Crystals are cellular structures that have a regular repeating pattern, and are present in inorganic minerals and in metals. Different materials have specific optical properties when exposed to frequencies of visible light or higher energy of x-rays. An x-ray diffractometer produces radiation or energy in x-ray frequencies, and can be used to study crystalline structures. Diffraction is a term referring to the bending of light or energy from its interaction with a material or liquid.
The construction of an x-ray diffractometer includes several key parts. An x-ray source includes a source tube and collimating slit that creates a narrow beam. Samples are placed in a sample holder at a fixed distance from the source. The detector includes a scintillation counter, which measures the diffracted energy. Some units add a goniometer, which is a movable detector that measures the angle of the x-ray energy.
When the x-ray frequency is sent to the sample, it is diffracted at specific angles based on the material. This is caused by the x-ray beam interacting with the crystal structure. The beam is bent and leaves the surface of the material, and can then be measured by the scintillator. W.L. Bragg developed a calculation in the early 1900s to define the angle, and this became a standard method for interpreting diffraction data.
X-ray diffraction can be used to characterize crystalline materials and metals because very small distances separate the crystal structure. Energy of an x-ray has wavelengths that are similar to the inter-crystal spacing. As a result, the crystal structures will bend the x-ray energy in measurable and consistent patterns.
As materials have been exposed to x-rays, a library of data has been developed to summarize the characteristics of a wide range of materials. Metals, solids and some liquids have specific refraction properties. An x-ray diffractometer can be used to determine the properties of a known mineral, or help analyze an unknown one by referencing the library.
Thin film technology is used in electronics manufacturing for microcircuits. The film is deposited on a solid substrate, and an x-ray diffractometer can be used for quality control. Analysis of the diffraction angles can determine the quality of the film and substrate interface.
Materials with crystalline structures will develop different molecular structures when stressed. An x-ray diffractometer can measure the differences in stressed materials. A reference standard of unstressed crystal is compared with the tested material, and the comparison can be used to measure the stress. This technique can be used for analysis of metal parts that have failed from age or overloading.