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Refractory tungsten (W) plays an important role in high temperature photonic/plasmonic applications. Previously room temperature bulk single/poly-crystalline optical constants were extensively used to calculate the optical properties of W nanostructures at high temperatures. This might lead to a significant deviation between the predicted and measured optical properties due to the exclusion of electron–phonon interaction, as well as grain-boundary and surface-scattering. Herein, we show experimentally, how film thickness and temperature affects the optical losses in W. A drastic increase in the effective electron collision frequency is observed with decreasing the film thickness down to 5 nm, due to the grain-boundary and surface-scattering mechanisms. At sufficiently high temperatures (greater than 200 °C for W), the electron–phonon interaction eventually becomes the dominant mechanism, linearly increasing collision frequency with temperature, and it is independent of the geometry of the thin film structure. The impact of thickness and temperature-dependent optical properties of W is showcased with a hyperbolic 1D metamaterial structure acting as a thermophotovoltaic emitter. This work opens new directions in accurate prediction of the optical properties of nanostructures and design of efficient devices in various applications, such as aerospace, energy-efficient lighting, radiative cooling and energy harvesting, by incorporating thickness and temperature-dependent optical constants. Deutsche Forschungsgemeinschaft (DFG)

Titanium nitride (TiN) has emerged as one of the most promising refractory materials for plasmonic and photonic applications at high temperatures due to its prominent optical properties along with mechanical and thermal stability. From a high temperature standpoint, TiN is a substitution for Au and Ag in the visible to near-infrared wavelength range, with potential applications including thermophotovoltaics, thermoplasmonics, hot-electron and high temperature reflective coatings. However, the optical properties and thermal stability of TiN films strongly depend on the growth conditions, such as temperature, partial pressure of the reactive ion gas, ion energy, and substrate orientation. In this work, epitaxial TiN films are grown at 835 °C on an Al2O3 substrate using a radio frequency sputtering method. The oxidization behavior of TiN is investigated at 1000 °C under a medium vacuum condition of 2 × 10–3 mbar, which is relevant for practical technical applications, and the thermal stability at 1400 °C under a high vacuum condition of 2 × 10–6 mbar. The TiN film structure shows an unprecedented structural stability at 1000 °C for a minimum duration of 2 h under a medium vacuum condition, and an exceptional thermal stability at 1400 °C, for 8 h under a high vacuum condition, without any protective coating layer. The work reveals, for the first time to the authors’ knowledge, that the TiN film structure with columnar grains exhibits remarkable thermal stability at 1400 °C due to low-index interfaces and twin boundaries. These findings unlock the fundamental understanding of the TiN material at extreme temperatures and demonstrate a key step towards fabricating thermally stable photonic/plasmonic devices for harsh environments.

We measure and compare the optical properties of thin refractory metal films (TiN, W, Mo and Ir) at temperatures up to 1000 °C. In-situ ellipsometry is used to measure the optical constants. Refractory metals show long-term structural stability at 1000 °C for 120 h.

The high-temperature stability of thermal emitters is one of the critical properties of thermophotovoltaic (TPV) systems to obtain high radiative power and conversion efficiencies. W and HfO2 are ideal due to their high melting points and low vapor pressures. At high temperatures and given vacuum conditions, W is prone to oxidation resulting in instantaneous sublimation of volatile W oxides. Herein, we present a detailed in-situ XRD analysis of the morphological changes of a 3-layer-system: HfO2/W/HfO2 layers, in a high-temperature environment, up to 1520 °C. These samples were annealed between 300 °C and 1520 °C for 6 h, 20 h, and 40 h at a vacuum pressure below 3 × 10–6 mbar using an in-situ high-temperature X-ray diffractometer, which allows investigation of crucial alterations in HfO2 and W layers. HfO2 exhibits polymorphic behavior, phase transformations and anisotropy of thermal expansion leads to formation of voids above 800 °C. These voids serve as transport channels for the residual O2 present in the annealing chamber to access W, react with it and form volatile tungsten oxides. An activation energy of 1.2 eV is calculated. This study clarifies the limits for the operation of W-HfO2 spectrally selective emitters for TPV in high-temperature applications.

Boron carbide and platinum are two suitable coating materials for X-ray mirrors at free-electron lasers worldwide. The achieved thickness uniformity for boron carbide is less than 1 nm peak-to-valley over 1500 mm mirror length., Large X-ray mirrors are required for beam transport at both present-day and future free-electron lasers (FELs) and synchrotron sources worldwide. The demand for large mirrors with lengths up to 1 m single layers consisting of light or heavy elements has increased during the last few decades. Accordingly, surface finishing technology is now able to produce large substrate lengths with micro-roughness on the sub-nanometer scale. At the Helmholtz-Zentrum Geesthacht (HZG), a 4.5 m-long sputtering facility enables us to deposit a desired single-layer material some tens of nanometers thick. For the European XFEL project, the shape error should be less than 2 nm over the whole 1 m X-ray mirror length to ensure the safe and efficient delivery of X-ray beams to the scientific instruments. The challenge is to achieve thin-film deposition on silicon substrates, benders and gratings without any change in mirror shape. Thin films of boron carbide and platinum with a thickness in the range 30–100 nm were manufactured using the HZG sputtering facility. This setup is able to cover areas of up to 1500 mm × 120 mm in one step using rectangular sputtering sources. The coatings produced were characterized using various thin-film methods. It was possible to improve the coating process to achieve a very high uniformity of the layer thickness. The movement of the substrate in front of the sputtering source has been optimized. A variation in B4C layer thickness below 1 nm (peak-to-valley) was achieved at a mean thickness of 51.8 nm over a deposition length of 1.5 m. In the case of Pt, reflectometry and micro-roughness measurements were performed. The uniformity in layer thickness was about 1 nm (peak-to-valley). The micro-roughness of the Pt layers showed no significant change in the coated state for layer thicknesses of 32 nm and 102 nm compared with the uncoated substrate state. The experimental results achieved will be discussed with regard to current restrictions and future developments.

Journal of synchrotron radiation 25(1), 77 - 84 (2018). doi:10.1107/S1600577517017362, The durability of grazing- and normal-incidence optical coatings has been experimentally assessed under free-electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10% of the single-shot damage threshold. The experiment was performed at FLASH, the Free-electron LASer in Hamburg, using 13.5 nm extreme UV (EUV) radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20° and 10° grazing incidence, respectively. Mo/Si periodical multilayer structures were tested in the Bragg reflection condition at 16° off-normal angle of incidence. The exposed areas were analysed post-mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X-ray photoelectron spectroscopy. The analysis revealed that Ru and Mo/Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV-induced oxidation of the surface., Published by IUCr, Chester

An accurate transmission measurement of thin foils (usually made of elemental metals and/or semiconductors), which routinely are used as attenuators in soft x-ray beamlines, end-stations and instruments, represents a long standing problem over the wide experimentation field with photon beams, see for example [1-4]. Such foils are also frequently utilized for blocking long wavelength emission, i.e., UV-Vis-IR radiation, from plasma and high order harmonic sources, whilst soft x-rays emitted from the source pass through the foil with only a slight attenuation. Despite the enormous amount of data available in the literature, e.g., Henke’s tables [5], measurements made on real foils often provide surprising results. In this study, a procedure based on the ablation imprints method is utilized for determination of soft x-ray filter transmission, namely the f-scan technique [6,7]. This technique combines the GMD (Gas Monitor Detector) pulse energy measurement and attenuation of the beam by foils (made of different metallic/semiconducting elements of varying thickness) with areas of ablation imprints created on a suitable target, e.g. PMMA – Poly(methyl methacrylate). The results show only a partial overlap with transmission values found in Henke’s tables. Nevertheless, a good agreement with transmission values determined by conventional radiometry techniques at synchrotron radiation beamlines has been found. Such a difference between the experimentally obtained values and transmissions calculated for a pure element is usually explained by spontaneous formation of oxidized layers on the filter surface and in the near-surface layer and their possible alteration by intense FEL radiation. The first results obtained with Al, Nb, Zr and Si filters at FLASH/FLASH2 (Free-electron LASer in Hamburg tuned to 13.5 nm) facilities will be shown and discussed in this presentation. References 1. F. R. Powell, P. W. Vedder, J. F. Lindblom, S. F. Powell: Thin film filter performance for extreme ultraviolet and x-ray applications, Opt. Eng. 29, 614 (1990). 2. E. M. Gullikson, P. Denham, S. Mrowka, J. H. Underwood: Absolute photo absorption measurements of Mg, Al, and Si in the soft x-ray region below the L2,3 edges, Phys. Rev. B 49, 16 283 (1994). 3. R. Keenan, C. L. S. Lewis, J. S. Wark, E. Wolfrum: Measurements of the XUV transmission of aluminium with a soft x-ray laser, J. Phys. B 35, L449 (2002). 4. A. Joseph, M. H. Modi, A. Singh, R. K. Gupta, G. S. Lodha: Analysis of soft x-ray/VUV transmission characteristics of Si and Al filters, AIP Conf. Ser. 1512, 498 (2013). 5. B. L. Henke, E. Gullikson, J. C. Davis: X-ray interactions: photoabsorption, scattering, transmission, and reflection at E = 50-30000 eV, Z =1-92, At. Data Nucl. Data Tables 54, 181 (1993). 6. J. Chalupsky et al.: Spot size characterization of focused non-Gaussian X-ray laser beams, Opt. Express 18, 27836 (2010). 7. J. Chalupský, T. Burian, V. Hajkova, L. Juha, T. Polcar, J. Gaudin, M. Nagasono, R. Sobierajski, M. Yabashi, J. Krzywinski: Fluence scan: an unexplored property of a laser beam, Opt. Express 21, 26363 (2013).

We investigate spectrally selective high temperature stable metamaterial emitters for thermophotovoltaics. We demonstrate band-edge emitters based on a W-Hf02 multilayer metamaterial stable up to 1400°C. Conditions for improved selectivity and thermal stability are discussed.

The Materials Imaging and Dynamics (MID) station is located at the SASE2 undulator beamline of European XFEL and has become operational in 2019. The MID instrument operates in the medium to hard X-ray range (5 - 25 keV) and its scientific focus is on time-resolved coherent X-ray scattering and diffraction studies in materials science, with particular interest in ultrafast pump-probe experiments where the pump can be either X-rays, an optical laser beam or a pulsed magnetic field. The optical setup of the MID instrument includes two vertically offset mirrors equipped with cryogenic cooling. The top mirror will be employed for grazing incidence experiments on liquid surfaces, and the bottom mirror will be used to spatially overlap two split beams generated by a “split and delay” line. The mirrors are 500 mm long and are coated with boron carbide (B4C) and platinum (Pt) in two adjacent stripes. Deterministic mirror polishing is done to compensate the gravitational sag in order to achieve a perfectly flat mirror when it is installed. The requirements were very challenging for the surface shape and the needed ion-beam deterministic polishing, so also the coating process had to be performed and monitored with particular care. We present the metrological characterization of the mirrors, carried out before and after the B4C and Pt coating, and performed with a large aperture Fizeau interferometer. The measurements were made at European XFEL’s metrology lab in grazing incidence setup and with the mirrors facing sideways. Analyzing these data, we can deduce many important parameters, as the peak-to-valley of the central profile, the bending radius, and the gravity compensation profile. We show metrological results before and after coating and give details about the calculations performed to decide whether the mirror shapes are still complying with specifications after all these processes.

The challenging specifications for long X-ray mirrors for upcoming free-electron lasers can be achieved, especially for maintaining below 2 nm peak-to-valley shape error along the optical aperture of approximately 1 m-long mirrors., X-ray optical elements are required for beam transport at the current and upcoming free-electron lasers and synchrotron sources. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors with single layers consisting of light or heavy elements has increased during the last few decades; surface finishing technology is currently able to process mirror lengths up to 1 m with microroughness at the sub-nanometre level. Additionally, thin-film fabrication is able to deposit a suitable single-layer material, such as boron carbide (B4C), some tens of nanometres thick. After deposition, the mirror should provide excellent X-ray optical properties with respect to coating thickness errors, microroughness values and slope errors; thereby enabling the mirror to transport the X-ray beam with high reflectivity, high beam flux and an undistorted wavefront to an experimental station. At the European XFEL, the technical specifications of the future mirrors are extraordinarily challenging. The acceptable shape error of the mirrors is below 2 nm along the whole length of 1 m. At the Helmholtz-Zentrum Geesthacht (HZG), amorphous layers of boron carbide with thicknesses in the range 30–60 nm were fabricated using the HZG sputtering facility, which is able to cover areas up to 1500 mm long by 120 mm wide in one step using rectangular B4C sputtering targets. The available deposition area is suitable for the specified X-ray mirror dimensions of upcoming advanced research light sources such as the European XFEL. The coatings produced were investigated by means of X-ray reflectometry and interference microscopy. The experimental results for the B4C layers are discussed according to thickness uniformity, density, microroughness and thermal stability. The variation of layer thickness in the tangential and sagittal directions was investigated in order to estimate the achieved level of uniformity over the whole deposition area, which is considerably larger than the optical area of a mirror. A waisted mask was positioned during deposition between the sputtering source and substrate to improve the thickness uniformity; particularly to prevent the formation a convex film shape in the sagittal direction. Additionally the inclination of the substrate was varied to change the layer uniformity in order to optimize the position of the mirror quality deposited area during deposition. The level of mirror microroughness was investigated for different substrates before and after deposition of a single layer of B4C. The thermal stability of the B4C layers on the various substrate materials was investigated.

SASE1 is the first beamline of the European XFEL that became operational in 2017. It consists of the SASE1 undulator system, the beam transport system, and the two scientific experiment stations: Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX), and Femtosecond X-ray Experiments (FXE). The beam transport system comprises mirrors to offset and guide the beam to the instruments and a set of X-ray optical components to align, manipulate and diagnose the beam. The SASE1 beam transport system is described here in its initial configuration, and results and experiences from the first year of user operation are reported.

Optics express 26(15), 19665 - 19685 (2018). doi:10.1364/OE.26.019665, Ruthenium is a perspective material to be used for XUV mirrors at free-electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser-matter interaction. In this work, we present single-shot damage studies of thin Ru films irradiated by femtosecond XUV free-electron laser pulses at FLASH. Ex-situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte-Carlo code XCASCADE(3D) and the two-temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologies., Published by OSA, Washington, DC

Physical review / B 96(21), 214101 (2017). doi:10.1103/PhysRevB.96.214101, All carbon materials, e.g., amorphous carbon (a-C) coatings and $C_{60}$ fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and $C_{60}$ layers to the extreme ultraviolet (SPring-8 Compact SASESource in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation are investigated by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular ($C_{60}$) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation of a fullerene crystal (estimated to be around 0.15 eV/atom for $C_{60}$ vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact $C_{60}$ molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling., Published by Inst., Woodbury, NY

The use of soft X-rays near the carbon edge of absorption (270–300 eV) greatly enhances studies in various branches of science. However, the choice of reflecting coatings for mirrors operating in free-electron and X-ray free-electron laser (FEL and XFEL) beamlines in this spectral range is not so evident and experimental justifications of the mirror efficiency are rather limited. In the present paper it is demonstrated experimentally that the reflectivity of B4C- and Ni-coated grazing-incidence mirrors is high enough for their operation in FEL or XFEL beamlines near the carbonK-edge of absorption. The minimal reflectivity of both mirrors proves to exceed 80% near the carbon absorption edge at a grazing angle of 0.6°. An in-depth profile of the chemical elements composing the reflecting coatings is reconstructed based on analysis of a set of reflectivity curves measuredversusthe grazing angle at different photon energies in the soft X-ray spectral region. This allows us to predict correctly the mirror reflectivity at any X-ray energy and any grazing angle.

Simple analytic equation is deduced to explain new physical phenomenon detected experimentally growth of nano dots 40 55 nm diameter, 8 13 nm height, 9.4 dots amp; 956;m2 surface density on the grazing incidence mirror surface under the three years irradiation by the free electron laser FLASH 5 45 nm wavelength, 3 degrees grazing incidence angle . The growth model is based on the assumption that the growth of nano dots is caused by polymerization of incoming hydrocarbon molecules under the action of incident photons directly or photoelectrons knocked out from a mirror surface. The key feature of our approach consists in that we take into account the radiation intensity variation nearby a mirror surface in an explicit form, because the polymerization probability is proportional to it. We demonstrate that the simple analytic approach allows to explain all phenomena observed in experiment and to predict new effects. In particular, we show that the nano dots growth depends crucially on the grazing angle of incoming beam and its intensity growth of nano dots is observed in the limited from above and below intervals of the grazing angle and the radiation intensity. Decrease in the grazing angle by 1 degree only from 3 to 2 degree may result in a strong suppression of nanodots growth and their total disappearing. Similarly, decrease in the radiation intensity by several times replacement of free electron laser by synchrotron results also in disappearing of nano dots growth

Improvement in high-temperature stable spectrally selective absorbers and emitters is integral for the further development of thermophotovoltaic (TPV), lighting and solar thermal applications. However, the high operational temperatures (T>1000oC) required for efficient energy conversion, along with application specific criteria such as the operational range of low bandgap semiconductors, greatly restrict what can be accomplished with natural materials. Motivated by this challenge, we demonstrate the first example of high temperature thermal radiation engineering with metamaterials. By employing the naturally selective thermal excitation of radiative modes that occurs near topological transitions, we show that thermally stable highly selective emissivity features are achieved for temperatures up to 1000°C with low angular dependence in a sub-micron thick refractory tungsten/hafnium dioxide epsilon-near-zero (ENZ) metamaterial. We also investigate the main mechanisms of thermal degradation of the fabricated refractory metamaterial both in terms of optical performance and structural stability using spectral analysis and energy-dispersive X-ray spectroscopy (EDS) techniques. Importantly, we observe chemical stability of the constituent materials for temperatures up to 1000°C and structural stability beyond 1100°C. The scalable fabrication, requiring magnetron sputtering, and thermally robust optical properties of this metamaterial approach are ideally suited to high temperature emitter applications such as lighting or TPV. Our findings provide a first concrete proof of radiative engineering with high temperature topological transition in ENZ metamaterials, and establish a clear path for implementation in TPV energy harvesting applications.

We present a self-assembled refractory absorber/emitter without the necessity to structure the metallic surface itself, still retaining the feature of tailored optical properties for visible light emission and thermophotovoltaic (TPV) applications. We have demonstrated theoretically and experimentally that monolayers of zirconium dioxide (ZrO 2 ) microparticles on a tungsten layer can be used as large area, efficient and thermally stable selective absorbers/emitters. The band edge of the absorption is based on critically coupled microsphere resonances. It can be tuned from visible to near-infrared range by varying the diameter of the microparticles. We demonstrated the optical functionality of the structure after annealing up to temperatures of 1000°C under vacuum conditions. In particular it opens up the route towards high efficiency TPV systems with emission matched to the photovoltaic cell.

X-ray mirrors are needed for beam shaping and monochromatization at advanced research light sources, for instance, free-electron lasers and synchrotron sources. Such mirrors consist of a substrate and a coating. The shape accuracy of the substrate and the layer precision of the coating are the crucial parameters that determine the beam properties required for various applications. In principal, the selection of the layer materials determines the mirror reflectivity. A single layer mirror offers high reflectivity in the range of total external reflection, whereas the reflectivity is reduced considerably above the critical angle. A periodic multilayer can enhance the reflectivity at higher angles due to Bragg reflection. Here, the selection of a suitable combination of layer materials is essential to achieve a high flux at distinct photon energies, which is often required for applications such as microtomography, diffraction, or protein crystallography. This contribution presents the current development of a Ru/C multilayer mirror prepared by magnetron sputtering with a sputtering facility that was designed in-house at the Helmholtz-Zentrum Geesthacht. The deposition conditions were optimized in order to achieve ultra-high precision and high flux in future mirrors. Input for the improved deposition parameters came from investigations by transmission electron microscopy. The X-ray optical properties were investigated by means of X-ray reflectometry using Cu- and Mo-radiation. The change of the multilayer d-spacing over the mirror dimensions and the variation of the Bragg angles were determined. The results demonstrate the ability to precisely control the variation in thickness over the whole mirror length of 500 mm thus achieving picometer-precision in the meter-range.

Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial and the connected optical topological transition (OTT) are adjusted to selectively enhance and suppress the thermal emission in the near-infrared spectrum, crucial for improved TPV efficiency. The near-omnidirectional and spectrally selective emitter is obtained as the emission changes due to material properties and not due to resonances or interference effects, marking a paradigm shift in thermal engineering approaches. We experimentally demonstrate the OTT in a thermally stable metamaterial at high temperatures of 1,000 °C., The ability to control thermal radiation at high temperatures is of interest for thermal photovoltaics. Here, Dyachenko et al. engineer the epsilon-near-zero frequency of a metamaterial and connected optical topological transition to selectively enhance and suppress the thermal emission in the near-infrared spectrum.

X-ray diffraction data taken in Bragg-Brentano and glancing angle geometries are compared for stainless steel AISI 304 and CoCr alloys HS188 after nitriding by plasma immersion ion implantation. A direct inferring of the nitrogen depth profile from the line shape for expanded austenite is precluded as additional stress is present. Furthermore, conventional stress analysis is rather complicated as highly textured material is present and only a very much reduced set of reflections is available for evaluation. Nevertheless, a strong dependence of the lattice expansion and the resulting line shape on the detailed process conditions was observed.

Magnesium alloys have attracted increasing interest in the past years due to their potential as implant materials. This interest is based on the fact that magnesium and its alloys are degradable during their time of service in the human body. Moreover magnesium alloys offer a property profile that is very close or even similar to that of human bone. The chemical composition triggers the resulting microstructure and features of degradation. In addition, the entire manufacturing route has an influence on the morphology of the microstructure after processing. Therefore the composition and the manufacturing route have to be chosen carefully with regard to the requirements of an application. This paper discusses the influence of composition and heat treatments on the microstructure, mechanical properties and corrosion behaviour of cast Mg-Gd alloys. Recommendations are given for the design of future degradable magnesium based implant materials.

The influence of microstructure on the corrosion resistance of magnesium alloys was studied by comparing standard cast alloys with thin-film alloys (solid solution) of the same nominal composition. Latter were deposited on Si by means of magnetron sputtering. Results from potentiodynamic polarisation measurements, electrochemical impedance spectroscopy (EIS) and immersion tests with inductively coupled plasma (ICP) spectroscopy of the aqueous NaCl solution prove that beside lower corrosion rates for the thin films, a different corrosion mechanism is active in both systems, due to the dissimilar microstructure. Localised or pitting corrosion is dominating for the bulk alloys and uniform corrosion (on a much lower level) for the coatings.

Physical vapor deposition (PVD) was used to prepare pure magnesium coatings on silicon substrates at various argon pressures and deposition angles. The film morphology was observed to depend on the deposition conditions. The approximately 3 µm thick Mg films exhibited columnar growth with voided boundaries and a fiber texture of the basal planes parallel to the substrate surface, which is typical of low temperature deposition. At low pressure and angle, the films were more compact, the surface roughness was lower, the texture was stronger, and the corrosion performance was improved. A free corrosion potential of −1 735 mV and a corrosion rate of 335 µm per year were determined.

The range of applications for magnesium alloys is still limited due to their relatively poor corrosion behavior. In recent years, various new magnesium alloys were developed, some of them with improved corrosion properties, thus opening new fields of application. However, the number of alloying elements for the use in conventional cast processes is limited due to their interaction with liquid magnesium, other alloying elements or large differences in the melting temperatures. The possibilities for grain refinement by post-processing are also restricted. PVD techniques can help to produce supersaturated precipitation free and microcrystalline magnesium layers. Using ion beam and magnetron sputtering, binary or ternary Mg-Al, Mg-Ti and Mg-Sn alloy systems as well as standard alloys (AM50, AZ91 and AE42) were deposited on silicon and on magnesium substrates. The effect of the microstructure on the corrosion properties was studied by comparing as cast material and PVD coatings using potentiodynamic polarization, linear polarization resistance, and electrochemical impedance techniques.

A new phenomenon on X-ray optics surfaces has been observed: the growth of nano-dots (40–55 nm diameter, 8–13 nm height, 9.4 dots µm−2surface density) on the grazing-incidence mirror surface under irradiation by the free-electron laser (FEL) FLASH (5–45 nm wavelength, 3° grazing-incidence angle). With a model calculation it is shown that these nano-dots may occur during the growth of a contamination layer due to polymerization of incoming hydrocarbon molecules. The crucial factors responsible for the growth of nano-dots in the model are the incident peak intensity and the reflection angle of the beam. A reduction of the peak intensity (e.g.replacement of the FEL beam by synchrotron radiation) as well as a decrease of the incident angle by just 1° (from 3° to 2°) may result in the total disappearance of the nano-dots. The model calculations are compared with surface analysis of two FLASH mirrors.

Amorphous plasma electrolytic oxidation (PEO) coating with sealed discharge channels can be formed in alkaline phosphate electrolyte containing montmorillonite clay particles. The effect of various concentrations of phosphate and hydroxide ions in the clay-containing electrolyte on the microstructure of the coatings was studied in the present work and correlated with the corrosion behavior. The clay particles were reactively incorporated into the coating. Single amorphous phase appears in PEO coatings produced from electrolytes containing higher concentration of phosphate. These amorphous coatings are degrading within a relatively short period in 0.5 wt% NaCl solution. Electrolytes containing higher concentration of KOH tend to produce mixed PEO coatings composed of crystalline and amorphous phases. These layers demonstrate higher corrosion resistance and degradation stability. Thus, the degradation rate of PEO coatings is governed mostly by the stability of their phase composition, which might be controlled by varying electrolyte composition. (C) 2014 Elsevier B.V. All rights reserved.

Due to the present shortage of 3He and the associated tremendous increase of its price, the supply of large neutron detection systems with 3He becomes unaffordable. Alternative neutron detection concepts, therefore, have been invented based on solid 10B converters. These concepts require development in thin film deposition technique regarding high adhesion, thickness uniformity and chemical purity of the converter coating on large area substrates. We report on the sputter deposition of highly uniform large-area 10B4C coatings of up to 2 μm thickness with a thickness deviation below 4% using the Helmholtz-Zentrum Geesthacht large area sputtering system. The 10B4C coatings are x-ray amorphous and highly adhesive to the substrate. Material analysis by means of X-ray-Photoelectron Spectroscopy, Secondary-Ion-Mass-Spectrometry, and Rutherford-Back-Scattering (RBS) revealed low impurities concentration in the coatings. The isotope composition determined by Secondary-Ion-Mass-Spectrometry, RBS, and inelastic nuclear reaction analysis of the converter coatings evidences almost identical 10B isotope contents in the sputter target and in the deposited coating. Neutron conversion and detection test measurements with variable irradiation geometry of the converter coating demonstrate an average relative quantum efficiency ranging from 65% to 90% for cold neutrons as compared to a black 3He-monitor. Thus, these converter coatings contribute to the development of 3He-free prototype detectors based on neutron grazing incidence. Transferring the developed coating process to an industrial scale sputtering system can make alternative 3He-free converter elements available for large area neutron detection systems.

X-ray Free Electron Lasers (XFELs) have the potential to contribute to many fields of science and to enable many new avenues of research, in large part due to their orders of magnitude higher peak brilliance than existing and future synchrotrons. To best exploit this peak brilliance, these XFEL beams need to be focused to appropriate spot sizes. However, the survivability of X-ray optical components in these intense, femtosecond radiation conditions is not guaranteed. As mirror optics are routinely used at XFEL facilities, a physical understanding of the interaction between intense X-ray pulses and grazing incidence X-ray optics is desirable. We conducted single shot damage threshold fluence measurements on grazing incidence X-ray optics, with coatings of ruthenium and boron carbide, at the SPring-8 Angstrom compact free electron laser facility using 7 and 12 keV photon energies. The damage threshold dose limits were found to be orders of magnitude higher than would naively be expected. The incorporation of energy transport and dissipation via keV level energetic photoelectrons accounts for the observed damage threshold.

International audience; The time evolution of the electron structure is investigated in a molybdenum foil heated up to the warm dense matter regime by a femtosecond laser pulse, through time-resolved x-ray absorption near-edge spectroscopy. Spectra are measured with independent characterizations of temperature and density. They are successfully compared with ab initio quantum molecular dynamic calculations. We demonstrate that the observed white line in the L-3 edge reveals the time evolution of the electron density of state from the solid to the hot (a few eV) and expanding liquid. The data indicate a highly nonequilibrated state, 5 ps after heating.

Advanced research light sources, such as free-electron lasers, require ultra-precise and long x-ray mirrors that provide high reflectivity, high flux and a wide wavelength range. An X-ray mirror is a combination of a substrate and a coating. The demand for large mirrors has increased during the last few years, since surface finishing technology is able to process longer substrate lengths on the rms-level of a few nanometers. A state-of-the-art X-ray mirror could be coated with more than one single layer to allow a selection of thin-film materials suitable for the large wavelength range of a free-electron laser. Presented here is an X-ray mirror fabrication method to achieve low variation in thickness of less than 1 nm (peak-to-valley) over the whole mirror length of about 1 m. Low figure errors and low roughness are essential for a wave front preserving transport of photons and a high reflectance of a mirror surface. At FLASH II, the new extension of the Free-electron LASer in Hamburg (FLASH) at DESY, Germany, the wavelength range will be 4-80 nm. It is further expected that the photon beam will possess average single pulse energy of 1-500 μJ, pulse duration of 10-300 fs (FWHM), and peak power of 1-5 GW. At the Helmholtz-Zentrum Geesthacht, an in-house designed magnetronsputtering facility enabled us to deposit single layers and multilayers on up to 1.5 m long substrates. Earlier results confirmed the excellent uniformity of X-ray optical coating properties in the tangential and sagittal direction of the mirrors. Moreover, the deposition facility provided the simultaneous fabrication of two mirrors to achieve identical properties. Thin films of amorphous carbon (a-C), boron carbide (B4C) and nickel (Ni) are deposited by means of magnetron sputtering. The thin-film properties were investigated and analyzed by means of X-ray reflectometry (XRR), atomic force (AFM), and interference microscopy. The experimental results were analysed using simulations for the determination of layer thickness, density and roughness.

International audience; The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called "molecular movie'' within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

State-of-the-art ex situ metrology for characterizing the quality of ultraprecise reflective synchrotron optics is reported. Beside slope measuring deflecometry the current state of mirror coating technology for single layer and multilayer coatings for very long mirror substrates is discussed., To fully exploit the ultimate source properties of the next-generation light sources, such as free-electron lasers (FELs) and diffraction-limited storage rings (DLSRs), the quality requirements for gratings and reflective synchrotron optics, especially mirrors, have significantly increased. These coherence-preserving optical components for high-brightness sources will feature nanoscopic shape accuracies over macroscopic length scales up to 1000 mm. To enable high efficiency in terms of photon flux, such optics will be coated with application-tailored single or multilayer coatings. Advanced thin-film fabrication of today enables the synthesis of layers on the sub-nanometre precision level over a deposition length of up to 1500 mm. Specifically dedicated metrology instrumentation of comparable accuracy has been developed to characterize such optical elements. Second-generation slope-measuring profilers like the nanometre optical component measuring machine (NOM) at the BESSY-II Optics laboratory allow the inspection of up to 1500 mm-long reflective optical components with an accuracy better than 50 nrad r.m.s. Besides measuring the shape on top of the coated mirror, it is of particular interest to characterize the internal material properties of the mirror coating, which is the domain of X-rays. Layer thickness, density and interface roughness of single and multilayer coatings are investigated by means of X-ray reflectometry. In this publication recent achievements in the field of slope measuring metrology are shown and the characterization of different types of mirror coating demonstrated. Furthermore, upcoming challenges to the inspection of ultra-precise optical components designed to be used in future FEL and DLSR beamlines are discussed.

Metastable, supersaturated alloys of the thermally immiscible systems Ag/Fe ( 111 In tracers. In both systems the magnetic hyperfine fields B n were found to decrease linearly with the number n of Ag or In neighbor atoms next to the probe site (10.9% per Ag atom; 4.5% per In atom). From the observed distribution of the fractions f n in the laser-deposited samples, the maximum solubility S =15(5) at% of In in Fe was determined after laser deposition. This concentration compares well with the maximum solubility S =16(3) at% of Ag in Fe previously found for supersaturated Ag/Fe alloys. The solubility of In in Fe in thermal equilibrium at room temperature and at 970–1370 K was determined for samples having In concentrations of less than 0.1–2.1 at%.

Pulsed laser deposited (PLD) metallic alloys and multilayers are characterized by the formation of amorphous or metastable nanocrystalline phases with high solid solubilities, unusually enlarged lattice spacings in growth direction and intermixed interfaces. The differences to sputtered and evaporated samples are discussed with respect to the high instantaneous deposition rate, which is about 105 times larger than during sputtering or thermal evaporation, and the high kinetic energy of the deposited particles of up to more than 100 eV at high laser fluences inducing atomic mixing, a large number of defects and a high stress in the deposited films.

During pulsed laser deposition (PLD) of metals (and other materials) one typical problem occurs: beside atoms and ions macroscopic droplets (up to some μm) are expelled from the roughening target and are deposited on the film surface. In the case of metals two kinds of droplets are observed during laser ablation, which have different sizes, angular distributions, velocities, and dependencies on the number of pulses, target roughening and energy density. These experiments indicate different origins for the two types of droplets: expelling from the cones growing out of the target and expelling from the molten surface. Consequences for the reduction and avoidance of these droplets are discussed.

Laser deposited FeAg alloys exhibit a supersaturation of the Fe(Ag) solid solution of up to 13 at.% Ag and an unusual lattice expansion in the growth direction. The relaxation process, grain coarsening, decomposition and mixing processes occurring during 350 keV Ar + irradiation at 77 K in these alloys were studied by X-ray diffraction. Depending on the original state of the samples, different processes dominate, but always lead to the same dynamic phase equilibrium under irradiation.

The structure of metallic alloys and multilayers prepared by pulsed laser deposition using KrF radiation (248 nm) and a pulse duration of 30 ns was investigated by X-ray diffraction. In comparison with conventional deposition techniques, the structural properties of laser-deposited FeNb and FeAg films can be characterized by the formation of amorphous or metastable nanocrystalline phases with higher solubilities, unusually enlarged lattice spacings in the growth direction and different film textures. Often these films are in a state further away from the equilibrium state than sputtered or evaporated samples. Fe Nb multilayers exhibit much broader amorphous interfaces, while Fe Ag superlattices show a different texture and sharp interfaces visible by satellite reflections in the X-ray spectra. These differences can be understood by the about 105 times higher instantaneous deposition rate and the high kinetic energy of the deposited particles in the range of up to 100 eV.

The structure of metallic alloys grown by pulsed KrF laser deposition is examined by x‐ray diffraction and compared with results from literature on sputtered and evaporated films. In general, the phases and structures obtained are similar, while laser deposited films often exhibit unusually enlarged lattice parameters in direction of growth, small grain sizes, larger extensions of the single‐phase regions and sometimes better alignment of the grains. These differences can be explained by the approximately 105 times higher instantaneous deposition rate of the pulsed laser ablation process and the high kinetic energy of the deposited particles of up to more than 100 eV.

The structure of metallic elements and alloy thin films grown by pulsed KrF laser deposition was examined by X-ray diffraction and Mossbauer spectroscopy, and compared with results on triode sputtered films. While, in general, the obtained phases and structures are similar, laser ablated films often exhibit smaller grain sizes, enlarged lattice parameters in the growth direction, larger extensions of the single-phase regions and sometimes a better alignment of the grains. It can be concluded, that often laser deposited metallic material is in a state further away from equilibrium than after preparation by classical thin film techniques . The differences can be explained by the 10 5 –10 6 times higher momentary deposition rate of the pulsed laser ablation process.

The increasing use of magnesium castings for automotive components and the number of newly developed alloys raise the question of suitable recycling processes. Remelting offers a high potential of energy saving and thereby improves the live cycle balance of magnesium components. Effective recycling processes are likely to involve the mixing of different alloys but little is known about the interaction of alloying elements. In order to approach this issue, the influence of strontium, silicon and calcium on phase formation and mechanical properties of magnesium alloy AM50 has been investigated. After strontium addition, X-ray diffraction demonstrated the formation of the Al4Sr and the Mg 17Sr 2 phases. However, after simultaneous alloying with strontium, silicon and calcium the ternary Zintl phase Sr 6.33Mg 16.67Si 13 was detected. This phase forms preferably instead of Al 4Sr,Mg 17Sr 2 andMg 2Si. Compared to the two strontium-containing phases, precipitates of the ternary Zintl phase exhibit a rather compact morphology. This results in a higher elongation-at-fracture under tensile stress.

We present the results of an experiment where amorphous carbon undergoes a phase transition induced by femtosecond 830 eV x-ray free-electron laser pulses. The phase transition threshold fluence is found to be 282 +/- 11 mJ/cm(2). Atomic force microscopy, photoelectron microscopy, and micro-Raman spectroscopy give experimental evidence for the phase transition in terms of a volume expansion, graphitization, and change of local order of the irradiated sample area. The interaction is modeled by an accurate time-dependent treatment of the ionization dynamics coupled to a two-temperature model. At the phase transition fluence threshold the free-electron density N-e is found to be at maximum 9 x 10(20) cm(-3) while the ion (atom) temperature is found to be 1050 K, e.g., above the crystallization activation temperature reported in the literature. This low ionization rate and high atom temperature suggest a thermally activated phase transition.

The interaction of free electron laser pulses with grating structure is investigated using 4.6 +/- 0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7 +/- 8.7 mJ/cm(2), the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold. (C) 2012 Optical Society of America

X-ray mirrors are needed for beam steering, beam alignment and monochromatisation at advanced research light sources like 3rd generation synchrotron sources (e.g. PETRA III in Hamburg) or Free-Electron Lasers (for instance FLASH or the European XFEL). At the Helmholtz-Zentrum Geesthacht (formerly GKSS), an in-house designed magnetron sputtering facility for the deposition of single layers and multilayers has been installed for the development of x-ray optics. Earlier results showed that the thin-film fabrication of 1.5 m long amorphous carbon coatings was very successful. These single layers are currently used as total reflection mirrors at FLASH to steer the photon beam to the various beamlines. A major advantage of the sputtering facility is that it is now possible to prepare one, two or more mirrors with similar properties over the whole deposition length. In this contribution we present results for the x-ray optical properties of C, B4C and W coatings and W/C multilayers. The goal of the development of x-ray mirrors is to optimize the deposition conditions in order to control the thickness of a single layer or the lateral period of a multilayer, and to achieve high reflectivity over the whole deposition length according to the application.

We present results of damage studies performed at the Free-Electron LASer in Hamburg (FLASH) on amorphous carbon (a-C). The experiment was performed in the total external reflection geometry representing the working configuration of X-ray mirrors. The 177 eV photon laser beam was focused on a 40 nm thin layer of a-C coated on a silicon substrate. Single-shot damages were produced at two different grazing angles (4.3 degrees and 7.7 degrees) below the critical angle (0(c)=8 degrees) calculated for this photon energy. The corresponding damage fluence thresholds were determined to be 43.7 and 74 mJ/cm(2). No evidence of delamination or mechanical damages (cracks) under grazing angles on the 40 nm thin sample was observed. The results are compared with the results of the previous experiment done on thicker layers (900 nm) of a-C with the same experimental conditions [1]. (C) 2010 Elsevier B.V. All rights reserved.

We present a new technique for the characterization of non-Gaussian laser beams which cannot be described by an analytical formula. As a generalization of the beam spot area we apply and refine the definition of so called effective area (A(eff)) [1] in order to avoid using the full-width at half maximum (FWHM) parameter which is inappropriate for non-Gaussian beams. Furthermore, we demonstrate a practical utilization of our technique for a femtosecond soft X-ray free-electron laser. The ablative imprints in poly(methyl methacrylate) - PMMA and amorphous carbon (a-C) are used to characterize the spatial beam profile and to determine the effective area. Two procedures of the effective area determination are presented in this work. An F-scan method, newly developed in this paper, appears to be a good candidate for the spatial beam diagnostics applicable to lasers of various kinds. (C) 2010 Optical Society of America