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We present a general method for designing XUV aperiodic multilayer mirrors that can mimic a given target spectrum, specifically, the spectral transmission of an XUV optical system. The method is based on minimizing a merit function and using fidelity parameters that quantify the matching of the multilayer reflectivity spectrum with that of the target spectrum. To assess the feasibility of fabricating such a system, we show how to reduce the layer-to-layer thickness variations throughout the aperiodic layer stack. We demonstrate the design method using an example of an EUV optical system composed of 12 identical Mo/Si multilayer mirrors having a reflectivity peak at 13.5 nm. We found that the target spectrum can be mimicked with high fidelity either with a single reflection at an aperiodic multilayer mirror combined with standard absorbing filters or, if required, with two subsequent reflections at a mimic mirror. These examples demonstrate the applicability for metrology at XUV sources, including spectrally proper source imaging. Because our approach is of general applicability, the process can be used to mimic any other narrowband, single-peaked target spectrum in the XUV region.

We demonstrate a theoretical approach whereby light backscattering toward the incident beam can be suppressed entirely for a high-reflectivity, rough-surfaced multilayer mirror fabricated using oblique deposition, such that the interface relief is replicated at a certain angle β to the sample normal. The mirror comprises two parts: a main (lower) multilayer consisting of N identical bi-layers growing at the angle βML to the mirror normal, and an additional bi- or tri-layer forming the topmost section of the mirror, which grows at another angle βBL. We show that choosing appropriate growth angles βML and βBL results in a disappearance of backscattering toward the incident beam due to the destructive interference of waves scattered from the main multilayer and uppermost bi- or tri-layer. The conditions for the scattering suppression are formulated, and the suitability of different mirror materials is discussed.

The problem of X-ray diffraction from multilayer-coated blazed diffraction gratings is analyzed. Invalidity of the conventional condition of maximal diffraction efficiency observed in previous experiments is explained theoretically. This is attributed to two factors: contribution of anti-blaze facets to diffraction efficiency and effect of strongly asymmetric diffraction. We demonstrate that a proper choice of the multilayer d-spacing allows to design grating with the diffraction efficiency close to the maximal possible one throughout the tender X-ray range (E∼1-5 keV). An optimization procedure is suggested for the first time to choose the optimal grating parameters and the operation diffraction order to obtain a high fix-focus constant and high diffraction efficiency simultaneously in a wide spectral range.

Effective area is one of the most important parameters of x ray telescopes. It can be increased by enlarging the entrance aperture or maximizing the reflectivity through the proper designing and optimization of the reflecting coating. A method to increase the reflectivity of grazing incidence x ray mirrors in the 0.5 to 8 keV energy region is analyzed. The idea consists in the use of a trilayer reflecting coating instead of single layer one e.g., C Ni Pt mirror instead of Pt one . Deposition of low absorbing medium Z and low Z layers onto the top of strongly absorbing high Z material results in essential increase in the reflectivity while keeping the same width of the reflectivity plateau. In particular, C Ni Pt trilayer mirror demonstrates enhancement of the double reflection coefficient by a factor achieving 1.5 to 3.5 compared to that of Pt coated mirror. The effective area of a telescope is also considerably increased. The experimental results are in a very good agreement with the theoretical predictions. In addition, the C Ni Pt trilayer mirror exhibits a reasonable thermal stability and a relatively low compressive stress of about amp; 8722;550 amp; 8201; amp; 8201;MPa

The reflection and transmission of a wave falling onto a stratified medium is analyzed in terms of the RT-matrixes establishing a relation between the wave amplitudes in the asymptotic regions z → ± ∞ . The RT-matrixes are considered as a generalization of the characteristic matrixes introduced by Abeles with elements expressed via the amplitude reflectance and transmittance of a wave falling onto the medium from the right and left sides. If the medium is divided into several parts, the product of their RT-matrixes is equal to the matrix of the whole medium, whose reflectance and transmittance are thus expressed via the reflectance and transmittance of its parts. The easy use of the RT-matrix in practical calculations was shown through analysis of the wave reflection from periodic and aperiodic multilayer structures with abrupt or smooth interfaces.

We present the first experimental demonstration of a novel type of narrowband and wavelength-tunable multilayer transmission filter for the extreme ultraviolet (EUV) region. The operating principle of the filter is based on spatially overlapping the nodes of a standing wave field with the absorbing layers within the multilayer structure. For a wavelength with a matching node pattern, this increases the transmission as compared to neighboring wavelengths where anti-nodes overlap with the absorbing layers. Using Ni/Si multilayers where Ni provides strong absorption, we demonstrate the proper working of such anomalous transmission filter. The demonstration is carried out at the example of 13.5 nm wavelength and at normal incidence, providing a 0.27 nm-wide transmission peak. We also demonstrate wavelength tunability by operating the same Ni/Si filter at different wavelengths by varying the angle of incidence. As the multilayer filter is directly deposited on the active area of an EUV-sensitive photodiode, this provides an extremely compact device for easy spectral monitoring in the EUV. The transmission spectrum of the filter is modeled and found to be in good agreement with the experimental data. The agreement proves that such filters and compact monitoring devices can be straightforwardly designed and fabricated, as desired, also for other EUV wavelengths, bandwidths and angles of incidence, thereby showing a high potential for applications.

Cr/V multilayer mirrors are suitable for applications in the &ldquo, water window&rdquo, spectral ranges. To study factors influencing the internal microstructure of Cr/V multilayers, multilayers with different vanadium layers thicknesses varying from 0.6 nm to 4.0 nm, and a fixed thickness (1.3 nm) of chromium layers, were fabricated and characterized with a set of experimental techniques. The average interface width characterizing a cumulative effect of different structure irregularities was demonstrated to exhibit non-monotonous dependence on the V layer thickness and achieve a minimal value of 0.31 nm when the thickness of the V layers was 1.2 nm. The discontinuous growth of very thin V films increased in roughness as the thickness of V layers decreased. The columnar growth of the polycrystalline grains in both materials became more pronounced with increasing thickness, resulting in a continuous increase in the interface width to a maximum of 0.9 nm for a 4 nm thickness of the V layer.

We theoretically demonstrate the possibility of entirely suppressing light backscattering towards the incident beam from a rough bilayer fabricated by deposition at an oblique angle, such that the substrate relief is replicated at a certain angle to the substrate surface. The necessary conditions of the scattering suppression were formulated. Interference suppression was observed experimentally (633 nm wavelength, 45° incidence angle, −35° scattering angle) with a set of SiO2-on-Ta2O5 bi-layers fabricated at different deposition angles. We detected a suppression of the scattering from the bi-layer fabricated at the deposition angle of 7.7° by a factor of about 30 compared with that from the sample deposited at normal incidence. The observed value of the scattering suppression was limited by the background noise of the measurements.

Ru/B

This study theoretically analyzes an increase in X ray absorption by a grazing incidence mirror due to its surface roughness. We demonstrate that the increase in absorption can be several hundred times larger than predicted by the Nevot Croce formula. As a result, absorption enhances by several times compared to a perfectly smooth mirror despite the extremely small grazing angle of an incident X ray beam a fraction of the critical angle of the total external reflection and the high quality of the reflecting surface the roughness height was 0.5 nm in modeling . The main contribution to the absorption increase was dictated by the mid scale roughness waviness of the virgin substrate surface, whose quality thus defines an absorption enhancement. The approach was applied to the analysis of two real mirrors used in a synchrotron BESSY I and a European X ray free electron laser XFEL beamline. The modern surface finishing technology of elastic emission machining provides extremely low substrate waviness, guaranteeing the negligible effect of the surface roughness on the absorption increase

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.

Using the coupled wave approach (CWA), we introduce the analytical theory for alternate multilayer grating (AMG) operating in the single-order regime, in which only one diffraction order is excited. Differing from previous study analogizing AMG to crystals, we conclude that symmetrical structure, or equal thickness of the two multilayer materials, is not the optimal design for AMG and may result in significant reduction in diffraction efficiency. The peculiarities of AMG compared with other multilayer gratings are analyzed. An influence of multilayer structure materials on diffraction efficiency is considered. The validity conditions of analytical theory are also discussed.

Reactive sputtering with a mixture of argon and nitrogen (N

Reactive sputtering with a mixture of argon and nitrogen (N2 partial pressure of 4%, 8%, and 15%) as the working gas is used to develop the high reflectance Pd/B4C multilayers for soft X-ray region application. Compared to the pure Ar fabricated sample, the interface roughness of the nitridated multilayer is slightly increased while the compressive stress is essentially relaxed from -623 MPa (pure Ar) to -85 MPa (15% N2). A maximum reflectance of 32% is measured at the wavelength of 9.5 nm for the multilayer fabricated with 15% N2. After storing the multilayers in an air environment for 6-17 months, a distinct aging effect is observed on the nitridated samples. The transmission electron microscopy results indicate that a large part of the top layers of the nitridated samples is deteriorated with severe interdiffusion, essential decrease in d-spacing, and compacted multilayer structure. The deterioration is less pronounced for the multilayers fabricated with a higher ratio of N2. Energy dispersive X-ray spectroscopy reveals that the concentration of nitrogen and boron in the degraded area is much reduced compared to the intact layers. A primitive model of upward diffusion of nitrogen and boron is proposed to explain the aging effects of the nitridated structure.

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

We explored the possibility to quantify the atomic in-depth distributions by using the energy-dependent soft X-ray reflectivity (SXRR) measurements, in particular, the possibility to obtain the profiles of low- Z elements [C, N, O, Si] in heterostructures containing high concentration of higher- Z atoms [Ti, Sr, Hf]. We have shown that the SXRR technique allows one not only to quantify the atomic composition of the Sr-rich SrTi x O y insulators grown on (1 0 0)Si by the Atomic Layer Deposition method but also to obtain atomic profiles across a few-nm thick underlayer (UL) inserted between SrTi x O y film and the Si substrate. The accuracy of atomic concentrations and densities estimated is already sufficient to trace even small variations in composition of the SrTi x O y grown by ALD on the chemically different underlayers and most it is important the composition and extension of an interfaces.

The optimized design of multilayer-coated blazed gratings (MLBG) for high-flux tender X-ray monochromators was systematically studied by numerical simulations. The resulting correlation between the multilayer d-spacing and grating blaze angle significantly deviated from the one predicted by conventional equations. Three high line density gratings with different blaze angles were fabricated and coated by the same Cr/C multilayer. The MLBG with an optimal blaze angle of 1.0 degrees showed a record efficiency reaching 60% at 3.1 keV and 4.1 keV. The measured efficiencies of all three gratings were consistent with calculated results proving the validity of the numerical simulation and indicating a more rigorous way to design the optimal MLBG structure. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

Graphical abstractDisplay Omitted Air-exposed Sr-rich-SrTiO3/B/Si-ALD systems (B: SiO2, Si3N4 and HfO2) are studied.Surfaces of all the films are carbonate-enriched by SrCO3 compound.Density of films and Si-B interface width depends on the interlayer material.Only the Si3N4 interlayer stabilizes Sr enrichment of the film in atmosphere.HfO2 interlayer provokes an enhancement of the film structure imperfection. The paper is focused on the methods developed by the Authors for mathematical analysis of the data obtained by three independent spectroscopic nondestructive techniques and on their application to the air-exposed SrTiO3 based heterostructures. It was established that the surfaces of all the investigated SrTiO3 films are carbonate-rich surfaces in the form of SrCO3, of which the content in different samples varied. The density of SrTiO3 films and the interface width between Si-substrate and interlayer depends on the interlayer material. Only the Si3N4 interlayer supports the Sr-surface enrichment of the film in atmosphere. The HfO2 interlayer promotes the damage of the structure creating numerous defects.

Extremely low intensity of most existing laboratory X-ray sources (λ ∼ 0.01–10 nm) calls for the development of collimating and concentrating optics, which allow to increase significantly the radiation power on the sample surface. The problem of optimizing concentrator parameters is analytically solved in this study. This solution allows one to determine (without any auxiliary calculations) the maximum possible efficiency of a concentrator at any wavelength and analyze the dependence of its efficiency on the source size, wavelength, the source-sample distance, etc.

The key features of the inverse problem of X-ray reflectometry (i.e., the reconstruction of the depth profile of the dielectric constant using an experimental angular dependence of reflectivity) are discussed and essential factors leading to the ambiguity of its solution are analyzed. A simple approach to studying the internal structure of HfO2 films, which is based on the application of a physically reasonable model, is considered. The principles for constructing a film model and the criteria for choosing a minimal number of fitting parameters are discussed. It is shown that the ambiguity of the solution to the inverse problem is retained even for the simplest single-film models. Approaches allowing one to pick out the most realistic solution from several variants are discussed.

A multilayer-based collimated plane-grating monochromator (cPGM) with efficiency one order of magnitude higher than the traditional cPGM is proposed for the tender X-ray range. The resolving power can also be increased with improved photon flux by using a large blaze angle and working at high diffraction order., Collimated plane-grating monochromators (cPGMs), consisting of a plane mirror and plane diffraction grating, are essential optics in synchrotron radiation sources for their remarkable flexibility and good optical characteristics in the soft X-ray region. However, the poor energy transport efficiency of a conventional cPGM (single-layer-coated) degrades the source intensity and leaves reduced flux at the sample, especially for the tender X-ray range (1–4 keV) that covers a large number of K- and L-edges of medium-Z elements, and M-edges of high-Z elements. To overcome this limitation, the use of a multilayer-based cPGM is proposed, combining a multilayer-coated plane mirror with blazed multilayer gratings. With this combination, the effective efficiency of cPGMs can be increased by an order of magnitude compared with the conventional single-layer cPGMs. In addition, higher resolving power can be achieved with improved efficiency by increasing the blaze angle and working at higher diffraction order.

Multilayer mirrors (MLM) with narrow spectral bandwidth are important for X-ray spectroscopy and imaging experiments in order to improve the spectral resolution. To overcome the bandwidth limit of conventional multilayers, single order lamellar multilayer grating (LMG) is one of the most promising methods. Driven by the high resolution spectroscopy for the plasma diagnosis at E=~1keV, single order LMG based on MoSi2/Si multilayer is developed. The multilayer period is 5.0 nm, with the Si thickness ratio of 0.6. An LMG with 600 nm grating period and 1:2 line-to-space ratio is designed. As it works at the single order diffraction regime, the 0th order peak reflectance (in theory) of the LMG is 45.4% at E=1.2 keV, which is the same as the multilayer mirror. The bandwidth can be reduced by 3 times compared to the planar multilayer. To demonstrate this LMG structure, MoSi2/Si multilayers have been deposited using direct current magnetron sputtering. Deep reactive ion etching technique is under optimization in order to produce the multilayer grating structure with a high aspect-ratio of around 5.

An approach to designing wideband blazed multilayer gratings is introduced and applied to gratings operating at 17–25 nm. We demonstrate single-order operation of broadband multilayer gratings, despite their very wide spectral and angular bandpass, when only one diffraction wave is excited and the diffraction efficiency reaches the reflectivity of a conventional depth-graded multilayer mirror, eliminating overlapping of different-order diffraction waves. The selection principles for the geometrical parameters of gratings are discussed. We formulate a “law of similarity” for wideband gratings that allows us to design gratings with different geometrical parameters but practically the same spectral dependence of the diffraction efficiency.

Is shown that, if the expansions of the Debye-Waller formulas for the reflection and total scattering coefficients in the roughness height σ are limited to terms of order σ2, these expressions are valid for any layered inhomogeneous medium with conformal (depth-periodic) roughness and for any distribution function of the roughness heights if the roughness correlation length along the surface is sufficiently large. The advantages of measuring the total reflection coefficient, which characterizes the total intensity of radiation (both specularly reflected and diffusively scattered) directed by a rough surface back into vacuum, for solving the inverse problem of X-ray reflectometry (i.e., the reconstruction of the permittivity profile from a measured reflection curve) are discussed.

For the first time the genus Wollea Bornet et Flahault was recorded in Eastern Siberia (Yenissei River, Karskoe See Basin) and isolated to monoclonal axenic strain ACCS 045. The strain was characterized by a combination of morphological and molecular approaches. It shares the diacritical features of the type-species W. saccata (Wolle) Bornet et Flahault and W. bharadwajae R.N. Singh such as macroscopic gelatinous colonies, tube-like, trichomes more or less straight or slightly curved, sheaths around trichomes are absent, heterocytes intercalary, and paraheterocytic akinete development at both sides of heteocytes in short series. A morphological comparison shows that it differs from W. saccata in the form of colonies being saccule, the form of vegetative cells and the heterocytes being barrel-shaped, the form of terminal cells being conical-rounded, and from W. bharadwajae in the form of akinetes being cylindrical or ellipsoid. The first available 16S rRNA gene sequence of Wollea appeared poorly related to other cyanobacterial sequences. According to the traditional classification systems based on morphological and ecological observations genus Wollea appears closest to Anabaena and Nostoc. However, the phylogenetic placement of Wollea based on 16S rRNA gene sequence was distant from Nostoc and the most closely related to taxa in benthic Anabaena, Sphaerospermopsis, Cylindrospermopsis, and Raphidiopsis.

We describe several techniques to design X-ray multilayer mirrors with enhanced bandwidth and, more especially, bandwidth with a shape that optimizes its matching with a given source angular distribution. A Gaussian angular distribution source emitting at the characteristic Mo- K α radiation ( λ =0.071 nm), a radiation regularly used in X-ray analytical applications, is used for the demonstration. Three approaches are developed and compared to design multilayer structures with maximum efficiency, where efficiency is defined here as the convolution of the source and reflectance angular profiles. The first (most general) approach, which can be applied for arbitrary source profiles, is based on the exact Euler–Lagrange equation and a general expression for the multilayer mirror reflectivity of arbitrary wideband. With this method, the depth-distribution of the multilayer bi-layer thickness was found to be smooth. Numerical refinements of the obtained analytical solution were not useful, giving insignificant efficiency increases despite significant complication of the thickness depth-distribution of the multilayer stack. The efficiency of some of these depth-graded structures exceeds that of a periodic mirror by a factor of two in our case. The main factor limiting the efficiency was absorption of the radiation by the materials. The second approach is based on designing a simpler depth-graded multilayer mirror with a linear variation of bi-layer thickness and a constant thickness ratio. Such a mirror proved to have an efficiency close to the maximum possible one. The same conclusion is also true for the simplest design approach, where several periodic substructures are stacked on top of each other, our third described approach. We found that about only four substructures are necessary. In this case the optimization procedure is based on simply three fitting parameters, independently of the number of periodic substructures. We show that the efficiency decreases quickly with increasing interface width. Therefore, multilayer structures with abrupt interfaces, e.g., Mo 2 C/Si multilayers instead of the more conventional Mo/Si multilayers, are preferable in practice. The efficiency also depends strongly on the mean grazing angle incident on the mirror and the angular width of the source (for a fixed number of bi-layers). This must be taken into consideration when designing wide-band multilayer coated X-ray collimators or concentrators.

Ru/B4C multilayer mirrors are used for hard X-ray monochromators with moderate spectral resolution and high integral flux. To overcome the problem of large compressive stress inherent in Ru/B4C multilayers, a reactive sputtering technique using a mixture working gas of argon and nitrogen with different partial pressures was tested, and the fabricated multilayers had a period of 3 nm. The intrinsic stress was essentially reduced after nitridation and relaxed to zero value at approximately 15% partial pressure of nitrogen in the working gas. Interface roughness was slightly increased which can be caused by the polycrystalline structure inside the nitridated samples. More importantly, the nitridated multilayers showed an enhanced reflectance (67% at 8.04 keV photon energy) as compared with the one fabricated with pure Ar (54%). The structure analysis with transmission electron microscopy and X-ray photoelectron spectroscopy demonstrated that nitrogen incorporated into a multilayer structure was mostly located in the B4C layers forming BN compounds, which suppressed the diffusion of boron, stabilized the interfaces and enhanced the reflectance.

The optical theorem is generalized for the general case of X-ray wave reflection from an arbitrary layered rough medium. It is proven strictly that in the absence of absorption the energy conservation law is exactly satisfied within the distorted wave Born approximation if the angular scattering distribution is calculated taking into account only the single wave scattering from the inhomogeneities of the medium and if the specular reflectance and transmittance are calculated with allowance for both single and double scattering.

The possibility of smoothening aspherical X-ray mirrors by irradiation of the surface with a low-energy ion beam is investigated. Nanofocusing being the primary application of these mirrors the ion beam conditions must be optimized to achieve a surface roughness of the order of 0.1–0.2 nm. To address this issue a first study was performed on silicon flat substrates etched using ion energies ranging from 400 to 1200 eV. A second study consisted of eroding the silicon surface while varying the ion grazing incidence angle between 10° and 90° for a fixed value of the ion energy. The surface topography of the samples was characterized at various scales using atomic force microscopy (probed area: 1−10 μm2), interferential optical microscopy (probed area: 1 mm2) and X-ray scattering (probed area: 100 mm2). Finally, a study by AFM of the evolution of the surface finish level of a silicon mirror after ion erosion at various depth values up to 10 μm allowed a trade off to be found between total etch time and the finish quality level in view of profiling a highly aspherically shaped mirror starting from a flat surface.

We present a fast and robust ion beam etching technique to profile initially flat surfaces into aspherical ones. The surfacing method is based on the displacement at variable speed of a double-blade system placed between a broad ion beam source and a mirror, thus allowing a spatial modulation of the ion dose along the mirror surface. The fabrication process was validated using various metrology techniques to assess both mirror figure and finish. The method was successfully applied to produce two strongly elliptically shaped mirror prototypes (source–mirror distance 150 m and demagnification 3000). The residual slope errors were found to be 18 μrad over a mirror length of 40 mm while the root mean squared roughness remains below 0.2 nm for spatial periods less than 130 μm.

The paper deals with the study of the roughness parameters of sapphire substrates as studied by atomic force microscopy and X-ray dispersion. It is shown that the functions of the central power density of the roughness height calculated from data of both methods are in good agreement. A complex approach to the surface analysis enables the stable manufacturing of plates with the effective roughness height less than 0.2 nm, which is not inferior to data given in the specification of the producers outside Russia

The paper shows the importance of soft X-ray reflection spectroscopy as a non-destructive in-depth characterization tool for the middle atomic ordering in TiO2 thin films. The microstructure of TiO2 films synthesized by magnetron sputtering on Si(100) wafers was characterized by X-ray reflection spectroscopy (XRS), X-ray Diffraction (XRD) method and X-ray reflectometry (XRR). Reflection spectra and calculated absorption spectra were analyzed in the vicinity of Ti L2,3 and O K absorption edges. It was established that the 70 nm TiO2 film is polycrystalline with an anatase structure and homogeneous in depth. The 10 nm TiO2 film is amorphous. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The whispering gallery effect in the hard X-ray region (0.15-0.3 nm) has been theoretically and experimentally investigated using a concave spherical mirror with a 25-cm radius of curvature and a diameter of 6 cm. A spherical mirror finds and captures the rays incident on its surface in the whispering gallery mode; there is no need to perform an exact alignment of the mirror with respect to the incident X-ray beam in order to observe the effect. To analyze the experimental data, we used the ray tracing method. It is shown that the results of the experiment and computer simulation are in good agreement.

Institute of Crystallography, Leninsky prospect 59, Moscow 119333, Russia Received 25 September 2006, revised 7 January 2007, accepted 2 April 2007 Published online 1 August 2007 PACS 61.10.Kw, 68.35.Ct, 81.15.Cd, 81.65.Cf An apparatus and a characterization technique have been developed at the ESRF beamline BM5 to inves-tigate in-situ the evolution of the morphology of a film using grazing incidence X-ray reflectometry. The instrument is capable of measuring in-situ and in real time the X-ray intensity specularly and diffusely scattered from a rough thin film during various surfacing processes. The variation of the specular intensity as a function of the processing time, recorded simultaneously with each X-ray scattering diagram, is ana-lyzed to infer the film growth rate, the film density and the variation of roughness conformity during sur-face processing. The potential of the method is demonstrated for two particular cases: thin film deposition by magnetron sputtering and subsequent film etching by low energy ion bombardment. The paper describes some recent achievements and present examples of on-line diagnostics for which real time in-situ X-rays reflectometry proves to be a unique probe.

The evolution of a tungsten thin film grown by magnetron sputtering was studied using a dynamic scaling approach. Film growth was followed in-situ and in real-time by monitoring both the specular and the diffuse X-ray scattered intensities as a function of the time of deposition. The analysis of the scattering data allowed us to determine the two Power Spectral Density (PSD) functions, which describe the thin film topography. The time-dependent PSD-function, which describes the dynamic of the external film surface, is found to obey a universal scaling form, which characterizes the thin film growth. The data collapse of these PSDs into a single master curve was achieved using scaling exponents α = 0.18 ± 0.02 and β = 0.06 ± 0.01. In addition, by analyzing the temporal variation of the roughness conformity, it has been demonstrated that the replication factor decreases exponentially with increasing film thickness and spatial frequency. Hence, for a 25 nm thick film the vertical correlation disappears for spatial frequencies p greater than 3.6 μm − 1 .

Peculiarities of X-ray diffraction from a rough surface at an extremely small grazing angle of an incident beam are theoretically studied. The interrelation of four diffraction channels (coherent reflectance, coherent transmittance, diffuse scattering in vacuum, and scattering into the matter depth) is analyzed for different limiting cases (large and small correlation length of roughness and large and extremely small grazing angle of incident radiation). Both the Debye-Waller and the Nevot-Croce factors are demonstrated to describe improperly the features of X-ray diffraction at extremely small grazing angles. More appropriate simple analytic expressions for the specular reflectivity and total integrated scattering in vacuum are obtained instead. Transformation of one limiting diffraction regime into another one with variation in the correlation length of roughness is discussed.

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.

Wideband multilayers designed for various applications in hard X-ray to Extreme UV spectral regions are based on a layered system with layer thicknesses varying largely in depth. However, because the internal structure of a thin film depends on its thickness, this will result in multilayers in which material properties such as density, crystallinity, dielectric constant and effective thickness vary from layer to layer. This variation causes the fabricated multilayers to deviate from the model and negatively influences the reflectivity of the multilayers. In this work we solve this problem by developing designs of wideband multilayers with strongly reduced layer thickness variations in depth, without essential degradation of their optical characteristics.

We present a short review of our activities carried out in Tongji University (Shanghai, China) in the field of theory and technology of soft X-ray multilayer diffraction gratings. Diffraction gratings are widely used to study the structure and dynamics of a matter in laboratory and space by spectral analysis techniques. Combining multilayer and grating structures into a single unit allows to increase essentially both the spectral resolution and the efficiency of the diffraction optics. The unified analytical theory of soft X-ray diffraction from multilayer gratings operating in the single-order regime is briefly discussed. The single-order regime occurs when incident wave excites the only diffraction order and it is characterized by ultimately high diffraction efficiency tending to the reflectivity of conventional multilayer mirror. Our first experiments in fabrication of the blazed multilayer gratings by anisotropic etching of a silicon crystal with small roughness of the facet surfaces are described.

International audience; Pd/Y multilayer mirrors operating in the soft X-ray region are characterized by a high theoretical reflectance, reaching 65% at normal incidence in the 8-12 nm wavelength range. However, a severe intermixing of neighboring Pd and Y layers results in an almost total disappearance of the interfaces inside the multilayer structures fabricated by direct current magnetron sputtering and thus a dramatic reflectivity decrease. Based on grazing incidence X-ray reflectometry and X-ray photoelectron spectroscopy, we demonstrate that the stability of the interfaces in Pd/Y multilayer structures can be essentially improved by adding a small amount of nitrogen (4-8%) to the working gas (Ar). High resolution transmission electron microscopy shows that the interlayer width is only 0.9 nm and 0.6 nm for Y(N)-on-Pd(N) and Pd(N)-on-Y(N) interfaces, respectively. A well-defined crystalline texture of YN (200) is observed on the electron diffraction pattern. As a result, the measured reflectance of the Pd(N)/Y(N) multilayer achieves 30% at λ = 9.3 nm. The peak reflectivity value is limited by the remaining interlayers and the formation of the YN compound inside the yttrium layers, resulting in an increased absorption.

Applications of the X-ray scattering technique for studying supersmooth surfaces with rms roughness of 0.1– 0.2 nm are discussed. The experimental schemes are analyzed and systematic errors on the determination of 2D and 1D PSD-functions are evaluated. Results of laboratory and synchrotron experiments are presented on the study of roughness of superpolished substrates made of different materials as well as for B4C films of different thickness.

The unique potentialities and prospects for practical use of the X-ray scattering method as applied to the study and testing of surface roughnesses are considered. The high sensitivity, informative capability, and reliability of this method are demonstrated by using numerous examples. The results obtained by the X-ray scattering method at different wavelengths are compared with the available data of atomic-force microscopy.

We present first experimental results on the fabrication and characterization of depth-graded x-ray multilayers providing a broad and well-defined reflectivity profile. We have designed and deposited irregular multilayer structures providing a practically constant reflectivity of about 20% around the first Bragg-reflection and a bandwidth of about 20% in both incident angle and photon energy. Detailed numerical simulations allow for the determination of residual errors in the layer stack.

The scattering of X-rays from a rough multilayer structure is analyzed in the framework of the first-order scalar perturbation theory. As known, the scattering diagram from a multilayer mirror is expressed as a double sum of partial scattering amplitudes from each interface. In the present work the summation is performed in an explicit form. The simple analytic formulas are deduced, which are well suited for analysis of physical phenomena observed in experiments and describe all the features of X-ray scattering.

We present first experimental results on the fabrication and characterization of depth-graded X-ray multilayers providing a broad and well-defined reflectivity profile. Following a theoretical approach including analytical and numerical techniques we have designed and deposited multilayer structures with a practically constant reflectivity of about 20% around the first Bragg-reflection and a bandwidth of about 20% in both incident angle and photon energy. A precise characterization using numerical simulations allows the determination of residual errors in the structure, which can appear during or after the coating process. The discussion includes practical issues and technical limitations of the deposition process as well as novel applications in modern X-ray optics.