Regimes in depositing dielectric barrIer discharges

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This project aims to a better fundamental knowledge of discharge development and structure for low cost thin film deposition processes using low temperature plasmas at atmospheric pressure.Plasma technology is a key technology for the modification of surfaces by deposition of thin protective or functional layers. It is usually done by means of low-pressure plasmas, which require extensive vacuum equipment, require batch processing and disable in-line treatment of objects. Plasmas operated at atmospheric pressure, such as Dielectric Barrier Discharges (DBDs) can overcome these disadvantages as it could already be demonstrated for silicon containing films. However DBDs are usually strongly non-uniform and thus deposition of layers will be inhomogeneous. A full understanding of the underlying physics of discharge formation is still missing, in particular for conditions for layer deposition. For example the control of discharge uniformity in gas mixtures containing precursor molecules (deposit monomers) is rarely studied. Furthermore, layer deposition on surfaces can influence the discharge characteristics as the charging and emission of charge carriers is crucial for the operation of DBDs. Furthermore, the control of such discharges is still poor as an increase of the frequency, and consequently of the power dissipated in the gas, can drastically change the flow and the energy of the plasma species created in the gas phase and interacting with the surface.To study such processes and give experimental benchmarks for numerical simulation special dedicated DBD arrangement will be studied by means of electrical and optical diagnostics. Based on these results the correlation with layer deposition studies will result in a better understanding of the control of such processes. In detail it will be studied, how distinct discharge modes (filamentary DBD, homogenous DBD, patterned and self-organized DBD) can be controlled by means of operation parameters and discharge geometry. On one hand the discharge development of monofilaments in the filamentary mode will be investigated with special attention on the surface processes. Therefore systematic variation of the dielectrics (nature, thickness) as well as a quantitative measurement of the surface charges on the dielectrics by means of electro-optical effects are foreseen. In order to study the role of surface charging studies with liquid dielectrics, where deposited charges can be moved from the active discharge zone are also foreseen. On the other hand utilizing a novel DBD arrangement with structured electrode the collective effects between discharge channels and columns as well as the radial dynamics of discharge formation will be studied.