Fine-tuning longitudinal plasmon resonances of nanorods by thermal reshaping in aqueous media

Abstract

Metallic nanoparticles that support surface plasmons are potential building units for future nanophotonic circuits, metamaterials, high-density optical data storage, etc. Many of these applications require the ability to 'dial-up' the desired plasmonic resonance modes and frequencies with high precision. Here, we demonstrate a thermal reshaping route that can be used to tailor longitudinal plasmon resonance energies of gold nanorods almost continuously from ~800 to ~560 nm. The longitudinal plasmon resonance wavelength exhibits an exponential decay function of the thermal annealing time at a given temperature. This correlates with the transmission electron microscopy characterization (TEM) which showed that the nanorod aspect ratio decreases exponentially with time, accompanying a gradual shape transformation from rod to sphere. The exponential decay half-time decreases with increasing annealing temperatures, with a value of 1.43 × 10(5) s at 50 °C down to 0.02 × 10(5) s at 100 °C. Our experimental results show that the shape transformation could be attributed to desorption of silver ions and side facet-binding Ag-Br-CTA ligands, which therefore promote the side growth leading to nanorod fattening. Compared to other synthetic methodologies to tune plasmonics, our thermal reshaping approach presents a straightforward paradigm for precisely tailoring plasmon resonance energy with a single parameter.

Plasmon-Modulated Excitation-Dependent Fluorescence from Activated CTAB Molecules Strongly Coupled to Gold Nanoparticles

“…CTAB is a popular ionic surfactant used for either stabilizing or reshaping AuNPs during synthesis and post-thermal processes555657585960; CTAB* has prominent advantages of chromophore generation as well as strong exciton-plasmon coupling with AuNPs. In the Fourier transform infrared (FTIR) spectrum as shown in Fig.…”

Morphology and optical absorption change of Ag/SiO2 core-shell nanoparticles under thermal annealing

“…This can be explained by the localized surface plasmon resonance change that is sensitive to Ag particles size and shape and their dielectric environment. [17][18][19] Besides, it is very important to note that due to the inherent nature of silver, the Ag surface is easily oxidized to AgO x in the air, especially at high temperature. 6 This would lead to a larger environmental dielectric constant and cause a red-shift of the Ag/SiO absorption band.…”

Colloidal self-assembly concepts for light management in photovoltaics

“…Two representative TEM images of the highly monodisperse spherical particles are shown. (d) Gold nanorods with finely tuned plasmon resonances prepared via thermal reshaping [103]. Shown are UVVis absorbance spectra and respective TEM images after different times of thermal treatment.…”

“…The position of this resonance can be finely tuned over a broad range of wavelength by adjusting the aspect ratio of the rods. This can be achieved for example either by the growing conditions [97] or by thermal decomposition [103]. Figure 3(d) shows absorbance spectra for gold nanorods of different aspect ratios obtained after different times of thermal treatment.…”