The metal-catalyzed etching and growth of diamond
Smith, Cynthia Corinna
Margrave, John L.
Doctor of Philosophy
Metals have been used in the past to grow diamond in high temperature/high pressure reactors. In our research we used metals to grow diamond at low pressures and low temperatures. A vertical vibratory hot-walled reactor was used along with metal powders. We started our investigation by first examining the etching of polished diamond windows coated with metal films. Metal films made from Fe, Ni and Co were deposited on diamond windows then scratched for post-reaction analysis with an Atomic Force Microprobe (AFM). The etching gases used were hydrogen, oxygen and nitrous oxide. A stable diamond interface formed between the diamond and the metal film. This interface allows for the removal of carbon from the diamond lattice. The carbon diffuses through the film to the surface were it forms C-O, and C-H species with dissociated H2 and O2 on the film surface. We analyzed the impact of various parameters on the etching reaction such as film thickness, length of reaction, temperature, crystal face, % of N2O and % of O2 in H2. Problems with surface poisoning and film adherence created problems with reaction reproducibility. Metal films were replaced with metal powders. In a hot-walled vibratory reactor the metal particles continuously collide with the surfaces of the diamond suspended in the powder. During these collisions, carbon transfer occurs at the diamond-metal interface which results in either etching or growth depending on the carbon potential of the gas phase. Metal sintering limited the maximum temperature to 400°C or less. In a series of fourteen reactions the pit depth and volume of six etch pits were monitored using the AFM. A gas mixture of CO/CO2 was used and its carbon potential varied. We were able to document growth and etching by measuring the change in pit depth and pit volume. Under growth conditions a decrease in pit depth and pit volume occurred. Under etching conditions an increase in pit depth and pit volume occurred.
Inorganic chemistry; Engineering; Materials science