Gold Nanorod Arrays: Excitation of Transverse Plasmon Modes and Surface-Enhanced Raman Applications

Abstract

In this paper we describe a method for the fabrication of gold nanorod arrays and their characterization. The initial requirements were for a robust substrate with strong surface enhancement of Raman scattering with minimal surface contamination. The rods with length up to 20 µm were electrochemically deposited in alumina templates bonded to gold coated silicon wafers. After removal of the template, surface bound cyanide from the deposition process was removed by mild electropolishing. Reflectance and cathodoluminescence measurements revealed transverse dipole and quadrupole plasmon modes. Surface enhancement of 10 6 was determined by taking Raman spectra of self-assembled monolayers of 4-aminothiophenol. The enhancement factor (EF) was found to be independent of nanorod aspect ratio because only the length of the nanorods was varied while their diameter was kept constant and due to the large length of nanorods only the transverse plasmons were excited.

Quantum Plasmonics in Nanorods: A Time-Dependent Orbital-Free Density Functional Theory Study with Thousands of Atoms

“…For the larger size nanorods, although the T2 mode is not as clear as that in the smaller size, the asymmetric adsorption spectrum (Figure b) indicates the presence of the multipolar resonance modes. These multipolar modes, such as the quadruple mode, have been reported for Au nanorods in transverse polarization . To understand the transverse LSPRs further, we analyze the optical absorption of two selected nanorods, that is, l / d = 6.5 ( l = 55.8 Å and d = 8.6 Å for the smaller size) and 2.1 ( l = 55.8 Å and d = 27.1 Å for the larger size) in more detail.…”

“…These multipolar modes, such as the quadruple mode, have been reported for Au nanorods in transverse polarization. 18 To understand the transverse LSPRs further, we analyze the optical absorption of two selected nanorods, that is, l/d = 6.5 (l = 55.8 Å and d = 8.6 Å for the smaller size) and 2.1 (l = 55.8 Å and d = 27.1 Å for the larger size) in more detail. We resolve each absorption spectrum as the sum of the Gaussian functions 57 and derive three distinctive resonance modes termed T1, T2, and T3, as shown in Figure 2c,d (green curves).…”

“…Electromagnetic radiation can excite collective oscillations of conduction electrons in metallic nanostructures, known as localized surface plasmon resonances (LSPRs). , These LSPRs on individual metal nanostructures can be tuned by adjusting their sizes, shapes, compositions, and environments. − Among various nanostructures, particular attention has been paid to nanorods because they exhibit anisotropic LSPRs with electron oscillations in different directions, giving rise to phenomena such as a broad spectral range, − extremely large electric-field enhancements around the two ends, , striking photothermal conversion capabilities, nanoantenna characteristics, and so on, which enable novel applications in biomedical sensing, imaging, cancer therapy, drug delivery, and nanophotonics. − …”

Current achievements of nanoparticle applications in developing optical sensing and imaging techniques

“…5 a [ 93 ]. In imaging and Raman spectroscopic integrations, Durr et al introduced two-photon tumour cell imaging using gold nanorods that were functionalized as a specific molecular tracer [ 94 ], and Mirza et al [ 95 ] described the possibility of gold nanorods serving as a highly efficient platform for SERS molecular detections. Several researchers investigated metallic nanoparticles with sharp tips called nanostars to improve the localized electromagnetic field efficiency and applied them in developing high-sensitivity probes.…”

Up-conversion luminescence coupled to plasmonic gold nanorods for light harvesting and hydrogen production

“…We have measured the Au nano-rods for their particular plasmon resonance response in the IR and Visible (figure 2) light range. This has resulted in extending the Au plasmon energy into the IR region due to both the transversal and longitudinal plasmons 29,30 ). This wide spectral range, most likely due to light scattering, was in our favor, as it coincided with the absorbance edge of the up-converter (980 nm); and this is needed to enhance light adsorption which in turn is poised to enhance light emission.…”