Formation and characterization of nanoparticles formed by sequential ion implantation of Au and Co into SiO2

Nanoparticles (NPs) were formed by sequential ion implantation of Au and Co into thin SiO2. After Au implantation and annealing, Co implantations were carried out at room temperature (RT) and 400 °C, respectively, with no subsequent annealing. The NPs were investigated by means of Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) and extended X-ray absorption fine structure spectroscopy (EXAFS). TEM shows the formation of Co-Au core-shell NPs for the Co implantation at 400 °C. EXAFS measurements indicate significant strain in the NPs and a bond-length expansion of the Co-Co bonds in the NP core with a concomitant contraction of the Au-Au bonds in the Au shells. NPs are also observed by TEM for the Co implantation performed at RT, however, a lack of crystallinity is apparent from electron diffraction and EXAFS measurements.