UK researchers announce breakthrough in low temperature growth of carbon nanotubes

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Researchers at the University of Surrey claim to have discovered a way to grow high quality carbon nanotubes over large areas of substrate temperatures below 350ºC.

According to findings published this month in Carbon Journal, this breakthrough means that lowering the substrate temperature below 400ºC would make the technology compatible with cmos and suitable for large area substrates. Researchers at the University's Advanced Technology Institute claim as as a result, potential applications of carbon nanotubes would become feasible and affordable if the growth temperature of the substrates were to be reduced from its current 700ºC. Typical applications include interconnectors for integrated circuits, solar cell electrodes, supercapacitors, electrodes for batteries and fuel cells to nano-composite materials for high strength materials. Carbon nanotubes are rolled up sheets of honeycomb structured carbon atoms that are typically one hundred thousandth of a millimetre in diameter. The single or multiwalled carbon nanotube structures have conductivity better than any other known single element material, thermal conductivity better than diamond, and mechanical strength surpassing that of high tensile steel. The breakthrough reported by a group headed by Prof Ravi Silva, pictured, at the University of Surrey allows researchers to couple plasma energy more efficiently to the catalyst particles used to grow carbon nanotubes. The researchers demonstrated that high quality carbon nanotubes can be grown controllably, reliably and over large areas while maintaining the device substrates at low temperatures. Researcher, Dr Vlad Stolojan said that metallic interconnects based on the metal copper used in integrated circuits currently suffer from poor electrical conduction. "And, the smaller they get in diameter, the more resistive they become," he observed. "In addition to the electromigration issues, they dissipate so much heat energy that they can damage the surrounding devices. With our innovative technology, using a top down heating methodology, we can precisely grow carbon nanotubes within interconnect vias at cmos compatible temperatures." The technology has been developed with a team from Surrey NanoSystems and has demonstrated growth of carbon nanotubes which have similar properties to those obtained at temperatures of 700ºC, over 4in wafers, while maintaining the substrate below 350ºC. The system provides energy from the top via an infrared lamp array, whilst having several functional layers with carefully designed thicknesses which reflect this heat and/or act as thermal barriers for the substrate. The substrate itself sits on a water cooled holder, to further protect it from harmful heating. Prof Silva believes it is an innovation that UK industry can be proud of. "This is an example of how private public partnership can deliver real world solutions to roadblocks in cutting edge technologies," he said. "We are currently in talks with major semiconductor manufacturers to transfer this technology to the wider market and are continuing our internationally leading research into novel contacting technologies."