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

原子排列的可视化在理解微观世界中起着至关重要的作用。目前已有几种原子结构成像的方法，但每种方法都有其局限性。扫描探针显微镜仅限于对表面的原子结构进行成像。透射电子显微镜可以分辨原子，但只能分辨厚度小于~ 30nm的样品。x射线晶体学可以根据衍射现象揭示全局平均的三维原子结构，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，该显微镜基于相干x射线散射，并结合称为过采样的直接相位恢复方法。相干x射线衍射显微镜已成功应用于纳米材料和生物样品的二维和三维成像，最高空间分辨率达到7 nm。利用第三代同步辐射，我们提出开发下一代相干x射线衍射显微镜，用于纳米级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1nm级别；（ii）数据采集将实现自动化；iii) 3D图像将直接从过采样的衍射图案重建，而不使用低分辨率的图像；Iv)样品将安装在氦气环境中，氦气环境可以是室温或液氮温度；v)更快、更精确的相位检索算法将用于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。目前可获得的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。目前正在积极开发的一种很有前途的方法是利用计算机进行x射线和图像重建。这种方法已被用于材料和生物标本的成像，分辨率约为14个原子直径。通过使用目前国内最亮的x射线源——芝加哥的先进光子源，我们建议开发下一代x射线显微镜，将分辨率提高到3个原子直径左右。新的显微镜将包括一个更大的探测器和更好的软件，用于快速准确的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找到广泛的应用。

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.