X-ray diffraction has long been an important tool for deducing crystal structures. The x rays scatter off the crystal’s electrons, giving a pattern of diffraction peaks related to the electron density; points of concentrated electron density indicate the nuclear positions. In recent decades time-resolved x-ray diffraction has probed faster and faster structural changes, up to and including atomic movements on the femtosecond time scale.
Until now, the fastest time-resolved experiments have used samples in the form of single crystals. But many materials of interest, such as the transition-metal complexes used in organic photovoltaic cells, can’t readily be made into crystals of sufficient size and quality.
Michael Woerner, Thomas Elsaesser, and colleagues at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy in Berlin have now demonstrated femtosecond x-ray powder diffraction, in which the sample is a collection of randomly arranged micro-crystals, and the diffraction pattern is a set...
