A photoemission electron microscope investigation of chemical vapor deposition diamond films and diamond nucleation
CVD diamond nucleation is investigated using the hot filament technique. The stability of CVD diamond at elevated temperatures in vacuum, O{sub 2}, and atomic hydrogen environments are studied using photoemission electron microscopy (PEEM) combined with in-vacuo x-ray photoelectron spectroscopy (XPS). Dissolution, oxidation, and atomic hydrogen etching processes of CVD diamond are observed in real-time. Low field cold electron emission from CVD diamond films has been observed for the first time by PEEM. Nucleation density Mo substrates could be increased from 10{sup 4} to 10{sup 8}/cm{sup 2} by polishing. Heating the substrate to 870{degrees}C in vacuum prior to deposition, or above 1000{degrees}C at the beginning of deposition, reduced nucleation by more than 100-fold. Reduction in nucleation sites is attributed to annealing. Nucleation on Mo{sub 2}C substrates was found to be very poor (10{sup 4}/cm{sup 2}), which shows carbide alone does not promote nucleation. Carbide formation may remove nucleation sites. CVD diamond was found to dissolve into the Mo substrate in vacuum at about 1200{degrees}C. XPS showed formation of Mo{sub 2}C when the diamond dissolved. Diamond oxidation to gas phase products occurred directly at about 600{degrees}C, with no observable participation by the substrate. No detectable etching by atomic hydrogen at a pressure 1 {times} 10{sup {minus}4} torr was observed. Boron doped and `pure` CVD diamond films were found to emit electrons at room temperature under the action of the accelerating electric field of the PEEM (about 30 kV/cm) without photon excitation. The mechanism underlying this phenomenon was investigated with PEEM and by studying the emission current-vs-voltage characteristics of the CVD diamond films. Morphology and crystalline orientation were found to play only a minor role. Impurities in the CVD diamond structure lowers the potential barrier substantially; tunneling of electrons into the vacuum is facile.
- Research Organization:
- Ohio Univ., Athens, OH (United States)
- OSTI ID:
- 50584
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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