Crystallography is the experimental science of determining the arrangement of atoms in the crystalline solids (crystal structure).
- study of crystals was based on their geometry. This involves measuring the angles of crystal faces relative to theoretical reference axes (crystallographic axes)
- X-ray crystallography is used to determine the structure of large biomolecules such as proteins.
International Year of Crystallography 2014 – United Nations declaration
most popular crystals of 2014 – National Science Foundation spotlighted a crystal each week.
What’s the problem?
Crystallography is not limited by the wavelength of visible light. An image of a small object is made using a lens to focus the beam, similar to a lens in a microscope. However, the wavelength of visible light (about 4000 to 7000 ångström) is three orders of magnitude longer than the length of typical atomic bonds and atoms themselves (about 1 to 2 Å). Therefore, obtaining information about the spatial arrangement of atoms requires the use of radiation with shorter wavelengths, such as X-ray or neutron beams.
- Ask – Employing shorter wavelengths implied abandoning microscopy and true imaging, however, because there exists no material from which a lens capable of focusing this type of radiation can be created.
- Imagine – Diffracted X-ray or neutron beams cannot be focused to produce images, so the sample structure must be reconstructed from the diffraction pattern.
- Design, Build – Sharp features in the diffraction pattern arise from periodic, repeating structure in the sample, which are often very strong due to coherent reflection of many photons from many regularly spaced instances of similar structure
- Improve – 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.