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September 04, 2004— Ottawa, Ontario

NRC researchers observe photoluminescence from bare carbon nanotubes

Researchers from NRC's Institute for Microstructural Sciences and Japan's NTT Basic Research Laboratories teamed up to make an important discovery in the area of carbon nanotubes, a key material in the growing nanotechnology sector.

Nanotubes are probably the leading example of new materials in the emerging field of nanotechnology. Nanotubes are cylindrical tubes of carbon taken to the limit of extreme size and simplicity; single-walled carbon nanotubes consist of a single layer of carbon atoms rolled up into a seamless cylinder. Carbon nanotubes are prized, among other things, for their extreme strength and ability to conduct electricity. Worldwide, numerous new structures, devices and technologies are being developed. Some of this important work is taking place at NRC.

Nanotubes

In the past year, researchers from the NRC Institute for Microstructural Sciences (NRC-IMS) observed that bare, unprocessed nanotubes are capable of absorbing and emitting light. Physicists usually call the process in question photoluminescence (PL), while chemists usually call it fluorescence. The result will enable to a new generation of optoelectronic devices which are used widely in telecommunications, environmental consumer products and medical sensors, etc.

Project coordinator Paul Finnie recounted, "I attended NT'02 (a nanotube-related conference) where Prof. Weisman (of Rice University) presented beautiful results showing the fluorescence of nanotubes in specially prepared soap suspensions. It seemed to us here that we could get away from the soap altogether and, anyway, that was just a detriment to the kind of devices that we were interested in. At NTT, Dr. Homma had been making nanotubes suspended on pillar substrates. At NRC-IMS, Jacques Lefebvre had been doing a similar kind of spectroscopy on indium phosphide-based materials. We put it all together and, much to our surprise it worked, pretty much right off the bat. Jacques and I had to spend a few weeks convincing ourselves that we were really seeing what we had hoped to see."

NanotubesSingle walled nanotubes have been made for over a decade, and from theory they were expected to emit photoluminescence (PL). But until recently, researchers failed to detect it. One of the main reasons is that nanotubes can interact with their surroundings in such a way as to prevent photoluminescence. To get around this, the researchers suspended nanotubes in air, on microscopic towers on silicon substrates. The bulk of the samples were prepared by collaborators at Japan's NTT Basic Research Laboratories, but a few were also prepared by NRC-IMS's own deposition method. The research received significant funding from Japan's New Energy and Industrial Development Organization (NEDO).

Dr. Finnie noted, "As far as applications go, I think it is very promising because of the potential of nanotubes to provide low-cost access to a broad range of wavelengths, with the benefit of strong quantum confinement. It is really very much at the exploratory stage right now, but the capabilities are so important I am sure that as the field matures 'killer applications' will emerge. There is really great potential in any application where you want to generate infrared or detect infrared, visible or ultraviolet light. Telecommunications is just one example."

The team has already made use of some of these advantages. For example, performing single nanotube spectroscopy, the team has explored how individual nanotubes polarize light. Also, since the nanotubes are not in solution, they can be cooled to very low temperatures – a classic experimental method used in the characterization of semiconductors and other materials. The NRC-IMS researchers have already done pioneering work in the temperature dependence of nanotube PL, discovering surprising new spectral features, and confirming that nanotube luminescence is remarkably stable with temperature.

The result of this initial breakthrough and subsequent experiments represents not only exciting science but also holds great technological promise. This is especially the case in the area of optoelectronics. This research shows that bare nanotubes are efficient at light emission, work which suggests that nanotubes are very promising for optoelectronic devices. Ultimately, by virtue of their interaction with light, nanotubes may find their way into the telecommunications networks of the world, or they might be used to monitor pollutants in the atmosphere. And, no doubt, they will enable optoelectronic applications which are just now being invented.


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National Research Council of Canada
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