1. Atomic-resolution CDI
        One of the most important potential applications of HXFEL is the atomic-resolution X-ray CDI (Coherent Diffraction Imaging), which originated from the concepts of "oversampling phasing" [1, 2] and "crystallography without crystals" [3, 4]. The purpose of atomic-resolution X-ray CDI or "crystallography without crystals" is to extend X-ray crystallographic methods beyond the scope of crystalline materials. This ultimately enables atomic-resolution structure analysis for all kinds of condensed matter. There may be still a long way to go before we can reach the goal. Apart from that the X-ray source and instrumentation should be further improved, new methods for diffraction analysis should also be explored. Among methods widely used in crystal structure analysis, direct methods may have good chance to combine with oversampling phasing in a dual-space iterative phasing framework [5].

        2. Serial Crystallography
        Serial crystallography (SX) is a kind of experiment techniques designed to avoid radiation damage of the sample during diffraction data collection [6-10]. While SX is a byproduct in the development of high-resolution X-ray CDI using an XFEL as the light source, it can also be implemented under 3rd generation synchrotron sources and, more importantly it may cause revolutionary changes in X-ray diffraction analysis owing to its unique features:
        (i) Diffraction before Destruction;
        (ii) Single-crystal X-ray diffraction data from polycrystalline samples.

        In life science, SX enables protein structure determination using polycrystalline samples with submicron-sized crystal grains. While with conventional single-crystal structure analysis for proteins at 3rd generation synchrotrons, the sample crystals are about ten times larger than a micron. Moreover, SX diffraction experiments for proteins can be implemented at room temperature, which is much closer to the living condition of protein moleclues than the cryo-cooling enviroment uesd in single-crystal diffraction at 3rd generation synchrotrons. Prominent successes in SX application to protein crystallogrgaphy have been reported [11-16]. On the other hand, so far only the molecular replacement method did succeed in phasing of SX data for solving structures of originally unknown proteins. This implies that there are problems with the quality of SX diffraction data. Apart from the problem of partial diffraction recorded for each Bragg reflection and the inaccuracy of integration methods, the heterogeneity of micro crystals used in SX experiments also forms an important source of experimental errors. A post-experiment identification/purification process has been proposed in our group for an improved treatment of SIR data or SAD data from SX diffraction snapshots [17-19].

        In material science, SX may cause a revolution in X-ray powder diffraction analysis. Many important materials are polycrystalline and cannot be grown as single crystals suitable for conventional X-ray single-crystal structure analysis. X-ray powder diffraction is thus widely used for characterizing and solving the structures of such materials. However, owing to the serious overlapping of reflections with similar diffraction angles, the ability of X-ray powder diffraction in solving crystal structures is lower than that of the single-crystal X-ray diffraction by more than an order of magnitude. Now SX is capable of collecting three dimensional single-crystal diffraction data using polycrystalline samples. It provides the possibility of dramatically enhancing the power of X-ray powder diffraction. An SX based method has been proposed in our group, which enables simultaneous X-ray phase identification and structure solution for multiphase polycrystalline samples [17, 20].

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