Center for Functional Nanomaterials Seminar

Carbon-related structures, such as carbon nanotubes and graphene sheets, are promising nano-materials for nano-electronics beyond silicon. Among them, graphene nanoribbon (GNR) has attracted great attention because its energy band structure can be easily tailored, which enables us to use it as a material for field effect transistors. The electronic properties of GNRs significantly depend on the edge geometry of the ribbons. For instance, a zigzag-edged graphene nano-ribbon (Z-GNR shows a partly-flat electronic band structure near the Fermi energy and an electronic wavefunction that is localized near the edges of the GNR. A field-effect current controllability of the Z-GNR based transistor has been also reported. Detailed theoretical calculations, where the spin-dependent electron-electron interaction is taken into account, actually show that those edge localized states stimulate the edge spin-polarization with opposite spins along the opposite edges. We have performed a three dimensional device simulation of Z-GNR based spin filtering devices assuming the side gated field effect transistor (FET) structure. We show that the populations of opposite spin states can be modulated by the transverse electric field to induce a half-metallic band structure, which makes it possible to realize GNR spin-filtering devices.