Development of nanodevice processes for carbon nanotubes

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Device processes have been developed for carbon nanotubes to be applied for nanodevices. First of all, a process to fabricate electrical contacts to individual carbon nanotubes was developed, based on the mark alignment technique in electron beam lithography. For single-wall carbon nanotubes (SWCNTs), the tunnel barrier is formed at the edge of the metallic contact, and a whole nanotube between the contacts form a single quantum dot. This fact indicates that the SWCNTs underneath the contact is insulating. The barrier height of the tunnel barrier was estimated by measuring a temperature dependence of the electronic transport, and was turned out to be several meV. This means that despite the large charging energy of the SWCNT single electron transistor, the operation temperature is not limited by the charging energy, but is limited by the barrier height. This coincides with an experimental observation that the Coulomb blockade effect is observed up to around 20K.In the course of this study, we have pointed out the important factor for the carbon nanotube device process. These are 1)a need to form artificial tunnel barriers, 2)a need to overcome the bundle effect, and 3)a need to grow carbon nanotubes with possible position control. To tackle these problems, we have attempted following approaches. 1)Tunnel barrier : We have developed a local Ar beam irradiation technique to multi-wall carbon nanotubs. 2)Bundle effect : To overcome the problem, the large current flowing process has been developed, where the peaks from single quantum dots were selectively observed. 3)Position control growth : To do this, we have developed a chemical vapor deposition technique with patterned catalysts and an applied electric field.In the present project, we believe that the basic technique to fabricate nanodevices with carbon nanotubes have been established