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A microwave plasma CVD reactor was used for the deposition of carbon nanotubes on substrates. Hydrocarbon or oxyhydrocarbon mixtures were used as the carbon source. Hot electrons in the microwave plasma at temperatures exceeding 10,000C provided a means of dissociating the vapor or gas feedstock, heating the substrate, and allowing gas species to react in the gas phase as well as on the surface of the substrate leading to the deposition of desired carbon coatings. A high vacuum chamber was used to characterize the electron emission properties of these carbon nanotube coatings using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon nanotube coatings served as the cathode. The current-voltage characteristics of the carbon nanotube coatings were measured and used for calculating the electric field at which electron emission turned on as well as calculating the field enhancement factor of the carbon nanotubes. Field emission of electrons from carbon nanotubes starting from an electric field lower than 1 volt per micrometer has been achieved.
Low-temperature chemical vapor deposition processes were studied for coating carbon films on metal-coated glass plates. Thermal CVD in hydrocarbon mixtures was used for carbon deposition at temperatures between 300°C and 550°C. Carbon deposited on metal coated glass plates were examined by SEM and analyzed using a pin to disk setup in an ultra high vacuum chamber for measuring the electron emission characteristics. Using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon coatings as the cathode, current-voltage characteristics of the carbon coatings were measured and used for calculating the electric field at which electron emission started as well as calculating the field enhancement factor of the carbon coatings. Field emission of electrons from carbon coatings starting from an electric field as low as 1.4 volts per micrometer has been achieved.
Diamond films have been deposited on silicon wafers by scanning an oxyacetylene flame against water-cooled silicon substrates. High quality diamond films about 20 um thick can be achieved by scanning the flame at a speed of about 0.2 mm per minute. The as-deposited films exhibit high electrical resistivity exceeding 1014Ωcm. Current voltage measurement shows the trap-dominated current conduction characteristics similar to that for dehydrogenated diamond films deposited by methane/hydrogen plasmas.
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