TEM of epitaxial thin films controlled by planes extending (near) normal to interface; with application to two methods to reduce crystal orientations in polycrystalline magnetic media

This work is a study of heteroepitaxial interfaces as applied to multilayer-thin films for magnetic information storage media. With a goal to develop a film crystallography that optimizes the alignment of magnetic dipoles to coincide with the write/read signal of the recording head, two TEM observations have elucidated a better understanding of what controls heteroepitaxial interfaces. The classical approach to establishing “lattice matching” of interfaces is to model the top plane of atoms of the substrate and then align the next plane of atoms in the subsequently deposited film, i.e. plane A and plane B should “match” (with minimal misfit), with both planes being parallel to the interface. Such mechanism is valid for idealized slow MBE growth where the planes remain atomically flat. However, most film deposition conditions quickly violate this atomically flat configuration. Here growth on a roughened interface is shown to be controlled by the matching of planes that extend (normal or near-normal) across the interface. A second classical observation is the nucleation of bi-crystals, which naturally increases the number of crystal orientations in subsequent films. However, this work exhibits two cases of reducing orientations! One case has a 3-D isotropically oriented cubic film followed by a hexagonal film with 2-&-1/4-D isotropy, and a second case where a 2-D random cubic film is followed by a hexagonal film with 1-&-1/2-D isotropy. The understanding and control of these heteroepitaxial interfaces enables reduction of film orientations to enhance properties, such as 100 Gigabit per-square-inch magnetic recording.