Cost-effective, high quality carbon nanotubes
Carbon nanotubes are, as their name suggests, tube-shaped carbon materials with diameters on the scale of nanometres. Their walls are formed by one atom-thick sheets of graphite and they act as metals or semiconductors depending on structural variations. Single-wall carbon nanotubes (SWNTs) are a new type of 1-dimensional (1D) structures that have received growing attention. While experimental data and modelling have led to better understanding of SWNT characteristics and behaviours, techniques are required for cost-effective fabrication and successful integration of SWNTs into microelectronic products. As such, European researchers initiated the ‘Spark ablation for nanotube growth’ (SPANG) project to develop cost-effective methods to synthesise high quality SWNTs and to evaluate their use in printed circuit boards (PCBs). Numerous methods are available for producing SWNTs. While chemical vapour deposition and the carbon arc method are relatively inexpensive, they produce defective material affecting electrical and mechanical properties of the SWNTs. Researchers set out to compare the quality of nanotubes produced by three different techniques. Laser ablation produces long nearly defect-free SWNTs. Although good control over process parameters is achieved, throughput is low and lasers are expensive. Channel spark ablation allows similar control and product quality but with lower cost. The arc-jet method facilitates control similar to laser ablation but with the important benefit of enabling continuous as opposed to batch processing. SPANG investigators compared SWNTs produced by the three methods using a variety of technologies including electron microscopy, optical absorption and X-ray diffraction. Extensive standardisation work was done to facilitate quality control. In addition, investigators studied the use of nanotube networks in lead resistors and capacitors of PCBs. SPANG project results should help advance the state of the art regarding fabrication and functional applications of SWNTs, thus facilitating development of a new generation of electronic devices.