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.
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.
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.
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