Papers by Author: W.L. Wang

Abstract: The field electron emission from carbon nanotube films on polycrystalline diamond films was investigated. The carbon nanotubes and diamond films on Si substrates were prepared by a conventional hot filament chemical vapour deposition. The films obtained were characterized by scanning electron microscopy and Raman spectroscopy. The field emission properties of the samples were measured in an ion-pumped vacuum chamber at a pressure of 10-6 Pa.. The experimental results showed that the field emission behaviours of carbon nanotubes/diomond films structure have greatly been improved as compared with carbon nanotubes and diamond films, respectively. A turn-on field of 1.0 V/µm and a maximum current of 500 µA at 1.5 V/µm were observed, which were lower than those of carbon nanotubes and polycrystalline diamond films, respectively. This improvement was attributed to the tip shape of sample surface, which provided an additional local increase in electric field at the tube ends.

Abstract: In this paper, the optical properties and structure of CdS films were investigated by SEM, X-ray diffraction, and x-ray photoelectron spectroscopy. The CdS films in this study were deposited on the plane transparent glass by chemical bath deposition technique. The experimental results have shown that the annealing treatment has an important effect on the optical properties and structure of CdS films. This may be ascribed to decreasing surface contaminations and oxide content in the films.

Abstract: We have performed the various measurements of the transformation strain with and without the different external magnetic fields on the Ni51.6Mn23.4Ga25 single crystals. A stress-free and two-way thermoelastic shape memory, with -1.15% strain (negative sign represents the shrinkage) and 6 K temperature hysteresis, has been found in the single crystal. The deformation can be enhanced up to -2.35% with a bias field 1.2 T applied along the measurement direction of the parent phase [001] crystallographic axial direction. Turning the field laterally applied to [010] and [100] directions of the parent phase, however, the strain was suppressed by the field of 1.2 T to 0.56% and –0.55%, respectively, a different deformation scene. Moreover, it is found that even the field of 1.2 T does not have a significant influence on the phase transition temperature and the temperature hysteresis, which indicates that the mechanism of field-enhanced strain in this material is the twin boundary motion.

Abstract: The carbon nanotubes with carboxyl groups were obtained by using different chemical treatment methods. The electrical properties of the carbon nanotube films were investigated and voltammetric responses for Fe3+ / Fe2+ were measured at the carbon nanotube film electrodes.

Abstract: The piezoresistive effect in iodine-doped carbon nanotube films was investigated by a three-point bending test. Carbon nanotubes were synthesized by hot filament chemical vapor deposition. The experimental results showed that the gauge factor for I-doped and undoped carbon nanotube films under 500 microstrain was about 350 and 65 respectively at room temperature, exceeding that of polycrystalline silicon (30) at 35°C. The origin of the piezoresistivity in the films may be ascribed to a strain-induced change in the band gap for the doped tubes and the intertube contact resistance and defects for the undoped tubes.

Abstract: Electrochemical behaviors of epinephrine and ascorbic acid have been studied at the carbon nanotube electrode using cyclic voltammetry. Electrocatalysis has been found for epinephrine redox reactions at the carbon nanotube electrode in the comparison with the glassy carbon electrode. A well-defined oxidative peak for ascorbic acid was observed at the carbon nanotube electrode with the peak potential negative shift versus the glassy carbon electrode. Low level of epinephrine can be determined at the carbon nanotube electrode selectively with high sensitivity in the presence of a large excess of ascorbic acid in the acidic media and in the physiological pH buffer solution.

Abstract: The carboxyl modified carbon nanotubes were obtained by treating them in the concentrated nitric acid with a little surfactant. The complete electrochemical combustion of phenol has been found under 5 M at the carboxyl modified carbon nanotube electrode in phosphate buffer solution. The reaction was discussed in details. Due to the porous tubule of the structure of the carbon nanotube and large quantity of hydroxyl exists in the carboxyl modified carbon nanotube electrode, which were necessary for the continually electrochemical combustion of phenol. Long time potentiostatic oxidation showed that the phenol could be eliminated from the aqueous media without any foul at the carbon nanotube electrode.

Abstract: The gas sensitivity properties of carbon nanotubes were investigated. The carbon nanotubes in this study were fabricated by hot filament chemical vapor deposition using Ni/Fe catalyst. The sensor samples were treated by chemical etching using H2SO4/HNO3. The experimental results have shown that the electrical resistance of carbon nanotubes was sensitively changed on exposure to gaseous ambient containing ethanol and water vapor. It was found that the gas sensitivity of carbon nanotubes was greatly enhanced after chemical treatment. It was also shown that the response time of nanotube sensor was faster than that of usual sensors.

Abstract: The electron field emission from carbon nanotubes on nanocrystalline diamond films was investigated. Carbon nanotubes and nano-diamond films were deposited on Si substrates by hot filament chemical vapor deposition. The experimental results showed that the carbon nanotubes on nanostructured films exhibited a lower value of the turn-on electric field than those of carbon nanotubes and nano-diamond. It was found that the turn-on field of nanotubes on nano-diamond was about 0.9V/μm, which was lower than those of carbon nanotubes and nano-diamond.