FREE CARBON STRUCTURE IN SILICON OXYCARBIDE THIN FILMS
Open Access
- Author:
- Ryan, Joseph V
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 10, 2007
- Committee Members:
- Carlo G Pantano, Committee Chair/Co-Chair
Elizabeth C Dickey, Committee Member
Mark William Horn, Committee Member
Paul Voyles, Committee Member
Paolo Colombo, Committee Member
Joseph Patrick Stitt, Committee Member - Keywords:
- fluctuation electron microscopy
thin films
sputtering
silicon oxycarbide
carbon nanoparticles
tribology - Abstract:
- Silicon oxycarbide is a metastable material that has generated interest because of the great flexibility in properties that is attainable with a mixture of divalent and tetravalent anions within the network structure. In addition to the network bonding, however, these materials have also exhibited a strong propensity to include carbon-carbon bonding – so-called “free carbon” – within the structure regardless of synthesis method. While evidence for the presence of free carbon is overwhelming, traditional diffraction methods have been unable to characterize the degree of ordering and spatial distribution in the material. The primary theme of this thesis is the structural characterization of this elusive phase, hopefully leading to a better understanding of how to engineer the presence or absence of this phase to tailor the material properties for certain applications. To this end, rf-magnetron sputtering was utilized to synthesize silicon oxycarbide thin films over a wide composition range. The inorganic and amorphous nature of sputter-deposited films offers an opportunity for an in-depth study of this material with limited complications from phase separation, the presence of residual organics and hydrogen, or a limited range of available compositions. One example of the effect of free carbon on material characteristics is given in a study of the mechanical and tribological properties of the films. A relatively new transmission electron microscopy technique known as variable coherence fluctuation electron microscopy (FEM) is applied to probe the possibility of ordered regions in silicon oxycarbides on the length scale of roughly 8 to 50Å. We utilize this method to identify semi-ordered bonding present in silicon oxycarbide thin films similar to turbostratic carbon. An interesting approach to variable resolution FEM is also presented which holds promise as a means to extract the characteristic length scale of any ordered regions in the material. This data is utilized in conjunction with other film characterization and a full review of the literature to propose a new model for free carbon in silicon oxycarbide glasses.