Synthesis of hybrid Au-In₂O₃ nanoparticles exhibiting dual plasmonic resonance

Hybrid nanoparticles composed of multiple material systems provide a platform for studying the coupling between nanoparticles with distinct properties. Here, we describe a nontraditional synthetic pathway to Au-In₂O₃ hybrid nanoparticles that contain two distinct plasmonic domains: Au, with a localized surface plasmon resonance (LSPR) in the visible, and In₂O₃, with a LSPR in the mid-infrared. The hybrid nanocrystals are produced by slowly introduce In(III) stock solution to Au nanoparticle seeds using a syringe pump. Rather than forming through a traditional heterogeneous seeded-growth process, a series of in situ and ex situ studies reveal an alternate multistep pathway. The Au nanoparticles first combine with In to form an alloy of Au and In, which is colloidally stable up to 300 °C in 1-octadecene. The Au-In alloy nanoparticles then transform into intermetallic AuIn₂ nanoparticles that are surrounded by a shell of amorphous indium oxide (AuIn₂@InO_x), followed by the final Au-In₂O₃ heterodimers upon complete phase segregation.