Search

The Covid-19 pandemic is a major global crisis the impact of which is likely to exceed the upheavals caused by the last financial and economic crisis of 2008/2009. Germany as an export-oriented economy faces tremendous economic threats in the aftermath of the pandemic such as the collapse of global supply chains, the lockdown of economic sectors and impending job losses. As a reaction, the German government adopted, much as in the previous financial crisis, fiscal stimulus packages as part of a Keynesian-style public spending programme to stabilise its economy. Yet, in addition, the German government explicitly conceptualised its reactions as part of a 'Package for the Future' (Zukunftspaket), interlinking it with the second big global challenge: climate change and environmental degradation. We evaluate the German stimulus package on both these goals by comparing it with stimulus packages passed in other G20 countries. Based on a Qualitative Comparative Analysis (QCA) added by a case study of Germany, we identify the driving determinants behind the fiscal policy reactions with regard to the size of the stimulus package as well as its contribution to adopt long-term environmental transformations. [ABSTRACT FROM AUTHOR]

The article introduces the special issue on 'The First Year of the COVID-19 Pandemic in Germany'. Besides a brief description and analysis of COVID-19 management in Germany in the first year of the pandemic from an international comparative perspective, it provides insight into the question of how the COVID-19 Pandemic was analysed in political science research. Finally, it gives an overview of the contributions of the special issue that focus on three substantive themes: first, trust and support in politics in the wake of the COVID-19 crisis in Germany; second, impact of the pandemic on German parliaments, parties, and political leadership; and third, selected imminent and future consequences of COVID-19 for policies and policymaking in Germany. [ABSTRACT FROM AUTHOR]

Co-Zr amorphous alloys exhibit soft magnetic properties, whereas the Co-rich crystalline magnetic phases in this alloy system displayed a hard magnetic behavior. In this study, an initial two-phase Co-Zr composite with an overall composition of 75 at.% Co and 25 at.% Zr was processed by high-pressure torsion (HPT), and the effects of severe plastic deformation and subsequent thermal treatment on the composite's structural evolution and its magnetic properties were investigated. HPT processing allowed us to achieve an amorphous microstructure with low coercivity in its as-deformed state. To further tune the alloy's magnetic properties and study its crystallization behavior, various annealed states were investigated. The microstructural properties were correlated with the magnetic properties, and a decreasing coercivity with increasing annealing temperatures was observed despite the onset of crystallization in the amorphous alloy. At higher annealing temperatures, coercivity increased again. The results appear promising for obtaining tuneable rare-earth free magnetic materials by severe plastic deformation. [ABSTRACT FROM AUTHOR]

The suitability of refractory high entropy metal sublattice nitride (HEAN) thin films to act as diffusion barrier between Cu and Si was evaluated. For this purpose, bi-layers comprising a 150 nm thick Cu layer and a 20 nm thick layer based on (MoNbTaW)N and alloyed with either Ti, V, Cr, Mn, Zr or Hf have been deposited onto Si substrates using high power impulse magnetron sputtering. Subsequently, the bi-layers were annealed up to 950 °C in vacuum and analyzed by X-ray diffraction, confocal laser scanning microscopy and resistance measurements to check for barrier failure. Depending on the elements present in the HEAN layer, two failure modes were identified: (1) interdiffusion of Cu and Si leading to the formation of Cu 3 Si starting at 850 °C and (2) dewetting of the Cu layer starting at 900 °C. A better barrier performance could be correlated to a lower formation enthalpy of the binary nitride of metals present in the HEAN layer leading to the conclusion that more stable metal‑nitrogen bonds in the HEAN phase are beneficial for its diffusion barrier performance. • Diffusion barrier performance of refractory high entropy alloy nitride films assessed • Synthesis by high power impulse magnetron sputtering at room temperature • No barrier failure observed up to 800 °C for all films • Cu 3 Si formation at 850 °C and dewetting of Cu at 950 °C identified as failure modes [ABSTRACT FROM AUTHOR]

The changes of magnetic properties upon heat treatment of a metastable supersaturated solid solution processed by severe plastic deformation are investigated by in situ AC-hysteresis measurements. Data are analyzed in the framework of dynamic loss theory, with correlative investigations of the microstructural properties. The evolution of hysteresis upon annealing points out that the single-phase supersaturated solid solution remains stable up to 400° C, then hindering of domain wall motion sets in at this temperature. At 600° C, a multi phase microstructure is present, causing a significant increase in coercivity. [ABSTRACT FROM AUTHOR]

In the face of accelerating climate change, the transition towards a nonnuclear renewable energy system represents a key political challenge, which can be aggravated by the increasing energy supply uncertainty created by the shift away from fossil fuels. In this article, we conduct a comparison of the expansion of renewable energy sources in Austria, Belgium, and Germany at the level of their subnational units (federal states), thereby covering three economically very important central European federal European Union members. We consider potentially influential factors in a fuzzy-set qualitative comparative analysis: In addition to state-specific socioeconomic and geographical characteristics, political factors, such as parties in government, and specific energy-related policy instruments are included in the analysis. We find that a high potential for renewable electricity expansion in combination with low financial prosperity is most likely to lead to a successful expansion of renewable electricity production from wind and photovoltaics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Formation of ferromagnetic rare-earth free α-MnBi by applying severe plastic deformation using HPT and subsequent annealing. • Initial α-MnBi formation studied by in-situ HE-XRD annealing. • Enhanced α-MnBi formation by HPT-deformation and magnetic field assisted annealing. • Shear deformation induced magnetic anisotropy. Bulk composites using powder blends of Mn and Bi with equal atomic ratios are consolidated and severely deformed by high-pressure torsion (HPT). Subsequent annealing treatments lead to the formation of the ferromagnetic and rare-earth free hard magnetic α-MnBi phase. The initial phase formation is studied by in-situ high-energy XRD annealing experiments showing a beneficial influence of HPT-deformation on the amount of α-MnBi. The nucleation sites are strongly increased, thus the volumetric α-MnBi phase content exceeds 50 vol%. A lower HPT-pressure of 2 GPa is found to be preferred over 5 GPa to obtain high α-MnBi contents. Annealing is done with or without applying an external magnetic field. Additionally, influences of the HPT-induced shear deformation are discussed and correlated with preferred diffusion path ways fostering the formation of anisotropic α-MnBi phase. [ABSTRACT FROM AUTHOR]

The fracture behaviour of pure, ultrafine grained 100 μm tungsten foil was investigated as a function of testing direction and temperature in the range from −196 °C to 800 °C. To study the influence of the anisotropic microstructure on the fracture process, the single-edge-notched specimens were extracted in three different crack orientations relative to the rolling direction. This thorough investigation shows the positive impact of deformation induced grain refinement through extraordinary values of fracture toughness and a reduction of the ductile-to-brittle transition temperature to about room temperature. Furthermore, it was demonstrated that the grain shape anisotropy and a strong rotated cubic texture are decisive factors for anisotropic fracture properties. Fracture surface investigations reveal distinctive behaviour with an increase in temperature. The pronounced transition in failure mode was observed going from brittle, transcrystalline fracture at −196 °C towards pronounced delamination at intermediate temperatures and to ductile failure at highest temperatures. The measurement of the crack tip opening displacement for specimen fracturing in a completely ductile manner enables the determination of more accurate fracture toughness in the elastic plastic regime. [ABSTRACT FROM AUTHOR]

Combinatorial magnetron co-sputtering from elemental sources was applied to produce W-alloy thin film composition spread materials libraries with well-defined, continuous composition gradients (film thicknesses between 1 and 2.5 μm). Three systems were studied: W-Fe (0–7 at.%), W-Ti (0–15 at.%) and W-Ir (0–12 at.%). High-throughput characterization of the materials libraries comprised of chemical, morphological and microstructural analyses. Scanning electron microscope investigations revealed that the films have a columnar structure of inverted cone-like units separated by voided boundaries, with a strong correlation to the alloying element content. Significant morphological changes occurred with an increase in the amount of the added element; W films with lower at.% of the alloying element had higher density and tighter grain boundaries, altering towards an increased amount of voids as the concentration of the alloying element increased. Electron backscatter diffraction scanning was used to determine microstructural components (grain size, grain shape, texture evolution), in dependence on the concentration of the alloying element. [ABSTRACT FROM AUTHOR]

Rapid progress in the reduction of substrate thickness for silicon-based microelectronics leads to a significant reduction of the device bending stiffness and the need to address its implication for the thermo-mechanical fatigue behavior of metallization layers. Results on 5 μm thick Cu films reveal a strong substrate thickness-dependent microstructural evolution. Substrates with hs = 323 and 220 µm showed that the Cu microstructure exhibits accelerated grain growth and surface roughening. Moreover, curvature-strain data indicates that Stoney's simplified curvature-stress relation is not valid for thin substrates with regard to the expected strains, but can be addressed using more sophisticated plate bending theories. [ABSTRACT FROM AUTHOR]

Fatigue is an important reliability issue for microelectronics. In this work, a technique for fast thermal cycling of thin films on substrates is introduced using an infrared laser beam. The advantages of this method are the significantly increased heating and cooling rates compared to conventional slow furnace processes, and the use of readily available small pieces of metallized wafers, which avoid complicated sample preparation. To demonstrate the applicability of the new experimental setup two copper metallization films, differing in their content of additives used for film deposition, on silicon substrates were investigated with respect to microstructural, topographical and electrical changes due to pulsed thermo-mechanical loading. The results, such as grain growth and roughness evolution, are compared to results from specimens which experienced slow infrared furnace cycling. Furthermore, changes in electrical sheet resistance are shown. When analyzing the outcomes from processes of different heating/cooling rates, it can be stated that accelerated laser heating leads to faster changes in these properties which enables fast screening of metallization materials under development. [ABSTRACT FROM AUTHOR]

Here we show that cold-rolling of tungsten (W) decreases the stable crack growth onset temperature. Furthermore, we show that stable crack growth is accompanied by crack bridging, which in turn is triggered by dislocation activity. The entire stable crack growth regime shows ductile intergranular fracture. Our ductilisation approach is the modification of microstructure through cold-rolling. In this work, we assess two different microstructures obtained from (i) cold-rolled and (ii) severely cold-rolled tungsten plates. From these plates, single-edge cracked-plate tension (SECT) specimens were cut and tested in the L-T direction. Crack growth resistance (R) curves were obtained using the direct-current-potential-drop method (DCPM). The experiments show the following results: cold-rolled plates are brittle at room temperature (RT), but show stable crack growth at 250 °C (523 K) and a fracture toughness, K IQ , of about 100 MPa(m) 1/2 at a crack extension, Δa, of 0.6 mm. Severely cold-rolled tungsten plates show stable crack growth at RT and a fracture toughness, K IQ , of 100 MPa(m) 1/2 at a crack extension, Δa, of 0.3 mm. Scanning electron microscopy (SEM) analyses of the stable crack growth region show intergranular fracture with microductile character. The question of why cold-rolling causes the stable crack growth onset temperature to decrease (or in other words, why cold-rolling causes the brittle-to-ductile transition (BDT) temperature to decrease) is discussed against the background of (i) intrinsic and extrinsic size effects, (ii) crystallographic texture, (iii) impurities and (iv) the role of dislocations. Our results suggest that the spacing between the dislocation nucleation sites (high angle grain boundaries (HAGBs) act as dislocation source) is the most important parameter responsible for the decrease of the stable crack growth onset temperature. [ABSTRACT FROM AUTHOR]

In this study, two different electrodeposited 5 μm thick copper films were subjected to thermal cycling. The microstructural evolution of both films was studied with a site specific tracking technique. It was observed that the initially similar microstructures develop differently upon cycling with respect to grain size and texture. In detail, a Cu film which contains residual inorganic species from the organic additives used during Cu plating, in the ppm regime, showed a constrained surface roughness evolution and marginal grain growth coupled with a stable twin boundary network. Furthermore, voiding in the film interior was observed. In comparison, a high-purity Cu film exhibited strong surface roughening in conjunction with pronounced grain growth promoted by twin boundary migration. Moreover, the film showed a (100) texture intensity increase as a result of strain energy minimization upon cycling and no void formation. These observations underline the influence of film processing related impurities on the thermo-mechanical behaviour of Cu thin films. [ABSTRACT FROM AUTHOR]

The paper describes the capability of magnetic softening of a coarse-grained bulk material by a severe deformation technique. Connecting the microstructure with magnetic properties, the coercive field decreases dramatically for grains smaller than the magnetic exchange length. This makes the investigation of soft magnetic properties of severely drawn pearlitic wires very interesting. With the help of the starting two-phase microstructure, it is possible to substantially refine the material, which allows the investigation of magnetic properties for nanocrystalline bulk material. Compared to the coarse-grained initial, pearlitic state, the coercivities of the highly deformed wires decrease while the saturation magnetization values increase—even beyond the value expectable from the individual constituents. The lowest coercivity in the drawn state is found to be 520 A m−1 for a wire of 24-µm thickness and an annealing treatment has a further positive effect on it. The decreasing coercivity is discussed in the framework of two opposing models: grain refinement on the one hand and dissolution of cementite on the other hand. Auxiliary measurements give a clear indication for the latter model, delivering a sufficient description of the observed evolution of magnetic properties. [ABSTRACT FROM AUTHOR]

Considering the ecological sustainability performance of different political regimes, it seems questionable whether the assumption of the general superiority of democracy can be maintained in this policy field. This paper compares the performance of democracies and autocracies (and their institutional subtypes) with regard to weak and strong ecological sustainability targets, on the one hand, while also analysing the impact of democracy and autocracy on different areas of ecological sustainability, on the other. This will be verified by quantitative analysis to measure the influence of regime type on ecological sustainability performance, as opposed to the effect of other possible explanatory factors. [ABSTRACT FROM AUTHOR]

Authoritarianism research has evolved into one of the fastest growing areas in comparative politics and political economy. However, the newly awakened interest in autocratic regimes goes hand in hand with a lack of systematic research on the results of the political and substantive policy performance of variants of autocratic regimes. In this article we introduce the individual contributions to this special issue and summarize their findings with regard to three core research questions: What are the differences between autocracies and democracies, as well as between different forms of authoritarian regimes, with regard to their outcome performance in selected policy fields? Does policy performance matter for the persistence of authoritarian rule? How can we conceptualize different types of autocratic regimes and do differences in the availability of performance data matter for the results of empirical studies comparing democracies and autocracies or different types of non-democratic regimes? [ABSTRACT FROM AUTHOR]

Technologies based on artificial intelligence (AI) represent a crucial governance challenge for policymakers. This study contributes to the understanding of how states plan to govern AI with respect to the role they assume and to the way they develop AI in a responsible manner. In different policy instruments across 22 countries plus the European Union, there is considerable variation in how governments approach the governance of AI, both regarding the policy measures proposed and their focus on public responsibility. Analysing a set of policy instruments we find multiple modes of AI governance, with the major difference being between self-regulation-promoting and market-based approaches, and a combination of entrepreneurial and regulatory governance approaches. Our analysis also indicates that the approach to public responsibility is largely independent of the chosen policy mix of AI governance. Therefore, responsibility seems to be a cross-cutting issue that cannot be tied to a specific approach of states towards technology. [ABSTRACT FROM AUTHOR]

Fracture experiments using micrometer-sized notched cantilevers were conducted to investigate the possibility of determining fracture mechanical parameters for the semi-brittle material tungsten. The experiments were also used to improve the understanding of semi-brittle fracture processes for which single crystalline tungsten serves as a model material. Due to the large plastic zone in relation to the micrometer sample size, linear elastic fracture mechanics is inapplicable and elastic-plastic fracture mechanics has to be applied. Conditional fracture toughness values J Q were calculated from corrected force vs. displacement diagrams. Crack growth was accessible by direct observation of in-situ experiments as well as with the help of unloading compliances. As a further tool, fracture toughness can be determined via crack tip opening displacement. The micro samples behave more ductile and exhibit higher fracture toughness values compared to macro-sized single crystals and fail by stable crack propagation. [ABSTRACT FROM PUBLISHER]

Abstract: Dislocation structure and slip plane are two key elements to understanding the basic mechanism of plastic deformation in metal alloys. Using density-functional theory (DFT), we investigate the influence of Ta and Re on the non-planar screw dislocation in body-centered cubic W. The dislocation-core structure is modeled by the dislocation–dipole approach, and the effect of alloying is determined from the virtual-crystal approximation as well as the supercell method. Both reveal symmetric core structures for W–Ta alloys but asymmetric ones for W–Re. Our ab initio results allow for an evaluation of the inter-row model, which is found to produce dislocation-core structures consistent with DFT results, but fails to describe the dislocation movement in these alloys. DFT finds the slip plane to be altered by Re alloying. This result is confirmed by microcantilever bending tests. [Copyright &y& Elsevier]

Abstract: The influence of both microstructure and chemical composition on the fracture behaviour of tungsten–tantalum, tungsten–vanadium composites and alloys of varying chemical compositions are investigated. Industrial solid solution tungsten–tantalum alloys with different tantalum contents in the as-forged condition are investigated along with different tungsten–tantalum and tungsten–vanadium composites and alloys made by powder consolidation, severe plastic deformation using high pressure torsion and different subsequent heat treatments. To investigate the fracture behaviour, several crack propagation directions in relation to the forging direction and shear direction, respectively, are taken into account. Heat treatment of the composite material results in a more homogeneous distribution of the alloying element and the impacts of these specific heat treatments on microstructure and fracture toughness are discussed. The fracture experiments are performed within a temperature range from room temperature to 600°C and reveal a strong dependence of the fracture toughness and fracture morphology on temperature and on the microstructure, and hence the processing history of the materials. [Copyright &y& Elsevier]

Abstract: A big problem when using tungsten as plasma facing components in a future fusion reactor is the very low fracture toughness at low temperatures. Tungsten–rhenium alloys outclasses other tungsten-based materials in terms of increased ductility. We study the reason for this positive effect by investigating the influence of rhenium on the fracture process of tungsten–rhenium alloys at different temperatures (between room temperature and 900°C). The experiments are performed in a furnace-equipped tensile testing machine with a vacuum chamber, which allows us to perform fracture experiments at elevated temperature without oxidizing the material. Antecedent and subsequent electron backscattered diffraction scans are used to analyse the extent of plastic deformation and the interaction of plastic deformation and the fracture process. Furthermore, the consequences of recrystallization on the fracture process of tungsten–rhenium alloys will be analysed. [Copyright &y& Elsevier]

Abstract: Particle irradiation has a pronounced influence on the mechanical and thermal properties of materials, largely due to the generation of point defects. Owing to their large free surface to volume ratio, nanostructured metals show improved irradiation resistance. This nanostructuring can negatively impact the creep resistance of these materials, but by introducing fine precipitates this effect can be balanced. [Copyright &y& Elsevier]

• enhanced effective saturation magnetostriction in FeCr alloys. • formation of supersaturated solid solution by high pressure torsion probed by magnetostriction. • remarkable thermal stability of FeCr alloys up to 520 °C. This work gives insights into processing and characterisation of bulk nanocrystalline FeCr materials. The investigated FeCr alloys, consisting of 30, 50 and 70 at.% ferromagnetic Fe and remaining anti-ferromagnetic Cr, are processed by arc melting and subsequent severe plastic deformation by high pressure torsion. The physical similarities between elemental Fe and Cr in combination with the nanocrystalline structure of the as-deformed alloys, necessitates advanced characterisation techniques for the as-deformed state: In-situ annealing synchrotron X-ray diffraction measurements as well as electron microscopy experiments are linked to magnetostrictive measurements and reveal a single phase microstructure. Surprisingly, the nanocrystalline FeCr alloys remain supersaturated solid solutions upon annealing above 500 °C, meaning a decomposition in a FeCr nanocomposite is suppressed. For the chosen annealing conditions grain growth is faster than decomposition and enhanced magnetostrictive values are found compared to materials in the as-deformed state. [ABSTRACT FROM AUTHOR]

Exchange-coupling between soft- and hard-magnetic phases plays an important role in the engineering of novel magnetic materials. To achieve exchange coupling, a two-phase microstructure is necessary. This interface effect is further enhanced if both phase dimensions are reduced to the nanometer scale. At the same time, it is challenging to obtain large sample dimensions. In this study, powder blends and ball-milled powder blends of Fe-SmCo5 are consolidated and are deformed by high-pressure torsion (HPT), as this technique allows us to produce bulk magnetic materials of reasonable sizes. Additionally, the effect of severe deformation by ball-milling and severe plastic deformation by HPT on exchange coupling in Fe-SmCo5 composites is investigated. Due to the applied shear deformation, it is possible to obtain a texture in both phases, resulting in an anisotropic magnetic behavior and an improved magnetic performance. [ABSTRACT FROM AUTHOR]

• Detailed parameter variation during sputter deposition of MoNbTaWZr films. • Influence of duty cycle, Ar pressure and pulse frequency analyzed and discussed. • Parameters enabling high energetic growth conditions lead to amorphous microstructure. • Films deposited with low energetic growth conditions have a crystalline bcc structure. • Impact of microstructure and morphology on electrical resistivity discussed. Within this study a series of MoNbTaWZr thin films were synthesized using high power impulse magnetron sputtering (HiPIMS) with varying the deposition parameters: duty cycle from 0.5 to 100 % (i.e. DC magnetron sputtering (DCMS)), Ar pressure from 0.5 to 3 Pa and pulse frequency from 25 to 200 Hz. The structure of the deposited films was analyzed by X-ray diffraction and scanning and transmission electron microscopy. In addition, the electrical resistivity and the residual stress of the films was determined. The influence of the deposition parameter variation on structure and properties of the MoNbTaWZr films is discussed on the established framework of film growth conditions achievable with HiPIMS and DCMS and how they can be influenced by adapting the deposition parameters. The performed work is intended to contribute to a comprehensive understanding about synthesis-structure-property relations for refractory high entropy alloy thin films while using MoNbTaWZr films as a model system. [ABSTRACT FROM AUTHOR]

The article addresses the question of how successful the European natural gas reforms of 1998, 2003, and 2009 have been in terms of increasing competition in the sector. We argue that regulatory provisions are policy output variables, which as such do not affect competition directly. However, successful reforms can have an impact on the market structure, which might lead to increased competition and price reductions. Thus, it is pivotal to differentiate between policy output and outcome variables. Therefore, we first conduct a cross-sectional analysis of the regulatory impact on the market structure. Second, we apply error-correction models to test whether changes in the market structure affected the price development. Our findings suggest that the market reforms were successful in terms of liberalizing the sector, whereas the market structure did not affect the natural gas prices. Thus, we see a “successful failure” of the European natural gas market reforms. [ABSTRACT FROM AUTHOR]

Mixtures of Fe and Cu powders are cold-compacted and subsequently deformed with severe plastic deformation by high-pressure torsion, leading to bulk samples. The dilution of Fe in the Cu matrix is investigated with SQUID-magnetometry, whereas the magnetic properties change as a function of Fe-content from a frustrated regime to a thermal activated behaviour. The magnetic properties are correlated with the microstructure, investigated by synchrotron X-ray diffraction and atom probe tomography. Annealing of the as-deformed states leads to demixing and grain growth, with the coercivity as a function of annealing temperature obeying the random anisotropy model. The presented results show that high-pressure torsion is a technique capable to affect the microstructure even on atomic length scales. [ABSTRACT FROM AUTHOR]

High entropy alloy (HEA) thin films are potential candidates to act as diffusion barrier between Cu and Si in microelectronics. To evaluate the suitability of refractory HEAs, six different HEA thin films based on the MoNbTaW system and alloyed with Ti, V, Cr, Mn, Zr or Hf have been deposited by high power impulse magnetron sputtering with a thickness of 20 nm on Si substrates. The bi-layer architecture was completed by a 150 nm thick top-layer of Cu. The microstructure of the bi-layers before and after annealing in vacuum up to 800 °C was investigated by X-ray diffraction to observe possible phase changes or formations. In addition, resistance measurements and confocal laser scanning microscopy were employed to check for potential barrier failure. The lowest onset temperature for barrier failure of 600 °C was found for MoNbTaWZr, whereas the highest of 700 °C was observed for CrMoNbTaW. The obtained results for the failure temperature are discussed in terms of microstructure, strain and cohesive energy of the HEA films as well as the enthalpy of mixing between the elements in the HEA and Cu. A direct correlation between the mixing enthalpy of the fifth alloying element with Cu and the barrier failure temperature was observed. [Display omitted] • Suitability of refractory high entropy alloys as diffusion barriers. • Synthesis by high power impulse magnetron sputtering. • Best barrier performance for CrMoNbTaW with failure temperature at 750 °C • No correlation between film microstructure and diffusion barrier performance. • Mixing enthalpy of elements in HEA with Cu plays decisive role. [ABSTRACT FROM AUTHOR]

Metallic nanoparticles are widely explored for boosting light-matter coupling, optoelectronic response, and improving photocatalytic performance of two-dimensional (2D) materials. However, the target area is restricted to either top or bottom of the 2D flakes. Here, we introduce an approach for edge-specific nanoparticle decoration via light-assisted reduction of silver ions and merging of silver seeds. We observe arrays of the self-limited in size silver nanoparticles along tungsten diselenide WSe2 nanoribbon edges. The density of nanoparticles is tunable by adjusting the laser fluence. Scanning electron microscopy, atomic force microscopy, and Raman spectroscopy are used to investigate the size, distribution, and photo-response of the deposited plasmonic nanoparticles on the quasi-one-dimensional nanoribbons. We report an on-surface synthesis path for creating mixed-dimensional heterostructures and heterojunctions with potential applications in opto-electronics, plasmonics, and catalysis, offering improved light matter coupling, optoelectronics response, and photocatalytic performance of 2D materials. Metallic nanoparticles are widely explored for boosting light-matter coupling of 2D materials, however, the target area for nanoparticle deposition is typically restricted to either the top or the bottom of 2D flakes. Here, the authors show tunable, edge-specific nanoparticle decoration using a laser, achieving arrays of silver nanoparticles that are self-limited in size along tungsten diselenide nanoribbon edges. [ABSTRACT FROM AUTHOR]

The inherent brittleness of the refractory metal tungsten represents a major challenge for its application as divertor material in future nuclear fusion reactors. Grain refinement to the ultrafine-grained regime is a promising strategy to increase the fracture toughness of W, but it also promotes intercrystalline crack growth. Therefore, the strengthening of grain boundary cohesion in W is of great importance. In this work, grain boundary doping with B and Hf, two elements that were identified in previous work to increase bending strength and ductility, is applied to ultrafine-grained W. The fracture toughness is measured utilizing small-scale testing techniques. Fracture mechanical experiments on the microscale provide a plethora of challenges to correctly assess size-independent toughness values, which are presented and discussed within this work. It was found that the toughness of W can be under- and overestimated, depending on the sample dimensions and plastic zone size. When assessing the valid and size-independent fracture toughness measured for the differently doped W specimen, doping with the strengthening element B maintained the already remarkably high toughness of the undoped ultrafine-grained W of around 20 MPa√m. The samples doped with Hf even improved the fracture toughness to values of up to 27 MPa√m. Hence, the effects of GB doping on the fracture toughness of ultrafine-grained W are explored, while simultaneously the influence of sample dimensions on measured fracture toughness is discussed. These insights are expected to have a great impact on the development of superior materials for use in harsh environments, as well as the application of small-scale fracture mechanical experiments, as used, for example, in the assessment of control samples in nuclear technology. [Display omitted] [ABSTRACT FROM AUTHOR]

Tungsten, while showing many favorable properties, faces challenges in high-performance applications due to its brittle nature. One strategy to improve strength and toughness in tungsten is to refine the grain size down to the ultra-fine grained (ufg) regime. However, as the grain size is reduced, the fraction of grain boundaries that provide easy paths for crack growth increases, thereby limiting the gain in ductility. Therefore, strengthening the grain boundaries is of great importance if one wants to tap the full potential of this material. Using ab-initio calculations, potential grain boundary cohesion enhancing doping elements were identified, and doped ultra-fine grained tungsten samples were fabricated from powders and characterized extensively using small-scale testing techniques. We found that additions of boron and hafnium improve the mechanical properties of tungsten remarkably. Furthermore, an additional low-temperature heat treatment of the boron-doped sample promotes grain boundary segregation, enhancing the properties even further. Thus, in this work we provide an effective pathway of improving mechanical properties in ultra-fine grained tungsten using grain boundary segregation engineering. This opens the door for many challenging applications of ufg W in harsh environments. To further underline the potential employment of ufg W in nuclear fusion reactors, a favorable swelling behavior and mechanical property response after irradiation with helium is presented within this work. • A powder-based fabrication route of ultrafine-grained W utilizing severe plastic deformation is presented. • Strength and ductility of ultrafine-grained W are improved by increasing grain boundary cohesion via doping with B and Hf. • Annealing leads to hardening-by-annealing effects and increased dopant segregation, improving strength even further. • Ultrafine-grained W is resistant to blister formation and pronounced swelling after irradiation with He ions. • Helium bubble softening & radiation hardening effects compete and result in a retained hardness after irradiation with He. [ABSTRACT FROM AUTHOR]

The focused ion beam technique has become a standard tool for micro-mechanical sample preparation in the last decade due to its high precision and general applicability in material removal. Besides disadvantages such as possible ion damage and high operation costs especially the characteristically small removal rates represent a bottleneck for this application. In contrast, femtosecond lasers provide material removal rates orders of magnitude higher, with small or ideally without thermal impact on the surrounding material. Hence, a combination of these two methods offers an ideal tool for time-efficient, micrometer-sized sample preparation. A prototype implementing this idea is presented here in combination with a case study. Cantilevers with a length of several hundred micrometers were machined into 25 μ m, 50 μ m and 100 μ m thick, cold rolled tungsten foils. Scanning electron microscopy analyses reveal the influence of laser parameters and different scanning routines on the resulting sample quality and the effect of the laser pulse length (femtoseconds versus nanoseconds) on the ultra-fine grained microstructure. Finally, the performance for unprecedented rapid sample preparation is demonstrated with a sample array consisting of 100 cantilevers with a dimension of 420 ×60 ×25 μ m 3 processed in only half an hour, opening completely new testing possibilities. [ABSTRACT FROM AUTHOR]

The effect of residual inorganic elements on the local plastic deformation behaviour of two different copper films was investigated. It was found that a film containing inorganic elements in the ppm range, has a distinctively higher hardness at twin boundaries and high angle grain boundaries compared to the grain interior. An almost pure copper film shows no distinct difference regarding the plastic deformation compared to the same microstructural features. The results suggest that such residual elements form hard boundaries, leading to higher hardness on a local microstructural level. Moreover, the influence of the local topography was demonstrated. The use of atomic force microscopy before and after indentation illustrated that significant errors in the determination of hardness occurs when the local surface topography matches the dimensions of the indenter tip. This was further confirmed by the quantitative comparison of the elastic properties of the loading and unloading segments of the corresponding load-depth curves using Hertzian contact mechanics and the Oliver-Pharr method. It is demonstrated that the measured hardness values can be directly correlated to local microstructural and topographical features. [ABSTRACT FROM AUTHOR]

Ferromagnetic (Fe or Fe20Ni80) and antiferromagnetic (NiO) phases were deformed by high-pressure torsion, a severe plastic deformation technique, to manufacture bulk-sized nanocomposites and demonstrate an exchange bias, which has been reported predominantly for bilayer thin films. High-pressure torsion deformation at elevated temperatures proved to be the key to obtaining homogeneous bulk nanocomposites. X-ray diffraction investigations detected nanocrystallinity of the ferromagnetic and antiferromagnetic phases. Furthermore, an additional phase was identified by X-ray diffraction, which formed during deformation at elevated temperatures through the reduction of NiO by Fe. Depending on the initial powder composition of Fe50NiO50 or Fe10Ni40NiO50 the new phase was magnetite or maghemite, respectively. Magnetometry measurements demonstrated an exchange bias in high-pressure torsion-processed bulk nanocomposites. Additionally, the tailoring of magnetic parameters was demonstrated by the application of different strains or post-process annealing. A correlation between the amount of applied strain and exchange bias was found. The increase of exchange bias through applied strain was related to the microstructural refinement of the nanocomposite. The nanocrystalline maghemite was considered to have a crucial impact on the observed changes of exchange bias through applied strain. [ABSTRACT FROM AUTHOR]

• Liver SBRT. • Active motion management. • Deep inspiration breath hold. • Robotic tracking. Local treatment of metastases in combination with systemic therapy can prolong survival of oligo-metastasized patients. To fully exploit this potential, safe and effective treatments are needed to ensure long-term metastases control. Stereotactic body radiotherapy (SBRT) is one means, however, for moving liver tumors correct delivery of high doses is challenging. After validating equal in-vivo treatment accuracy, we analyzed a pooled multi-platform liver-SBRT-database for clinical outcome. Local control (LC), progression-free interval (PFI), overall survival (OS), predictive factors and toxicity was evaluated in 135 patients with 227 metastases treated by gantry-based SBRT (deep-inspiratory breath-hold-gating; n = 71) and robotic-based SBRT (fiducial-tracking, n = 156) with mean gross tumor volume biological effective dose (GTV-BED α/β=10Gy) of 146.6 Gy 10. One-, and five-year LC was 90% and 68.7%, respectively. On multivariate analysis, LC was significantly predicted by colorectal histology (p = 0.006). Median OS was 20 months with one- and two-year OS of 67% and 37%. On multivariate analysis, ECOG-status (p = 0.003), simultaneous chemotherapy (p = 0.003), time from metastasis detection to SBRT-treatment (≥2months; p = 0.021) and LC of the treated metastases (≥12 months, p < 0.009) were significant predictors for OS. One- and two-year PFI were 30.5% and 14%. Acute toxicity was mild and rare (14.4% grade I, 2.3% grade II, 0.6% grade III). Chronic °III/IV toxicities occurred in 1.1%. Patient selection, time to treatment and sufficient doses are essential to achieve optimal outcome for SBRT with active motion compensation. Local control appears favorable compared to historical control. Long-term LC of the treated lesions was associated with longer overall survival. [ABSTRACT FROM AUTHOR]

The present work provides an analytic solution for the stiffness to crack length relation in microscopic cantilever shaped fracture specimens based on classical beam theory and substitution of the crack by a virtual rotational spring element. The resulting compact relationship allows for accounting of the actual beam geometry and agrees very well with accompanying finite element simulations. Compared with the only other model present in literature the proposed relationship reduces the deviation between model and data to a maximum of 1.6% from the previous minimum of 15%. Thus, the novel solution will help to reduce the necessity for individual simulations and aim to increase the comparability of elastic-plastic microcantilever fracture experiments in the future. [ABSTRACT FROM AUTHOR]

The capability of high-pressure torsion on the preparation of supersaturated solid solutions, consisting of Cu-14Fe (wt.%), is studied. From microstructural investigations a steady state is obtained with nanocrystalline grains. The as-deformed state is analyzed with atom probe tomography, revealing an enhanced solubility and the presence of Fe-rich particles. The DC-hysteresis loop shows suppressed long range interactions in the as-deformed state and evolves towards a typical bulk hysteresis loop when annealed at 500∘ C. AC-susceptometry measurements of the as-deformed state reveal the presence of a superparamagnetic blocking peak, as well as a magnetic frustrated phase, whereas the transition of the latter follows the Almeida-Thouless line, coinciding with the microstructural investigations by atom probe tomography. AC-susceptometry shows that the frustrated state vanishes for annealing at 250∘ C. [ABSTRACT FROM AUTHOR]

Highlights • First-time presentation of a method for in-vivo -accuracy analysis of dose-delivery with active motion-management (gating/tracking), which can serve as a benchmarking-tool for other treatment techniques. • IVA is based on registration of post-radiotherapeutic MRI-morphologic-alterations to the corresponding isodose-structures of gantry-based/robotic SBRT-plans and structure analysis regarding volumes, surface-distance, conformity metrics and center-of-mass-differences. • Liver-SBRT with active motion-management has shown median deviations <5 mm of planned dose and MR-morphologic alterations. Abstract Background/purpose In-vivo -accuracy analysis (IVA) of dose-delivery with active motion-management (gating/tracking) was performed based on registration of post-radiotherapeutic MRI-morphologic-alterations (MMA) to the corresponding dose-distributions of gantry-based/robotic SBRT-plans. Methods Forty targets in two patient cohorts were evaluated: (1) gantry-based SBRT (deep-inspiratory breath-hold-gating; GS) and (2) robotic SBRT (online fiducial-tracking; RS). The planning-CT was deformably registered to the first post-treatment contrast-enhanced T1-weighted MRI. An isodose-structure cropped to the liver (ISL) and corresponding to the contoured MMA was created. Structure and statistical analysis regarding volumes, surface-distance, conformity metrics and center-of-mass-differences (CoMD) was performed. Results Liver volume-reduction was −43.1 ± 148.2 cc post-RS and −55.8 ± 174.3 cc post-GS. The mean surface-distance between MMA and ISL was 2.3 ± 0.8 mm (RS) and 2.8 ± 1.1 mm (GS). ISL and MMA volumes diverged by 5.1 ± 23.3 cc (RS) and 16.5 ± 34.1 cc (GS); the median conformity index of both structures was 0.83 (RS) and 0.80 (GS). The average relative directional errors were ≤0.7 mm (RS) and ≤0.3 mm (GS); the median absolute 3D-CoMD was 3.8 mm (RS) and 4.2 mm (GS) without statistically significant differences between the two techniques. Factors influencing the IVA included GTV and PTV (p = 0.041 and p = 0.020). Four local relapses occurred without correlation to IVA. Conclusions For the first time a method for IVA was presented, which can serve as a benchmarking-tool for other treatment techniques. Both techniques have shown median deviations <5 mm of planned dose and MMA. However, IVA also revealed treatments with errors ≥5 mm, suggesting a necessity for patient-specific safety-margins. Nevertheless, the treatment accuracy of well-performed active motion-compensated liver SBRT seems not to be a driving factor for local treatment failure. [ABSTRACT FROM AUTHOR]

We address the impact of tantalum alloying on dislocation properties of tungsten. To that aim, we calculate elastic constants, atomic-row displacement energy, dislocation core energy, and Peierls stress for different degrees of alloying within the framework of density-functional theory. We show that the elastic shear constants decrease monotonously with Ta content. Conversely, atomic-row displacement energy and, consequently, core energy and Peierls stress show a nonmonotonous behavior. These quantities peak at 25 at% Ta, indicating a tendency for embrittlement of W at such alloying concentrations. Our findings are in agreement with the experimental literature. [ABSTRACT FROM AUTHOR]

Purpose: Although the metric precision of robotic stereotactic body radiation therapy in the presence of breathing motion is widely known, we investigated the dosimetric implications of breathing phase-related residual tracking errors.Methods and Materials: In 24 patients (28 liver metastases) treated with the CyberKnife, we recorded the residual correlation, prediction, and rotational tracking errors from 90 fractions and binned them into 10 breathing phases. The average breathing phase errors were used to shift and rotate the clinical tumor volume (CTV) and planning target volume (PTV) for each phase to calculate a pseudo 4-dimensional error dose distribution for comparison with the original planned dose distribution.Results: The median systematic directional correlation, prediction, and absolute aggregate rotation errors were 0.3 mm (range, 0.1-1.3 mm), 0.01 mm (range, 0.00-0.05 mm), and 1.5° (range, 0.4°-2.7°), respectively. Dosimetrically, 44%, 81%, and 92% of all voxels differed by less than 1%, 3%, and 5% of the planned local dose, respectively. The median coverage reduction for the PTV was 1.1% (range in coverage difference, -7.8% to +0.8%), significantly depending on correlation (P=.026) and rotational (P=.005) error. With a 3-mm PTV margin, the median coverage change for the CTV was 0.0% (range, -1.0% to +5.4%), not significantly depending on any investigated parameter. In 42% of patients, the 3-mm margin did not fully compensate for the residual tracking errors, resulting in a CTV coverage reduction of 0.1% to 1.0%.Conclusions: For liver tumors treated with robotic stereotactic body radiation therapy, a safety margin of 3 mm is not always sufficient to cover all residual tracking errors. Dosimetrically, this translates into only small CTV coverage reductions. [ABSTRACT FROM AUTHOR]

Background: We retrospectively evaluated the efficacy and toxicity of gross tumor volume (GTV) mean-dose-optimized and real-time motion-compensated robotic stereotactic body radiation therapy (SBRT) in the treatment of liver metastases.Methods: Between March 2011 and July 2015, 52 patients were treated with SBRT for a total of 91 liver metastases (one to four metastases per patient) with a median GTV volume of 12 cc (min 1 cc, max 372 cc). The optimization of mean GTV dose was prioritized during treatment planning at the potential cost of planning target volume (PTV) coverage reduction while adhering to safe normal tissue constraints. The delivered median GTV biological effective dose (BED10) was 142.1 Gy10 (range, 60.2 Gy10 -165.3 Gy10) and the prescribed PTV BED10 ranged from 40.6 Gy10 to 112.5 Gy10 (median, 86.1 Gy10). We analyzed local control (LC), progression-free interval (PFI), overall survival (OS), and toxicity.Results: Median follow-up was 17 months (range, 2-49 months). The 2-year actuarial LC, PFI, and OS rates were 82.1, 17.7, and 45.0 %, and the median PFI and OS were 9 and 23 months, respectively. In univariate analysis histology (p < 0.001), PTV prescription BED10 (HR 0.95, CI 0.91-0.98, p = 0.002) and GTV mean BED10 (HR 0.975, CI 0.954-0.996, p = 0.011) were predictive for LC. Multivariate analysis showed that only extrahepatic disease status at time of treatment was a significant factor (p = 0.033 and p = 0.009, respectively) for PFI and OS. Acute nausea or fatigue grade 1 was observed in 24.1 % of the patients and only 1 patient (1.9 %) had a side effect of grade ≥ 2.Conclusions: Robotic real-time motion-compensated SBRT is a safe and effective treatment for one to four liver metastases. Reducing the PTV prescription dose and keeping a high mean GTV dose allowed the reduction of toxicity while maintaining a high local control probability for the treated lesions. [ABSTRACT FROM AUTHOR]

Tungsten is, due to a combination of high strength and good physical properties, frequently considered for high-performance applications in the harshest environments. Oftentimes its inherent brittleness and low ductility stand in the way of a successful deployment in these fields. Since tungsten has been proposed as divertor material for nuclear fusion reactors, an improvement of ductility and fracture toughness is essential. An obvious first step to increase these properties is to reduce the grain size to the ultrafine-grained regime. As this still leaves the material with a relatively low-energy intercrystalline fracture mode, this work takes a step further. With the help of doping elements, which are identified from ab-initio simulations, an attempt to increase grain boundary cohesion of ultra-fine grained tungsten to improve ductility is made. After fabrication of the doped samples from powders using severe plastic deformation, thorough microstructural investigations and extensive mechanical characterization, utilizing various small-scale testing techniques, are combined to assess the properties of the materials. We report that the addition of boron and hafnium can significantly increase the bending strength and bending ductility of ultra-fine grained tungsten. An additional heat treatment of the boron doped sample amplifies this effect even further, drastically increasing the strength and overall mechanical properties due to a combination of hardening-by-annealing and increased grain boundary segregation. Thus, an effective way to adaptively improve the mechanical properties of tungsten by manipulating grain boundary chemistry is reported, validating grain boundary segregation engineering as a powerful tool for enhancing damage tolerance in brittle materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• Oxide evolution in severely deformed Cu-Co alloys during annealing is studied. • The investigation combines SEM, TEM WAXS, SAXS and APT. • Powder-based alloys show a better thermal stability compared to bulk-based alloys. Nanocrystalline materials are well known for their beneficial mechanical and physical properties. However, it is of utmost importance to stabilize the microstructure at elevated temperatures to broaden the window of application e.g. by pinning grain boundaries through impurities or oxides. CuCo alloys, severe plastically deformed using high-pressure torsion, were used to investigate the evolution of oxides upon annealing. These investigations were performed using electron microscopy, synchrotron high-energy X-ray scattering and atom probe tomography. Monitoring the evolution of oxides by in-situ small angle scattering investigations indicates the growth of primary oxides as well as the formation of another species of oxide at elevated temperatures. Slightly different coarsening can be observed in heat-treated samples, which can be traced back to the influence of different oxide amounts. The initially supersaturated CuCo matrix changes by the decomposition process as well as Co- and Cu-based oxides formation and growth. It has been found that the major number of oxides which are present after annealing, can already be found in the starting materials. [ABSTRACT FROM AUTHOR]

Samples consisting of one ferromagnetic and one diamagnetic component which are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are processed by high-pressure torsion at various compositions. The received microstructures are investigated by electron microscopy and synchrotron X-ray diffraction, showing a microstructural saturation. Results gained from microstructural investigations are correlated to magnetometry data. The Co-Cu samples show mainly ferromagnetic behavior and a decrease in coercivity with increasing Co-content. The saturation microstructure of Fe-Cu samples is found to be dual phase. Results of magnetic measurements also revealed the occurrence of two different magnetic phases in this system. For Fe-Ag, the microstructural and magnetic results indicate that no intermixing between the elemental phases takes place. [ABSTRACT FROM AUTHOR]