|Ph.D Student||Ternyak Orna|
|Subject||Formation of CVD Diamond Films and Correlation of|
Structural, Electron Emission and Electron
Transport Properties with Film Thickness
|Department||Department of Chemistry||Supervisor||Professor Alon Hoffman|
|Full Thesis text|
Formation, microstructural and electronic properties of thin diamond films deposited by hot filament CVD have been studied as a function of film thickness. Continuous undoped polycrystalline diamond films of varying thickness from 100 nm to several microns have been deposited on Si substrates pretreated by poly-dispersed diamond+alumina mixed slurry. With increasing deposition time, a columnar microstructure develops and the sp2-carbon content decrease. All as-grown diamond films have good quality hydrogenated diamond surfaces and contain only a trace amount of adsorbed oxygen. Electron emission induced by ions, electrons and electric fields was investigated and compared for diamond films of varying thickness. Electron emission induced by ions was measured by a newly developed experimental system at very low ion flux (105 ions/sec cm2) avoiding the fast degradation of diamond surfaces under ion bombardment. It was found, that the film thickness influences electron emission from these films and that the film thickness has stronger influence on the electron emission when the outgoing current of electrons is higher. When the thickness effect is present, the electron emission exhibits maximum values for near-coalescent 100 nm thick continuous diamond films. Theoretical analysis shows that the decrease of the electron escape probability from diamond surface with thickness is responsible for the decrease of the electron yield with film thickness. Since the surface chemistry is the same for diamond films of different thicknesses, the most possible reason for that is a difference in electric conductivity of diamond films of different thicknesses resulting in the different ability to replenish the emitted electrons at the diamond surface. Indeed, the resistance of diamond films in the vertical direction, measured in sandwich configuration after suppression of surface conductivity, strongly increases with increasing film thickness, indicating a much higher resistance of grain boundaries in the thicker films in comparison to the thin diamond films. The electrically conducting pathways were also experimentally investigated using conducting probe atomic force microscopy. The 100 nm thick continuous diamond films have been found to be the most conductive with the dominant conductive pathways between the diamond grains. Thicker films are less conductive and the conductive pathways appear to be mostly on the surface. The phenomenon of enhanced electron emission from the 100 nm thick diamond films has been primary attributed to the enhanced conductivity due to especially short conductive pathways via single particle shells resulting in a highly effective electron supply to the emitting surface and positive charge withdraw.