Recently, a number of works have been performed to measure quantum transport in nanometer-scale systems. Quantum effect is dominant in such a nanoscale system and the electron transport properties of atomic wires, single molecules, and carbon nanotubes have been investigated. Furthermore, towards a development of constructing nanometer-scale devices, considerable effort has been made in experiments using single molecules and nanotubes for fabricating nanoscale field-effect transistors. To detect electric signals, electrodes must be connected to the conductors. Contact with the electrodes sensitively influences the transport properties. Therefore, it is important to discuss the transport properties on the basis of the detailed electronic state calculation that includes the effect of contact with the electrodes.
We have investigated quantum transport in nanometer-scale systems between electrodes. The electronic states are calculated using a numerical atomic orbital basis set in the framework of the density functional theory, and the conductance is calculated using the Green's function method. We have analyzed transport properties of the finite size of carbon nanotubes connected to metallic electrodes, and show the contact effect of the electrodes on the transport properties. We reveal their dependency on the electrode materials and the length of the nanotube.
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