Sub-ångström-resolution diffractive imaging of single nanocrystals

Diffractive imaging has the potential to succeed in structure determination of single nanoparticles using probes such as pulsed X-rays or medium-energy electrons where an atomic-resolution imaging lens is not available and radiation damage can be remedied. Although diffractive imaging has been demonstrated for particles and single cells at several nanometres in resolution, ultimately, atomic resolution is required to determine their three-dimensional structure. A major difficulty in atomic-resolution diffractive imaging is the loss of weak coherent scattering signals in recorded diffraction patterns. Here, we show that this can be overcome using information from low-resolution images. By combining information from both diffraction and imaging, we succeeded in phasing experimental electron diffraction patterns of individual CdS quantum dots at sub-ångström resolution. The low-resolution image provides the starting phase, real-space constraint, missing information in the central beam and essential marks for aligning the diffraction pattern, and diffraction provides high-resolution information. We show that for CdS nanocrystals, the improved image resolution enables determination of their atomic structures. As low-resolution images can be obtained from different sources, the technique developed here is general and provides a basis for imaging the three-dimensional atomic structure of single nanoparticles, where correct orientation of the recorded diffraction patterns is critical.