Detailed understanding of growth termination in vertically aligned single-walled carbon nanotubes (SWNTs) made via supergrowth, or water-assisted growth, remains critical to achieving the ultralong SWNTs necessary for next-generation applications. We describe the irreversible catalyst morphology evolution that occurs during growth, and which limits the lifetime of surface supported catalysts. Growth termination is strongly dependent on growth temperature, but not sensitive to C2H2:H2O ratio. In addition to both planar Ostwald ripening of small (sub-5 nm) Fe catalyst particles and diffusion of metal atoms into the alumina support, other features that contribute to growth termination or deceleration are described, including center-of-mass particle motions and coalescence of smaller species of surface supported Fe nanoparticles. Additionally, a temperature-induced structural transition in the alumina catalyst support is found to be coincident with abrupt growth termination at temperatures of 800 °C and higher. In situ electron microscopy observations are used to directly support these observations.

Electron spin resonance investigations on the angular dependence of carbon nanotubes are reported. It is proved that the resonance line is a convolution of three lines one due to electron delocalized over carbon nanotubes, the second assigned either to amorphous carbon or to conducting electrons in interaction with metallic impurities, and the last one originating from catalyst residues.

In situ quantitative studies of the effects of substrate temperature, methane and chlorine flow rates on homoepitaxial diamond growth rates on (110) surfaces in a chlorine-activated diamond CVD reactor have been carried out using a Fizeau interferometer. The temperature dependence of diamond growth rates was found to display three distinct growth activation energies, ranging from 9±2 kcal/mol in the substrate temperature of 750-950°C, to 3.2±0.2 kcal/mol in the temperature range of 300-650°C, followed by 1.2±0.2 kcal/mol in the temperature range of 102-250°C. Atomic hydrogen is believed to be the dominant activating species in the highest temperature range, and atomic chlorine is believed to be the dominant species in the lower temperature regions. Studies of the methane flow effect on diamond growth rates revealed a linearity, indicating that the diamond growth rate was of the first order in methane flows. Diamond growth rates were also found to increase linearly with the chlorine flow. At high chlorine flow rates, however, an accelerated diamond growth rate was observed. Discussion is given to explain the observed results.

Equal amounts of carbon-12 methyl halides and carbon-13 methane, along with hydrogen, have been introduced into a hot-filament diamond CVD chamber. The isotopic ratios of the as-deposited diamond films on tantalum have been measured by Raman spectroscopy. It was found that methyl chloride yielded carbon-12 enriched diamond films, while the other methyl halides resulted in equal amounts of carbon-13 and carbon-12 in the films. Furthermore, the carbon-12 enrichment was more enhanced as the substrate temperature was lowered. Matrix-isolation FTIR analyses of the gas samples collected during the deposition indicated that there was no straightforward agreement between the 12C/13C ratios of the gas phase species, methane and acetylene, and that of the diamond films. The results imply the presence of a new chlorocarbon radical such as CH2Cl, which is postulated as a more effective growth species than the methyl radical.

A model for diamond growth on stepped diamond (100)2×1 surfaces is proposed, involving adsorption and reaction of CH3 and H on a dimer-reconstructed surface. Surface rearrangments and the breaking of C-C dimer bonds by H and/or H2 are suggested to be important The energetics were estimated by molecular mechanics (MM3). Growth is concluded to occur predominantly by extension of dimer rows, yielding a smooth surface, due to steric and bond-strain constraints on the positions of precursor-addition reactions and the kinetic stability of type SB steps against etching.

Growth rates of homoepitaxial (110), (111), and (100) diamond films were experimentally determined, for the first time, in a hot filament reactor using methane and carbon tetrachloride as the carbon source. Methane concentrations from 0.07 % to 1.03 % in H2 were studied at a substrate temperature of 970°C. Growth rates were found to be crystal-face dependent with respect to methane concentration, being linear or first order for the (100)-orientation, sublinear for (110), and sigmoidal for (111). The observed growth kinetics of (111) suggest the viability of an acetylene mechanism for (111), along with the methyl radical mechanism at methane concentrations above 0.73%. CC14 concentrations from 0.06% to 0.69% in H2 were also investigated at a substrate temperature of 970°C. Growth rate behavior was similar to that of methane for all three crystal faces.

The temperature dependence of the growth rates was also crystal-orientation dependent. At substrate temperatures above 730°C, growth rates are thought to be mainly transport limited, yielding effective activation energies of 8±3, 18±2, and 12±4 kcal/mole for (100), (110), and (111) orientations, respectively. At substrate temperatures below 730°C, growth rates are thought to be surface reaction rate-limited, with an overall effective activation energy of 50±19 kcal/mole for the three crystal-orientations studied.

Mixed carbon-12/carbon-13 diamond films were synthesized by hot-filament chemical vapor deposition, using mixtures of 13CH4 and 12CH4 or 12C2H2 in H2. The first-order Raman peak at 1332 cm−1 for 12C-diamond was found to shift by 50 cm−1 to 1282 cm−1 for pure 13C-diamond. For mixed-isotope films, the Raman peak frequency shifts linearly between these values as a function of the 13C mole fraction. The mechanism of diamond film growth by hot-filament CVD has been investigated by growth from mixtures of 13CH4 and 12C2H2, using the shifted Raman frequency to determine the relative incorporation rates of 13C and 12C into the film. The 13C mole fraction in the film agrees closely with the 13C mole fraction inferred for the methyl radical but differs substantially from that of acetylene, indicating that the methyl radical is the dominant growth precursor under the conditions studied.

The success of the emerging CVD diamond film industry will depend to a great extent on how well these films can be put to practical applications. Our research is presently focusing on the development of methods for the growth of large thin wall diamond shapes which can be subsequently strongly bonded to other support materials. The shapes such as cylinders, hemispheres, etc. will be designed to take advantage of diamond's superior hardness and thermal conductivity. As these diamond shapes also promise low friction and long wearing surfaces, they have potential uses as bearing surfaces as well as very scratch resistant covers for mirrors and lenses. Our primary research objectives will be concerned with: 1. The development of various apparatus to grow selected shapes of CVD diamond. 2. The development of techniques to transfer and bond the films onto materials other than the original substrates. 3. The physical and chemical characterization of the diamond films, composites, and final products.

The incorporation of methane into low-pressure CVD diamond thin films has been compared to that of acetylene. 13CH4 and 12C2 H2 were used as the hydrocarbon sources in a heated-filament CVD diamond growth process at a total concentration of 0.5% hydrocarbon in 99.5% hydrogen. Results indicated that methane and/or methyl radical is the dominant carbon source for diamond growth in a hot filament reactor under steady state conditions and that acetylene is rapidly hydrogenated to methane. Results also indicated that diamond surface reactions play an important role in determining the relative methane to acetylene ratios.

Diamond powders, single crystal diamonds (slabs and naturally occurring stones), and CVD diamond films have been fluorinated via direct fluorination and plasma techniques at a variety of temperatures and reaction times. Infrared, ESCA, and mass spectrometric studies verify that the diamond surfaces are altered by fluorination and that fluorine is attached to the surface to some degree in most instances. Based on spectra obtained using the FT-IR techniques of DRIFTS and ATR, the fluorine appears to have an effect on the diamond surfaces at relatively low temperatures in short reaction times by the removal of surface contaminants. A relatively high temperature (600ºC) or long reaction time at slightly lower temperatures is needed to attach a significant number of fluorine atoms onto the diamond surface. Once fluorinated, the diamonds show enhanced resistance to further oxidation. The outward appearance of the diamonds remains unchanged even at fluorination temperatures nearing 800ºC.