Jing Xu

Intrinsic stress analysis of sputtered carbon film

Intrinsic stresses of carbon films deposited by direct current (DC) magnetron sputtering were investigated. The bombardments of energetic particles during the growth of films were considered to be the main reason for compressive intrinsic stresses. The values of intrinsic stresses were determined by measuring the radius of curvature of substrates before and after film deposition. By varying argon pressure and target-substrate distance, energies of neutral carbon atoms impinging on the growing films were optimized to control the intrinsic stresses level. The stress evolution in carbon films as a function of film thickness was investigated and a void-related stress relief mechanism was proposed to interpret this evolution.

Determination of layer-thickness variation in periodic multilayer by x-ray reflectivity

A method basically determining individual layer thicknesses in actual periodic multilayers has been developed, that solves simultaneous equations of positions of peaks appearing in wavelet transform curve of x-ray grazing incidence reflectivity. The determination was demonstrated on a Ni/C periodic multilayer fabricated by magnetron sputtering. Using the layer thicknesses obtained by the method, further accurate of thickness, roughness, and density of each layer was performed by Parratt’s model. The special feature that the topmost and bottom-most layers were thicker than other layers was clearly observed. The former is attributed to oxidation and the latter is attributed to the effect of deposition on thick substrate. The mean fluctuations of other layers are 2.6% in C layers and 4.2% in Ni layers attributed to random fluctuations at deposition. Numerical analysis and statistical hypothesis tests have been carried out to discuss noncumulative and cumulative layer-thickness fluctuations in fabrication pro...

Angle alignment method for soft x-ray using double-periodic multilayer

A double-periodic multilayer method was proposed to test KBA system of 4.75keV using 8keV source. Alignment of angle is the key for most of grazing incidence systems in x-ray range. But for soft x-ray, strong absorption makes the alignment have to be operated in vacuum, which is difficult enough. A double-periodic multilayer was used to experiment at 8keV in air replacing 4.75keV in vacuum. This multilayer includes two parts, the top and the bottom. The top is W/B4C multilayer with four bilayers and 6.93nm periods. The bottom is W/B4C multilayer with 10 bilayers and 3.95nm periods. For 8keV energy, x-ray will penetrate through the top and reflected by the bottom. While for 4.75keV, x-ray will be reflected by the top directly. The full width of half maximum is 0.1° at 8keV and 0.3° at 4.75keV, so it is accurate enough for 4.75keV to experiment at 8keV, which was also verified by the 1-D KBA experiment. This double-periodic multilayer provides a valid solution for alignment in soft x-ray range.

Influence of interface roughness on reflectivity of tungsten/boron-carbide multilayers with variable bi-layer number by X-ray reflection and diffuse scattering

Influence of interface roughness on the reflectivity of Tungsten/boron-carbide (W/B4C) multilayers varying with bi-layer number, N, is investigated. For W/B4C multilayers with the same design period thickness of 2.5 nm, a real-structure model is used to calculate the variation of reflectivities with N=50, 100, 150, and 200, respectively. Then, these multilayers are fabricated by a direct current (DC) magnetron sputtering system. Their reflectivity and scattering intensity are measured by an X-ray diffractometer (XRD) working at Cu Kalpha line. The X-ray reflectivity measurement indicates that the reflectivity is a function of its bi-layer number. The X-ray scattering measured results show that the interface roughness of W/B4C multilayers increases slightly from layer to layer during multilayer growing. The variation of the reflectivity and interface roughness with bi-layer number is accurately explained by the presented real-structure model.

Extreme ultraviolet multilayer mirrors for astronomical observation

Multilayer mirrors are the important optical elements for astronomical observation at extreme ultraviolet region. In this article, three kinds of multilayer mirrors were introduced for solar observation and magnetosphere observation. Mo/Si multilayer mirror was fabricated for solar Fe-XII emission line at wavelength of 19.5nm. For solar He-II radiation at 30.4 nm, Mo/Si, Si/SiC, Si/C, Si/B4C and Mg/SiC multilayers were investigated, and the measurements results shows that Mg/SiC multilayer provides the highest reflectivity of 43.8% at incidence angle of 5 degree. The third multilayer mirror was a dual-function mirror used for earths magnetosphere observation, which requires high-reflective for He-II emission line at wavelength of 30.4nm but anti-reflectance at 58.4nm from ionosphere He-I emission. Using aperiodic Mg/SiC multilayer, the dual-function multilayer mirror was designed. Compared to periodic multilayer, the dual-function multilayer suppresses the reflectivity for He-I at 58.4nm from 2.2% to 0.1%, without loss of the reflection for He-II at 30.4nm, significantly.

An auxiliary visible imaging method for alignment of x-ray Kirkpatrick-Baez optics

An auxiliary visible imaging method was introduced to solve the axial and pointing alignment of x-ray Kirkpatrick-Baez optics. Through ZEMAX simulation and x-ray imaging experiments, the axial and pointing alignment accuracy were determined to be ±300μm and ±20μm respectively. The numerical aperture of x-ray Kirkpatrick-Baez optics is rather small, so its impossible to adjust Kirkpatrick-Baez system by visible imaging directly. An auxiliary visible lens was designed, which was equivalent to x-ray Kirkpatrick-Baez optics on conjugate relationship and accuracy control. The comparative experiments of visible imaging and x-ray imaging indicate that this auxiliary system could meet the alignment accuracy of Kirkpatrick-Baez optics.

Space environment experiments of SiC/Mg multilayer for astronomical observation

SiC/Mg, Mo/Si and SiC/Si period multilayer mirrors were developed for solar He-II radiation at 30.4 nm. The optical stabilities of the SiC/Mg multilayer were investigated before and after space environment simulation tests for the purpose of potential application in space extreme ultraviolet observation. The multilayers are deposited by using direct current magnetron sputtering method in Ar gas atmosphere on polished fused silica substrate. Then, the reflectivities were measured at synchrotron radiation. The SiC/Mg multilayer provides the highest reflectivity of 34.0%, only 18.6% and 13.9% for Mo/Si and SiC/Si multilayer mirrors. However, Mg is known to be highly reactive and low melting point. Therefore, the thermal cycling stability test and radiation exposure experiments were performed for SiC/Mg multilayer to simulate the space environment, respectively. The testing results indicate that the reflectivity of SiC/Mg multilayer decreases slightly. After thermal cycling from -45 to 145 Celsius degree three times, the reflectivity decrease from 34.0% to 31.0%. After gamma radiation exposure, the reflectivity decreases from 31.4% to 29.4%.

Development of Multilayer Optics in EUV, Soft X-Ray and X-Ray Range at IPOE

Multilayer coatings are key optical components in the EUV, soft X-ray and X-ray range. At Institute of Precision Optical Engineering (IPOE), the development of multilayer optics has been impelled for their wide applications in X-ray laser, plasma diagnostics, astronomical observation and synchrotron radiation. The paper presents our recent results of periodic multilayers of Mo/Si, Cr/C, Cr/Sc, La/B4C, Mo/B4C, Si/C, Si/SiC, Mg/SiC Mo/Y and Ru/Y. To improve the reflectivity of Ru/Y multilayer mirrors, Mo layers were inserted between Ru and Y layer. The Mo barrier layers suppress intermixing between Ru and Y, thereby increasing the reflectivity of Ru/Y multilayer. We also discuss the application of Mo/Si, Mo/Y, Mo/B4C, La/B4C non-periodic multilayers in EUV broadband polarization measurement.

Design of supermirrors for hard x-ray telescopes

X-ray grazing incidence supermirror which has extremely broad reflection band is a kind of multilayer with different each layer thickness down through the structure. The x-rays with different wavelengths or at different grazing incident angles can be reflected at different position in the supermirror structure and its band or angular response thus can be extended. These supermirrors have been developed and applied widely in many fields, especially in astrophysics. Existing approaches for designing similar neutron supermirrors are shown to provide respectable performance when applied to x-ray multilayers. However, none of these approaches consider the effects of imperfect layer interfaces and absorption in the overlying layers and all of them insist on the structure with the ratio of the layer thickness of absorbing material to the bi-layer spacing being a constant of 0.5. Adaptations of neutron designs that take these effects into account are presented in the present paper. In addition, other approaches, such as the method based on the combination of analytical and number methods, also are included and discussed in this paper. Two kinds of supermirrors with broad photon energy band or broad angular response have been designed using these different design methods. The results show that for specific applications, different optimization methods with different initial structures should be chosen accordingly to expect some overall improvement on performance of x-ray supermirrors.

Development of EUV multilayer mirrors for astronomical observation in IPOE

Three kinds of multilayer mirrors were developed for solar observation and earths magnetosphere observation at Extreme Ultraviolet (EUV) wavelength region. The first one is Mo/Si multilayer mirror, designed for solar Fe-XII emission line at wavelength of 19.5nm. The reflectivities are in the range of 38.7~42.9%, measured at National Synchrotron Radiation Laboratory (NSRL), Hefei, China. The second high-reflective multilayer is designed for solar He-II radiation at 30.4 nm. At this wavelength, SiC/Mg multilayers were investigated, and as high as 50.0% measured reflectivity was obtained at incident angle of 10°. Aperiodic SiC/Mg multilayers were also designed for wide angular ranges of 15-22° and 12-21°. The third multilayer mirror was a dual-function mirror used for earths magnetosphere observation, which requires high-reflective for He-II emission line at wavelength of 30.4nm but low-reflectance at 58.4nm from ionosphere He-I emission. Using aperiodic SiC/Mg multilayer stack, the dual-function multilayer mirror was designed by genetic algorithm. Compared to periodic multilayer, the dual-function multilayer suppresses the reflectivity for He-I at 58.4nm from 2.2% to 0.1%, without loss of the reflection for He-II at 30.4nm, significantly. These multilayer mirrors were all prepared by magnetron sputtering system in IPOE, and measured at NSRL, China.