged. Upon encountering the evanescent wave, the nanostructures radiate. This radiation causes a backward scattering from the structures and a forward perturbation of the wavefront of the surface wave. From the scattering and perturbation information about the physical characteristics of the nanostructures sufficient to form an image is derived.

Claims

1. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave; and

(d) determining a characteristic of the nanostructure by observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure.

2. The method according to claim 1, wherein step (b) comprises irradiating the waveguide with coherent electromagnetic energy.

3. The method according to claim 2, wherein step (d) comprises detecting one or more of scattering of electromagnetic surface wave energy due to perturbation of the evanescent wave as a result of impingement of the evanescent wave on the at least one nanostructure.

4. The method according to claim 2, wherein step (d) comprises detecting one or more of scattering of electromagnetic surface wave energy in a direction backward of the direction of propagation of the surface wave and perturbation of a wavefront in the direction of surface wave propagation.

5. The method according to claim 2, wherein step (d) comprises observing at least one of subtractive interference and associative reinforcement of the surface wave with electromagnetic effects of the impingement of the evanescent wave on the at least one nanostructure.

6. The method according to claim 1, further comprising repositioning the at least one nanostructure angularly with respect to the direction of propagation of the evanescent wave, and step (d) comprising observing the effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure in each relative angular position of the at least one nanostructure and incident evanescent wave.

7. The method according to claim 1, wherein step (a) comprises providing a waveguide including an array of particles of conductive material spaced apart in a binder having a higher dielectric constant than the material of the particles, the particles being of a cross-sectional dimension in the range from 1 to 100 nm.

8. The method according to claim 7, wherein the particles are of a noble metal.

9. The method according to claim 7, wherein the particles are gold.

10. The method according to claim 7, wherein the particles are spaced apart at distances in a range of 1 to 100 nm.

11. The method according to claim 10, wherein the particles have a cross-sectional dimension in a range from 10 to 50 nm.

12. The method according to claim 11, wherein the particles are spaced apart by distances in a range of 10 to 50 nm.

13. The method according to claim 7, wherein the binder is SiO₂.

14. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave;

(d) observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure; and

wherein irradiating the waveguide comprises irradiating the waveguide with electromagnetic energy having a free space wave length in the range from 400 nm. to 1000 nm. to create within the first medium a surface wave that is a slow wave having a wavelength that is ten times smaller or less.

15. The method according to claim 14, wherein the electromagnetic energy is blue light having a wavelength in free space of substantially 488 nm.

16. The method according to claim 15, wherein irradiating the waveguide to produce a surface wave comprises directing the blue light toward the surface within the first medium at an angle towards a discontinuity at the surface effective to create the surface wave.

17. The method according to claim 16, wherein the discontinuity is a surface plasmon resonant nanosphere optically coupled by proximity to the waveguide surface.

18. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a coherent surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave; and

(d) observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure by providing a reference coherent electromagnetic wave and applying to the reference coherent electromagnetic wave at least one of scattered electromagnetic energy and perturbed electromagnetic energy of the surface wave resulting from impingement of the evanescent wave upon the at least one nanostructure.

19. The method according to claim 18, wherein providing a reference coherent electromagnetic wave comprises splitting the coherent electromagnetic energy irradiating the wave guide and diverting a portion of the electromagnetic energy irradiating the wave guide to produce the reference coherent electromagnetic wave.

20. The method according to claim 19, wherein splitting comprises locating a beam splitter in the path of the evanescent wave in advance of the at least one microstructure to split the evanescent wave into first and second waves, and further including directing the first wave onto the at least one nanostructures, and then to a location of comparative interaction, directing the second wave into the location of comparative interaction to produce at least one of subtractive interference and additive reinforcement between the first and second waves.

21. The method according to claim 20, wherein directing the first wave includes providing a first reflecting mirror in the path of propagation of the first wave intermediate the location of the at least one nanostructure and the location of comparative interaction to direct the first wave to the location of comparative interaction, and providing a second reflective mirror in the path of the second wave intermediate the beam splitter and the location of comparative interaction to direct the second wave to the location of comparative interaction for comparative interaction with the first wave.

22. The method according to claim 21, further comprising locating a detector at the location of comparative interaction to detect the comparative interaction of the first and the second waves.

23. The method according to claim 22, wherein locating a detector at the location of comparative interaction comprises locating a detecting device comprising a series of fluorescent elements at the location of comparative interaction, at least a number of the series of fluorescent elements emitting a fluorescent light of a color differing from other of the fluorescent elements upon fluorescing, each of the number of fluorescent elements having an identified and distinct location relative to the first and second waves, for receiving the first and second waves upon or subsequent to confluence thereof, whereby a color signature caused fluorescing of elements of the detecting device at various locations thereon is indicative of subtractive interference and additive reinforcement of the first and second waves and thereby physical characteristics of the at least one nanostructure.

24. The method according to claim 23, wherein step (a) comprises providing a structure having spaced, conductive particles suspended in a medium of lesser permittivity than the elements.

25. The method according to claim 24, wherein the spaced, conductive particles are gold.

26. The method according to claim 25, wherein the medium of lesser permittivity is SiO₂.

27. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave; and

(d) observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure; and

wherein step (c) comprises moving at least one of the waveguides and the at least one nanostructure to bring the at least one nanostructure from farther into closer proximity with the surface and step (d) comprises-observing the electromagnetic interactions between the evanescent wave and the at least one nanostructure at differing degrees of proximity to the surface.

28. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave;

(d) observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure; and

wherein the at least one nanostructure comprises a plurality of nanostructures of varying heights, step (c) comprises varying the proximity of the nanostructures to the surface, and step (d) comprises observing the electromagnetic interactions between the evanescent wave and the nanostructures at differing degrees of proximity to the surface.

29. A method of gathering information concerning nanostructure characteristics including:

(a) providing a waveguide of a first medium having a surface bounding a second medium;

(b) irradiating the waveguide with an electromagnetic wave to produce a surface wave at the surface bounding the second medium and an evanescent wave in the second medium contiguous with the surface;

(c) locating at least one nanostructure in the second medium proximate the surface where it will encounter the evanescent wave; and

(d) observing at least one effect of electromagnetic interactions between the evanescent wave and the at least one nanostructure; and

wherein irradiating the waveguide comprises providing a conductive member optically coupled to the waveguide, and illuminating the conductive member with a laser to create a plasmon irradiating the waveguide with coherent light as a substantially point source of light from which the surface wave emanates.

30. The method according to claim 29, further comprising collimating the surface wave emanating from the conductive member.

31. The method of claim 30, further comprising splitting the collimated, coherent surface wave into a reference collimated, coherent surface wave and a collimated, coherent nanostructure illuminating surface wave, illuminating the at least one nanostructure with the collimated coherent nanostructure-illuminating surface wave, and bringing together the reference wave and the nanostructure-illuminating wave for additive reinforcement and subtractive interference indicative of the physical characteristics of the at least one nanostructure.

32. The method of claim 31, further comprising locating a detector at a position where the reference and nanostructure illuminating waves have been brought together to detect the additive reinforcement and subtractive interference of the waves.

33. The method of claim 32, wherein locating a detector comprises providing a series of fluorescent detector particles at locations to be illuminated by the combined reference and nanostructure-illuminating waves, at least a plurality of the fluorescent detector particles at different locations on the detector having differing fluorescent characteristics to thereby emit different wavelengths of light when fluorescing, whereby the wavelengths of light emitted by the detector are indicative of locations on the detector illuminated by the combined reference and nanostructure illuminating waves.

34. The method of claim 33, wherein providing a series of fluorescent detector particles comprises providing the fluorescent detector particles in a linear array across the wavefronts of the combined reference and nanostructure-illuminating waves, the fluorescent characteristics of the fluorescent detector particles differing with differing positions along the array, whereby emissions of light of particular wavelengths by the detector are indicative of additive reinforcement of the reference and the nanostructure illuminating waves upon their being combined at locations across their respective wavefronts.

35. The method of claim 34, wherein the fluorescent detector particles are particles having a cross-sectional dimension in the range from 10 to 100 nm. coated with fluorescent coatings.

36. A structure examination transducer including an electromagnetic illumination pattern detector comprising an array of fluorescent particles, at least a plurality of the particles differing in fluorescent characteristic to emit light of different wavelengths upon fluorescing, means for directing electromagnetic illumination from a structure under examination to the array and means for directing to the array a reference electromagnetic illumination having a frequency causing interfering cancellation and reinforcing enhancement of the illumination from the structure whereby the frequencies of fluorescent emissions from the array are indicative of characteristics of the structure.

37. The transducer of claim 36, wherein the array of fluorescent particles of differing fluorescent characteristics have known locations in the array, whereby emission from the array of light having a profile of varying wavelengths will be indicative of varying illumination of locations on the array.

38. The transducer of claim 37, wherein the emitted light of different wavelengths is visible light exhibiting different colors, whereby the profile of varying wavelengths comprises a combination of colors, each of which is representative of a location on the array.

39. The transducer of claim 37, wherein the array is a linear array of the fluorescent particles, and the emitted light of different wavelengths is indicative of greater and lesser illumination at points along the linear array.

40. The transducer of claim 37, wherein the fluorescent particles are particles coated with fluorescent coatings.

41. The transducer of claim 36, wherein the fluorescent particles are particles of a cross-sectional dimension in a range from 1 to 100 nm.

42. In a transducer for examining nanostructures by irradiating with electromagnetic energy;

the improvement including a surface wave conducting waveguide for slowing the speed of electromagnetic energy irradiating the waveguide, and forming the surface wave therein, the waveguide comprising;

(a) an array of spaced conductive metal particles having cross-sectional dimensions in the range from 1 to 100 nm., and spaced 10 to 50 nm. apart,

(b) a binder material of higher dielectric constant coating the particles and filling separations therebetween.

43. The waveguide of claim 42, wherein the binder material is SiO₂.

44. The waveguide of claim 42, wherein the particles are gold.

45. The waveguide of claim 44, wherein the binder material is SiO₂.

46. The waveguide of claim 42, wherein the particles have a cross-sectional dimension in the range 10 to 50 nm. and are spaced 10 to 50 nm. apart in an array forming with the binder a planar surface for the propagation of a surface wave.

47. A nanostructure examination transducer including:

(a) a waveguide comprising an array of conductive, spaced-apart particles having cross-sectional dimensions in the range 1 to 100 nm. and an interstitial binder having a permittivity greater than that of the particles, said waveguide forming a surface for the propagation of a slow surface wave,

(b) means for coupling a source of radiant energy to the waveguide,

(c) a detector coupled to the waveguide, and

(d) means for locating nanostructures in proximity to the surface to be irradiated by an exponentially decaying evanescent wave associated with a slow surface wave propagated at the surface.

48. The transducer according to claim 47, further comprising:

(e) means for adjusting the relative position of the waveguide surface and the means for locating the nanostructures.

49. The transducer according to claim 47, further comprising a splitter located in a path of propagation of the surface wave for splitting the surface wave into a nanostructure-illuminating wave and a reference wave, a first mirror structure in the path of the first wave to direct the first wave to a location of comparison of the first and second waves and a second mirror structure in the path of the second wave to direct the second wave to the location of comparison and said detector being located to receive recombined first and second wave electromagnetic energy forming patterns of additive reinforcement and subtractive interference indicative of structural characteristics of the nanostructure affecting the first wave.

50. The transducer according to claim 49, wherein the means for coupling a source of radiant energy includes a source of coherent light.

51. The transducer according to claim 50, wherein the source of coherent light is a laser.

52. The transducer according to claim 51, wherein the laser is a source of blue light having a wavelength of substantially 488 nm.

53. The transducer according to claim 51, further comprising a collimating lens for collimating the coherent light prior to its reaching the splitter.

54. The transducer according to claim 47, wherein the means for coupling a source of radiant energy includes a source of light having a wavelength of 400 to 1000 nm. and the waveguide is adapted to slow the light to 1/10 or less of its speed in free space.

55. The transducer according to claim 54, wherein the particles of the waveguide are spaced apart 1 to 50 nm.

56. The transducer according to claim 55, wherein the particles are gold and the binder is SiO₂.

57. A method of displaying characteristics of an object comprising:

(a) illuminating the object with electromagnetic energy;

(b) providing an array of discrete fluorescent units having varying wavelengths of fluorescence when illuminated;

(c) providing a reference illumination of electromagnetic energy illuminating the array;

(d) directing the illuminating electromagnetic energy that has illuminated the object to the array;

whereby fluorescent emissions from the array represent reinforcing combining of the reference illumination and the illuminating electromagnetic energy, and a lack of fluorescent emissions from the array represents a canceling combining of the reference illumination and the illuminating electromagnetic energy.

58. The method according to claim 57, wherein illuminating the object with electromagnetic energy comprises directing electromagnetic energy to a waveguide to produce in the waveguide a surface wave and an evanescent wave extending outwardly of the waveguide, and locating the object for irradiation by an evanescent electromagnetic wave from the waveguide.

59. The method according to claim 58, wherein the object is a nanostructure and step (a) comprises locating the nanostructure proximate a surface of the waveguide, at which the surface wave is produced so as to be irradiated by the evanescent wave.

60. The method according to claim 57, wherein step (c) comprises:

(i) providing a beam splitter; and

(ii) illuminating the beam splitter with electromagnetic energy to divide the electromagnetic energy into the reference illumination and illuminating electromagnetic energy.

61. The method according to claim 60, further comprising providing reflecting means for redirecting at least one of the reference illumination and the illuminating electromagnetic energy to the array of discrete fluorescent units.

62. The method according to claim 61, wherein the array of discrete fluorescent units is a linear array.

63. The method according to claim 62, wherein providing reflecting means comprises locating the reflecting means to direct the reference illumination and the illuminating electromagnetic energy to opposite sides of the linear array.

64. The method according to claim 57, wherein the array of discrete fluorescent units is a linear array.

65. The method according to claim 57, wherein steps (a) and (c) directing coherent electromagnetic energy to the object and the array.