The effect of implantation temperature and ionizing radiation on the microstructure of ion implanted sapphire

by Ononye, Lawretta L.

Single crystalline specimens of aluminum oxide (Al2O3) were irradiated with boron, nitrogen and iron ions at room temperature and 1000oC to fluences of 1×1017 B+/cm 2, 3×1016 N+/cm2 and 1×1017 Fe+/cm2 respectively with 150 keV of energy. Following irradiation, the structures were examined by several experimental techniques: transmission electron microscopy (TEM), Rutherford backscattering - ion channeling (RBS-C) spectroscopy, optical absorption measurements, x-ray diffraction (XRD) technique, and x-ray photoelectron spectroscopy (XPS). The samples implanted at room temperature were then annealed for one hour at 1000oC in a reducing (Ar-4%H2) gas and the microstructures examined. The implantation temperature significantly influenced the microstructure of the implanted samples. The room temperature boron-implanted microstructure consists of the typical “black spot” radiation damage, which differs from the microstructural features observed at 1000oC. Cross-sectional TEM micrograph for the nitrogen-implanted at room temperature reveals a band of bubbles or voids; whereas the 1000oC N-implanted specimen exhibits a different type of “black spot” radiation damage generally ascribed to defect clusters. The microstructure of the iron-implanted sapphire at room temperature contains “black spot damage” clusters and small (1-2 nm) precipitates at depths greater than about 25 nm. The sample implanted with iron at 1000°C contains particles of iron as large as 50 nm and no evidence of “black spot” radiation damage. These iron particles were identified as ?-Fe. The microstructures for all three species implanted into sapphire at room temperature followed by annealing in Ar-4% H2 for one hour at 1000°C were quite different from the as-implanted ones. None contained “black-spot damage” or interstitial defect clusters, but all contained evidence for small second phase particles. The annealing promoted the recombination of point defects and defect clusters and allowed the system to move toward the equilibrium phase compositions. The lattice disorder as measured by RBS-C was greater for iron and boron implantation at room temperature than at 1000°C, but higher for nitrogen-implanted at v 1000°C. The highest lattice disorder was produced by the iron implantation and is attributed to the higher density of displacements in the cascades. The optical absorption measurements indicate the presence of oxygen vacancies and defect clusters involving oxygen vacancies. The number of F-type centers was highest for boron-implanted at 1000° C. The depth-dependent microstructures of the irradiated specimens, the energy deposited (elastic and inelastic) as a function of depth from the surface, the range of implanted species, and the defect production were modeled using the transport and range of ions in materials (TRIM) program. The results of the model showed that the ionizing component of the irradiation did not noticeably affect the microstructures. The ENSP ratios {(dE/dx)e/(dE/dx)n} obtained from the TRIM simulations did not differ significantly for the three species through the range where significant displacements occurred. The range of boron-implanted into sapphire is more than that for nitrogen and iron. Iron has the shortest range. The density of vacancy (and interstitial) production is much higher for the Fe than for the B or N. The number of Al vacancies produced at all positions along the range is greater than the concentration of O vacancies. vi