X-ray diffraction (XRD) is a non-destructive method used to analyze the structure of crystalline materials in order to identify the phases present in a material that reveal information about the chemical composition. Identification of phases is achieved by comparison of the acquired data to that in reference databases (ICSD). Specification of our STOE Stadi MP diffractometer with optimized geometry for thin film analysis (see figure 1). Mythen detector performing high resolution measurements with fast scan rates. Spot size of the beam and sample holder configuration can easily adjusted with customized modular equipment.

Diffraction occurs when light is scattered by a periodic array with long-range order, producing constructive interference at specific angles. Amorphous materials like glass do not have a periodic array with long-range order, so they produce broad scattering peaks instead of a defined diffraction pattern. The scattering of X-rays from atomic electrons produces a diffraction pattern only if the conditions for constructive interference, which are determined by Bragg's law, are fulfilled: Fig. 1

d is the spacing between diffracting planes, θ is the incident angle, n is any integer, and λ is the wavelength of the beam. These specific directions appear as spots on the diffraction pattern called reflections, which are associated to planes of atoms labeled by Miller indices (hkl). Usual scan mode works with Bragg-Brentano geometry (moving 2 Theta/Omega value with fixed ration ratio).

Fig. 2 shows an example of diffraction patterns of amorphous material with broad reflections is illustrating the typical feature of nanocrystalline grains (blue) and larger grains are obtained after heat treatment, by increasing intensities of distinguishable reflections (red). A comparison with the reference database provides information of the phase (chemical composition and crystal symmetry).

The Scherrer formula can be used to determine the crystallite size (coherently scattering domain size). Peak width (B) is inversely proportional to crystallite size (L)
B(2θ)=  K λLcosθ

Advanced Techniques

Grazing angle XRD: Method to analyze ultrathin film for e.g. film prepared by ALD to minimize the contribution related to the substrate. The beam geometry works with moving 2 Theta (Detector) and fixed small omega (Sample holder) values.

Strain analysis: Strain and stress between the substrate and deposited film could be calculate using Williamson-hall theorem.

High Temperature XRD: Modular oven for powders and thin films. Temperature range from 25 up to 1000°C. Application for in-situ analysis for e.g. decomposition of precursor to solid material or phase-change materials.