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The strong influence of the orientation of an external magnetic field of a system of permanent magnets on the crystal structure of cobalt films grown on an amorphous carbon sublayer was revealed by the methods of transmission electron microscopy and selected area diffraction. While the horizontal component of the magnetic field strength impedes the process of cobalt grains growth, the vertical one, on the contrary, contributes to this process. The vertical component of the magnetic field promotes strong growth of crystalline cobalt grains with an axis [0001] perpendicular to the film surface at the expense of grains with different orientations. As the strength of the vertical component of the magnetic field increases to H ≈ 1.2 × 104 Oe, the size of some crystalline grains with orientation [0001] reaches about 1 μm in the cobalt film with a nominal thickness of 8 nm. In a horizontal magnetic field of the order of 1.2 × 104 Oe, the average grain size is only 16 nm, which is only twice the nominal film thickness. The paper discusses issues related to the influence of magnetic crystallographic anisotropy and external magnetic field on the processes of nucleation during structure rearrangement.

Structural evolution of the ultra-thin cobalt layers grown on amorphous carbon by DC magnetron sputtering were studied in detail by transmission electron microscopy and low-angle X-ray diffraction for a range of the cobalt thickness from 1.5 nm to 4.6 nm. It was shown that atomic structure of cobalt layers was amorphous at the layer thicknesses below 2 nm, an amorphous matrix with embedded nuclei of the crystalline phase with in-plane size of 1–2 nm in the thickness range from 3 nm to 3.2 nm, and polycrystalline with the randomly oriented HCP cobalt grains at thicknesses over 4 nm. Increase of the cobalt thickness from 3.2 nm to 4.6 nm led to growth of the cobalt grains with in-plane average size up to ~ 70 nm by the normal grain coarsening process. Transition of the atomic structure of cobalt from the isotropic amorphous state to the anisotropic crystalline state in the thickness range of ~ 2–4 nm was accompanied by deterioration of the magnetization vector direction within the ferromagnetic domains due to high magnetic anisotropy of HCP lattice of cobalt.

International audience; This review paper summarizes and provides an overview of our recent studies related to two types of short-period multilayer X-ray mirrors, W/B 4 C and Co/C. It deals with the experimental observation of the layer intermixing effects and how they affect the X-ray mirror's optical performance. The paper presents also some examples of using the fabricated X-ray mirrors in focusing and imaging experiments at the working wavelengths 2.48 nm and 4.47 nm.

Wear is an important phenomenon that affects the efficiency and life of all moving machines. In this regard, extensive efforts have been devoted to achieve the lowest possible wear in sliding systems. With the advent of novel materials in recent years, technology is moving toward realization of zero wear. Here, we report on the development of new functional coatings comprising periodically stacked nanolayers of amorphous carbon and cobalt that are extremely wear resistant at the micro and macro scale. Because of their unique structure, these coatings simultaneously provide high elasticity and ultrahigh shear strength. As a result, almost zero wear was observed even after one million sliding cycles without any lubrication. The wear rate was reduced by 8-10-fold compared with the best previously reported data on extremely low wear materials.

Structure characterization of Sb/B4C multilayers for soft X-ray optics with a layers thickness from 0.5 nm to 7 nm is reported for the first time. Sb/B4C coatings were manufactured via magnetron sputtering. Amorphous and crystalline phases of the layers and the multilayer structure parameters were characterized with the X-ray diffraction data and the TEM data. The Sb/B4C multilayers demonstrated long term stability of their parameters and performances. The reached value of the reflectance of the Sb/B4C multilayers is 19–28% measured at the near-normal incidence in the wavelength range of 6.64–8.5 nm. The influence of reduced Sb density on the reflectivity is discussed.

The structural evolution of a C/Si periodical multilayers is studied by small-angle X-ray diffraction and cross-section transmission electron microscopy. Mixed zones 0.6–0.65 nm thick with different densities are detected at the C/Si and Si/C interfaces in the initial state. The effect of annealing on the thickness, the density, and the phase composition of the layers and the mixed zones is investigated in the temperature range 300–1050°C. Two stages of changing the multilayer composition period upon heating are found. The period increases as the temperature increases up to 700°C and then decreases. The fracture of the composition begins in the silicon layers, where pores and cubic 3C-SiC nanocrystals form at 900°C. The fracture of the layered structure of the composition is completed at T > 1000°C.

The frictional and wear characteristics of nanostructured DLC films were investigated. The coatings were deposited on silicon substrates by irradiation of a mass-separated C 60 ion beam with 5 keV of energy and a deposition temperature ranging from 100 to 450 °C. The effects of deposition temperature on the surface morphology, nano-structure, mechanical properties and tribological characteristics of the coatings were assessed. Results showed that deposition temperature strongly affects the nanostructure and surface morphology of the coatings. Coatings deposited at temperatures exceeding 350–400 °C exhibited an increase in surface roughness as well as compressive stress due to the formation of graphite, which led to a significant increase in the friction coefficient and wear rate. Coatings deposited at 300 °C showed the best tribological properties.

The quantitative characteristics of the interlayer interaction in multilayer W/B4C periodic compositions produced by magnetron sputtering are studied by small-angle X-ray diffraction using CuK α radiation and by electron microscopy of transverse cuts. It is found that approximately 0.85 nm of the tungsten layer thickness is consumed for the formation of mixed zones at layer boundaries. The mixed layers have a density of 13.4 ± 0.7 g/cm3 and contain tungsten in a bound chemical state. The effect of these mixed zones on the X-ray reflectivity of multilayer W/B4C compositions is estimated. A method is proposed to determine the layer thickness at a small number of peaks in an X-ray diffraction pattern.

We report an exceptionally stable honeycomb carbon allotrope obtained by deposition of vacuum-sublimated graphite. The allotrope structures are derived from our low temperature electron diffraction and electron microscopy data. These structures can be both periodic and random and are built exclusively from sp^{2}-bonded carbon atoms, and may be considered as three-dimensional graphene. They demonstrate high levels of physical absorption of various gases unattainable in other carbon forms such as fullerites or nanotubes. These honeycomb structures can be used not only for storage of various gases and liquids but also as a matrix for new composites.

In this work, we present results on study of DLC, nanocomposite and nanocrystal nanographite films synthesized utilizing mass-separated beam of C60-ions with energy in range from 2 to 6 keV (energy dispersions approximately 1 keV) and at Ts in the range of RT - 873 K. The dependence of the structure, mechanical and electrical properties from the ion energy and substrate temperature was revealed. We demonstrate a possibility to control the orientation of the base planes in the nanographite grains during the film growth. The dependence of mechanical properties of the films from the orientation of the base planes was defined. It is discussed a mechanisms of oriented growth for nanocrystal graphite. Possible applications of the textured nanocomposite and nanographite films are nanodevices, thin-filmed lithium batteries and field-emitter arrays.

The structure of molybdenum layers deposited by direct current magnetron sputtering onto the amorphous silicon (a-Si) layers as function of nominal layer thickness was studied by methods of transmission electron microscopy. Molybdenum layers with nominal thickness 1.5 1 1 ¯ 0 direction. As the metal layer thickness increases Mo-crystallites take the more regular form at the expense of recrystallization.

We study two C(5 nm)/Co/C(5 nm) multilayer stacks with cobalt layer thicknesses of 4 and 13 nm. Structural analysis of fabricated systems reveals corresponding cobalt layers to be in amorphous (nanocrystalline) and [0001]-textured hcp-phase. The magnetic measurements for both systems agree well with structural data. For the amorphous cobalt layer magnetic data reveal the absence of carbides, high saturation field of 1.6 × 10 4 Oe and vanishing inplane coercive field. We also show that strong inplane anisotropy can be introduced into the amorphous cobalt film by controlling the process parameters of DC-magnetron sputtering. For the textured hcp-cobalt film we have deduced the presence of randomly close-packed (rcp) structure. We assume this defect-rich cobalt hcp-phase to be responsible for the detected elimination of the out-of-plane magnetic anisotropy in the corresponding multilayer sample.

Методами рентгенівської дифракції (0,154 нм), просвічувачої електронної мікроскопії поперечних зрізів і рефлектометрії в області екстремального ультрафіолету (41-51 нм) досліджені бар'єрні властивості шарів CrB2 товщиною 0.3-1.3 нм в багатошарових рентгенівських дзеркалах (БРД) Sc/CrB2/Si, виготовлених методом прямоточного магнетронного розпилення. Показано, що бар'єрні шари товщиною ~ 0,3 нм повністю розділяють шари Sc і Si і перешкоджають утворенню перемішаних зон ScSi. Більш тонкі шари діборида хрому взаємодіють з матричними шарами, формуючи шари з переважним вмістом ScB2 на кордонах Si-on-Sc і CrSi2 на кордонах Sc-on-Si. Показано, що БРД Sc/Si з бар'єрами на обох кордонах зберігають високу відбивну здатність на довжині хвилі ~ 47 нм. Methods of X-ray reflectometry (0.154 nm), cross-sectional transmission electron microscopy and reflectometry in the EUV region (41-51 nm) were used to investigate the barrier properties of CrB2 layers 0.3-1.3 nm thick in Sc/CrB2/Si multilayer X-ray mirrors (MXMs) deposited by DC magnetron sputtering. It is shown that barrier layers of ~ 0.3 nm separate Sc and Si layers completely and prevent interacting the Sc and Si layers. Thinner chromium diboride layers interact with the matrix layers forming interlayers containing mostly ScB2 on the Si-on-Sc interfaces and CrSi2 on the Sc-on-Si ones. Scandium-silicon MXMs with barrier layers on the both interfaces are shown to retain high reflectivity at the wavelength of ~ 47 nm.

The interaction of low-energy bismuth ions with a fullerite surface at ion energies in the range from 50 to 200 eV and at target temperatures from 100 to 270°C has been studied experimentally. Investigation of the structure of the condensates formed by a flow of the eroding target material has revealed that the emitted flow consists of C60 molecules and bismuth atoms. The erosion of fullerite is explained by a superposition of three main processes, namely, thermal evaporation, radiation-enhanced sublimation, and physical molecular sputtering, which dominate in different temperature ranges.

Interdiffusion in periodic Sc/Si multilayers with W-based diffusion markers was studied by cross-section transmission electron microscopy and small angle X-ray diffractometry (SAXD). Formation of amorphous ScSi silicide was observed as a result of solid-state amorphization taking place in the Sc/Si multilayers in the 210–250 °C temperature range. The diffusion-governed growth behavior of the amorphous silicide was revealed. The diffusion marker analysis was applied to determine a ratio of intrinsic diffusion coefficients of scandium and silicon. The diffusion-induced shift of the diffusion markers was measured by SAXD with accuracy better than 0.2 nm. It was determined that the intrinsic diffusion coefficient of Si in amorphous silicide was twenty times higher than the one of Sc.

The Sc/Si multilayers are suggested as high-reflectivity coatings for a VUV interval of 35–50 nm. Fabricated mirrors show the normal incidence reflectivity of 30–50% which is high enough to effectively manipulate the beams of synchrotron radiation and compact discharge and laser-driven X-ray lasers. The obtained values are not, however, limiting for the Sc/Si coatings. Theoretical estimations as well as electron microscopy studies of Sc–Si interfaces indicate a large potential for further raising the reflectivity.

Structural, phase, and chemical stabilities of x-ray multilayer mirrors Mo-(B + C) with periods in the range 8-11.5 nm were studied at temperatures of 250-1100°C by small-angle and large-angle x-ray diffraction and electron microscopy methods. Two amorphizations at ~450 and ~750°C and two crystallizations at ~650 and ~850°C of Mo-based layers were observed, which were due to the formation of the molybdenum carbides MoC (hex), γ-MoC, and Mo2C instead of the metal Mo, and to the formation of the molybdenum borides MoB2 and Mo2B5 instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothing of interfaces and by an increase of the multilayer x-ray reflectivity at λ = 0.154 nm. Both crystallizations of Mo-based layers promoted the development of interface roughness and a decrease of multilayer x-ray reflectivity. The destruction of Mo-(B + C) multilayers at ~ 1100°C was caused by the recrystallization of Mo2B5 layers.

The problems inherent in the fabrication of short period multilayer mirrors are discussed and results of the synthesis of multilayer structures with nanometer period are presented. The shortest period observed is 13 A for WSi and WB 4 C sputtered multilayers. Measurements of near normal incidence reflectivity at λ = 31–32A are presented for WSc multilayers with a period approximately 16 A. The measured reflectivity reaches a maximum of 3.3% and is in good agreement with theoretical modeling after the inclusion of interfacial roughness.

Reflection sliced multilayer gratings with 4900 grooves/mm and number of periods N =500 have been produced by sputter-slice technique. Spectra of laser produced plasma of aluminum in the range of 124–250 A have been recorded with a spectral resolution of about 300 in the first order. Comparison with a high resolution spectrum obtained with a conventional spectrograph and theoretical calculations of the diffraction efficiency is given.

By methods of cross-sectional transmission electron micros- copy and small-angle x-ray scattering (λ ¼ 0.154 nm) the influence of Ar gas pressure (1 to 4 mTorr) on the growth of amorphous interfaces in Mo/Si multilayers (MLs) deposited by DC magnetron sputtering is stud- ied. The significant reduction in the ML period, which is evident as a volu- metric contraction, is observed in MLs deposited at Ar pressure where the mean-free path for the sputtered atoms is comparable with the magnetron- substrate distance. Some reduction in the thickness of the amorphous interlayers with Ar pressure increase is found, where the composition of the interlayers is enriched with molybdenum. The interface modification resulted in an increase in EUV reflectance of the Mo/Si MLs.©2013 Society of

Annealing effects in the short-period multilayers Cr3C2/C, TiC/C, Cr3C2/(B + C), and CrB2/C were studied in a wide temperature range ∼200–1200°C by x-ray scattering and cross-sectional electron microscopy. It was shown that the thermodynamic equilibrium of the layer materials at their interfaces and stabilization of layer structure by impurities and heat treatment are effective approaches to short-period multilayers with enhanced thermal stability of their structure and optical properties.

Processes undergoing in Sc/Si multilayer X-ray mirrors (MXMs) with periods of ∼27 nm and barrier layers of CrB20.3- and 0.7-nm thick within the temperature range of 420–780 K were studied by methods of small-angle X-ray reflectivity (λ=0.154 nm) and cross-sectional transmission electron microscopy. All layers with the exception of Sc ones are amorphous. Barrier layers are stable at least up to a temperature of 625 K and double the activation energy of diffusional intermixing at moderate temperatures. Introduction of barriers improves the thermal stability of Sc/Si MXMs at least by 80 degrees. Diffusion of Si atoms through barrier layers into Sc layers with formation of silicides was shown to be the main degradation mechanism of MXMs. A comparison of the stability for Sc/Si MXMs with different barriers published in the literature is conducted. The ways of further improvement of barrier properties are discussed.

Structure and stressed state of molybdenum layers in Mo/Si multilayer periodical compositions prepared by direct current magnetron sputtering have been investigated by methods of X-ray tensometry in grazing-incidence asymmetrical geometry, cross-sectional transmission electron microscopy and small-angle X-ray reflectometry. The level of symmetrical biaxial stresses depends non-monotonously on the thickness of Mo layers. Value and sign of stresses are defined by the following processes: bombardment of the growing surface of metallic layers by particles with enhanced energy, recrystallization of Mo grains and the formation of silicon-substitutional solid solution in molybdenum. The bombardment is accompanied by a formation of self-interstitial Mo atoms that sink at internal dislocation defects, an increase in quantity of lattice points in the film plane and a generation of biaxial compressive stresses. The recrystallization reduces the density of grain boundaries, at the same time decreases the average specific volume of condensed atoms and generates tensile stresses in Mo layers. Compared to those for pure bulk molybdenum, notably lower average lattice spacing was measured in unstressed sections for Mo layer thicknesses less than 20 nm. This indicates the formation of a solid solution of Si in molybdenum presumably in vicinity of Mo-on-Si interface.

The influence of a negative substrate-applied bias potential on the structure of periodic Mo/Si multilayer compositions has been investigated by means of cross-sectional electron microscopy, small-angle X-ray reflectivity, X-ray diffraction and by modeling the small-angle spectra. It is known that the crystalline structure of molybdenum layers is the main source of interface roughness. In the absence of a bias potential application, the interface roughness tends to develop from the substrate towards the surface of a Mo/Si multilayer composition. A negative bias potential (up to -200 V) applied to a substrate during silicon layer deposition leads to smoother interfaces and improves the layer morphology. After increasing the bias potential over -200 V a considerable growth of an amorphous interlayer transition zone can be observed at Si-on-Mo interfaces. By raising the bias potential during the deposition of Mo layers a development of roughness at Mo-on-Si interfaces as well as growing interlayer thicknesses were found.

Multilayer mirrors for the extreme ultraviolet (EUV) are key elements for numerous applications of coherent EUV sources such as new tabletop lasers and free-electron lasers. However the field of applications is limited by the radiation and thermal stability of the multilayers. Taking into account the growing power of EUV sources the stability of the optics becomes crucial. To overcome this problem it is necessary to study the degradation of multilayers and try to increase their temporal and thermal stability. In this paper we report the results of detailed study of structural changes in Sc/Si multilayers when exposed to intense EUV laser pulses. Various types of surface damage such as melting, boiling, shock wave creation and ablation were observed as irradiation fluencies increase. Cross-sectional TEM study revealed that the layer structure was completely destroyed in the upper part of multilayer, but still survived below. The layers adjacent to the substrate remained intact even through the multilayer surface melted down, though the structure of the layers beneath the molten zone was noticeably changed. The layer structure in this thermally affected zone is similar to that of isothermally annealed samples. All stages of scandium silicide formation such as interdiffusion, solid-state amorphization, silicide crystallization etc., are present in the thermally affected zone. It indicates a thermal nature of the damage mechanism. The tungsten diffusion barriers were applied to the scandium/silicon interfaces. It was shown that the barriers inhibited interdiffusion and increased the thermal stability of Sc/Si mirrors.

In summary, we have realized a series of experiments with a compact 46.9 nm wavelength laser that produces intense pulses of nanosecond duration to study the ablation behavior of metals, common polymers, and Sc/Si multilayers. The key ablation process in polymers is likely to be a radiolysis of the polymer chains by EUV photons, resulting in the formation of numerous small molecular fragments that are subsequently removed from the surface of the samples. The EUV ablation rates for different polymers were found to be almost material independent, ∼ 50 – 400 nm/pulse. In each material EUV irradiation was observed to leave smooth craters with well defined edges and without signs of thermal damage. No threshold behavior was detected in the EUV ablation of the polymers in the range of fluences used in the experiment. In contrast to polymers the irradiation damage in metals and in Sc/Si multilayers is thermal in nature. A damage threshold of 0.08 J/cm2 was measured in the multilayer mirror coatings deposited on Si or borosilicate glass substrates, compared with a measured value of 0.7 J/cm2 for bare Si substrates. These results are relevant to the use of these mirrors with newly developed high-power EUV laser sources and provide a benchmark for their further improvement. In combination, the experiments demonstrate that compact extreme ultraviolet lasers are new tools available for surface modification studies and patterning.

Processes of diffusion and silicide formation in stressed multilayers of Mo/Si, as a result of their isothermal annealing, were studied in this paper by methods of cross-sectional transmission electron microscopy and X-ray diffraction techniques. It was found that reaction with growth of molybdenum disilicide of reduced density takes place at Mo-on-MoSi2 interfaces up to formation of similar to 7 mn thick layers, due to annealing treatment within 350-400 degrees C temperature range. Silicon atoms were found to be the dominating diffusive components. As a result of Si atoms' diffusion from Si layer, sublayers of a somewhat lower density are being formed at MoSi2-on-Si interfaces. Growth of molybdenum disilicide is accompanied by reduction of multilayer period. Activation energy of diffusion process (phase formation) makes up similar to 2.2 eV. Influence of compressive stresses (that exist in Mo layers) on process of phase formation, both in as-deposited and in annealed samples, is discussed in this paper.

We demonstrate the use of a tabletop capillary-discharge Ne-like Ar laser emitting na nosecond duration pulses at a wavelength of 46.9 nm for investigation of radiation damage mechanism and damage threshold in Sc/Si extreme ultraviolet multilayer mirrors. To vary th e emission load at the surface of the mi rror under test the intense 0.13 mJ laser pulses were focused using a spherical Sc/Si multilayer mirror to obtain fluences ranging from ~ 0.01 to >10 J/cm 2 . Single spots and large area patterns (2x2 mm 2 ) were irradiated depending on the type of surface analysis technique employed. Damage threshold fluences of ~ 0.08 J/cm 2 were measured for Sc/Si coatings deposited on both borosilicate glass and Si substrates, compared to the 0.7 J/cm 2 found necessary to damage a bare Si substrate. The use of scanning and transmission electron microscopy, and small-angle X-ray diffraction techniques revealed the thermal nature of the damage mechanism. These results are relevant to the use of the Sc/Si mirrors in combination with newly developed high power EUV sources, and provide a benc hmark for their further improvement. Keywords: EUV laser, Sc/Si mirrors, optical damage 1. INTRODUCTION High reflectivity mirrors for the extreme ultraviolet (EUV) range with high damage threshold gain importance as key elements for enabling numerous applications of the rapidly advancing high power coherent EUV sources that include new table-top sources

The damage threshold and damage mechanism of extreme-ultraviolet Sc/Si multilayer mirror coatings are investigated with focused nanosecond pulses at 46.9-nm radiation from a compact capillary-discharge laser. Damage threshold fluences of approximately 0.08 J/cm2 are measured for coatings deposited on both borosilicate glass and Si substrates. The use of scanning and transmission electron microscopy and small-angle x-ray diffraction techniques reveals the thermal nature of the damage mechanism. The results are relevant to the use of newly developed high-flux extreme-ultraviolet sources in applications.

The formation of interlayer transition zones (ITZs) in sputtered Mo/Si multilayer structures was studied by means of cross-section electron microscopy and grazing incidence reflectivity measurements. For the evaluation and calculation of interface effects the multiperiodic design of Mo/Si structure was used. It was found that the thickness asymmetry of ITZs (Mo-on-Si and Si-on-Mo) in Mo/Si multilayer structures depends on the degree of perfection of the crystalline structure of the molybdenum layer. A transition from asymmetrical to symmetrical ITZs with a disordering of the molybdenum crystalline structure was shown. A model for the formation mechanism of asymmetrical ITZs at the different interfaces in Mo/Si multilayer structures is suggested. According to this model, ITZ formation at the Mo-on-Si interface is controlled by the surface diffusion of Si atoms on the growing molybdenum surface. In contrast, ITZ formation at the Si-on-Mo interface is determined by the bulk diffusion of Si atoms in textured molybdenum grains

To improve the thermal stability of Si/Sc multilayer mirrors, thin layers of W were deposited at interlayer boundaries. Using X‐ray scattering and transmission electron microscopy, we studied the interaction of Si and Sc layers at elevated temperatures. It was shown that the W layers of 0.5–0.8 nm thickness form dense WSi2 barriers, which prevent a direct contact between Si and Sc and greatly slow down the formation of scandium silicides. Presented measurements show that Si/W/Sc/W multilayers fabricated by dc‐magnetron sputtering possess long thermal stability up to 250° C and the normal incidence reflectivity of 24 %.

By methods of cross-sectional transmission electron microscopy and small-angle x-ray scattering ( λ = 0.154 nm ) the influence of Ar gas pressure (1 to 4 mTorr) on the growth of amorphous interfaces in Mo/Si multilayers (MLs) deposited by DC magnetron sputtering is studied. The significant reduction in the ML period, which is evident as a volumetric contraction, is observed in MLs deposited at Ar pressure where the mean-free path for the sputtered atoms is comparable with the magnetron-substrate distance. Some reduction in the thickness of the amorphous interlayers with Ar pressure increase is found, where the composition of the interlayers is enriched with molybdenum. The interface modification resulted in an increase in EUV reflectance of the Mo/Si MLs.

Multilayer X-ray optics with enhanced thermal and radiation stabilityFedorenko A. I., Kondratenko V. V., Bugaev E. A., Pershin Yu. P., Ponomarenko A. G., Poitseva 0. V.,Kopylets I. A., Yulin S. A., Zubarev E. N.Kharkiv State Polytechnic University, Department of Metal and Semiconductor PhysicsFrunze Street 21, Kharkiv, 3 10002, UkraineABSTRACTThermal stability of structure, period and X-ray reflectivity of multilayer mirrors for the whole range of soft X-rays withwavelengths 1-30 nm was studied in wide temperature range 350-1400 K by X-ray scattering and cross-sectional electronmicroscopy methods. Irradiation by He particles with energy 30 keV and doses 1x1019-4x102° ion/rn2 and by 10 MeV-electrons with dose up to 1O Gray was carried out for evaluation of radiation stability of Mo/Si and MoSi2/Si multilayermirrors. It was shown that thermodynamic equilibrium of layer materials at their interfaces and stabilization of layer structureby impurities and heat treatment are effective approach to multilayer X-ray optics with enhanced thermal and radiationstability.Keywords: multilayer X-ray optics, thermal stability, phase transformations, crystallization of amorphous layers1. INTRODUCTIONHigh-intensity X-ray sourceuI (synchrotrons, laser plasma, X-ray lasers, etc.) require high stability multilayer opticswithstanding high temperatures and dense fluxes of energetic photons and particles1 . Multilayer X-ray optics with enhancedstability of reflectivity and period is the first of all the problem of multilayer superfluous free energy EG connected with

Space test of x-ray multilayer mirrors on the surface of Russian orbital station 'Mir' revealed that after a 5-month space exposure, multilayers consisting of chemically interacting materials (Mo - Si and WSi 2 - Si) preserved their periods. Preannealing at 570 K for one hour was sufficient to stabilize reflectivity at 1.54 angstroms of mirror WSi 2 - Si with period 33.6 angstroms. Preannealing at 770 K for one hour was not enough to stabilize reflectivity at 1.54 angstroms of MoSi 2 - Si mirror with period 77.7 angstroms (after space exposure its reflectivity was increased by 18% as a result of interface smoothing influenced by space effect agents).

Structure and optical properties (at (lambda) equals 0.154 nm and (lambda) equals 3.16 nm) of W - Ti, W - TiN, W - Sc and Cr - Sc multilayer x-ray mirrors for the long wave part of 'water window' wavelength range were studied by methods of the x-ray diffractometry and cross-sectional electron microscopy. The reflectivities at (lambda) equals 0.154 nm are increased going from W - TiN, Cr - Sc, W - Ti to W - Sc multilayers. Cr - Sc mirrors have highest reflectivity and resolution at (lambda) equals 3.16 nm. Influence of the ambient atmosphere on optical properties of multilayer mirrors is shown.

The effect of elevated temperatures on the structural stability of Mo - Si and MoSi 2 - Si X-ray multilayer mirrors was studied. Multilayers deposited by magnetron sputtering were annealed at temperatures ranging from 300 to 1300 K. A detailed picture of the thermally induced changes in the microstructure is obtained using several techniques including small- and large-angle X-ray scattering and transmission electron microscopy. The main causes of the degradation of Mo - Si mirrors is an interdiffusion mixing of silicon and molybdenum layers and a formation of MoSi 2 in both the hexagonal and tetragonal phases. The smoothening of interfaces in MoSi 2 - Si mirrors and increasing of their reflectance were observed after annealing at temperatures T 2 - Si mirrors undergo a catastrophic degradation at T > 1000 K caused by a crystallization of amorphous Si and a recrystallization of hexagonal MoSi 2 .

Annealing effects in short-period multilayers Cr 3 C 2 /C, TiC/C, Cr 3 C 2 /(B+C) and CrB 2 /C were studied in wide temperature range approximately equals 200-1200 degree(s)C by X-ray scattering and cross-sectional microscopy. It was shown that thermodynamic equilibrium of layers materials at their interfaces and stabilization of layer structure by impurities and heat treatment are effective approaches to short-period multilayers with enhanced thermal stability of their structure and optical properties.

Structural, phase and chemical stabilities of X-ray multilayer mirrors Mo-(B + C) with period in range 8 - 11.5 nm were studied at temperatures 250 to 1100 degree(s)C by small-angle and large-angle X-ray diffraction and electron microscopy methods. Two amorphizations at approximately equals 450 degree(s)C and approximately equals 750 degree(s)C and two crystallizations at approximately equals 650 degree(s)C and approximately equals 850 degree(s)C of Mo-based layers were observed due to formation of molybdenum carbides MoC (hex), (gamma) - MoC and Mo 2 C instead of metal Mo and formation of molybdenum borides MoB 2 and Mo 2 B 5 instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothening of interfaces and by increase of multilayer X-ray reflectivity at (lambda) equals 0.154 nm. Both crystallizations of Mo-based layers promoted development of interface roughness and decrease of multilayers X-ray reflectivity. The destruction of Mo-(B + C) multilayers at approximately equals 1100 degree(s)C was caused by Mo 2 B 5 layers recrystallization.

A beam of accelerated C60 ions is used to deposit superhard (∼50 GPa) carbon films that exhibit high index plasticity (∼0.13–0.14) and high conductivity (up to 3000 S m−1). Transmission electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy are subsequently used to study the microstructure and bond character of the deposited films. The films consist of textured graphite nanocrystals and diamond-like amorphous carbon (DLC). The graphene plane of the nanocrystals is aligned perpendicular to the film surface. It is shown that sp2 bonds dominate in the films. The percentage of sp3 bonds depends on the ion energy and the substrate temperature, and does not exceed 40%. The obtained results suggest that a new nanocomposite material consisting of oriented graphite nanocrystals reinforced by a DLC matrix is synthesized. A simple model is proposed to correlate the excellent mechanical properties with the observed structure.

Problems of short period multilayer mirrors fabrication are discussed. Results of synthesis of multilayer structures with nanometer period are presented. The shortest period observed is 13 angstroms for W - Si and W - B4C sputtered multilayers. Measurements of near normal incidence reflectivity at (lambda) equals 31 - 32 angstroms are described for W - Sc multilayers with period about 16 angstroms. Measured reflectivity achieves 3.3% and is in good agreement with theoretical model.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Specific structural changes in Sc/Si multilayer mirrors irradiated with extreme ultraviolet (EUV) laser single pulses (λ = 46.9 nm) at near damage threshold fluences (0.04–0.23 J cm −2 ) are analysed. We have identified melting of surface layers as the basic degradation mechanism for the mirrors. Both heat generation during silicide formation and low heat conduction of the layered system significantly decreases the degradation threshold of Sc/Si multilayer mirrors compared with bulk materials. The results are relevant to the use of the multilayer mirrors for shaping and directing the intense beams produced by the new generation of coherent EUV sources.

The thermal stability of Mo-Si multilayers prepared by magnetron sputtering is studied. It is found that degradation of x-ray reflectivity of Mo-Si multilayers under heat loading is connected with the roughening of Mo-Si interfaces and the formation of compounds Mo(x)Si(y),. To avoid these degradation mechanisms we fabricated and tested MoSi(2)-Si multilayers under heat loading. The MoSi(2)-Si multilayer appeared to be much more stable both in period and x-ray reflectivity because of thermodynamic equilibrium of the components MoSi(2) and Si at the interface. The working temperature of MoSi(2)-Si multilayers reaches 1000 K.

X-ray diffraction and SEM microscopy were used to study the structural and phase changes in a thin film obtained by magnetron sputtering of a Ti52Zr30Ni18 target (at.%) on a steel substrate under the radiation-thermal influence of pulsed hydrogen plasma on an QSPA Kh-50 accelerator. A technique has been worked out for the formation of the quasicrystalline and crystal-approximant phases as a result of high-speed quenching using pulsed action with a heat load of 0.6 MJ/m2. The changes in the contents of these phases as well as in their structure and substructure parameters were studied during isothermal vacuum annealing at a temperature of 550 °C and also as a result of irradiation with 5 plasma pulses in the range of heat load from 0.1 to 0.4 MJ/m2. The quasicrystalline phase was found to be resistant to irradiation with hydrogen plasma.

We report results of the development of capillary discharge driven metal-vapor plasma waveguides for the development of efficient laser-pumped soft x-ray lasers; and of the use of a previously developed capillary discharge Ne-like Ar 46.9 nm laser in study of the interaction of intense soft x-ray laser with materials. The guiding of a laser beam in a dense capillary discharge plasma channel containing a large density of Ag ions is reported. In term of applications we have conducted studies of materials modification and ablation with focalized 46.9 nm laser radiation at fluences between 0.1 and 100 J cm -2 . The experiments demonstrated that the combined high repetition rate and high energy per pulse of the capillary discharge laser allows for the first time the processing of large surface areas with intense soft x-ray laser radiation. The damage threshold and damage mechanism of extreme ultraviolet Sc/Si multilayer mirror coatings was studied . Damage threshold fluences of ~ 0.08 J/cm 2 were determined for coatings deposited on both borosilicate glass and Si substrates. Scanning and transmission electron microscopy, and small-angle X-ray diffraction techniques revealed the thermal nature of the damage mechanism. These results provide a benchmark for the use of Sc/Si multilayer mirrors in high fluence applications, and for the development of higher damage threshold mirrors. Soft x-ray laser ablation studies were also conducted for silicon and several plastic materials, including PMMA, Polyamide and PTFE.