Part I. Thermodynamic properties of buckminsterfullerene and carbon-70:Heats of sublimation, total vapor pressures, and heat capacities. Part II. Chlorine-activated diamond CVD

[摘要] 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, $Delta Hsbsp{sub}{o}$ (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 $imes$ 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$spcirc$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.

[发布机构] Rice University

[效力级别] chemistry