Kinetics of the Amorphous →γ→α Transformations in Aluminum Oxide: Effect of Crystallographic Orientation

Abstract

Time‐resolved reflectivity (TRR) measurements have been used to determine the growth kinetics of both the amorphous‐to‐γ‐phase and the γ‐to‐α phase transformations of alumina films that have been deposited on (0001), (1210), and (0112) sapphire substrates. The activation energies for the amorphous‐to‐γ‐phase and γ‐to‐α transformations respectively are 4.5 and 5.2 eV, irrespective of the crystallographic orientation of the underlying sapphire substrate. For both transformations, the relative transformation rates seem to reflect the symmetry of the sapphire substrates, with the fastest kinetics being on the lowest symmetry orientation and slowest kinetics being on the highest symmetry orientation. These relative rates are attributed to the differences in step mobility on the different substrate orientations.