The influence of annealing conditions on the growth and structure of embedded Pt nanocrystals

The growth and structure of Pt nanocrystals (NCs) formed by ion implantation in $a-SiO2$ has been investigated as a function of the annealing conditions. Transmission electron microscopy and small-angle x-ray scattering measurements demonstrate that the annealing ambient has a significant influence on NC size. Samples annealed in either Ar, $O2$⁠, or forming gas (95% $N2$⁠: 5% $H2$⁠) at temperatures ranging from $500°C–1300°C$ form spherical NCs with mean diameters ranging from 1–14 nm. For a given temperature, annealing in Ar yields the smallest NCs. $O2$ and forming gas ambients produce NCs of comparable size though the latter induces H chemisorption at $1100°C$ and above, as verified with x-ray absorption spectroscopy. This H intake is accompanied by a bond-length expansion and increased structural disorder in NCs of diameter $>3nm$⁠.