Observation of a Quadrupole Surface Plasmon Mode for Au Nanorods: Effects of Surface Roughness and Crystal Facets

Abstract

This paper describes how the surface roughness and synthetic methods of Au nanorods affect the optical properties that are often associated with localized surface plasmon resonances. We synthesized Au nanorods with different aspect ratios and surface roughness by using two different synthetic strategies to observe surface plasmon resonance bands. One set of nanorods was prepared in high yield by using a seed-mediated dropwise-addition method with a growth-directing surfactant in aqueous solution (Au nanorods in aqueous phase, GNRA). The other set of Au nanorods were synthesized by the electrochemical deposition of Au onto an anodized aluminum oxide (AAO) template (Au nanorods by AAO template, GNRT). The length of the nanorods was controlled by changing the total charge that was passed through the cell and their diameter was monitored by changing the diameter of the template channel. The as-prepared Au nanorods were optimized to observe a quadrupole mode, which is one of the higher-order surface plasmon bands. Our results showed differences between the optical properties of GNRA and GNRT. The roughness and crystal structure of the Au nanorods affected their optical properties. Smooth and single-crystal surface on GNRA had larger and sharper peaks than GNRT. The discrete dipole approximation (DDA) method was used to calculate the optical properties of the Au nanorods and these results were in good agreement with our experimental results.

Kinetically Controlled Growth of Gold Nanoplates and Nanorods via a One-Step Seed-Mediated Method

“…2(f)) showed the typical transverse and longitudinal modes of gold nanorod structures at 522 nm and beyond 1200 nm, respectively, while we assigned the peak at 793 nm to longitudinal quadruple surface plasmon resonance. 35 These results indicate that kinetic control during synthesis facilitates the growth of GNPs with various shapes.…”

Combined Extinction and Absorption UV–Visible Spectroscopy as a Method for Revealing Shape Imperfections of Metallic Nanoparticles

“…A final source of non-sphericity that we will discuss here is surface roughness. As for the case of NP faceting, many studies on the e↵ect of NP surface roughness on plasmon resonance have been published, [65][66][67] with di↵erent and sometimes contradicting conclusions. 31,68 We do not intend here to give a definitive conclusion on the e↵ect of surface roughness on the optical properties of NPs, as it may depend on a number of factors like the NP shape, size, material, detailed type of roughness, etc.…”

Synthesis and Surface Plasmonic Characterization of Asymmetric Au Split Nanorings

“…With straight nanorods, it was known that the higher-order modes usually only appeared when the aspect ratio was larger than a certain limit (i.e., >7.3 for 37 nm thickness). 37 It seemed that symmetry breaking occurring from the straight to bent morphology transition allowed the appearance of higher-order modes in an easier fashion, although the aspect ratio was much less than the threshold value of the straight nanorods.…”

“…1202 nm (the extinction spectrum of straight long nanorods is represented in Figure S7). 37 On the other hand, the SDOIP mode corresponded to the longitudinal mode of Au nanorods whose thickness and length were ca. 65 ± 5 and 111 ± 8 nm, respectively.…”