Within this work we present a new class of shaped silver nanoparticle ensembles which have demonstrated high
sensitivities to variations in the refractive index of their surrounding environment. The ensembles' collective response
has proven to exceed that of other sensitivities quoted in literature by various other nanoparticle structures, with
sensitivity values of up to 376.6 nm/RIU recorded. A quick, simple sucrose sensitivity test has been developed in which
any corresponding shift in the nanoparticles' spectrum can be associated solely to a change in the surrounding refractive
index. AFM, TEM and dynamic light scattering characterisation of the mean diameter and height distributions of the
nanoparticle ensembles provides information on the relationship between the structural properties of the nanoparticles
and their sensitivity.
Thanks to their cheap processability, organic optoelectronic devices are believed to gradually gain a non-negligible place on the market. However, their performances remain low, mainly because of the poor electron transport in conventional polymers used in such devices. Carbon nanotubes, with a bulk conductivity as high as 10E5 S/m, could therefore be seen as potential candidates to address this important issue. In this work, we have studied the use of a carbon nanotube and polymer composite as an active layer in organic light-emitting diodes and organic photovoltaic devices. Enhanced brightness was achieved using the composite as an electron-transport layer in organic light-emitting diodes, the best efficiency being obtained for those devices with a nanotube content of 1.2 %. Secondly, we have studied the use of the polymer and carbon nanotube composite as the active layer in organic photovoltaic cells. Photocurrents in such devices were greater than that of the cells without carbon nanotubes. It is believed that carbon nanotube composites could act as efficient transport media for charges, which were originally dissociated. This study has demonstrated that carbon nanotubes can be used as functional materials in organic optoelectronic devices and enhance the charge transport, hence the efficiency in such devices.
We have studied the effects of using a composite fabricated from carbon nanotubes and a host polymer, poly(m-phenylene-vinylene-co-2,5-dioctyloxy-p-phenylene-viny lene) (PmPV), as an electron-transport layer in organic light-emitting diodes. Double layer devices using this composite as an electron-transport layer, triple layer devices with a composite electron-transport layer and poly(9-vinylcarbazole) (PVK) as a hole-transport layer, as well as poly(2,5-dimethoxy-1,4-phenylene-vinylene-2-methoxy-5(2'-eth ylhexyloxy)-1,4-phenylene-vinylene (M3EH-PPV) single layer devices were prepared. Current-voltage-luminance and electroluminescent spectral measurements were performed using six different nanotube powder to polymer mass ratios (0, 2, 4, 8, 16, and 32%) for all device structures studied. DC transport and photoluminescence behavior of the polymer-nanotube composite were also investigated. Although a potential barrier is introduced at the M3EH-PPV/composite interface, a significant increase in efficiency was observed using the composite. The best efficiency was obtained for those devices with an electron-transport layer of mass ratio 8%. In addition, on doping with nanotubes, electron conductivity in the composite increased by over four orders of magnitude with little quenching of photoluminescence.
A new route for nanotube-based applications in molecular electronics was developed. Individual polymer strands were assembled onto single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT) by mechanical agitation. The SWNT hybrid systems have been characterized by electron microscopy (TEM, STM), optical absorption and Raman spectroscopy and a fully nondestructive technique, using electron paramagnetic resonance (EPR), has been developed to estimate the purity of MWNT soot and hybrids. It is demonstrated that solutions of the polymer are capable of suspending nanotubes indefinitely while the majority of the accompanying amorphous graphite precipitates out of solution. Electron microscopy and Raman scattering indicate that through an intercalation process, the ropes of SWNT are destroyed, resulting in individual nanotubes being well dispersed within the polymer matrix. Moreover, Raman and absorption studies suggest that the polymer interacts preferentially with nanotubes of specific diameters or a range of diameters. STM studies showed that the chiral angle of the underlying nanotube is reflected in the polymer coating, demonstrating that the lattice structure of the SWNT templates the ordering in the coating. This could lead to design of specific polymer architectures for selection of desired chiral angles, and hence specific electronic properties.
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