The Oxidation of Diamond
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
The objective of this project is to develop a fundamental understanding of the oxidation behavior of diamond. Research efforts on oxidation and phase transition of diamond have been undertaken through a combination of experimental and computational approaches. Heat treatments are carried out on CVD diamond film ET100, manufactured by Norton Diamond Film, in a wide temperature (420 to 1500 oC) and oxygen partial pressure range (from 6x10-10 to 95 kPa). Theoretically, surface chemisorption and reconstruction of diamond surfaces are investigated using density functional theory. Taking both oxidation and phase transition into consideration, we propose that diamond can take either one of the two different paths during the heat treatment of diamond in oxygen at elevated temperatures: 1) direct gasification of sp3-bonded carbon; and 2) sp3 to sp2 phase transition (surface reconstruction) first, then gasification of sp2-bonded carbon. Diamond oxidation and phase transition are results of these two competing mechanisms. We further suggest that surface oxygen coverage and temperature are the two most influential factors that govern the surface reaction of diamond. The reaction between oxygen and diamond (111) surface at ambient pressure is summarized as: • Room temperature and 0 % coverage: The (111) surface reconstructs to (2x2) or (2x1) reconstruction. This occurs without any change of the bond character. • Elevated temperature (~ 700 oC to 1500 oC), zero coverage: The bond character of diamond (111) surface changes from sp3 to sp2. Thus, diamond goes through a phase transition and forms amorphous, sp2-bonded carbon. If the temperature reaches 1600 oC or higher, the amorphous carbon graphitizes and becomes crystalline. • Elevated temperature (~ 700 oC and higher), low coverage (up to 20%): Diamond converts to amorphous, sp2-bonded carbon first. Then the oxidation of carbon proceeds, yielding gaseous products CO and/or CO2. • Elevated temperature (~ 500 oC and higher), high coverage (more than 50%): Diamond converts to amorphous, sp3-bonded carbon first. Then the oxidation proceeds, yielding gaseous products CO and/or CO2.
Advisory committee members: Scott Misture, Alastair Cormack, Robert Condrate. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University