Use of a CCD diffractometer in crystal structure determinations at high pressure
Use of a CCD diffractometer in crystal structure determinations at high pressure
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DOI：
10.1107/s0021889804007149
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发表时间：
2004-06-01
影响因子：
6.1
通讯作者：
Ruf, M
中科院分区：
文献类型：
--
作者：
Dawson, A;Allan, DR;Ruf, M
虽然CCD仪器现在被广泛用于单晶衍射，但它们还没有被广泛用于高压下的晶体学研究。本文介绍了一种CCD仪器--Bruker-Nonius SMART APEX（一种固定式X线仪）的应用经验。将样品置于压力室中的中心由于室体对观察样品施加的限制而变得复杂。数据收集策略由以下要求定义：（i）入射光束必须照射样品，以及（ii）压力池主体应遮蔽不超过80%的检测器。高压衍射图像被来自垫圈和背衬盘材料的粉末线和来自金刚石砧的非常强烈的斑点所污染，垫圈和背衬盘材料形成压力单元的一部分。描述了用于索引的点的选择的程序。集成例程试图从被压力单元的主体遮蔽的检测器的区域收获强度数据，并且描述了用于生成动态掩模的过程。阴影也减少了可以采样的倒易空间的体积，尽管这可以通过在多个压力传感器设置下执行数据收集来增加。在两阶段程序中进行吸收的校正，所述两阶段程序包括对细胞吸收的分析校正，接着是第二多扫描校正。在高压下收集的数据集通常包含一些显著的异常值;这些异常值可以在合并期间使用鲁棒的抗性加权方案来识别，如Blessing [J. Appl. Cryst.（1997），30，421 - 426]所述。
Although CCD instruments are now widely used in single-crystal diffraction, they have not been employed so extensively in crystallographic studies at high pressure. This paper describes some practical experience in the application of one CCD instrument, the Bruker - Nonius SMART APEX (a fixed-chi instrument). Centring a sample in a pressure cell is complicated by the restrictions on viewing the sample imposed by the body of the cell. The data collection strategy is defined by the requirements that (i) the incident beam must illuminate the sample and (ii) no more than 80% of the detector should be shaded by the body of the pressure cell. High-pressure diffraction images are contaminated by powder lines from the gasket and backing-disk materials, which form part of the pressure cell, and very intense spots from the diamond anvils. Procedures for the selection of spots for indexing are described. Integration routines attempt to harvest intensity data from regions of the detector that are shaded by the body of the pressure cell, and a procedure for generating dynamic masks is described. Shading also reduces the volume of reciprocal space that can be sampled, although this can be increased by performing data collections at more than one pressure-cell setting. Corrections for absorption are carried out in a two-stage procedure comprising an analytical correction for absorption by the cell, followed by a second multi-scan correction. Data sets collected at high pressure often contain some significant outliers; these can be identified during merging using a robust resistant weighting scheme, as described by Blessing [J. Appl. Cryst. (1997), 30, 421 - 426].