This project addresses tunneling characteristics of spin-polarized electrons in GaAs utilizing a novel double-tip scanning tunneling microscope (STM) approach. Measurements of I-V characteristics of a three terminal electrical device structure will make use of a spin-polarized source, a spin-polarized drain, and a spin-friendly transport channel between the source and drain with the entire unit housed inside a vacuum chamber. The source and drain will be made of single-crystal, <110>-oriented nickel wire electrochemically etched into a needle shape to also serve as an STM tip. The STM tips will be brought within 1 nm of an n-type GaAs sample, so spin polarized electrons can tunnel from Ni to GaAs. A unique double-cleave sample allows the tips to be placed on orthogonal surfaces so as to have their points of tunneling be as close as 5 nm from the other. The source-to-drain current will be measured as a function of the lateral separation distance between the two tips. As the second tip is scanned downward the distance between the two tips will grow. As this distance grows so does the distance from the source to the drain, making this a tunable channel length device structure. As the electron's path length grows, the orientation of the electron's spin changes (due to precession about the external magnetic field of the tips). When the path length is just right, the electron's spin will rotate just such as to leave the orientation of the spin matched with the orientation of the second tip, resulting in a high current flow. If the electron's spin is not well matched, then a lower current is expected. The current is expected to oscillate in space as the second tip is scanned across the cleaved GaAs surface. Additionally, ultra-thin ferromagnetic GaMnAs layers will be grown by MBE. After double cleaving the sample, spin transfer properties will be measured by injecting spins into one surface and pulling them out of the side surface above, inside, and below the GaMnAs layer to allow local transport properties through the layers to be investigated. %%% The project addresses basic research issues in a topical area of electronic materials with high technological relevance. An important feature of the project is the strong emphasis on education, with emphasis on integration of research and education including special classroom techniques that promote students' participation through question/answer portions of lectures. The integrated research and education project will improve fundamental understanding of factors important to the evolving field of spintronics, which combines conventional electronics and spin transport. Additionally, the project assists development of strong technical, communication, and organizational skills in students made possible by a forefront research environment. ***
