Jun 30, 2011
Carbon nanotube gas sensor arrays get selective
Multi-walled carbon nanotubes (MWCNTs) have been widely reported as effective and highly sensitive chemical and biological sensors. However, imparting selectivity to these sensors has been a major challenge. Reporting their results in the journal Nanotechnology, researchers based at the University of Kentucky, US, have come up with a fabrication scheme that offers good control over the sensitivity of the device and makes the composite films gas-specific. The team has used the approach to develop composite films of MWCNTs and conducting polymers, which can selectively detect reducing and oxidizing agents even at low concentrations.
First, the group grows MWCNT arrays on thin layers of silicon dioxide grown on top of silicon substrates. These are then incorporated into hybrid sensor devices after functionalizing them with various conducting polymers.
The nanotubes were fabricated by a CVD process, during which a thin amorphous carbon (a-C) layer formed on the surface of MWCNTs. The team used a plasma etch technique to not only tailor the a-C layer thickness, but also create additional active sites for the bonding of functional groups. A simple solvent modification of the polymer resulted in a gas selective response from the nanocomposite sensors.
FTIR characterization results revealed that the conducting polymers are covalently bonded with the nanotube surface and are responsible for obtaining selectivity and enhanced sensitivities.
Even though there are several reports on the fabrication of CNT–polymer nano-composite films and solvent effects on polymer conductivity, this work presents a uniquely simple method for fabricating CNT–polymer nanocomposites and integrating them into sensor devices that exhibit selectivity to analyte gases.
The fabrication technique allows for a wide range of control over device sensitivity and selectivity, thus constituting an important step toward the commercialization of CNT-based sensor technologies.
The group is now investigating new MWNT-polymer-solvent combinations and compositions for further improvements in sensitivity, detectability and selectivity.
Full details can be found in the journal Nanotechnology.
About the author
The researchers are members of the Electronic Devices Research Group (EDRG) based in the Department of Electrical & Computer Engineering at University of Kentucky, USA. Many experiments were carried out in the Center for Nanoscale Science & Engineering (CeNSE), at the University of Kentucky. Raghu Mangu is a PhD student; Suresh Rajaputra is a Senior Research Scientist and Prof. Vijay Singh is the director of EDRG and CeNSE.