HRTEM analysis of solid precipitates in Xe-implanted aluminum

High-resolution transmission electron microscopy (HRTEM) was carried out to determine the shape and atomic arrangement of solid Xe precipitates in Al. Polycrystalline Al TEM specimens were implanted with 30 keV Xe+ at room temperature to a dose of 3 x 10(20) ions/m(2) and were subsequently annealed at 523 K. Below a size of approximately 4 nm in diameter, Xe precipitates are solid with an FCC crystal structure that are mesotacticly aligned with the Al lattice. In HRTEM along the [011] projection, the difference in the lattice parameters of solid Xe and Al produces a precipitate image dominated by a two-dimensional Moire pattern that repeats in both the [001] and [111] directions every 3 Al (or 2 Xe) lattice spacings, Multi-slice image simulations, using a three-dimensional atomic model, demonstrates that the precipitates are tetradecahedra with faces parallel to the dense {111} planes and the {100} planes, Off-Bragg illumination of the precipitates minimizes Al lattice fringes and generates precipitate images which are in good agreement with the model.