Atomistic study of the role of contact properties on nanotube conduction

Summary form only given. Transport through nanoelectronic systems is known to depend sensitively on the properties of their interfaces with bulk contacts. This becomes particularly important in the ballistic limit, where the contact resistance dominates conduction. Carbon nanotube field effect transistors, for example, are typically controlled by a Schottky-barrier at the contacts. There has been some progress in achieving low barrier heights to large diameter nanotubes, but producing good contacts is still something of an art. The theoretical understanding of the specific conditions required to generate ohmic or Schottky contacts, their dependence on the metal workfunctions or their wetting properties, is still limited. The challenge though in developing a rigorous simulation procedure is the need to do justice to the bonding geometry and surface chemistry of the metal-carbon bonds, the bulk bandstructures of the contact and the nanotube, the overall electrostatics, and the nonequilibrium quantum kinetics - all at the same time. We have developed a formalism that self-consistently combines electronic structure codes describing the nanotube Hamiltonian and the open-boundary contact self-energies with a non-equilibrium Green´s function (NEGF)-based transport formalism. This formalism has been successfully used in the past to derive various first-principles properties of molecular conductors. We use extended Huckel theory parametrized to match ab-initio calculations to describe the bulk nanotube and metal bandstructures. The self-consistent potential describes both local charge transfers due to the interfacial bonding chemistry, as well as global transfers due to the differences in bulk electrochemical potentials of the contact and the nanotube. We are using this atomistic formalism to simulate transport through various metal-nanotube contacts. We discuss the formalism and its implementation, and present preliminary results that provide insights into the nature of metal contacts to nanotubes.