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An expanding part of electron beam technology developed at Fraunhofer FEP tackles ecological and biotechnological challenges of highest relevance. Antimicrobial and fungicidal effects of electron beam are exploited in the chemical-free phytosanitary treatment of seeds. Chemical pollutants but also pathogens in gaseous effluents and waste water can be efficiently neutralized. Medical products such as tools, packaging and implants can be sterilized, disinfected, or even biologically advantageously functionalized. Viruses can be inactivated via electron beam to produce vaccines with an excellent antigen conservation leading to a high degree of immunization with good reproducibility, but without the usage of additional chemicals. Plasma synthesis in electron beam-sustained discharges allows for an exceptionally efficient energy transfer to non-reactive greenhouse gases like CO2 and CH4 and is a promising approach to the economical, scalable production of media for sustainable chemical energy storage (Power to X - PtX), driving the energy transition and reducing greenhouse gases. The publication gives an overview of the recent advances of electron beam technology at Fraunhofer FEP in these emerging fields of application.

Highly productive substrate pre-treatment, coating, and post-treatment methods are required to combine versatile and environmentally-friendly vacuum deposition processes with economic demands. Electron beam (EB) technologies are very promising to address these requirements. This paper gives an overview of various types of electron sources for different steps along the process chains in thin-film technology, and which are based on the generation of free electrons by gas discharges: Compact low-voltage EB sources based on the hollow-cathode arc discharge, which can generate intense plasma to assist or stimulate high-rate sputter etching, PVD, and PECVD processes; and high-voltage glow-discharge EB sources with hybrid cathode, which combine the simplicity of cold cathode EB guns with the superior beam quality of hot cathode EB sources.

Increasing performance requirements of coatings on components and tools drive new approaches and developments, e.g.,in the field of thermal (TBC) and environmental (EBC) barriercoatings on turbine components, characterized by more complex compositions and a desire for morphology control. Consequently, the corresponding PVD processes become more challenging and call for advanced monitoring and control means. Plasma activation by hollow cathode arc (HAD) or spotless arc (SAD) discharges has been proven in various EBPVD processes as an enabling tool for achieving enhanced film properties at high deposition rates - facilitated by the energy gain of the condensing particles. In this paper, another beneficial effect of the plasma assist shall be discussed: Due toexcitation of vapor and gas species, the discharge also stimulates element-specific light emission. Hence, optical emissionspectroscopy (OES) can be utilized to monitor and control thePVD process in-line, which has been done in electron beam(EB) co-evaporation of several metal ingots in inert vacuum aswell as of yttria-stabilized zirconia (YSZ) in oxygen atmosphere, both activated by an HAD plasma. In both examples, OES was utilized to create an automatic control loop tuningthe beam scan pattern, the beam power and/or the feeding speed of the individual source materials to maintain the desired deposition rate and stoichiometry of the coatings. Thecombination of EB (co)evaporation, plasma activation and OES-based control demonstrated great potential to become aversatile tool for the development of complex coating systems and their reliable deposition in future production processes.

Die vorliegende Dissertation behandelt Charakterisierung, Modellbildung sowie Anwendung einer magnetfeldgestützten Hohlkathoden-Bogenentladung. Hohlkathoden sind seit den 1960er Jahren Gegenstand grundlagen- sowie anwendungsorientierter Forschung und werden seit 20 Jahren am Fraunhofer-Institut für Elektronenstrahl- und Plasmatechnik für die Anwendung auf dem Gebiet der Vakuumbeschichtung weiterentwickelt. Ziel dieser Arbeit ist es, die technologischen Fortschritte physikalisch zu verstehen und gezielte Weiterentwicklungen für spezifische Einsatzgebiete zu ermöglichen. In der untersuchten Hohlkathodenbauform ist das aus Tantal bestehende, vom Arbeitsgas Argon durchströmte Kathodenröhrchen koaxial von einer Ringanode sowie von einer Magnetfeldspule umgeben. Die Entladung wird durch Hochspannungspulse gezündet, worauf sich ein diffuser Bogen im Röhrchen (internes Plasma) ausbildet. Das Röhrchen wird von Plasmaionen auf hohe Temperaturen geheizt, die eine thermionische Emission von Elektronen ermöglichen, welche das Plasma speisen. Das technologisch nutzbare externe Plasma wird im Vakuumrezipienten durch Wechselwirkung der Gasteilchen mit Strahlelektronen aus der Kathode erzeugt. Bei starker Reduktion des Arbeitsgasflusses wird die Entladung durch das Magnetfeld der Spule stabilisiert. Der experimentelle Befund, dass dadurch Plasmadichte und -reichweite sowie ggf. die Ladungsträgerenergien im Rezipienten aufgrund des intensiveren Elektronenstrahls wesentlich gesteigert werden können, wird durch ortsaufgelöste Langmuir-Sondenmessung, optische Emissionsspektroskopie und energieaufgelöste Massenspektrometrie ausführlich belegt und nach der Lösung von Strom- und Wärmebilanzgleichungen durch die Verhältnisse im Kathodenröhrchen begründet. Neben Argon werden auch typische Reaktivgase der Vakuumbeschichtung im Hohlkathodenplasma betrachtet: zum einen Stickstoff und Sauerstoff, die in reaktiven PVD-Prozessen (physikalische Dampfphasenabscheidung) zur Beschichtung mit Oxid- bzw. Nitridschichten zum Einsatz kommen und durch Ionisation, Dissoziation und Anregung im Hohlkathodenplasma verbesserte Schichteigenschaften ermöglichen; zum anderen Azetylen, das bei PECVD (plasmagestützte chemische Dampfphasenabscheidung) von amorphen wasserstoffhaltigen Kohlenstoffschichten z. B. für tribologische oder biokompatible Beschichtungen genutzt wird. Azetylen wird durch Streuprozesse mit Elektronen und Ionen im Plasma aufgespalten, wodurch schichtbildende Spezies erzeugt werden, die am Substrat kondensieren. Durch die Wahl der Plasmaparameter sowie durch abgestimmte Substratbiasspannung und Substratkühlung lassen sich die Beschichtungsrate einstellen sowie polymer-, graphit- oder diamantartige Eigenschaften erzielen. Neben der Plasmadiagnostik mittels energieaufgelöster Massenspektrometrie werden die erzeugten Kohlenstoffschichten vorgestellt und hinsichtlich Härte, Zusammensetzung und Morphologie analysiert. In the present thesis, characterization, modeling and application of a magnetically enhanced hollow cathode arc discharge are presented. Since the 1960s, hollow cathodes are being studied in basic and applied research. At Fraunhofer Institute for Electron Beam and Plasma Technology, further development concerning the application in vacuum coating technology has been carried out for about twenty years. The present work targets on physically understanding the technological progress in order to enable specific further development and application. In the investigated hollow cathode device, a ring-shaped anode and a magnetic field coil are arranged coaxially around the tantalum cathode tube, which is flown through by argon as the working gas. The discharge is ignited by high voltage pulses establishing a diffuse arc within the cathode tube (internal plasma). The cathode is being heated by the plasma ions to high temperatures, which leads to thermionic emission of electrons sustaining the plasma. The external plasma in the vacuum chamber, which can be used for technological applications, is generated by collisions of gas atoms with beam electrons originating from the cathode. In the case of strongly reduced working gas flow, the discharge is stabilized by the magnetic field of the coil; the related experimental findings such as significantly increased plasma density and range as well as higher charge carrier energies in the external plasma are extensively proved by spatially resolved Langmuir probe measurements, optical emission spectroscopy, and energy-resolved ion mass spectrometry. Furthermore, the results are correlated to the conditions within the cathode tube by solving the current and heat balance equations. Besides argon, typical reactive gases used in vacuum coating are examined in the hollow cathode plasma, too. First, nitrogen and oxygen, which are applied in PVD (physical vapor deposition) processes for the deposition of oxide and nitride layers, are ionized, dissociated, and excited by plasma processes. In the case of practical application, this plasma activation leads to improved film properties. Second, acetylene is used as a precursor for PECVD (plasma-enhanced chemical vapor deposition) of amorphous hydrogenated carbon films, e.g. for tribological or biocompatible applications. Acetylene is cracked by electron and ion scattering in the plasma providing film-forming species to be deposited on the substrate. The deposition rate as well as the polymeric, graphitic, or diamond-like properties can be controlled by plasma parameters, a defined substrate bias, and substrate cooling. The hollow cathode-generated acetylene plasma has been characterized by energy-resolved ion mass spectrometry, and the carbon films obtained are analyzed regarding hardness, film composition, and morphology.