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Bacteria are ubiquitous and colonize all types of surfaces, including those in close proximity to humans, such as skin, food, and everyday objects. This raises the question of whether their presence represents a problem to be mitigated or a potential source of benefit to be harnessed, thereby stimulating scientific inquiry into the role of surface-associated bacteria in diverse domains ranging fromhuman health to industrial biotechnology. Aim: The objective of this project is to explore the impact of modifying surface topography on bacterial adhesion behavior. By manipulating the physical characteristics of the substrate, the attachment and detachment dynamics of bacteria can potentially be modified, leading to novel strategies for controlling bacterial colonization in various applications, such as medical devices. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were tested on LIPSS-covered Fused Silica samples.
Die Funktionalität von modernen technischen Komponenten liegt meist in der Oberfläche und in Beschichtungen. Das Design und die Herstellungsqualität von Beschichtungen ist essenziell für die optischen, elektrischen, mechanischen und chemischen Eigenschaften von Bauteilen, sowie für den Korrosions- und Verschleißschutz. In diesem Gremium bearbeiten wir Normen für die Qualitätssicherung von dünnen Schichten verschiedener Art. Dabei betrachten wir Eigenschaften wie Schichtdicke, Zusammensetzung, Haltbarkeit, Korrosionsbeständigkeit und physikalische Parameter von dünnen Schichten mit sehr vielfältigen Techniken. Neben klassischen Verfahren aus der Galvanik und Schichtmesstechnik, werden dabei auch neuere spektroskopische Verfahren wie Ellipsometrie und THz-Reflektion bedeutend. Unser Gremium ist offen für neue Mitglieder aus der Oberflächen- und Beschichtungsgemeinschaft.
A giant Zn segregation transition is revealed using CALPHAD-integrated density-based modeling of segregation into Fe grain boundaries (GBs). The results show that above a threshold of only a few atomic percent Zn in the alloy, a substantial amount of up to 60 at.% Zn can segregate to the GB. We found that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy required for triggering the segregation transition decreases. Direct evidence of the Zn segregation transition is obtained using high-resolution scanning transmission electron microscopy. Base on the model, we trace the origin of the segregation transition back to the low cohesive energy of Zn and a miscibility gap in Fe-Zn GB, arising from the magnetic ordering effect, which is confirmed by ab-initio calculations. We also show that the massive Zn segregation resulting from the segregation transition greatly assists with liquid wetting and reduces the work of separation along the GB. The current predictions suggest that control over Zn segregation, by both alloy design and optimizing the galvanization and welding processes, may offer preventive strategies against liquid metal embrittlement.
The development of more powerful and more efficient lithium-ion batteries (LIBs) is a key area in battery research, aiming to support the ever-increasing demand for energy storage systems. To better understand the causes and mechanisms of degradation, and thus the diminishing cycling performance and lifetime often observed in LIBs, in operando techniques are essential, because battery chemistry can be monitored non-invasively, in real time. Moreover, there is increasing interest in developing new battery chemistries. Beyond LIBs, sodium ion batteries (NIBs) have gained increasing interest in recent years, as they are a promising candidate to complement LIBs, owing to their improved sustainability and lower cost, while still maintaining high energy density.[1] Initial phases of NIB commercialisation have occurred in the past year. However, for the widespread commercialisation of NIBs, there are still challenges that need to be overcome in developing optimized electrode materials and electrolytes. For the development of such materials and greater understanding of sodium storage mechanisms, solid electrolyte interface (SEI) formation and stability, and degradation processes, in operando methodologies are crucial.
Among the techniques available for in operando analysis, nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) are becoming increasingly used to characterize the chemical composition of battery materials, study the growth and distribution of dendrites, and investigate battery storage and degradation mechanisms. In situ and in operando 1H, 7Li and 23Na NMR and MRI have recently been used to study LIBs and NIBs, identifying chemical changes in Li and Na species respectively, in metallic, quasimetallic and electrolytic environment as well as directly and indirectly studying dendrite formation in both systems.[2-4] The ability of NMR and MRI to probe battery systems across multiple environments can further be complemented by the enhanced spatial resolution of micro-computed X-ray tomography (μ-CT) which can provide insight into battery material microstructure and defect distribution.
Here, we report in operando 1H and 7Li NMR and MRI experiments that investigate LIB performance, and the identification of changes in the Li signal during charge cycling, as well as the observation of signals in both 1H and 7Li NMR spectra that we attribute to diminishing battery performance, capacity loss and degradation. Additionally, recent operando methodology are adapted and implemented to study Sn based anodes in NIBs. 23Na spectroscopy is performed to monitor the formation and evolution of peaks assigned to stages of Na insertion into Sn, while 1H MRI is used to indirectly visualize the volume expansion of Sn anodes during charge cycling. Battery operation and degradation is further explored in these NIBs, using μ-CT, where the anode is directly visualized to a higher resolution and the loss of electrolyte in the cell, during cycling is observed
The lattice enthalpies and monotropic relationship of two dehydroepiandrosterone (DEHA) polymorphs (forms I and II) were evaluated through a combination of differential scanning calorimetry (DSC), isothermal solution microcalorimetry, and drop-sublimation Calvet microcalorimetry experiments. The standard molar enthalpy of transition between both forms was determined as ΔtrsHom (II→I, 298.15 K) = - 0.90 ± 0.07 kJ mol-1 and ΔtrsHom (II→I, 417.8 K) = - 1.7 ± 1.0 kJ mol- 1, from measurements of standard molar enthalpies of solution in dimethyl sulfoxide and enthalpies of fusion, respectively. Drop-sublimation Calvet microcalorimetry experiments on form I led to ΔsubHom (cr I, 298.15 K) = 132.0±3.3 kJ mol - 1. This result, when combined with the more precise ΔtrsHom (II→I) value obtained by solution calorimetry, afforded ΔsubHom (cr II, 298.15 K) = 131.1±3.3 kJ mol - 1. The overall data indicate that on enthalpic grounds form I is more stable than form II from 298.15 K up to fusion. This conclusion, and the fact that DSC experiments indicated that form I has also a considerably higher temperature fusion, namely, Tfus(cr I)= 422.5±0.2 K and Tfus(cr II) = 413.1±0.2 K, suggest that the two polymorphs are monotropically related.
Determining thermal transitions in thin polymer layers by means of spectroscopic ellipsometry
(2023)
Thin polymer layers have enormous technical significance as polymer coatings on materials are very cost-effective for tailoring properties of surfaces. Apart from technical aspects in their use, thin polymer layers can be used to determine dimensional aspects in properties of material, such as confinement effects.
In this work, we investigated several different polymer layer materials and determined their glass transition region by means of temperature-dependent spectroscopic ellipsometry. We have optimised our fitting procedure of the ellipsometric data produced in temperature ramp experiments. By this, we could measure the dependence of Tg on the layer thickness in a wide variety of thickness values, proving the existence of confinement effects in the investigated systems. We compare numerical methods for determining the location of the glass transition and discuss the possibilities of different analysis methods when determining thermal transitions. We also discuss the simultaneous existence of these transitions and annealing effects and the implications on the accuracy of the determined data.
Cyclic and linear poly(L-lactide)s by ring-expansion polymerization with Bu2SnO, Oct2SnO, and Bu2SnS
(2023)
To elucidate the usefulness of commercial Bu2SnO as catalyst for syntheses of linear and/or cyclic polylactides L-Lactide was polymerized in bulk with variation of the LA/Cat ratio, temperature and time. Based on a ring-expansion polymerization (REP) mechanism cyclic polylactides (PLAs) with weight average molecular weights in the range of 200,000–300,000 are obtained at the highest temperature (180 °C). Polymerizations at 150 °C yielded crystalline, mainly cyclic polylactides which, after annealing, showed high melting temperatures (up to 197.5 °C) and high crystallinities (>80%). Polymerization at 120 °C confirmed the trend towards more linear chains with lower temperatures but yielded extended-ring crystals showing a “saw-tooth pattern” in the mass spectra. Oct2SnO gave similar results as Bu2SnO. Bu2SnS proved a sluggish polymerization catalyst, but a good transesterification catalyst in solid PLA.
Im statistischen Mittel steht eine Windkraftanlage (WKA) in Deutschland alle 6 Jahre wegen eines Schadens an den Rotorblättern und verursacht Kosten von 20k€-40k€ infolge Ertragsausfall und Reparaturkosten. Bei über 30.000 WKA in Deutschland verursacht dies jährlichen Kosten von 100-200 Mio. €. Zu 70% sind die Ursachen Fertigungsfehler. Diesem Themenkomplex widmet sich FB-5.3 in Kooperation mit FBs der Zerstörungsfreien Prüfung (Abt. 8) schon seit Jahren.
Im aktuellen Projekt geht es um einen vorzeitigen Verschleiß der Rotorblätter infolge der Verwendung gealterter Glasfaser-Rovings. (GF). Die Entwicklung moderner Windkraftanlagen hatte in Europa seinen Ursprung in den 90er Jahren. OEMs und GF-Hersteller waren dicht beisammen. Die Globalisierung des Marktes führt heute zu einer weltweiten Verschiffung der GF in feucht-warmen Containern. Je nach Beschaffenheit (Chemie) der Schlichten (Oberflächenbehandlung) von GF können diese stark altern (Hydrolyse-Effekte) und die Festigkeit kann im Bauteil um bis zu 50% abgemindert sein.
In einer Kooperation mit der Rotorblattallianz, einem Zusammenschluss der OEMs, Halbzeugherstellern und Forschungsinstituten, wurden schon vor 5 Jahren in einem Forschungsprojekt (FB-5.3; VH 5538) die chemischen Mechanismen der Alterung exemplarisch für eine Glasfaser-Roving-Type aufgeklärt. Im aktuellen Projekt (FB-5.3; VH 5304) wird ein beschleunigtes Alterungsverfahren (erhöhte Temperatur und Feuchte) am Roving im un-impregnierten Zustand entwickelt und die Festigkeit nachfolgend nach Einbettung in eine Epoxid-Harz-Matrix bestimmt. Je nach Alterungszustand zeigt sich eine Abnahme der Zwischenfaserbruchfestigkeit von bis zu 50%. Nicht alle Glasfaser-Roving-Typen zeigen diesen Effekt. Es ist gelungen für OEMs und Halbzeughersteller ein handhabbares Verfahren zur innerbetrieblichen Qualitätssicherung zu entwickeln, da die wenigsten Firmen über komplexe Analyseverfahren, wie an der BAM, verfügen.
Ellipsometry is a highly valuable technology for bridging different measurement methods. As a fast, highly sensitive, and non-destructive optical technique with low environmental requirements, it is ideal for transporting measurement accuracy and for up-scaling measurements in the production environment. It can be used for highly precise determination of properties, material identity and correctness confirmation, as well as defect detection.
Comparable, traceable, and accurate electrical measurements, especially at small scales are one of the biggest challenges in the development of the electrical and electronic devices of the future.
In this project, we develop structured thin layer systems of the transparent conductive material indium tin oxide (ITO) to prove the concept of using these systems as standards for conductivity and permittivity. The layers are produced in a reactive magnetron sputtering process from raw ITO targets with additional oxidation achieved by oxygen injection. We present results of a study correlating the coating process conditions with the properties of the final layer material. We found that especially the temperature development during coating is of key importance and determines the layer properties to a large extent. We will discuss questions of homogeneity and reproducibility of the coating processes used. The finished layers undergo lithographic structuring and etching to produce patterns to serve as reference structures for scanning probe electrical measurements. TCOs have a large variety of applications. In this work we also study the usability of ITO for other purposes and investigate the stability of this material under application conditions.
Knowing phonon properties is beneficial for predicting low thermal conductivity thermoelectric materials. Employing DFT consumes lots of computational resources. Using ML-driven interatomic potentials (MLIP, e.g., GAP) opens up a faster route, but most potentials are specifically tailored to a certain compound. We aim to generalize the MLIP generation in a Python code-based workflow, combining automatic DFT runs with automated GAP fits. Automation enables easier tests, benchmarks, and validation.
Argyrodite-type materials have lately sparked a lot of research interest due to their thermoelectric properties. One promising candidate is canfieldite (Ag8SnS6), which has a Pna21 orthorhombic crystal structure at room temperature (RT). Recently, experimentalists have found a new low-temperature (LT) phase transition of canfieldite at 120K. Therefore, we investigate structural, vibrational and thermodynamic properties of Ag8SnS6 at room- and low-temperature employing density-functional theory (DFT) and lattice dynamics computations. Thermal properties calculations were based on the quasi-harmonic approximation (QHA) as implemented in phonopy. We achieve good agreement with experiments. Lattice parameters were overestimated by 2%, and thermal properties such as the constant-pressure heat capacity Cp are very close to experimental measurements. Our simulations also reveal a possible new phase transition at around 312 K. Furthermore, we compared RT and LT Ag8SnS6 Grüneisen parameters with some argyrodites analogues, Ag8TQ6 (T = Si, Ge, Ti and Sn; Q = S, Se), finding a relationship between the anharmonicity and low thermal conductivity.
Zirconium vanadate (ZrV2O7) is a well-known negative thermal expansion (NTE) material that exhibits significant isotropic contraction over a broad temperature range (~150°C < T < 800°C). Therefore, it can be used to create composites with controllable expansion coefficients and prevent thermal stress, fatigue, cracking, and deformation at interfaces. We implement interdisciplinary research to analyze such material. We study the influence of the synthesis methods and their parameters on the sample's purity, crystallinity, and homogeneity. Moreover, we implement ab initio-based vibrational computations with partially treated anharmonicity in combination with experimental methods to follow temperature-induced structural changes and rationalize the negative thermal expansion in this material, including the influence of the local structure disorder.
We demonstrate the determination of anharmonic acoustic phonon properties via second-order Raman scattering exemplarily on copper iodide single crystals. The origin of multi-phonon features from the second-order Raman spectra was assigned by the support of the calculated 2-phonon density of states. In this way, the temperature dependence of acoustic phonons was determined down to 10 K. To determine independently the harmonic contributions of respective acoustic phonons, density functional theory (DFT) in quasi-harmonic approximation was used. Finally, the anharmonic contributions were determined. The results are in agreement with earlier publications and extend CuI's determined acoustic phonon properties to lower temperatures with higher accuracy. This approach demonstrates that it is possible to characterize the acoustic anharmonicities via Raman scattering down to zero-temperature renormalization constants of at least 0.1 cm⁻¹.
Physical adsorption at cryogenic temperature (cryoadsorption) is a reversible mechanism that can reduce the pressure of conventional compressed gas storage systems. Metal–organic framework (MOF) materials are remarkable candidates due to the combination of high specific surface area and density which, in some cases, provide a high volumetric storage capacity. However, such extensive use of MOFs for this application requires the selection of affordable structures, easy to produce and made from feasible metallic and organic components. Herein, we introduce a MOF database detailing the crystallographic and porous properties of 3600 existing MOFs made from industrially relevant metals and their organic composition. The comparison of the available minimum costs of linkers allowed the creation of a database to select affordable structures with high potential for volumetric hydrogen storage by cryoadsorption, considering their composition based on individual or mixed building blocks. A user interface, available online, facilitates the selection of MOFs based on the properties or names of structures and linkers.
Unwanted X-ray emission in ultrashort pulse laser processing: From metallic to biological materials
(2023)
X-rays can be generated as an unwanted side effect during ultrashort pulse laser material processing of technical work pieces and even biological samples with laser intensities above 10^13 W/cm^2. First studies demonstrate the need to address this effect in industrial as well as in medical applications. This secondary hazard should be considered in work safety and risk assessment.
Alcohol-initiated ROPs of L-Lactide were performed at 140 ◦C in bulk with variation of the initiator/catalyst ratio and time. Lower ratios favor the formation of cycles which upon annealing display a change of the MALDI mass peak distribution towards a new maximum with a “saw-tooth pattern” of the mass peaks representing the cycles.
Such a pattern was not observed for the mass peak of the linear chains. The coexistence of these patterns indicate that linear and cyclic poly (L-lactide)s (PLA) crystallize in separate crystals, and that the crystallites of the cycles are made up by extended rings. High Tm and ΔHm values confirm that these extended-ring crystallites represent a thermodynamically optimized form of PLA. Experiments with preformed cyclic and linear PLAs support this interpretation.
Newly developed methodical approaches with an emphasis on correlative imaging analysis of morphology and chemistry of nanomaterials will be presented. Correlative imaging by high-resolution SEM with STEM-in-SEM as well as with EDS, and further with AFM, or with the new technique TKD (Transmission Kikuchi Diffraction) will be explained on various examples of nanostructures, both as starting materials and as embedded/functionalized nanoparticles in products. The unique analytical benefits of the Auger electron probe as a veritable nano-tool for the local surface chemistry will be highlighted. Examples of hybrid analysis of the bulk of nanomaterials by X-ray Spectroscopy and the highest surface-sensitive methods XPS and ToF-SIMS as advanced surface characterization methods available in the Competence Centre nano@BAM will be showed. Particularly for the spatially resolved analysis of the chemistry of nanostructures, such in-depth and lateral gradients of chemistry within mesoporous thin layers, or the completeness of the shells of core-shell nanoparticles, the latter methods are inherent.
Other dedicated developments like approaches for the quantitative determination of the porosity of thin mesoporous layers by electron probe microanalysis (EPMA) with SEM or the quantitative determination of the roughness of particle surface by high-resolution imaging with electron microscopy will be also presented.
Laser powder bed fusion (PBF-LB/M) is a metal-based additive manufacturing (AM) process that utilizes a laser to melt powder particles selectively and form the desired product through a layer-by-layer fabrication process. It allows access to a vast new design space and can produce parts with far greater geometrical complexity than traditional methods. However, PBF-LB/M induces inevitable microstructural defects, such as voids and pores, that can adversely affect the quality and performance of the manufactured components. Hence, knowledge of pore formation, types, and suppression is essential for successful future AM applications. This research investigates the formation of different types of pores and their quantification from X-ray micro-computed tomography images of a formerly reported sample. It also examines the influence of the volumetric energy density (VED) on the size, shape, and location of pores for 316L stainless steel parts produced by the PBF-LB/M process.