|Ph.D Student||Shpilman Ze'ev|
|Subject||Interaction of polycrystalline CVD Diamond Thin Films with|
|Department||Department of Physics||Supervisors||Professor Alon Hoffman|
|Dr. Joan Adler|
|Dr. Irina Gouzman|
|Full Thesis text|
Diamond is a material with superior properties. It has electron emitting capabilities, optical transparency from the ultraviolet to infrared wavelengths, a high hardness and heat conductivity, and is chemically inert. The study of diamond durability in harsh environments is important for the development of diamond-based applications. At low altitudes above the Earth (from 200-800 km), the space environment contains hyper-thermal ground state atomic oxygen (AO), as the most abundant specie, and thus due to its radical nature it is extremely hazardous for carbon-based materials. Single crystal diamond has been shown to be stable in space environment but is expensive and has less versatility in processes and applications. Cheaper, synthetic polycrystalline CVD (Chemical Vapor Deposition) diamond films contain along with sp3 bonded diamond material, sp2 bonded graphitic like disordered material in grain boundaries and defect sites. The latter is easily damaged by hyper-thermal atomic oxygen.
A study of bonding states and morphology of CVD polycrystalline diamond films interacting with thermal and hyper-thermal AO was undertaken in ground-based facilities that simulate the space environment. Following exposure to AO the diamond surface consists of an ill defined hydrocarbon and oxygen bonded material layer while the diamond spectral features were absent in the surface sensitive vibrational spectrum. Utilizing isotopes in the diamond growth revealed that the hydrocarbons are adventitious, and that hydrogen is abstracted from the diamond surface by oxygen. Hyper-thermal AO exposure also resulted in the creation of a graphitic layer on the diamond surface.
Morphological observations reveal that thermal AO exposure result in mild smoothing of crystallites edges, while hyper-thermal AO result in severe preferential etching. (111) facets are severely roughen, and (100) facets endure and are etched only at their edges. This result is correlated with the surface sensitive vibrational spectroscopy, and computer simulations. Computer simulations reveal that (111) diamond surfaces partially transforms into graphite (also observed in the surface sensitive vibrational spectroscopy), and experience damage by CO2 desorption under hyper-thermal AO exposure, resulting in an easily eroded surface. Alternatively, (100) diamond surfaces completely covered with a keton functionalization does not react with the hyper-thermal AO.
Utilizing the morphological results, highly durable diamond films can be grown using directional growth methods. These could allow the development of diamond-based applications in space, such as radiation detectors, heat-sink devices, protective coatings for solar cells, and optical elements in satellites.