Research project P6/08 (Research action P6)
Domain:
The physical chemistry of plasmas – the fourth state of the matter- is a field of growing importance with both fundamental and industrial challenges. Highly reactive species generated in plasmas have found many applications in surface treatment and material processing. Although many industrial applications have been developed, the understanding of the actual mechanisms in the core of plasmas as well as at interfaces remains, to a large extent, unknown. Physical and chemical phenomena in plasmas are of course important in many other fields including thermal, fusion and astrophysical plasmas, and results from these areas will contribute to unravelling fundamental mechanisms. It is the role of university research groups to explore, understand and master these mechanisms
Objectives:
the present project aims at federating most of the Belgian groups involved in research activities on reactive plasmas in order to improve our fundamental understanding of these systems. The output of this project, combining experimental and theoretical activities, is expected to drive technological developments in the areas of new materials, new surfaces or coating processes, and thereby sustain the economic development of our country.
We plan to develop a multidisciplinary and integrated approach, merging together research units specialized in in-situ plasma diagnostic (optical, mass spectrometry and electrical probe techniques) (Hecq, Delplancke, Reniers), in the fundamental study of the ionized gas phase and its (magneto-)hydrodynamics (Degrez, Carati, Van Oost), in the electrical characterization and engineering of plasmas (Leys, Van Oost), and in modelling of plasmas (van der Mullen –Eindhoven). Other research groups will focus on plasma surface interaction (Reniers, Segers, Delplancke, Lucas, Houssiau, Pireaux, Hecq, Leys, Van Oost, Schneider), in close coordination with the groups focussed on the plasma itself. A fundamental study will be made of the interaction between the various species created in the plasmas (ions, neutrals, electrons, UV...) with model surfaces.
Methodology:
Based on our analysis, seven fundamental topics must be studied to reach a better understanding of plasmas and plasma-surface interactions. These topics are: the sources of excitation, the physics of partially and fully ionized plasmas, the radiation emitted by the plasma, the plasma confinement, the plasma phase transformations, the plasma boundary conditions at surfaces and the characterization of plasma modified surfaces and interfaces (structure and composition). These seven fields are highly interconnected. Each step must involve experimental characterization and numerical simulation to get a full picture of what’s happening in the plasma and at the surfaces and interfaces.
For example, different energy sources are available to create plasma at the laboratory scale: MW, DC, AC, RF (capacitivly and inductively coupled), HF, Arc. The coupling of the source with the gas phase influences the plasma composition, the concentration and nature of ions, electrons, excited neutrals and photons. Creation and losses of plasma species as well as recombination, impact ionization, ion-atom interchange and charge exchange are responsible for density and temperature gradients in the plasma. The plasma composition must be carefully characterized in terms of species and energy distributions to be able to understand gas phase nucleation or the surface interactions (substrate or chamber wall). These interactions with substrates and walls in turn modify the composition and interactions between species in the plasma. They also lead to functionalization, deposition (nucleation and growth), etching and implantation in the substrate. A thorough characterization (structure and composition) of the modified surface must be carried out to understand the role of species and energies.
We will start by studying model systems (gaseous phases containing a limited number of reactants, i.e. oxygen and/or nitrogen, giving a limited number of products) for which it is possible to characterize experimentally a maximum of key parameters and for which the geometry is not too complex for numerical simulations. A limited number of substrates will be selected as representative examples of material types (i.e. a polymer, a metal and a semi-conductor).The experiments will provide inputs for numerical modelling, and the simulation results will allow improvement of the experimental procedures.
Progressively, the systems will get more complex to approach the practical plasma conditions used in surface treatment or encountered in astrophysical environments.
