High performance multilayer La/B4C mirrors with carbon barrier layers

Recent results from manufacturing multilayer La/B₄C mirrors at wavelengths above 6.7 nm with carbon barrier layers are presented. It is shown that maximum reflection R = 58.6% is attained at λ = 6.661 nm.     

Formation of short-period multilayer W/B4C compositions

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 _?? 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.     

Multilayer La/B4C mirrors in the spectral region near 6.7 nm

The results from measuring reflection factors are presented for multilayer La/B₄/C mirrors with barrier layers of carbon and scandium. It is shown that a higher reflection factor is obtained by depositing a layer of carbon onto a surface of boron carbide. This effect is caused by diminishing absorption in the structure and the reduced width of transition regions.     

Design and fabrication of broad angular range depth-graded C/W multilayer mirror for hard X-ray optics

In this paper, a depth-graded C/W multilayer mirror with broad grazing incident angular range, consisting of three multilayer stacks, each of which has different period thickness d and the layer pair number,was designed and fabricated by direct current (DC) magnetron sputtering.     

Atomic structure of icosahedral B4C boron carbide from a first principles analysis of NMR spectra

Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B (12) structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.     

Measurement of the birefringence properties of the reflecting surface of an interferential mirror

We have set up an apparatus to measure the ellipticity acquired by a linearly polarized light beam after a single quasi-normal reflection on an interferential mirror. Results of measurements performed on a standard 10 cm diameter interferential mirror are presented.     

Investigation of roughness cross correlation in a Ni/C multilayer mirror by X-ray diffuse scattering method

The possibility of applying X-ray diffuse scattering for studying roughness in multilayer X-ray mirrors, including the correlation of roughnesses of neighboring interfaces (roughness cross-correlation) is considered. It is shown that the reliability and informativeness of this method can be improved by rejecting the classical experimental schemes and using alternative schemes in which not only the intensity of diffuse scattering itself, but also its dependence on certain experimental parameters (conditions), vary. Such parameters can be the spatial coherence of incident radiation, the direction of the momentum transfer relative to the specular diffraction plane, or the X-ray wavelength. In the framework of this approach, the results of comparative measurements of diffuse scattering from a Ni/C multilayer X-ray mirror prepared by laser ablation are considered for two close values of photon energy: below (8.325 keV) and above (8.350 keV) the K absorption edge for nickel. It is shown that, in view of effective screening of deep layers in the hard photoabsorption mode, this method provides more reliable (as compared to the standard diffuse scattering method) information on the evolution of interfaces between the layers. It is found that the smoothing of roughness in the experimental sample occurs over large spatial scales such as the micrometer scale. Only large-scale defects with a size exceeding 10 µm are replicated well from layer to layer. Possible physical reasons for the observed effect are considered. It is shown that effective smoothing on the micrometer and submicrometer spatial scales is of fundamental importance for preparing multilayer X-ray mirrors with high reflectances.     

Deformation twinning in boron carbide particles within nanostructured Al 5083/B4C metal matrix composites

The presence of deformation twins is documented in boron carbide reinforcement particles within a nanostructured Al 5083/B₄C metal matrix composite. High resolution transmission electron microscopy analysis suggests that these are (0001) twins. This work discusses the mechanisms responsible for their formation based on crystallographic analysis and mechanical loading conditions. Specifically, we propose that there are two potential models that can be used to describe twin formation in boron carbide particles. The structural models involve slip in the 1/3[1100] (0110) or 1/3[0110] (0110) planes of C–C–C chains and the appropriate reconfiguration of B–C bonds. Analysis of the loading conditions experienced by the boron carbide particles indicates that local high stress intensity and the presence of a high shear force around the boron carbide particles are two factors that contribute to twin formation.     

Design of chirped Mo/Si multilayer mirror in the extreme ultraviolet region

The chirped Mo/Si multilayer mirror in the extreme ultraviolet region is designed to obtain sub-femtosecond pulses from high-order harmonics. Numerical simulations of temporal profile of the pulses are made for superposition of incident high-order harmonics and that of reflected ones by the chirped multilayer mirror.The normal incidence reflectivity and chirp in the wavelength range of 12.5 - 16.5 nm are 6.7% ±0.5%and-3617±171 as2, respectively. Simulation results indicate that the designed chirped multilayer mirror can be used for producing 104-as pulses.     

Effect of defects on the reflectivity of Cr/C multilayer soft X-ray mirror at 4.48 nm

Cr/C is a promising material combination for multilayer mirror in the “near water window region” (4.4-6.7 nm). In the present paper, the effect of defects on the reflectivity of Cr/C soft X-ray multilayer mirror deposited by magnetron sputtering was studied. Formation of thin interlayer due to the interdiffusion, rough interface due to the non-sharp layer and contamination of O happened during the deposition process were found by a method combined by XPS, soft X-ray reflectivity at 4.48 nm and grazing incidence hard X-ray reflectivity at 0.154 nm. The XPS results show that both interlayers (Cr-on-C and C-on-Cr) are mixture composed of C sp2, C sp3, CO, CO, CrCr and CrO bondings. No chromium carbide was found at the interlayer probably due to the blocking of oxides’ formation. Through the analysis of X-ray reflectivity, we obtained the multilayer structure parameters (thickness and roughness) and optical constants of each layer at 4.48 nm. Based on those results, a further calculation was carried out. The result shows that the formation of the thin interlayer contributes little to the decrease of the reflectivity, the rough interface decreases the reflectivity most and the contaminant (O) not only decreases the reflectivity but also shifts the position of the peak.     

X-ray properties and interface study of B4C/Mo and B4C/Mo2C periodic multilayers

We present a comparative study of B₄C/Mo and B₄C/Mo₂C periodic multilayer structures deposited by magnetron sputtering. The characterization was performed by grazing incidence X-ray reflectometry at two different energies and high resolution transmission electron microscopy. The experimental results indicate the existence of an interdiffusion layer at the B₄C-on-Mo interface in the B₄C/Mo system. Thus, the B₄C/Mo multilayers were modeled by an asymmetric structure with three layers in each period. The thickness of B₄C-on-Mo interfacial layer was estimated about 1.1 nm. The B₄C/Mo₂C multilayers present less interdiffusion and are well modeled by a symmetric structure without interfacial layers. This study shows that B₄C/Mo₂C structure is an interesting alternative to B₄C/Mo multilayer for X-ray optic applications.     

Mo/Si aperiodic multilayer broadband reflective mirror for 12.5-28.5-nm wavelength range

Aperiodic molybdenum/silicon (Mo/Si) multilayer designed as a broadband reflective mirror with mean reflectivity of 10% over a wide wavelength range of 12.5-28.5 nm at incidence angle of 5° is developed using a numerical optimized method. The multilayer is prepared using direct current magnetron sputtering technology. The reflectivity is measured using synchrotron radiation. The measured mean reflectivity is 7.0% in the design wavelength range of 12.5-28.5 nm. This multilayer broadband reflective mirror can be used in extreme ultraviolet measurements and will greatly simplify the experimental arrangements.     

Use of cluster secondary ions for minimization of matrix effects in the SIMS depth profiling of La/B4C multilayer nanostructures

The elemental composition of La/B₄C multilayer metal structures is studied using SIMS on a TOF.SIMS-5 experimental setup. Analysis conditions that make it possible to considerably enhance the depth resolution are found. They include using low-energy O₂⁺ and Cs⁺ ions for sputtering and cluster secondary ions for registering matrix elements. The roughness evolution in the etching crater region is studied in a layer-by-layer analysis. It is shown that, at an incidence angle of 45° for sputtering ions, the rms roughness increases slightly (from an initial value of 0.5–0.7 nm) in the etching crater of the (La/B₄C)₇₀/Si structure at a depth of 0.5 μm. The profiles of elements in multilayer structures grown using two different types of magnetron systems with stationary and high-frequency discharges are compared. The main contaminations in the structures are determined.     

Reflective phase shift measurement of the Mo/Si multilayer mirror in extreme ultraviolet region

The reflective phase shift of multilayer mirror is one important property required in EUV lithography and attosecond pulses experiments. The reflective phase shift of the periodic Mo/Si multilayer mirror was characterized by combining the reflectivity with total electron yield signal at the synchrotron radiation in Hefei. The multilayer was fabricated using direct current magnetic sputtering method. Using the wavelet transform approach, the period and each layer thickness were obtained, the small angle X-ray reflective data from X-ray diffractometer were fitted using these data as the mutilayer's initial structure. The TEY signal of the multilayer is coincided with the surface electron field of the multilayer. A thick Si layer was used to eliminate the effect of the multilayer's surface layer on the TEY signal. The retrieved difference in reflected phase from the incident phase was obtained combining the reflectivity with the total electron yield signal and it is similar with the calculated phase shift of the multilayer.     

Ablative property of HfC-based multilayer coating for C/C composites under oxy-acetylene torch

To improve ablation resistance of C/C composites, HfC-based coating and SiC coating were prepared on the surface of C/C composites by chemical vapor deposition. The coating exhibits dense surface and outstanding anti-ablation ability. Compared with uncoated C/C, the linear and mass ablation rates of the coated C/C decreased by 33.3% and 66.7%, respectively, after ablation for 20 s. The residual oxides can prevent oxygen from diffusing inwardly; large amounts of heat can be taken away by the gas generated during ablation, which is also helpful for protection.     

Bilayer period dependence of CrN/CrAlN nanoscale multilayer thin films

CrN/CrAlN nanoscale multilayer thin films with a bilayer period (λ$\lambda$) ranging from 4.4 to 44.1 nm were deposited on Si wafers (100) by closed field unbalanced magnetron sputtering (CFUBMS). The λ$\lambda$ of the layers was controlled by the rotation speed of the substrate holder. The coatings were characterized by high resolution X-ray diffraction and field emission transmission electron microscopy. The CrN/CrAlN nanoscale multilayer thin films exhibited a CrN (200) and AlN (200) crystalline orientation. Nano-indentation testing revealed a hardness ranging from 37 to 46 GPa according to the bilayer period. The highest hardness was obtained with a bilayer period of 5.5 nm due to the high resistance to plastic deformation.     

磁控溅射法制备极紫外6.8～11.0nm波段Mo/B_4C横向梯度多层膜（英文）

用直流磁控溅射法结合掩模板控制膜厚的方法在Si衬底上制备了工作于6.8～11.0nm波段的[Mo/B_4C]60横向梯度多层膜。利用X射线掠入射反射测试以及同步辐射反射率测试对梯度多层膜的结构及性能进行了测试。X射线掠入射反射测试结果表明,多层膜周期厚度沿着长轴方向从4.39nm逐渐增加到7.82nm,周期厚度平均梯度为0.054nm/mm。对横向梯度多层膜沿长轴方向每隔5mm进行了一次同步辐射反射率测试,结果显示,横向梯度多层膜在45°入射角下的反射率约为10%,反射峰的半高全宽介于0.13nm到0.31nm之间。     

Ternary systems and the effect of parity on the multilayer mirror reflectance

The possibility of increasing the maximum reflectance of multilayer x-ray mirrors based on ternary systems is demonstrated. The effect is due to separate profiling of the real and imaginary components of the dielectric permittivity, which is impossible in binary systems.     

Design of the chirped Mo/Si multilayer mirror with SiC capping layer in extreme ultraviolet region

The design procedures were discussed in detail for a normal incident chirped Mo/Si multilayer mirror with Group Delay Dispersion (GDD) of ?3600 as² in the wavelength region of 13–17 nm. The GDD was calculated using an analytical approach by fitting the optical constants of the coating materials in the wavelength range of 12.8–17.2 nm, respectively. The final structure of the chirped mirror was obtained by using the simplex algorithm from the initial structure obtained by the genetic algorithm based on structure generated by a random generator. After considering the interfacial roughness and layers thickness deviation, the effects on the reflectivity and the GDD were discussed. It was found that the average reflectivity decreases from 5.98% to 4.22% and the average GDD decreases from ?3561.86 as² to ?3462.03 as², the vibration of GDD were larger than that of the reflectivity. The reflectivity was affected greatly by the 9th layer and the GDD was affected greatly by the 25th layer when each layer thickness changes ±0.2 nm. Compared with the GDD, the reflectivity was affected greatly by the layer thickness error.     

A multilayer x-ray mirror in the form of an ellipsoid of revolution

Laboratory technology for the preparation of multilayer mirrors in the form of an ellipsoid of revolution for the hard x-ray wavelength range (λ = 0.1 nm) has been developed on the basis of the replica method. A prototype mirror in the form of a sector of an ellipsoid of revolution is prepared. Its shape and reflection characteristics are studied.