FORMATION AND CHARACTERISATION OF NANOCRYSTALLINE COPPER IN AMORPHOUS SILICA

Samples were prepared by high-energy implantation of Cu ions into a SiO_2 (5μm)/Si (substrate) matrix. Cu ions were implanted to a nominal dose of 1×10^16 - 3×10^17 /cm^2 at a sequential beam energy of 5000 - 800 keV and at a current density of ~5 μA/cm2. Implantation was carried out at LN2 temperature in a vacuum of < 10^-7 Torr. Nucleation and growth was induced by subsequential anneals in 5%H_2+95%N_2 (forming gas) for one hour at 500, 800, and 1100C. Determination of the nanocrystal structure and morphology within the silica film was accomplished by correlating results from X-Ray Diffraction (XRD), Rutherford Backscattering Spectroscopy (RBS), Transmission Electron Microscopy (TEM) and Extended X-ray Absorption Fine Structure (EXAFS). Results show that a mean dose of 1×10^16 /cm2 tends to form a significant fraction of Cu-O bonds at all annealing temperatures, except 1100C at which most Cu evaporates from the SiO_2 film. Oxides are also apparent in the as-implanted and 500C annealed sample of dose 3×10^16 /cm2. All higher anneals and doses readily formed Cu nanocrystals. In particular a dose of 3×10^17 /cm^2 showed similar EXAFS to that of a bulk Cu standard largely independent of temperature, while 1×10^17 cm^2 exhibited a crystalline size growth with increasing temperature. TEM displayed the nanocrystal size distribution, while XRD and in particular EXAFS data verified a mean nanocrystal size growth with dose as well as annealing temperature. The latter exemplified by an increase in co-ordination number. Further, EXAFS showed the bond length remained constant for all samples, except 1×10^16 /cm2 possibly due to oxides, at all annealing temperatures. The bond length was found to be distinctively longer than that for a bulk Cu standard