Au–Pt alloy nanocrystals incorporated in silica films

Au, Pt and Au–Pt alloy nanocrystals have been prepared in thin SiO2 film matrices by sol–gel spin-coating, followed by heating at 450 °C in 10% H2–90% Ar. X-Ray diffraction patterns reveal that the Au and Au–Pt nanocrystals have a preferential (111) orientation. Upon increasing the Pt concentration, part of the Pt does not alloy with Au, but instead forms a shell around the Au–Pt alloy core. The alloy composition itself goes up to Au(50) : Pt(50), and the Pt shells are formed around the alloy above an alloy composition of Au(75) : Pt(25). The surface plasmon resonance (SPR) band at 544 nm of Au gradually disappears due to the formation of Au–Pt alloys and core–shell structures.