Owing to the considerable penetration depth of X-rays and the small angular rotation of the samples required to measure the entire 3D CXD pattern, BCDI is a suitable technique for imaging the complex morphologies of NPs from 100 nm to a few micrometers in size. Bragg coherent X-ray diffraction imaging (BCDI) 23, 24 could be a generalized platform for the 3D imaging of NPs with deep concave morphologies and hidden surfaces. 3D imaging in transmission geometry allows in both crystalline and non-crystalline samples, however, it is also constrained by the tilting angle that necessitates prior information about the sample geometry 21 or the assumption of identical sample copies 22 for constructing the 3D coherent X-ray diffraction (CXD) patterns.
#GOLD AMNESIA STRAIN FREE#
Since coherent X-rays are utilized from the synchrotron sources and X-ray free electron lasers, 3D coherent X-ray diffraction imaging is available in various geometries 19, 20. In particular, for NPs with complex 3D geometries, the loss of 3D information owing to the limited tilting angle of the sample, which is often referred to as the “missing wedge” 18, makes it challenging to obtain accurate imaging results and subsequently to use the NPs for quantitative plasmonics. These are the main obstacles in the imaging and crystallographic identification of NPs larger than a few tens of nanometers. An engraving of an atomic-scale 3D chiral morphology on the surface of plasmonic NPs serves as a vista for achieving unnatural optical chirality in the visible regime (i.e., optical helicity density, that is, the projection of the spin angular momentum density on the momentum direction) 1, 15.Īlthough tomographic imaging with electrons 16, 17 can be used to obtain an atomic resolution, it has limited inspection depth and a trade-off between the resolution and object size. This otherwise impossible light-matter interaction can be further extended to plasmonic chiro-optical properties (e.g., optical chirality) 13, 14, which has implications for advanced applications, such as metamaterials and chiral sensing. According to recent studies, even an atomic-scale topological protrusion of plasmonic NPs can play a pivotal role in squeezing and focusing a photon into a pico-volumetric space (referred to as pico-cavity) 11, 12. An important but unresolved example is plasmonic NPs, whose light-matter interactions at the subwavelength scale can be tailored by controlling the facets, vertices, and morphology of the metallic NPs. However, available methods are limited for revealing the three-dimensional, local arrangement of nanometric features, especially for hidden and concave surfaces. In this regard, the exact indexing of crystallographic planes and determining the corresponding strain distribution inside or on a single NP are important for correlating the properties with the overall morphology and further tuning the stabilized planes by surface doping or ligand coordination 6, 7, 8, 9, 10. The three-dimensional (3D) distribution of the exposed surfaces on a nanoparticle (NP) is a determinant of its catalytic, optical, and electronic properties 1, 2, 3, 4, 5. This approach can serve as a comprehensive characterization platform for visualizing the 3D crystallographic and strain distributions of nanoparticles with a few hundred nanometers, especially for applications where structural complexity and local heterogeneity are major determinants, as exemplified in plasmonics. The highly strained region adjacent to the chiral gaps is resolved, which was correlated to the 432-symmetric morphology of the nanoparticles and its corresponding plasmonic properties are numerically predicted from the atomically defined structures. The distribution of the high-Miller-index planes constituting the concave chiral gap is precisely determined. Here, we develop a methodology for visualizing the 3D information of chiral gold nanoparticles ≈ 200 nm in size with concave gap structures by Bragg coherent X-ray diffraction imaging.
However, it remains a challenge to image concave surfaces of nanoparticles. Identifying the three-dimensional (3D) crystal plane and strain-field distributions of nanocrystals is essential for optical, catalytic, and electronic applications.
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