Multilayer X-ray mirrors based on La/B<Subscript>4</Subscript>C and La/B<Subscript>9</Subscript>C

Multilayer X-ray mirrors that are based on La/B₄C and La/B₉C and intended for the reflection of X-ray radiation in the spectral region near λ = 6.7 nm are prepared and studied. Reflection coefficients at a level of 40–60% are achieved for mirrors with various periods. The difference in the interlayer roughnesses reconstructed from the data measured in the hard and soft X-ray spectral regions is explained using a structural model with an asymmetric permittivity profile in a mirror period. A proximate technique is developed to estimate the permittivity profile in a multilayer-structure period using reflectometry data. The effect of antidiffusion Sn, Cr, and Mo barriers on the reflection coefficient of multilayer La/B₄C structures is studied experimentally     

Aperiodic multilayer mirrors for efficient broadband reflection in the extreme ultraviolet

Recent extreme ultraviolet sources using high-harmonic generation in a rare gas make new optics developments necessary. We report on the study and development of multilayer structures with efficient reflectivity in the 35–75 eV energy range. We have optimized, deposited and characterized two aperiodic broadband mirrors consisting of a Mo, Si and B₄C thin-film stack. We used the needle procedure in order to optimize mirror reflectivity. The magnetron sputter deposited multilayers have been calibrated and characterized using Cu K _α grazing incidence X-ray reflectometry. Reflectivity measured at near-normal incidence on a synchrotron radiation source reaches 12% with a full width at half maximum of nearly 40 eV. Experimental results are compared with theoretical simulation using available optical constants for Mo, Si and B₄C in this spectral range.     

Soft X-ray microscopy in the spectral region of “carbon window” with the use of multilayer optics and a laser-plasma source

This paper reports on the fabrication and testing of multilayer mirrors for X-ray optical systems operating in the “carbon window” region (at wavelengths from 4.5 to 5.0 nm) and the results of their application in soft X-ray imaging of the internal structure of organic objects. The developed approaches to the fabrication and control of graded Co/C multilayer coatings have made it possible to create an X-ray multimirror system with a maximum known entrance aperture and throughput. The use of the developed high-spatial-resolution X-ray optics can significantly extend the field of practical application of soft X-ray absorption microscopy based on compact laser-plasma sources.     

23.4nm软X射线多层膜反射镜研制

为了满足类氖-锗X射线激光研究的需要,设计制备了23.4 nm软X射线多层膜反射镜.依据多层膜选材原则并考虑材料的物理化学特性选择新的材料Ti与Si组成材料对.设计优化材料多层膜的周期厚度(d),材料比例(Γ),周期数(N),计算出Ti/Si反射率曲线.通过实验优化各种镀膜工艺参数,制备出了23.4 nm的Ti/Si多...     

Hydrogen interaction with EUVL-relevant optical materials

Mo/Si multilayer mirrors were exposed to deuterium ions with well-defined energies in order to gain insight into the effects of Extreme UV light driven plasma generation on reflective elements in commercial lithography equipment. Post-irradiation analysis by Rutherford Backscattering Spectrometry showed erosion of both Mo and Si layers for the highest energy 50 eV/D and exposure time 5.4 × 10⁴ s. Nuclear Reaction Analysis revealed detectable deuterium retention for energies ⩾25 eV/D. Surface analysis by X-ray Photoelectron Spectroscopy showed erosion of the first Si layer for energies ⩾5 eV/D. Inferences on the spatial distribution of trapped deuterium are made on the basis of available data regarding deuterium retention in the materials in question.     

Investigation in the interface roughness of DC-sputtered Mo/B4C multilayer mirrors with variable layer pairs for 7-nm soft X-ray polarizers

The surface and interface roughness of Mo/B₄C multilayer mirrors for 7-nm soft X-ray polarizer with variable layer pairs (N = 50, 70, 90 and 110), fabricated by DC sputtering technique is investigated by atomic force microscopy and X-ray scattering and reflecting. The experimental results present that the surface and interface roughness of Mo/B₄C multilayer mirrors increase layer by layer from its substrate as its Mo layer thickness greater than 2 nm, and the roughness grown tendency could be characterized by a quadratic function.     

Multilayer mirror for x rays below 190 eV

La/B(4)C multilayers have been fabricated by magnetron sputtering for use as x-ray mirrors at energies below 190 eV, particularly for detection of boron K and alpha x rays at 183 eV, their performance has been compared with that of Mo/B(4)C multilayers, which are currently the best-performing multilayers for this energy range. Transmission electron microscopy and synchrotron soft-x-ray reflectometry were used to study the structural quality of the multilayers and their performance as x-ray mirrors. The results show a significant improvement of the peak reflectivity and the spectral purity, indicating that La/B(4)C has a high potential to replace Mo/B(4)C in many x-ray optical applications below 190 eV.     

Co/C and W/Si multilayers deposited by ion-beam sputtering for the soft X-ray range

We deposited Co/C multilayer mirrors for a wavelength of 4.77 nm and W/Si multilayer mirrors for a wavelength of 1.77 nm by use of ion-beam sputtering. The small-angle diffraction spectrum was used to analyze the structure of the multilayers. With a combination of the experimental diffraction spectra and Apeles’ theory for calculation of the interfacial roughnesses of the multilayers, the interfacial roughnesses of Co/C and W/Si are 0.80 nm and 0.60 nm, respectively, which are lower than that of the substrate. The reflectivity of the Co/C multilayer is measured to be about 20% and that of the W/Si multilayer about 1% at the grazing incidence angle of about 12°. Received: 30 May 2000 / Accepted: 1 August 2000 / Published online: 11 February 2002     

Silver ions adsorbed to self-assembled monolayers of alkanedithiols on gold surfaces form Ag–dithiol–Au multilayer structures

Double-ended alkanedithiols, 1,9-nonanedithiol and 1,5-pentanedithiol, formed self-assembled monolayers (SAMs) on Au(l11) substrates and were used to adsorb silver ions from an ethanolic solution of silver nitrate and formed Ag–dithiol–Au multilayer structures. Ellipsometry, contact angle measurement and X-ray photoelectron spectroscopy (XPS) confirmed that the alkanedithiol molecules formed SAMs with only one-ended thiol groups attached to the Au substrates, which was supported by molecular mechanics calculation. XPS and X-ray Auger electron spectroscopy (XAES) indicated that silver ions were deposited onto the SAMs from the solution by the chemical reaction of silver nitrate with another-ended thiol groups of the SAMs. Atomic force microscopy (AFM) was used to observe SAMs and multilayer structures. Received: 20 January 2000 / Accepted: 18 April 2000 / Published online: 9 August 2000     

Ultrathin multilayer of Fe and Ge: structure and magnetic properties

Metal-semiconductor multilayers are interesting, artificial structures as prospective candidates for spin injection devices. A Fe–Ge multilayer sample with very thin individual layers (few crystallographic planes) has been deposited by sputtering on Si[1 0 0] substrate. We have characterized the structure of this multilayer sample using X-ray diffraction, X-ray reflectometry and neutron reflectometry. The magnetic moment density in the ferromagnetic Fe layer has been obtained by polarized neutron reflectometry and the bulk magnetic behavior of the thin film by SQUID magnetometer measurements. We found that the film is a soft ferromagnet at room temperature with a substantially reduced magnetic moment of the Fe atoms.     

La/B4C small period multilayer interferential mirror for the analysis of boron

An La/B₄C multilayer interferential mirror with small period d (4.8 nm) was produced by diode sputtering for the detection of the boron K emission by wavelength‐dispersive x‐ray spectrometry at a large Bragg angle (close to 45°). The structure of the mirror was characterized by grazing incidence x‐ray reflectometry and its performance at the energy of the boron K emission (183 eV) was evaluated by means of polarized synchrotron radiation. Spectrometric measurements showed that the La/B₄C mirror improved the detection limit of boron using by a factor of 2 with respect to similar Mo/B₄C mirrors and by a factor of 4 with respect to a lead stearate crystal. Copyright © 2005 John Wiley & Sons, Ltd.     

Integrated characterization of multilayer periodic systems with nanosized layers as applied to Mo/Si structures

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.     

Reactive diffusion in Sc/Si multilayer X-ray mirrors with CrB2 barrier layers

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.     

Nanostructuring with laser radiation in the nearfield of a tip from a scanning force microscope

Platinum-carbon multilayer mirrors with a bilayer spacing of 50 Å were fabricated in an ultrahigh vacuum electron beam evaporator. The thermal stability of these multilayers was studied under vacuum annealing using X-ray reflectivity and X-ray diffraction. Up to 450°C, the bilayer spacing increases monotonically accompanied by a gradual increase in crystallite size and grain texture. At 500°C multilayer reflection vanishes, platinum crystallites grow abruptly, and there is a strong texture of platinum in the [220] -plane. Possible reasons for thermally induced structural modifications in these multilayers are discussed.     

Grazing incidence systems with multiple reflections

The theory of turning soft x-ray SXR radiation beams by means of concave surfaces through multiple reflections (the “whispering-gallery” effect) is developed. It is demonstrated that concave mirrors are capable of turning an SXR beam by an arbitrary angle determined by their aperture angle. The reflectivities are of the same order of magnitude as those of multilayer mirrors (20–80% at a turn by 90°). The turning mirrors feature a wide spectral transmission band (Δλ ∼ λ). The potentialities of concave mirrors and hollow cylindrical waveguides with respect to concentration and collimation of SXR radiation are considered. The requirements imposed on the smoothness of the reflecting surfaces are obtained and the optimal (as to their optical properties) materials are chosen for their fabrication. The theoretical results are compared to experimental data. Translated from Trudy Fizicheskogo Instituta im. P. N. Lebedeva (Proceedings of the Lebedev Physical Institute, Russian Academy of Sciences, Moscow), Vol. 196, pp. 143–167, 1989.     

Space solar telescope in soft X-ray and EUV band

In this paper we have reviewed our achievements in soft X-ray and extreme ultraviolet (EUV) optics. Up to now, the research system of soft X-ray and EUV optics has been established, including light sources, detectors, calibrations, optical testing and machining of super smooth mirrors, and fabrications of multilayer film mirrors. Based on our achievements, we have developed two types of solar space telescopes for the soft X-ray and EUV space solar observations. One is an EUV multilayer normal incident telescope array including 4 different operation wavelength telescopes. The operation wavelengths of the EUV telescope are 13.0, 17.1, 19.5 and 30.4 nm. The other is a complex space solar telescope, which is composed of an EUV multilayer normal incident telescope and a soft X-ray grazing incident telescope. The EUV multilayer normal incident telescope stands in the central part of the soft X-ray grazing incident telescope. The normal incident telescope and the grazing incident telescope have a common detector. The different operation wavelengths can be changed by rotating a filter wheel.     

Structural characterization of ultrathin Cr and Sc films for soft X-ray mirrors

The structure of multilayers of ultrathin scandium (Sc) and chromium (Cr) films has been characterized by means of transmission electron microscopy (TEM). Face centered cubic Sc was found both in magnetron sputtered thin Sc layers on Si(0 0 1) and in Cr/Sc multilayers for soft X-ray mirrors. The single Sc and Cr layers are polycrystalline with randomly oriented grains, while Sc and Cr within the Cr/Sc multilayer show a strong [0 0 1] texture in the deposition direction. From high-resolution images the orientation-relationship at the Cr/Sc interfaces could be deduced as: Sc_[110]//Cr_[100] and Sc_[010]//Cr_[110], which was confirmed by image simulations.     

Si adhesion interlayer effects in hydrogen passivated Si/W soft X-ray multilayer mirrors

The use of hydrogen passivation of the silicon layers in Si/W soft X-ray reflective multilayer mirrors is investigated. Standard passivation, corresponding to Si:H/W structures, led to reduced growth properties of the W layers. The additional use of atomically thin Si adhesion layers, corresponding to Si:H/Si/W, led to improved growth and increased soft X-ray reflectivity. The effects taking place at the interfaces are analysed by bright field planar TEM and in situ X-ray reflectivity, and are described in terms of interface and surface energies, with quantitatively analysis of intermixing, materials density, and geometrical optical effects.     

磁控溅射方法制备直径120mm高均匀性Mo/Si多层膜

为满足极紫外、软X射线和X射线大口径多层膜反射镜的需求,采用基板扫掠过矩形靶材表面的镀膜方法,在直径120 mm的平面基板上镀制了Mo/Si周期多层膜。通过调整基板扫掠过矩形靶材表面的速率修正了薄膜的沉积速率,极大地提高了薄膜厚度的均匀性。采用X射线衍射仪对反射镜不同位置多层膜周期厚度进行了测量,结果表明,在直径120 mm范围内,Mo/Si多层膜周期厚度的均匀性达到了0.26%。同步辐射测量多层膜样品不同位置处的反射率,结果表明,在直径120 mm范围内,多层膜的膜层厚度均匀,在入射角10°时13.75 nm波长处平均反射率为66.82%。     

Measurement of the profile and curvature of cylindrical multilayer mirrors irradiated by a divergent X-ray beam

Two techniques for determining the local period and curvature of the surfaces of cylindrical multilayer mirrors are discussed. These techniques make it possible to measure the mentioned parameters of mirrors in a divergent X-ray beam with the wavelength λ = 0.154 nm and differ in the boundary conditions selected.