A nanocomposite electrode of single-walled carbon nanotube ͑SWNT͒ and polypyrrole ͑Ppy͒ is fabricated to improve the specific capacitance of the supercapacitor. The individual nanotubes and nanoparticles are uniformly coated with Ppy by in situ chemical polymerization of pyrrole. To characterize the SWNT-Ppy nanocomposite electrodes, a charge-discharge cycling test for measuring specific capacitance, cyclic voltammetry, and an ac impedance test are executed. The SWNT-Ppy nanocomposite electrode shows much higher specific capacitance than pure Ppy and as-grown SWNT electrodes, due to the uniformly coated Ppy on the SWNTs. The effects of the conducting agent added in the nanocomposite electrodes on specific capacitance and internal resistance of supercapacitors are also investigated.

We have investigated the structural transformation of fluorinated singlewalled nanotubes (SWNTs) induced by electron-beam irradiation during the transmission electron microscope observations. Heavily fluorinated SWNT bundles were systematically transformed into multiwall-like nanotubes by releasing fluorine atoms during electron-beam irradiation and even broken into two pieces of the capped graphitic structures. Such structural transformations at relatively low kinetic energy (< or = 300 keV) could be explained by the local strains induced by fluorination, where C-C bonds that were fluorine-attached became 1.53 A, a single bond similar to that of a diamond, from our density functional calculations. We propose a possible concerted pathway for the structural transformation of fluorinated SWNTs induced by electron-beam irradiation based on the experimental observations.

InP nanowires [20] for polarized light detection, and is attributed to the polarization-dependent light absorption due to the dielectric contrast between the nanowire and its air surroundings. Because of the confinement in the nanowire radial direction, where the nanowire diameter is far smaller than the incident wavelength, an incident electric field that is perpendicular to the nanowire would be effectively attenuated compared to the electric field parallel to the nanowire, therefore leading the observed polarization-dependent photocurrent.[20] The current ratio for parallel and perpendicular excitation is around 4:3, comparable to the ratio obtained with single-walled carbon nanotube polarization infrared detectors. [19] The non-zero current measured with the UV radiation polarized perpendicular to the nanowire is likely caused by depolarization of light when scattered by the nearby metal electrodes. Theoretical simulations are currently underway for a better understanding. We stress that our results represent a significant step toward using nanowires as polarized UV detectors and further optimization will lead to even better performance. In summary, high-quality and large-quantity tin oxide nanowires were synthesized using a laser ablation technique and their composition and single crystalline structures were confirmed using XRD, TEM, and SAED. The growth mechanism was confirmed to follow the vapor±liquid±solid model. Precise control over the nanowire diameter was achieved by using mono-dispersed gold clusters as the catalyst. Field-effect transistors were made based on our SnO 2 nanowires, and excellent n-type transistor characteristics have been observed with threshold voltages~± 50 V and on/off ratios of~10 3 at room temperature. Photoconduction properties of SnO 2 nanowires were also studied based on our devices, where a strong modulation of the conductance by UV illumination was observed. Typical devices showed substantial increases in conductance up to four orders of magnitude upon UV illumination. SnO 2 nanowire transistors have furthermore been found to work as polarized UV detectors. ExperimentalTin oxide nanowires were prepared using a pulsed Nd:YAG laser with a repetition rate of 10 Hz and a pulse power of 1.0 W. A pure Sn (Alfa Aeser, 99.995 %) target was mounted at the upper-stream of a quartz tube furnace and then ablated to supply the vapor, which was carried downstream by diluted oxygen in argon. SiO 2 ±Si substrates coated with Au nanoparticles were placed at the downstream of the tube furnace with the Au particles serving as the catalyst for growth. The reaction was typically carried out around 900 C for 10±30 min with 100 standard cubic centimeters per minute Ar±O 2 mixture flowing. The chamber pressure was controlled at 400 torr during the growth.The as-synthesized nanowires were characterized and identified using XRD (Rigaku RV-120 apparatus, Cu Ka = 1.5418 radiation), SEM (Philips XL30 apparatus operated at 15 keV), and TEM (Phillips 420 apparatus operated at 120 keV).SnO 2 nanowires fie...