For a series of (111) textured thin films, the degree of preferred orientation increased with film thickness. For thick film, it has larger grain size and higher (111) peak intensity in XRD. Can I explain the increasing of (111) intensity by saying that it is due to the larger grains with higher crystallinity have higher periodicity? Is there any references talking about relationship between grain size, crystallinity and periodicity?
It can be simply imagined that larger grains would include more lattice sites. You will have a single crystal with the highest periodicity if this process continues. So, with thickness increasing that usually is accompanied with grain growth, the periodicity will increase and naturally the grain boundaries get narrower. Especially, the latter case has an active role in homogeneity of the crystal structure to be considered as a single crystal due to cut off the periodicity in borders. With thickness and thereby the grain size, the incident x-ray will be diffracted from several lattice surfaces and causes higher intensity.
Maybe this book can help : Hans Lüth,
Solid Surfaces,
Interfaces
and Thin Films
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