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- ItemReactive ion beam figuring of optical aluminium surfaces(Bristol : IOP Publ., 2017) Bauer, Jens; Frost, Frank; Arnold, ThomasUltra-smooth and arbitrarily shaped reflective optics are necessary for further progress in EUV/XUV lithography, x-ray and synchrotron technology. As one of the most important technological mirror optic materials, aluminium behaves in a rather difficult way in ultra-precision machining with such standard techniques as diamond-turning and subsequent ion beam figuring (IBF). In particular, in the latter, a strong surface roughening is obtained. Hence, up to now it has not been possible to attain the surface qualities required for UV or just visible spectral range applications. To overcome the limitations mainly caused by the aluminium alloy structural and compositional conditions, a reactive ion beam machining process using oxygen process gas is evaluated. To clarify the principle differences in the effect of oxygen gas contrary to oxygen ions on aluminium surface machining, we firstly focus on chemical-assisted ion beam etching (CAIBE) and reactive ion beam etching (RIBE) experiments in a phenomenological manner. Then, the optimum process route will be explored within a more quantitative analysis applying the concept of power spectral density (PSD) for a sophisticated treatment of the surface topography. Eventually, the surface composition is examined by means of dynamic secondary ion mass spectrometry (SIMS) suggesting a characteristic model scheme for the chemical modification of the aluminium surface during oxygen ion beam machining. Monte Carlo simulations were applied to achieve a more detailed process conception.
- ItemResidual Layer Removal of Technical Glass Resulting from Reactive Atmospheric Plasma Jet Etching by Pulsed Laser Irradiation(Dordrecht : Springer Science + Business Media B.V., 2020) Kazemi, Faezeh; Arnold, Thomas; Lorenz, Pierre; Ehrhardt, Martin; Zimmer, KlausUltrahigh-precision machining of glass is indispensable for optical component fabrication and therefore for applications. In this regard, plasma jet assisted chemical etching technologies enable new fabrication processes for enhanced optical functionalities due to their deterministic localized machining capabilities. This technique has been successfully applied to fused silica and silicon. However, applications require specific glass properties are related to complex material compositions of the glass. Hence, reactive plasma etching of these optical glasses is a challenging task. For instance, etching of metal oxide containing glass like N-BK7 by a fluorine-based reactive atmospheric plasma jet (RAPJ) exhibits currently limitations due to the formation of non-volatile reaction products that remain on the glass surface as a layer. Therefore, a procedure consisting of RAPJ etching and laser ablation is proposed for the machining of N-BK7. The capability of laser-based removal of residual layers is compared to water-based solving of the residual layer. After RAPJ etching of N-BK7 using a CF4–O2 gas mixture with an average microwave power of 16 W, the samples are cleaned either by a water-based solvent or by the ablation with a nanosecond-pulsed ultraviolet laser. The laser irradiation with fluences of 2.8 J/cm2 results in a localized removal of the residual layer. It is demonstrated that the roughness of the laser-cleaned N-BK7 surface is similarly low as solvent-based cleaned samples but the pulsed laser enhanced cleaning allows a dry processing at atmospheric pressure as well as a localized processing with a high lateral resolution.
- ItemDevelopment of a model for ultra-precise surface machining of N-BK7® using microwave-driven reactive plasma jet machining(Hoboken, NJ : Wiley Interscience, 2019) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasIn this paper, extensive studies are conducted as key to overcoming several challenging limitations in applying fluorine-based reactive plasma jet machining (PJM) to surface machining of N-BK7®, particularly regarding the manufacture of freeform optical elements. The chemical composition and lateral distributions of the residual layer are evaluated by X-ray photoelectron spectroscopy and scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis aiming at clarifying the exact chemical kinetics between plasma generated active particles and the N-BK7 surface atoms. Subsequently, a model is developed by performing static etchings to consider the time-varying nonlinearity of the material removal rate and estimate the local etching rate function. Finally, the derived model is extended into the dynamic machining process, and the outcomes are compared with the experimental results.
- ItemAn investigation on effectiveness of temperature treatment for fluorine-based reactive plasma jet machining of N-BK7®(Hoboken, NJ : Wiley Interscience, 2020) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasIn this study, a fluorine-based reactive plasma jet is investigated as a promising tool for ultraprecise surface machining of N-BK7®. Plasma-generated particles react with an N-BK7 surface to create volatile and nonvolatile compounds. The desorption of volatile compounds results in an etched surface, whereas nonvolatile compounds form a residual layer in the etched area, causing unpredictable effects on the etching rate. Surface temperature treatment is proposed to improve the machining procedure with respect to deterministic material removal, leading to predictable results. It is shown that, at an elevated surface temperature, the residual layer properties are modified in favor of improved etching performance. The etching behavior of N-BK7 is compared with fused silica to verify the optimality of the obtained results.
- ItemA novel Deal–Grove-inspired model for fluorine-based plasma jet etching of borosilicate crown optical glass(Hoboken, NJ : Wiley Interscience, 2021) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasThe Deal–Grove model is a state-of-the-art approach proposed for describing the thermal oxidation of silicon and the oxide thickness over time. In this study, the Deal–Grove concept provided the inspiration for a mathematical model for simulating plasma jet-based dry etching process of borosilicate crown glass (N-BK7®). The whole process is contained in two so-called Deal–Grove parameters, which are extracted from experimental data including local etching depth and surface temperature distribution. The proposed model is extended for the evolution of dynamic etch profiles, and the obtained results are validated experimentally. By establishing such a model, it is possible to predict the effect of the residual layer and surface temperature on the evolution of local etching depths over dwell time.
- ItemLow-temperature atmospheric pressure plasma conversion of polydimethylsiloxane and polysilazane precursor layers to oxide thin films(Weinheim : Wiley VCH, 2023) Rudolph, Martin; Birtel, Peter; Arnold, Thomas; Prager, Andrea; Naumov, Sergej; Helmstedt, Ulrike; Anders, André; With, Patrick C.We study the conversion of two polymeric silicon precursor compound layers (perhydropolysilazane and polydimethylsiloxane) on a silicon wafer and polyethylene terephthalate substrates to silicon oxide thin films using a pulsed atmospheric pressure plasma jet. Varying the scan velocity and the number of treatments results in various film compositions, as determined by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The mechanism suggested for the conversion process includes the decomposition of the precursor triggered by plasma-produced species, the oxidation of the surface, and finally, the diffusion of oxygen into the film, while gases produced during the precursor decomposition diffuse out of the film. The latter process is possibly facilitated by local plasma heating of the surface. The precursor conversion appears to depend sensitively on the balance between the different contributions to the conversion mechanism.
- ItemImproved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces([Bellingham, Wash.] : SPIE, 2018) Bauer, Jens; Ulitschka, Melanie; Pietag, Fred; Arnold, ThomasAluminum mirrors offer great potential for satisfying the increasing demand in high-performance optical components for visible and ultraviolet applications. Ion beam figuring is an established finishing technology and in particular a promising technique for direct aluminum figure error correction. For the machining of strongly curved or arbitrarily shaped surfaces as well as the correction of low-to-mid spatial frequency figure errors, the usage of a high-performance ion beam source with low tool width is mandatory. For that reason, two different concepts of ion beam generation with high ion current density and narrow beam width are discussed. (1) A concave ion beam extraction grid system is used for apertureless constriction of ion beams in the low millimeter range. An oxygen ion beam with a full-width at half-maximum (FWHM) of 4.0 mm with an ion current density of 29.8  mA  /  cm2 was achieved. (2) For even smaller ion beams, a conic aperture design with a submillimeter-sized exit opening was tested. A nitrogen ion beam with an FWHM down to 0.62 mm with an ion current density of 4.6  mA  /  cm2 was obtained. In situ ion current density mapping is performed by scanning Faraday probe measurements. Special interest is set on the data evaluation for submillimeter ion beam analysis.
- ItemFinishing of metal optics by ion beam technologies(Bellingham, Wash. : SPIE, 2019) Bauer, Jens; Frost, Frank; Lehmann, Antje; Ulitschka, Melanie; Li, Yaguo; Arnold, ThomasUltraprecise mirror devices show considerable potential with view to applications in the visible and the ultraviolet spectral ranges. Aluminum alloys gather good mechanical and excellent optical properties and thus they emerge as important mirror construction materials. However, ultraprecision machining and polishing of optical aluminum surfaces are challenging, which originates from the high chemical reactivity and the heterogeneous matrix structure. Recently, several ion beam-based techniques have been developed to qualify aluminum mirrors for short-wavelength applications. We give an overview of the state-of-the-art ion beamprocessing techniques for figure error correction and planarization, either by direct aluminum machining or with the aid of polymer or inorganic, amorphous surface films. © The Authors.
- ItemSide effects by oral application of atmospheric pressure plasma on the mucosa in mice(San Francisco, California, US : PLOS, 2019) Jablonowski, Lukasz; Kocher, Thomas; Schindler, Axel; Müller, Karolina; Dombrowski, Frank; von Woedtke, Thomas; Arnold, Thomas; Lehmann, Antje; Rupf, Stefan; Evert, Matthias; Evert, KatjaCold atmospheric pressure plasma (CAP) has been investigated with promising results for peri-implant diseases treatment. However, prior to in-vivo applications of CAP sources in humans, short-term harmful mucosal damage or other unwanted side effects have to be reviewed. 180 male mice (B6C3F1) were divided into twelve treatment groups (n = 15). The right buccal cheek mucosa was treated with CAP. The first and second group each received continuous 10 sec irradiation with 2 different plasma sources (kINPen09, PS-MWM). The third group was treated with the kINPen09 for one minute. Control groups were treated with a corresponding dose of ultraviolet light for 8 seconds or 48 seconds and the other one was left untreated. The animals were weighed before and after treatment. The animals were sacrificed one day or one week after exposure. Stained tissue samples were histologically examined for tissue damage independently by two experienced pathologists. One day after CAP treatment histological analysis showed focal mucosal erosion with superficial ulceration and necrosis accompanied by a mild inflammatory reaction. One week after CAP treatment, the mucosal defects were completely re-epithelialized, associated with remnants of granulation tissue in the stroma irrespective of treatment duration. Furthermore, no cytological atypia was found and no severe weight loss occurred. The control groups did not show any alterations at all. CAP treatment led to a superficial mucosal damage that healed within few days. Nonetheless, further long-term experiments are necessary to exclude undesirable side effects after longer observation time. Particularly, potential carcinogenic effects must be ruled out prior to the application of CAP treatment in daily dental practice.
- ItemMicro-embossing of micro-structures in RSA-501 as mold inserts for the replication of micro-lens arrays(Amsterdam : Elsevier, 2022) Kober, Julian; Rolón, Daniel; Hölzel, Florian; Kühne, Stefan; Oberschmidt, Dirk; Arnold, ThomasThe production of mold inserts for the replication of micro-lens arrays through micro-embossing could be an alternative process route compared to diamond turning or milling in order to reduce time and costs. The rapidly solidified aluminum alloy RSA-501 is expected to form micro-structures with low surface roughness because of its ultra-fine grain structure. In micro-embossing challenges like elastic spring back effect, pile-ups, and forming accuracy depend on the material behavior. Therefore, RSA-501 was further characterized and the influence of polishing or flycutting on the material behavior was investigated. To further understand the grain and microstructure samples were sectioned along their cross and longitudinal directions. The grain structure of RSA-501 was oriented along the extrusion direction and the mean grain sizes were <1.00 μm. Furthermore, RSA-501 was micro-embossed to investigate the influence of the material behavior and surface preparation on the forming of micro-structures. The induced surface integrity through flycutting was not deep enough to influence the forming of micro-structures. Therefore, the workpiece surface can be prepared either by polishing or flycutting. When micro-embossing RSA-501, cross and longitudinal sections can be used. However, it is recommended to process the cross section because of its isotropic grain structure. It was shown that the curvature radius of micro-embossed concave structures differs from the tool radius. This is due to the elastic spring back effect. Since the embossed structure remains spherical, the spring back effect can be compensated by adjusting the tool radius.