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

低维碳的同素异形体，即一维碳纳米管(CNTs)和二维石墨烯，具有极好的电学、力学和光学性能。尽管高性能纳米碳设备已经被展示出来，但它们还没有在现实世界的应用中留下自己的印记。商业化的主要障碍在于，当传统(自上而下)技术扩展到纳米级物体、制造电子设备、传感器、致动器和其他此类架构时，其重复性和可扩展性有限。虽然这些传统路线已经产生了可测试的概念验证器件，但我们需要一种新的、非传统的方法来以高集成密度大规模制造这些器件。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性质，以实现商业可行性和技术共存。对于碳纳米管，最有希望的方法是使用交流(A/C)介电泳法(DEP)自下而上地将活性碳纳米管元件整合到预定的位置。DEP可以与密度梯度超速离心法(DGU)等碳纳米管分选方法结合使用，以生产纯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，可以克服设备应用中碳纳米管的多分散性问题。由于滴状干燥过程中强大的反表面张力，基于DEP的器件制造到目前为止仅限于衬底支撑的器件，即活性纳米碳元素在沉积时必须躺在衬底上，而不是自由地悬浮在两个电极之间。到目前为止，在几乎所有基于碳纳米管或石墨烯电子器件的研究中，悬浮器件的表现都明显好于衬底支持的器件。像谐振器这样的设备只能在暂停配置下工作。由于碳纳米管或石墨烯中的每个原子都是表面原子，纳米碳器件的性质和性能受到与衬底的相互作用的严重干扰。典型的影响包括重掺杂，由于增强的散射导致迁移率降低，更高的1/f噪声，从而降低信噪比，以及传感器应用中的低灵敏度，因为一些表面区域被衬底遮挡。我们将首次尝试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的大规模自底向上组装和集成，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路线。自旋阀是通过调整源电极和漏电极以在不同的场切换而形成的。衬底栅极将用于调制自旋电流。悬浮结构有望消除衬底散射并改善自旋相干长度。NEMS器件，如用于质量传感器的谐振器，只有与悬浮的碳纳米管/石墨烯器件一起才能实现，由于碳纳米管/石墨烯具有良好的机械和电学性能，因此具有很大的前景；然而，要求此类谐振器阵列具有高品质因数，该项目将展示一条可扩展的制造此类谐振器阵列的路线。该项目中提出的设备，特别是基于纳米碳的传感器，是未来基于能源和环境的行业的关键部件。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中微量有毒或环境有害气体的传感器。

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.