Preparation of nanometer-size dispersions of iron in sapphire by ion implantation and annealing

Some of the metal ions implanted into sapphire (α-Al ₂O ₃) are often present as metallic colloids or dispersions. Nano-composites of iron colloids in sapphire were prepared by implantation of 160 keV Fe ⁵⁶ at room temperature. The colloids were coarsened by annealing in the temperature range of 973 to 1673 K in a reducing atmosphere. Rutherford backscattering-ion channeling (RBS) and transmission electron microscopy (TEM) were used to determine the lattice damage as well as the nature, size and distribution of the iron. Second phase particles having diameters of 1-3 nm, and accounting for 45% of the implanted iron at a fluence of 1 × 10 ¹⁷ Fe/cm ² were identified by electron diffraction as having the α-Fe (body-centered cubic) structure. Annealing samples implanted at lower fluences produced metallic iron particles (3-20 nm diam.) with attached voids. The matrix was amorphous at 2 × 10 ¹⁷ Fe/cm ² and contained "strings" of crystalline iron particles (5-10 nm). Annealing in the reducing atmosphere produced iron platelets several hundreds nanometers long by 25-35 nm thick. It was observed that a range of particle sizes and shapes can be obtained by choice of implantation and/or annealing parameters.