Svrcek V, Kleps I, Cracioniou F, Paillaud J L, Dintzer T, Louis B, Begin D, Pham-Huu C, Ledoux M-J, Le Normand F
Nanoarchitectronics Research Center, AIST, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305 8565, Japan.
J Chem Phys. 2006 May 14;124(18):184705. doi: 10.1063/1.2192515.
The growth of multiwalled carbon nanotubes (MWCNTs) produced by a catalytic chemical vapor deposition (CCVD) process has been monitored using a tapered element oscillating microbalance (TEOM) probe. This technique displays a high sensitivity (<1 microg). Growths in the TEOM microreactor are investigated with catalytic particles (Fe, Ni) dispersed on different supports. First, high surface area FeAl2O3 or Fe (Ni) exchanged on zeolite powders is used. Second, growths are performed on array of nickel dots or FeSi-nc particles dispersed on large holes patterned on Si(100) substrates. An accurate monitoring of the early stages of growth permits a precise evaluation of the growth rates and shows substantial differences between these samples which greatly differ by the surface area. On catalysts dispersed on Si(100) the mass uptake is linear throughout the process. On high surface area catalysts, however, a saturation of the mass uptake is indifferently observed. This saturation is explained either by diffusion limitation by the growing MWCNTs or by internal diffusion through the pores or external diffusion through the grains of the catalyst. The kinetic dependence with partial pressure of the incoming C2H6:H2 gas mixture is then explored on the FeAl2O3 catalyst. A linear dependence of the MWCNT growth an (P(C2H6)/P(H2))(1/2) is found. A simple model is then developed that accounts for this dependence only if an associative and competitive adsorption of ethane is the rate determining step of the overall process. These results thus bring insight to improve and control the CCVD growth kinetics of MWCNTs.
采用锥形元件振荡微天平（TEOM）探头监测了通过催化化学气相沉积（CCVD）工艺制备的多壁碳纳米管（MWCNT）的生长情况。该技术具有高灵敏度（<1微克）。在TEOM微反应器中，研究了分散在不同载体上的催化颗粒（Fe、Ni）对生长的影响。首先，使用高比表面积的FeAl2O3或负载在沸石粉末上的Fe（Ni）。其次，在分散于Si(100)衬底上的大孔图案化镍点阵列或FeSi-nc颗粒上进行生长。对生长早期阶段的精确监测能够准确评估生长速率，并显示出这些样品之间存在显著差异，这些差异主要体现在比表面积上。对于分散在Si(100)上的催化剂，整个过程中的质量吸收呈线性关系。然而，在高比表面积催化剂上，质量吸收出现了饱和现象。这种饱和现象可以用生长的MWCNT的扩散限制、通过催化剂孔隙的内扩散或通过催化剂颗粒的外扩散来解释。随后，在FeAl2O3催化剂上研究了MWCNT生长与进料C2H6:H2气体混合物分压的动力学关系。发现MWCNT生长与（P(C2H6)/P(H2)）(1/2)呈线性关系。然后建立了一个简单模型，只有当乙烷的缔合和竞争吸附是整个过程的速率决定步骤时，该模型才能解释这种关系。因此，这些结果为改进和控制MWCNT的CCVD生长动力学提供了深入见解。
