Preparation and measurement of an x-ray Laue-type monochromator based on a WSi2/Si multilayer.

The Laue-type multilayer monochromator (LMM) is a promising optical element with a small size and high efficiency in a synchrotron radiation facility. By the dynamical diffraction theory, using DC magnetron sputtering technology, an LMM with a total thickness of 47 µm and a periodic thickness of 4.7 nm W S i 2/S i multilayer at 26 keV is designed and fabricated. During the preparation, the total number of layers is up to 20000, and every 300th layer of Si is replaced by WSi2 as the marker, so the multilayer is divided into 67 areas. The cross section of the multilayer is measured by a scanning electron microscope (SEM), and the marker region thickness error is 0.28% (RMS). The diffraction test experiment of the LMM is carried out at the Shanghai synchrotron radiation facility (SSRF). The 1st-order peak angle is 5.05 mrad, and the efficiency is 75.0%, which is close to the theoretical calculation result of 5.1 mrad and 79.1%. The Darwin width of the LMM is 0.17 mrad which is equal to the theoretical calculation. Based on the Bragg's diffraction equation, the energy resolution (Δ E/E) is 3.3%.

Preparation and testing of laterally graded multilayer with a double genetic algorithm and root mean square error optimization in differential deposition.

Lateral graded multilayer can realize reflection, collimation and focusing of hard X-ray, and are currently the research frontier and hotspot of synchrotron radiation and high-performance X-ray sources. To reduce the d-spacing error of graded multilayers, a root mean square error optimization method based on double genetic algorithm (DGA-RMSE) is proposed. The theoretical d-spacing distribution is obtained by optical design, and the range is 1.9 ∼ 3.1 nm. The optimized d-spacing distribution is obtained by convolution of particle beam function and continuous monotonic rate distribution line (RDL) which is constructed in the form of a polynomial. The GA is applied to optimize variables from the polynomial twice, and the RMSE of thickness error is optimized and converged to 0.0065 nm. The final thickness error which is measured by the grazing incidence X-ray reflectivity (GIXRR) is consistent with the theoretical calculation. The results show that DGA-RMSE can precisely select polynomial function of RDL, reducing the error in high-precision magnetron sputtering and mask technology.

Novel figuring method for a multilayer Laue lens.

A new, to the best of our knowledge, figuring method for a multilayer Laue lens (MLL) in the hard X-ray region is proposed in this paper. Theoretical simulation at 20 keV shows that the figuring method can compensate for the structure error. The phase errors of the first-order diffracted wave decrease from 0.85π to 0.26π after figuring. The spatial resolution changes from 45 nm to 26 nm after figuring, which is almost the same as that of the ideal MLL with a spatial resolution of 24 nm. The figured MLL can achieve 36% of the ideal MLL's first-order diffraction efficiency. Such method may reduce the requirements for the fabrication of the MLLs, and may make it possible to manufacture the larger numerical aperture MLL with the longer working distance in the future.

Refurbishment of W/B4C multilayers on Si substrate by etching a chromium buffer layer.

In synchrotron facilities, optics with multilayer coatings are used for beam monochromatization, focusing, and collimation. These coatings might be damaged by high heat load, poor film adhesion, high internal stress, or poor vacuum. Optical substrates always need high quality, which is expensive and has a long processing cycle. Therefore, it is desired to make the substrate reusable and the refurbished coating as good as a brand-new one. In this study, a W/B4C multilayer coating with a 2 nm Cr buffer layer was prepared on a Si substrate. The coating was successfully stripped from the Si substrate by dissolving the Cr buffer layer using an etchant. The roughness and morphology after the different etching times were investigated by measuring the GIXRR and 3D surface profiler. It is shown that the time required to etch the W/B4C multilayer coating with a Cr buffer layer, is quite different compared with etching a single Cr film. A layer of silicon dioxide was introduced during the fitting. After the new etching process, the roughness of the sample is as good as the one on a brand-new substrate. The W/B4C multilayer coatings with a Cr buffer layer were recoated on the etched samples, and the interface roughness was not damaged by the etching process.

Single-order focus multilayer Laue lens.

A novel sinusoidal multilayer Laue lens (MLL) in the hard X-ray region is proposed, to the best of our knowledge. The theoretical design shows that the structure function of the MLL is a sine function of the radius such as that of a sinusoidal transmission zone plate. A numerical simulation at the energy of 12 and 24 keV reveals that the MLL can suppress higher-order diffractions effectively, the characteristic of single-order diffraction with spatial resolution is the same as that of the corresponding classical MLL, and the MLL can achieve the first-order diffraction efficiency of 6.8% at 12 and 8.7% at 24 keV. The sinusoidal MLL can also work for single-order focusing at other energies.

In situ determination of the extreme damage resistance behavior in stomatopod dactyl club.

The structure and mechanical properties of the stomatopod dactyl club have been studied extensively for its extreme impact tolerance, but a systematic in situ investigation on the multiscale mechanical responses under high-speed impact has not been reported. Here the full dynamic deformation and crack evolution process within projectile-impacted dactyl using combined fast 2D X-ray imaging and high-resolution ex situ tomography are revealed. The results show that hydration states can lead to significantly different toughening mechanisms inside dactyl under dynamic loading. A previously unreported 3D interlocking structural design in the impact surface and impact region is reported using nano X-ray tomography. Experimental results and dynamic finite-element modeling suggest this unique structure plays an important role in resisting catastrophic structural damage and hindering crack propagation. This work is a contribution to understanding the key toughening strategies of biological materials and provides valuable information for biomimetic manufacturing of impact-resistant materials in general.

A Freestanding Chitin-Derived Hierarchical Nanocomposite for Developing Electrodes in Future Supercapacitor Industry.

Crustacean cuticles are receiving extensive attention for its potential in developing environmentally friendly and high energy density electrodes for supercapacitor applications. In the current work, the demineralized tergite cuticle of mantis shrimp was employed as a precursor for the fabrication porous biochar. The structural benefits of the cuticle, including the hierarchical nanofiber networks, and the interpenetrating pore systems were maximumly retained, providing a high carbon content and specific surface area scaffold. Graphene oxide sheets were deposited across the biochar through the pore canal systems to further increase the conductivity of the biochar, forming a novel freestanding carbon composite. Throughout the modification process, the material products were examined by a range of methods, which showed desired structural, chemical and functional properties. Our work demonstrates that high performance carbon materials can be manufactured using a simple and green process to realize the great potential in energy storage applications.

A method to stabilize the incident X-ray energy for anomalous diffraction measurements.

A method to calibrate and stabilize the incident X-ray energy for anomalous diffraction data collection is provided and has been successfully used at the single-crystal diffraction beamline 1W2B at the Beijing Synchrotron Radiation Facilities. Employing a feedback loop to control the movement of the double-crystal monochromator, this new method enables the incident X-ray energy to be kept within a 0.2 eV range at the inflection point of the absorption edge.

Large-aperture prism-array lens for high-energy X-ray focusing.

A new prism-array lens for high-energy X-ray focusing has been constructed using an array of different prisms obtained from different parabolic structures by removal of passive parts of material leading to a multiple of 2π phase variation. Under the thin-lens approximation the phase changes caused by this lens for a plane wave are exactly the same as those caused by a parabolic lens without any additional corrections when they have the same focal length, which will provide good focusing; at the same time, the total transmission and effective aperture of this lens are both larger than those of a compound kinoform lens with the same focal length, geometrical aperture and feature size. This geometry can have a large aperture that is not limited by the feature size of the lens. Prototype nickel lenses with an aperture of 1.77 mm and focal length of 3 m were fabricated by LIGA technology, and were tested using CCD camera and knife-edge scan method at the X-ray Imaging and Biomedical Application Beamline BL13W1 at Shanghai Synchrotron Radiation Facility, and provided a focal width of 7.7 µm and a photon flux gain of 14 at an X-ray energy of 50 keV.

Focusing performance of a multilayer Laue lens with layer placement error described by dynamical diffraction theory.

The multilayer Laue lens (MLL) is essentially a linear zone plate with large aspect ratio, which can theoretically focus hard X-rays to well below 1 nm with high efficiency when ideal structures are used. However, the focusing performance of a MLL depends heavily on the quality of the layers, especially the layer placement error which always exists in real MLLs. Here, a dynamical modeling approach, based on the coupled wave theory, is proposed to study the focusing performance of a MLL with layer placement error. The result of simulation shows that this method can be applied to various forms of layer placement error.

Dominance of HIV-1 subtype CRF01_AE in sexually acquired cases leads to a new epidemic in Yunnan province of China.

BACKGROUND: Dating back to the first epidemic among injection drug users in 1989, the Yunnan province has had the highest number of human immunodeficiency virus type 1 (HIV-1) infections in China. However, the molecular epidemiology of HIV-1 in Yunnan has not been fully characterized. METHODS AND FINDINGS: Using immunoassays, we identified 103,015 accumulated cases of HIV-1 infections in Yunnan between 1989 and 2004. We studied 321 patients representing Yunnan's 16 prefectures from four risk groups, 11 ethnic populations, and ten occupations. We identified three major circulating subtypes: C/CRF07_BC/CRF08_BC (53%), CRF01_AE (40.5%), and B (6.5%) by analyzing the sequence of p17, which is part of the gag gene. For patients with known risk factors, 90.9% of injection drug users had C/CRF07_BC/CRF08_BC viruses, whereas 85.4% of CRF01_AE infections were acquired through sexual transmission. No distinct segregation of CRF01_AE viruses was found among the Dai ethnic group. Geographically, C/CRF07_BC/CRF08_BC was found throughout the province, while CRF01_AE was largely confined to the prefectures bordering Myanmar. Furthermore, C/CRF07_BC/CRF08_BC viruses were found to consist of a group of viruses, including C, CRF08_BC, CRF07_BC, and new BC recombinants, based on the characterization of their reverse transcriptase genes. CONCLUSIONS: This is the first report of a province-wide HIV-1 molecular epidemiological study in Yunnan. While C/CRF07_BC/CRF08_BC and CRF01_AE are codominant, the discovery of many sexually transmitted CRF01_AE cases is new and suggests that this subtype may lead to a new epidemic in the general Chinese population. We discuss implications of our results for understanding the evolution of the HIV-1 pandemic and for vaccine development.