Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire array was successfully fabricated on an Al 2 O 3 substrate by a simple physical vapor-deposition method at a low temperature of 450 °C. The diameter and growth rate of ZnO nanowires increased as a function of growth temperature. TEM observation showed that the ZnO nanowires were synthesized along the c-axial direction of the hexagonal crystal structure. We demonstrate that ZnO nanowires followed the self-catalyzed growth mechanism on the ZnO nuclei. Besides high-quality ZnO nanowires, sometimes a fascinating hierarchically ordered ZnO structure was also observed.

For 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 (0.95NKN-0.05BT) ceramics sintered at 1040–1075°C, abnormal grain growth occurred but the grain size decreased when the sintering temperature exceeded 1075°C. The dielectric constant (ϵ3T∕ϵ3), electromechanical coupling factor (kp), and piezoelectric constant (d33) were considerably increased with increasing relative density and grain size. Evaporation of Na2O deteriorated the piezoelectric properties by decreasing the resistivity. To minimize Na2O evaporation, specimens were muffled with 0.95NKN-0.05BT powders during the sintering. Improved piezoelectric properties of d33=225pC∕N, kp=36%, and ϵ3T∕ϵ3=1058 were obtained for specimen sintered at 1060°C for 2h with muffling.

We investigated the effect of temperature on the growth rate and structure of carbon nanotubes using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The carbon nanotubes were grown vertically aligned on iron nanoparticle deposited silicon substrate by thermal chemical vapor deposition of acetylene in the temperature range 800-1100 °C. As the growth temperature increases from 800 to 1100 °C, the average diameter increases from 20 to 150 nm and the growth rate also increases by about 20 times. All carbon nanotubes exhibit a bamboo-like structure over this temperature range. In the carbon nanotubes grown at higher temperature, the thicker compartment layers appear more frequently. The relative amount of crystalline graphitic sheets increases progressively with the growth temperature. The Arrhenius plot provides the activation energy of carbon nanotube growth to be at least 30 kcal/mol. The results indicate that the bulk diffusion of carbons would be an important factor in the growth of carbon nanotubes.

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Nitrogen-doped carbon nanotubes were grown vertically aligned on the iron nanoparticles deposited on silicon substrates, by thermal chemical vapor deposition of methane/ammonia and acetylene/ammonia mixtures in the temperature range 900-1100 °C. The concentration of the nitrogen atoms has been controlled in the range 2-6 atomic %, by the flow rate of ammonia. All nanotubes exhibit a bamboo-like structure over this temperature range. The growth rate is insensitive to this nitrogen content, but the structure is strongly dependent on it. As the nitrogen content increases, the thicker compartment layers form uniformly at a regular distance and the relative amount of crystalline graphitic sheets is notably reduced. Electron energy-loss spectroscopy reveals the higher nitrogen concentration and the lower crystallinity for the compartment layers compared to the wall. The growth of nitrogen-doped carbon nanotubes has been explained using a base growth mechanism proposed for carbon nanotubes. We suggest that the nitrogen doping would produce more flexible compartment layers connecting the wall under a less strain.