Growing concern

UK-developed process for producing cost-efficient nanomaterials at room temperature receives commercialisation funding. Stuart Nathan reports.

A low-cost technique for growing nanotubes has received funding from the South East England Development Agency (SEEDA) to aid its commercialisation.

Developed by the University of Surrey and its plasma processing partner, CEVP, the process can be used to make nanomaterials for use in semiconductors, solid-state lighting and solar cells.

Known as NanoGrowth, the technique is capable of producing nanomaterials at room temperature, rather than the 700-1000oC needed for chemical vapour deposition. These high temperatures, along with the difficulty of achieving precise deposition, have limited the use of nanoparticles in integrated circuits and for components for flat-panel displays.

NanoGrowth, on the other hand, is a plasma-enhanced process that uses tight temperature control. According to CEVP’s Ben Jensen, the technique can currently direct nanomaterial growth across substrates up to three inches in diameter.

‘The goal of this tool is to make precision carbon nanotube fabrication possible at low temperatures, together with a scale of growth area that is suitable for many hi-tech applications. We believe that it will be the first platform for making nanowires a practical proposition in commercial high technology applications.’

Plasma-enhanced chemical vapour deposition (PECVD), the technique used by the NanoGrowth process, uses a chemical reaction to make the nanomaterial in a gaseous form, which solidifies when it hits the substrate. A plasma is created inside the substrate vessel to make more energy available for the chemical reaction, which accelerates its rate. NanoGrowth is capable of controlling the density, length and position of the nanotubes, and can also make the tubes ‘flower’ to cover large surface areas, CEVP claimed.

Because the process is carried out at room temperature, substrates are not limited to materials which tolerate high temperatures. Even highly heat-sensitive materials like polymers and metallised paper can be used. The system can also grow nanostructures from non-carbon materials, such as doped silicon and tungsten oxide low-resistance nanowires for use in integrated circuits.

Other possible products include semiconducting nanotubes for high-perfomance transistors; micro- miniature heatsinks, polymer composites, gas sensors and light sources for flat panel displays, which could be made on soda lime glass rather than the expensive heat-resistant glass needed for traditional nanotube deposition.

The method was originally developed at the University of Surrey‘s Advanced Technology Institute by Ravi Silva and colleagues, who described their first successes in room temperature nanotube growth in 2002.

‘SEEDA funding will help us transform the prototype NanoGrowth machine into a world-beating technology platform for nanomaterials,’ said Silva. ‘We are already talking with multinationals about a range of hi-tech products, and as well as developing this tool we are actively examining routes to create a spin-out vehicle for this exciting technology.’

The SEEDA funding — a £215,000 grant, increasing the project’s development capital to £450,000 — will help Silva and the CEVP team to further improve the process so that it can deposit nanotubes over a 30cm-diameter substrate, said Silva.

This, he hopes, will open up two sources of revenue: sales of nanomaterial-coated substrates, and sales of the NanoGrowth equipment itself. ‘We’ve already demonstrated that precision nanotube fabrication is feasible at low temperatures and on a large scale,’ said Jensen. ‘The SEEDA funding will help us bring the process to the commercial world.’