TY - JOUR A1 - Bischoff, Kay A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Femtosecond reductive Laser Sintering under multiple focus conditions for rapid production of conductive copper layers JF - Procedia CIRP KW - Femtosekundenlaser KW - Laserstrahlsintern Y1 - 2024 U6 - https://doi.org/http://dx.doi.org/10.1016/j.procir.2024.08.189 SN - 2212-8271 VL - 124 SP - 629 EP - 633 PB - Elsevier BV ER - TY - CHAP A1 - Bischoff, Kay A1 - Mücke, Dominik A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UV-Femtosecond-Laser Structuring of Silicon Carbide T2 - International Congress on Applications of Lasers & Electro-Optics (ICALEO) 2023 N2 - We report on ultraviolet ultrashort pulsed laser processing of silicon carbide. Laser ablated cavities are evaluated with respect to their ablation rates, surface roughness and overall quality by varying the laser pulse fluence. Using this type of laser, high edge quality and surface roughness down to 107 nm can be achieved with an ablation efficiency of up to 0.228 mm 3 W −1 min −1. Functional surfaces are produced by generating laser induced periodic surface structures. The comparison with infrared wavelength underlines the advantages of the ultraviolet wavelength for laser micro machining this material. Significant differences with respect to the measured ablation depths and roughness as well as generated micro-and nanostructures appear. While infrared ablation is dominated by a chipping mechanism above a critical fluence of 9.93 Jcm −2 , higher ablation rates are observed with strong quality losses at the same time. In comparison to the infrared emission wavelength, in general , a significantly higher processing quality is achieved with the ultraviolet emission wavelength. In addition, the influence of spot size and repetition rate in UV processing is investigated. By increasing these parameters, a process acceleration without quality losses is enabled. The generation of a sophisticated microstructure exemplifies the advantages of processing silicon carbide with the UV laser reported here. KW - Femtosekundenlaser KW - Siliciumcarbid Y1 - 2023 ER - TY - CHAP A1 - Bischoff, Kay A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Acceleration of Femtosecond Reductive Laser Sintering of Copper(II) Oxide for Conductive Copper Patterns on Cyclic Olefin Copolymers T2 - International Congress on Applications of Lasers & Electro-Optics (ICALEO) 2023 N2 - We report on the acceleration of femtosecond reductive laser sintering of copper (II) oxide on the surface of transparent cyclic olefin copolymers (COC) by varying the focus size to generate metallic copper (Cu) layers. By using different focusing conditions, different process speeds are achieved, and the structural accuracies are controlled. The formation of Cu lines is observed for different focus sizes at various scan speeds, which is attributed to laser exposure duration and chemical reaction time. The formed lines are categorized and measured by optical microscopy and provide the basis for two-dimensional Cu surfaces. By hatching, high quality conductive films are produced with an increased focus diameter of up to 400 µm at a scan speed of 400 mm/s and a hatch distance of 250 µm resulting in a multiple increased process speed by a factor of thirteen compared to previous research. Using 4-tip measurement , a low sheet resistance of 0.165 Ω/sq was validated on these Cu films, which have an atomic Cu content of 89.5%. KW - Femtosekundenlaser Y1 - 2023 ER - TY - JOUR A1 - Bischoff, Kay A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Preparation of Dispersed Copper(II) Oxide Nanosuspensions as Precursor for Femtosecond Reductive Laser Sintering by High-Energy Ball Milling JF - Nanomaterials N2 - This contribution demonstrates and discusses the preparation of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS). Since the presence of agglomerates interferes with the various RLS sub-processes, fine dispersion is required, and oversized particles must be identified by a measurement methodology. Aside from the established method of scanning electron microscopy for imaging individual dried particles, this work applies the holistic and statistically more significant laser diffraction in combination with dynamic image analysis in wet dispersion. In addition to direct ultrasonic homogenization, high-energy ball milling is introduced for RLS, to produce stable nanosuspensions with a high fine fraction, and, above all, the absence of oversize particles. Whereas ultrasonic dispersion stagnates at particle sizes between 500 nm and 20 μm, even after 8 h, milled suspension contains a high proportion of finest particles with diameters below 100 nm, no agglomerates larger than 1 μm and a trimodal particle size distribution with the median at 50 nm already, after 100 min of milling. The precursor layers produced by doctor blade coating are examined for their quality by laser scanning microscopy. The surface roughness of such a dry film can be reduced from 1.26 μm to 88 nm by milling. Finally, the novel precursor is used for femtosecond RLS, to produce homogeneous, high-quality copper layers with a sheet resistance of 0.28 Ω/sq and a copper mass concentration of 94.2%. KW - Laserstrahlsintern KW - Femtosekundenlaser Y1 - 2023 U6 - https://doi.org/https://doi.org/10.3390/nano13192693 VL - 13 IS - 19 SP - 2693 EP - 2693 ER - TY - JOUR A1 - Bischoff, Kay A1 - Mücke, Dominik A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UV-Femtosecond-Laser Structuring of Cyclic Olefin Copolymer JF - Polymers N2 - We report on the laser ablation of cyclic olefin copolymer using an amplified ultrashort pulsed laser in the ultraviolet spectral range. In addition to a high ablation depth per laser-structured layer up to 74 μm at a fluence of 22 J cm−2, an excellent mean roughness 𝑅𝑎 of laser-patterned surfaces down to 0.5 μm is demonstrated. Furthermore, with increasing fluence, increasing ablation efficiencies up to 2.5 mm3 W−1 min−1 are determined. Regarding the quality of the ablation, we observed steep ablation flanks and low debris formation, though for fluences above 10.5 J cm−2 the formation of troughs was observed, being attributed to multiple reflections on the ablation flanks. For comparison, laser ablation was performed under identical conditions with an infrared laser wavelength. The results highlight that UV ablation exhibits significant advantages in terms of ablation efficiency, surface roughness and quality. Moreover, our results show that a larger UV focus spot accelerates the ablation process with comparable quality, paving the way for high-power UV ultrashort pulsed lasers towards an efficient and qualitative tool for the laser machining of cyclic olefin copolymer. The production of complex microfluidics further underlines the suitability of this type of laser. KW - Femtosekundenlaser Y1 - 2022 U6 - https://doi.org/https://doi.org/10.3390/polym14142962 VL - 14 IS - 14 SP - 2962 EP - 2962 ER - TY - JOUR A1 - Kefer, Stefan A1 - Bischoff, Kay A1 - Roth, Gian-Luca A1 - Haubner, Julian A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles JF - Advanced Optical Materials N2 - This contribution demonstrates and discusses electrically tunable polymer planar Bragg gratings based on bulk cyclic olefin copolymers. A lithographic single-writing-step method and femtosecond laser reductive sintering of copper(II) oxide nanoparticles are subsequently employed in order to generate buried photonic structures and copper conducting paths on top of the polymer substrate. This way, the necessary number of process steps for fabricating a planar polymer-based electro-optical device is greatly reduced. The response of a fully electrified grating structure follows temperature changes, induced by the copper conducting path, with sensitivities up to −31 pm K−1. Dilatometric measurements show that the specimen's behavior is correlated to the situationally reduced thermal expansion of the bulk polymer substrate. In consequence, the tuning response of the photonic platform follows a second order polynomial, whereas a direct current of 30 mA, which correlates to a power consumption of 18.3 mW, leads to a local temperature increase and a residual Bragg wavelength shift of 19.6 K and −547 pm, respectively. Moreover, the outstanding flexibility of the proposed fabrication concept is underlined by demonstrating alternative conducting path geometries, whereas one of the additional designs is adapted to control the spectral width of the Bragg grating's reflection peak. KW - Bragg gratings KW - CuO nanoparticles KW - cyclic olefin copolymers KW - electro-optic tuning KW - integrated photonics KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2021 UR - https://onlinelibrary.wiley.com/doi/10.1002/adom.202002203 U6 - https://doi.org/https://doi.org/10.1002/adom.202002203 VL - 9 IS - 13 SP - 2002203 EP - 2002203 ER - TY - GEN A1 - Kefer, Stefan A1 - Bischoff, Kay A1 - Roth, Gian-Luca A1 - Haubner, Julian A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles (Advanced Optical Materials 13/2021) N2 - This cover image outlines the fabrication method of a polymer planar Bragg grating electrified via femtosecond laser reductive sintering of CuO nanoparticles (see article number 2002203 by Stefan Kefer and co-workers). Based on this sophisticated methodology, bulk cyclic olefin copolymer substrates can be equipped with integrated photonic structures comprising a waveguide as well as a Bragg grating. Its reflective characteristics can be efficiently tuned by means of the subsequently generated Cu conducting path, whereas the applied femtosecond laser process enables an almost limitless degree of freedom towards conducting path geometries. N2 - Cover zum zugehörigen Artikel KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2021 UR - https://onlinelibrary.wiley.com/doi/10.1002/adom.202170048 U6 - https://doi.org/https://doi.org/10.1002/adom.202170048 ER -