Optimierung von strukturellen und funktionellen Eigenschaften von NiTi mit Pseudoelastizität /Formgedächtnis für den medizinischen Einsatz

In der vorliegenden Arbeit sollten die Auswirkungen von Wärmebehandlungen kurzer Dauer (t ≤ 30min) bei verschiedenen Temperaturen auf die Af-Temperatur, die Umwandlungscharakteristik und die Dicke der erzeugten Oxidschichten im Zusammenhang mit deren Verhalten und Schädigung bei pseudoelastischer Verformung des Grundmaterials untersucht werden. Die Ergebnisse dieser Arbeit ermöglichen die Optimierung der strukturellen und funktionellen Eigenschaften von NiTi für den medizinischen Einsatz

Solving the puzzle of hierarchical martensitic microstructures in NiTi by (111)-oriented epitaxial films

The martensitic microstructure decides on the functional properties of shape memory alloys. However, for the most commonly used alloy, NiTi, it is still unclear how its microstructure is built up because the analysis is hampered by grain boundaries of polycrystalline samples. Here, we eliminate grain boundaries by using epitaxially grown films in (111)B2 orientation. By combining scale-bridging microscopy with integral inverse pole figures, we solve the puzzle of the hierarchical martensitic microstructure. We identify two martensite clusters as building blocks and three kinds of twin boundaries. Nesting them at different length scales explains why habit plane variants with ⟨011⟩B19' twin boundaries and {942} habit planes are dominant; but also some incompatible interfaces occur. Though the observed hierarchical microstructure agrees with the phenomenological theory of martensite, the transformation path decides which microstructure forms. The combination of local and global measurements with theory allows solving the scale bridging 3D puzzle of the martensitic microstructure in NiTi exemplarily for epitaxial films

Dynamic deformability of Plasmodium falciparum-infected erythrocytes exposed to artesunate in vitro

Artesunate (ART) is widely used for the treatment of malaria, but the mechanisms of its effects on parasitized red blood cells (RBCs) are not fully understood. We investigated ART's influence on the dynamic deformability of ring-stage Plasmodium falciparum infected red blood cells (iRBCs) in order to elucidate its role in cellular mechanobiology. The dynamic deformability of RBCs was measured by passing them through a microfluidic device with repeated bottleneck structures. The quasi-static deformability measurement was performed using micropipette aspiration. After ART treatment, microfluidic experiments showed 50% decrease in iRBC transit velocity whereas only small (~10%) velocity reduction was observed among uninfected RBCs (uRBCs). Micropipette aspiration also revealed ART-induced stiffening in RBC membranes. These results demonstrate, for the first time, that ART reduces the dynamic and quasi-static RBC deformability, which may subsequently influence blood circulation through the microvasculature and spleen cordal meshwork, thus adding a new aspect to artesunate's mechanism of action.Singapore-MIT Alliance for Research and Technology CenterNational Institutes of Health (U.S.) (Grant R01 HL094270-01A1

Ion irradiation-induced sinking of Ag nanocubes into substrates

Ion irradiation can cause burrowing of nanoparticles in substrates, strongly depending on the material properties and irradiation parameters. In this study, we demonstrate that the sinking process can be accomplished with ion irradiation of cube-shaped Ag nanoparticles on top of silicon; how ion channeling affects the sinking rate; and underline the importance of the amorphous state of the substrate upon ion irradiation. Based on our experimental findings, the sinking process is described as being driven by capillary forces enabled by ion-induced plastic flow of the substrate.Comment: the manuscript has 25 pages and 6 figure

Nanostructured Cu2_2O Synthesized via Bipolar Electrochemistry

Cuprous oxide (Cu$_2$O) was synthesized for the first time via an open bipolar electrochemistry (BPE) approach and characterized in parallel with the commercially available material. As compared to the reference, Cu$_2$O formed through a BPE reaction demonstrated a decrease in particle size; an increase in photocurrent; more efficient light scavenging; and structure-correlated changes in the flat band potential and charge carrier concentration. More importantly, as-synthesized oxides were all phase-pure, defect-free, and had an average crystallite size of 20 nm. Ultimately, this study demonstrates the impact of reaction conditions (e.g., applied potential, reaction time) on structure, morphology, surface chemistry, and photo-electrochemical activity of semiconducting oxides, and at the same time, the ability to maintain a green synthetic protocol and potentially create a scalable product. In the proposed BPE synthesis, we introduced a common food supplement (potassium gluconate) as a reducing and complexing agent, and as an electrolyte, allowing us to replace the more harmful reactants that are conventionally used in Cu$_2$O production. In addition, in the BPE process very corrosive reactants, such as hydroxides and metal precursors (required for synthesis of oxides), are generated in situ in stoichiometric quantity, providing an alternative methodology to generate various nanostructured materials in high yields under mild conditions

Single Femtosecond Laser-Pulse-Induced Superficial Amorphization and Re-Crystallization of Silicon

21 pags., 9 figs., 1 tab. -- This article belongs to the Special Issue Advanced Pulse Laser Machining TechnologySuperficial amorphization and re-crystallization of silicon in and orientation after irradiation by femtosecond laser pulses (790 nm, 30 fs) are studied using optical imaging and transmission electron microscopy. Spectroscopic imaging ellipsometry (SIE) allows fast data acquisition at multiple wavelengths and provides experimental data for calculating nanometric amorphous layer thickness profiles with micrometric lateral resolution based on a thin-film layer model. For a radially Gaussian laser beam and at moderate peak fluences above the melting and below the ablation thresholds, laterally parabolic amorphous layer profiles with maximum thicknesses of several tens of nanometers were quantitatively attained. The accuracy of the calculations is verified experimentally by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (STEM-EDX). Along with topographic information obtained by atomic force microscopy (AFM), a comprehensive picture of the superficial re-solidification of silicon after local melting by femtosecond laser pulses is drawn.C.F. acknowledges the support from the European Commission through the Marie Curie Individual Fellowship—Global grant No. 844977 and funding from the Horizon 2020 CellFreeImplant European project. D.F., M.D., S.S., A.H. and U.B. gratefully acknowledge the funding from the German Central Innovation Program (AiF-ZIM) under grants No. ZF4044219AB7 and ZF4460401AB7. K.F., M.R. and A.U. acknowledge support by the German Research Foundation (grant Nos. UN 341/3-1 and Inst 275/391-1). J.B. acknowledges the projects CellFreeImplant and LaserImplant. These two projects have received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 800832 (CellFreeImplant) and No. 951730 (LaserImplant).Peer reviewe

How to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation

Understanding the martensitic microstructure in nickel-titanium (NiTi) thin films helps to optimize their properties for applications in microsystems. Epitaxial and single-crystalline films can serve as model systems to understand the microstructure, as well as to exploit the anisotropic mechanical properties of NiTi. Here, we analyze the growth of NiTi on single-crystalline MgO(100) and Al2O3(0001) substrates and optimize film and buffer deposition conditions to achieve epitaxial films in (100)- and (111)-orientation. On MgO(100), we compare the transformation behavior and crystal quality of (100)-oriented NiTi films on different buffer layers. We demonstrate that a vanadium buffer layer helps to decrease the low-angle grain boundary density in the NiTi film, which inhibits undesired growth twins and leads to higher transformation temperatures. On Al2O3(0001), we analyze the orientation of a chromium buffer layer and find that it grows (111)-oriented only in a narrow temperature range around 500 ∘C. By depositing the Cr buffer below the NiTi film, we can prepare (111)-oriented, epitaxial films with transformation temperatures above room temperature. Transmission electron microscopy confirms a martensitic microstructure with Guinier Preston-zone precipitates at room temperature. We identify the deposition conditions to approach the ideal single crystalline state, which is beneficial for the analysis of the martensitic microstructure and anisotropic mechanical properties in different film orientations

Dimensional Stability of Mirror Substrates Made of Silicon Particle Reinforced Aluminum

In the present study, the thermal cycling stability of mirrors made of silicon particle reinforced aluminum compounds, containing an amount of 42 ± 2 wt.% silicon particles, is investigated with respect to thermal loading. The compound is processed by single-point diamond turning to optical mirrors that were subsequently thermally cycled in a temperature range between 40 °C to −60 °C and between 20 °C and −196 °C, respectively. The residual shape change of the optical surface was analyzed using Fizeau interferometry at room temperature. The change of shape deviation of the mirrors is compared with dilatometric studies of cylinders using the same temperature regime. Due to different coefficients of thermal expansion of the two constituents of the compound, thermal mismatch stresses in the ductile aluminum matrix and the brittle silicon particles are induced by the investigated thermal loads. The plasticity that occurs causes the formation of dislocations and stacking faults as substantiated by Transmission Electron Microscopy. It could be shown that the silicon particles lead to the cold working process of the reinforced aluminum matrix upon thermal cycling. By using interferometry, a higher dimensional stability of mirrors made of silicon particle reinforced aluminum due to thermal loads is demonstrated

Data for "How to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation"

This dataset belongs to the paper "How to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation" and contains all raw data used for the paper. It includes AFM, SEM, R(T), TEM, Texture measurements and rocking curves. Information about samples, measurement techniques and file naming conventions can be found in README.txt