Carbon Nanotube and Polypyrrole Composites: Coating and Doping

Abstract

the plane surface and the diffusion rate decreases with decreasing pore size. With decreasing pore size, the pH gradient at the bottom of the pore, which is imposed by the electroreduction of protons, increases. Therefore, the growth rate of the nanowire is enhanced as the pore size decreases.In conclusion, we have investigated the growth of singlecrystal CdS nanowires using electrochemically induced deposition in the pores of an AAO template from acidic chemical baths containing CdCl 2 and TAA. TEM and HREM investigations indicated that these nanowires have a uniform hexagonal CdS single-crystal structure and the {100} surfaces of the CdS crystals are parallel to the axes of the nanowires. The above results imply that the growth of the nanowire may be influenced profoundly by different electrochemical processes. ExperimentalThe AAO templates with pore sizes of about 8, 20, and 90 nm were grown by potentiostatic anodization of high-purity aluminum plates (0.15 mm thick, 99.9+ % purity) in aqueous solutions of 14 % H 2 SO 4 and 4 % and 2 % oxalic acid, respectively, at 0±20 C. After the anodization, the remaining aluminum was etched by a 20 % HCl±0.1 M CuCl 2 mixed solution. Then the barrier layer was dissolved using 20 % H 2 SO 4 . Finally, a silver film was deposited by vacuum evaporation onto one surface of the template membrane to provide a conductive contact.The deposition of CdS was performed potentiostatically at a potential value of ±0.65 V referred to the saturated calomel electrode (SCE) in a three-electrode configuration in a glass cell at 70 C by immersing the cell in a water bath for 5±8 h. A platinum plate, SCE, and the Ag/AAO substrate were used as counter, reference, and working electrodes, respectively. The electrolyte solution consisted of 0.05 M CdCl 2 and 0.10 M TAA, as in the work by Yamaguchi et al. [25]. In order to avoid the erosion of the template, the initial pH of this mixture was adjusted to 4.6 by adding appropriate amounts of HCl. In all cases, the electrolyte was freshly prepared and heated for 1 h at 70 C prior to each deposition. After the deposition, the nanowires in the AAO templates were ultrasonically washed in water for 1 min, rinsed with double distilled water, and finally dried in air at room temperature before being subjected to further analysis.AAO was completely removed from the Ag/AAO/CdS samples by mounting the foil on a glass using epoxy resin and then dissolving the AAO template in 1 M NaOH at 25 C for 1 h and washing several times with double distilled water. For transmission electron microscopy (TEM), the nanowires were detached from the substrate by being ultrasonically dispersed in 1 cm 3 water, then a small drop of the solution was placed on a Cu grid covered with carbon film. A transmission electron microscope, JEM-200CX, operated at 160 keV and fitted with X-ray energy dispersion analysis equipment (EDAX 9100/6, Philips), was employed to study the morphology of the nanowires. For the high-resolution electron microscopy (HREM) observations, a JEOL-2010 electron ...

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