Microstructure and magnetism in amorphous rare-earth–transition-metal thin films. I. Microstructure

A microscopic examination of vapor- or sputter-deposited amorphous rare-earth–transition-metal thin films reveals that they possess anisotropic microstructure. The morphology of the structure is similar in all of the films. It consists of small (50–250 Å in diameter) rod-shaped regions of high density that are surrounded by a network of less-dense material (10–25 Å thickness). The column axes are mutually parallel and are oriented at an angle β that is described by the relationship: tanβ= (1/2) tanα, where α is the angle of incidence of the vapor beam, measured with respect to the substrate normal. The columnar structure is formed during deposition by self-shadowing of the incident atoms by the atoms in the growing film. The columnar structure persists when multiple or distributed vapor sources are used to deposit the film. The structure is stable upon heating to temperaures in excess of the crystallization temperature of the amorphous deposits. Vapor deposition at large α leads to the formation of rowlike column aggregates in a direction perpendicular to the plane of incidence.