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.
|Effective start/end date||9/1/12 → 8/31/14|
- National Science Foundation (National Science Foundation (NSF))