X射线相衬成像光子筛

基于 Zernike相衬成像原理和光瞳切趾原理,提出一种将相位板和切趾光子筛集成为一个相衬显微物镜的 X射线相衬成像光子筛的设计方法.这种 X射线相衬成像物镜可以实现生物体组织或者其他弱吸收材料的高分辨率和高衬度成像.通过优化光子筛透镜的衍射结构,可以抑制成像系统的点扩展函数的旁瓣和消除高阶衍射焦点,从而提高成像分辨率;另外,将光子筛透镜和变相板合为一体,克服了成像透镜和变相板难以对准的缺陷.以高斯切趾光子筛为例,实验验证了设计方法的可行性. 关键词： X射线显微技术 相衬成像 光瞳切趾 光子筛     

Lacunar fractal photon sieves

We present a new family of diffractive lenses whose structure is based on the combination of two concepts: photon sieve and fractal zone plates with variable lacunarity. The focusing properties of different members of this family are examined. It is shown that the sieves provide a smoothing effect on the higher order foci of a conventional lacunar fractal zone plate. However, the characteristic self-similar axial response of the fractal zone plates is always preserved.     

Zernike apodized photon sieves for high-resolution phase-contrast x-ray microscopy

We present a type of diffractive lens, Zernike apodized photon sieves (ZAPS), used as the objective for high spatial resolution and high phase-contrast imaging of weakly absorbing materials in x rays. The structure of ZAPS is based on the combination of two concepts: apodized photon sieves and Zernike phase contrast. The ZAPS is a single optic that integrates the appropriate ±π/2 rad phase shift through selective zone placement shifts in an apodized photon sieve. Analysis of the focusing properties of the apodized photon sieve in terms of point-spread function show that the sidelobes have been significantly suppressed at the expense of slightly widening the width of the main lobe. In combination with synchrotron light sources, ZAPS offers new opportunities for high-resolution phase-contrast x-ray microscopy in the physical and life sciences.     

Quadratic grating apodized photon sieves for simultaneous multiplane microscopy

We present a new type of imaging device, named quadratic grating apodized photon sieve (QGPS), used as the objective for simultaneous multiplane imaging in X-rays. The proposed QGPS is structured based on the combination of two concepts: photon sieves and quadratic gratings. Its design principles are also expounded in detail. Analysis of imaging properties of QGPS in terms of point-spread function shows that QGPS can image multiple layers within an object field onto a single image plane. Simulated and experimental results in visible light both demonstrate the feasibility of QGPS for simultaneous multiplane imaging, which is extremely promising to detect dynamic specimens by X-ray microscopy in the physical and life sciences.     

卢卡斯光子筛的聚焦特性研究

介绍了一种基于卢卡斯数编码设计的轴上四焦点光子筛,其各焦距分布与黄金分割比密切相关.实验上利用相移数字全息验证了设计器件具有轴上四焦点聚焦特性,测量结果表明:轴向焦距和横向焦斑光强分布与理论设计值一致.该振幅型光子筛具有体积小、重量轻、易加工等优点,可应用于X波段显微和生物细胞阵列成像等领域.     

HRTEM investigation of mesoporous molecular sieves

High resolution transmission electron microscopic (HRTEM) studies of some typical mesoporous molecular sieves, such as MCM-41, SBA-2 and STAC-1, etc. are presented. Since the materials consist of amorphous silica and their unit cell dimensions are in a range of 1.5 to over 10 nm, the conventional X-ray diffraction method gives us very limited information about the detailed structures. On the other hand, HRTEM has been found to be the most powerful technique to detect the local structures and to image metal clusters inside the channels of these materials.     

氢气分子在沸石中的吸附模拟研究

采用巨正则蒙特卡罗方法模拟了氢气在沸石中的吸附行为,并采用Dubinin-Astakhov微孔分析方法,分析了沸石结构对储氢量大小的影响,总结了影响储氢量大小的物理因素,该工作有利于指导合理的设计与合成储存材料,为改善材料储氢能力提供了有力的理论支撑. 关键词： 储氢 吸附等温线 巨正则蒙特卡罗     

spin-lattice relaxation in cobalt-containing aluminophosphate molecular sieves

Phosphorus spin-lattice relaxation was studied in aluminophosphate molecular sieves containing various concentrations of either framework or non-framework cobalt. The behaviour of nuclear magnetisation in the presence of these paramagnetic centres was described successfully in the limit of no spin-diffusion. The diffusionless regime was strongly indicated with non-exponential magnetisation recovery and was therefore easy to recognise. According to the model, spin-lattice relaxation rates depend on the square of cobalt concentration. Measured relaxation rates agreed well with calculations if effective cobalt concentration was considered rather than the average one. The latter was obtained by bulk elemental analysis, while the former was extracted from cobalt concentration depth-profiles measured with Auger electron spectroscopy. These measurements indicated that in impregnated samples containing non-framework cobalt there could be much more cobalt near the crystal surface than within the crystal. Because high cobalt concentration can lead to an invisible phosphorus, only nuclei deep within the crystal contribute to the NMR signal. In such a case, the effective concentration is simply the concentration of cobalt far from the crystal surface. In our case, two impregnated samples with different bulk cobalt concentrations exhibited equal relaxation rates. Previously, such a case was misinterpreted as a case, in which nuclear spin-lattice relaxation was independent of cobalt concentration. AES measurements, however, revealed, that although average concentrations of the two samples were different by a factor of two, their effective concentrations were equal and thus in complete agreement with observed relaxation rates.     

Double rotation27Al NMR in molecular sieves

Although high-resolution NMR spectra can be obtained in solids, the use of²⁷Al NMR to investigate the structure of aluminosilicate and aluminophosphate molecular sieves has been severely limited because anisotropic second-order quadrupolar interactions, responsible for spectral broadening, cannot be eliminated by conventional magic angle spinning (MAS) or multiple pulse techniques. Here we give the principles of the double rotation (DOR) NMR technique which can remove not only the first-order broadenings but also the second-order broadenings in the NMR spectra of quadrupolar nuclei in solids. High-resolution²⁷Al NMR using DOR is capable of resolving discrete framework aluminum sites in aluminophosphate molecular sieves, permitting quantitative investigation of site-specific adsorbate-host interactions, and of discriminating different aluminum species in zeolites.     

软X光谱学光子筛衍射特性的实验表征

 概述了谱学光子筛的设计原理,计算了其透射率,并对设计的软X光谱学光子筛的衍射模式在光学波段进行了模拟计算和实验表征。结果表明,这种新型色散元件具有良好的、与设计预期一致的单级衍射特性,3级及以上的高级衍射能被有效抑制。与传统的透射光栅和以前设计的单级衍射光栅相比,新设计的软X光谱学光子筛更易于实现自支撑,可望在极紫外和软X光谱测量过程中得到广泛应用。     

软X光谱学光子筛衍射特性的实验表征

概述了谱学光子筛的设计原理,计算了其透射率,并对设计的软X光谱学光子筛的衍射模式在光学波段进行了模拟计算和实验表征。结果表明,这种新型色散元件具有良好的、与设计预期一致的单级衍射特性,3级及以上的高级衍射能被有效抑制。与传统的透射光栅和以前设计的单级衍射光栅相比,新设计的软X光谱学光子筛更易于实现自支撑,可望在极紫外和软X光谱测量过程中得到广泛应用。     

硬X射线光子筛波导效应研究

基于快速傅里叶变换光束传播法,研究了硬X射线光子筛中高高宽比金属结构的波导效应,确定了硬X射线光子筛的物理边界条件,采用角谱法计算了硬X射线光子筛的点扩展函数,并分析了吸收体厚度对聚焦性能的影响.研究结果表明波导效应一定程度上有利于抑制光子筛高级衍射的产生,提高聚焦性能.在同样的特征尺寸下,硬X射线光子筛的空间分辨率优于菲涅尔波带片,其缺点是衍射效率的下降.吸收体厚度的提高有利于提高光子筛的聚焦性能和衍射效率,但是相应的纳米加工工艺难度会增加. 关键词： 菲涅尔波带片 硬X射线光子筛 光束传播法 角谱法     

基于光子筛的软X光谱仪

介绍了采用新型软X光谱学光子筛作为分光元件的软X光谱仪的原理和结构参数设计。新谱仪理论测量范围为100 eV~2 keV,光谱分辨力达0.35 nm。应用该谱仪在SILEX-Ⅰ装置上测量了飞秒激光与固体铜靶相互作用产生的X射线发射谱。实验结果表明,该谱仪主要性能指标达到设计要求,适合于激光与等离子体相互作用产生的软X射线研究。     

基于光子筛的软X光谱仪

 介绍了采用新型软X光谱学光子筛作为分光元件的软X光谱仪的原理和结构参数设计。新谱仪理论测量范围为100 eV~2 keV,光谱分辨力达0.35 nm。应用该谱仪在SILEX-Ⅰ装置上测量了飞秒激光与固体铜靶相互作用产生的X射线发射谱。实验结果表明,该谱仪主要性能指标达到设计要求,适合于激光与等离子体相互作用产生的软X射线研究。     

Magnetic properties of iron loaded MCM-48 molecular sieves

Mesoporous molecular sieves of MCM-48 type were loaded with iron by the wet impregnation method, using Fe(III) nitrate or Fe(II) sulfate aqueous solutions as Fe sources, to obtain a magnetic porous composite. The iron loaded materials were characterized by XRD, N₂ adsorption and DRUV-vis and compared with the Si-MCM-48 host. Their magnetic properties were studied by measuring the hysteresis loops up to 1.5 T at different temperatures (5-300 K) and by magnetization vs. temperature curves following the conventional zero field cooling (ZFC) and field cooling (FC) protocols. Materials with high structure regularity and surface area are obtained, which exhibit a mixed paramagnetic and superparamagnetic behavior, arising in isolated iron ions inserted in the host framework, and in small iron oxide clusters or nanoparticles forming inside the pores, respectively. Larger hematite particles (8-13 nm) grown on the external surface provide a quite small ferromagnetic contribution to the hysteresis loop.     

Dynamics of water in molecular sieves by dielectric spectroscopy

We present recent dielectric data on the dynamics of water confined in molecular sieves with pore sizes 5 and 10 A. The dielectric measurements in the frequency and temperature ranges 10(-2)-10(6) Hz and 120-300 K show three relaxation processes for both samples. In the case of the 10 A pore the slowest process shows an Arrhenius temperature dependence at low temperatures (<220 K), while at high temperatures the relaxation appears to follow a more Vogel-Fulcher-Tammann (VFT) like behaviour. The relaxation time for this process is 100 s at about 170 K. The second slowest process is at low temperatures very similar to the main process of (bulk-like) water in a fully hydrated clay, but also this process seems to exhibit some kind of dynamical transition, in this case at T approximately 185 K. All the three processes in the 5 A pore exhibit Arrhenius temperature dependence, and two of them are considerably slower than the main relaxation in the hydrated clay. Thus, dynamics of bulk-like water is only observed in the 10 A molecular sieves, and most of the water molecules in both 5 and 10 A pores have considerably slower dielectric relaxation than has been observed for water confined in clay, most likely due to strong interactions with the considerably more hydrophilic inner surfaces of molecular sieves.     

Dynamics of water in molecular sieves by dielectric spectroscopy

A short review of our thermodynamic and structural work on Ar, N₂, CO, O₂, and the n-alkane C₁₉H₄₀ in mesoporous glasses is presented. The experimental information comes from X-ray diffraction, vapour pressure isotherms, optical transmission, heat capacity, and dielectric measurements. The filling in the pore centre formed by capillary condensation is distinguished from the adsorbed layers on the pore walls and is compared to the bulk state. Special attention is paid to metastable states and to the rearrangement of partial fillings that show up as a consequence of phase transitions.Received: 1 January 2003, Published online: 21 October 2003PACS: 61.43.Gt Powders, porous materials - 78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures - 75.75. + a Magnetic properties of nanostructures - 77.22.-d Dielectric properties of solids and liquids     

Torus quantization for spinning particles

We derive semiclassical quantization conditions for particles with spin. These generalize the Einstein-Brillouin-Keller quantization in such a way that, in addition to the Maslov correction, there appears another term which is a remnant of a non-Abelian geometric or Berry phase. This correction is interpreted in terms of a rotation angle for a classical spin vector.     

Canonical transformations for relativistic particles

A class of relatively simple canonical transformations of the Dirac equation, which contains as a particular case the Foldy-Wouthuysen transformation, is determined. An exact form for the hamiltonian of a Dirac-Pauli electron is obtained.