Abstract

We investigate the limits of one-photon fluorescence as a contrast mechanism in nanoscale-resolution tip-enhanced optical microscopy. Specifically, we examine the magnitude of tip-induced signal enhancement needed to resolve individual fluorophores within densely-packed ensembles. Modulation of fluorescence signals induced by an oscillating tip followed by demodulation with a lock-in amplifier increases image contrast by nearly two orders of magnitude. A theoretical model of this simple modulation/demodulation scheme predicts an optimal value for the tip-oscillation amplitude that agrees with experimental measurements. Further, as an important step toward the eventual application of tip-enhanced fluorescence microscopy to the nanoscale structural analysis of biomolecular systems, we show that requisite signal enhancement factors are within the capabilities of commercially available silicon tips.

© 2008 Optical Society of America

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  1. L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
    [CrossRef]
  2. Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
    [CrossRef]
  3. H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
    [CrossRef] [PubMed]
  4. J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
    [CrossRef] [PubMed]
  5. C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
    [CrossRef]
  6. H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
    [CrossRef]
  7. A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
    [CrossRef] [PubMed]
  8. V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
    [CrossRef]
  9. E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
    [CrossRef]
  10. E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
    [CrossRef]
  11. T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
    [CrossRef]
  12. R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
    [CrossRef]
  13. L. Novotny and B. Hecht, Principles of Nano-Optics (Cambridge, 2006).
  14. R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
    [CrossRef] [PubMed]
  15. B. Knoll and F. Keilmann, "Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy," Opt. Commun. 182, 321-328 (2000).
    [CrossRef]
  16. R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
    [CrossRef]
  17. P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
    [CrossRef]
  18. F. Keilmann and R. Hillenbrand, "Near-field microscopy by elastic light scattering from a tip," Phil. Trans. R. Soc. London, Ser. A 362, 787-805 (2004).
    [CrossRef] [PubMed]
  19. J. W. Strutt, "On the resultant of a large number of vibrations of the same pitch and of Arbitrary Phase," Philos. Mag. X, 73-78 (1880).

2006 (3)

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
[CrossRef]

2004 (3)

F. Keilmann and R. Hillenbrand, "Near-field microscopy by elastic light scattering from a tip," Phil. Trans. R. Soc. London, Ser. A 362, 787-805 (2004).
[CrossRef] [PubMed]

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

2003 (3)

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
[CrossRef] [PubMed]

2002 (1)

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

2001 (1)

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

2000 (3)

B. Knoll and F. Keilmann, "Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy," Opt. Commun. 182, 321-328 (2000).
[CrossRef]

R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
[CrossRef]

T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
[CrossRef]

1999 (1)

E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

1997 (2)

L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
[CrossRef]

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

1880 (1)

J. W. Strutt, "On the resultant of a large number of vibrations of the same pitch and of Arbitrary Phase," Philos. Mag. X, 73-78 (1880).

Aizpurua, J.

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

Allegrini, M.

P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
[CrossRef]

Bachelier, G.

P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
[CrossRef]

Bian, R. X.

L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
[CrossRef]

Cox, J. R.

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

Dorn, R.

R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
[CrossRef] [PubMed]

Felderer, K.

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

Frey, H. G.

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

Gallagher, A.

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

Gerton, J. M.

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

Gucciardi, P. G.

P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
[CrossRef]

Guckenberger, R.

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

Hamann, H. F.

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

Hanarp, P.

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

Hartschuh, A.

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

Hillenbrand, R.

F. Keilmann and R. Hillenbrand, "Near-field microscopy by elastic light scattering from a tip," Phil. Trans. R. Soc. London, Ser. A 362, 787-805 (2004).
[CrossRef] [PubMed]

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
[CrossRef]

Holtom, G. R.

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

Keilmann, F.

F. Keilmann and R. Hillenbrand, "Near-field microscopy by elastic light scattering from a tip," Phil. Trans. R. Soc. London, Ser. A 362, 787-805 (2004).
[CrossRef] [PubMed]

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
[CrossRef]

B. Knoll and F. Keilmann, "Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy," Opt. Commun. 182, 321-328 (2000).
[CrossRef]

Knoll, B.

B. Knoll and F. Keilmann, "Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy," Opt. Commun. 182, 321-328 (2000).
[CrossRef]

R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
[CrossRef]

Kuno, M.

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

Lessard, G. A.

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
[CrossRef]

Leuchs, G.

R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
[CrossRef] [PubMed]

Ma, Z.

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

Mu, C.

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

Nesbitt, D. J.

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

Novotny, L.

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
[CrossRef]

Protasenko, V. V.

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

Quabis, S.

R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
[CrossRef] [PubMed]

Quake, S. R.

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
[CrossRef]

Sanchez, E. J.

E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

Snchez, E. J.

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

Strutt, J. W.

J. W. Strutt, "On the resultant of a large number of vibrations of the same pitch and of Arbitrary Phase," Philos. Mag. X, 73-78 (1880).

Sutherland, D. S.

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

Wade, L. A.

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

Witt, S.

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

Xie, C.

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

Xie, X. S.

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
[CrossRef]

Yang, T. J.

T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
[CrossRef]

Appl. Phys. Lett. (3)

C. Xie, C. Mu, J. R. Cox, and J. M. Gerton, "Tip-enhanced fluorescence microscopy of high-density samples," Appl. Phys. Lett. 89, 143117 (2006).
[CrossRef]

T. J. Yang, G. A. Lessard, and S. R. Quake, "An apertureless near-field microscope for fluorescence imaging," Appl. Phys. Lett. 76, 378-380 (2000).
[CrossRef]

R. Hillenbrand, F. Keilmann, P. Hanarp, D. S. Sutherland, and J. Aizpurua, "Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe," Appl. Phys. Lett. 83, 368-370 (2003).
[CrossRef]

J. Appl. Phys. (1)

P. G. Gucciardi, G. Bachelier, and M. Allegrini, "Far-field background suppression in tip-modulated apertureless near-field optical microscopy," J. Appl. Phys. 99, 124309 (2006).
[CrossRef]

J. Chem. Phys. (1)

H. F. Hamann, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Molecular fluorescence in the vicinity of a nanoscopic probe," J. Chem. Phys. 114, 8596-8609 (2001).
[CrossRef]

J. Microsc (1)

R. Hillenbrand, B. Knoll, and F. Keilmann, "Pure optical contrast in scattering-type scanning near-field microscopy," J. Microsc  202, 77-83 (2000).
[CrossRef]

J. Phys. Chem. A (1)

E. J. Sanchez, L. Novotny, G. R. Holtom, and X. S. Xie, "Room-temperature fluorescence imaging and spectroscopy of single molecules by two-photon excitation," J. Phys. Chem. A 101, 7019-7023 (1997).
[CrossRef]

Opt. Commun. (2)

B. Knoll and F. Keilmann, "Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy," Opt. Commun. 182, 321-328 (2000).
[CrossRef]

V. V. Protasenko, M. Kuno, A. Gallagher, and D. J. Nesbitt, "Fluorescence of single ZnS overcoated CdSe quantum dots studied by apertureless near-field scanning optical microscopy," Opt. Commun. 210, 11-23 (2002).
[CrossRef]

Phil. Trans. R. Soc. London, Ser. A (1)

F. Keilmann and R. Hillenbrand, "Near-field microscopy by elastic light scattering from a tip," Phil. Trans. R. Soc. London, Ser. A 362, 787-805 (2004).
[CrossRef] [PubMed]

Philos. Mag. (1)

J. W. Strutt, "On the resultant of a large number of vibrations of the same pitch and of Arbitrary Phase," Philos. Mag. X, 73-78 (1880).

Phys. Rev. Lett. (7)

R. Dorn, S. Quabis, and G. Leuchs, "Sharper focus for a radially polarized light beam," Phys. Rev. Lett. 91, 233901 (2003).
[CrossRef] [PubMed]

E. J. Sanchez, L. Novotny, and X. S. Xie, "Near-field fluorescence microscopy based on two-photon excitation with metal tips," Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

A. Hartschuh, E. J. Snchez, X. S. Xie, and L. Novotny, "High-Resolution Near-Field Raman Microscopy of Single-Walled Carbon Nanotubes," Phys. Rev. Lett. 90, 095503 (2003).
[CrossRef] [PubMed]

L. Novotny, R. X. Bian, and X. S. Xie, "Theory of Nanometric Optical Tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
[CrossRef]

Z. Ma, J. M. Gerton, L. A. Wade, and S. R. Quake, "Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution," Phys. Rev. Lett. 97, 260801 (2006).
[CrossRef]

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-resolution imaging of single fluorescent molecules with the optical near-field of a metal tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-enhanced fluorescence microscopy at 10 nanometer resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

Other (1)

L. Novotny and B. Hecht, Principles of Nano-Optics (Cambridge, 2006).

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Figures (6)

Fig. 1.
Fig. 1.

(Color Online) Experimental setup for TEFM. Labeled elements are as follows: He-Ne Laser — helium-neon laser (λ=543 nm); Mask — laser-beam mask; RPC — radial polarization converter; DM — dichroic mirror; OBJ — microscope objective; Probe — AFM probe; PZT — piezoelectric transducer; SF — spectral filters; APD — avalanche photodiode; LA — lock-in amplifier; DDS — digital synthesizer; PC — personal computer. The arrows indicate the polarization of the laser beam. Axial polarization at the sample plane can be achieved either by simply focusing a radially polarized laser beam, or by placing a laser beam mask before the microscope objective such that only super-critical rays are allowed to propagate. This focused total internal reflection fluorescence (TIRF) set-up is sometimes used because of its broadband capabilities and its large focal spot (~1.5 µm×0.5 µm) lends itself to easy tip alignment, while radial polarization is preferred for smaller focal spots, ~(250 nm)2.

Fig. 2.
Fig. 2.

Cartoon of a fluorescent particle imaged by TEFM and the corresponding signal profile.

Fig. 3.
Fig. 3.

(Color Online) Phase-space plot showing how photon arrivals (vertical lines) are correlated to tip-oscillation phase. Squiggly arrows represent photons emitted from fluorophores within the laser focus. Higher photon count rates occur at a preferred phase θp corresponding to tip-sample contact, resulting in the strongest near-field signal.

Fig. 4.
Fig. 4.

(Color Online) Expected phase dependency of lock-in signal. Each detected photon is considered as a unit vector with a direction corresponding to the instantaneous oscillation phase of the tip. A lock-in amplifier performs the vector addition of all such unit vectors. The near-field photon phases are Gaussian distributed around θp , which corresponds to tip-sample contact. Far-field background photons are detected randomly at all phases so the corresponding vector addition is simply a random walk.

Fig. 5.
Fig. 5.

TEFM images of a high-density quantum dot sample. Panel (a) shows the AFM topography (~50 total dots/µm2). Panel (b) shows the scalar photon sum (~14 bright dots/µm2). Panel (c) shows the same image after lock-in demodulation. The scale bar is 200 nm.

Fig. 6.
Fig. 6.

TEFM image contrast, panel (a), and signal-to-noise ratio, panel (b), for isolated quantum dots as a function of the tip oscillation amplitude. Data were obtained using BudgetSensors Multi-75 silicon tips. Data points correspond to the average value of ~15 measurements for the lock-in demodulation signal (closed symbols) and the scalar sum (open symbols). Dashed and dotted lines are the corresponding theoretical predictions.

Equations (24)

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C = S peak S ff S ff = S nf S ff
SNR = S peak S ff Noise in S ff = S nf σ ff
k = I 0 × σ 0 × τ × Q × CE × λ hc
SNR = S nf σ ff = f k N FA > 1 .
C = S nf S ff = f N FA > 1 .
S ff osc = S ff = k N FA .
γ = 1 2 π π π exp ( ( θ i θ p ) 2 2 θ σ 2 ) d θ i θ σ 2 π
S nf osc = S nf γ = k f γ = k f θ σ 2 π .
C osc sum = f γ N FA
SNR osc sum = f γ k N FA
P ( r ) = 2 r N steps e r 2 N steps
μ r = π N steps 4
σ r = 1 2 N steps ( 4 π ) .
FF = π 4 β N FA
σ FF = 1 2 β k N FA ( 4 π )
NF = i cos ( θ i θ p ) = S nf osc × cos ( θ i θ p )
α = π π cos ( θ i θ p ) e ( θ i θ p ) 2 2 θ σ 2 d θ i π π e ( θ i θ p ) 2 2 θ σ 2 e θ σ 2 2 .
NF = k f γ α k f θ σ 2 π e θ σ 2 2 .
L peak = NF 2 + FF 2 = ( k f γ α ) 2 + π 4 k N FA β .
C LI = L peak FF FF = [ 4 k ( f γ α ) 2 π N FA β + 1 ] 1 2 1
SNR LI = L peak FF σ FF 2 C LI
C LI > 1 f > 1 α γ 3 π N FA β 4 k .
d d θ σ ( θ σ e θ σ 2 2 ) = 0
A opt = z σ 1 cos ( 1 ) 2.1 z σ .

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