EAGER: Flame Synthesis of Graphene Films

碳基纳米结构和薄膜定义了一类新的工程材料，具有显著的光子、电学和机械性能。石墨烯是二维结构中sp2键碳原子的单层。这层原子可以包裹成0维的富勒烯，卷成一维的纳米管，或者像三维石墨那样堆积起来。开发了一种在开放环境中以甲烷为燃料的多重反向扩散火焰在衬底上生长石墨烯薄膜的新技术。作为碳基增长试剂的火焰后碳氢化合物物种(富含CHm和CN)的生成量远远超过稳定的、自我维持的预混合火焰中所能产生的数量。此外，反向扩散火焰几何结构确保氧气在火焰前沿完全消耗，从而能够生产高质量的薄膜。这种火焰合成配置具有潜在的变革性，打破了传统的受限合成需求(如标准的室内化学气相沉积)，能够在开放的大气环境中合成纳米材料，不仅提供可扩展的大批量生产，而且还可以在不同的轮廓表面上以高速率大面积生长(例如，通过光栅化燃烧器或平移衬底)。这一探索性计划旨在增加对火焰中石墨烯生长机理的基本了解，并利用这种了解来确定能够高速高质量合成石墨烯薄膜的工艺条件。具体地说，实验将表征燃料组成、火焰温度、惰性添加、氢添加、氧浓度、压力、衬底材料、衬底温度、燃烧器-衬底距离以及其他可控工艺参数对石墨烯生长和性能的影响。基于激光的原位诊断，包括自发拉曼光谱、激光诱导荧光和激光诱导击穿光谱，将被用来确定局部生长条件，如关键的气相化学物种浓度和温度。通过微解理分离单层石墨烯并发现其惊人的性质，引发了对其制备的激烈的实验研究。然而，石墨烯的广泛使用将需要大规模的合成方法。目前存在的生产方法通常昂贵，需要较长的处理时间，并且限于受限合成。这些纳米结构和薄膜的大面积生长仍然特别具有挑战性。因此，显然迫切需要更好的方法来合成纳米结构，特别是碳基纳米结构。火焰合成已经证明了可伸缩性的历史，并提供了以更低的成本进行大批量连续生产的潜力。在利用燃烧时，一部分碳氢化合物气体提供所需的高温，剩余的燃料用作碳氢化合物试剂，从而构成能源和碳氢化合物反应物的有效来源。这些方面可能特别重要，因为生产先进材料的运营成本，特别是在半导体行业，远远超过设备成本。此外，这项研究提供了在开放环境中用石墨烯覆盖大型现有结构的可能性，这在目前是不可能的。

Carbon-based nanostructures and films define a new class of engineered materials that display remarkable photonic, electrical, and mechanical properties. Graphene is a monolayer of sp2-bonded carbon atoms in a two-dimensional (2-D) structure. This layer of atoms can be wrapped into 0-D fullerenes, rolled into 1-D nanotubes, or stacked as in 3-D graphite. A novel technique to grow graphene films in open environments on substrates has been developed using multiple inverse-diffusion flames with methane as fuel. The post-flame hydrocarbon species (rich in CHm and Cn), which serve as reagents for carbon-based growth, are generated in quantities much greater than that achievable in stable, self-sustained premixed flames. Moreover, the inverse diffusion flame geometry ensures that oxygen is completely consumed at the flame front, permitting the production of high-quality films. This flame synthesis configuration is potentially transformative and breaks away from the conventional need for confined synthesis (as in standard chambered Chemical Vapor Deposition), and is capable of nanomaterials synthesis in open-atmosphere environments, affording not only scalable large volume production, but also large-area growth over different contoured surfaces (e.g. by rasterizing burner or translating substrate) at high rates. This exploratory program is aimed at increasing fundamental understanding of the mechanisms of graphene growth in flames, and utilization of that understanding to define process conditions that enable high-rate and high-quality synthesis of graphene films. Specifically, experiments will be conducted to characterize the effects of fuel composition, flame temperature, inert addition, hydrogen addition, oxygen concentration, pressure, substrate material, substrate temperature, burner-substrate distance, and other controllable process parameters on graphene growth and properties. In-situ laser-based diagnostics, including spontaneous Raman spectroscopy, laser-induced fluorescence, and laser-induced breakdown spectroscopy, will be used to determine the local growth conditions, such key gas-phase chemical species concentrations and temperature.Isolating monolayer graphene by microcleaving and discovering its amazing properties has generated intense experimental research on its fabrication. However, widespread use of graphene will require large-scale synthesis methods. Production methods that currently exist are typically expensive, require long processing times, and are limited to confined synthesis. The growth of these nanostructures and films over large areas remains especially challenging. Accordingly, it is evident that there is a strong need for better methods of synthesizing nanostructures, particularly carbon-based nanostructures. Flame synthesis has demonstrated a history of scalability and offers the potential for high-volume continuous production at reduced costs. In utilizing combustion, a portion of the hydrocarbon gas provides the elevated temperatures required, with the remaining fuel serving as the hydrocarbon reagent, thereby constituting an efficient source of both energy and hydrocarbon reactant. These aspects can be especially important as the operating costs for producing advanced materials, especially in the semiconductor industry, far exceed the equipment costs. In addition, the research affords the possibility of coating large existing structures with graphene in open environments, which is currently not possible.