It is planned to visualize the internal strains that occur naturally within nanocrystals due to their small size. Use of a coherent beam of X-rays provided by the new, NSF-funded Coherent X-ray Diffraction (CXD) facility at Sector 34 of the Advanced Photon Source (APS) results in a continuous diffraction pattern surrounding each Bragg reflection. Two scientific areas are to be explored: the study of the surface melting of nanocrystals and to the growth of macromolecular crystals. In the latter case, the roles of seeding and nucleation will lead to an understanding of the remarkable transition from an inspecific aggregate into a crystal. The broader impact of the project will be to stimulate interactions with the nascent community of scientists interested in single-molecule structure determination of biological molecules using X-ray Free-Electron Lasers (XFEL). An XFEL is expected to have sufficient power in a single 50fs shot to obtain a diffraction pattern from a single biomolecule, before it becomes destroyed by radiation. This is the natural extension of our method to a nanocrystal containing a single unit cell. %%% This project will develop the science of Coherent X-ray Diffraction (CXD), which allows three-dimensional (3D) imaging of the interiors of crystals on the nanometer size scale. The virtue of the 3D information over previous methods is analogous to the advantage medicine of a CAT-scan over a conventional X-ray radiogram: sectional views of internal features, such as material defects and dislocations, can be obtained. During the term of the project, the method will be applied to granular materials, both metals and biological crystals, to map out their internal strains. This should lead to a greater understanding of protein crystallization, the critical first step in the methods behind the widely-advertised "structural genomics" revolution. In the longer term, our methods will pave the way towards single-molecule imaging by X-ray diffraction, which is one of the strongest motivations for the United States to build X-ray Free-Electron Lasers (XFEL) over the next several years. ***
