@misc{GerhardLetienCressentetal.2019, author = {Gerhard, Christoph and Letien, Emilie and Cressent, Thomas and Hofmann, Mandy}, title = {Impact of the plasma power on plasma-induced increase in absorption of fused silica}, series = {Wissenschaftliche Beitr{\"a}ge 2019}, volume = {23}, journal = {Wissenschaftliche Beitr{\"a}ge 2019}, issn = {0949-8214}, doi = {10.15771/0949-8214_2019_5}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-10802}, pages = {33 -- 37}, year = {2019}, abstract = {In the last decades, laser machining of fused silica has gained in importance where the main challenge is to overcome the high transmission of this medium in order to achieve surface absorption. One approach is plasma treatment using hydrogenous process gases. In doing so, a near-surface glass layer is chemically modified by a removal of oxygen and an implantation of hydrogen, resulting in the formation of optically active defects and an increase in absorption. Against this background, the impact of the plasma power on plasma-induced increase in absorption of fused silica was investigated in the present work. Here, the highest efficiency of the plasma treatment process was found at the lowest applied plasma power whereas for higher plasma powers, a notably lower increase in absorption was observed. This effect is attributed to the decomposition of plasma species required for initiating the formation of optically active defects within the glass. Such decomposition increases with rising power due to the corresponding increase in electric field strength within the plasma. This finding is of substantial interest for an extensive understanding of plasma-glass interactions.}, language = {en} } @article{GerhardLetienCressentetal.2020, author = {Gerhard, Christoph and Letien, Emilie and Cressent, Thomas and Hofmann, Mandy}, title = {Inline monitoring of hydrogenous plasma-induced defect formation within fused silica via plasma emission spectroscopy}, series = {Applied Physics A: Materials Science and Processing}, volume = {126}, journal = {Applied Physics A: Materials Science and Processing}, issn = {1432-0630}, doi = {10.1007/s00339-020-3347-5}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13118}, year = {2020}, abstract = {In this paper, the indirect monitoring of plasma-induced defect formation within fused silica via plasma emission spectroscopy is presented. It is shown that low-pressure plasma treatment with hydrogen as process gas leads to a decrease in UV transmission of fused silica. This decrease can be directly attributed to oxygen vacancy-related defects and the presence of hydrogen within the silicon dioxide glass network. By the analysis of the plasma composition, it was observed that the amount of oxygen within the plasma increases with increasing treatment duration. Hence, oxygen was continuously released from glass network in the course of the plasma treatment. It was further observed that this release is strongly dependent on the applied plasma power where the lowest process efficiency occurs at the highest plasma power. It is shown that an increase in plasma power leads to a remarkable increase in light emission from the working gas, hydrogen. This observation indicates that the higher the degree of excitation and ionisation of the plasma, the lower the efficiency of plasma-induced formation of oxygen deficiency-related defects. This finding is of mentionable relevance for a better understanding of plasma-induced surface modification and coating processes.}, language = {en} } @article{BoehmeDoehlerHofmannetal.2023, author = {B{\"o}hme, Andrea and D{\"o}hler, Torsten and Hofmann, Mandy and Neumann, Jens and Bochem, Reinhard and Geißler, Ute and Foitzik, Andreas}, title = {Electrolytical Coating of Inhomogeneous Structures Distributed on Metallic Surfaces}, series = {Materials Science Forum}, volume = {1106}, journal = {Materials Science Forum}, publisher = {Trans Tech Publications}, issn = {0255-5476}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-18825}, pages = {75 -- 80}, year = {2023}, abstract = {In modern electrochemical coating technology, it is common practice to create uniform layers. However, this study focuses on the deposition of non-uniform layers achieved through a deliberate arrangement of micro structured electrodes on the anode side. The "dog bone effect" was employed as the primary approach [1]. When electroplating on an otherwise uniform surface, this effect selectively processes an area influenced by the geometric edge effect (figure 1 left). The coating within this area is intended to be (i) unevenly distributed and (ii) non-reproducible. Process data was obtained through electrochemical simulations and subsequently applied to a specially designed micro-galvanic setup. This enabled the production of suitable micro structured anodes, validation of coating parameters, and the deposition of visually imperceptible structured areas with inhomogeneous properties using "adhesive gold" on appropriate substrates such as silver and nickel. The layers and their local topography were characterized and analyzed using confocal laser microscopy, X-Ray fluorescence analysis (XRF), as well as a self-designed and constructed laser interference device. As a result, this specific galvanic process technology successfully produced metallic layers that (i) cannot be visually confirmed by the naked eye, (ii) exhibit varied microstructural anode geometries, (iii) display unique differences in layer thickness, (iv) possess non-reproducible and chaotic topographies, and (v) can be detected and identified using conventional analysis techniques or a simple interference setup.}, language = {en} }