多层膜劳厄透镜对8keV X射线的聚焦性能模拟研究

基于多层膜技术的劳厄(Laue)透镜能实现硬X射线纳米级聚焦,在X射线微纳分析领域具有重要的应用前景.基于衍射动力学理论,分析了X射线在多层膜劳厄透镜中的传播,计算了不同结构的多层膜劳厄透镜对8 keVX射线的聚焦性能.结果表明,最外层厚度为5 nm的倾斜多层膜劳厄透镜可获得5.7 nm的聚焦光斑和26%的平均衍射效率...     

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.     

Hard X-ray one dimensional nano-focusing at the SSRF using a WSi2/Si multilayer Laue lens

The multilayer Laue lens (MLL) is a novel diffraction optics which can realize nanometer focusing of hard X-rays with high efficiency. In this paper, a 7.9 μm-thick MLL with the outmost layer thickness of 15 nm is designed based on dynamical diffraction theory. The MLL is fabricated by first depositing the depth-graded multilayer using direct current (DC) magnetron sputtering technology. Then, the multilayer sample is sliced, and both cross-sections are thinned and polished to a depth of 35-41 μ. The focusing property of the MLL is measured at the Shanghai Synchrotron Facility (SSRF). One-dimensional (1D) focusing resolutions of 205 nm and 221 nm are obtained at E=14 keV and 18 keV, respectively. It demonstrates that the fabricated MLL can focus hard X-rays into nanometer scale.     

X-ray nanometer focusing at the SSRF based on a multilayer Laue lens

We designed and fabricated a multilayer Laue lens(MLL) as a hard X-ray focusing device.WSi_2/Si multilayers were chosen owing to their excellent optical properties and relatively sharp interface.The multilayer sample was fabricated by using direct current(DC) magnetron sputtering technology and then was sliced and thinned to form an MLL.The thickness of each layer was determined by scanning electron microscopy(SEM) image analysis with marking layers.The focusing property of the MLL was measured at Beamline 15 U,Shanghai Synchrotron Facility(SSRF).One-dimensional(1D) focusing resolutions of 92 nm are obtained at photon energy of 14 keV.     

A unique approach to accurately measure thickness in thick multilayers

X‐ray optics called multilayer Laue lenses (MLLs) provide a promising path to focusing hard X‐rays with high focusing efficiency at a resolution between 5 nm and 20 nm. MLLs consist of thousands of depth‐graded thin layers. The thickness of each layer obeys the linear zone plate law. X‐ray beamline tests have been performed on magnetron sputter‐deposited WSi₂/Si MLLs at the Advanced Photon Source/Center for Nanoscale Materials 26‐ID nanoprobe beamline. However, it is still very challenging to accurately grow each layer at the designed thickness during deposition; errors introduced during thickness measurements of thousands of layers lead to inaccurate MLL structures. Here, a new metrology approach that can accurately measure thickness by introducing regular marks on the cross section of thousands of layers using a focused ion beam is reported. This new measurement method is compared with a previous method. More accurate results are obtained using the new measurement approach.     

Submicron focusing of XUV radiation from a laser plasma source using a multilayer Laue lens

The focusing properties of a one-dimensional multilayer Laue lens (MLL) were investigated using monochromatic soft X-ray radiation from a table-top, laser-produced plasma source. The MLL was fabricated by a focused ion beam (FIB) structuring of pulsed laser deposited ZrO₂/Ti multilayers. This novel method offers the potential to overcome limitations encountered in electron lithographic processes. Utilizing this multilayer Laue lens, a line focus of XUV radiation from a laser-induced plasma in a nitrogen gas puff target could be generated. The evaluated focal length is close to the designed value of 220 μm for the measurement wavelength of 2.88 nm. Divergence angle and beam waist diameter are measured by a moving knife edge and a far-field experiment, determining all relevant second-order moments based beam parameters. The waist diameter has been found to be approximately 370 nm (FWHM).     

基于多层膜技术的硬X射线Laue透镜衍射效率的理论研究

采用耦合波理论分析了X射线在多层膜Laue透镜中的传播,选择Cu的Kα线作X射线光源,计算了多层膜Laue透镜的衍射效率.材料为WSi2/Si,最外层宽度为10 nm,深度为8 500 nm的多层膜Laue透镜,倾斜情况下外层区域局部光栅的衍射效率可达59%,理论上证明了多层膜Laue透镜是实现X射线聚焦的有效手段.     

Thinning and polishing of cross-section of depth-graded WSi2 /Si multilayer for linear zone plate application

A linear zone plate named multilayer laue lens (MLL) is fabricated using a depth-graded multilayer structure. The lens shows considerable potential in focusing an X-ray beam into a nanometer scale with high efficiency. In this letter, a depth-graded multilayer consisting of 324 alternating WSi 2 and Si layers with a total thickness of 7.9 μm is deposited based on the thickness sequence according to the demands of the zone plate law. Subsequently, the multilayer sample is sliced and thinned to an ideal depth along the cross-section direction using raw abrasives and diamond lapping. Finally, the cross-section is polished by a chemical mechanical polishing (CMP) technique to remove the damages and improve the surface smoothness. The final depth of the MLL is approximately 7 μm with an achieved aspect ratio greater than 400. Results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate that interfaces are sharp, and the multilayer structure remains undamaged after the thinning and polishing processes. The surface roughness achieved is 0.33 nm.     

Development of laser deposited multilayer zone plate structures for soft X-ray radiation

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO₂/Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si₃N₄ substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.     

Point focusing with flat and wedged crossed multilayer Laue lenses

Point focusing measurements using pairs of directly bonded crossed multilayer Laue lenses (MLLs) are reported. Several flat and wedged MLLs have been fabricated out of a single deposition and assembled to realise point focusing devices. The wedged lenses have been manufactured by adding a stress layer onto flat lenses. Subsequent bending of the structure changes the relative orientation of the layer interfaces towards the stress‐wedged geometry. The characterization at ESRF beamline ID13 at a photon energy of 10.5 keV demonstrated a nearly diffraction‐limited focusing to a clean spot of 43 nm × 44 nm without significant side lobes with two wedged crossed MLLs using an illuminated aperture of approximately 17 µm × 17 µm to eliminate aberrations originating from layer placement errors in the full 52.7 µm × 52.7 µm aperture. These MLLs have an average individual diffraction efficiency of 44.5%. Scanning transmission X‐ray microscopy measurements with convenient working distances were performed to demonstrate that the lenses are suitable for user experiments. Also discussed are the diffraction and focusing properties of crossed flat lenses made from the same deposition, which have been used as a reference. Here a focal spot size of 28 nm × 33 nm was achieved and significant side lobes were noticed at an illuminated aperture of approximately 23 µm × 23 µm.     

Design and performance of an X‐ray scanning microscope at the Hard X‐ray Nanoprobe beamline of NSLS‐II

A hard X‐ray scanning microscope installed at the Hard X‐ray Nanoprobe beamline of the National Synchrotron Light Source II has been designed, constructed and commissioned. The microscope relies on a compact, high stiffness, low heat dissipation approach and utilizes two types of nanofocusing optics. It is capable of imaging with ～15 nm × 15 nm spatial resolution using multilayer Laue lenses and 25 nm × 26 nm resolution using zone plates. Fluorescence, diffraction, absorption, differential phase contrast, ptychography and tomography are available as experimental techniques. The microscope is also equipped with a temperature regulation system which allows the temperature of a sample to be varied in the range between 90 K and 1000 K. The constructed instrument is open for general users and offers its capabilities to the material science, battery research and bioscience communities.     

软X射线Bragg-Fresnel二维聚焦镜的设计理论和方法

Ｘ射线Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件是近十年发展起来的一种用于Ｘ射线波段的新型光学元件。本文介绍一种具有二维聚焦效能的Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件的设计理论和方法。设计中采用衍射理论并用Ｃ语言编制计算机程序系统对衍射图形进行设计。对于使用波长１３．８ｎｍ，入射角５°，使用焦距２００ｍｍ的使用条件，设计结果为３５Ｍｏ／Ｓｉ双层多层膜，周期厚度７．１４ｎｍ，理论反射率约为６０％；衍射图形共４００个环带，最内环半宽度５２．５μｍ，最外环宽度１．３μｍ。     

X-ray zone plates in combination with diffraction reflection

We have studied focusing of X-ray beams with use of X-ray zone plates combined with diffraction reflection. Expressions are obtained for the focal length of a zone plate combined with two or one diffraction reflection. We propose to simplify the technology of fabrication of zone plates and indicate the possibility of obtaining zone plates with ultrashort focal lengths. A zone plate as combined with diffraction reflection may become a focusing element of X-ray microscope. It may also be used for both focusing X-ray radiation from laboratory sources and synchrotron radiation.     

Point spread function measurement of an X‐ray beam focused by a multilayer zone plate with narrow annular aperture

The experimental procedure for obtaining the point spread function (PSF) of a focusing beam generated using an X‐ray multilayer zone plate (MZP) with a narrow annular aperture has been developed. It was possible to reconstruct the PSF by applying the tomographic process to the measured dataset consisting of line spread functions (LSFs) in every radial direction on the focal plane. The LSFs were measured by a knife‐edge scanning method of detecting scattered intensity. In the experimental work, quasi‐monochromatic undulator radiation with a first harmonic energy of 20 keV was directly focused without a monochromator by the MZP, and the PSF was measured using this procedure. As a result, a near diffraction‐limited focused beam size of 46 nm full width at half‐maximum was obtained.     

Design study of hard X-ray tomography system to obtain a spatial resolution of 100 nm

An optic-based X-ray tomography system of a high spatial resolution using a conventional X-ray tube was proposed. The system had several X-ray optics: multilayer mirror for monochromatic X-ray, capillary optic for focusing X-ray onto a sample, and objective zone plate. The X-ray tomography system was designed for obtaining a spatial resolution of 100 nm. Design parameters for each optic were determined and optimized by ray tracing in considering X-ray intensity and reflectivity. The X-ray tomography system with a spatial resolution of 100 nm will provide a good inspect tool in bio-medical field and semiconductor applications.     

Nanometer-scale ablation with a table-top soft x-ray laser

Ablation of holes with diameters as small as 82 nm and very clean walls was obtained in poly(methyl methacrylate) focusing pulses from a Ne-like Ar 46.9 nm compact capillary-discharge laser with a freestanding Fresnel zone plate diffracting into third order. These results demonstrate the feasibility of using focused soft x-ray laser beams for the direct nanoscale patterning of materials and the development of new nanoprobes.     

Effect of the Mismatch of Layer Thicknesses on the Focusing of X Rays by Multilayer Laue Lens

JETP Letters - A numerical simulation has been performed to study the effect of the mismatch of layer thicknesses of multilayer Laue lenses (MLLs) on X-ray focusing. The spatial distributions of...     

微束斑X射线源及X射线光学元件

高质量的X射线源,尤其高亮度的微纳束斑X射线源是现代X射线光学高清晰成像最为关键的部件之一,在工业无损探伤、生命科学、材料科学等科学研究和实际应用中具有重要的意义。简单介绍了微束斑X射线源的产生方法及发展历史,并对微束X射线光学涉及到的聚焦X射线光学元件（如X射线掠入射反射镜、布拉格法反射镜、多层膜反射镜、多层膜光栅、X射线波带片、毛细管聚焦透镜和复合折射透镜等）的主要特点作了简要的系统介绍。最后展望了微细束X射线在微纳检测与分析等方面的应用前景。     

2D Laue focusing of X-ray radiation by a double-crystal system

The theory of the dynamic 2D focusing of an X-ray wave upon its Laue diffraction by a system of two bent crystals is developed. The reflecting planes of the crystals are perpendicular to their surfaces. 2D focusing is shown to be highly sensitive to the bending radius of the crystals and to the difference in their thicknesses. The effect of astigmatism on 2D Laue focusing is described, and conditions for stigmatic focusing are found. One-dimensional focusing inside the crystals is discussed. The spectral characteristics of a double-crystal 2D-focusing spectrometer are considered.     

螺旋型波带片聚焦特性研究

提出了一种计算螺旋型波带片聚焦特性的方法。从衍射积分理论出发对螺旋型波带片的聚集特性进行了理论计算,推导出了级数形式的解析解,获得了螺旋型波带片"空心"焦点的场强分布。利用螺旋型波带片的聚焦特性,对其成像进行了数值模拟和理论分析。理论分析表明螺旋型波带片的空间分辨率与其"空心"焦点的环宽有关。通过验证实验证明理论分析与实验测试一致,为螺旋型波带片成像理论和模拟计算提供了一种有效手段。