Synthesis of Small Au-Ag Core-Shell Cubes, Cuboctahedra, and Octahedra with Size Tunability and Their Optical and Photothermal Properties

Abstract

summary, small Au-Ag core-shell nanocubes, cuboctahedra and octahedra have been synthesized in an aqueous solution at 30 -C in 1 h through deposition of Ag shells on octahedral Au cores with an edge length of 29 nm by tuning the amounts of ascorbic acid and NaOH solution used 41-49 and 34-40 nm can be tuned by simply varying the volume of Au core solution introduced. Au-Ag cuboctahedra are about 40 nm in opposite {100} face distance. Visual observation of solution color changes suggests a faster growth rate for Au-Ag octahedra. Ag shells have been controlled to be ultrathin below 2 nm for the smallest particles. These Au-Ag nanocrystals with various shapes display distinctly different UV-vis spectra. Slight blue-shifts in the position of the major SPR absorption band with increasing particle sizes have been observed due to greater Ag shell thickness. Furthermore, ultrasmall Au-Ag cubes and octahedra with respective edge lengths of 34 and 26 nm were also prepared using octahedral Au cores having an edge length of 21 nm. Effi cient photothermal properties have been recorded for Au-Ag octahedra and cuboctahedra with temperatures reaching 80 -C when irradiated with a 405 nm laser. The high uniformity of these Au-Ag nanocrystals has enabled their facile assembly into large supercrystals on a substrate. Availability of these really small Ag-based nanocrystals, especially the octahedra, in large quantity should greatly broaden the use of Ag nanoparticles for diverse applications.