Abstract
We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI’s quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 ± 1.0 nm and 4.0 ± 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity.
Highlights
Core-shell nanoparticles exhibit unique electronic, chemical, catalytic and optical properties that have found applications across many disciplines[1,2,3,4]
Au/Pd core-shell nanoparticles were synthesized by a seed mediated growth method from soluble precursors[46]
The formation of the Au/Pd core-shell structure was implicated by the alternating bright and dark fringes in the Transmission Electron Microscope (TEM) image caused by the superposition of two misfit crystalline lattices in a core-shell construction
Summary
XFEL experiment and 3D reconstruction of core-shell nanoparticles. Au/Pd core-shell nanoparticles were synthesized by a seed mediated growth method from soluble precursors[46]. For all the top 10% independent reconstructions from a single-shot diffraction pattern, the parameters of the recorded models were averaged to obtain the core size, shell thickness, and ratio of core to shell density (Fig. 4). High Poisson noise was added to approximately the same level as that observed in the experiment and the central data were removed to simulate a beam stop (Fig. 5a,b) These diffraction patterns were each reconstructed 1,000 separate times using OSS with 1,000 iterations, 10 progressive filters, and a loose cubic support. The overall size of the structure was determined correctly within less than 1 nm, and the small deviation between the fitted and true values of the two models is due to high Poisson noise added to the diffraction patterns These results further validate the feasibility of using super-resolution CDI to extract 3D structural information beyond the diffraction signal
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