Gold Nanorod-Seeded Growth of Silver Nanostructures:  From Homogeneous Coating to Anisotropic Coating

Abstract

Single crystalline gold nanorods (Au NRs) dominated by {110} side facets were employed as seeds to tailor the deposition of Ag. Apart from homogeneous coating, anisotropic coating of Ag was observed and resulted in an orange slice-like shape for the Au@Ag nanocrystal. Different growth rates for the {110} side facets were responsible for this shape: among the four {110} facets, two of the neighboring {110} facets grew more quickly and another two grew more slowly, thus inducing the anisotropic deposition of Ag around the Au NR. This growth behavior is believed to be a consequence of competition between the strong stabilization of cetyltrimethylammomium bromide (CTAB) molecules to the {110} facets of Ag and minimization of the overall surface energy. Although the reason for the anisotropic coating remains to be clarified, our results lead to one important conclusion: The interaction of CTAB and metal can be utilized to tune the shapes of bimetallic structures.

Unraveling the Evolution and Nature of the Plasmons in (Au Core)–(Ag Shell) Nanorods

“…We defi ne the plasmon bands from low to high energies sequentially as peaks 1 − 4, respectively. The peak 1, which has been ascribed to the longitudinal dipolar plasmon mode in previous studies, [33][34][35] blue-shifts. The peak 2, which has been ascribed to the transverse dipolar plasmon mode, [33][34][35] fi rst blue-shifts and then stays at a nearly constant wavelength.…”

“…At the same time, the plasmon wavelengths of the core − shell nanorods can be tailored in the visible to near-infrared spectral regions by varying the Au core size and the Ag shell thickness. On the basis of this reasoning, (Au core) − (Ag shell) nanostructures in different shapes, including dumbbells, [ 30 , 31 ] rods, [32][33][34][35] and octahedrons, [ 36 ] have been prepared by different methods. Upon Ag coating, the lowest-energy plasmon band is generally blue-shifted and new plasmon bands are generated simultaneously at higher energies.…”

“…Upon Ag coating, the lowest-energy plasmon band is generally blue-shifted and new plasmon bands are generated simultaneously at higher energies. [32][33][34][35] The lowest-energy plasmon band is usually attributed to the longitudinal mode. The number of the newly generated plasmon bands is dependent on the shape of the core − shell nanostructures.…”

“Elastic” Property of Mesoporous Silica Shell: For Dynamic Surface Enhanced Raman Scattering Ability Monitoring of Growing Noble Metal Nanostructures via a Simplified Spatially Confined Growth Method

“…By increasing the amount of deposited Ag, the longitudinal SPR band obviously blue-shifted as a result of the decrease of the aspect ratio of AuNR during the Ag coating. 31 In addition to the transverse SPR of AuNR, a new peak at approximately 340 nm appeared in the shorter wavelength region, which can be assigned to a transverse dipole resonance of the Ag shell. Moreover, the peak at 380 nm resulting from the transverse dipole resonance of electrons at the thick side of the Ag shell became stronger during silver growth.…”

Coating matters: the influence of coating materials on the optical properties of gold nanoparticles

“…Although this phenomenon has been successfully reproduced, it remains unclear. Apart from homogeneous coating, anisotropic coating of Ag was observed, when single crystalline Au NRs were employed as seeds, resulting in an orange slice-like shape for the Au@Ag nanocrystals as shown in Figure 10 [197] . This unusual growth behavior is again ascribed to the unique properties of the stabilizing surfactant, CTAB, namely as a consequence of competition between its strong stabilization of certain lateral facets of Ag and the minimization of the overall surface energy.…”