Uniform and controllable preparation of Au–Ag core–shell nanorods using anisotropic silver shell formation on gold nanorods

Abstract

Anisotropic and controllable silver shell formation on gold nanorods was realized in a micellar solution of hexadecytrimethylammonium chloride. Uniformity of the anisotropic Au-Ag core-shell particles contributes separation of four extinction bands. The ability to manipulate the shapes and sizes of these nanoparticles offers a wide-range control of the surface extinction from the visible to the near infrared regions (450-800 nm).

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.…”

“…The (Au core) − (Ag shell) nanorods were prepared according to a reported procedure with slight modifi cations. [ 35 ] Specifi cally, for the coating of the large Au nanorod sample, eight aliquots (2 mL) of the Au nanorod solution were centrifuged and redispersed into aqueous CTAC solutions (0.08 M ) at the same volume. 0.04, 0.12, 0.24, 0.4, 0.56, 0.72, 0.88, and 1.2 mL of AgNO 3 (0.01 M ) were subsequently added into the eight aliquots, respectively, followed by the addition of ascorbic acid solutions (0.1 M ).…”

“…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.…”

“…The (Au core) − (Ag shell) nanorods were prepared according to a previously reported method [ 35 ] with slight modifi cations. Briefl y, 2 mL of the uncoated Au nanorod solution was centrifuged and redispersed into an aqueous cetyltrimethylammonium chloride (CTAC) solution at the same volume.…”

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

“…Furthermore, the blue-shifting effect of the silver shell with a certain thickness on the plasmon resonance of gold NRs is larger for longer nanorods than for shorter ones. If the Ag shell is not cylindrical and is instead a parallelepiped, more than one new peak from the Ag shell is observed due to loss of rotational symmetry [197,204] . Besides spherical and elongated gold nanoparticles, silver also has been overgrown onto core shapes such as nanotriangles, nanopods, or octohedra [205,206] in a similar fashion.…”