A new algorithm for XFEL single particle scattering data analysis
Update: 2018-02-24 09:44:28      Author: yangjuan@csrc.ac.cn

X-ray Free Electron Lasers (XFELs) generate ultrabright X-ray pulses with duration of 4-100 femtoseconds, possible to outrun X-ray radiation damage using the ‘diffract-before-destroy’ experimental approach. Using core-shell nanoparticles as model systems, we carried out a proof-of-principle experiment at LCLS, the first XFEL user facility (Figure 1 & 2). Over a million diffraction patterns were collected, and Haiguang Liu and coworkers analyzed about 54k patterns after initial screening. Because the synthetic nanoparticles have size variations, the pre-sorting based on particle sizes is necessary before merging the data to 3D fourier space. On the other hand, the size analysis from scattering patterns relies on correct orientation information. Using a reduced representation of the raw data, Haiguang Liu’s group successfully recovered particle orientation and sorted out the particle sizes. The idea is to integrate the intensity information along the radial axis, the resulting 1D intensity profile at azimuth angles is less sensitive to the variations of particle sizes (Figure 3). The 1D profiles are then compared to the standard reference models to recover the particle orientation. The q-spacing (distance between speckles along scattering streaks) is then converted to particle size information. The recovered size distribution from XFEL data is very consistent with the data obtained using STEM experimental approach (Figure 4). This is the first time that the analysis of XFEL scattering data resulted from heterogeneous particles. The data description is summarized in the Scientific Data, and the new algorithm is published in the IUCrJ.

The experiment was carried out at LCLS in Stanford Linear Accelerator Center National Laboratories, by an international collaboration team under the leadership of Haiguang Liu, Brenda Hogue, Ilme Schlichting, and John Spence. The analysis work is mainly carried out by Ph.D student, Xuanxuan Li.

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Figure 1. The core-shell nanoparticles. (a) view under STEM; (b) schematic drawing of the particle, with gold core and palladium shell; (c) a closer view of a single particle.


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Figure 2. Experimental setup at XFEL using diffract-before-destroy approach. Over 1 million raw images were collected at LCLS in SLAC national lab.


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Figure 3. Data reduction from 2D raw image to 1D intensity profile.


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Figure 4. The recovered particle size distribution and the average particle size (52nm) obtained from STEM.


References:

[1]     Li Xuanxuan et al., Diffraction data of coreshell nanoparticles from an X-ray free electron laser, Scientific Data, 4:170048 (2017)

[2]     Li Xuanxuan, John Spence, Brenda Hogue, Haiguang Liu. Merging single-shot XFEL diffraction data from inorganic nanoparticles: a new approach to size and orientation determination. IUCrJ, 4, 741-750 (2017)




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