Key Reference: Mohseni, P.K.; Lawson, G.; Couteau, C.; Weihs, G.; Adronov, A.; LaPierre, R.R. "Growth and Characterization of GaAs Nanowires on Carbon Nanotube Composite Films: Towards Flexible Nano-Devices" Nano Lett. 2008, 8, 4075-4080; Mohseni, P. K.; Lawson, G.; Adronov, A.; LaPierre, R. R. “Hybrid GaAs nanowire-carbon nanotube flexible photovoltaics” IEEE J. Sel. Top. Quant., 2010, in press.
Covalent Functionalization of SWNTs
Click Coupling to SWNTs - This work involves the functionalization of SWNTs with terminal alkyne groups, allowing for Cu(I)-catalyzed "click" coupling to azide-terminated polymers. This high-yielding coupling reaction enables covalent attachment of a variety of small molecules and polymers to the nanotube surface. Attachment of narrow-polydispersity azide-terminated polystyrene resulted in increased solubility of the nanotube-polymer complex in organic solvents. Current efforts include the introduction of functional polymers, capable of serving as polymeric linkers for nanotubes with other nano-structured materials. The general and orthogonal nature of the click coupling reaction enables the study of structure-activity relationships, including the effect of molecular weight and polymer architecture on solubility and self-assembly properties.
Key Reference: J. Am. Chem. Soc., 2005, 127, 14518-14524.
Ultrafiltration of carbon nanotube solutions through narrow-pore-diameter membranes (depicted below) results in the formation of thin films or "mats" of carbon nanotubes (sometimes referred to as "bucky paper"). Such films are best made from homogeneous nanotube solutions. Polymer-functionalized nanotubes not only produce homogeneous solutions ideal for the filtration process, but also result in films that can be peeled away from the filtration membrane to produce flexible, free-standing nanotube films (see images at left). The thickness of these films is easily controlled by varying concentration and filtrate volume. We are currently investigating the effect of varying the polymer structure on the properties of the films.
Above is a schematic diagram of the filtration of a carbon nanotube solution to produce a nanotube thin film. At left are images of free standing films films as produced on the filtration membrane, peeled away from the membrane, demonstration of flexibility, and formation of a very thin, transparent film (top to bottom).
We have found that these nanotube thin films can be prepared from nanotubes functionalized with poly(ethylene imine) (PEI), as depicted in the scheme below, which allows the reduction of HAuCl4 solutions to form Au nanoparticles (see before and after images below). The density and size of the particles can be controlled by varying the concentration, incubation time, and temperature. Catalytic activity of these particles within the nanotube films is currently under investigation.
Key Reference: Lawson, G.; Gonzaga, F.; Huang, J.; de Silveira, G.; Brook M. A.; Adronov, A. "Au - Carbon Nanotube Composites From Self-Reduction Of Au3+ Upon Poly(Ethylene Imine) Functionalized SWNT Thin Films", J. Mater. Chem. 2008, 18, 1694-1702.
HAuCl4
PEI functionalized carbon nanotube thin films, decorated with Au nanoparticles, were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films, which provided a flexible substrate for the nanowires. We showed that the NWs exhibited high optical quality and, if prepared with a core-shell pn-junction structure, rectifying asymmetric current-voltage behaviour was observed. We then produced a working, flexible photovoltaic device from the nanotube-supported nanowires, demonstrating that such hybrid nanostructured constructs could indeed be utilized in working devices.
SEM images above show different views of NWs grown on a flexible SWNT thin film substrate.
Schematic diagram of a PV device prepared from NWs grown on SWNT films (left), and actual data from the working device (right).

© 2011 Alex Adronov