ABSTRACT
The growth of carbon nanotubes (CNTs) in a flame requires conditions that are difficult to achieve in a highly heterogeneous environment. Therefore, the analysis of the properties of the reaction zone within the flame is critical for the optimal growth of CNTs. In the present study, a comprehensive comparison between the CNT synthesis using a methane diffusion flame and a premixed flame is conducted regarding the morphology and crystallinity of the as-grown nanotubes. The premixed burner configuration created a flame that is stabilized through axisymmetric stagnation flow through sintered metal with one-dimensional geometry, different from a conventional co-flow flame. The significant difference in temperature distribution between the two flames causes a difference in the characteristics of the growth products. In the diffusion flame, the growth is limited to specific regions at certain height-above-burner (HAB) values with a temperature range of 750 to 950 °C at varying radial locations. The identified growth regions at different HAB values showed similar temperature distributions that yield CNTs of similar characteristics. Interestingly, the growth of CNTs in the premixed flame is dictated by only the HAB because the temperature distribution is relatively uniform along the radial directions but significantly different in the vertical direction. 17.3% variation in temperature in the axial direction successfully led to 44% and 66% variation in CNT diameter and crystallinity, respectively. The morphology control capability demonstrated in the present study is important for CNT functionalization for energy storage, nanosensor, and nanocomposite applications, where diameter and crystallinity are influential properties that govern the overall performance of the components.
ABSTRACT
Studies on depositions of chemical vapour deposition (CVD) diamond films have shown that flame combustion has the highest deposition rates without involving microwave plasma and direct current arc. Thus, here we report on our study of few-layer graphene grown by flame deposition. A horizontal CVD reactor was modified for the synthesis of flame deposition of few-layer graphene on a Cu substrate. It was found that graphene obtained has comparable quality to that obtained with other flame deposition setups reported in the literature as determined from Raman spectroscopy, sheet resistance, and transmission electron microscopy. Calculation of the chemical kinetics reveals a gas phase species that has a close correlation to the growth rate of graphene. This was further correlated with van't Hoff analysis of the reaction, which shows that the growth reaction has a single dominating mechanism for temperatures in the range of 400 °C to 1000 °C. Arrhenius analysis also was found to be in good agreement with this result. This study shows few-layer graphene growth proceeds through different pathways from a CVD grown graphene and also highlights flame deposition as a viable method for graphene growth.
