Oriented Au–Cu nanoalloy particle incorporated SiO2 films using a new layer by layer deposition technique

Abstract

Oriented Au–Cu nanoalloys have been generated in SiO₂ films using a new two-layer (TL) coating approach. Two successive overlapping coating layers were deposited on silica glass substrate using Au- and Cu-incorporated inorganic–organic hybrid silica sols. The concentrations of the Au and Cu (3 equivalent mol% metal–97% SiO₂ in each case) in the respective layers and their individual coating thicknesses were kept similar for the generation of Au–Cu alloys of an approximate atomic ratio 1 : 1. The UV-visible and X-ray diffraction (XRD) spectra of the TL films show the formation of nanoalloys with a gradual increase of Cu content with increasing heat-treatment temperature up to 750 °C in 10% H₂–90% Ar. The XRD patterns reveal that the Au and Cu gradually formed Au–Cu nanoalloys of different ratios with a <111> orientation. Estimation shows that the final nanoalloy composition reaches Au_0.58Cu_0.42. The transmission electron microscope (TEM) image obtained from an Au_0.58Cu_0.42 nanoalloy containing film shows the presence of mainly <111> oriented plate-like circular nanoalloys of diameter 9–14 nm. XRD and TEM confirm that the alloy formation took place mainly through the diffusion and gradual dissolution of Cu atoms onto the <111> planes of Au and intermediate Au–Cu nanoalloy crystals.