Development of nanodevice processes for carbon nanotubes

已经开发了用于将碳纳米管应用于纳米器件的器件工艺。首先，基于电子束光刻中的标记对准技术，开发了一种制造单个碳纳米管的电接触的工艺。对于单壁碳纳米管（SWCNT），隧道势垒形成在金属接触的边缘，并且接触之间的整个纳米管形成单个量子点。这一事实表明，接触下方的SWCNT是绝缘的。通过测量电子输运的温度依赖性来估计隧道势垒的势垒高度，结果为几meV。这意味着尽管SWCNT单电子晶体管的充电能量大，但操作温度不受充电能量的限制，而是受势垒高度的限制。这与实验观察到的库仑阻塞效应在20 K左右被观察到相吻合。在本研究的过程中，我们指出了影响碳纳米管器件工艺的重要因素。这些是1）需要形成人工隧道势垒，2）需要克服束效应，以及3）需要生长具有可能的位置控制的碳纳米管。为了解决这些问题，我们尝试了以下方法。1)隧道势垒：我们开发了一种局部Ar束辐照多壁碳纳米管的技术。2)捆绑效应：为了克服这个问题，已经开发了大电流流动过程，其中选择性地观察到来自单个量子点的峰。3)仓位控制增长：为此，我们开发了一种化学气相沉积技术，利用图案化催化剂和外加电场，在本项目中，我们相信已经建立了用碳纳米管制造纳米器件的基本技术

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