Influences of Hydrogen Gas on Carbon Nanotube Growth

  • PDF / 702,670 Bytes
  • 7 Pages / 612 x 792 pts (letter) Page_size
  • 67 Downloads / 260 Views

DOWNLOAD

REPORT


1081-P08-05

Influences of Hydrogen Gas on Carbon Nanotube Growth Fumitaka Ohashi1, Guan Yow Chen2, Vlad Stolojan1, and S. Ravi P. Silva1 1 Advanced Technology Institute, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom 2 Surrey NanoSystems, Unit 24 Euro Business Park, New Road, Newhaven, BN9 0DQ, United Kingdom ABSTRACT For practical deployment of carbon nanotubes for real world applications, an understanding of their growth mechanism is required in order to obtain better control over their crystallinity, chirality and other structural properties. In this study, we focus on the influences of gas species on carbon nanotube synthesis using thermal chemical vapour deposition. The influences of methane, hydrogen and helium gases were investigated from the viewpoint of gas chemistry in relation to structural changes in the resulting nanotubes, by varying the growth pressure, the gas-flow ratio and the growth temperature. Simple changes in the hydrogen gas concentration during different growth stages have been found to induce surprising changes to the nanotube structure, varying from amorphous to graphitic as the growth temperature and the concentration of hydrogen in the initial periods of growth decreased. The excess hydrogen tends to give rise to poor crystalline carbon nanofibres but has the effect of increasing the yield. Hydrogen gas is typically used in reducing the metal catalyst particles during the pre-treatment and the carbon nanotube growth periods. We show that while hydrogen species can improve yield, it can also result in the degradation of the nanotube’s crystallinity. The use of hydrogen in the growth process is one of the key parameters for enhanced control of carbon nanotube/nanofibre growth and their resulting crystallinity. INTRODUCTION Carbon nanotubes have been actively investigated due to their potential applications [1,2,3], with a significant effort directed at understanding and controlling their growth [4]. For the synthesis of carbon nanotubes, catalytic chemical vapour deposition (CCVD) is the technique of choice because it enables the selective growth of carbon nanotubes directly onto the substrate through the patterning of the catalyst, as well as their alignment through electric fields applied during growth [5,6]. However, not many carbon nanotube products have been commercialized yet due to the lack of control of the growth mechanism of carbon nanotubes and their subsequent electrical properties. For instance, the respective roles of the gas species during carbon nanotube growth are not understood well enough to provide good control over the growth process, despite many significant advances over the last decade. In this study, we focused on the influences of methane, hydrogen and helium on the carbon nanotube synthesis by thermal chemical vapour deposition. These gases have been widely used to grow carbon nanotubes/fibres and they are used as the carbon source, for the activation of catalysts during the pre-treatment stage and for the dilution of the carbon gas species res