Novel physical properties of glancing angle deposited nanowire arrays for spintronics.

摘要

Highly oriented perpendicular nanowire arrays with novel structures were fabricated by the technique of glancing angle deposition with substrate rotation. The nanowires are considered as a potential tool for the fundamental study of spin transport, and promising candidates for applications in perpendicular recording media. The detailed spin arrangements and dynamics in such devices have not been explored yet, and can only be understood if the atomic scale structure of the devices is precisely known.; The growth and resulting crystallography of self assembled Cu nanowire arrays deposited both on native oxide Si(100) and H-terminated Si(110) substrates, respectively, were studied and compared. On native oxide Si(100), the nanowires exhibited a strong (110) texture for a deposition angle theta = 75° with rotational symmetry of the low energy Cu[111] directions about the wire's long axis. On H-terminated Si(110), the wires have an epitaxial orientation relationship with the substrate up to the critical height limit of 300 nm. Individual nanowires were confirmed to be single crystal by examination by transmission electron microscopy. The critical height for epitaxial growth is maximal (2800 nm) at a deposition angle theta = 35° and decreases rapidly with increasing deposition angle.; Atomic self-shadowing and surface diffusion, which depend on the incidence angle, have a strong effect on morphology and texture formation. As the angle of incidence is increased, Cu grows as isolated columns with a spacing that increases as the angle of incidence is increased. Based on these observations, the growth mechanisms in glancing angle deposited materials and the theory of structural transitions in epitaxial overlayers of thin films, a theory for the growth mode in epitaxial nanowire arrays is proposed with a description of the recrystallization process that takes place above the critical height.; The epitaxial Cu nanoarrays were used as seed layers to grow Ni 80Fe20 nanowire arrays. The nanowires exhibited a strong [311] texture, with the [111] directions having rotational symmetry about the wire's long axis. At low aspect ratios (∼0.5--1.5), the angular remanence lies on the surface of a cone with its axis along the substrate normal. A model to explain this behavior is presented.