Accelerated growth from amorphous clusters to metallic nanoparticles observed in electrochemical deposition of platinum within nanopores of porous silicon

•Pt nanoparticles electrochemically formed in nanoporous silicon templates.•Temporal change in chemical states of the Pt nanoparticles analyzed by XAFS.•Accelerated penetration of Pt precursor resulting in formation of amorphous Pt nanoparticles

This study examined the formation of amorphous platinum (Pt) clusters in nanopores of porous silicon at an initial stage of pore filling. The time dependency of the chemical state and local structure of Pt in the nanoporous silicon were characterized by X-ray absorption fine structure spectroscopy (XAFS). Initially, the Pt deposits showed non-negligible amounts of PtO2, formed by surface oxidation from the atmosphere, suggesting that the particle size was quite small. Deep analysis of extended XAFS (EXAFS) strongly suggested that Pt at the early stage of deposition was amorphous. The mechanism of amorphous Pt formation is discussed based on the confinement effect for Pt complex anions in nanopores.