Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
Department of Neuroradiology, Vascular and Interventional Radiology, Medical University Graz, Auenbruggerplatz 9, 8036, Graz, Austria.
Rev Sci Instrum. 2022 Jun 1;93(6):063906. doi: 10.1063/5.0088176.
Grazing incidence x-ray diffraction (GIXD) is a frequently used tool for the crystallographic characterization of thin films in terms of polymorph identification and determination of the crystallographic lattice parameters. Even full structure solutions are possible. To obtain highly accurate diffraction patterns, the thin film sample has to be aligned carefully with the center of the goniometer, which allows a defined incidence of the primary x-ray beam relative to the sample surface. This work studies the effect of misalignment of a thin film sample on the acquired diffraction pattern. Three potential types of misalignments are considered: the deviation of the sample surface from the center of the goniometer, an error in the incidence angle of the primary beam, and an inclination of the goniometer rotation axis from the normal of the substrate surface. The consequence of these types of sample misalignments is the shift of diffraction peaks toward specific directions in reciprocal space. Mathematical equations are given that relate the error in positions of Bragg peaks for each type of sample misalignment. Experiments with intentionally misaligned samples confirm the given formulas. In a subsequent step, the errors in the peak positions are translated to systematic errors in the estimation of the unit cell parameters. Depending on the type of misalignment, some alignment errors can be reduced or even corrected; in particular, azimuthal sample rotations prove to be advantageous in these cases. The results in this work improve the quality of GIXD measurements, in general, enabling deeper analysis like the full structure solution from the GIXD pattern on everyday basis.
掠入射 X 射线衍射（GIXD）是一种常用于对薄膜进行晶体学表征的工具，可用于确定多晶型和晶体晶格参数。甚至可以进行完整的结构解析。为了获得高度精确的衍射图案，薄膜样品必须与测角仪的中心精确对准，这允许相对于样品表面定义初级 X 射线束的入射角度。本工作研究了薄膜样品的不对准对获得的衍射图案的影响。考虑了三种潜在的不对准类型：样品表面相对于测角仪中心的偏差、初级光束入射角的误差以及测角仪旋转轴相对于基底表面法线的倾斜。这些类型的样品不对准的结果是衍射峰向倒易空间的特定方向移动。给出了与每种类型的样品不对准相关的布拉格峰位置误差的数学方程。通过故意不对准的样品进行实验，验证了给出的公式。在随后的步骤中，将峰位置的误差转换为对单元胞参数估计的系统误差。根据不对准的类型，一些对准误差可以减小甚至纠正；在这些情况下，特别是方位角样品旋转被证明是有利的。本工作的结果提高了 GIXD 测量的质量，通常能够从 GIXD 图案上进行更深入的分析，例如每天进行完整的结构解析。
