Nanocoating of Metallic Nanocrystals: Study of the Effect of Crystal Shape and Shell Thickness on Their Optical Properties

Abstract

Nanoprisms, snapped prisms and nanorods of gold particles have been obtained chemically. New absorption features different from that of the classical surface plasmon absorption bands of rods and spheres are found to be associated with the appearance of the nanoprism, and snapped prism shaped gold nanoparticle in the TEM images. We were able to modify the seed method in order to get more control on the shape of the gold nanoparticles and we developed a new method to prepare gold nanoprisms by changing the concentration of seed and Ag'ions. Our results indicate that the presence of Ag"ions and the seed concentration are the key parameters for obtaining the anisotropic shape of gold particles, and their concentrations play an important role in controlling the shape of the particles, e.g. rods, prisms or snapped prisms.

We developed a method to coat different shaped gold nanoparticles (spheres, rods, and nanoprisms) and we determined the critical condition at which alloying occurred instead of coating.

The thermal and photostability of these different shapes and coated particles have been studied. Great enhancement of the thermal stability has been achieved by adding specific amount of polyvinyl pyrrolidone (PVP) to the gold particles of different shapes capped with cetyltrimethylammonium bromide (CTAB). It is worth to mention that our gold nanorods stabilized by PVP are totally stable up to 220 °C. Optically, these gold particles stabilized by PVP are remarkably much stable towards UV light and even upon exposure to Nd-Yag pulsed nanosecond lasers.