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Nanoparticle (NP) colloidal stability plays a crucial role in biomedical application not only for human and environmental safety but also for NP efficiency and functionality. NP agglomeration is considered as a possible process in monodispersed NP colloidal solutions, which drastically affects colloidal stability. This process is triggered by changes in the physicochemical properties of the surrounding media, such as ionic strength (IS), pH value, or presence of biomolecules. Despite different available characterization methods for nanoparticles (NPs), there is a lack of information about the underlying mechanisms at the early stage of dynamic behaviors, namely changing in NP size distribution and structure while placing them from a stable colloidal solution to a new media like biological fluids. In this study, an advanced in situ approach is presented that combines small angle X-ray scattering (SAXS) and microfluidics, allowing label-free, direct, time-resolved, and dynamic observations of the early stage of NP interaction/agglomeration initiated by environmental changes. It is shown for silica NPs that the presence of protein in the media enormously accelerates the NP agglomeration process compared to respective changes in IS and pH. High IS results in a staring agglomeration process after 40 min, though, in case of protein presence in media, this time decreased enormously to 48 s. These time scales show that this method is sensitive and precise in depicting the dynamics of fast and slow NP interactions in colloidal conditions and therefore supports understanding the colloidal stability of NPs in various media concluding in safe and efficient NP designing for various applications.

The mechanical properties of cancellous bone in the humeral head are increasingly interesting due to the increased popularity of stemless prosthetic fixation in the cancellous bone of the metaphysis. Age or pathology‐related systemic osteoporosis, inactivity, or pathology of the shoulder joint may influence the primary bonding of implants that rely on good cancellous bone quality. We assessed the bone mineral density (BMD) and anisotropy using micro‐computed tomography (micro‐CT) (0.04 mm voxel size) and correlated the results with indentation load/displacement response. Resected parts of humeral heads (from patients undergoing total shoulder replacement, n = 18) were used as probes. The region of interest was defined as 2 mm medial from the resection plane, presuming that it mirrored the bone quality lateral to the resection plane. The indentation tests were performed with a large probe (diameter 10 mm) in a single destructive loading procedure. The BMD and trabecular orientation were determined by micro‐CT. Our results showed a correlation between the BMD and the slope of the load/displacement curve. Furthermore, the trabeculae were predominantly oriented orthogonal to the joint surface. In conclusion, the predominant factor determining the bone quality and mechanical resistance to pressure appears to be the BMD, while trabecular orientation could not be related to load/displacement response. Statement of clinical significance: Bone quality predominately determines the mechanical properties of cancellous bone. This might be crucial when prosthetic implants need to be anchored in metaphyseal bone. Therefore, clinical decision‐making processes should also include local BMD measurements.

Electrospinning is a versatile technique to produce nanofibrous membranes with applications in filtration, biosensing, biomedical and tissue engineering. The structural and therefore physical properties of electrospun fibers can be finely tuned by changing the electrospinning parameters. The large parameter window makes it challenging to optimize the properties of fibers for a specific application. Therefore, a fundamental understanding of the multiscale structure of fibers and its correlation with their macroscopic behaviors is required for the design and production of systems with dedicated applications. In this study, we demonstrate that the properties of poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) electrospun fibers can be tuned by changing the rotating drum speed used as a collector during electrospinning. Indeed, with the help of multiscale characterization techniques such as scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS), we observe that increasing the rotating drum speed not only aligns the fibers but also induces polymeric chain rearrangements at the molecular scale. Such changes result in enhanced mechanical properties and an increase of the piezoelectric beta-phase of the PVDF-HFP fiber membranes. We detect nanostructural deformation behaviors when the aligned fibrous membrane is uniaxially stretched along the fiber alignment direction, while an increase in the alignment of the fibers is observed for randomly aligned samples. This was analyzed by performing in situ SAXS measurements coupled with uniaxial tensile loading of the fibrous membranes along the fiber alignment direction. The present study shows that fibrous membranes can be produced with varying degrees of fiber orientation, piezoelectric beta-phase content, and mechanical properties by controlling the speed of the rotating drum collector during the fiber production. Such aligned fiber membranes have potential applications for neural or musculoskeletal tissue engineering., Nanoscale Advances, 4 (2), ISSN:2516-0230

Devices such as sensors, actuators, or micro-electromechanical systems (MEMS) are obtained by a variety of microfabrication processes. Many of these processes influence the material systems by the introduction of strain and defects, which may affect the final device's performance and reliability. Indeed, controlling materials' status during the microfabrication is fundamental for the process optimization itself and for guaranteeing the highest devices performances during their lifetime. In this work, a conjoint analytical approach between high-resolution X-ray diffraction (HRXRD) and X-ray micro-computed tomography (CT) evaluates an innovative silicon-to-sapphire wafer bonding process. Large cracks 30–60 µm-thick were identified in both crystals by micro-CT and related to the interfacial high-stress release. In parallel, a multi-domain microstructure associated with strain and tilt affect the silicon crystallinity due to smaller cracks and defects which originate at the bonding interface and travel to the outer part of the crystal. The effectiveness of the bonding is also assessed by our approach and further enforced by means of SEM observation of the sample cross-section. Here, a unique approach by combining X-ray micro CT with HRXRD for a holistic evaluation of silicon-to-sapphire wafer-bonding processes and correlate the micrometer scale and volumetric defect detection (voids and cracks) with atomic-level strain and defect analysis is presented.

Fibrous biocomposites like bone and tendons exhibit a hierarchical arrangement of their components ranging from the macroscale down to the molecular level. The multiscale complex morphology, together with the correlated orientation of their constituents, contributes significantly to the outstanding mechanical properties of these biomaterials. In this study, a systematic road map is provided to quantify the hierarchical structure of a mineralized turkey leg tendon (MTLT) in a holistic multiscale evaluation by combining micro-Computed Tomography (micro-CT), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). We quantify the interplay of the main MTLT components with respect to highly ordered organic parts such as fibrous collagen integrating inorganic components like hydroxyapatite (HA). The microscale fibrous morphology revealing different types of porous features and their orientation was quantified based on micro-CT investigations. The quantitative analysis of the alignment of collagen fibrils and HA crystallites was established from the streak-like signal in SAXS using the Ruland approach and the broadening of azimuthal profiles of the small and wide-angle diffraction peaks. It has been in general agreement that HA crystallites are co-aligned with the nanostructure of mineralized tissue. However, we observe relatively lower degree of orientation of HA crystallites compared to the collagen fibrils, which supports the recent findings of the structural interrelations within mineralized tissues. The generic multiscale characterization approach of this study is relevant to any hierarchically structured biomaterials or bioinspired materials from the μm-nm-A scale. Hence, it gives the basis for future structure-property relationship investigations and simulations for a wide range of hierarchically structured materials. Statement of significance Many fibrous biocomposites such as tendon, bone, and wood possess multiscale hierarchical structures, responsible for their exceptional mechanical properties. In this study, the 3-dimensional hierarchical structure, the degree of orientation and composition of mineralized tendon extracted from a turkey leg were quantified using a multimodal X-ray based approach combining small-angle X-ray scattering and wide-angle X-ray diffraction with micro-Computed Tomography. We demonstrate that hydroxyapatite (HA) domains are co-aligned with the nanostructure of mineralized tissue. However, the lower degree of orientation of HA crystallites was observed when compared to the collagen fibrils. The generic multiscale characterization approach of this study is relevant to any hierarchically structured biomaterials or bioinspired materials from the micrometer over the nanometer to the Angstrom scale level.

Cathodic arc evaporation was applied to form a layer stack on a Ni-based superalloy single crystalline substrate in a single in-situ vacuum deposition process. The initial layer was deposited using a target with the same nominal composition as the superalloy substrate. Subsequently, a second layer was deposited using a target with a composition of 70 at.% Al and 30 at.% Cr, and the deposition was conducted in flowing oxygen to form Al-Cr-O. The thermal stability of the layer stack was investigated by means of a heat treatment at 1100 °C in air. The substrate-like coating recrystallized at elevated temperature and showed epitaxial growth on the superalloy single crystal, according to transmission Kikuchi diffraction measurements. A thin layer of pure α-alumina formed on top of the substrate-like coating and a compact Al-Cr-O phase with corundum structure developed towards the top of the coating. Microstructural and chemical analyses of the coating architectures in the as-deposited and annealed states were performed by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Rutherford backscattering spectrometry, and utilized to explain the recrystallization and diffusion processes in the layer stack.

We introduce the design and study of a hybrid electrospun membrane with a dedicated nanoscale structural hierarchy for controlled functions in the biomedical domain. The hybrid system comprises submicrometer-sized internally self-assembled lipid nanoparticles (ISAsomes or mesosomes) embedded into the electrospun membrane with a nanofibrous polymer network. The internal structure of ISAsomes, studied by small-angle X-ray scattering (SAXS) and electron microscopy, demonstrated a spontaneous response to variations in the environmental conditions as they undergo a bicontinuous inverse cubic phase (cubosomes) in solution to a crystalline lamellar phase in the polymer membrane; nevertheless, this phase reorganization is reversible. As revealed by in situ SAXS measurements, if the membrane was put in contact with aqueous media, the cubic phase reappeared and submicrometer-sized cubosomes were released upon dissolution of the nanofibers. Furthermore, the hybrid membranes exhibited a specific anisotropic feature and morphological response under an external strain. While nanofibers were aligned under external strain in the microscale, the semicrystalline domains from the polymer phase were positioned perpendicular to the lamellae of the lipid phase in the nanoscale. The fabricated membranes and their spontaneous responses offer new strategies for the development of structure-controlled functions in electrospun nanofibers for biomedical applications, such as drug delivery or controlled interactions with biointerfaces.

Hydroxyapatite (HA) coatings have become very popular in uncemented total hip arthroplasty (THA). Analysis of retrievals and tissue samples from an HA-coated femoral stem, which failed within 14 months after THA, provides exceptional insights into the failure mechanism, as well as the process of osteointegration of such an implant. Methods: Retrievals were photo-documented. Samples were examined by micro-computed tomography, X-ray diffraction (XRD) and embedded in polymethylmethacrylate for histology. Results: The coating had partially delaminated. The sandblasted surface of the stem was partially polished by the delaminated HA coating, indicating failure before revision. In the tissue samples, the HA coating was well integrated by newly formed bone trabeculae. No adverse biological reaction was observed. XRD analysis showed that residues of the HA coating were still present and could clearly be differentiated from the surrounding bone. Preferential orientation of the HA crystallites could be identified within the newly formed bone, representing a potential mechanical weakness induced either by physiologic strain or by the coating. Conclusion: current HA coatings, relatively thick and made of high crystallinity HA, may be prone to delamination, as also seen in our study. Recent efforts have aimed towards thinner (&lt, 1 &mu, m) coatings with nanocrystalline HA structures that possibly relate to lower delamination risks. However, the question arises if HA coatings are beneficial since sandblasted non-coated stems offer similar results without the risk of delamination. XRD not only permits differentiation between the HA from the coating and the HA of the ongrown bone, it also provides new insights into the microstructure of this newly formed bone.

Silicon nanowire-based sensors find many applications in micro- and nano-electromechanical systems, thanks to their unique characteristics of flexibility and strength that emerge at the nanoscale. This work is the first study of this class of micro- and nano-fabricated silicon-based structures adopting the scanning X-ray diffraction microscopy technique for mapping the in-plane crystalline strain (epsilon(044)) and tilt of a device which includes pillars with suspended nanowires on a substrate. It is shown how the micro- and nanostructures of this new type of nanowire system are influenced by critical steps of the fabrication process, such as electron-beam lithography and deep reactive ion etching. X-ray analysis performed on the 044 reflection shows a very low level of lattice strain (, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (FWF)

In this work we show our result of in-situ nitrocarburizing and nitriding treatments AISI316L specimens. Part of the samples have been depassivated ex-situ and coated with a Ni layer, while other specimens received in-situ depassivation. Processing was carried out in a custom built reaction chamber attached to a Bruker D8 Advance diffractometer. We monitored the 111 peak of both the base material and expanded austenite. From the shrinkage of the base material peak the total thickness of the expanded austenite can be determined. Applying both N and C resulted in a more than 10 times faster growth of the expanded austenite than with N only. The growth is thermally activated. The activation energy for nitrocarburizing is 164 kJ/mol. This is in agreement with the activation energy of the diffusion of interstitials. Detailed analysis of the expanded austenite peak allowed the derivation of a “master curve” for the composition depth profile. This suggest that two interacting process controls the evolution. The width of the reaction zone is limited by the diffusion at low concentration side. The total concentration is determined by the reaction at the interface.

The reliability of semiconductor materials with electrical and optical properties are connected to their structures. The elastic strain field and tilt analysis of the crystal lattice, detectable by the variation in position and shape of the diffraction peaks, is used to quantify defects and investigate their mobility. The exploitation of high-resolution X-ray diffraction-based methods for the evaluation of structural defects in semiconductor materials and devices is reviewed. An efficient and non-destructive characterization is possible for structural parameters such as, lattice strain and tilt, layer composition and thickness, lattice mismatch, and dislocation density. The description of specific experimental diffraction geometries and scanning methods is provided. Today's X-ray diffraction based methods are evaluated and compared, also with respect to their applicability limits. The goal is to understand the close relationship between lattice strain and structural defects. For different material systems, the appropriate analytical methods are highlighted.

Superalloy targets were produced from Ni-(Al-C-Co-Cr-Mo-Ta-Ti-W) powders by spark plasma sintering technology. The crystalline structure of the as-produced targets was investigated by XRD analysis and compared with the evolution of phases resulting from the operation of the cathodic arc at the target (cathode) surface. Coatings were synthesized at superalloy substrates utilizing these superalloy targets in non-reactive and reactive evaporation processes. Synthesized coatings and target surfaces were compared with respect to chemical composition and crystal structure. The interface between coating and superalloy substrates was investigated by TEM. As an example, a complete layer stack was synthesized by cathodic arc evaporation starting from the superalloy substrate - superalloy coating interface to a fully oxidized superalloy coating showing epitaxial growth in the interface to the superalloy substrate.

New methods are needed in microsystems technology for evaluating microelectromechanical systems (MEMS) because of their reduced size. The assessment and characterization of mechanical and structural relations of MEMS are essential to assure the long-term functioning of devices, and have a significant impact on design and fabrication. Within this study a concept for the investigation of mechanically loaded MEMS materials on an atomic level is introduced, combining high-resolution X-ray diffraction (HRXRD) measurements with finite element analysis (FEA) and mechanical testing. In situ HRXRD measurements were performed on tensile loaded single crystal silicon (SCSi) specimens by means of profile scans and reciprocal space mapping (RSM) on symmetrical (004) and (440) reflections. A comprehensive evaluation of the rather complex XRD patterns and features was enabled by the correlation of measured with simulated, ‘theoretical’ patterns. Latter were calculated by a specifically developed, simple and fast approach on the basis of continuum mechanical relations. Qualitative and quantitative analysis confirmed the admissibility and accuracy of the presented method. In this context [001] Poisson’s ratio was determined providing an error of less than 1.5% with respect to analytical prediction. Consequently, the introduced procedure contributes to further going investigations of weak scattering being related to strain and defects in crystalline structures and therefore supports investigations on materials and devices failure mechanisms.

Thin coatings were synthesized by cathodic arc evaporation of powder metallurgically fabricated Al-Ni targets with the chemical compositions of Al75Ni25, Al67Ni33 and Al52Ni48 atomic percent. The coatings were produced both either from pure metallic vapour or in reactive oxygen atmosphere. Phase transformations and chemical composition at the target surface were investigated by X-ray diffraction (XRD) and by energy-dispersive X-ray spectroscopy (EDS) techniques and compared with the phases composition obtained in the coating. The deposition in non-reactive mode produces intermetallic coatings containing different Ni aluminides. The formation of the aluminides can be controlled by the target composition and is by trend predictable from the Al-Ni phase diagram. The coatings produced in reactive mode are composed of both Al3Ni and Al3Ni2 with the additional formation of AlNi and Al2NiO4 in all the coatings. The coatings composed of intermetallics show high indentation hardness in the range of 10 GPA while the coatings composed of both oxides and intermetallics demonstrate exceptional high hardness of about 30 GPa. All coatings have been annealed in ambient air up to 1200 °C and were investigated by in-situ XRD analysis in order to follow in detail their oxidation process. For all coatings, the formation of α-Al2O3 and Al2NiO4 could be observed after annealing forming a thin high temperature stable protective layer for remaining AlNi. The coatings deposited in reactive atmosphere contain additional NiO, independently of their original composition.

A multiscale analytical approach is presented for understanding the structure of micro- and nano-fabricated nanowire-based sensors. Using scanning X-ray diffraction microscopy, crystal deformation is evaluated with respect to lattice strain and tilt caused by the manufacturing process of a silicon monolith., Silicon nanowire-based sensors find many applications in micro- and nano-electromechanical systems, thanks to their unique characteristics of flexibility and strength that emerge at the nanoscale. This work is the first study of this class of micro- and nano-fabricated silicon-based structures adopting the scanning X-ray diffraction microscopy technique for mapping the in-plane crystalline strain (∊044) and tilt of a device which includes pillars with suspended nanowires on a substrate. It is shown how the micro- and nanostructures of this new type of nanowire system are influenced by critical steps of the fabrication process, such as electron-beam lithography and deep reactive ion etching. X-ray analysis performed on the 044 reflection shows a very low level of lattice strain (

A dedicated nanofiber design for applications in the biomedical domain is based on the understanding of nanofiber structures. The structure of electrospun nanofibers strongly influences their properties and functionalities. In polymeric nanofibers X-ray scattering and diffraction methods, i.e. SAXS and WAXD, are capable of decoding their structural insights from about 100 nm down to the Angstrom scale. Here, we present a comprehensive X-ray scattering and diffraction based study and introduce new data analysis approaches to unveil detailed structural features in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFhfp) nanofiber membranes. Particular emphasis was placed on anisotropic morphologies being developed during the nanofiber fabrication process. Global analysis was performed on SAXS data to derive the nanofibrillar structure of repeating lamella crystalline domains with average dimensions of 12.5 nm thickness and 7.8 nm spacing along with associated tie-molecules. The varying surface roughness of the nanofiber was evaluated by extracting the Porod exponent in parallel and perpendicular direction to the nanofiber axis, which was further validated by Atomic Force Microscopy. Additionally, the presence of a mixture of the monoclinic alpha and the orthorhombic beta PVDFhfp phases both exhibiting about 6% larger unit cells compared to the corresponding pure PVDF phases was derived from WAXD. The current study shows a generic approach in detailed understanding of internal structures and surface morphology for nanofibers. This forms the basis for targeted structure and morphology steering and the respective controlling during the fabrication process with the aim to engineer nanofibers for different biomedical applications with specific requirements.

Here we present measurements of surface tension and viscosity of the bulk glass-forming alloy Pd43Cu27Ni10P20 performed during containerless processing under reduced gravity. We applied the oscillating drop method in an electromagnetic levitation facility on board of parabolic flights. The measured viscosity exhibits a pronounced temperature dependence following an Arrhenius law over a temperature range from 1100 K to 1450 K. Together with literature values of viscosity at lower temperatures, the viscosity of Pd43Cu27Ni10P20 can be well described by a free volume model. X-ray diffraction analysis on the material retrieved after the parabolic flights confirm the glassy nature after vitrification of the bulk samples and thus the absence of crystallization during processing over a wide temperature range.

Despite its crucial role, the placenta is the least understood human organ. Recent clinical studies indicate a direct association between placental calcification and maternal and offspring health. This study reveals distinct characteristics of minerals formed during gestational ageing using cutting-edge nano-analytical characterization and paves the way for investigations focused on the identification of potential markers for disease risks in a clinical setting based on atypical placental mineral fingerprints.

The heat protective performance of thermal protective fabrics is related to the multiscale structure of the fibrous material and the composite design of a multilayered fabric system. In this study, a molecular interpretation is provided to explain the structural changes within fibers to correlate with the mechanical properties of the outermost layer fabric made up of m-aramid blended with (5–10) % p-aramid upon various radiant heat exposures. An increase in crystallinity due to limited polymer chain movement but no change in lamellar spacing was observed when fabrics were exposed below the glass transition temperature which resulted in no change in mechanical properties. A noticeable increase in lamellar spacing and crystallinity was obtained when the temperature during the heat exposures is in the proximity of 375 °C of the fabric layer due to the fibrillar-to-lamellar transformation. Even though no visible changes were observed by scanning electron microscopy (SEM) in the fabric exposed to the aforementioned thermal conditions, we found that their mechanical properties are compromised due to the structural changes within fibers of the fabrics. Therefore, further use of fabrics could be potentially dangerous for the user. Furthermore, for expoheat exposures where the temperature of the fabrics reaches above the degradation point, thermal decomposition occurs which is noticed by its hard and brittle behavior. The inner layers of both the fabric systems mostly remain intact until the thermal degradation of the outermost layers. This study provides an in-depth understanding of molecular mechanisms of structural changes that are in line with changes in the mechanical properties. The understanding of the structure-mechanical property relationship could serve as basic knowledge for the design and fabrication of high-performance fabrics for various fire environments.

Adverse reaction to metal debris (ARMD) is an issue in metal-on-metal (MoM) total hip replacements (THR). It mainly affects large-head MoM THR, whereas 28–32 mm MoM pairings are associated with low long-term revision rates. However, the bearing surface is not necessarily the only cause of metal debris. This report documents with advanced analysis of the retrievals a particular cause of trunnionosis in late failure of a small diameter MoM THR and illustrates the importance of cleaning of the taper when seating the head in THR. A 65-year-old patient was revised due to ARMD 16 years after small diameter MoM THR. Debridement and exchange of the inlay and the head had been performed through an anterior approach. While the cup and the outer surface of the head were accessible to direct analysis by an optical coordinate measuring machine, the female taper had to be analysed indirectly by measuring an imprint. Wear from the cup and the head was within expected low ranges. The analysis of the female taper identified bone fragments, which contributed to trunnionosis. Failure due to ARMD after MoM THR is not necessarily caused by the bearing, but can be due to trunnionosis. Bone fragments within the taper contact in this case highlight the importance of meticulous cleaning of the taper before seating the head, to avoid trunnionosis.

Extending the functionality of ubiquitous Si-based microelectronic devices often requires combining materials with different lattice parameters and thermal expansion coefficients. In this paper, scanning X-ray nanodiffraction is used to map the lattice bending produced by thermal strain relaxation in heteroepitaxial Ge microcrystals of various heights grown on high aspect ratio Si pillars. The local crystal lattice tilt and curvature are obtained from experimental three-dimensional reciprocal space maps and compared with diffraction patterns simulated by means of the finite element method. The simulations are in good agreement with the experimental data for various positions of the focused X-ray beam inside a Ge microcrystal. Both experiment and simulations reveal that the crystal lattice bending induced by thermal strain relaxation vanishes with increasing Ge crystal height.

Interpreting the polarimetric data from fiber-like macromolecules constitutive of tissue can be difficult due to strong scattering. In this study, we probed the superficial layers of fibrous tissue models (membranes consisting of nanofibers) displaying varying degrees of alignment. To better understand the manifestation of membranes’ degree of alignment in polarimetry, we analyzed the spatial variations of the backscattered light’s Stokes vectors as a function of the orientation of the probing beam’s linear polarization. The degree of linear polarization reflects the uniaxially birefringent behavior of the membranes. The rotational (a-)symmetry of the backscattered light’s degree of linear polarization provides a measure of the membranes’ degree of alignment.

Imperfections, like surface roughness and defects, introduced by common manufacturing processes are recognized to favor failure of microfabricated components and systems. Up to now only a reduced part of the ideal strength prediction by zero Kelvin quantum mechanical ab initio calculations could be recovered for micrometer-sized structures manufactured with DRIE. Within the present work the high-loading fracture behavior of group IV semiconductors is investigated on the basis of specific DRIE-etched micrometer-sized single crystal silicon (SCSI) specimens. Aiming an enhancement of the surface quality, the samples are post-treated using wet etchants, such as KOH and HNA and oxidation processes, such as thermal and hydrogen oxidation. The resistance of the specimens against mechanical loading is assessed by 2-point bending tests applying a testing procedure which is outstanding due to its simplicity in handling and reproducibility of the measurement results. The experiments are analyzed and evaluated for Young's modulus, fracture and bending strength. Dependent on the particular treatment method, remarkable improvements of fracture strain and stress of up to epsilon(max) = 5.7% and sigma(max) = 8.8 GPa are realized. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Al–Hf and Al–Hf–O coatings were synthesized by cathodic arc evaporation utilizing composite targets with composition of Al 75 Hf 25 . The reaction at the target surface and the composition of the film were analyzed by energy-dispersive X-ray spectroscopy (EDX), Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD) techniques. The Al–Hf coatings deviate distinctively from target composition showing a deficiency in Al. XRD phase analysis shows the synthesis of Al 3 Hf intermetallic compound for the Al–Hf coatings while the oxide coatings indicate an amorphous matrix and monoclinic HfO 2 . The coatings were annealed in ambient air up to 1290 °C to study the oxidation process. In-situ XRD analysis of the coatings was performed during annealing. The intermetallic phase undergoes phase transformations at temperatures between 700 °C and 1100 °C, with the formation of a metastable face-centered cubic ( fcc ) HfO 2 simultaneously with the monoclinic polymorph. After this transition period, the cubic phase disappears and the coating stabilizes with two oxide phases: corundum (α-Al 2 O 3 ) and monoclinic HfO 2 ( m -HfO 2 ). Applying the same treatments to the Al–Hf–O coatings results in a similar evolution with an improvement of crystallinity for the monoclinic HfO 2 phase and the crystallization of the fcc HfO 2 starting at about 860 °C. This phase disappears above 1200 °C, where the coating stabilizes with corundum and m -HfO 2 phases. The formation of the metastable fcc HfO 2 phase is discussed and associated with a deficiency in oxygen during the oxidation process.

The evolution of the composition of tungsten carbide and silicon surfaces initiated by the bombardment with Zr and Cr ions has been investigated as a function of the substrate bias voltage. Surface composition profiles were measured by Rutherford backscattering and have been compared with the results obtained by the TRIDYN simulation program. It is found that the general dependence of film thickness on substrate bias is satisfactorily reproduced by this model. Deviations between experiment and simulation are attributed to possible partial oxidation of the surface or uncertainties in the charge state distribution of metal ions. The results confirm that TRIDYN facilitates the predictability of the nucleation of metallic vapor at substrate surfaces.

This work reports on the development and the experimental proof of a novel concept of miniaturized X-ray source. This concept is based on microsystems technology and carbon nanotube electron field emitters. Thereby, unseen features such as fast switching and reduced imaging time will be enabled in future applications, such as, for instance, static computed tomography. In this work we describe the fabrication, assembly, and testing of micro-fabricated electrodes and carbon nanotube cold cathodes, based on a new design concept, to be packaged in a miniaturized X-ray source. The source design concept was experimentally validated. X-rays were generated with a total current of up to 4 μA extracted from the cathode and an acceleration voltage of 3.1 kV. The total current collected on the anode was 0.2–0.4 μA which thus corresponds to a collection efficiency on the anode of approx. 10%. The components were assembled and operated in a high vacuum chamber at −6 mbar. The achieved results from both, the electron and the X-ray emission experiments will be discussed in detail. Furthermore, we comment on the individual components’ limitations as well as on the next steps to be taken in order to optimize the characteristics and performance of the final X-ray source.

We present a method for monolithically integrating mismatched semiconductor materials with Si, coined three-dimensional (3D) heteroepitaxy. The method comprises the replacement of conventional, continuous epilayers by dense arrays of strain- and defect-free, micron-sized crystals. The crystals are formed by a combination of deep-patterning of the Si substrates and self-limited lateral expansion during the epitaxial growth. Consequently, the longstanding issues of crack formation and wafer bowing can be avoided. Moreover, threading dislocations can be eliminated by appropriately choosing pattern sizes, layer thicknesses and surface morphology, the latter being dependent on the growth temperature. We show this approach to be valid for various material combinations, pattern geometries and substrate orientations. We demonstrate that Ge crystals evolve into perfect structures away from the heavily dislocated interface with Si, by using a synchrotron X-ray beam focused to a spot a few hundred nanometers in size and by recording 3D reciprocal space maps along their height. Room temperature photoluminescence (PL) experiments reveal that the interband integrated PL intensity of the Ge crystals is enhanced by almost three orders of magnitude with respect to that of Ge epilayers directly grown on flat Si substrates. Electrical measurements performed on single heterojunction diodes formed between 3D Ge crystals and the Si substrate exhibit rectifying behavior with dark currents of the order of 1 mA/cm2. For GaAs the thermal strain relaxation as a function of pattern size is similar to that found for group IV materials. Significant differences exist, however, in the evolution of crystal morphology with pattern size, which more and more tends to a pyramidal shape defined by stable {111} facets with decreasing width of the Si pillars. © 2013 Elsevier B.V.

A five-layer stack of lead zirconate titanate (PZT) thin films with Pt electrodes was fabricated for potential applications in nanoactuator systems. The 1 mu m thick PZT films were deposited by a sol-gel technique, the platinum electrodes by sputtering. The PZT films were crack-free, in spite of the use of silicon as a substrate, suggesting an increased toughness of the metal-ceramic composite. For piezoelectric characterization, the intermediate electrodes were liberated by successive etching of the PZT and Pt layers, obtaining a functional three-layer stack. A total thickness change of 5.2 nm was achieved with 10 V, measured by double beam laser interferometry. The small signal response was obtained as 0.49 nm/V. Finite element simulations were made to account for the thickness change in the substrate due to the transverse piezoelectric effect. The average response corresponds to an average d(33,f) of 120 pm/V. The multiple annealed buried layers show clearly a better performance with up to 175 pm/V. It is concluded that the electrode interfaces in the interior exhibit higher qualities, as supported by transmission electron microscopy, and that the multiple anneals were beneficial for PZT thin film quality.

Monolithic integration of absorber layer and readout electronics is expected to greatly improve spatial resolution and sensitivity of X-ray imaging detectors. It requires, however, heteroepitaxial growth of thick, lattice, and thermally mismatched absorber layers on a Si substrate. Wafer bowing and layer cracks induced by temperature changes have so far appeared to be insurmountable obstacles in the way of realizing such a device. Here we present first results on a detector concept which does not suffer from such shortcomings. The absorber consists of closely spaced, tall Ge crystals, typically a few microns in width, each forming a heterojunction diode with the Si substrate. Electrical measurements on such diodes reveal reverse dark currents of the order of 1 mA/cm2, low enough for detector fabrication. We present a preliminary version of such a detector, where the pixel size is determined by the CMOS circuits rather than individual Ge crystals.

We report on the maskless integration of micron-sized GaAs crystals on patterned Si substrates by metal organic vapor phase epitaxy. In order to adapt the mismatch between the lattice parameter and thermal expansion coefficient of GaAs and Si, 2 μm tall Ge crystals were first grown as virtual substrate by low energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs structures grown on top of the Ge crystals at the transition towards full pyramids with energetically stable {111} facets. A substantial release of strain is shown in GaAs crystals with a height of 2 μm and lateral sizes up to 15×15 μm2 by both X-ray diffraction and photoluminescence.

The pre-treatment of substrate surfaces prior to deposition is important for the adhesion of physical vapour deposition coatings. This work investigates Si surfaces after the bombardment by energetic Cr ions which are created in cathodic arc discharges. The effect of the pre-treatment is analysed by X-ray diffraction, Rutherford backscattering spectroscopy, scanning electron microscopy and in-depth X-ray photoemission spectroscopy and compared for Cr vapour produced from a filtered and non-filtered cathodic arc discharge. Cr coverage as a function of ion energy was also predicted by TRIDYN Monte Carlo calculations. Discrepancies between measured and simulated values in the transition regime between layer growth and surface removal can be explained by the chemical reactions between Cr ions and the Si substrate or between the substrate surface and the residual gases. Simulations help to find optimum and more stable parameters for specific film and substrate combinations faster than trial-and-error procedure., Science and Technology of Advanced Materials, 17 (1), ISSN:1468-6996, ISSN:1878-5514

Zr―(N)―O coatings being synthesized by cathodic arc evaporation (P3e ™ technology) show that cubic zirconia, ZrO 2 , can be formed at low substrate temperatures of 550 °C using nitrogen-oxygen reactive gas mixtures during deposition. The structural properties of the coatings obtained for different nitrogen-oxygen ratios have been investigated by X-Ray Diffraction (XRD) techniques. The composition of the layers was studied by RBS and ERDA and the layers morphology by cross sectional SEM. For low oxygen flows, the cubic ZrNand ZrO phase were formed while increased oxygen flow results in a transition starting from the orthorhombic to the cubic and to the monoclinic ZrO 2 phase. The phase stability of the cubic ZrO 2 phase has been investigated by in situ high temperatures XRD studies in air and reveals a multi step phase transformation starting at about 550 °C with a change to the tetragonal ZrO 2 phase and the further transition to the monoclinic phase at higher temperatures.

The deposition parameters of reactive cathodic arc are correlated with processes at the surface of the composite Al–Cr targets and the nucleation and phase formation of the synthesized Al–Cr–O layers. The oxygen pressure and the pulsed operation of the arc current influence the formation of intermetallic phases and solid solutions at the target surface. The nucleation of the ternary oxide coatings at the substrate site appears to be, to some extent, controllable by the intermetallics or solid solutions formed at the target surface. A specific nucleation process at the substrate site can therefore be induced by the free choice of target composition in combination with the oxygen pressure and a pulsed arc operation. It also allows the control over the oxide island growth at the target surface which occurs occasionally at higher oxygen pressure. This hypothesis is supported by the X-ray diffraction analysis of the layers as well as of the target surface, and the layer analysis by cross-sectional scanning electron microscopy and Rutherford backscattering spectroscopy.

A process for the deposition of a solid layer onto a liquid is presented. The polymer poly-di-chloro-para-xylylene, also known as Parylene C, was grown on low vapour pressure liquids using the conventional low pressure chemical vapour deposition process. A reactor was built and a process developed to enable the deposition of Parylene C at atmospheric pressure over high vapour pressure liquids. It was used to deposit Parylene C over water among others. In all cases Parylene C encapsulated the liquid without influencing its initial shape. The results presented here show also that the Parylene C properties are not affected by its growth on liquid templates and the roughness of the Parylene C surface in contact with the liquid during the deposition is extremely low.

Al–Cr–O layers were synthesized by reactive cathodic arc evaporation utilizing DC as well as pulsed operation of the arc sources. The observed increase of the substrate ion current in the pulsed mode is attributed to the increased ionization of the oxygen reactive gas. The influence of the substrate ion current and the oxygen flow on the microstructure of the layers has been investigated. A strong influence of the oxygen gas flow on morphology and crystal structure has been observed. The increased substrate ion current in the pulsed mode has seemingly no influence on layer morphology at low bias voltages, but influences the nucleation behavior of the layer. The appearance of a multi-layer structure in the synthesized layers utilizing a single composite target has been ascribed to partial ion splitting of the target constituents in the curvilinear arc discharge.