Plasma Chemical Processes
The research topic of “plasma chemical processes” focusses on the physics and chemistry of reactive plasma. The team develops approaches and methods for control of plasma chemical processes. This particularly also includes the determination of concentrations of charged and uncharged plasma species, its energy distribution, as well as the analysis of emissions by the plasma and the interaction of plasma with the adjacent surfaces. For this purpose, state-of-the-art infrared absorption spectroscopy methods are available, which represent a highly sensitive and accurate way for (in situ) determining molecule concentrations in plasmas and which are also capable of measuring the plasma kinetics. For examination of the processes during electric breakdown and morphology of plasmas, fast spectroscopic or imaging methods are used. The diagnostic work is supplemented by modelling and is performed in close cooperation with partners from science and industry. Its priority is the development of new methods for the control of plasmas in 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.
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.
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.
Within the framework of the project funded by the German Research Foundation (DFG), "Development of new plasma-assisted methods for thermal-chemical boundary layer treatments of ferrous materials with an active screen of carbon", in cooperation with the Freiburg University of Mining and Technology, the foundations should be laid for development of a new method for boundary layer treatment of ferrous materials with an active screen of carbon reinforced carbon (CFC).
The objective of the project is to research the essential active mechanisms of this plasma diffusion treatment in various media, particularly carbon-containing media. For this purpose, on a laboratory reactor at the INP, and at an industry-oriented facility of the Freiberg University of Mining and Technology, IR-absorbtion and optical emissions spectroscopic investigations are underway to analyze the plasma-chemistry reactions in conjunction with the achieved treatment results, and to derive parameters for controlled generation of carburized and nitrocarburized boundary layers with defined properties, as well as safe process control.
Prof. Jürgen Röpcke
Phone: +49 3834 - 554 444
In this project, funded by the DFG, in cooperation with the Laboratory of Plasma and Energy Conversion (LAPLACE) at the University of Toulouse (France), development and formation of non-thermal atmospheric pressure plasmas are being investigated for surface coating applications. Plasmas at atmospheric pressure, such as dielectric barrier discharge, as a rule do not form a uniform plasma, and this can cause inhomogeneous coating results. Particularly in gas atmospheres with precursor molecules, to this point in time an understanding of the discharge physics has been lacking. Inversely, a change of the surface properties in the coating process results in a change of the plasma parameters.
Thus, control of the processes is still difficult, particularly at high power levels. In the project, the different discharge regimes (single-filaments, self-organized structures in so-called patterned discharges, diffuse discharges) are investigated under process-relevant operating conditions via systematically established electrical, optical, and spectroscopic methods. The goal is to carry out which mechanisms and surface properties are responsible for control of the plasma parameters and structure formation in the gas discharges.
Prof. Dr. Ronny Brandenburg
Phone: +49 3834 - 554 3818