PHASE FORMATION STUDY IN ALPHA-AL2O3 IMPLANTED WITH NIOBIUM IONS

Niobium ion.s of 150 keV energy have been implanted at temperatures of 77 or 300 K in α-Al2O3 with doses ranging from 5 × 1015 to 3 × 1017 ions/cm2 and subsequently thermal annealed up to 1273 K in H2 gas or in air. The structure of the implanted layer has been characterized by X-ray diffraction at glancing incidence and its physical properties have been investigated by means of optical absorption spectroscopy and electrical conductivity measurements. For implantation performed at 77 K, the sapphire reaches an amorphous state at a fluence of 5 × 1015 ions/cm2 whereas an implantation dose of 5 × 1016 Nb/cm2 is required at 300 K. For heavily implanted samples the amorphous layer has an electrical resistivity typical of poor metal. Annealing treatment performed in Hi gas leads to the formation of an Nb2O5 oxide plus clusters of niobium, whereas a NbA104 compound is observed after annealing in air. © 1990.