Surfactantless photochemical growth of Ag nanostructures on GaN epitaxial films with controlled morphologies and their application for SERS

Abstract

Ag nanostructures with controlled morphologies have been synthesized on GaN epitaxial films through a convenient, fast, and surfactantless photochemical method. On n-type GaN, uniform spheroidic Ag nanoparticles (NPs) of high density were obtained after photochemical reaction for a short time (30 s to 5 min) in AgNO₃ aqueous solution. Reducing AgNO₃ concentration yielded branched Ag nanostructures. The Ag NPs on the GaN substrates exhibit a Fabry–Perot-type surface plasmon resonance (SPR). On p-type GaN, Ag nanocrystals (NCs) with well-defined shapes ranging from cubes, truncated cubes, cuboctahedra, truncated octahedra, and octahedra were obtained through varying the concentration of AgNO₃ solution. We propose that the formation of polyhedral Ag NCs is induced by the separation of the nucleation and growth processes by the GaN surface. Both surface states and carrier concentration are considered to play substantial roles during the growth process. This surfactantless photochemical method is general and enables the facile synthesis of Ag nanostructures at room temperature, which may be extended for the synthesis of other noble metal nanostructures, e.g.Au, Pt, and Pd, on GaN or other wide bandgap semiconductors, e.g.SiC. The obtained Ag/GaN hybrid systems show potential application as solid substrates for surface enhanced Raman scattering (SERS) analysis.