Search

The Möbius strip, a fascinating loop structure with one-sided topology, provides a rich playground for manipulating the non-trivial topological behaviour of spinning particles, such as electrons, polaritons and photons, in both real and parameter spaces. For photons resonating in a Möbius-strip cavity, the occurrence of an extra phase—known as the Berry phase—with purely topological origin is expected due to its non-trivial evolution in parameter space. However, despite numerous theoretical investigations, characterizing the optical Berry phase in a Möbius-strip cavity has remained elusive. Here we report the experimental observation of the Berry phase generated in optical Möbius-strip microcavities. In contrast to theoretical predictions in optical, electronic and magnetic Möbius-topology systems where only Berry phase π occurs, we demonstrate that a variable Berry phase smaller than π can be acquired by generating elliptical polarization of resonating light. Möbius-strip microcavities as integrable and Berry-phase-programmable optical systems are of great interest in topological physics and emerging classical or quantum photonic applications.

We report the monolithic fabrication of twin microtube cavities by a nanomembrane origami method for achieving collective coupling of 3D confined optical modes. Owing to the well-aligned twin geometries, two sets of 3D confined optical modes in twin microtubes are spectrally and spatially matched, by which both the fundamental and higher-order axial modes are respectively coupled with each other. Multiple groups of the coupling modes provide multiple effective channels for energy exchange between coupled microcavities illustrated by the measured spatial optical field distributions. The spectral anticrossing and changing-over features of each group of coupled modes are revealed in experiments and calculations, indicating the occurrence of strong coupling. In addition, the simulated 3D mode profiles of twin microcavities confirm the collective strong coupling behavior, which shows good agreement with experiments. The collective coupling of 3D confined resonant modes promises broad applications in multichannel optical signal processing, nanophotonics, and 3D non-Hermitian systems.

Inspired by origami art, we demonstrate a tubular microsupercapacitor (TMSC) by self-assembling two-dimensional (2D) films into a “swiss roll” structure with greatly reduced footprint area. A polymeric framework consisting of swelling hydrogel and polyimide layers ensures excellent ion transport between poly(3,4-ethylenedioxythiophene) (PEDOT)-based electrodes and provides efficient self-protection of the TMSC against external compression up to about 30 MPa. Such TMSCs exhibit an areal capacitance of 82.5 mF cm–2 at 0.3 mA cm–2 with a potential window of 0.8 V, an energy density and power density of 7.73 μWh cm–2 and 17.8 mW cm–2 (0.3 and 45 mA cm–2), and an improved cycling stability with a capacitance retention up to 96.6% over 5000 cycles. Furthermore, as-fabricated TMSC arrays can be detached from their surface and transferred onto target substrates. The connection of devices in parallel/series greatly improves their capacity and voltage output. Overall, our prototype devices and fabrication methodolo...

We present a superconducting bolometer fabricated by a rolled-up technology that allows one to combine the two-dimensionality (2D) of the superconducting layer with a helical spiral curvature. The bolometer is formed as a free-standing Nb nanohelix acting as an ultrathin transition-edge sensor (TES) and having a negligible thermal contact to the substrate. We demonstrate the functionality of the thin-film TES by examining its microwave-detection performance in comparison with a commercial cryogenic bolometer from QMC Instruments. The nanohelix has been revealed to feature a noise equivalent power (NEP) of about 2 × 10

Many modern electronic applications rely on functional units arranged in an active-matrix integrated on a single chip. The active-matrix allows numerous identical device pixels to be addressed within a single system. However, next-generation electronics requires heterogeneous integration of dissimilar devices, where sensors, actuators, and display pixels sense and interact with the local environment. Heterogeneous material integration allows the reduction of size, increase of functionality, and enhancement of performance; however, it is challenging since front-end fabrication technologies in microelectronics put extremely high demands on materials, fabrication protocols, and processing environments. To overcome the obstacle in heterogeneous material integration, digital electrochemistry is explored here, which site-selectively carries out electrochemical processes to deposit and address electroactive materials within the pixel array. More specifically, an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film-transistor (TFT) active-matrix is used to address pixels within the matrix and locally control electrochemical reactions for material growth and actuation. The digital electrochemistry procedure is studied in-depth by using polypyrrole (PPy) as a model material. Active-matrix-driven multicolored electrochromic patterns and actuator arrays are fabricated to demonstrate the capabilities of this approach for material integration. The approach can be extended to a broad range of materials and structures, opening up a new path for advanced heterogeneous microsystem integration.

Silicon, although widely used in modern electronic devices, has not yet been implemented in thermoelectric applications mainly due to its high thermal conductivity, κ, which leads to an extremely low thermoelectric energy conversion efficiency (figure of merit). Here, we present an approach to manage κ of Si thin-film-based nanoarchitectures through the formation of radial and planar Si/SiOx hybrid nanomembrane superlattices (HNMSLs). For the radial Si/SiOx HNMSLs with various numbers of windings (1, 2, and 5 windings), we observe a continuous reduction in κ with increasing number of windings. Meanwhile, the planar Si/SiOx HNMSL, which is fabricated by mechanically compressing a five-windings rolled-up microtube, shows the smallest in-plane thermal conductivity among all the reported values for Si-based superlattices. A theoretical model proposed within the framework of the Born–von Karman lattice dynamics to quantitatively interpret the experimental data indicates that the thermal conductivity of Si/SiOx...

Relying on the combination of lithium phosphorous oxynitride (LiPON) as electrolyte and cobalt oxide (Co3O4) as electrode material it is possible to fabricate symmetric all-solid-state micro-supercapacitors (ASTSCaps) on rigid and flexible substrates. Due to the nanoscale active layer dimensions, the excellent performance of the component materials and the high nominal voltage of 2 V, an exceptionally high volumetric energy and power densities of up to 8 (±2) mW h/cm3 and 16 (±2) W/cm3, respectively, are obtained. These results are going far beyond the current state-of-the-art performance limits. The ASTSCaps are temperature stable up to 215 °C (for 1 V nominal voltage) and experience an endurance of more than 30,000 cycles. These ultra-thin all-solid-state micro-supercapacitors bring strong benefits for on-chip energy storage and open up interesting new avenues for autonomous and flexible electronic microsystems.

We report the fabrication of Ni2.7Mn0.9Ga0.4/InGaAs bilayers on GaAs (001)/InGaAs substrates by molecular beam epitaxy. To form freestanding microtubes the bilayers have been released from the substrate by strain engineering. Microtubes with up to three windings have been successfully realized by tailoring the size and strain of the bilayer. The structure and magnetic properties of both, the initial films and the rolled-up microtubes, are investigated by electron microscopy, X-ray techniques and magnetization measurements. A tetragonal lattice with c/a = 2.03 (film) and c/a = 2.01 (tube) is identified for the Ni2.7Mn0.9Ga0.4 alloy. Furthermore, a significant influence of the cylindrical geometry and strain relaxation induced by roll-up on the magnetic properties of the tube is found. Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

A novel method relying on strain engineering to realize arrays of on-chip-integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils is put forth. The geometrical transformation of an initially planar layout into a tubular 3D architecture stabilizes favorable azimuthal magnetic domain patterns. This work creates a solid foundation for further development of CMOS compatible GMI sensorics for magnetoencephalography.

Methods to integrate different crystal orientations, strain states, and compositions of semiconductors in planar and preferably flexible configurations may enable nontraditional sensing-, stimulating-, or communication-device applications. We combine crystalline-silicon nanomembranes, patterning, membrane transfer, and epitaxial growth to demonstrate planar arrays of different orientations and strain states of Si in a single membrane, which is then readily transferable to other substrates, including flexible supports. As examples, regions of Si(001) and Si(110) or strained Si(110) are combined to form a multicomponent, single substrate with high-quality narrow interfaces. We perform extensive structural characterization of all interfaces and measure charge-carrier mobilities in different regions of a 2D quilt. The method is readily extendable to include varying compositions or different classes of materials.

Flexible electronics has emerged as a standalone field and matured over past decades.1–6 This alternative formulation of electronics offers the unique possibility to adjust the shape of devices at will after their fabrication. The flexibility provides vast advantages over conventional rigid electronics; flexible printed circuit (FPC) boards have become an industrial standard for consumer electronics and medical implants,7–10 where large area, extreme thinness, and compliance to curved surfaces are the key requirements for the functional passive and active elements. Flexible devices strongly benefited from the recent developments of organic6,11,12 as well as inorganic10,13,14 electronics, which are prepared using printing and/or thin film technologies. Being synergetically combined with either inkjet, screen, or dispenser printing approaches, flexible electronics has witnessed fascinating innovations in several application areas including displays,15 organic light-emitting diodes,16 various types of sensors,17–21 radio frequency identification tags,22–24 and organic solar cells.25

Hierarchically designed SiOx /SiOy rolled-up bilayer nanomembranes are used as anodes for lithium-ion batteries. The functionalities of the SiO(x,y) layers can be engineered by simply controlling the oxygen content, resulting in anodes that exhibit a reversible capacity of about 1300 mA h g(-1) with an excellent stability of over 100 cycles, as well as a good rate capability.

We have introduced a facile strategy to fabricate sandwich-stacked SnO2/Cu hybrid nanosheets as multichannel anodes for lithium-ion batteries applying rolled-up nanotechnology with the use of carbon black as intersheet spacer. By employing a direct self-rolling and compressing approach, a much higher effective volume efficiency is achieved as compared to rolled-up hollow tubes. Benefiting from the nanogaps formed between each neighboring sheet, electron transport and ion diffusion are facilitated and SnO2/Cu nanosheet overlapping is prevented. As a result, the sandwich-stacked SnO2/Cu hybrid nanosheets exhibit a high reversible capacity of 764 mAh g(-1) at 100 mA g(-1) and a stable cycling performance of ~75% capacity retention at 200 mA g(-1) after 150 cycles, as well as a superior rate capability of ~470 mAh g(-1) at 1 A g(-1). This synthesis approach presents a promising route to design multichannel anodes for high performance Li-ion batteries.

Logarithmic spirals are found on different length scales in nature, e.g., in nautilus shells, cyclones, and galaxies. The underlying formation laws can be related to different growth mechanisms, pressure gradients, and density waves. Here, we report on the self-organized formation of symmetric logarithmic crystallization spirals in a solid material on the micrometer length scale, namely, in an amorphous Ge:Mn layer on a Ge substrate. After exposure to a single light pulse of a flashlamp array, the Ge:Mn layer is crystallized and reveals a partially rippled surface and logarithmic microspirals. Finally, we present a model describing the formation of the crystallization spirals by directional explosive crystallization of the amorphous Ge:Mn layer, which is triggered by the flashlamp light pulse.

Ultrafine structured Ti 70.5 Fe 29.5 and Ti 67.79 Fe 28.36 Sn 3.85 eutectic rods comprising of β-Ti and TiFe phases were prepared by copper mould casting. The corrosion and passivation behaviour were investigated in halide free aqueous media (pH 1–13) by means of potentiodynamic polarisation and potentiostatic current transient measurements. Both eutectic alloys exhibit excellent corrosion resistance due to spontaneous passivation. The passive film compositions grown several nanometres on single phase polycrystalline specimens were analyzed with Auger electron spectroscopy. They consist of oxidized Ti and Fe species. Layers grown in strongly acidic environment are depleted in Fe. Sn was detected only on layers grown on the constituent β-Ti phase and only in the metallic state. The pitting susceptibility was investigated in strongly acidic media (pH ≤ 1) containing 0.1–3 M of chloride ions. The Sn-containing eutectic alloy was found to be more susceptible to pitting corrosion.

In order to use the magnetic shape memory alloy Ni–Mn–Ga with its high achievable strain of up to 10% for microactuators, freestanding epitaxial films are required. Here we show that these conditions can be fulfilled when using chromium as a sacrificial layer. The low misfit towards Ni–Mn–Ga enables epitaxial growth. Furthermore, Cr can afterwards be removed selectively by wet-chemical etching and during deposition no significant interdiffusion is observed. The structure, microstructure and magnetic properties of micrometer thick films are not affected by the etching process. Films are ferromagnetic at room temperature and we observe the coexistence of non-modulated (NM) and seven layered modulated (14 M) martensite. Tensile stress–strain measurement of a freestanding bridge reveals a broad strain plateau of 12% at a twinning stress of 25 MPa, indicating reorientation of NM variants.

The influence of homogeneous magnetic fields with flux density up to 1 T superimposed during the deposition of CoFe thin films on their properties has been studied. It has been clearly demonstrated that the superimposition of magnetic fields influences the resulting layer properties significantly. A pronounced impact on the layer morphology has been observed. The layers deposited under the influence of the parallel-to-electrode magnetic field appear denser and more homogenous than those obtained without a magnetic field. On the contrary, the layers deposited in the perpendicular-to-electrode magnetic field appeared more diverse. A scaling analysis revealed a smoothing effect of a parallel- and a roughening effect of a perpendicular-to-electrode magnetic field. No influence of magnetic fields neither on the deposited layers chemical composition nor the structure and texture has been found, whereas the internal stress state of the layer is affected by the superimposition. The effects are discussed with respect to the Lorentz force driven convection, which increases the electrochemical reaction's rates and improves desorption of hydrogen from the electrode surface. The alterations of magnetic properties of the CoFe thin films correlate well with the observed microstructural changes. Moreover, an in-plane magnetic anisotropy is induced by a parallel magnetic field superimposition. This phenomenon origins from a preferential next neighbour atomic pair-ordering in the direction of the magnetic field, e.g. magnetization, during deposition of the ferromagnetic alloy.

The free corrosion behavior and the anodic passivation ability of the bulk glassy (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5 alloy were fundamentally analyzed. Electrochemical tests were performed in aqueous solutions with pH values in the interval 0.3–14. Corrosion current densities are below 3 μA/cm2 in the entire studied pH interval; compared with commercial grade steels, for example, X210Cr12 steel, the glassy alloy has lower corrosion rates in acidic electrolytes and higher in basic solutions. The alloy exhibits high dissolution rates upon anodic polarization in acidic environments, but with increasing pH values it tends to form passive layers showing the lowest passive current density at pH 11. The passive layers consist mainly of Fe and Cr oxides. There is a strong variation of the passive layer structure and composition with pH. The protective effect of the grown surface layers is negatively influenced by sulfate ions.

Low electromigration in Cu interconnect lines represents one of the major challenges for a good performance of semiconductor devices. Referring to this, experiments were carried out to study the influence of non-metallic impurities like Cl, S, and C incorporated in Cu during the electrochemical deposition. In the case of a lower impurity content a higher resistance against electromigration was verified. The electromigration activation energy for metallizations with small contaminations was found to be (1.00 ± 0.06) eV whereas Cu interconnect lines with high non-metallic impurities revealed an activation energy of (0.65 ± 0.03) eV. The electromigration induced degradation by void formation starts at the top interface between Cu and dielectric cap layer. Probably, this results from high mechanical stresses due to differences in material properties or due to an interface weakening by the segregation of S and C impurities.

The sinterability of pure aluminium powder was controlled in different sintering atmospheres, i.e. nitrogen, argon, nitrogen/hydrogen and nitrogen/argon gas mixtures, and also in vacuum. Dimensional changes occurring during sintering were monitored by dilatometry. Thermogravimetric analysis (TG) was used to recognize possible interactions between aluminium and nitrogen. Pure nitrogen was found to be the only active sintering atmosphere for aluminium, promoting shrinkage, associated with a weight gain by binding nitrogen, and enhancing mechanical properties of the sintered compacts. Hydrogen lowers the sinterability of aluminium very strongly, even when present in small concentrations in a nitrogen atmosphere. Auger electron spectroscopy was used to characterize the surface layers on aluminium powder particles, fractured green compacts and sintered samples. Distributions of aluminium, nitrogen, oxygen and other elements, contained as impurities, were obtained by depth profiling measurements on this surfaces. Indications are that enhanced concentration of magnesium within the powder particle surface film promotes sintering of aluminium. Entnommen aus TEMA

The microstructure of electroplated Cu thin films and the contamination with incorporated additives were investigated in dependence on the galvanostatic deposition parameters and thermal treatment. Sulfur, chlorine, and carbon were analysed as impurities by TEM, AES and SIMS. SIMS measurements revealed that at room temperature S and Cl show a local stability at their incorporation sites, whereas C is capable to segregate out of the Cu layer. Thermally treated Cu layers indicate a segregation of S and a local stability for incorporated Cl. The incorporation of impurities during Cu deposition is linked with a surface coverage of additives. With increasing time for additive adsorption on the sample surface an increased incorporation of impurities into the growing film occurs. Hence, every start of deposition leads to a significantly high incorporation of S, Cl, and C. The application of aged electrolytes generates very impure Cu layers with an increased film roughness. As a result, the recrystallization of the deposited Cu film is slowed down due to the Zehner pinning effect. The final metallization appears more fine-grained and exhibits worse electrical properties.

Smart biomimetics, a unique class of devices combining the mechanical adaptivity of soft actuators with the imperceptibility of microelectronics, is introduced. Due to their inherent ability to self-assemble, biomimetic microelectronics can firmly yet gently attach to an inorganic or biological tissue enabling enclosure of, for example, nervous fibers, or guide the growth of neuronal cells during regeneration.

A titanium dioxide (TiO2) interconnected porous structure has been fabricated by means of atomic layer deposition of TiO2 onto a reticular sponge template. The obtained freestanding TiO2 with large surface area can be easily taken out of the water to solve a complex separation procedure. A compact and conformal nanocoating was evidenced by morphologic characterization. A phase transition, as well as production of oxygen vacancies with increasing annealing temperature, was detected by x-ray diffraction and x-ray photoelectron spectroscopy, respectively. The photocatalytic experimental results demonstrated that the powder with appropriate annealing treatment possessed excellent photocatalytic ability due to the co-action of high surface area, oxygen vacancies and the optimal crystal structure.

Highly flexible bismuth Hall sensors on polymeric foils are fabricated, and the key optimization steps that are required to boost their sensitivity to the bulk value are identified. The sensor can be bent around the wrist or positioned on the finger to realize an interactive pointing device for wearable electronics. Furthermore, this technology is of great interest for the rapidly developing market of -eMobility, for optimization of eMotors and magnetic bearings.

Stretchable electronics1, 2 is one of the most vital technological research fields of the latest years, aiming to revolutionize custom electronic systems toward being arbitrarily reshapeable on demand after their fabrication. This opens up novel application potentials for multifunctional high‐speed electronic systems like smart skins,3, 4 active medical implants,5, 6 soft robotics,7, 8 or stretchable consumer electronics.9, 10 A variety of functional components that can be subjected to high tensile deformations have already been introduced, including light emitting diodes,11 solar cells,10 pressure and temperature sensors,12 integrated circuitry,13 batteries,14, 15 antennas,16 and many more. Introducing stretchable highly sensitive magnetosensorics into the family of stretchable electronics17 was envisioned to equip this novel electronic platform with magnetic functionalities. This can be of particular interest for smart skin and biomedical applications promoted by very recent developments of imperceptible12 and transient6 electronics, as magnetoelectronic components can add a sense of orientation, displacement, and touchless interaction.

Trilayered Pd/MnO x /Pd nanomembranes are fabricated as the cathode catalysts for Li-O2 batteries. The combination of Pd and MnO x facilitates the transport of electrons, lithium ions, and oxygen-containing intermediates, thus effectively decomposing the discharge product Li2O2 and significantly lowering the charge overpotential and enhancing the power efficiency. This is promising for future environmentally friendly applications.

Nitrides of refractory metals are investigated as diffusion barriers for Cu metallization. The composition, thermal stability and inter diffusion in layered systems are characterized by depth profile analysis. For the quantification of depth profiles determination of sensitivity factors is essential. For nitrogen and other light elements matrix specific standards are often not available and compound standards are used for calibration. We have investigated the systems Ta–N and Ta–Si–N and for comparison Cr–N by means of Auger electron spectrometry (AES) and glow discharge optical emission spectrometry (GDOES). A non-linear calibration curve for the N/Cr intensity ratio was observed with GDOES in the Cr–N-system, probably caused by self-absorption of the Cr line.

The corrosion behaviour of two bulk glass-matrix composite alloys formed by copper mould casting was analysed: (i) Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 with precipitated bcc dendrite phase and (ii) Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 with quasicrystalline phase, respectively. The electrochemical behaviour was tested on the cross-sectional areas of the composite rod samples in 0.5 M sulphuric acid solution with up to 0.5 M sodium chloride addition by potentiodynamic polarization measurements. The composition of anodically formed passive films was studied by means of Auger electron spectroscopy (AES). The morphology of local damages generated by a chloride-induced pitting process was examined with scanning electron microscopy. In result of those studies, a pitting mechanism is described. For both composites in chloride media, a pronounced selective dissolution of the glassy matrix phase occurs, whereas the crystalline phases are not attacked. Niobium and titanium components are beneficial in inhibiting the pitting initiation due to their participation in the passive film formation. The dissolution of the glassy matrix phase is explained by the principal higher chloride reactivity of metastable phases compared to that of stable crystalline phases and by the detected enrichment of copper in these phase regions. The chloride attack progressing along the matrix phase causes the formation of deep channels in the bulk composite material leading to an excavation and, finally, detachment of the bcc dendrites or quasicrystals, respectively. The re-passivation ability is very poor.

This paper presents results of a study on an insulating bilayer system for the application of capping surface acoustic wave (SAW) structures with embedded finger electrodes. It consists of a stack of two different layers. A Ta-Si-O film followed by a Ta-Si-N film is deposited by physical vapor deposition (PVD) on top of different substrate materials. Due to the deposition parameters both layers contain large amounts of the reactive gas species (N or O) resulting in insulating behavior especially for the Ta-Si-O film. Properties and applicability of the bilayer were evaluated by different analytical techniques, e.g. electrical measurements, X-ray techniques, depth profiling, atomic force microscopy, and scanning electron microscopy. The breakdown strength and the relative permittivity of the bilayer were found to be respectable compared to conventional used dielectric materials. The barrier properties offered by the bilayer system are poor when heat-treated at high temperatures. The failure is mainly attributed to a Cu diffusion through the bilayer stack towards the surface.

Amorphous Zr–Cu–Ni–Al–[Ti, Nb] ribbons prepared by melt spinning under argon atmosphere were subjected to electrochemical investigations. Passive films developed at potentiostatic anodic polarization in sulphuric acid solution were investigated by Auger electron spectroscopy (AES) and sputter depth profiling. Changes in the shape of the Auger peaks have been analyzed by factor analysis of the spectra obtained during depth profiling. Pronounced changes in shape and position occur for the Zr, Al, and Ti Auger transitions, but not for Cu and Ni. At least three different peak shapes for O(KVV) were found and attributed to different oxygen binding states. The alloy composition has no significant effect on the thickness and composition of the oxide layer. In multi-element alloys preferential sputtering is a common phenomenon. In the steady state of sputtering, a significant depletion in Cu is found. At the oxide/metal interface, a distinct enrichment of copper is found for all alloys and treatments. The degree of this Cu enrichment depends on the pretreatment. It is higher for the electrochemically-passivated samples than for samples with oxide layers grown during melt spinning.

Nd–Fe–B is a promising material system for the preparation of thin films with good hard magnetic properties. One problem of this material class is the sensitivity against oxidation, resulting in a degradation of the magnetic properties. Using XPS depth profiling in combination with peak-shape analysis it is shown that already after several hours oxygen can diffuse deep into the thin laser-deposited films and that Nd is mainly responsible for the oxidation. Local element analysis with AES revealed boron inhomogeneities from droplet formation during laser deposition. These problems can be solved by using a capping Cr layer and an FeB target for thin film preparation, respectively.

Electron spectroscopic methods as X-ray photoelectron spectrometry (XPS) and Auger electron spectrometry (AES) are well established in the field of thin-film and surface analysis. In the measured spectral information, always also chemical information on the sample is contained. It is discussed that often chemometrical methods are the only way to extract such (hidden) information from the measured data sets. We demonstrate for AES and XPS measurements, how factor analysis (FA) can help to derive chemical information at Ti-based material developed for body implants. An introduction to the methodology is given, and challenges and restrictions are discussed.

For the development of a low-cost MgB2 superconductor the “powder-in-tube” (PIT) technique is investigated. Mechanically alloyed MgB2 powder provides a favorable microstructure and phase composition for the low temperature preparation of MgB2 tapes with superconducting properties. The composition of sintered bulk samples and Fe-clad MgB2 tapes made of mechanically alloyed MgB2 has been investigated by Auger micro-analysis. Due to the process the samples contain about 15% oxygen. Pure MgB2 crystallites were investigated as standard for stoichiometry and peak shape analysis.

Cube textured substrate tapes were prepared by cold forming and annealing from nickel and microalloyed nickel in order to manufacture long flexible superconductors of the YBCO (YBa 2 Cu 3 O 7− δ ) type. It was shown that sulphur as a metallurgical trace impurity can hinder the processes of cube texture formation in nickel based materials. Experiments were performed to overcome this detrimental effect of sulphur by microalloying of different nickel qualities with Mo, W or Ag and by specific heat treatments.

The polarization behavior of glassy Zr 59 Ti 3 Cu 20 Al 10 Ni 8 alloy samples was investigated in 1N H 2 SO 4 solution to understand their passivation characteristics in strongly acidic environment. Pitting corrosion tests were performed in acidic chloride medium of 1N H 2 SO 4 containing 0.01–0.2N NaCl. Electrochemical investigations were carried out by potentiodynamic and potentiostatic anodic polarization methods at room temperature. The corroded sample surfaces were examined using scanning electron microscopy, and the alloying element distribution across the pits was analyzed using energy dispersive X-ray analysis. The passive films developed at potentiostatic anodic polarization were examined using Auger electron spectroscopy (AES). The results of the present investigation revealed (i) corrosion resistance of Zr-based amorphous alloys is very high in acidic medium and moderate in acidic chloride medium (ii) structural defects and clustered zones of alloying elements deteriorate the corrosion resistance, and (ii) copper plays a significant role in enriching below the passive film and affecting the corrosion behavior. In conclusion, a localized corrosion mechanism is proposed.

Amorphous and multiphase crystalline Mg65Y10Cu15Ag10 samples were subjected to potentiodynamic polarisation in electrolytes with pH=5–8.4 and 13. Potentiostatic current transients were recorded for studying anodic passive layers growth mechanisms. Surface states were characterised by Auger electron spectroscopy (AES) depth profiling and atomic force microscopy (AFM). The corrosion behaviour of the quaternary alloy samples containing silver is markedly different compared to that of the earlier studied Mg65Y10Cu25 alloy. The free corrosion potential is more noble and corrosion current densities are lower. Stable anodic passivation was observed in electrolytes with pH≥6, whereas in acidic media dissolution sets in. In neutral to weakly alkaline electrolytes, a mainly high field driven layer growth occurs which was similarly observed for the ternary alloy. In strongly alkaline electrolyte, the growth mechanism tended to shift from diffusion control (ternary alloy) to a more high field driven growth pattern due to the presence of silver in the alloy. Passive layers formed in weakly alkaline electrolyte under participation of all alloying elements, especially copper, are thick and porous. Magnesium and yttrium oxide/hydroxides are the main constituents of the thinner passive layer formed in the highly alkaline electrolyte, but also traces of silver oxides were detected. Also, for this quaternary alloy composition, the multiphase crystalline material exhibits a poorer stability and passivation ability than the single amorphous phase.

The corrosion behaviour of the amorphous Mg65Y10Cu15Ag10 alloy as well as of its crystalline multiphase counterpart was studied in alkaline electrolytes and compared with that of the amorphous Mg65Y10Cu25 alloy. Electrochemical investigations were carried out in 0.3 M H3BO3/Na2B4O7 buffer solution with pH=8.4 and in 0.1 M NaOH solution with pH=13. Tafel plots were recorded and cyclic potentiodynamic polarisation tests were conducted, transients were measured at anodic potentials. Potentiostatically formed surface layers were characterised by Auger electron spectroscopy and atomic force microscopy. Changes in the corrosion behaviour were noticed which are attributed to the presence of silver. The passive layers formed in the two electrolytes were quite different in the composition as well as in morphology. The layer growth mechanisms also showed some variation presumably mainly due to the presence of silver, though copper still seems to play a dominant role in the passivation of this alloy in the weakly alkaline solution. The amorphous alloys displayed superior corrosion behaviour compared to the crystalline alloy, because of the absence of the heterogeneties existing in crystalline alloys.

Co/Cu multilayers with individual layer thickness corresponding to the second maximum of the antiferromagnetic coupling were investigated as an attractive system for applications utilizing the giant magnetoresistance (GMR). Annealing causes distinct changes in the transport and magnetic properties of the multilayers. To obtain a deeper understanding of the triggering mechanisms, the variations in the layer and lattice structure occurring during heat treatment were studied by x-ray diffraction and electron microscopy. Structural and corresponding magnetic changes were observed according to characteristic temperature regions. The initial GMR of about 25% increased up to an annealing temperature of 400°C in correlation with the sharpening of the interfaces. Above 300°C grain growth sets in, and high coherency strains give rise to a transition from a 111 to a 100 texture. Above an annealing temperature of 400°C increasing layer defects cause a reduction of the GMR, and exceeding 600°C results in a complete transition from the multilayer configuration to a granular-like structure with large (~100 nm) domains of Co and Cu.

The corrosion behavior of the bulk glass-forming Mg65Y10Cu15Ag10alloy was studied in neutral and weakly acidic media. Potentiodynamic polarization studies in cyclic and linear modes were carried out in electrolytes with a pH = 7, containing different anions. The alloy corroded freely in electrolytes with sulfate and pthalate ions, whereas passivity was observed in the electrolyte with borate ions. Further tests were performed in boric-acid-added borate buffer solution with pH = 7, 6, and 5. From Tafel characteristics, corrosion potentials and corrosion current densities were estimated. The data were compared with those of the ternary Mg65Y10Cu15metallic glass. Potentiostatic anodic polarization tests were conducted on the Mg65Y10Cu15Ag10alloy in boric-acid-added borate buffer solution with pH = 7 at two different potentials, 800 and 300 mV, saturated calomel electrode, which revealed different current transient characteristics. Auger electron spectroscopy was employed to characterize the anodically generated passive layers. The depth distributions of the elements as well as their chemical states were detected to be different for layers formed in electrolytes (i) with different pH values (8.4 and 7) of the same anion, (ii) with the same pH value but containing different anions (borate, sulfate, and pthalate), and (iii) with the same pH value and anion (borate) but at two different anodic potentials.

Amorphous material of the class FeSiB-(Cu,Nb) has been investigated with a background of soft-magnetic application of the corresponding nanocrystalline material. Thin-film analytical methods (SIMS, AES, TEM) have been used to study the diffusion of Si in such materials prepared as layer systems by magnetron sputter deposition. Significant interdiffusion occurs even at low temperatures - approximately 400 degrees C. Quantitative description failed, however, because formation of new iron monosilicide phases begins above this temperature. It is concluded that only high-mass-resolution SIMS or radioactive tracer analysis can be used for successful acquisition of information at this material system.

The suitability of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for precise analysis of YNi(2)B(2)C has been investigated. The intensity ratios B/Y and Ni/Y were found to vary during ablation as a function of the ablation conditions. This could be because of fractionation, owing to incongruent ablation or transport and plasma effects. The bottoms and surroundings of the craters were investigated by scanning Auger electron spectrometry. The bottoms of the craters produced by ablation are covered with a thin oxide comparable with that on the polished crystal surface. The craters are surrounded by an oxide layer the dimensions and thickness of which depend on the laser conditions. The formation of this oxide can be assumed to be a result of partial oxidation of sample material during the ablation process; the oxide is then redeposited around the laser crater.

With Fe2O3 as a proof-of-concept, free-standing nanomembrane structure is demonstrated to be highly advantageous to improve the performance of Li-ion batteries. The Fe2O3 nanomembrane electrodes exhibit ultra-long cycling life at high current rates with satisfactory capacity (808 mAh g(-1) after 1000 cycles at 2 C and 530 mAh g(-1) after 3000 cycles at 6 C) as well as repeatable high rate capability up to 50 C. The excellent performance benefits particularly from the unique structural advantages of the nanomembranes. The mechanical feature can buffer the strain of lithiation/delithiation to postpone the pulverization. The two-dimensional transport pathways in between the nanomembranes can promote the pseudo-capacitive type storage. The parallel-laid nanomembranes, which are coated by polymeric gel-like film and SEI layer with the electrolyte in between layers, electrochemically behave like numerous "mini-capacitors" to provide the pseudo-capacitance thus maintain the capacity at high rate.

The oxidation of sputtered NiFe(20 wt.%, Permalloy) thin films with a thickness of 180 nm was studied during annealing up to 400 °C for 2 h in air. The composition and the thickness of the oxide layer and the compositional change in the NiFe alloy layer as well as the microstructure of the film were investigated by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Distinct oxidation starts at about 300 °C. The formed oxide layer consists of Fe 2 O 3 . The Fe concentration in the NiFe layer decreases with the oxidation which leads to changes of the properties of this layer.

Multilayer structures composed of 3d transition metals were investigated by AES in combination with sputter depth profiling. The samples were trilayers Permalloy/Cu/Permalloy, Co/Cu multilayers and a spin-valve structure. Overlapping Auger peaks were separated by a fit-to-spectra of bulk standards. Sample rotation during sputtering improves the depth resolution and made detection of unintentionally deposited Cu possible. For very thin films the depth profiles are influenced by measuring effects. The effects of atomic mixing, surface roughness and information depth onto the depth profiles in the spin-valve structure were simulated using the MRI model.

Nanoscale multilayers show properties completely different from bulk materials and are of great interest in the modern materials science. The characterisation of their structure and composition requires methods with spatial resolution of only few nanometers. The analytical transmission electron microscopy on cross sections is one of the most suitable methods. Imaging and spectroscopy of the same specimen details lead to essential information about correlation of structure and properties. The use of the analytical TEM with possibilities and limitations in the scanning mode will be demonstrated on four materials problems: oxygen bond in thin resistivity films (CuNi/NiCr), hard coating multilayers (TiN/Al 2 O 3 ), and Fe/Al multilayers, as well as the degree of mixing within nanoscale Co/Cu multilayers.

Fibre/matrix interfaces in δ-Al2O3/Mg8Li and δ-Al2O3/Mg composites have been investigated using XPS and SIMS analysis of extracted δ-Al2O3 fibres in context with previous XRD observations. Results obtained indicate that in MgLi based composites lithium enters preferentially the interfacial redox reactions producing Li+ ions that occupy vacant cation positions in the defect δ-Al2O3 lattice which results in a strong fibre/matrix interfacial bond. On the other hand, in Mg matrix composites the magnesium oxide appears to be the final reaction product that does not enter the solid state reaction with adjacent δ-Al2O3 fibre during the melt infiltration process, so that only relatively weak interfacial bond is created.