Nanotube forestry: X-rays see trees

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  • Published: Oct 1, 2013
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Nanotube forestry: X-rays see trees

Nanoforestry commission

X-ray photoelectron spectroscopy has been used by Cambridge scientists to follow the interaction of metals involved in fertilising the growth of carbon nanotube forests. The insights it offers could open up a new approach to boosting forest density and lead to novel electronic systems.

The intriguing mechanical, electrical and thermal properties of carbon nanotubes, the elongated successors to the fullerenes, have made them an enticing prospect for the designers and developers of the next generation of electronic circuitry. Unfortunately, it seems that growing high density arrays of the nanoscopic "graphene cylinders" en masse has proved difficult and stymied some development while researchers sought workarounds for this problem.

Now a team from the University of Cambridge, UK, has come up with a relatively simple approach to increasing the density of nanotube forests grown on conductive supports by some five times the number achievable using earlier methods. Offering details of their technique in the journal Applied Physics Letters, the team alludes to high density nanotube arrays perhaps one day displacing conventional metal or semiconductor electronic components reducing the size of such components and opening up a route to much faster devices for computation and other applications.

Density issues

"The high density aspect is often overlooked in many carbon nanotube growth processes, and is an unusual feature of our approach," explains team leader John Robertson. Nevertheless, high-density forests of carbon nanotubes are necessary for many potential applications such as electronic interconnects and thermal interface systems, he says.

Robertson and his colleagues grew carbon nanotubes on a conductive copper surface that was coated with cobalt and molybdenum as co-catalysts. In this approach, they were able to grow forests of nanotubes at much lower temperature than is typical in manufacturing approaches widely used in the semiconductor industry. The team used X-ray photoelectron spectroscopy to follow the interaction of the metals and discovered how formation of a more supportive substrate allowed the carbon nanotube forest to take root. The subsequent nanotube growth, they add, gave the highest mass density for such systems so far reported.

"From our perspective, we'd like to understand the growth mechanism properly as the discovery is a bit accidental. The spectra in the paper were measured after growth, so things could happen during the cool down. We will try to do in situ XPS to understand it better, not just ex situ," Robertson told SpectroscopyNOW. To understand the mechanism fully, he suggests that they will need to carry out environmental XPS, at temperature, in the growth gas, at realistic pressure, in a synchrotron.

Outperforming

"In microelectronics, this approach to growing high-density carbon nanotube forests on conductors can potentially replace and outperform the current copper-based interconnects in a future generation of devices," team member Hisashi Sugime suggests. In the future, more robust carbon nanotube forests may also help improve thermal interface materials, battery electrodes, and supercapacitors. Robertson and Sugime worked with colleagues Santiago Esconjauregui, Junwei Yang, Lorenzo D’arsié, Rachel Oliver, Sunil Bhardwaj and Cinzia Cepek on this project centred in Cambridge and the Istituto Officina dei Materiali-CNR, Laboratorio TASC, in Trieste and Sincrotrone Trieste, Italy.

Related Links

Appl Phys Lett 2013, online: "Low temperature growth of ultra-high mass density carbon nanotube forests on conductive supports"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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