Theoretical study of the properties of X‐ray diffraction moiré fringes. II. Illustration of angularly integrated moiré images

• Published in: Acta crystallographica. Section A, Foundations and advances Foundations and advances, 2019-07, Vol.75 (4), p.610-623
• Main Author: Yoshimura, Jun-ichi
• Format: Article
• Language: English
• Subjects: Bicrystals; Computer simulation; Curvature; diffraction moiré fringes; gap phase difference; integrated moiré images; Moire fringes; Pendellösung oscillation; Radiation; Research Papers; Rotation; rotation moiré Simulation; Thickness; X-ray diffraction
• ISSN: 2053-2733; 0108-7673; 2053-2733
• DOI: 10.1107/S2053273319004601

Using a theory of X‐ray diffraction moiré fringes developed in a previous paper, labelled Part I [Yoshimura (2015). Acta Cryst. A71, 368–381], the X‐ray moiré images of a silicon bicrystal having a weak curvature strain and an interspacing gap, assumed to be integrated for an incident‐wave angular width, are simulation‐computed over a wide range of crystal thicknesses and incident‐wave angular width, likely under practical experimental conditions. Along with the simulated moiré images, the graphs of characteristic quantities on the moiré images are presented for a full understanding of them. The treated moiré images are all of rotation moiré. Mo Kα1 radiation and the 220 reflection were assumed in the simulation. The results of this simulation show that fringe patterns, which are significantly modified from simple straight fringes of rotation moiré, appear in some ranges of crystal thicknesses and incident‐wave angular width, due to a combined effect of Pendellösung oscillation and an added phase difference from the interspacing gap, under the presence of a curvature strain. The moiré fringes which slope to the perpendicular direction to the diffraction vector in spite of the assumed condition of rotation moiré, and fringe patterns where low‐contrast bands are produced with a sharp bend of fringes arising along the bands are examples of the modified fringe pattern. This simulation study provides a wide theoretical survey of the type of bicrystal moiré image produced under a particular condition. Using a recently developed moiré‐fringe theory of X‐ray diffraction, the angularly integrated moiré images of a lightly strained silicon bicrystal having an interspacing gap were simulation‐computed over a wide range of crystal thicknesses and incident‐beam angular width.