Synthesis of Carbon Nanotubes coated with Gate Insulator and its Application to Quantum Nanodevices

碳纳米管(CNTs)以其独特的物理化学性质成为未来纳米电子学的重要材料。例如，场效应晶体管(FETs)是一种以库仑阻塞和弹道导电等量子现象为特征的量子纳米器件，由于每个CNT-FET需要独立驱动才能作为集成电路的构建块，因此导通通道上方具有栅极的顶栅结构是必不可少的。具有顶栅结构的CNT-FET的制备强烈依赖于传统的纳米制造技术，本项目的目标是利用脉冲激光沉积(PLD)技术将栅绝缘层涂覆碳纳米管作为量子纳米器件的构建块来开发具有顶栅结构的CNT-FET的高通量工艺。值得特别指出的新发现如下：(1)利用PLD对碳纳米管进行了与各种无机材料的同轴包覆。对于氧化物材料，沉积呈现出均匀的层状结构，其组成受到精确的控制。此外，还通过重复PLD的方法在碳纳米管上连续涂覆了单层和多层。(2)将涂覆了无机材料的碳纳米管和以碳纳米管为模板合成的杂化无机纳米线应用于扫描隧道显微镜针尖和纳米机电系统的构建块等纳米器件中。对于杂化纳米线，其结构是夹在氧化铝和氧化钨之间的碳纳米管模板，我们观察到了热诱导的纳米机械偏转。由于包覆层的热膨胀系数不同，随着样品温度的升高，杂化纳米线被弯曲。这种机械偏转表现出重复性。

Carbon nanotubes (CNTs) have been the promising materials for future nanoelectronics due to their unique physical and chemical properties. For example, field-effect transistors (FETs), quantum nanodevices characterized by quantum phenomena such as Coulomb blockade and ballistic conduction have been proposed.Since independent drive of each CNT-FET is required to operate CNT-FETs as building blocks of the integrated circuit, the top gate structure with gate electrodes above the conduction channel separated from the channel by a thin dielectric is indispensable. The fabrication of CNT-FETs with the top gate structure strongly depends on the conventional nano-fabrication techniques.In this project, it is an aim to develop the high-throughput process for CNT-FETs with the top gate structure using gate insulator coated CNTs by pulsed laser deposition (PLD) as a building block for quantum nanodevices. The new findings worthy of special mention are as follows.(1)Using PLD, coaxial coating of CNTs with various inorganic materials has been performed. For oxide materials, the deposits exhibited a uniform layer structure the composition of which was precisely controlled. Moreover, not only a single layer but also multiple layers were sequentially coated on CNTs by repeating PLD.(2)CNTs coated with inorganic materials and hybrid inorganic nanowire synthesized using a CNT template were applied to the nanodevices such as tips of scanning tunneling microscopy and building blocks for nanoelectromechanical systems (NEMS). For the hybrid nanowire, the structure is a CNT template sandwiched by aluminum oxide and tungsten oxide, we observed thermally induced nanomechanical deflection. The hybrid nanowire was bent with increasing the specimen temperature due to the different coefficients of thermal expansion of the coated layers. This mechanical deflection exhibited repeatability.