Papers by Author: C. Cai

Abstract: In this paper, the microstructure of chafer cuticle is observed with a scanning electron microscope (SEM). The observation shows that the insect cuticle is a kind of biocomposite with hybrid structural characteristic of various chitin fibers embedded in protein matrix. The reinforced chitin fibers vary in size, shape, property and distribution, which are related to their location in the cuticle. Near the surface of the cuticle, the chitin fibers are smaller, stiffer, more circular, and the orientations of the chitin-fiber plies are various. A kind of helicoidal layup is found. The dependence of fracture strength on the fiber diameter and the dependence of fracture toughness on the parameters related to helicoidal layup are experimentally investigated. It shows that the smaller fiber and the helicoidal layup endow the surface of the cuticle with higher fracture strength and toughness.

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: 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.