共查询到18条相似文献,搜索用时 62 毫秒
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介绍了2005年国家自然科学奖二等奖获奖项目“微小晶体结构测定的电子晶体学研究”.研究目的是建立一种借助高分辨电子显微像测定晶体结构的新方法.为此提出了高分辨电子显微学与衍射晶体学相结合的思想,在实现此思想的过程中,研究了像衬的规律,得出实用的像衬公式和理论,阐明了不同种类原子像衬与晶体厚度的关系,而且用理论指导实验,观察到晶体中锂原子的像衬.以此理论为依据,把衍射晶体学中的多种分析方法特包是直接法引入到高分辨电子显微学中,建立了一套全新的电子晶体学图像处理技术,开发了相应的可视化专用软件包,并应用于测定多个未知晶体结构.文中逐一介绍了研究工作全过程的关键问题和研究结果. 相似文献
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试把直接法应用于抗生蛋白链菌素(streptavidin)沿[001]方向投影的模拟像和相应的理论结构因子作图像处理.先用两张高分辨电子显微像作直接法解卷,以互补因衬度传递函数的作用而损失的结构信息,求得的欠焦值比用单张像解卷的结果更接近真实值.把从结构模型计算出的030nm以内的相位,以及025nm以内的振幅作为起始数据,进行直接法相位外 推,并借助团簇分析方法得到030nm至025nm之间的相位.所得分辨率为030nm的解卷像 和分辨率为025nm的晶体结构投影均与理论结构模型的相应投影电
关键词:
高分辨电子显微学
直接法
图像处理 相似文献
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介绍了一种测定晶体结构的图像处理技术,它基于高分辨电子显微学与电子电子衍射的结合。中给出了其方法的示意图。 相似文献
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像差校正透射电子显微镜是材料微观结构和物态高分辨率表征最常用的工具之一,极大地推动了相关学科的发展。近年来,电子显微学领域一个新的突破是电子叠层衍射成像技术。它突破了常规成像技术分辨率的极限,实现了原子晶格振动决定的终极分辨率,并且能够实现纳米尺度电磁物态的高精度成像。文章主要简述了电子叠层衍射成像技术的发展历程、原理和最新进展,最后讨论其应用前景和未来展望。 相似文献
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近年来冷冻电子显微镜成像技术突飞猛进,越来越广泛地应用于生物大分子的高精度结构研究中,尤其在解析其他方法难以应对的蛋白质复合物的结构研究方面取得了瞩目的进展。文章对冷冻电镜单颗粒重构技术近年来的发展做了回顾和总结,重点介绍了冷冻电镜单颗粒重构技术中的基本流程及其使用的图像处理技术和算法,并对近年来人们重点关注的问题进行了讨论。最后对冷冻电镜单颗粒重构技术未来的发展趋势,尤其是对细胞内原位的分子结构以及蛋白质分子的动态信息的捕捉等方面进行了初步的探讨。 相似文献
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In_2Se_3是一种常见的A_2~ⅢB_3~Ⅵ型半导体,在不同温度下可表现出不同的物相,对应的晶格参数与物理性质也会有所不同.在过去几十年间,In_2Se_3的多相性引起了人们的关注,各物相的晶体结构被广泛地研究.近年来,研究发现α-In_2Se_3具有优异的光电、压电性能以及独特的铁电性能,可以预见它将在未来的半导体电子器件中发挥出重要的作用.本文综述了一系列In_2Se_3化合物的晶体结构与电子特性,我们首先简要介绍了这些In_2Se_3化合物的基本知识,接着详细讨论了它们的晶体结构与电子特性,最后对In_2Se_3化合物的研究前景进行了展望. 相似文献
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Douglas L. Dorset 《Micron (Oxford, England : 1993)》1995,26(6):511-520
Applications of the Sayre equation to the electron crystallographic analysis of protein structures are demonstrated. Starting with a lower-resolution basis phase set obtained from the Fourier-transform of an electron micrograph, it is possible, for example, to extend directly to the higher resolution of the electron diffraction pattern. Examples of such analyses include bacteriorhodopsin, halorhodopsin and the Omp F porin from the outer membrane of Eschirichia coli. If a multisolution approach is taken, it may also be possible to carry out ab initio phase determinations, as demonstrated with low-resolution diffraction amplitudes from a negatively-stained membrane protein crystal. 相似文献
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Intergrowth microstructures of MnF2 subjected to shock compression at 4.4, 9.0 and 21.6 GPa were examined using transmission electron microscopy (TEM). Intergrowth microstructures consisting of rutile- and α-PbO2-type phases were observed in samples shock-loaded to 4.4 and 9 GPa. The sample subjected to 21.6 GPa consisted of a twin structure with stacking faults, with a rutile-type but not the α-PbO2-type phase. In the 9.0-GPa shocked sample, the phase ledge structure originating from a phase transition is directly captured by high-resolution transmission electron microscopy. 相似文献
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A tensor LEED analysis is reported for the Zr(0001)-(1 × 1)-O surface which involves oxygen at a total coverage of 2 monolayers. The structure is indicated to have two layers of O: one forms an overlayer in which the O atoms bond to hollow sites of three-fold coordination on the regular metal surface, while the other layer has the O atoms in tetrahedral hole sites between the first and second metal layers. The stacking sequence, designated as (C)B(A)AB... corresponds to the first three layers of anion-terminated cubic ZrO2, although some lateral compression is needed for superposition on the regular hcp Zr structure. The absorption of O in the tetrahedral holes results in a significant expansion in the first-to-second Zr---Zr interlayer spacing to about 3.44 Å from the bulk vaue of 2.57 Å. The O---Zr bond lengths are estimated to equal 2.07 Å for the overlayer O atoms, and 2.21 Å for the O atoms in tetrahedral hole sites. Comparisons are made with the structures of the corresponding 0.5 and 1 ML surfaces formed by the O/Zr(0001) system. 相似文献
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Low-energy electron diffraction and scanning tunneling microscopy have been used to probe the surface atomic structure of Cu2O(1 1 1) after various sample preparations. Annealing in oxygen gives a stoichiometric (1 × 1) oxygen terminated surface and further annealing in ultra-high vacuum results in a clear reconstruction and surface faceting. Tunneling from filled states in the reconstructed surface reveals a hexagonal pattern of large protrusions, which show an internal structure. The reconstruction is believed to be due to one-third of a monolayer of ordered oxygen vacancies. At areas on the surface where the large features are missing, another smaller type of protrusions is visible, which is associated with the ideal (1 × 1) surface. The relative position of the two types of features gives two possible models of the (1 1 1) surface. In the first model, the (1 × 1) surface is the ideal bulk terminated surface and coordinatively unsaturated oxygen ions are missing in the reconstructed surface. The second model agrees with the first model with the exception that coordinatively unsaturated copper ions in the outmost copper layer are missing in both the (1 × 1) and the reconstructed surface. The latter model is supported by previous surface free energy calculations. Since the undercoordinated copper ions have been suggested to be the catalytic active sites of Cu2O(1 1 1), the presence or absence of these cations could be of great importance for the fundamental understanding of the surface reactivity of Cu2O and of copper-based catalysts. 相似文献
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E. A. Soares C. Bittencourt E. L. Lopes V. E. de Carvalho D. P. Woodruff 《Surface science》2004,550(1-3):127-132
Quantitative low energy electron diffraction has been used to determine the structure of the Ni(1 1 1)(√3×√3)R30°-Sn surface phase. The results confirm that the surface layer comprises a substitutional alloy of composition Ni2Sn as previously found by low energy ion scattering (LEIS), and also shows that there is no stacking fault at the substrate/alloy interface as has been found in (√3×√3)R30°-Sb surface alloys on Ag and Cu(1 1 1). The surface alloy layer is rumpled with the Sn atoms 0.45 ± 0.03 Å higher above the substrate than the surrounding Ni atoms. This rumpling amplitude is almost identical to that previously reported on the basis of the LEIS study. Comparison with similar results for Sn-induced surface alloy phases on Ni(1 0 0) and Ni(1 1 0) shows a clear trend to reduced rumpling with reduced surface atomic layer density, an effect which can be rationalised in terms of the different effects of valence electron charge smoothing at the surface. 相似文献
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Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO2, TiO2 and Cu2O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO2, TiO2 and Cu2O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible. 相似文献