Browsing by Author "Pan, Chenyu"

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    Halogen-activated chemical vapor deposition of diamond
    (1996-12-31) Hauge, Robert H.; Pan, Chenyu; Rice University; United States Patent and Trademark Office
    The present invention is directed to a method of producing diamond films through the thermal dissociation of molecular chlorine into atomic chlorine in a heated graphite heat exchanger at temperatures of from about 1,100° C. to about 1,800° C. The atomic chlorine is subsequently rapidly mixed with molecular hydrogen and carbon-containing species downstream. Atomic hydrogen and the carbon precursors are produced through rapid hydrogen abstraction reactions of atomic chlorine with molecular hydrogen and hydrocarbons at the point where they mix. The mixed gases then flow across a heated substrate, where diamond is deposited as a film. Diamond deposits have been confirmed by Raman spectroscopy.
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    Part I. Thermodynamic properties of buckminsterfullerene and carbon-70: Heats of sublimation, total vapor pressures, and heat capacities. Part II. Chlorine-activated diamond CVD
    (1994) Pan, Chenyu; Margrave, John L.
    The first measurements of the heats of sublimation of C$\sb{60}$ and C$\sb{70}$ were carried out from a polycrystalline mixture of C$\sb{60}$ and C$\sb{70}$ using Knudsen effusion mass spectrometry. Average heats of sublimation of C$\sb{60}$ and C$\sb{70}$ were found to be respectively 40.1 $\pm$ 1.3 and 43.0 $\pm$ 2.2 kcal/mol, at the temperatures 707 and 739 K. The measured heat of sublimation of C$\sb{60}$ was extrapolated to 278.15 K, $\Delta H\sbsp{sub}{o}$ (298.15 K) 54 kcal/mol. The first measurements of the total vapor pressures of a polycrystalline C$\sb{60}$/C$\sb{70}$ solid solution were carried out with a quartz crystal microbalance (QCM) and by transpiration methods. The results from the two independent methods show good agreement. The solid solution was found to have a total vapor pressure of 8.1 $\times$ 10$\sp{-4}$ Torr at 800 K. It is estimated that the total vapor pressure of the C$\sb{60}$/C$\sb{70}$ solid solution could reach 1 atm at ca. 1523 K. The heat capacities of a polycrystalline mixture of C$\sb{60}$ and C$\sb{70}$ have been measured by a differential scanning calorimeter (DSC) over the temperature range 323-500 K. The measured heat capacities of C$\sb{60}$ and C$\sb{70}$ indicate that C$\sb{60}$ and C$\sb{70}$ are structurally more like graphite than diamond. Co-deposited thin films of C$\sb{60}$/C$\sb{70}$ and transition metals Ti, Cr, Fe, and Ni have been made in a multiple-furnace chamber. Studies of both infrared and ultraviolet spectroscopy showed no evidence in the formation of metal-fullerene complexes at room temperature. This study also demonstrated the application of a simple laser reflection interferometry in the calibration of thickness monitors. A novel method of producing atomic hydrogen and the active carbon species by first dissociating molecular chlorine in a graphite furnace has been demonstrated. It was found that the quality of the diamond deposits depends on both substrate temperatures and H$\sb2$/Cl$\sb2$ mole ratios. A Fizeau interferometer with a high sensitivity has been developed as an in situ probe for homoepitaxial diamond CVD process. This interferometer has permitted the determination of growth and etching rates within 10-15 minute time periods. The substrate temperature studies of the diamond growth rate revealed three different activation energies over the temperature range 102-950$\sp\circ$C. The effects of furnace temperature, system pressure, gas velocity, methane and chlorine flow rates on diamond growth rates were also investigated. A simplified kinetic model was derived to explain the observed experimental results. Diamond growth rates in the chlorine-activated CVD reactor were found to be much higher at low temperatures than is the case in hydrogen only reactors. The ability to scale up the CA-CVD process has also been demonstrated.