Abstract

We propose a method to fabricate a probe with a nanometric protrusion for near-field optical microscopy. The method involves a tapering process based on selective etching of a GeO2-doped fiber in a buffered hydrogen fluoride solution and a metallizing process by vacuum evaporation and chemical polishing. We fabricated a tapered probe which has a protrusion emerging from a metal film. The protrusion has an apex diameter less than 10nm and a foot diameter less than 20nm. Employing the probe, we succeeded in obtaining a highly resolved image of 20nm gold particles.

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References

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  1. W. Pohl and D. Courjon, eds., Near field optics, Vol. 242 of NATO ASI Series E (Kluwer Academic, Dordrecht, 1993).
    [CrossRef]
  2. E. Betzig and J. K. Trautman, Near-field optics: microscopy, spectroscopy, and surface modification beyond the diffraction limit, Science 257, 189-195 (1992).
    [CrossRef] [PubMed]
  3. M. Ohtsu, Progress of high-resolution photon scanning tunneling microscopy due to a nanometric fiber probe, J. Lightwave Technol. 13, 1200-1221 (1995).
    [CrossRef]
  4. Special issue on NFO-3, Ultramicroscopy 61 (1995), edited by M. Paesler and N. van Hulst.
  5. S. Mononobe, M. Naya, R. Uma Maheswari, T. Saiki, and M. Ohtsu, in The 3rd International Conference on Near Field Optics and Related Techniques (NFO-3), Brno, Czech Republic, May 1995, Vol. 8 of EOS Topical Meeting Digest, (European Optical Society, Orsay, 1995), pp. 105-106.
  6. S. Mononobe, M. Naya, T. Saiki, and M. Ohtsu, Reproducible fabrication of a fiber probe with a nanometric protrusion for near-field optics, Appl. Opt. 36, 1496-1500 (1997).
    [CrossRef] [PubMed]
  7. M. Naya, R. Micheletto, S. Mononobe, R. Uma Maheswari, and M. Ohtsu, Near-field optical imaging of flagellar filaments of salmonella in water with optical feedback control, Appl. Opt. 36, 1681-1683 (1997).
    [CrossRef] [PubMed]
  8. A. Zvyagin, J. D. White, and M. Ohtsu, Near-field optical microscope image formation: a theoretical and experimental study, Opt. Lett. 22, 955-957 (1997).
    [CrossRef] [PubMed]
  9. S. Mononobe and M. Ohtsu, Fabrication of a pencil-shaped fiber probe for near-field optics by selective chemical etching, J. Lightwave Technol. 14, 2231-2235 (1996); Erratum, J. Lightwave Technol. 15, 162 (1997).
    [CrossRef]
  10. S. Mononobe and M. Ohtsu, "A model based on geometrical construction in designing a pencil-shaped fiber probe for near-field optics," J. Lightwave Technol. 15, 1051-1055 (1997).
    [CrossRef]
  11. R. Uma Maheswari, H. Tatsumi, Y. Katayama, and M. Ohtsu, Observation of subcellular nanostructure of single neurons with an illumination mode photon scanning tunneling microscope, Opt. Commun. 120, 325-334 (1995).
    [CrossRef]
  12. R. Uma Maheswari, H. Kadono, and M. Ohtsu, Power spectral analysis for evaluating optical near-field image of 20nm gold particles, Opt. Commun. 131, 133-142 (1996).
    [CrossRef]

Other (12)

W. Pohl and D. Courjon, eds., Near field optics, Vol. 242 of NATO ASI Series E (Kluwer Academic, Dordrecht, 1993).
[CrossRef]

E. Betzig and J. K. Trautman, Near-field optics: microscopy, spectroscopy, and surface modification beyond the diffraction limit, Science 257, 189-195 (1992).
[CrossRef] [PubMed]

M. Ohtsu, Progress of high-resolution photon scanning tunneling microscopy due to a nanometric fiber probe, J. Lightwave Technol. 13, 1200-1221 (1995).
[CrossRef]

Special issue on NFO-3, Ultramicroscopy 61 (1995), edited by M. Paesler and N. van Hulst.

S. Mononobe, M. Naya, R. Uma Maheswari, T. Saiki, and M. Ohtsu, in The 3rd International Conference on Near Field Optics and Related Techniques (NFO-3), Brno, Czech Republic, May 1995, Vol. 8 of EOS Topical Meeting Digest, (European Optical Society, Orsay, 1995), pp. 105-106.

S. Mononobe, M. Naya, T. Saiki, and M. Ohtsu, Reproducible fabrication of a fiber probe with a nanometric protrusion for near-field optics, Appl. Opt. 36, 1496-1500 (1997).
[CrossRef] [PubMed]

M. Naya, R. Micheletto, S. Mononobe, R. Uma Maheswari, and M. Ohtsu, Near-field optical imaging of flagellar filaments of salmonella in water with optical feedback control, Appl. Opt. 36, 1681-1683 (1997).
[CrossRef] [PubMed]

A. Zvyagin, J. D. White, and M. Ohtsu, Near-field optical microscope image formation: a theoretical and experimental study, Opt. Lett. 22, 955-957 (1997).
[CrossRef] [PubMed]

S. Mononobe and M. Ohtsu, Fabrication of a pencil-shaped fiber probe for near-field optics by selective chemical etching, J. Lightwave Technol. 14, 2231-2235 (1996); Erratum, J. Lightwave Technol. 15, 162 (1997).
[CrossRef]

S. Mononobe and M. Ohtsu, "A model based on geometrical construction in designing a pencil-shaped fiber probe for near-field optics," J. Lightwave Technol. 15, 1051-1055 (1997).
[CrossRef]

R. Uma Maheswari, H. Tatsumi, Y. Katayama, and M. Ohtsu, Observation of subcellular nanostructure of single neurons with an illumination mode photon scanning tunneling microscope, Opt. Commun. 120, 325-334 (1995).
[CrossRef]

R. Uma Maheswari, H. Kadono, and M. Ohtsu, Power spectral analysis for evaluating optical near-field image of 20nm gold particles, Opt. Commun. 131, 133-142 (1996).
[CrossRef]

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Figures (3)

Fig. 1
Fig. 1

Fabrication method of a pencil-shaped fiber probe with a protrusion from a metal film. Here, the method involves five steps; [A] tapering the cladding by meniscus etching in hydrofluoric (HF) acid with a surface layer of organic solution, [B] sharpening the core by selective etching in buffered hydrogen fluoride solution (BHF), [C] increasing the taper angle in HF-containing aqueous solution [D], coating a metal film by vacuum evaporation, and [E] removing the metal that covers the apex region by chemical polishing. α is the taper angle of the cladding. θ and θ B are the taper angles of the core. In vacuum evaporation, the fiber is tilted with the angle ϕ and rotated.

Fig. 2
Fig. 2

(a) Scanning electron micrographs (SEM) of (a) pencil-shaped fiber with a taper angle of 20°, (b) the magnified top region. Here, the fiber is coated with gold having a thickness of 3nm. The apex diameter is less than 10nm; SEM images of (c) the top region and (d) the apex region of the metallized probe which has a protrusion from a metal film. Here, the metal is gold. The radial thickness of the gold film is 150nm. The foot diameter of the protrusion as shown by the dark portion is less than 20nm. Because the length of the protrusion is less than 10nm, nearing the limit of SEM, it is difficult to get a visualization in (d).

Fig. 3
Fig. 3

Near-field optical image of 20nm-gold particles illuminated by a 488nm argon ion laser. Here the scan area is 200nm×200nm. The dark portions as indicated by the arrow show single gold particles.

Equations (1)

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sin ( θ B 2 ) = ( R 1 R 2 ) sin ( α 2 ) .

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