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 uC in 10% $H_{2}$-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