Synthesis of carbon and tungsten based thin films by plasma enhanced chemical vapor deposition
Date
2007-04-26
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ORCID
Type
Degree Level
Doctoral
Abstract
The main objective of this thesis is to find optimum discharge conditions in plasma reactors to realize controlled synthesis of various carbon-based materials with desired properties. Experimental conditions including substrate biasing, substrate pretreatment, gas flow rate, catalyst coating, and the type of carbon source, play important roles in controlling the nucleation and growth of carbon-based materials. In this Ph.D. work, the effects of various processing factors on nucleation and growth of carbon based materials were systematically investigated. The work has led to a better understanding of how each experimental parameter affects the carbon-based materials growth. Optimization of experiment conditions based on this understanding is beneficial for the controlled synthesis of carbon-based materials with desired properties. In addition, the controlled synthesis of tungsten-based nanostructures using a hot filament reactor was studied.The main results presented in this thesis are: (1) Synthesis of well-aligned carbon nanotube or carbon nanocone films with a glow discharge under a negative substrate biasing. The electric field in the plasma sheath above the substrate has been found to play an important role in controlling the alignment and orientation of nanotubes or nanocones. (2) Synthesis of high purity diamond films using solid graphite as the carbon source by graphite etching. The technique provides a route to realizing deposition of high quality diamond films at low substrate temperatures (typically as low as 350 °C.) (3) Successful synthesis of high quality diamond films on aluminum-coated steels using a graphite etching technique. The aluminum interlayer effectively reduces the graphitization which occurs on a steel substrate. (4) Synthesis of nanocrystalline diamond films with smooth surfaces under high gas flow rates with a positive substrate biasing. Both high gas flow rate and positive biasing effectively increase the nucleation density of diamond and therefore reduce the diamond grain size. (5) Synthesis of high purity crystalline tungsten or tungsten oxide nanorod films by optimizing the filament temperature in a hot filament reactor.
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Keywords
chemical vapor deposition, plasma, carbon
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Physics and Engineering Physics
Program
Physics and Engineering Physics