Peak Profile Evaluation for Thin Films

Abstract

The special phenomena in X-ray diffraction line profile analysis occurring in thin films is overviewed in this chapter. In the case of textured nanocrystalline thin films, the line broadening caused by the crystallite size increases with the length of the diffraction vector. This effect is explained by the interference of X-rays scattered coherently from adjacent crystallites with close orientations. The partial coherence of adjacent nanocrystallites is caused by the overlapping of their reciprocal lattice points. The smaller the size and the stronger the orientation preference of crystallites, the better the coherence. This interference effect yields narrowing of line profiles at small diffraction angles, while it has no influence on line broadening at large angles. Therefore, the traditional line profile evaluation methods give much larger crystallite size than the real value and may detect a false microstrain broadening. Some ways for the correction of the interference effect are proposed. Detailed case studies are given for the determination of the defect structure in thin films by line profile analysis.