Structural characterization of bimetallic Ag-Au nanoparticles in glass

Metal nanoparticles embedded in glass have been thoroughly studied because of their specific optical properties. The present work is directed to the fabrication of bimetallic Ag/Au nanoparticles by double ion implantation and their structural investigation. Ion-implanted samples were measured at the Ag K- and Au L₃-edge at HASYLAB/Hamburg and ESRF/Grenoble, respectively, in fluorescence mode (at 10 and 20 K). The Fourier transformed spectra show Ag-Ag and Ag-O bonds for small ion doses. For high ion doses two different correlations (Ag-Ag and Ag-Au) can be found between 2 and 3 Å. At the Au L₃-edge, the high-dose implantation creates an additional Au-Ag correlation visible in the Fourier transformed spectra. These results indicate the formation of Ag-Au alloy nanoparticles for high-dose sequential implantation of Ag and Au ions (4×10¹⁶ ions/cm² in each case) whereas for lower doses mainly the ionic state of implanted ions should exist. Transmission electron microscopy characterization revealed the formation of smaller homogeneous particles of ≈5 nm mean size and larger ones of ≈15 nm that exhibit an internal void, i.e. hollow core-shell particles. EXAFS data prove bimetallic structures for all nanoparticles.