Evolution of precipitates in lead-implanted aluminum: A backscattering and channeling study

The behavior of lead atoms implanted at 150 keV into (110) aluminium single crystals is studied by Rutherford backscattering (RBS) and a channeling technique. Channeling observed for the lead signal in the as-implanted samples for implantation fluences in the region of 1 x 10 exp 15 -3.1 x 10 exp 16 cm exp -2 is ascribed to the formation of nanometer-sized Pb inclusions growing in topotaxy (epitaxy in three dimensions) within the Al matrix. Monte Carlo channeling simulations have been performed based on average sizes of the inclusions obtained from transmission electron microscopy and depth distributions of Pb atoms from RBS. It was shown that channeling in the inclusions strongly depends on their size. Large inclusions demonstrate by far the best channeling due to the relative reduction of the surface (interface) peak effect. In the simulations multiple intersections of the inclusion/matrix interfaces were found to be of importance for dechanneling of the analyzing ions. Comparison of the simulations with experimental data showed that in the as-implanted samples a considerable fraction of the Pb atoms is in supersaturated solution and in small ( < = 1 nm) inclusions which do not show significant channeling. Upon annealing the larger inclusions grow by absorption of atoms from the solution and coalescence with smaller precipitates. It is shown that the inclusions grow nearly perfectly aligned with the Al matrix in a cube-cube orientation relationship and with a possible misorientation of < 0.1 deg . Features related to the coherency of the inclusion/matrix interface are discussed and a comparison with other channeling measurements for nanometer-sized crystallites is made.