Abstract

A finite element model was built to investigate how to optimize localized plasmon resonances of an Ag-coated dielectric tip for tip-enhanced Raman spectroscopy (TERS). The relation between the resonance frequency, the electric field enhancement and the optical constant of the dielectric tip was numerically investigated. The results show that increasing the refractive index of the dielectric tip can significantly red shift the localized plasmon modes excited on the Ag-coated dielectric tip, and consequently alter the field enhancement. Moreover, the influence of the width of the resonance on the Raman enhancement was also considered. When taking all the factors into account, we find that an Ag-coated low-refractive index dielectric tip provides the best Raman enhancement in the blue—green spectral range. This is consistent with our prior experimental results.

© 2007 Optical Society of America

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References

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    [CrossRef]
  2. N. Hayazawa, Y. Inouye, Z. Sekkat, and S. Kawata, "Metallized tip amplification of near-field Raman scattering," Opt. Commun. 183, 333-336 (2000).
    [CrossRef]
  3. A. Hartschuh, E. J. Sanchez, X. S. Xie, and L. Novotny, "High-resolution near-field Raman microscopy of single-walled carbon nanotubes," Phys. Rev. Lett. 90, (2003).
    [CrossRef] [PubMed]
  4. C. C. Neacsu, J. Dreyer, N. Behr, and M. B. Raschke, "Scanning-probe Raman spectroscopy with single-molecule sensitivity," Phys. Rev. B 73, 193406 (2006).
    [CrossRef]
  5. K. F. Domke, D. Zhang, and B. Pettinger, "Toward Raman fingerprints of single dye molecules at atomically smooth Au(111)," J. Am. Chem. Soc. 128, 14721-14727 (2006).
    [CrossRef] [PubMed]
  6. W. Zhang, B. Yeo, S. Thomas, and R. Zenobi, "Single molecule tip-enhanced Raman Spectroscopy with silver tips," J. Phys. Chem. C 111, 1733-1738 (2007).
    [CrossRef]
  7. L. Novotny, R. X. Bian, and X. S. Xie, "Theory of nanometric optical tweezers," Phys. Rev. Lett. 79, 645-648 (1997).
    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  14. J. B. Jackson, and N. J. Halas, "Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates," PNAS 101, 17930-17935 (2004).
    [CrossRef] [PubMed]
  15. M. D. Malinsky, K. L. Kelly, G. C. Schatz, and R. P. Van Duyne, "Nanosphere lithography: Effect of substrate on the localized surface plasmon resonance spectrum of silver nanoparticles," J. Phys. Chem. B 105, 2343-2350 (2001).
    [CrossRef]
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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef]
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  22. I. Notingher, and A. Elfick, "Effect of sample and substrate electric properties on the electric field enhancement at the Apex of SPM Nanotips," J. Phys. Chem. B 109, 15699-15706 (2005).
    [CrossRef]
  23. A. Otto, I. Mrozek, H. Grabhorn, and W. Akemann, "Surface-enhanced Raman-Scattering," J. Phys.: Condens. Matter 4, 1143-1212 (1992).
    [CrossRef]
  24. M. Moskovits, "Surface-enhanced spectroscopy," Rev. Mod. Phys. 57, 783-826 (1985).
    [CrossRef]
  25. H. Wang, D. W. Brandl, F. Le, P. Nordlander, and N. J. Halas, "Nanorice: A hybrid plasmonic nanostructure," Nano Lett. 6, 827-832 (2006).
    [CrossRef] [PubMed]

2007

W. Zhang, B. Yeo, S. Thomas, and R. Zenobi, "Single molecule tip-enhanced Raman Spectroscopy with silver tips," J. Phys. Chem. C 111, 1733-1738 (2007).
[CrossRef]

B. Yeo, T. Schmid, W. Zhang, and R. Zenobi, "Towards rapid nanoscale chemical analysis using tip-enhanced Raman spectroscopy with Ag-coated dielectric tips," Anal. Bioanal. Chem. 387, 2655-2662 (2007).
[CrossRef] [PubMed]

2006

T. A. Yano, Y. Inouye, and S. Kawata, "Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra," Nano Lett. 6, 1269-1273 (2006).
[CrossRef] [PubMed]

C. C. Neacsu, J. Dreyer, N. Behr, and M. B. Raschke, "Scanning-probe Raman spectroscopy with single-molecule sensitivity," Phys. Rev. B 73, 193406 (2006).
[CrossRef]

K. F. Domke, D. Zhang, and B. Pettinger, "Toward Raman fingerprints of single dye molecules at atomically smooth Au(111)," J. Am. Chem. Soc. 128, 14721-14727 (2006).
[CrossRef] [PubMed]

H. Wang, D. W. Brandl, F. Le, P. Nordlander, and N. J. Halas, "Nanorice: A hybrid plasmonic nanostructure," Nano Lett. 6, 827-832 (2006).
[CrossRef] [PubMed]

B. S. Yeo, W. H. Zhang, C. Vannier, and R. Zenobi, "Enhancement of Raman signals with silver-coated tips," Appl. Spectrosc. 60, 1142-1147 (2006).
[CrossRef] [PubMed]

2005

I. Notingher, and A. Elfick, "Effect of sample and substrate electric properties on the electric field enhancement at the Apex of SPM Nanotips," J. Phys. Chem. B 109, 15699-15706 (2005).
[CrossRef]

Y. Saito, T. Murakami, Y. Inouye, and S. Kawata, "Fabrication of silver probes for localized plasmon excitation in near-field Raman spectroscopy," Chem. Lett. 34, 920-921 (2005).
[CrossRef]

2004

J. B. Jackson, and N. J. Halas, "Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates," PNAS 101, 17930-17935 (2004).
[CrossRef] [PubMed]

2003

K. L. Kelly, E. Coronado, L. L. Zhao, and G. C. Schatz, "The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment," J. Phys. Chem. B 107, 668-677 (2003).
[CrossRef]

A. Hartschuh, E. J. Sanchez, X. S. Xie, and L. Novotny, "High-resolution near-field Raman microscopy of single-walled carbon nanotubes," Phys. Rev. Lett. 90, (2003).
[CrossRef] [PubMed]

2001

M. D. Malinsky, K. L. Kelly, G. C. Schatz, and R. P. Van Duyne, "Nanosphere lithography: Effect of substrate on the localized surface plasmon resonance spectrum of silver nanoparticles," J. Phys. Chem. B 105, 2343-2350 (2001).
[CrossRef]

2000

H. X. Xu, J. Aizpurua, M. Kall, and P. Apell, "Electromagnetic contributions to single-molecule sensitivity in surface-enhanced Raman scattering," Phys. Rev. E 62, 4318-4324 (2000).
[CrossRef]

R. M. Stöckle, Y. D. Suh, V. Deckert, and R. Zenobi, "Nanoscale chemical analysis by tip-enhanced Raman spectroscopy," Chem. Phys. Lett. 318, 131-136 (2000).
[CrossRef]

N. Hayazawa, Y. Inouye, Z. Sekkat, and S. Kawata, "Metallized tip amplification of near-field Raman scattering," Opt. Commun. 183, 333-336 (2000).
[CrossRef]

1999

A. V. Zayats, "Electromagnetic field enhancement in the context of apertureless near-field microscopy," Opt. Commun. 161, 156-162 (1999).
[CrossRef]

1997

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

1996

R. J. Hamers, "Scanned probe microscopies in chemistry," J. Phys. Chem. 100, 13103-13120 (1996).
[CrossRef]

1992

A. Otto, I. Mrozek, H. Grabhorn, and W. Akemann, "Surface-enhanced Raman-Scattering," J. Phys.: Condens. Matter 4, 1143-1212 (1992).
[CrossRef]

1985

M. Moskovits, "Surface-enhanced spectroscopy," Rev. Mod. Phys. 57, 783-826 (1985).
[CrossRef]

1972

R. W. C. P. B. Johnson, "Optical Constants of the Noble Metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

Anal. Bioanal. Chem.

B. Yeo, T. Schmid, W. Zhang, and R. Zenobi, "Towards rapid nanoscale chemical analysis using tip-enhanced Raman spectroscopy with Ag-coated dielectric tips," Anal. Bioanal. Chem. 387, 2655-2662 (2007).
[CrossRef] [PubMed]

Appl. Spectrosc.

Chem. Lett.

Y. Saito, T. Murakami, Y. Inouye, and S. Kawata, "Fabrication of silver probes for localized plasmon excitation in near-field Raman spectroscopy," Chem. Lett. 34, 920-921 (2005).
[CrossRef]

Chem. Phys. Lett.

R. M. Stöckle, Y. D. Suh, V. Deckert, and R. Zenobi, "Nanoscale chemical analysis by tip-enhanced Raman spectroscopy," Chem. Phys. Lett. 318, 131-136 (2000).
[CrossRef]

J. Am. Chem. Soc.

K. F. Domke, D. Zhang, and B. Pettinger, "Toward Raman fingerprints of single dye molecules at atomically smooth Au(111)," J. Am. Chem. Soc. 128, 14721-14727 (2006).
[CrossRef] [PubMed]

J. Phys. Chem.

R. J. Hamers, "Scanned probe microscopies in chemistry," J. Phys. Chem. 100, 13103-13120 (1996).
[CrossRef]

J. Phys. Chem. B

M. D. Malinsky, K. L. Kelly, G. C. Schatz, and R. P. Van Duyne, "Nanosphere lithography: Effect of substrate on the localized surface plasmon resonance spectrum of silver nanoparticles," J. Phys. Chem. B 105, 2343-2350 (2001).
[CrossRef]

K. L. Kelly, E. Coronado, L. L. Zhao, and G. C. Schatz, "The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment," J. Phys. Chem. B 107, 668-677 (2003).
[CrossRef]

I. Notingher, and A. Elfick, "Effect of sample and substrate electric properties on the electric field enhancement at the Apex of SPM Nanotips," J. Phys. Chem. B 109, 15699-15706 (2005).
[CrossRef]

J. Phys. Chem. C

W. Zhang, B. Yeo, S. Thomas, and R. Zenobi, "Single molecule tip-enhanced Raman Spectroscopy with silver tips," J. Phys. Chem. C 111, 1733-1738 (2007).
[CrossRef]

J. Phys.: Condens. Matter

A. Otto, I. Mrozek, H. Grabhorn, and W. Akemann, "Surface-enhanced Raman-Scattering," J. Phys.: Condens. Matter 4, 1143-1212 (1992).
[CrossRef]

Nano Lett.

H. Wang, D. W. Brandl, F. Le, P. Nordlander, and N. J. Halas, "Nanorice: A hybrid plasmonic nanostructure," Nano Lett. 6, 827-832 (2006).
[CrossRef] [PubMed]

T. A. Yano, Y. Inouye, and S. Kawata, "Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra," Nano Lett. 6, 1269-1273 (2006).
[CrossRef] [PubMed]

Opt. Commun.

N. Hayazawa, Y. Inouye, Z. Sekkat, and S. Kawata, "Metallized tip amplification of near-field Raman scattering," Opt. Commun. 183, 333-336 (2000).
[CrossRef]

A. V. Zayats, "Electromagnetic field enhancement in the context of apertureless near-field microscopy," Opt. Commun. 161, 156-162 (1999).
[CrossRef]

Phys. Rev. B

C. C. Neacsu, J. Dreyer, N. Behr, and M. B. Raschke, "Scanning-probe Raman spectroscopy with single-molecule sensitivity," Phys. Rev. B 73, 193406 (2006).
[CrossRef]

R. W. C. P. B. Johnson, "Optical Constants of the Noble Metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

Phys. Rev. E

H. X. Xu, J. Aizpurua, M. Kall, and P. Apell, "Electromagnetic contributions to single-molecule sensitivity in surface-enhanced Raman scattering," Phys. Rev. E 62, 4318-4324 (2000).
[CrossRef]

Phys. Rev. Lett.

A. Hartschuh, E. J. Sanchez, X. S. Xie, and L. Novotny, "High-resolution near-field Raman microscopy of single-walled carbon nanotubes," Phys. Rev. Lett. 90, (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]

PNAS

J. B. Jackson, and N. J. Halas, "Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates," PNAS 101, 17930-17935 (2004).
[CrossRef] [PubMed]

Rev. Mod. Phys.

M. Moskovits, "Surface-enhanced spectroscopy," Rev. Mod. Phys. 57, 783-826 (1985).
[CrossRef]

Other

http://www.comsol.com.

C. F. Bohren, and D. R. Juffman, Absorption and scattering of light by small particles (John Wiley: New York, 1983).

U. Kreibig, and M. Voller, Optical Properties of Metal Clusters (Springer: Berlin, 1995).

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Figures (5)

Fig. 1.
Fig. 1.

(a). Dimension size and mesh of the tip used for the simulation. Here, r1=10 nm, r2=30 nm. (b) SEM picture from side-view. The scale bar denotes 100 nm.

Fig. 2.
Fig. 2.

Calculated electric field distribution of the p-component.

Fig. 3.
Fig. 3.

Spectral responses of the field enhancement for an Ag coated Si3N4 tip, glass and AlF3 tip.

Fig. 4.
Fig. 4.

(a). Field enhancement against the refractive index and the wavelength (i.e. as two dimensional intensity plot) to reveal the resonance behaviors of the Ag-coated AFM tip. (b) The same plot for an Ag coated spherical particle. In these two plots, dark blue and deep red represent the lowest and highest intensities respectively.

Fig. 5.
Fig. 5.

Spectral response of the field enhancement for an Ag coated dielectric tip with different conductivities. The refractive index of the tip is 3.48, the conductivities of these two tips are 10-12 S·m-1 and 1 S·m-1.

Equations (1)

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α = 4 π 3 ε 0 ( R + d ) 3 ( ε s 1 ) ( ε c + 2 ε s ) + ( R R + d ) 3 ( ε c ε s ) ( 1 + 2 ε s ) ( ε s + 2 ) ( ε c + 2 ε s ) + ( R R + d ) 3 ( ε c ε s ) ( 2 ε s 1 )

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