Uwe Schumacher

Sterilisation with low-pressure microwave plasmas

Abstract The aim of this article was to show that low-pressure microwave plasmas are suitable for the sterilisation of materials for all kinds of applications. Therefore, several microwave plasma sources were used to treat test substrates with a defined initial contamination of 10 6 test spores. Spore reduction kinetics are presented for four different test spores obtained with different plasma sources and different working gases. A fast spore reduction of four orders of magnitude after less than 1 s of plasma treatment could be achieved. Furthermore, the results prove that the main mechanism responsible for this fast inactivation is the effect of UV and VUV light that is produced in the plasma.

Dielectric barriers for flexible CIGS solar modules

Abstract Cu(In,Ga)Se 2 (CIGS)-based thin-film solar modules are commonly deposited on float glass substrates at temperatures of approximately 550°C. For the preparation of flexible and monolithically integrated solar modules on metal foils, the substrates first have to be coated by an electrically insulating barrier. In this study, dielectric barrier layers of Al 2 O 3 and SiO x were deposited on metal foils of Ti, Kovar ® and ferritic Cr steel. The insulation properties were tested by sputtering small Mo contacts onto the barriers and measuring the resistance and breakdown voltages of the layers before and after CIGS deposition. Best insulating barriers could be achieved with 6-μm-thick combi layers of SiO x (plasma CVD)/SiO x (sol–gel) and SiO x (plasma CVD)/Al 2 O 3 (sputtered). These layers additionally act as diffusion barriers. Results of solar cell and module characterisation are presented to demonstrate the progress in barrier development.

Plasma polymerized barrier films on membranes for direct methanol fuel cells

The methanol permeation through fuel cell relevant Nafion® membranes is investigated at different concentrations of methanol in aqueous solutions. Thin plasma polymerized barrier films are deposited on Nafion® membranes in a low pressure microwave generated plasma to reduce their methanol permeability. The methanol permeability was measured as a function of time using a gas chromatograph with a flame ionisation detector. It is shown that a plasma polymer layer with a thickness of approximately 0.27 μm on Nafion® membranes reduces the permeability to methanol by a factor of approximately 20.

High resolution emission and absorption spectroscopy for erosion product analysis in boundary plasmas

The highly resolved spectra of the silicon multiplet around 251 nm are studied for plasmas in front of a C/C-SiC target interacting with a nearly cylindrically symmetric low temperature plasma jet. The erosion rates from this target are deduced from the silicon density distribution, which is determined from the line intensity ratios and details of the line profiles. Under the conditions of the plasma parameters in this plasma-target interaction experiment these spectral line parameters depend on the optical depths of the emitting and absorbing silicon atoms along the line of sight. The spectral line central branching ratios of lines with quite different products of absorption oscillator strength and statistical weight are most sensitive to the optical depth. In the case of high plasma jet currents the density of the eroded silicon is found to reach values of up to 5×1018 m−3 in agreement with gravimetric measurements.

Development and Characterization of an Atmospheric-Pressure Microwave Plasma Torch

The presented microwave plasma torch finds application in many areas of treatment and conversion of different gases as well as in surface treatment. The torch is based on an axially symmetric resonator. Microwaves of 2.45 GHz are fed into the cavity, resulting in a sufficient high electric field for ignition and maintaining stable plasma operation. The characterization of the plasma is performed by optical-emission spectroscopy, which revealed a rotational temperature of about 3600 K in the center of the plasma.

Status and problems of fusion reactor development.

Abstract. Thermonuclear fusion of deuterium and tritium constitutes an enormous potential for a safe, environmentally compatible and sustainable energy supply. The fuel source is practically inexhaustible. Further, the safety prospects of a fusion reactor are quite favourable due to the inherently self-limiting fusion process, the limited radiologic toxicity and the passive cooling property. Among a small number of approaches, the concept of toroidal magnetic confinement of fusion plasmas has achieved most impressive scientific and technical progress towards energy release by thermonuclear burn of deuterium–tritium fuels. The status of thermonuclear fusion research activity world-wide is reviewed and present solutions to the complicated physical and technological problems are presented. These problems comprise plasma heating, confinement and exhaust of energy and particles, plasma stability, alpha particle heating, fusion reactor materials, reactor safety and environmental compatibility. The results and the high scientific level of this international research activity provide a sound basis for the realisation of the International Thermonuclear Experimental Reactor (ITER), whose goal is to demonstrate the scientific and technological feasibility of a fusion energy source for peaceful purposes.

Spectroscopic investigations of pulsed microwave generated Ar, N2 and silane plasmas

Abstract The Plasmodul (Proc. ISPC 15, Orleans, V (2001) 1853), an array of four parallel coaxial microwave guides is used as source for (square wave) pulsed plasmas in argon, nitrogen and silane at pressures of 5–50 Pa. The plasma is homogeneously extended over an area of 12 by 12 cm 2 . The temporal and radial behaviour of the electron temperature T e (r, t), the electron density n e (r, t) and the densities of several molecules, atoms and ions are investigated with different diagnostic tools. The data are compared and discussed for the three different plasma gases.

Determination of neutral carbon concentration in electron cyclotron resonance generated plasma discharges

Carbon containing plasmas play an important role not only in plasma technology but also in thermonuclear fusion research. In order to understand and control the processes taking place in the plasma, the knowledge of the carbon ground state density is of major importance. It can be determined by absorption and emission spectroscopy. Detailed measurements were performed in the past to determine the silicon ground state density by means of spectroscopy of the self-absorbed spectral lines of the silicon ground state multiplet at 251 nm. The same procedure was applied for the determination of the carbon concentration, for which the carbon multiplet at 165 nm was analyzed and compared to a simulated spectrum. The ground state density was determined by two independent methods.

Spectroscopic investigations on silicon nitride deposition with the Plasmodul

Abstract Investigations by emission light spectroscopy and mass spectrometry at gas mixture variations between the plasma compounds H 2 , N 2 , NH 3 and SiH 4 are presented to get information about the processes taking place in a silicon nitride deposition with the Plasmodul ® out of the monomers NH 3 and SiH 4 . The Plasmodul ® is a microwave sustained low pressure plasma reactor with a modular concept based on the Duo-Plasmaline ® principle which provides an easy upscaling for industrial applications.

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators - a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.