Morphology of Ni (core)/Au (shell) nanoparticles

Abstract

We obtained sphere-like nanoparticles Ni/Au with a core-shell structure. They are variable in size (7–14 nm of Ni nuclei) and have a narrow-size particle distribution. It was done by means of stepwise (sequential) reduction of the calibrated portions of tetrahydroborate sodium and nickel sulfate solutions. It was done under the presence of sodium citrate as a stabilizer and the combination with a two-step deposition of Au film: (1) electrochemical substitution of Ni0 + Au+3 → Ni+2 + Аu0 and (2) reduction of chloroauric acid by tetrahydroborate sodium. The study of the particles was provided by TEM, XRD, SAXS, CV, ICP OES, and XPS. It significantly allowed to broaden out the existing knowledge on their morphology, phase, and chemical composition. Au shell with averaged 0.6-nm thickness is formed as an irregular polyhedron, composed of polyhedral pieces (scales) with the structure of fcc-type. The shell has pores around the joints of polyhedral pieces. So, Ni nuclei are oxidized under storage of samples at these locations to form nickel hydroxide. The nanophase of solid solution of Au-Ni (rich in gold) is formed on the Ni-Au contact. This is the result of interdiffusion of metals (mainly nickel in gold). Its volume fraction can reach up to 17%. Ni core then contains small amounts of impurities of boron or its compounds.