Sources for plasma activated synthesis

In several areas of society, new demands on materials and specific functional surfaces would benefit from the use of plasmas. Plasmas have the advantage of very efficient dissociation which allows for freedom of choice in atomic constituents. Alternatively functional groups in the feed molecules can be retained and deposited at surfaces. An important advantage is that operation at low ambient temperatures and pressure is possible. The complexity of the plasma medium and the need for proper scale up and economic feasibility require a detailed understanding and control of the process and sufficient source strength of the used plasma source. The proposal relates to the following areas of application: 1) Generation of new molecules, for example ammonia from hydrogen and nitrogen, or hydrogen from methane. Conversion of effluents and recovery of CFCs and toxic gases is a related subject. 2) Synthesis of new precursors for deposition of high purity materials in thin layers, that can be nanostructured, for example semi-conductive layers, tribological coatings such as diamond(like) films , transparent conductive oxides and biological coatings. In all these processes the following fundamental steps can be distinguished: - Plasma production and primary chemistry in the plasma source. - Fast plasma transport and efficient mixing with injected molecules/precursors. - Dissociation of the precursors, i.e. secondary chemistry. This dissociation can vary from very strong, i.e. full atomization, to only weak fragmentation, depending whether chemical structure and/or biological properties should be retained. - Deposition / molecule synthesis at the surface, leading to the formation of thin films and/or the generation of new molecules. In all these processes a first order picture is that the plasma dissociates and that formation of new molecules by association occurs primarily at the surface. The surface chemistry is totally modified by radicals adsorbed at the surface. Plasma synthesis in the high flux regime, in which new molecules are formed from interaction of plasma radicals with surface adsorbed radicals, is therefore a primary point of study. For this high flux regime the plasma source is crucial: it has to produce the required radical fluxes via efficient dissociation. The new microwave plasma sources ("microwave plasmatrons") developed by the Russian partners offer important advantages over more classical plasma sources: the plasmatrons are efficient, clean, electrode free, simple, economic and reliable. The microwave sources, developed further in the course of the project, will then be used for plasma synthesis. Optimization will take place by modelling of the kinetics and dynamics. At the TU/e and FOM-Institute a parallel experimental and theoretical study will be performed for plasma synthesis with a thermal plasma source. Concluding, the main goals and milestones of this project are: - Detailed experimental study of the plasma characteristics and of the performance of microwave plasmatron as a function of power, wavelength, pressure and type of molecules. - Design of a self-consistent physical and physical-chemical model, of the plasma source and of the downstream conversion, including kinetics, dynamics and electromagnetic interactions. - Study of the performance in terms of molecular conversion. Keywords: Microwave discharge, plasma, plasma sources, plasma chemistry, dissociation, hydrogen production, surface association, molecule formation, molecule synthesis.