Random Access Direct Parallel Detection of Electron Energy Loss Spectra with a New Photodiode Array

A new type of photodiode array (PDA) which allows the individual access of single diodes is used to record energy loss electrons directly without electron photon conversion. The detector is part of an electron energy loss parallel detection system which consists of a sector field spectrometer and a quadrupole lens system to magnify the spectra electron-optically. The parallel detector is a new random access PDA (RAPDA) which allows the individual access of single diodes. Therefore, different parts of the spectrum with dramatically different electron rates (zero loss peak, plasmon loss, ionization edges) can be recorded, each with optimum acquisition time and number of read-outs. This method allows the use of all available information in one recording of a spectrum for an increased intensity range compared to self-scanning PD As (SSPDAs) where all the diodes have to be read out in a row. Direct illumination of the diodes increases the sensitivity of the detector by two orders of magnitude for 40 keV electrons compared to detectors with electron photon conversion. No apparent radiation damage of the diodes was observed if the detector was cooled down to temperatures below -80°C

Bistable Actuation Based on Antagonistic Buckling SMA Beams

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery

Magnetron-Sputtered, Biodegradable FeMn Foils: The Influence of Manganese Content on Microstructure, Mechanical, Corrosion, and Magnetic Properties

FeMn alloys show a great potential for the use as a biodegradable material for medical vascular implants. To optimize the material properties, with respect to the intended application, new fabrication methods also have to be investigated. In this work different Fe-FeMn32 multilayer films were deposited by magnetron sputtering. The deposition was done on a substrate structured by UV lithography. This technique allows the fabrication of in-situ structured foils. In order to investigate the influence of the Mn content on the material properties foils with an overall Mn content of 5, 10, 15, and 17 wt % were fabricated. The freestanding foils were annealed post-deposition, in order to homogenize them and adjust the material properties. The material was characterized in terms of microstructure, corrosion, mechanical, and magnetic properties using X-ray diffraction, electron microscopy, electrochemical polarization, immersion tests, uniaxial tensile tests, and vibrating sample magnetometry. Due to the unique microstructure that can be achieved by the fabrication via magnetron sputtering, the annealed foils showed a high mechanical yield strength (686-926 MPa) and tensile strength (712-1147 MPa). Owing the stabilization of the non-ferromagnetic ε- and γ-phase, it was shown that even Mn concentrations of 15-17 wt % are sufficient to distinctly enhance the magnetic resonance imaging (MRI) compatibility of FeMn alloys

Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators

The high work density and beneficial downscaling of shape memory alloy (SMA) actuation performance provide a basis for the development of actuators and systems at microscales. Here, we report a novel monolithic fabrication approach for the co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double-beam cantilevers are chosen for the actuator layout to enable electrothermal actuation by Joule heating. The SMA materials under investigation are NiMnGa and NiTi(Hf) films with tunable phase transformation temperatures. We show that Joule heating of the cantilevers generates increasing temperature gradients for decreasing cantilever size, which hampers actuation performance. In order to cope with this problem, a new method for design optimization is presented based on finite element modeling (FEM) simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in the perpendicular direction to the active beam cantilevers. Thereby, power consumption can be reduced by more than 35 % and maximum deflection can be increased up to a factor of 2 depending on the cantilever geometry

Shape Memory Alloy Thin Film Auxetic Structures

Auxetic structures provide an interesting approach to solving engineering problems due to their negative Poisson’s ratio, which allows for elongation perpendicular to applied stresses, opposite to a conventional structure’s necking behavior. Thus, they can function well in applications requiring com-pacting the device into a small volume during the deployment (e.g., implants inserted with catheters) or stretchability with area coverage (e.g., stretchable electronics). Fabricating them with shape memory alloys (SMAs) expands the possibilities. The high strains experienced by auxetic structures may become reversible compared to ordinary metals due to superelastic or shape memory effect. This work studies four different auxetic microstructures using thin film SMAs that are capable of surviving strains up to 57.4%. Since these structures are fabricated by layer deposition and lithography, other components, such as microelectronics, can be seamlessly integrated into the fabrication process. These auxetic thin films are investigated for their mechanical behavior under tension for their stretchability and stability. Under tension, thin films are known to show wrinkling instabilities. In two of four designs, the large auxetic behavior leads to wrinkling, while the other two display stable, non-wrinkling behavior. These designs can be candidates for stretchable electronics, wear-able medical devices (e.g., biosensors), or implants (e.g., stents)

Knowledge and Technology Transfer in Materials Science and Engineering in Europe

Advanced Materials is one of the Key Enabling 3 Technologies identified by the European Commission1. Together with Advanced Manufacturing it underpins almost all other Key Enabling and Industrial Technologies. The basic science and engineering research that results in the development of Advanced Materials lies within the field of Materials Science and Engineering (MSE). The transfer of knowledge from basic research into final products and applications in the field of MSE involves certain MSE-typical motifs and specific issues, as well as certain aspects that are special to Europe. In comparison with underlying traditional (or basic) disciplines such as physics, chemistry or biology, MSE involves a range of aspects that are more characteristic of applied science, where relevance has equal importance to curiosity in order to drive the research effort and justify expenditure – the defined goals often being a proven innovative technology or indeed a particular product. MSE and the related transfer of knowledge and technology includes consideration of factors such as materials and product life cycles, the abundance of materials, the technical, ecological and economic feasibility of materials engineering and processing, as well as the multidisciplinarity of the ‘background’ knowledge and the efficiency of the academic effort involved. This is even more the case for situations that involve successful validation of technologies and effective transfer of knowledge between academia and industry. The state of knowledge and technology transfer in Europe differs from that of other global players, such as the US, China or Japan. Europe’s cultural diversity gives rise to both positive and negative factors. Positive aspects include the high standard of general education and Europe’s highly skilled work force (for both technical and academic staff), and the flexibility and variety of research topics and directions. Major negative factors are the fragmentation of national research efforts, and the lack of a European mechanism to create critical mass in new technologies and to invest in pilot lines. These negative issues are manifested by the fragmentation of research programmes, the lack of venture capital and a general risk aversion on the part of investors in Europe, in particular in the light of the current economic crisis in Europe. The present situation has often been described as a malfunctioning interface between strong basic research and poor, inefficient technological development and commercial exploitation of knowledge. MSE spans this interface. ‘European’ knowledge is world-class, and even leads the world in certain fundamental areas of MSE, for example in the investigation and understanding of materials properties, the development and application of new concepts of materials design, computational materials sciences, and several other fields. However, Europe’s MSE knowledge and technological progress will not readily lead to the establishment of new technologies and products by European industries without dedicated intervention. This knowledge must be delicately directed in a highly impact-oriented way. To accelerate development and validation of technological applications and the introduction of technological innovation into the market, to intensify the collaboration between academic institutions and industry in Europe, and to facilitate the creation of spin-out companies and new industrial–academic career paths, MatSEEC recommends the creation of European Technology Research and Validation Platforms (ETVPs). Such platforms would provide powerful tools for innovation and allow better protection of intellectual property rights in Europe. We recommend the creation of an ‘Open-Access-Open-Innovation’ European Technology Research and Validation Infrastructure Initiative to streamline and improve technology and knowledge transfer in Europe. The initiative would be dedicated to technology research and validation. It could be based on a similar model to the current Integrated Infrastructure Initiatives (I3s) for research infrastructures of the European Commission (the I3 Programme in H2020 and the Seventh Framework Programme,FP7)

Tunnel Magnetoresistance Sensors with Magnetostrictive Electrodes: Strain Sensors

Magnetostrictive tunnel magnetoresistance (TMR) sensors pose a bright perspective in micro- and nano-scale strain sensing technology. The behavior of TMR sensors under mechanical stress as well as their sensitivity to the applied stress depends on the magnetization configuration of magnetic tunnel junctions (MTJ)s with respect to the stress axis. Here, we propose a configuration resulting in an inverse effect on the tunnel resistance by tensile and compressive stresses. Numerical simulations, based on a modified Stoner–Wohlfarth (SW) model, are performed in order to understand the magnetization reversal of the sense layer and to find out the optimum bias magnetic field required for high strain sensitivity. At a bias field of -3.2 kA/m under a 0.2 × 10$^{-3}$ strain, gauge factors of 2294 and -311 are calculated under tensile and compressive stresses, respectively. Modeling results are investigated experimentally on a round junction with a diameter of 30 ± 0.2 μm using a four-point bending apparatus. The measured field and strain loops exhibit nearly the same trends as the calculated ones. Also, the gauge factors are in the same range. The junction exhibits gauge factors of 2150 ± 30 and -260 for tensile and compressive stresses, respectively, under a -3.2 kA/m bias magnetic field. The agreement of the experimental and modeling results approves the proposed configuration for high sensitivity and ability to detect both tensile and compressive stresses by a single TMR sensor

Magnetism, elasticity, and magnetostriction of FeCoGa alloys

It is known that the substitution of Co for Fe gives rise to increases in magnetization and Curie temperature, not only in the bcc metals, but also in intermetallic compounds and alloys as well. With the expectation that this is the case in Co-substituted FeGa, we measured magnetization, Curie temperature, magnetostriction and elastic constants of a series of polycrystalline FeCoGa ternary alloys with up to 17% Ga and up to 10% Co. The magnetostriction at saturation for Fe0.93−xCo.07Gax increases to 90 ppm for x=0.17. For larger percentages of Co, the rise in magnetostriction is not as sharp as it is in the 7% case. The shear elastic modulus decreases with Ga, again in keeping with the results for FeGa. The magnetostriction and the elastic constants are sensitive to sample preparation for the high-Ga material. We conclude that the substitution of small (\u3c0.10)percentages of Co for Fe in bcc FeCoGa alloys enhances the magnetic and magnetostrictive properties of the parent FeGa material