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The effect of electrochemical phenomena on the deposition of carbon containing inorganic thin films from supersonic expansion of aqueous supercritical solutions

Ali Osman Sezer, University of Nebraska - Lincoln

Abstract

The supersonic expansion of dilute aqueous solutions for the synthesis of new materials is a complex flow system. Flow prediction and modeling are, therefore, quite challenging. Electrokinetic streaming potentials generated during the supersonic nozzle expansion further complicate the nature of these flow processes. Flow-generated potentials are believed to significantly affect the electrochemical environment of the flow, and therefore, may influence the properties of the product. This dissertation research was an attempt to experimentally and theoretically investigate the significance of flow-generated electrochemical phenomena and their possible effect on the deposited thin carbon films. ^ Brand's computer model was used to predict the physical properties of the expanding jet at the nozzle. The sensitivity of the predicted flow parameters to operating conditions was then analyzed. The results of this parametric flow modeling were used to identify deposition regions of flow space that have less sensitivity to fluctuations in process temperatures and pressures. Streaming currents were predicted from measured nozzle currents. The first high-temperature-pressure Pourbaix diagrams were constructed for the carbon-water system. Equilibrium Pourbaix diagrams together with predicted streaming currents suggested a possible CVD-like mechanism for the deposition of thin carbon films. ^ Deposited carbon films were analyzed for morphology, composition and structure by vibrational spectroscopy and electron microscopy. IR and Raman analysis of carbon samples were not conclusive in revealing any measurable differences in samples. Although Raman spectra showed considerable shifts in peak positions, the lack of internal standard in the spectra made it difficult to draw any reliable conclusions. Significant variations in surface morphology were found for samples grown under different substrate bias. Electron diffraction analysis conclusively showed the presence of a cubic diamond and Lonsdaleite phase in a carbon sample, which supports the predicted CVD-like deposition mechanism in the process that enables the phase transition from hexagonal graphite to cubic diamond. ^

Subject Area

Engineering, Chemical|Engineering, Materials Science

Recommended Citation

Sezer, Ali Osman, "The effect of electrochemical phenomena on the deposition of carbon containing inorganic thin films from supersonic expansion of aqueous supercritical solutions" (2003). ETD collection for University of Nebraska - Lincoln. AAI3104626.
http://digitalcommons.unl.edu/dissertations/AAI3104626

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