Plasma Chemical Processes
The research topic "Plasma Chemical Processes" focusses on the physics and chemistry of reactive plasmas, develops approaches and methods for controlling plasma chemical processes as well as new concepts for plasma reactors. To this end, the composition of various types of plasmas, i.e. the concentrations of charged and uncharged plasma constituents, the energetic distribution within the plasma, the plasma emission, as well as the interaction of the plasmas with adjacent surfaces, are analysed. State-of-the-art infrared absorption spectroscopy methods are available for this purpose, which allow a very sensitive determination of the concentrations of molecules in plasmas and are able to probe their physico-chemical plasma kinetics. In addition, fast spectroscopic or imaging techniques are employed to investigate the processes during electrical breakdown and to record the various discharge regimes, thus opening up the correlation between discharge physics and plasma chemistry. Based on this, plasma reactors can be designed or optimized. These diagnostics are complemented by modeling and this is carried out in close cooperation with partners from science and industry. The focus is on the development of new methods to control plasmas for surface treatment or plasma-chemical synthesis.
Reactive plasmas are among the most important working mediums in the industry. Plasma processes are state-of-the-art, particularly for activation, cleaning, coating and etching. Careful use of resources and compliance with ever more rigorous quality requirements are necessary for economical and environmental reasons and these aspects require research and development activities. Measuring the concentration of important plasma components, such as radicals or stable byproducts, and ascertaining their temporal behavior, enables statements to be made concerning the dominant processes, e.g. for layer deposition or for etching. Monitoring of key species, which due to their high reactivity are extremely short-lived and occur in small concentrations, gives users a unique tool for controlling plasmas with which the process is optimized and the treatment results become reproducible. This approach has already been successfully implemented in the semiconductor industry.
The plasma nitriding method is one of the most important methods for mediating a higher surface hardness of workpieces. Higher surface hardness increases resistance to abrasive, adhesive and corrosive wear of these components. Together with our partner Freiburg University of Mining and Technology, at the INP a new procedure for nitriding is being developed that should overcome the disadvantages of the existing technology. Through an innovative process design, so-called active screen plasma nitriding avoids effects (hollow cathode effect, arcing, boundary effects) that result in an inhomogeneous machining of the workpiece, e.g. through localized melting or sputtering. For this procedure the INP is working out a new process control based on infrared laser absorption spectroscopy, that is coupled with the electrical power supply. The essential main species in this process has already been identified. Its concentration constitutes a control parameter that enables active adaptation of process conditions, and thus the optimization of the hardening process.
Atmospheric pressure plasmas are increasing in significance, and are opening up new application fields, such as plasma synthesis, plasma medicine or decontamination. However, due to their characteristics, it is difficult to make statements concerning composition of these plasmas, and other important plasma parameters. Classic plasma diagnostic methods are either unusable or they can only be used with limitations due to the high density, high collision rates and short lifetimes. Modern imaging and spectroscopy methods (e.g. streak camera, time-correlated single-photon counting) offer the possibility of analyzing electrical breakdown and making statements concerning the strength of the electric field. Here important contributions can be made towards interpreting and controlling these sources. Moreover, in cooperation with Oxford University, the INP succeeded in detecting the hydrogen peroxl radical in the effluents of a non-thermal argon plasma jet in air, via optical feedback cavity-enhanced absorption spectroscopy method. This method makes available the high sensitivity desired for detection of reactive, short-lived species, and consequently should be further extended in the future, to help explain the active mechanisms and develop approaches for process control.
The anthropogenic emission of carbon dioxide is regarded as the central cause of climate change. Therefore, besides the avoidance of CO2 emissions, the use of this gas as a potential raw material in terms of "power-to-gas" or "power-to-fuel" approaches is also on the agenda. It is known that a non-thermal plasma converts carbon dioxide into carbon monoxide, whereas the plasma can also be fed by electrical energy from renewable sources. Carbon monoxide acts as a feedstock for the production of other chemicals. In addition, other processes, such as reforming, are also known. However, plasma chemical reactors and processes are still far from reaching sufficient energy efficiency and conversion efficiencies. The INP is researching new approaches for plasma reactors as well as the fundamentals of CO2 plasma chemistry, including the coupling with catalysts. Current projects are aimed at the use of biogenic CO2.
The detection of atoms and molecules, but also electrons and ions in very low concentrations with high accuracy is very important for the understanding of plasma processes. In addition to the established methodology of infrared absorption spectroscopy, the methodology of terahertz (THz) spectroscopy and its possible applications are explored. Not only a large laser system based on THz time domain spectroscopy is used, but also the application of compact quantum cascade lasers in the THz spectral range is investigated. This work is carried out in close cooperation with the Paul-Drude-Institut für Festkörperelektronik (PDI), another Leibniz Institute.
High-accuracy verification of gases in very low concentrations is important in the medical sector, for environmental protection, in safety technology and in many other areas. Unlike other measurement methods in special laboratories, analysis of trace gases via laser absorption spectroscopy offers many advantages, such as fast measuring times and low detection limits. This method also offers clear measurement results without interfering cross-sensitivities. For realization of high sensitivities, extending down into the ppt range, methods are used at the INP that combine modern infrared laser light sources and optical resonators. After successfully validating the suitability of this technology for provision of compact transportable, ultra-sensitive, multi-component trace gas sensors, currently a prototype based on this technology is being developed at the INP as part of a transfer project.
As part of the DFG-funded project "Development of new plasma-assisted processes for thermochemical surface treatment of ferrous materials with an active grid made of carbon", the basics for the development of a new process for the surface treatment of ferrous materials with an active grid made of carbon-reinforced carbon (CFC) are to be developed in cooperation with the TU Bergakademie Freiberg. The aim of the project is to investigate the main mechanisms of this plasma diffusion treatment in various media, especially carbon-containing media. For this purpose, IR absorption and optical emission spectroscopy are applied to a laboratory reactor at the INP as well as to an industrial plant at the TU Freiberg in order to analyze the plasma-chemical reactions in connection with the achieved treatment results. Based on this in situ parameters for the controlled generation of carburized and nitrocarburized boundary layers with defined properties and for safe process control will be deduced.
Prof. Jürgen Röpcke
Phone: +49 3834 - 554 444
In its research and innovation funding program KMU-Innovativ Photonik, the BMF supports the collaborative project "Innovative plasma nitriding through dynamic process control using optical frequency combs (InPro-F)". At the INP, the sub-project "High-resolution VIPA detection system for dynamic process control" is being processed. The network consists of the companies Menlo Systems GmbH, neoplas control GmbH and RÜBIG GmbH & Co. KG. The aim of the project is to develop a demonstrator of an optical measurement and control system based on frequency comb laser spectroscopy in the mid infrared, which is suitable for the process control of a plasma-assisted nitriding or nitrocarburizing process under industrial conditions. The project result is intended to bring about a technological leap forward for the plasma-assisted nitriding and nitrocarburizing processes by introducing a controlled procedure based on in-situ concentration measurements of molecular plasma species for the first time.
Dr. Norbert Lang
Phone: +49 3834 - 554 452
The project "Terahertz Detection of Atoms in Plasma Processes" aims at the development of spectroscopic methods in the terahertz (THz) spectral range for the determination of the absolute density of atoms and ions for a variety of species in technologically relevant plasma processes such as plasma-aided deposition of AlN and Si-based films. The joint proposal brings together the expertise of the Paul-Drude-Institut für Festkörperelektronik in the field of manufacturing customized THz quantum-cascade lasers for spectroscopic applications and of the Leibniz-Institut für Plasmaforschung und Technologie in the field of spectroscopic plasma diagnostics. Our novel approach is based on the detection of hyperfine transitions of the ground state in metal atoms and ions in the THz spectral range using quantum-cascade lasers. These lasers can be conveniently used in coolant-free Stirling coolers allowing for a compact setup. For the detection of Si, Al, N+, and O, single-mode quantum-cascade lasers emitting at 2.31, 3.36, 3.92, and 4.75 THz, respectively, will be developed and manufactured. Frequency combs spanning the spectral range from 3.3 to 4.0 THz will be developed for the simultaneous detection of Al and N+ allowing for a compact process control system based on dual-comb spectroscopy for the deposition of AlN films.
Dr. Jean-Pierre van Helden
Phone: +49 3834 - 554 3811
The aim of this DFG-funded project is the investigation of individual discharges in dielectric barrier discharges (DBDs) in multi-filament arrangements. For this purpose, individual discharges in a multi-filament arrangement will be characterized and the interaction of the filaments will be analyzed, while to entire discharge, i.e. the sum of all filaments is considered. Since the plasma chemical reactions are initiated by the physical processes in the single filaments, pulsed DBDs offer the possibility to influence and control certain plasma parameters in such a way that plasma chemical processes can be initiated more selectively and efficiently. Since a large number of filaments occur simultaneously in DBD reactors used in applications, it has to be clarified whether the existing knowledge from the single filament can be transferred to such arrangements. Furthermore, it has to be investigated how the electrical breakdown and the discharge development are influenced by the mutual influence of volume and surface processes in multifilament arrangements in order to work out possible correlations of discharge physics and plasma chemistry.
Dr. Hans Höft
Phone: +49 3834 - 554 3926
The subject of this DFG project is the model-based analysis of spatial layer structures as well as spontaneous mode transitions and instabilities in dielectric barrier discharges at atmospheric pressure. For this purpose, a self-consistent hydrodynamic plasma model for the time-dependent, spatially two-dimensional description of a single-filament discharge in argon at atmospheric pressure is developed and used to explore experimentally observed phenomena. The main aim is to gain a deeper physical understanding of the influence and mode of action of external discharge parameters such as voltage amplitude and frequency as well as the effect of gas impurities on the stability of the discharge by means of parameter studies based on statistical test planning. Finally, the input sizes can be optimized and various discharge modes can be controlled and therefore, be used for applications.
Dr. Markus Becker
Phone: +49 3834 - 554 3821