An efficient method for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films.,Acta Crystallographica Section A: Foundations and Advances

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An efficient method for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films.
Acta Crystallographica Section A: Foundations and Advances ( IF 1.9 ) Pub Date : 2020-04-02 , DOI: 10.1107/s2053273320001266
Josef Simbrunner ₁ , Benedikt Schrode ₂ , Jari Domke ₃ , Torsten Fritz ₃ , Ingo Salzmann ₄ , Roland Resel ₂

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Crystal structure identification of thin organic films entails a number of technical and methodological challenges. In particular, if molecular crystals are epitaxially grown on single-crystalline substrates a complex scenario of multiple preferred orientations of the adsorbate, several symmetry-related in-plane alignments and the occurrence of unknown polymorphs is frequently observed. In theory, the parameters of the reduced unit cell and its orientation can simply be obtained from the matrix of three linearly independent reciprocal-space vectors. However, if the sample exhibits unit cells in various orientations and/or with different lattice parameters, it is necessary to assign all experimentally obtained reflections to their associated individual origin. In the present work, an effective algorithm is described to accomplish this task in order to determine the unit-cell parameters of complex systems comprising different orientations and polymorphs. This method is applied to a polycrystalline thin film of the conjugated organic material 6,13-pentacenequinone (PQ) epitaxially grown on an Ag(111) surface. All reciprocal vectors can be allocated to unit cells of the same lattice constants but grown in various orientations [sixfold rotational symmetry for the contact planes (102) and (102)]. The as-determined unit cell is identical to that reported in a previous study determined for a fibre-textured PQ film. Preliminary results further indicate that the algorithm is especially effective in analysing epitaxially grown crystallites not only for various orientations, but also if different polymorphs are present in the film.

中文翻译：

一种用于索引外延生长薄膜的掠入射 X 射线衍射数据的有效方法。

薄有机薄膜的晶体结构识别带来了许多技术和方法上的挑战。特别是，如果分子晶体在单晶衬底上外延生长，则经常会观察到吸附物的多个优选取向、几种对称相关的面内排列和未知多晶型物的出现的复杂情况。理论上，简化的晶胞的参数及其方向可以简单地从三个线性独立的倒易空间向量的矩阵中获得。然而，如果样品呈现出不同方向和/或具有不同晶格参数的晶胞，则有必要将所有实验获得的反射分配给它们相关的个体原点。在目前的工作中，描述了一种有效的算法来完成这项任务，以确定包含不同方向和多晶型的复杂系统的晶胞参数。该方法应用于在Ag(111)表面外延生长的共轭有机材料6,13-并五苯醌(PQ)的多晶薄膜。所有的互易向量都可以分配给具有相同晶格常数但以不同方向生长的晶胞[接触平面 (102) 和 (102) 的六倍旋转对称]。所确定的晶胞与先前研究中报告的为纤维纹理 PQ 薄膜确定的晶胞相同。初步结果进一步表明，该算法在分析外延生长的微晶时特别有效，不仅适用于各种取向，而且适用于薄膜中存在不同多晶型物的情况。

更新日期：2020-04-02

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