Tunnel barrier formation in carbon nanotubes for quantum dot devices

Our effort to form reliable tunnel barriers in single and multi-wall carbon nanotubes is presented. As well as the standard method which uses a simple deposition of contact metal on nanotubes, we uses a narrow SiO2 deposition and Ar ion beam irradiation to form the tunnel barrier, in nanotubes. Such devices as a single electron transistor, double coupled quantum dots and a single electron inverter have been fabricated. Their performance has been measured from 20mK up to liquid helium temperature. The unique microwave response of coupled quantum dots is also presented. We show that the carbon nanotubes are attractive material for the building block of quantum-dot based nanodevices with extremely small dimensions, and our method may be useful to realize the devices and circuits.