X射线扫描相干衍射成像方法学及其应用研究

The coherent X-ray diffractive imaging (the abbreviation is CDI) is a novel lensless imaging method with the great potential of imaging single molecule. However, the conventional plane-wave CDI requires full coherence of light source, rigidly limits the sample size and has the significant defaults of nonunique solution and slow convergence, which greatly depress the popularization and application of CDI method. The newly emerging scanning CDI (SCDI) overcomes the above shortcomings and will probably become one of the main imaging methods of the future synchrotron radiation light source. In this project which will be based on Shanghai Synchrotron Radiation Facility (SSRF), we will systematically explore the influence of various experimental conditions and parameters on the imaging quality of scanning CDI, to increase the signal-noise ratio with efforts, and restrain or eliminate the system unstabilities and various decoherence effects, which will help to perfect the method and the experiment platform and push them forward into applications in the research of cells and nano-catalysts. The focusing-light SCDI and the parallel-light SCDI will be investigated contrastively, and the soft X-ray SCDI and the hard X-ray SCDI will be studied comparatively. We will build up and develop new SCDI reconstruction algorithms which will be able to correct the scanning positions, remove the background noise, retrieve the fluctuating intensities of the incident light, and reconstruct the images from a partial coherent light or a broadband light. The research of this project will not only help SSRF to improve its spatial resolution power, but also promote the development and perfecting of the CDI methodology in itself.

相干X射线衍射成像（缩写为CDI）是一种新型的无透镜成像方法，具有单分子成像的巨大潜力。然而传统的平面波CDI对光源的高相干性要求，对样品尺寸的严格限制，及重建收敛慢、解不唯一的明显缺陷，大大限制了其普及应用。新近出现的扫描CDI方法则克服了上述缺点，有望成为未来三代光源的主流成像方法。本项目将依托上海光源，系统地探讨各种实验条件和参数对扫描CDI成像质量的影响规律，努力提高实验信噪比，抑制或消除实验系统的不稳定性及各种退相干效应，从而完善该方法及实验平台，使其能用于细胞及纳米催化剂的研究中；对比研究聚焦扫描CDI和平行光扫描CDI的特点和差异，及软线和硬线扫描CDI的优劣；建立和发展具有位置校正、背底扣除、光源涨落修复、部分相干光和宽带光重建等功能的新型扫描CDI重建算法及软件。本项目的研究不仅有助于提升上海光源的极限空间分辨能力，而且还将有力推动扫描CDI方法学本身的发展和完善。

本项目基于上海光源STXM线站，成功建立了软X射线扫描相干衍射成像（Ptychography，或PCDI）实验平台，并自主发展了多算法多功能的高效Ptychography重建软件，成功实现了低剂量、高分辨、高效率的ptychography成像能力，将上海光源空间分辨能力由30nm提升至8nm，而剂量降低至STXM技术的1/12，而数据获取时间仅为STXM的1/3。与国外同类线站相比，我们在分辨率/剂量的效能比方面具有独特优势，综合性能居国际最好水平之列。. 本项目还将所建立的扫描CDI方法由单纯成像拓展到了双能元素分析和多能量谱学显微领域；将扫描CDI的原理和算法思想与自由电子激光的多样品CDI相结合，发展出空间关联CDI等方法，有望提升自由电子激光的成像稳定性和成功率。初步开展了3D扫描CDI的成像实践和探索，实现了多切片三维ptychography成像方法。利用该平台我们开展了材料样品（合金纳米颗粒、金纳米线、锂电池等）和生物样品（竹切片、癌细胞、神经纤维等）的成像实验，分别取得了最高8.5nm和13nm的空间分辨率。目前我们建立的新方法已开始对用户开放，支持能源、材料、生命、环境等领域的前沿研究。. 本项目发表标注受本项目资助的论文13篇，其中SCI论文8篇。毕业博士两名，硕士一名；在读博士一名，硕士一名。