Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
EXAFS study on metal cluster doped silica glass obtained by ion implantation procedures
Introduction
Glasses containing nanometer-sized metal clusters exhibit intensity-dependent refractive index values up to 7 orders of magnitude larger than that of silica glass, owing to dielectric and quantum confinement effects [1]. The preparation of “mixed” colloidal structures, containing clusters of either different metals or formed by metal alloys, has recently attracted attention, due to the possibility of tailoring the optical performances of these composites. In particular, multicomponent nanoclusters of Ag/Cu, In/Cu, In/Ag, Ag/Sb and Cd/Ag were claimed to form by sequential implantation in silica 2, 3, 4, 5, 6. In this work, the use of X-ray absorption techniques is investigated in the case of Ag+Cu and Au+Cu implantation in silica glass, showing the potential of X-ray experiments in giving information on the microscopic structure of these composite glasses.
Section snippets
Experimental
Thin (0.1 mm) silica glass sheets were implanted with double implantation routes of either Ag+(1.65 MeV)+Cu+(1 MeV) or Au+(3.1 MeV)+Cu+(1 MeV), all the implants at a fluence of 3 × 1016 ions/cm2. The implantation energies were chosen from TRIM [7]calculation to get a good overlap of the implanted profiles. Calculated peak concentrations were in the range 0.8–1 at.% at a depth of about 0.85 μm. Optical absorption spectra in the 200–800 nm range were recorded using a Cary 5 dual-beam
Ag+Cu implant
The Cu–Ag system has an extremely low partial solid solubility at room temperature [11]. Indeed, metastable alloys are formed by implanting Ag in bulk Cu, creating the condition for an extremely rapid quenching during the decay of the thermal spike and thus for the formation of Cu–Ag alloys [12]. As shown in Fig. 1, the optical absorption spectrum of the Ag+Cu sample exhibits an absorption band at about 400 nm, attributed to surface plasmon resonance of metallic Ag clusters [13], while no
Discussion and conclusions
The local atomic order around noble metals in Ag+Cu and Au+Cu implanted pure silica was studied by X-ray absorption spectroscopy techniques. From the analysis shown in Fig. 2, Fig. 3, no evidence of alloying between the co-implanted species is observed, although it should be well visible in EXAFS, considering the difference in atomic number of the involved atoms. The three elements in this study exhibit quite a different behavior. Cu exhibits a strong reactivity with the surrounding matrix. In
Acknowledgements
This work has been partially supported by Italian MURST and CNR.
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