This article includes a list of references, but its sources remain unclear because it has insufficient arthur levitt bitcoin citations. A crystalline solid: atomic resolution image of strontium titanate.
Brighter atoms are strontium and darker ones are titanium. The word “crystallography” derives from the Greek words crystallon “cold drop, frozen drop”, with its meaning extending to all solids with some degree of transparency, and graphein “to write”. Crystallographic methods now depend on analysis of the diffraction patterns of a sample targeted by a beam of some type. This is facilitated by the wave properties of the particles. X-rays interact with the spatial distribution of electrons in the sample.
Electrons are charged particles and therefore interact with the total charge distribution of both the atomic nuclei and the electrons of the sample. Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies. An image of a small object is made using a lens to focus the beam, similar to a lens in a microscope. Because of their highly ordered and repetitive structure, crystals give diffraction patterns of sharp Bragg reflection spots, and are ideal for analyzing the structure of solids.
Some materials that have been analyzed crystallographically, such as proteins, do not occur naturally as crystals. Typically, such molecules are placed in solution and allowed to slowly crystallize through vapor diffusion. Once a crystal is obtained, data can be collected using a beam of radiation. Although many universities that engage in crystallographic research have their own X-ray producing equipment, synchrotrons are often used as X-ray sources, because of the purer and more complete patterns such sources can generate. Producing an image from a diffraction pattern requires sophisticated mathematics and often an iterative process of modelling and refinement.