Filament-Assisted Chemical Vapor Deposition of Diamond and Its Mechanism
Chen, Zhong-Jia
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https://hdl.handle.net/2142/72170
Description
Title
Filament-Assisted Chemical Vapor Deposition of Diamond and Its Mechanism
Author(s)
Chen, Zhong-Jia
Issue Date
1993
Doctoral Committee Chair(s)
Brown, Sherman D.,
Department of Study
Materials Science and Engineering
Discipline
Ceramics Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Engineering, Materials Science
Abstract
Diamond films were deposited on various substrates by filament-assisted chemical vapor deposition (FACVD). Different experimental conditions were employed to determine the effects of parameters such as filament temperature, methane concentration in the starting gas, and substrate temperature on diamond growth. The deposited films were characterized by techniques such as Raman spectroscopy, X-ray diffraction (XRD), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM).
Films deposited by FACVD were found to be sensitive to the experimental conditions. Beyond a narrow range of conditions, only amorphous carbon or graphite films formed. Within the range, the growth rate and morphology of deposited films also depended on the experimental conditions. For instance, the films deposited with a filament temperature of 2100$\sp\circ$C showed well-faceted diamond particles and Raman spectra of the film showed a sharp peak at 1332 cm$\sp{-1}$, a characteristic line of crystalline diamond. The films deposited at a filament temperature of 1600$\sp\circ$C showed a cauliflower-like structure and the corresponding Raman spectra showed a broad peak centered at 1558 cm$\sp{-1}$ that is attributed to graphitic carbon. The effects of these parameters are discussed.
Based on the experimental results from this research and the literature, new kinetic and thermodynamic models were developed. The kinetic model dealt with the evolution of the gas phase. Results from the kinetic model showed that the thermodynamic state of the gas plays a role in determining the influence of some parameters (e.g., the concentration of methane or the addition of oxygen) on diamond growth. Some transport parameters, such as flow rate and filament-substrate distance determined the thermodynamic state of gas phase just above the substrate. In many FACVD of diamond systems, this gas phase was found to be at a non-equilibrium state, i.e., the gas composition is kinetically controlled. The model results also suggested that the CH$\sb3$ radical is most likely a major precursor of diamond films. From the results of thermodynamic modeling, it was concluded that the deposition of diamond is dominated by one of three processes, viz, etching, diamond deposition and co-deposition of diamond and graphite, depending upon the initial methane concentration. Once again, the results suggest the CH$\sb3$ is more likely a precursor of diamond in FACVD system than C$\sb2$H$\sb2$. The results from modeling work interpret well several experimental observations obtained in this study and reported in the literature that have not been previously understood. A mathematic expression is given to describe semi-quantitatively the relationship of diamond deposition to the initial composition of the starting gas.
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