Expertise

Research is oriented towards fundamental aspects of Low Temperature Plasma Physics. They are the key to plasma technology - an enabling technology for many modern products. Plasma technology is indispensable in microeletronics, for example. Questions we actually address are the coupling of energy into the discharge, the distribution of energy among the plasma particles, formation of raducals and, in particular, the mechanisms of plasma surface interactions. New and rapidly developing areas of research we are concentrating on are e.g. the investigation of formation and growth of nano particles in these discharges (dusty plasmas) and of non-thermal plasmas at atmospheric pressure (micro plasmas). One of our main activities is the development of tate-of-the-art plasma and particle diagnostics. Among them are cutting edge worldwide unique in situ methods like Rayleigh-Mie Scattering Ellipsometry, multy-pass IR absorption spectroscopy, atomic beam supported spectroscopy, high frequency and wave diagnostics etc.

Despite the outstanding technological importance of reactive plasmas, numerous fundamental phenomena are not yet understood. Progress in this field and the targeted development of future thin film materials and novel plasma processes require a more detailed knowledge of the interaction of reactive plasmas with the surrounding surfaces. The central theme of experimental physics II is to elucidate the underlying mechanisms of action at the boundary reactive plasma surface. The treatment of this topic leads to two fundamental questions:

1. Which are the reactive species responsible for the growth of the film in the gas discharge?
2. What are the heterogeneous surface reactions by which these species lead to material synthesis or surface modification?

Three main topics are dealt with:

Material Synthesis in Reactive Plasmas

Reactive plasmas are often used to produce thin films or to modify or etch surfaces. Important input variables for these processes are the particle fluxes which impinge on the surrounding surfaces and the composition of this surface, which is set in dynamic equilibrium. Mass spectrometry serves as an essential diagnostic tool since it allows a large number of species to be identified and, in the case of known cross-sections, also quantified for the detection. In addition, optical in-situ and real-time processes play a central role in the elucidation of surface processes. New developments here are the microplasms, which can be used to realize non-equilibrium processes at atmospheric pressure.

Non-equilibrium Atmospheric Pressure Plasmas

The non-equilibrium character of plasmas was for a long time best realised by low pressure plasmas, but now atmospheric pressure plasmas are emerging as an attractive alternative and generated a huge interest over the last decade. The non-equilibrium character of these plasmas can be controlled by large gas flows or by short pulsed excitation assuring strong cooling mechanisms or combinations of both. This is expanded to multi-frequency concepts by applying and combining different excitation frequencies and schemes. Thereby, any desired plasma chemistry or emission pattern can be adjusted. This implies a very direct coupling of, for example, catalytically active surfaces with the chemistry in the plasma bulk. This led to the successful development of the fields of localised surface treatments or the emerging field of plasmas interacting with biological systems such as bacteria or even human cells and to the novel field of plasma catalysis. Especially, non-equilibrium atmospheric pressure plasmas are optimal to bring them in contact with liquids or solids.

Elementary Processes of Plasma Surface Interaction

Elementary processes of plasma surface interaction are specifically investigated in particle beam experiments. Special attention is given to the interaction with biological systems. H / O / F atoms and low-energy ions are used as quantified particle beams. A phenomenon of reactive plasmas is their ability to form small particles in plasma or self-assembled structures on surfaces. However, control and control of these dust particles is difficult.