Transport properties of carbon-nanotube devices studied by tight-binding and ab-initio calculations

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In the near future, the scaling down of semiconductor devices to smaller and smaller sizes will reach fundamental limits (~ 50 nm) below which the devices become inoperable. On the other hand, the discovery of carbon nanotubes in 1991 with their remarkable electronic, structural, mechanical and conductive properties has opened the door to build nanodevices from these large molecules with sizes below the limits for common semiconductor devices. Depending on their chirality carbon nanotubes show metallic as well as semiconducting properties. By contacting such nanotubes to metal leads or even contacting different nanotubes, devices like field-effect transistors, single electron transistors, or rectifiers have been created. However, there are still a number of serious problems to be solved. For example contact resistances between the metal leads and the nanotubes are still too large for the desired application as fast devices with low power dissipation. Little is known about the responsible effects and theoretical effort seems necessary to gain more insight. Other open questions concern the conduction in nanotube junctions, the resistance of nanotubes, electromigration as well as the operation and control of devices by external fields. In this project we intend to tackle some of these problems using tight-binding as well as ab-initio calculations. While the semi-empirical tight-binding calculations will allow large-scale systems and reveal the main underlying physical principles they may be insufficiently accurate in details. Therefore, we intend to perform ab-initio calculations in the second stage of this project.