X-ray Diffraction（XRD）

When X-rays are incident on a crystalline sample, the diffracted X-rays are detected and analyzed to identify the crystal phases present in the sample. The relationship between the interplanar spacing ｄ and the incident and diffracted X-rays is described by Bragg’s law,  2d sin⁡θ = λ , as shown in the diagram below. By measuring the diffraction angleθ  and the intensity of the diffracted X−rays, the crystal phases present in the sample can be identified. 

The left figure shows the XRD pattern of a mixed α-Ga₂O₃ and β-Ga₂O₃ crystal. The red curve represents the XRD profile of the mixed crystal. 









The bar graph on the left shows the calculated 2θ  values and intensities for each crystal phase. Peaks in the XRD profile are observed at the calculated 2θ  values for each crystal phase.

・Crystallinity evaluation: Thin-film crystallinity

When a film is deposited on a crystalline substrate, the deposited crystals may grow as randomly oriented polycrystals, with only the out-of-plane direction aligned with the substrate, or with the same crystallographic orientation as the substrate.

The appropriate measurement techniques for each purpose are as follows:

1) Crystal phase identification: Thin-film XRD

2) Crystal orientation: Pole figure measurement

3) Epitaxial film crystallinity: Rocking curve measurement

＜Features＞

1. Nondestructive analysis is possible.

2. Crystal phase identification, crystallinity evaluation, degree of crystallinity (crystalline/amorphous ratio).

3. Crystal orientation analysis and precise crystallinity assessment in epitaxial thin films. 

＜Limitations＞

1. Elemental composition cannot be determined (complementary analytical techniques are recommended).

2. Only crystalline samples can be analyzed.

3. Detection of trace phases is difficult; it typically requires concentrations on the order of 1% or higher.