Wang Feng-Li

Determination of Tungsten Layer Profiles in Bilayer Structures Using X-Ray Reflectivity Method

An effectual method is presented to determine the profiles of a tungsten (W) layer, such as the density, the thickness and the roughness in the multilayer structures, using the x-ray reflectivity technique. To avoid oxidation effects of tungsten, a B4C capping layer is deposited onto to the W layer. To observe the profiles of the tungsten layer with different thicknesses, three groups of W/B4C bilayers with different thicknesses are prepared by using ultra high vacuum dc magnetron sputtering and measured by an x-ray diffractometer. A type of genetic algorithm called the differential evolution is used to simulate the measurement data so as to obtain the parameters of bilayers. According to the simulation, it is shown that the W layer density varies from 95.26% to 97.51% compared to the bulk. In our experiment, the deposition rate is 0.044 nm/s, and the thickness is varied in the range of 9.8–19.4 nm.

Design of Grazing-Incidence Broad-Band Multilayers for Hard X-Ray Reflectors

A new method of designing x-ray supermirrors with broad angular or energy response for use as coatings in x-ray optics is presented. The design is based on an analytical method with oversimplified analytical and semi-empirical formulae, and an extensive numerical method is used in the optimization design. A better initial multilayer is obtained with the former method and optimized with the latter method. In the optimization, a good design is achieved with much less computing time. In addition, the saturation effect due to the interfacial roughness in multilayer also emerges in the design of x-ray supermirrors with definite performances. The reflectivity of C/W x-ray supermirrors as a function of photon energy at the fixed grazing incident angle 0.5 degrees is presented.

Fabrication and Characterization of Ni Thin Films Using Direct-Current Magnetron Sputtering

Ni films are deposited by using ultra high vacuum dc magnetron sputtering onto silicon substrates at room temperature, and the high-quality and high-density films are prepared. The parameters, such as thickness, density and surface roughness, are obtained by using small-angle x-ray diffraction (XRD) analyses with the Marquardt gradient-expansion algorithm. The deposition rate is calculated and the Ni single layer can be fabricated precisely. Based on the fitting results, we can find that the surface roughness of the Ni films is about 0.7 nm, the densities of Ni films are around 97% and the deposition rate is 0.26 nm/s. The roughness of the surface is also characterized by using an atomic force microscope (AFM). The changing trend of the surface roughness in the simulation of XRD is in good agreement with the AFM measurement.

Spectral Resolution Improvement of Mo/Si Multilayers

Theoretically, the spectral resolution of a multilayer can be improved through a combination of utilizing high reflectance orders and by decreasing the thickness of the scattering layer. We fabricate Mo/Si multilayers in the first, second, third, fourth and fifth reflectance orders with Mo layer thicknesses of 3.0 nm and 2.0 nm, respectively, using direct current magnetron sputtering. The structure of the multilayers is characterized with a grazing angle x-ray diffractometer (XRD). Then the reflectivity of the multilayers is measured in a synchrotron radiation facility. The results show that the spectral resolution increases with the increasing reflectance order and with the decreasing Mo layer thickness. The highest spectral resolution is improved to 117.5 in the 5th order for dMo = 2 nm, where the reflectivity is 18%.

Design, Fabrication and Measurement of Ni/Ti Multilayer Used for Neutron Monochromator

Ni/Ti multilayers, which can be used for neutron monochromators, are designed, fabricated and measured. Firstly, their reflectivities are simulated based on the Nevot–Croce model. Reflectivities of two Ni/Ti multilayer mirrors with periods d = 10.3 nm (M1) and d = 7.8 nm (M2) are calculated. In the calculation, the reflectivity of the Ni/Ti multilayer is taken as a function of the grazing angle with different roughness factors δ = 1.0 nm and δ = 1.5 nm. Secondly, these two multilayers are fabricated by the direct current magnetron sputtering technology. Thirdly their structures are characterized by small-angle x-ray diffraction. The roughness factors are fitted to be 0.68 nm and 1.16 nm for M1 and M2, respectively. Finally their reflective performances are measured on the V14 neutron beam line at the Berlin Neutron Scattering Centre (BENSC), Germany. The experimental data show that the grazing angle of the reflected neutron intensity peak increases, but the reflected neutron intensity decreases, with the decreasing periods of the multilayers.

High Spectral Resolution Mo/Si Multilayers Working at High Order Reflection

The high reflectance orders are used to improve the spectral resolution of Mo/Si multilayers. The multilayers for the first-, second- and third-order reflectance are designed and optimized, respectively. These multilayers are fabricated by using a directed current magnetron sputtering system, and the reflectivity is measured in an extreme ultraviolet range by synchrotron radiation. The experimental results show that the spectral resolution λ/Δλ (λ = 14 nm) increases from 24.6 for the first order to 66.6 for the third order.

Design and Fabrication of Ni/Ti Multilayer for Neutron Supermirror

In the applications of neutron guides and focusing devices, by using the Ni/Ti multilayer supermirrors (SM), the neutron flux is significantly enhanced, because the critical reflective angle of supermirrors increases m times compared to the one of natural bulk Ni. We design and fabricate the Ni/Ti multilayer supermirrors by considering the effect of the interfacial imperfection, such as interface roughness and diffusion, and by using the direct current magnetron sputtering technology. The reflective performances of these supermirrors are measured on a V14 neutron beam line at the Berlin Neutron Scattering Centre (BENSC), Germany. The measurement data suggest that the critical angles of the supermirrors are 1.5 and 2.2 times that of bulk Ni, respectively.

Design and Fabrication of Broad Angular Response Supermirror for Hard X-Ray Optics

A broad angular response supermirror is designed by the simplex optimization method and fabricated by dc magnetron sputtering. The negative effect of the interfacial imperfection, mainly consulting from interface roughness and diffusion, is emerged in the calculation of the precise performance of the supermirror. The reflectivity of such a supermirror is measured by the x-ray diffraction instrument (XRD) at Cu K? line (? = 0.154?nm). The experimental reflectivity is about 30% in a fixed broad grazing incident angular range (0.55??0.85?). The fitting data prove that the thickness of each layer, which is larger than the prospect 0.5?nm, is different from the designed one and the roughness in the supermirror is about 0.85?nm.

真空紫外波段Al膜保护层MgF 2 的光学常数

由于Al膜的保护层MgF 2 薄膜的光学常数对Al/MgF 2 高反射镜的性能有极大的影响，本文研究了获取MgF 2 薄膜光学常数的方法。用热舟蒸发的方法在室温B270基底上镀制了3块不同MgF 2 厚度的Al/MgF 2 反射镜样品，通过掠入射X射线小角反射方法表征样品，获得了膜层厚度和粗糙度。在国家同步辐射实验中心计量站测试了入射角为5°时，样品在105~130 nm波段的反射率。在Al、MgF 2 膜层的厚度和Al的光学常数已知条件下，依据菲涅尔公式，得出了满足某波长处样品反射率的等值曲线，然后从三条曲线的交点得出了MgF 2 薄膜在108~128 nm波段的光学常数。对比和分析显示：利用此方法得到的108~128 nm波段MgF 2 薄膜光学常数计算的反射率曲线和实际测试得到的反射率曲线吻合较好。

Design, fabrication and characterization of the X-ray supermirrors

The design, fabrication and characterization of the X-ray supermirrors are discussed in this paper. Using the local optimization method of simplex algorithm and the global one of simulated annealing algorithm with different initial multilayer structures, we designed the broad angular band supermirrors with different grazing incidence angle intervals at the energy of 8.0 keV (the Kα line of Cu) and the broad energetic band supermirrors with different energy intervals at fixed grazing incidence angles. The fabricating techniques for depositing non-periodic multilayers are also studed. The W/C and W/Si supermirrors are deposited on silicon substrates and characterized by a high resolution X-ray D1 diffractometer from Bede Company, UK. Choosing the interface roughness and the densities of the materials as independent variables, some measured reflectivity curves are fitted using the Debye-Waller factor with interface roughness. The experimental results show that the optical performances of the fabricated supermirrors are in agreement with the designed ones.