This proposal was received in response to the Spin Electronics for the 21st Century Initiative, Program Solicitation NSF 02-036. The proposal focuses on spin dependent transport and spintronics functionality in a unique nanostructured system - Y-junction Carbon Nanotubes. The Y-junction nanotubes, first fabricated by one of the PIs (JMX)-combine the attractive properties of carbon nanotubes (effectively 1D electronic transport with long ballistic mean free paths and exceptionally high current densities)with a three-terminal geometry and a built-in heterojunction barrier at the Y-branching point. Spin transport in ordinary, straight ferromagnetically contacted multi-walled carbon nanotubes, first studied by another of the PIs, has yielded excellent spin-polarized injection efficiencies and long spin-scattering lengths on the order of 0.25 um, making ferromagnet-nanotube hybrids a promising spintronics platform. The spin transport in a Y-junction with the built-in heterobarrier is already interesting and unexplored. But what makes the proposed devices unique is the possibility applying both ferromagnetic and normal metal contacts to the three terminals of the Y-junction, as well as using different ferromagnetic materials (with separately switchable magnetizations)for contacts to the same device. This unprecedented flexibility will enable us, for example, to clearly distinguish spin-mediated injection and extraction of currents from ordinary injection, tune the transmission of spin up and spin down electrons by means of a control voltage on the third terminal, witch the spin-coherent current from one Y-junction arm to another by switching the magnetization with an external field, and more generally produce a true three-terminal spintronic transistor. However great the potential of this new nanostructured system may be, a great amount of challenging work, from fabrication of the Y-junction nanotubes to fabrication of nano-scale contacts to cryogenic measurements of the contacted Y-junctions in the presence of magnetic fields externally modulated, will have to done first to prove the concepts. This NSF project is launched for these proof-of-concept explorations, and for paving the pathway to this new and exciting field of opportunities.
