Characterization of iron implanted sapphire nanocomposites

Nanocomposites of iron in sapphire (α-Al₂;O₃;) were prepared by implantation of 160 keV Fe⁵⁶; at room temperature with several fluences, and then annealed at selected temperatures between 700 and 1400°C in an Ar-4% H₂; atmosphere for 1 hour. The structure of these nanocomposites was characterized using Rutherford backscattering spectroscopy and high resolution transmission electron microscopy (TEM). Measurements showed that damage depth extended to about 300 nm and the embedded iron to approximately 200 nm. This region became amorphous when the fluence reached 2 x 10¹⁷; Fe/cm²;, at which oriented precipitates with diameters of 2 to 3 nm were identified by TEM techniques as α-Fe. Thermal annealing restored crystallinity to the damaged near-surface region, formed metallic colloids, and coarsened the precipitates. Optical density and luminescence spectra were also determined. The predominant defects were F centers (an oxygen vacancy containing two electrons) indicated by an absorption peak of 200 nm. Hardness and elastic modulus were determined using the Nano-indenter^TM;. The results exhibited a radiation-induced softening and a decrease in modulus through the crystalline- to-amorphous transition, and also a radiation-induced hardening below the transition.