6.2 Material- und Oberflächentechnologien
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Paper des Monats
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The identification of the peak intensity threshold for X-ray generation during ultrashort pulse laser material processing is critical for ensuring operational safety and regulatory compliance. Thus far, laser peak intensities below 10^13 W/cm^2 have been regarded as safe, typically resulting in negligible or undetectable X-ray emissions under most experimental conditions. In this study, an industrial-grade ultrashort pulse laser setup delivering 71.9 W maximum average power was employed in materials processing. Both single-pulse irradiations and various laser burst modes were investigated. A laser beam at two different laser wavelengths, 1030 and 515 nm, was investigated. In addition, the pulse duration was varied, ranging between 250 fs and 10 ps. The maximum X-ray dose rates for representative metallic materials, semiconductors and insulators are presented. Notably, as a key finding, the study reveals that X-ray emissions exceeding the German legal limit of 1 μSv/h in 100 mm distance may occur at laser peak intensities below 10^12 W/cm^2. This is significantly lower than previously assumed for safe laser processes. At the chosen measurement distance of 40 cm, the highest X-ray dose rates (>500 mSv/h) were detected in the 2-pulse burst mode regime during irradiation of tungsten at peak intensities up to 8.2 × 10^14 W/cm^2.
Im Übersichtsvortrag wurden Ausführungen zu ultrakurzen Laserimpulsen und der Materialbearbeitung mit Ultrakurzpulslasern mit dem Schwerpunkt der Strukturierung von Oberflächen gemacht. Oberflächen können mit einem Laserverfahren funktionalisiert werden. Die mögliche Emission von unerwünschter sekundärer Röntgenstrahlung bei der Laserbearbeitung wurde adressiert und mögliche Schutzmaßnahmen diskutiert. Der Vortrag schloss mit einem Ausblick.
Given their unique properties, ultrashort laser pulses with durations in the femtosecond to picosecond range currently open new avenues in the field of laser materials processing, resulting in groundbreaking new applications based on laser-induced surface functionalization. This article reviews the usability of temporally distributed energy deposition via double-pulse irradiation in applications based on laser ablation. This includes simple new techniques for surface nanostructuring and improved sensitivities in spectroscopic material analyses, nanoparticle production, secondary X-ray emission, as well as recent developments towards advanced extreme ultraviolet photolithography.
Bacterial biofilms are aggregates of bacterial cells, often attached to a surface, and enclosed by a self-produced extracellular matrix which confers increased stress tolerance and resistance to cleaning and disinfection. Biofilm formation leads to biofouling which gives rise to high costs in numerous technical settings due to biocorrosion and biodegradation. However, biofilms can also be attractive for industrial settings such as wastewater treatment systems or for soil bioremediation processes. Hence, the control of bacterial adhesion to a surface is of major concern. Surface topography strongly influences bacterial adhesion. Therefore, one promising way to achieve bacteria-guiding surfaces lies in the contactless and aseptic large-area laser processing of technical surfaces. We used short and ultrashort pulsed laser systems to generate different surface textures, mainly high-spatial-frequency and low-spatial-frequency laser-induced periodic surface structures, LIPSS (HFSL and LFSL), on Ti, Ti-alloy, steel, and polymers (PET and PE). Pristine (polished) and laser processed samples were subjected to bacterial adhesion experiments with two different Escherichia coli strains and Staphylococcus aureus as test organisms. The bacterial strains differed in their cell wall structure (grampositive vs. gramnegative strains), in size, shape, the occurrence of cell appendages, and in their biofilm forming capabilities. Adhesion patterns were analyzed microscopically and compared regarding the respective test strain and surface topography. Our results revealed that adhesion behavior strongly depends not only on the material’s topography and chemistry, but also on the specific bacterial strain, the presence of cell appendages, and ambient growth conditions.
The precise laser-based surface structuring on the micro- and nanoscale allows to create functional properties for innovative applications, e.g., in medicine, optics, and biology. Among the various types of surface structures, laser-induced periodic surface structures (LIPSS) are characterized by their versatility and the relatively simple manufacturing process. However, the fabrication of highly regular LIPSS patterns remains challenging. The systematic investigation of LIPSS formation, as well as of the resulting functional properties, requires a precise evaluation of the surface morphology, especially regarding periodicity and regularity. Existing quantification methods such as Fast Fourier Transformation (FFT) tend to lack automation and objectivity, especially when dealing with large data sets and multi-scale structures. Although automated approaches exist with the Gini coefficient and the P³S method, their limited availability restricts a broader scientific use. ReguΛarity provides an innovative open-source software solution for objective, rapid, and reproducible evaluation of the regularity of structured surfaces. To ensure comprehensive surface morphological analysis, the software uses advanced image-processing techniques and integrates the already developed tools such as the P³S method, Gini coefficient, FFT analysis, and the calculation of DLOA (Dispersion of LIPSS Orientation Angle). The software allows to evaluate microscopic images obtained from standard scanning electron microscopy and atomic force microscopy. Light microscopy can also be employed, provided that its spatial resolution remains sufficient to clearly resolve the specific type of LIPSS under investigation. An intuitive PyQt5-based interface, enhanced by multi-threading capabilities, facilitates efficient data processing. Interactive features such as region-of-interest selection and plotting provide flexible adaptation to diverse applications. ReguΛarity offers a robust analysis tool that will contribute to the further development of precise laser-based surface structuring and to the optimization of the desired functional properties in both research and industry.
High spatial frequency laser‐induced periodic surface structures (HSFL) exhibiting sub‐100 nm spatial periods – far below the optical diffraction limit – can be easily manufactured on titanium and its alloys by laser‐based processes. The regularity of these HSFL – expressed in the length and local orientation of the ridges – is not only influenced by the parameters chosen for the laser scanning process but also by the microscale morphology of the titanium substrates. We processed HSFL on titanium materials with varying microscale morphology (bulk, film) by irradiation with near‐infrared ps‐laser pulses (1030 nm wavelength, ≈1 ps pulse duration) under different laser scanning conditions with the aim to increase the order of the nanoscale surface structures. For quantification of the regularity of the HSFL, a detailed analysis of scanning electron microscopic images is performed with our free ReguΛarity software to yield large area morphological and topographical surface characterization. Analyses of the regularity of the HSFL are performed with respect to the influences of sample- or laser-related parameters and the ablation thresholds.
The laser-induced fabrication of nanostructures with feature sizes below the optical diffraction limit is possible for almost any material for arbitrary sample geometries and dimensions by exploiting nonlinear excitations or optical near-field interactions. This overview highlights historical milestones, explains the underlying physical processes and associated challenges, and discusses current and future trends in the field of ultrafast laser nanostructuring.
Accurately distinguishing oxygen evolution reaction (OER) currents from anodic metal dissolution is essential for accurately evaluating metal electrocatalysts, as both processes often overlap in the transpassive potential region.1,2 This study explored multi-principal element alloys (MPEAs) as a pathway toward sustainable electrocatalysis by reducing reliance on noble and critical metals. CrCoNi and CrMnFeCoNi alloys are used as model systems to understand how complex compositions behave when OER and dissolution occur simultaneously, providing a benchmark for designing Co-reduced/free variants within the FeCrNi MPEA family.
To quantitatively separate these pathways, we employ an integrated operando approach: tip-substrate voltammetry in scanning electrochemical microscopy (TSV-SECM) for spatially resolved O2 detection, ICP-MS and UV-Vis spectroscopy for dissolution quantification and chromium speciation, and in-situ electrochemical AFM (EC-AFM) to identify the onset of corrosion and track nanoscale surface evolution. Converting dissolution data into electrochemical charge enables a precise attribution of transpassive currents to either OER or metal dissolution. To further assessmass-transport effects, MPEAs were examined using rotating disk electrode (RDE) methods. Controlled hydrodynamics separate kinetic from diffusion-limited regimes and reveal how dissolution rates, passive-film behavior, and OER activity respond under flow conditions.
Overall, this methodology provides a robust platform for reliably distinguishing catalytic OER performance from corrosion processes while guiding the design of next-generation electrocatalysts that minimize or eliminate Co and other critical and noble metals. Extending these insights to FeCrNi-based systems offers new opportunities for sustainable, high-performance materials capable of operating under technologically relevant anodic conditions.
LIPSS for beginners
(2026)
