Tuning the resonance frequency of Ag-coated dielectric tips.

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.

[1]  R. Zenobi,et al.  Single Molecule Tip-Enhanced Raman Spectroscopy with Silver Tips , 2007 .

[2]  Weihua Zhang,et al.  Enhancement of Raman Signals with Silver-Coated Tips , 2006, Applied spectroscopy.

[3]  Xu,et al.  Electromagnetic contributions to single-molecule sensitivity in surface-enhanced raman scattering , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[4]  R. Zenobi,et al.  Towards rapid nanoscale chemical analysis using tip-enhanced Raman spectroscopy with Ag-coated dielectric tips , 2007, Analytical and bioanalytical chemistry.

[5]  Robert J. Hamers,et al.  Scanned Probe Microscopies in Chemistry , 1996 .

[6]  Markus B. Raschke,et al.  Scanning-probe Raman spectroscopy with single-molecule sensitivity , 2006 .

[7]  N J Halas,et al.  Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[8]  George C. Schatz,et al.  The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment , 2003 .

[9]  Fei Le,et al.  Nanorice: a hybrid plasmonic nanostructure. , 2006, Nano letters.

[10]  Lukas Novotny,et al.  High-resolution near-field Raman microscopy of single-walled carbon nanotubes. , 2003, Physical review letters.

[11]  S. Kawata,et al.  Metallized tip amplification of near-field Raman scattering , 2000 .

[12]  Dai Zhang,et al.  Toward Raman fingerprints of single dye molecules at atomically smooth Au(111). , 2006, Journal of the American Chemical Society.

[13]  R. W. Christy,et al.  Optical Constants of the Noble Metals , 1972 .

[14]  R. Zenobi,et al.  Nanoscale chemical analysis by tip-enhanced Raman spectroscopy , 2000 .

[15]  I. Notingher,et al.  Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips. , 2005, The journal of physical chemistry. B.

[16]  Lukas Novotny,et al.  Theory of Nanometric Optical Tweezers , 1997 .

[17]  Michael Vollmer,et al.  Optical properties of metal clusters , 1995 .

[18]  A. Campion,et al.  Surface-enhanced Raman scattering , 1998 .

[19]  S. Kawata,et al.  Fabrication of Silver Probes for Localized Plasmon Excitation in Near-field Raman Spectroscopy , 2005 .

[20]  S. Kawata,et al.  Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra. , 2006, Nano letters.

[21]  A. Zayats.  Electromagnetic field enhancement in the context of apertureless near-field microscopy , 1999 .

[22]  George C. Schatz,et al.  Nanosphere Lithography: Effect of Substrate on the Localized Surface Plasmon Resonance Spectrum of Silver Nanoparticles , 2001 .

[23]  M. Moskovits.  Surface-enhanced spectroscopy , 1985 .

[24]  P. Barber.  Absorption and scattering of light by small particles , 1984 .