Ohashi Fumitaka, Chen Guan Yow, Stolojan Vlad, Silva S Ravi P
Nanoelectronics Centre, Advanced Technology Institute, University of Surrey, Guildford GU2 7XH, UK.
Nanotechnology. 2008 Nov 5;19(44):445605. doi: 10.1088/0957-4484/19/44/445605. Epub 2008 Sep 29.
In this paper, we investigate the several roles that hydrogen plays in the catalytic growth of carbon nanotubes from the point of view of gas species, catalyst activation and subsequent interaction with the carbon nanotubes. Carbon nanotubes and nanofibres were grown by thermal chemical vapour deposition, using methane and a mixture of hydrogen and helium, for a range of growth temperatures and pre-treatment procedures. Long, straight carbon nanotubes were obtained at 900 °C, and although the growth yield increases with the growth temperature, the growth shifts from nanotubes to nanofibres. By introducing a helium purge as part of the pre-treatment procedure, we change the gas chemistry by altering the hydrogen concentration in the initial reaction stage. This simple change in the process resulted in a clear difference in the yield and the structure of the carbon nanofibres produced. We find that the hydrogen concentration in the initial reaction stage significantly affects the morphology of carbon fibres. Although hydrogen keeps the catalyst activated and increases the yield, it prevents the formation of graphitic nanotubes.
在本文中，我们从气体种类、催化剂活化以及随后与碳纳米管的相互作用的角度，研究了氢气在碳纳米管催化生长过程中所起的几种作用。通过热化学气相沉积法，使用甲烷以及氢气和氦气的混合物，在一系列生长温度和预处理程序下生长碳纳米管和纳米纤维。在900°C时获得了长而直的碳纳米管，尽管生长产率随生长温度的升高而增加，但生长形态从纳米管转变为纳米纤维。通过在预处理程序中引入氦气吹扫，我们在初始反应阶段改变了氢气浓度，从而改变了气体化学性质。该过程中的这一简单变化导致所生产的碳纳米纤维在产率和结构上有明显差异。我们发现，初始反应阶段的氢气浓度会显著影响碳纤维的形态。虽然氢气能使催化剂保持活化状态并提高产率，但它会阻止石墨化纳米管的形成。
