Co-Au core-shell nanocrystals ͑NCs͒ were formed by sequential ion implantation of Au and Co into thin SiO 2. 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.
Nanoparticles (NPs) were formed by sequential ion implantation of Au and Co into thin SiO 2 . 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 Xray 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.
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