MRI: Development Of A Next-Generation Coherent X-Ray Diffraction Microscope For 3d Imaging Of Nanosclae Systems

可视化原子的排列对于理解微观世界起到了至关重要的作用。已经有几种方法可以对原子结构进行成像，但每种方法都有其局限性。扫描探针显微镜仅限于成像表面的原子结构。透射式电子显微镜可以分辨原子，但只能分辨厚度小于30 nm的样品。X射线结晶学可以揭示基于衍射现象的全球平均3D原子结构，但需要晶体。这些限制原则上可以通过相干X射线衍射显微镜(或无透镜成像)来克服，它是基于相干X射线散射和一种称为过采样的直接相位恢复方法相结合的。相干X射线衍射显微镜已经成功地应用于纳米材料和生物样品的二维和三维成像，并获得了最高7 nm的空间分辨率。利用第三代同步辐射，我们计划发展新一代相干X射线衍射显微镜，用于纳米系统的三维成像和表征。新显微镜将具有以下特点：i)将使用4K x 4K背光CCD相机将分辨率提高到1 nm水平；(Ii)数据采集将自动化；iii)将直接从过采样的衍射图重建3D图像，而不使用较低分辨率的图像；iv)样品将安装在氦环境中，可在室温或液氮温度下进行；v)将开发更快、更精确的相位恢复算法用于3D图像重建。一个多世纪以来，X射线成像一直被用来探测物质的结构。然而，与可见光不同的是，X射线很难操纵和聚焦。目前x射线图像的最高分辨率约为100个原子直径。对于无序的样品，x射线不能以如此高的分辨率成像。一种很有前途的方法，目前正在非常活跃的开发中，使用计算机进行X射线和图像重建。这种方法已经用于材料和生物标本的成像，分辨率约为14个原子直径。通过使用目前美国最亮的X射线源-芝加哥的先进光子源，我们计划开发新一代X射线显微镜，将分辨率提高到大约3个原子直径。新的显微镜将包括一个更大的探测器和更好的软件，以实现快速准确的3D图像重建。我们预计3D X射线显微镜将在科学和结构生物学的许多领域得到广泛的应用。

Visualizing the arrangement of atoms has played a crucial role in understanding the microscopic world. There are already a few ways of imaging atomic structures, but each has its limitations. Scanning probe microscopes are limited to imaging atomic structures at the surface. Transmission electron microscopes can resolve atoms but only for samples thinner than ~ 30 nm. X-ray crystallography can reveal the globally averaged 3D atomic structures based on the diffraction phenomenon, but requires crystals. These limitations can in principle be overcome by coherent x-ray diffraction microscopy (or lensless imaging) that is based upon coherent x-ray scattering in combination with a method of direct phase recovery called oversampling. Coherent x-ray diffraction microscopy has been successfully applied to 2D and 3D imaging of nanoscale materials and biological samples, and a highest spatial resolution of 7 nm has been achieved. By using 3rd generation synchrotron radiation, we propose to develop a next-generation coherent x-ray diffraction microscope for 3D imaging and characterization of nanoscale systems. The new microscope will have the following features: i) a 4K x 4K back-illuminated CCD camera will be used to improve the resolution to the 1 nm level; (ii) data acquisition will be automated; iii) 3D images will be directly reconstructed from oversampled diffraction patterns without using lower resolution images; iv) samples will be mounted in helium ambiance which can be at room or liquid nitrogen temperatures; and v) faster and more precise phase retrieval algorithms will be developed for 3D image reconstruction. X-ray imaging has been used to probe the structure of matters for more than a century. Unlike visible light, however, x-rays are difficult to manipulate and focus. The highest resolution of x-ray images currently achievable is about 100 atomic diameters. For disordered samples x-rays cannot image at such high resolution. A promising approach, which is currently under very active development, uses x-ray and image reconstruction using a computer. This approach has been used to image materials and biological specimens with a resolution of about 14 atomic diameters . By using currently the brightest x-ray source in the nation - the Advanced Photon Source in Chicago, we propose to develop a next-generation x-ray microscope for improving the resolution to around 3 atomic diameters. The new microscope will include a larger detector and better software for quick and accurate 3D image reconstruction. We anticipate the 3D x-ray microscope will find broad applications in many areas of science and structural biology.