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(Color online) Structures of the extended molecules: A mirror symmetrical straight SWNT heterojunction is coupled to two semi-infinite Al electrodes, and the extended molecule consists of (100) four layers of Al slab with 50 atoms per unit cell in the right lead, three layers of Al slab with 37 atoms in the left lead, and the mirror symmetrical SWNT heterojunction indicated as , where and describe the number of cells of zigzag carbon nanotubes. Here, we choose the values of to be 6, 7, and 8 and those of to be 1, 2, 3, and 5. The number of cells of the (6, 0) tube is fixed at 3. The distance between the SWNT end and the metal surface is chosen to be , which is a typical electrode-tube distance.
Transmission coefficient for the two-probe systems shown in Fig. 1 as a function of injected electron energy at zero bias : (a1), (a2), and (a3) correspond to (6, 0), (7, 0), and (8, 0) tubes without heterojunction; (b1), (b2), and (b3) correspond to the numbers of cells in systems; (c1), (c2), and (c3) correspond to in systems, respectively. Some frontier molecular orbitals have been denoted by dashed lines, and HOMO and LUMO have also been labeled. Here, the energy origin is set to be the Fermi level of the system.
Calculated current as a function of the applied bias for carbon-nanotube heterojunction devices: The curves are divided into two bundles. the above and below bundles (for positive bias) correspond to and carbon-nanotube heterojunctions, respectively. The solid, dashed, dotted, and dot-dashed curves correspond to , 2, 3, and 5, respectively. The insert gives of the system under biases , 1.2, and .
(Color online) The molecularly projected self-consistent Hamiltonian (MPSH) at the eigenvalue of the system under the biases , , and .
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