Colloidal CsPbBr3 nanocrystals (NCs) have emerged as promising candidates for various opto-electronic applications, such as light-emitting diodes, photodetectors, and solar cells. Here, we report on the self-assembly of cubic NCs from an organic suspension into ordered cuboidal supraparticles (SPs) and their structural and optical properties. Upon increasing the NC concentration or by addition of a nonsolvent, the formation of the SPs occurs homogeneously in the suspension, as monitored by in situ X-ray scattering measurements. The three-dimensional structure of the SPs was resolved through high-angle annular dark-field scanning transmission electron microscopy and electron tomography. The NCs are atomically aligned but not connected. We characterize NC vacancies on superlattice positions both in the bulk and on the surface of the SPs. The occurrence of localized atomic-type NC vacancies—instead of delocalized ones—indicates that NC–NC attractions are important in the assembly, as we verify with Monte Carlo simulations. Even when assembled in SPs, the NCs show bright emission, with a red shift of about 30 meV compared to NCs in suspension.

The concept of template-confined chemical reactions allows the synthesis of complex molecules that would hardly be producible through conventional method. This idea was developed to produce high quality nanocrystals more than 20 years ago. However, template-mediated assembly of colloidal nanocrystals is still at an elementary level, not only because of the limited templates suitable for colloidal assemblies, but also because of the poor control over the assembly of nanocrystals within a confined space. Here, we report the design of a new system called "supracrystalline colloidal eggs" formed by controlled assembly of nanocrystals into complex colloidal supracrystals through superlattice-matched epitaxial overgrowth along the existing colloidosomes. Then, with this concept, we extend the supracrystalline growth to lattice-mismatched binary nanocrystal superlattices, in order to reach anisotropic superlattice growths, yielding freestanding binary nanocrystal supracrystals that could not be produced previously.

The three-dimensional (3D) atomic structure of nanomaterials, including strain, is crucial to understand their properties. Here, we investigate lattice strain in Au nanodecahedra using electron tomography. Although different electron tomography techniques enabled 3D characterizations of nanostructures at the atomic level, a reliable determination of lattice strain is not straightforward. We therefore propose a novel model-based approach from which atomic coordinates are measured. Our findings demonstrate the importance of investigating lattice strain in 3D.

Shape-controlled synthesis of metal nanoparticles (NPs) requires mechanistic understanding toward the development of modern nanoscience and nanotechnology. We demonstrate here an unconventional shape transformation of Au@Ag core-shell NPs (nanorods and nanocubes) into octahedral nanorattles via room-temperature galvanic replacement coupled with seeded growth. The corresponding morphological and chemical transformations were investigated in three dimensions, using state-of-the-art X-ray energy-dispersive spectroscopy (XEDS) tomography. The addition of a reducing agent (ascorbic acid) plays a key role in this unconventional mechanistic path, in which galvanic replacement is found to dominate initially when the shell is made of Ag, while seeded growth suppresses transmetalation when a composition of Au:Ag (∼60:40) is reached in the shell, as revealed by quantitative XEDS tomography. This work not only opens new avenues toward the shape control of hollow NPs beyond the morphology of sacrificial templates, but also expands our understanding of chemical transformations in nanoscale galvanic replacement reactions. The XEDS electron tomography study presented here can be generally applied to investigate a wide range of nanoscale morphological and chemical transformations.

Large efforts have been made trying to understand the origin of the high catalytic activity of dealloyed nanoporous gold as a green catalyst for the selective promotion of chemical reactions at low temperatures. Residual silver, left in the sample after dealloying of a gold-silver alloy, has been shown to have a strong influence on the activity of the catalyst. But the question of how the silver is distributed within the porous structure has not finally been answered yet. We show by quantitative energy dispersive X-ray tomography measurements that silver forms clusters that are distributed irregularly, both on the surface and inside the ligaments building up the porous structure. Furthermore, we find that the role of the residual silver is ambiguous. Whereas CO oxidation is supported by more residual silver, methanol oxidation to methyl formate is hindered. Structural characterisation reveals larger ligaments and pores for decreasing residual silver concentration

Robust luminophores emitting light with broadly tunable colors are desirable in many applications such as light-emitting diode (LED)-based lighting, displays, integrated optoelectronics and biology. Nanocrystalline quantum dots with multicolor emission, from core- and shell-localized excitons, as well as solid layers of mixed quantum dots that emit different colors have been proposed. Here, we report on colloidal supraparticles that are composed of three types of Cd(Se,ZnS) core/(Cd,Zn)S shell nanocrystals with emission in the red, green, and blue. The emission of the supraparticles can be varied from pure to composite colors over the entire visible region and fine-tuned into variable shades of white light by mixing the nanocrystals in controlled proportions. Our approach results in supraparticles with sizes spanning the colloidal domain and beyond that combine versatility and processability with a broad, stable, and tunable emission, promising applications in lighting devices and biological research.

A new reconstruction approach for electron tomography is proposed, enabling a detailed 3D analysis of assemblies with as many as 10 000 particles.

396 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Reliable quantifi cation of 3D results obtained by X-ray energy-dispersive spectroscopy (XEDS) tomography is currently hampered by the presence of shadowing effects and poor spatial resolution. Here, a method is presented which overcomes these problems by synergistically combining quantifi ed XEDS data and high angle annular dark fi eld-scanning transmission electron microscopy tomography. As a proof of principle, the approach is applied to characterize a complex Au/Ag nanorattle obtained through a galvanic replacement reaction. However, the technique that is proposed here is widely applicable to a broad range of nanostructures.very challenging to use HAADF-STEM tomography for samples in which mixing of elements is expected. Also for samples that contain unknown elements or elements with atomic number Z close to each other, HAADF-STEM tomography may no longer be informative. However, it is well known that the properties and applications of nanostructures are strongly dependent on their morphology as well as their chemical composition. [ 4 ] Traditional electron microscopy techniques do not provide quantitative information on the composition of single nanoparticles. In an increasing number of recent studies, X-ray energy-dispersive spectroscopy (XEDS) is combined with tomography to understand complex nanostructure morphology and composition in 3D. These studies rely on newly developed XEDS detectors, [ 5,6 ] such as the Super-X detection system, which consists of four individual detectors, symmetrically arranged around the Transmission Electron Microscope (TEM) sample. Although qualitative results obtained by XEDS tomography have been reported, [7][8][9][10] it remains challenging to obtain quantitative information by 3D XEDS and therefore further progress is required. By using the Super-X detector, one is able to overcome problems that were previously related to extreme shadowing of the XEDS signal caused by the sampledetector confi guration. Although this problem can be largely overcome, some shadowing effects remain, [ 11,12 ] as illustrated in Figure 1 . Since such shadowing effects vary for different tilt angles, the XEDS signal integrated over the four detectors will also depend on the tilt angle [11][12][13] and the projection principle for electron tomography is no longer fulfi lled. [ 12 ] Different methodologies have been proposed to overcome this challenge. For example, signals from individual detectors can be combined, [ 11,14 ] the acquisition time can be adjusted as a function of the tilt angle [ 12 ] or the total signal for every map can be normalized to the same value. [ 13,15 ] However, in order to maximize the signal-to-noise ratio, it is of great importance to collect as many counts as possible. Selectively switching off detectors is therefore disadvantageous, while changing the acquisition time improves the quality of the tilt series, but a calibration of the holder is required and the fi nal result is still hampered by ...