Hart Anastasios John, Slocum Alexander H
Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 3-470, Cambridge, Massachusetts 02139, USA.
J Phys Chem B. 2006 Apr 27;110(16):8250-7. doi: 10.1021/jp055498b.
We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt transitions between areas of micrometer-thick tangled CNT films and millimeter-scale aligned CNT structures are manipulated by changing the duration of pretreatment by H2/Ar prior to introduction of C2H4 and by changing the configuration of the substrate sample in the furnace tube. This demonstrates that the flow profile over the sample mediates the supply of reactants to the catalyst and that pretreatment using H2 significantly affects the initial activity of the catalyst.
我们讨论了通过在电子束蒸发沉积的Fe/Al₂O₃催化剂薄膜上进行C₂H₄/H₂/Ar的常压热化学气相沉积（CVD），垂直排列的小直径多壁碳纳米管（VA-MWNTs）的薄膜和光刻模板微结构的快速生长。这些结构在15分钟内生长到1毫米高，在60分钟内接近2毫米。从催化剂图案生长的碳纳米管微结构的生长速率和最终高度强烈依赖于催化剂的局部面密度，这代表了与等离子体蚀刻过程中出现的负载效应相反的类似情况。通过改变引入C₂H₄之前H₂/Ar预处理的持续时间以及改变炉管中衬底样品的配置，可以控制微米厚的缠结碳纳米管薄膜区域和毫米级排列的碳纳米管结构之间的突然转变。这表明样品上方的流动分布介导了反应物向催化剂的供应，并且使用H₂进行预处理会显著影响催化剂的初始活性。
