Surface plasmon and photonic mode propagation in gold nanotubes with varying wall thickness

Abstract

Gold nanotube arrays are synthesized with a range of wall thicknesses (15 to >140 nm) and inner diameters of ∼200 nm using a hard-template method. A red spectral shift (>0.39 eV) with decreasing wall thickness is observed in dark-field spectra of nanotube arrays and single nanowire/nanotube heterostructures. Finite-difference-timedomain simulations show that nanotubes in this size regime support propagating surface plasmon modes as well as surface plasmon ring resonances at visible wavelengths (the latter is observed only for excitation directions normal to the nanotube long axis with transverse polarization). The energy of the surface plasmon modes decreases with decreasing wall thickness and is attributed to an increase in mode coupling between propagating modes in the nanotube core and outer surface and the circumference dependence of ring resonances. Surface plasmon mode propagation lengths for thicker-walled tubes increase by a factor of ∼2 at longer wavelengths (>700 nm), where ohmic losses in the metal are low, but thinner-walled tubes (30 nm) exhibit a more significant increase in surface plasmon propagation length (by a factor of more than four) at longer wavelengths. Additionally, nanotubes in this size regime support a photonic mode in their core, which does not change in energy with changing wall thickness. However, photonic mode propagation length is found to decrease for optically thin walls. Finally, correlations are made between the experimentally observed changes in dark-field spectra and the changes in surface plasmon mode properties observed in simulations for the various gold nanotube wall thicknesses and excitation conditions.

Intense proton acceleration in ultrarelativistic interaction with nanochannels

“…The wide literature in solid-state plasmonics can be, however, a reference source to try to extend our results in the 3D geometry. In nanochannels, finitedifference-time-domain simulations and experiments show a strong dependence of SPR wavelength and SPP modes on the size and the thickness of the gaps and on the composition of the medium in which nanochannels are embedded [35,36]. Similarly to nanowires, SPP waves with different azimuthal symmetry (m = 0 ± 1, ±2, ...) can be excited on the dielectric-metal interface [35,37,38].…”

Coaxial nanowires as plasmon-mediated remote nanosensors

“…Then, a pore widening process was performed, as reported in previous works. 6,36,37,41 The H3PO4 concentration and the etching time make possible to tune the opening size of the pores around the nanowires. 41 The pore wall, in contact with the gold nanowires, was first etched by phosphoric acid due to its richness in anions, 36,37 its higher amorphousness and hydration, and its softening by the localized pH change due to evolution of H2 during the Au 0 electrodeposition.…”

“…6,36,37,41 The H3PO4 concentration and the etching time make possible to tune the opening size of the pores around the nanowires. 41 The pore wall, in contact with the gold nanowires, was first etched by phosphoric acid due to its richness in anions, 36,37 its higher amorphousness and hydration, and its softening by the localized pH change due to evolution of H2 during the Au 0 electrodeposition. § We used a 0,9 M phosphoric acid solution in ultrapure water for 90 minutes to get a pore widening of about 5 to 15 nm.…”

Ultrafast Dynamics of Photoexcited Hot Carrier Generation and Injection in AgNWs@TiO2@GNS Nanostructures

“…Their extinction spectra are blue shifted from 574 to 559 nm as the GNS thickness increases (Figure 2c), which is consistent to previous reports on gold nanotube. [26][27] Simulation of the electric field distributions are shown in Figure S3b-3d which display strong field enhancement at interface and surface of shell. In addition, the theoretical extinction spectra were calculated via FDTD to quantify the effects of GNS on the optical response of the hybrid nanowires (Figure 2d).…”