Spin Filter of Graphene Nanoribbon Based Structure

Spin-dependent transport properties of the zigzag graphene nano-ribbon (zGNR) based structure Al-zGNR-Al are investigated by ab initio technique where density functional calculation is carried out within the Keldysh non-equilibrium Green's function formalism. The energy band structure of the infinite zigzag ribbon is sensitive to the dangling bonds of carbon atoms on both edge sides. For the three-circle-width zigzag ribbon with one edge monohydrogenated and the other edge dihydrogenated (zGNR(H-H2)), strongly spin-polarized energy bands are found. A spin-down branch is obtained just below the Fermi level while a spin up band appears above it. For the structure Al-zGNR(H-H2)-Al, where three-circle-width and seven-circle-length (3×7) zGNR(H-H2) is coupled by two (100) aluminium electrodes, an obvious spin filter property is found as the bias voltage changes. When the length of the sandwiched zGNR(H-H2) ribbon increases, the spin-up current is strongly restrained especially under higher bias voltage.