XRD - X-Ray Diffraction
Powder x-ray diffraction (XRD) uses x-rays to investigate and quantify the crystalline nature of materials by measuring the diffraction of x-rays from the planes of atoms within the material. It is sensitive to both the type of and relative position of atoms in the material as well as the length scale over which the crystalline order persists. It can, therefore, be used to measure the crystalline content of materials; identify the crystalline phases present (including the quantification of mixtures in favourable cases); determine the spacing between lattice planes and the length scales over which they persist; and to study preferential ordering and epitaxial growth of crystallites. In essence it probes length scales from approximately sub angstroms to a few nm and is sensitive to ordering over tens of nanometres.
The samples for analysis are typically in the form of finely divided powders, but diffraction can also be obtained from surfaces, provided they are relatively flat and not too rough. Moreover the materials can be of a vast array of types, including inorganic, organic, polymers, metals or composites and the potential applications cover almost all research fields, e.g. metallurgy, pharmaceuticals, earth sciences, polymers and composites, microelectronics and nanotechnology. Powder XRD can also be applied to study the pseudo crystalline structure of mesoporous materials and colloidal crystals provided that the length scales are in the correct size regime.
CMM has two XRD instruments currently available. The newly commissioned (2011) Di Vinci instruments is highly versatile and can be configured in both reflectance and transmission geometries, and with either divergent (Bragg-Brentano) or parallel-beam optics. It has a 90 position magazine sample changer for high-throughput analysis and can be configured for cobalt radiation to allow for the measurement of highly fluorescing samples, e.g. Fe rich powders. The D8 Advance is configured in parallel-beam geometry and allows for the measurement of low angles and moderately rough surfaces. As such we are able to investigate a wide range of material types which includes powers, thin films and moderately rough surfaces (e.g. composite fibre mats) as well as highly oriented samples (e.g. clays) and Fe and Mn bearing minerals. In addition to XRD it is also possible to carry x-ray reflectometery experiments of thin (< 200 nm) films on atomically smooth surfaces (e.g. silicon wafers).