Coherent X-Ray Diffraction Imaging of Nanocrystals

计划将纳米晶体由于其小尺寸而自然发生的内部应变可视化。在先进光子源（APS）的第34扇区，使用由nsf资助的相干x射线衍射（CXD）设备提供的相干x射线束，可以在每个布拉格反射周围产生连续的衍射图案。两个科学领域将被探索：纳米晶体的表面熔化的研究和大分子晶体的生长。在后一种情况下，种子和成核的作用将导致对从非特异性聚集体到晶体的显著转变的理解。该项目更广泛的影响将是刺激对使用x射线自由电子激光器（XFEL）测定生物分子的单分子结构感兴趣的新兴科学家群体的相互作用。在单个生物分子被辐射破坏之前，预计XFEL在单次50秒射击中具有足够的功率来获得单个生物分子的衍射图样。这是我们的方法的自然延伸到包含单个单元的纳米晶体。该项目将发展相干x射线衍射（CXD）科学，它允许在纳米尺度上对晶体内部进行三维（3D）成像。3D信息相对于先前方法的优点类似于cat扫描相对于传统x射线x线照片的优势：可以获得内部特征的断层视图，例如材料缺陷和位错。在项目期间，该方法将应用于颗粒材料，包括金属和生物晶体，以绘制其内部应变。这将导致对蛋白质结晶的更深入的理解，这是广泛宣传的“结构基因组学”革命背后方法的关键的第一步。从长远来看，我们的方法将为x射线衍射的单分子成像铺平道路，这是美国在未来几年内建造x射线自由电子激光器（XFEL）的最强烈动机之一

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.***