Making structures crystal clear
Crystal structures are determined through X-ray diffraction techniques. When an X-ray beam bombards a crystalline lattice, the beam is scattered in a manner characterised by the atomic structure of the lattice. The production of X-ray beams for the technique has improved dramatically with the development of the synchrotron. A synchrotron is a ring shaped particle accelerator that uses electric fields to accelerate charged particles, and magnetic fields to steer them in a circular path generating X-rays. When these are scattered it is necessary to have an adequate detection system. X-ray detectors have evolved from noisy photographic film to rapid, automatic charge-coupled devices (CCD). However, photoconductors have been found to be far more superior even to CCDs. Using the photoconductor selenium an X-ray detector has been developed based on direct conversion of X -rays to charges. Photoconductors are semiconductors. In the dark, these materials are insulators, but effectively become conductors under illumination. As light or X -ray photons are absorbed, the energy of the incoming photon excites electrons in the photoconductor to a state known as the conduction band. In the presence of an electric field, the electrons in the conduction band move along the electric field lines. Thus, charges released due to absorption of light or X -rays can be collected by applying a potential across a piece of photoconductive material. The charge collection reproduces the X -ray image. The properties of the detector have been found to be exceptional. Noise is minimal and sensitivity is high. It is extremely efficient and it is expected that it will allow large structures to be determined in record time. The detector can be employed in research institutes using synchrotrons, and also in home laboratories and it could prove to be a powerful tool for structure elucidation.
