Position dependence of growth rate in convection enhanced laser CVD of carbon rods

The ability to closely monitor LCVD rod growth in the growth region is demonstrated in the context of the first open-air axial convection enhanced micro-reactor. It was used to monitor carbon rod growth inside coaxial cylindrical flows of ethylene and argon. Monitoring and subsequent image analysis of the 656 nm atomic hydrogen emission from ethylene pyrolysis allowed real-time in-situ determination of axial growth rate and diameter along the axis of the produced carbon rods for the first time. Growth rates appear to vary greatly inside the growth region. This experiment raises questions about published qualitative models of LCVD rod growth that favor a uniform steady state regime. If the trend demonstrated in our experiments is not just an artifact of flow mixing, then it would indicate that published registered growth rates may just be an average value or an artifact of focus tracking. The results, therefore, point the way to experiments that would allow discrimination between the effect of flow mixing and the true nature of LCVD rod growth in the growth region. PACS 81.16.Mk; 81.10.Bk; 81.05.Uw