Suspended graphene and carbon nanotube device arrays by bottom-up assembly

碳的低维同素异形体，即一维碳纳米管（CNTs）和二维石墨烯，具有极高的电子、机械和光学性能的奇妙组合。尽管高性能的纳米碳器件已经被证明，但它们还没有在实际应用中发挥作用。商业化的主要障碍在于传统（自上而下）技术在扩展到纳米级对象、制造电子设备、传感器、致动器和其他此类体系结构时的可重复性和可扩展性有限。虽然这些传统的路线已经产生了可测试的概念验证设备，但我们需要一种新的，非常规的方法来大规模地以高集成密度制造这些设备。同时，这种方法必须与现有的CMOS技术兼容，尽管它们具有非常规的性质，以实现商业可行性和技术共存。在碳纳米管的情况下，最有希望的方法是使用交流（A/C） dielectrophoresis （DEP）将活性碳纳米管元件自下而上地集成到预定位置。DEP可以与密度梯度超离心（DGU）等碳纳米管分选方法结合使用，以生产仅半导体甚至单手性碳纳米管器件的高密度阵列，使其成为唯一在商业上可行的技术，可以克服碳纳米管在器件应用中的多分散性问题。由于液滴干燥过程中强烈的表面张力抵消作用，基于depp的器件制造迄今为止仅限于衬底支撑器件，即活性纳米碳元素在沉积时必须位于衬底上，而不能自由悬浮在两个电极之间。在迄今为止研究的几乎所有碳纳米管或石墨烯电子器件中，悬浮器件的性能明显优于基板支撑器件。诸如谐振器之类的设备只能在悬浮状态下工作。由于碳纳米管或石墨烯中的每个原子都是表面原子，因此与衬底的相互作用严重干扰了纳米碳器件的性能。典型的影响包括重掺杂，由于散射增强而降低迁移率，更高的1/f噪声，从而降低信噪比，以及由于衬底遮挡了某些表面积而降低传感器应用中的灵敏度。我们将首次尝试大规模自下而上组装和集成由铁磁电极和石墨烯/碳纳米管自旋通道组成的纳米碳自旋阀，这将为未来基于量子计算的纳米电子电路提供一条可行的途径。通过裁剪源极和漏极以在不同场切换而形成自旋阀。基片栅极将用于调制自旋电流。悬浮结构有望消除基片散射并提高自旋相干长度。NEMS器件，如用于质量传感器的谐振器，只能使用悬浮碳纳米管/石墨烯器件，由于碳纳米管/石墨烯的机械和电子性能的出色结合，这种器件具有很大的前景；然而，这种谐振器阵列需要具有高质量因子，本项目将展示一种可扩展的制造这种谐振器阵列的途径。在这个项目中提出的设备，特别是纳米碳传感器，是未来能源和环境工业的关键组成部分。许多领先的英国和全球公司目前正在寻找用于此类应用的下一代传感器，例如氢传感器，用于核反应堆等高辐射环境的传感器或用于检测排放物中痕量有毒或有害环境气体的传感器。

Low-dimensional allotropes of carbon, namely the 1D carbon nanotubes (CNTs)and 2D graphene, posses a fantastic combination of superlative electronic, mechanical and optical properties. Despite the fact that high-performance nano-carbon devices have been demonstrated, they have yet to make a mark for themselves in real-world applications. The primary barrier to commercialization lies in the limited reproducibility and scalability of conventional (top-down) technologies when extended to nano-scale objects, to fabricate electronic devices, sensors, actuators, and other such architectures. While these conventional routes have yielded testable proof-of-concept devices, we would need a new, unconventional approach to fabricate these devices on a large scale at high integration densities. Simultaneously, such a method must be compatible with existing CMOS technology despite their unconventional nature, in order to achieve commercial viability and technological co-existence. In the case of CNTs, the most promising approach is the bottom-up integration of active CNT elements into pre-defined locations using alternating-current (A/C) dielectrophoresis (DEP). DEP can be used in combination with CNT sorting methods such as density-gradient ultracentrifugation (DGU) to produce high-density arrays of only-semiconducting or even single-chirality CNT devices, making it the only commercially viable technique that can overcome the polydispersity problem in CNTs for device applications. Due to strong counteracting surface-tension forces during drop drying, DEP-based device fabrication has so far been limited to substrate-supported devices, i.e., where the active nano-carbon element has to lie on a substrate upon deposition and not freely suspended between the two electrodes. In almost every case of CNT or graphene electronics-based device that has been studied to date, suspended devices have significantly outperformed substrate-supported devices. Devices such as resonators can only function in suspended configuration. Since every atom in a CNT or graphene is a surface atom, the properties and performance of nano-carbon devices are severely perturbed by interactions with substrates. Typical effects include heavy doping, lower mobility due to enhanced scattering, higher 1/f noise and consequently lower signal to noise ratios, and lower sensitivity in sensor applications since some surface area is obscured by the substrate. We will carry out first attempt at large-scale bottom-up assembly and integration of nano-carbon spin-valves, comprised of ferromagnetic electrodes and graphene/CNT spin-channel, which will demonstrate a viable route for future nano-electronic circuits based on quantum-computing. A spin-valve is formed by tailoring the source and drain electrodes to switch at different fields. The substrate-gate will be used to modulate the spin current. The suspended configuration is expected to eliminate substrate-scattering and improve the spin-coherence length.NEMS devices, such as resonators for mass-sensors, are only possible with suspended CNT/Graphene devices, which hold great promise owing to the excellent combination of mechanical and electronic properties of CNT/graphene; however, an array of such resonators is required to have high quality factor, and this project will demonstrate a scalable route to fabricating such resonator arrays. The devices proposed in this project, particularly nano-carbon based sensors, are critical components in future energy and environment based industries. A number of leading UK and global companies are currently seeking next-generation sensors for such applications, for example, hydrogen sensors, sensors for high-radiation environments like nuclear reactors or sensors for detection of trace quantities of toxic or environmentally hazardous gasses in emissions.