Zhu Lingbo, Hess Dennis W, Wong Ching-Ping
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
J Phys Chem B. 2006 Mar 23;110(11):5445-9. doi: 10.1021/jp060027q.
A novel method is presented to monitor carbon nanotube (CNT) growth by formation of CNT stacks. By this process, CNT growth kinetics are investigated for densely packed CNT films in the gas-diffusion-controlled regime. CNT stacks are fabricated by water-assisted selective etching and the cyclic introduction of ethylene into the chemical vapor deposition (CVD) reactor. Formation of the CNT stacks allows monitoring of the CNT growth evolution, thereby providing insight into the growth kinetics. A parabolic increase of CNT length versus time is observed, indicating a gas-diffusion-controlled growth mode. The densely packed, well-aligned CNT films act as porous barrier layers to the diffusion of ethylene precursor to the catalyst nanoparticles, since these films form via a base-growth mode under the conditions invoked in our system. By adjustment of CNT growth time and temperature, a quantitative time-evolution analysis is performed to investigate the CNT growth model and extract the gas precursor mass transfer coefficient in the CNT films. The self-diffusion of gases in the densely packed CNT films is found to be Knudsen diffusion with a diffusion coefficient on the order of 10(-4) cm(2)/s.
本文提出了一种通过碳纳米管（CNT）堆叠的形成来监测碳纳米管生长的新方法。通过该过程，研究了在气体扩散控制区域中致密堆积的碳纳米管薄膜的碳纳米管生长动力学。通过水辅助选择性蚀刻以及将乙烯循环引入化学气相沉积（CVD）反应器中来制备碳纳米管堆叠。碳纳米管堆叠的形成允许监测碳纳米管的生长演变，从而深入了解生长动力学。观察到碳纳米管长度随时间呈抛物线增长，表明生长模式为气体扩散控制。由于这些薄膜是在我们系统所采用的条件下通过基生长模式形成的，因此致密堆积、排列良好的碳纳米管薄膜对乙烯前驱体向催化剂纳米颗粒的扩散起到了多孔阻挡层的作用。通过调整碳纳米管的生长时间和温度，进行了定量的时间演变分析，以研究碳纳米管生长模型并提取碳纳米管薄膜中的气体前驱体传质系数。发现气体在致密堆积的碳纳米管薄膜中的自扩散为克努森扩散，扩散系数约为10^(-4) cm²/s。
