Co–Au core-shell nanocrystals formed by sequential ion implantation into SiO2

Co–Au core-shell nanocrystals (NCs) were formed by sequential ion implantation of Au and Co into thin SiO2. The NCs were investigated by means of transmission electron microscopy and extended x-ray absorption fine structure spectroscopy. The latter reveals a bond length expansion in the Co core compared to monatomic Co NCs. Concomitantly, a significant contraction of the bond length and a significant reduction of the effective Au–Au coordination number were observed in the Au shells. Increased Debye-Waller factors indicate significant strain in the NCs. These experimental results verify recent theoretical predictions.