Carbon Nanotubes and Graphene - Research and Applications

Researchers studied the resistivity-strain dependence in an amino-functionalized carbon nanotube/polyurethane-urea elastomeric composite material. During the deformation of the composite, the relationship between electric resistivity and strain was found to be independent of the nanotube concentration. The exponential dependence was explained by the tunnel junction gap which increases proportionally with strain.

Researchers report the fabrication of dense MWCNT–TiN composites in the presence of various MWCNT amounts. The Raman and microstructure investigations show that the MWCNTs introduced in composites maintain their characteristics, and the nanotube-TiN interface interactions are good. The thermal conductivity of the composites increased with increasing nanotube amounts and temperature.

Researchers showed that multi-walled carbon nanotubes have gas pressure and gas species sensing capability which is based on electro-thermal effect: heated nanotubes exposed to gaseous environments change their resistance depending on the gas molecules. The gas sensing device was constructed by synthesising suspended multi-walled carbon nanotubes locally by chemical vapor deposition. The measurements could differentiate between gas species and showed sensitivity to vacuum pressure. These sensors are compact, have fast and reversible responses and can be integrated with the existing microelectronics.

Researchers have employed single-walled carbon nanotubes for the detection of biomolecules like Streptavidin or IgG. Two types of sensing mechanisms have been applied: one is monitoring the changes in electrical conductance caused by the molecules attached to the walls of nanotubes, and the other was the quantitative determination of biomolecule uptake of the matrix. The immobilization of the molecules on the nanotube surface was investigated by atomic force microscopy (AFM).

Researchers have demonstrated that carbon nanotubes can be used as the energy conversion materials in solar cells, which serves for the photogeneration process and charge carrier transport. The junctions formed between p-type double-walled carbon nanotubes and n-type Si act as conventional p-n junctions in the generation of electron-hole pairs, which are then transported through the nanotubes (holes) and n-Si (electrons), respectively. The nanotubes ensure much enhanced current density and power efficiency of solar cells compared with extensively studied polymer-nanotube composite structures. The researchers believe that the concept also could apply to other cheaper or flexible thin-film substrates in the future research for low-cost production.
Source: Nano Letters 2007 Vol. 7, No. 8, 2317-2321.