Design and fabrication of soft X-ray multilayer for broadband reflection

A random method used for improving light throughput of a soft X-ray multilayer has been developed in the 18-20 nm spectral region, based on the traditional theory of periodic multilayer, and an 8% gain in integrated reflectance is obtained. The ensemble calculation is presented at the same time, and the multilayer is fabricated by magnetron sputtering.

Hard X-ray focusing resolution and efficiency test with a thickness correction multilayer Laue lens

The multilayer Laue lens(MLL) is a diffractive focusing optical element which can focus hard X-rays down to the nanometer scale. In this study, a WSi_(2)/Si multilayer structure consisting of 1736 layers, with a 7.2-nm-thick outermost layer and a total thickness of 17 μm, is prepared by DC magnetron sputtering. Regarding the thin film growth rate calibration, we correct the long-term growth rate drift from 2 to 0.6%, as measured by the grazing incidence X-ray reflectivity(GIXRR). A one-dimensional line focusing resolution of 64 nm was achieved,while the diffraction efficiency was 38% of the-1 order of the MLL Shanghai Synchrotron Radiation Facility(SSRF) with the BL15U beamline.

Aging effect of Co/C soft X-ray multilayer mirrors BAI Haili, JIANG Enyong, TIAN Renyu and WANG Cunda

MULTILAYER X-ray mirrors are of one-dimensional period structures consisting of alternating layers of materials of high- and low-refractive index. In the applications of soft X-ray multilayer mirrors, such as microscopy, astronomy and microlithography, high reflectivity is so important that it is necessary to know if the multilayers in use show aging effects, e.g. reflectivity changing with time. In this study, the aging effects of Co/C multilayers are investigated,

Interdiffusion in Co/C soft X-ray multilayer mirrors

The observation of structural changes in multilayers （MLs） has been used to study the interaction of materials at interface under nonequilibrium conditions, and to measure atomic diffusion rate and activation energies for compound formation. Cook and Hilliard have developed a technique which allows the measurement of small interdiffusivities down to 10-27m2·s-1 by X-ray diffraction. Previous measurements are concentrated mainly on the crystalline metallic multilayers and amorphous metallic multilayers. To our knowledge, few interdiffusion measurements have been carried out for amorphous metallic-metalloid multilayers. As effective soft X-ray mirrors, Co/C multilayers have been successfully used in an X-ray telescope. Therefore, this note aims to report the interdiffusion of sputtered

Soft X-ray optical multilayer mirrors

The current research on the structure design, characterization and structural stability of soft X-ray optical multilayermirrors is reviewed and further studies on the currently existing problems and the possible solutions are made.

TEM and Raman scattering investigation of carbon in annealed Co/C soft X-ray multilayers

The structures of the carbon sublayers in the annealed Co/C soft X-ray multilayers fabricated by using a dual-facing-target sputtering system have been characterized by transmission electron microscopy (TEM) and Raman spectroscopy (RS). The results suggest that the structural variations in the carbon layers can be roughly divided into three stages, i e ordering, crystalline and grain growth stages. At the ordering stage with annealing temperatures below 400℃, the amorphous carbon layers change from ones of bond-angle disorder and fourfold-bonding only to ones of threefold-bonding. At the crystalline stage, the amorphous carbon layers in the as-deposited multilayers crystallize to graphite crystallites in the annealing temperature range of 500-600℃ At the grain growth stage, the specimens are annealed at temperatures higher than 700℃ A growth in the graphite crystallite dimensions is observed, which is consistent with the TEM results

Preparation and structural stability investigation of CoN/CN soft X-ray multilayers

The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques.The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100-200 degrees centigrade through doping with N.The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400℃,and the interface pattern still exists even if they were annealed at 700℃.The Raman spectra analyses give the evidence that the formation of the sp bonding in the CN sublayers can be suppressed effectively by doping N with atoms,and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably.The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding between C and N atoms,and the ionic bonding between Co and N atoms,which can slow down the tendency of the structural relaxation.The interstitial N atoms decrease the mobility of Co atoms,and thus the fee-Co and hep-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420℃,leading to the suppression of the grain growth.

Thermal Diffusion of Si Atoms at the Interface of Mo/Si Bilayers Studied with a Soft X-ray Emission Microscope

Thermal diffusion of Si atoms at the interface in Mo/Si multilayers was observed with an imaging type soft X ray emission microscope developed by us. It was possible to observe the diffusion with 0.2nm depth resolution in the direction normal to the interface by comparing the emission intensity for exactly the same position. The diffusion coefficient of Si atoms in Mo at 600℃ was roughly estimated to be 6.0×10 17 cm 2/s.

Present Status of EUV Interferometer Development at the Research Center for Soft X-ray Microscopy

A new interferometer for extreme ultraviolet (EUV) radiation with a laser produced plasma (LPP) laboratory source is under construction. The LPP source is operated with a Sn solid rod target on which pulsed YAG laser is focused to produce high temperature plasma emitting EUV radiation. The source is equipped with a newly designed debris stopper protecting a condenser multilayer mirror from the particle debris of the target. The condenser mirror focuses the light onto an EUV beam-splitter to form transmitted and reflected paths for producing interference fringes of a sharing type. The optical configuration is of a common path based on a triangular path type with a focusing at the beam-splitter, which is enabled to produce fringes by a low coherence radiation with a standard optical quality beam-splitter. The fringes are recorded by an imaging plate with pixels as small as 25μm. The dynamic range of linearity in detection of the EUV light was found to be more than 10 4 with sensitivity of 10 4 photons/pixel, enough for the purpose of interferogram recording, possibly with one laser shot.

Multilayer-based soft X-ray polarimeter at the Beijing Synchrotron Radiation Facility

A compact high precision eight-axis automatism and two-axis manual soft-ray polarimeter with a multi- layer has been designed, constructed, and installed in 3WlB at the Beijing Synchrotron Radiation Facility （BSRF）. Four operational modes in the same device, which are double-reflection, double-transmission, front-reflection-behind- transmission and front-transmission-behind-reflection, have been realized. It can be used for the polarization analysis of synchrotron radiation. It also can be used to characterize the polarization properties of the optical elements in the soft X-ray energy range. Some experiments with Mo/Si and Cr/C multilayers have been performed by using this polarimeter with good results obtained.

An analytical model for the polarization of synchrotronradiation in a soft X-ray region

Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.

Measurement of the polarization for soft X-ray magnetic circular dichroism at the BSRF beamline 4B7B

Three ultra-short-period W/B4C multilayers （1.244 nm, 1.235 nm and 1.034 nm） have been fabricated and used for polarization measurement at the 4BTB Beamline at the Beijing Synchrotron Radiation Facility （BSRF）. By using the rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700-860 eV. The first soft X-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.

Fabrication of the beam splitters for soft X-ray laser application

The soft X-ray interferometry is completed by the Mach-Zehnder interferometer using a soft X-ray laser, and it is also an important method to measure the electron densities of a laser-produced plasma near the critical surface. It is apparently demonstrated in this paper that the incident angle of each optical element in the soft X-ray Mach- Zehnder interferometer should be near normal incidence based on the polarized characteristics of the soft X-ray mul-tilayers, and the product of reflectivity and transmission of the beam splitter should be taken as a standard of design according to the structure of the soft X-ray Mach-Zehnder interferometer. The beam splitters used in the soft X-ray interferometry at 13.9 nm are fabricated using the ion beam sputtering. The figure error of the beam splitter has reached the nanometer magnitude, in which the product of reflectiv-ity and transmission of the beam splitter is more than 1.6%.

Mo/Si软X射线多层膜的界面粗糙度研究

用磁控溅射法分别制备了以Mo膜层和Si膜层为顶层的Mo/Si多层膜系列,利用小角X射线衍射确定了各多层膜的周期厚度。以不同周期数的Mo/Si多层膜的新鲜表面近似等同于同一多层膜的内界面,通过原子力显微镜研究了多层膜界面粗糙度随膜层数的变化规律。并在国家同步辐射实验室测量了各多层膜的软X射线反射率。研究表明:随着膜层数的增加,Mo膜层和Si膜层的界面粗糙度先减小后增加然后再减小,多层膜的峰值反射率先增加后减小。

用不同的Mo靶溅射功率制备Mo/Si多层膜

用磁控溅射法制备了周期厚度和周期数均相同的Mo/Si多层膜,用原子力显微镜和小角X射线衍射分别研究了Mo靶溅射功率不相同时,Mo/Si多层膜表面形貌和晶相的变化。随后在国家同步辐射实验室测量了Mo/Si多层膜的软X射线反射率。研究发现,随着Mo靶溅射功率的增大,Mo/Si多层膜的表面粗糙度增加,Mo的特征X射线衍射峰也增强,Mo/Si多层膜的软X射线峰值反射率先增大后减小。

提高光通量的软X射线非周期多层膜的数值模拟

在周期多层膜基础上，采用随机数方法找到适当的非周期膜系，极大地提高了反射光通量，并给出了整体设计步骤。模拟计算结果表明非周期多层膜能扩展带宽和提高反射率积分值。在１２．４～２０．１ｎｍ波段内，最佳非周期多层膜与峰值在中心波长λ＝１６．２５ｎｍ处的周期多层膜相比，理论积分反射率提高了７５％。

多层膜优化设计方法

传统多层膜设计所用的全局寻优法的速度非常慢,有时还很难得到理想的膜系。根据Frensnel反射系数公式计算多层膜的反射率,利用单纯形法对软X射线和X射线波段多层膜进行调优,可在短时间内优化出最接近目标光学性能的多层膜膜系结构。计算了不同波长软X射线周期性多层膜的最高理论反射率。单纯形调优算法在保证优化结果与随机搜索法优化结果近似相同的基础上,使优化计算速度提高了十倍以上。同时还用单纯形调优法优化设计了X射线超反射镜,得到了非常理想的非周期膜系。

基于动变形控制法的软岩路基填筑材料回弹模量控制

根据路基路面变形协调原理,结合国内公路相关规范对路面弯沉的控制标准,获得软岩路基顶面动变形允许值;利用传递-反射矩阵方法和叠加原理推导了双轮胎振动荷载作用下弹性层状公路结构的动力响应解;采用Hankel数值逆变换技术计算出实例工程中典型软岩公路路基顶面的动变形,基于动变形控制法确定了不同软岩填筑区域对应填料的回弹模量临界值;根据现有公路规范规定的路基结构层厚度,提出满足动变形条件下的软岩填筑区域所需回弹模量控制要求,并以回弹模量为依据对软岩填料进行了分类.研究成果可为软岩填料分区优化填筑提供指导.

膜厚控制误差对软X射线多层膜性能影响的分析

针对影响多层膜性能的关键因素———膜厚控制误差进行了全面的分析计算,指出影响多层膜性能的主要误差是仪器本身的系统偏差,它使多层膜的峰值反射波长偏离设计值,使得制作出的多层膜无法满足要求;镀膜过程中的随机误差使多层膜的反射率降低,但不影响多层膜峰值反射率波长的位置,因此,在制作多层膜过程中,不但要严格控制镀膜时的系统误差,而且要控制随机误差。