Plasmon resonances of silver nanowires with a nonregular cross section

Abstract

We investigate numerically the spectrum of plasmon resonances for metallic nanowires with a nonregular cross section, in the 20-50 nm range. We first consider the resonance spectra corresponding to nanowires whose cross sections form different simplexes. The number of resonances strongly increases when the section symmetry decreases: A cylindrical wire exhibits one resonance, whereas we observe more than five distinct resonances for a triangular particle. The spectral range covered by these different resonances becomes very large, giving to the particle-specific distinct colors. At the resonance, dramatic field enhancement is observed at the vicinity of nonregular particles, where the field amplitude can reach several hundred times that of the illumination field. This near-field enhancement corresponds to surface-enhanced Raman scattering ͑SERS͒ enhancement locally in excess of 10 12 . The distance dependence of this enhancement is investigated and we show that it depends on the plasmon resonance excited in the particle, i.e., on the illumination wavelength. The average Raman enhancement for molecules distributed on the entire particle surface is also computed and discussed in the context of experiments in which large numbers of molecules are used.

Strong Polarized Enhanced Raman Scattering via Optical Tunneling through Random Parallel Nanostructures in Au Thin Films

“…In this case, the strength of the Raman signal was intermediate between parts a and c of Figure 3. These results are in accordance with the polarization dependence calculated for the SERS from individual metallic nanowires 19 and from periodic silver structures (silver gratings). 23 In all these cases, the electrons in the conductor are only spatially confined in the nanometric range along the direction perpendicular to the main axis of the structures, and the surface plasmons can then only be excited when the polarization vector of the light field are oriented at the same direction.…”

“…19 These calculations showed that the SP resonances are highly localized at the tips of the nanostructures; consequently, the number of SP resonances per nanowire increases as the overall symmetry of the particle's cross section decreases. 19 The sharp tips and narrow channels presented within the substructures in Figure 2 should be ideal for the production of highly localized SP resonances and, consequently, SERS. Figure 3 shows the surface-enhanced Raman spectra from oxa dye adsorbed on the nanostructured gold surface (shown in Figure 2) obtained in the forward scattering geometry (using the experimental setup shown in Figure 1).…”

“…19,23 Therefore, for a scratch positioned along the y-axis defined in Figure 4b, the z-component of the field (E z ) will induce SP resonances with a local field (E z,local ), and for a scratch positioned along the z-axis, only the y-component of the field is relevant (E y,local ). Substituting eqs 1 and 2 into eq 3, we obtain the following angular dependence for the enhanced Raman signal for scratches aligned with the y-axis (I y ) and z-axis (I z ):…”

Effects of Silver Nanowires on The Electro-chemical Performance of LiFePO4

“…This is mainly because that the symmetry of the nanowires improves. It is consistent with the reported theory that the number of SPR peaks usually decreases with the increasing symmetry of nanowires [28]. In order to investigate the features of LiFePO 4 and LiFePO 4 /Ag nanowires cathodes, these cathodes are analyzed with XRD, FSEM and energy-dispersive X-ray spectroscopy (EDX).…”

Development of Nanostructured Plasmonic Substrates for Enhanced Optical Biosensing

“…Figures 8 and 9 show the field distributions of E Z for 1D gold nanogratings with a period of 100 nm, a width of 50 nm, and a thickness of 10 nm. The figures present well-known features of LSPs excited at a metallic nanostructures that are quite typical of the fields of nonregular metallic nanostructures [44]. On the assumption of an incident electric field of unit amplitude, maximum field amplitudes obtained by FDTD were E X = 59, H Y = 8, and E Z = 41.…”