May 18, 2004
Ion beams put nanotubes on the straight and narrow
Researchers at Rensselaer Polytechnic Institute, US, NTT Basic Research Laboratories, Japan, and Yokohama National University, Japan, have bombarded single-walled carbon nanotubes with ion beams in order to straighten them. They applied the technique to nanotubes grown between catalyst-coated pillars, as these often sag.
“During experiments using focused ion beams (FIB) we found that suspended single-walled carbon nanotubes were moving and becoming straightened,” Yung Joon Jung of Rensselaer told nanotechweb.org. “Based on our observation, we tried to modify single-walled carbon nanotube networks suspended on nanoscale-patterned structures using a gallium ion irradiation approach.”
Jung and colleagues used samples containing 200 nm diameter silicon pillars that were 300 nm high and 250 nm apart. They coated the substrate with a thin film of iron to act as a catalyst and grew single-walled nanotubes by chemical vapour deposition (CVD). In general, nanotubes formed between the pillars, but they were curved and did not connect the pillars along straight paths.
The researchers bombarded the nanotubes with a beam of Ga+ ions from a FIB instrument with an accelerating voltage of 30 keV. The treatment caused changes in the structure of the nanotubes even after just a few seconds. As well as straightening the nanotubes suspended between pillars, the technique also preferentially removed carbon nanotubes that were lying on the substrate and many of the iron nanoparticles that were formed during CVD.
While the ion irradiation straightened the nanotubes, Raman spectroscopy indicated that it had also damaged the structure of the tubes. “Finding the correct parameter range - one that does not destroy the nanotubes but is strong enough to change their morphology step by step - was one of the challenges in our experiment,” said Jung.
“These well organized nanoscale networks can serve in various applications such as sensors and biological templates,” he continued. “Also, if a more advanced nanotube-straightening process is developed, one that introduces fewer defects into the original structure of the carbon nanotubes, then these straightened nanotube networks could be a good candidate for interconnect materials in the semiconductor industry of tomorrow.”
The researchers reported their work in Nano Letters.
About the author
Liz Kalaugher is editor of nanotechweb.org.