Knowledge base: a short introduction to XRD

1. What are X-Rays?

  • Electromagnetic radiation
  • Originate in energy shells of atom
  • Produced when electrons interact with a target.
  • 2. How X-rays are produced?

    When fast-moving electrons slam into a metal object, x-rays are produced .The kinetic energy of the electron is transformed into electromagnetic energy.

    3. How X-ray Powder Diffraction Work?

    X-ray diffractometers consist of three basic elements: an X-ray tube, a sample holder, and an X-ray detector.

    When a monochromatic x-ray beam with wavelength l is incident on the lattice planes in a crystal planes in a crystal at an angle q, diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths. By varying the angleq, the Bragg’s Law conditions are satisfied by different d-spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffraction peaks produces a pattern which is characterized of the sample. Where a mixture of different phases is present, the diffractogram is formed by addition of the individual patterns.

    4. Bragg’s Law

    For parallel planes of atoms, with a space dhkl between them, constructive interference only occurs when Bragg’s law is satisfied. The X-ray wavelength ƛ is fixed. – Each plane of atoms produces a diffraction peak at a specific angle q. The direction perpendicular to the planes must bisect the incident and diffracted beams.

    4. What can we do with XRD?

  • Identify phase composition
  • Measure unit cell lattice parameters
  • Estimate crystallite size, microstrain, and defect concentration
  • Measure residual stress
  • Measure texture and/or epitaxy
  • Evaluate thin film quality
  • Measure multilayer thin film thickness, roughness, and density
  • Determine orientation of single crystals
  • Solve or refine crystal structures
  • Analyze ordered meso- and nanostructures