5 research outputs found
Supracrystalline Colloidal Eggs: Epitaxial Growth and Freestanding Three-Dimensional Supracrystals in Nanoscaled Colloidosomes
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
Designing Diameter-Modulated Heterostructure Nanowires of PbTe/Te by Controlled Dewetting
Heterostructures
consisting of semiconductors with controlled morphology
and interfaces find applications in many fields. A range of axial,
radial, and diameter-modulated nanostructures have been synthesized
primarily using vapor phase methods. Here, we present a simple wet
chemical routine to synthesize heterostructures of PbTe/Te using Te
nanowires as templates. A morphology evolution study for the formation
of these heterostructures has been performed. On the basis of these
control experiments, a pathway for the formation of these nanostructures
is proposed. Reduction of a Pb precursor to Pb on Te nanowire templates
followed by interdiffusion of Pb/Te leads to the formation of a thin
shell of PbTe on the Te wires. Controlled dewetting of the thin shell
leads to the formation of cube-shaped PbTe that is periodically arranged
on the Te wires. Using control experiments, we show that different
reactions parameters like rate of addition of the reducing agent,
concentration of Pb precursor and thickness of initial Te nanowire
play a critical role in controlling the spacing between the PbTe cubes
on the Te wires. Using simple surface energy arguments, we propose
a mechanism for the formation of the hybrid. The principles presented
are general and can be exploited for the synthesis of other nanoscale
heterostructures
Composite Supraparticles with Tunable Light Emission
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
Galvanic Replacement Coupled to Seeded Growth as a Route for Shape-Controlled Synthesis of Plasmonic Nanorattles
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
Cuboidal Supraparticles Self-Assembled from Cubic CsPbBr<sub>3</sub> Perovskite Nanocrystals
Colloidal
CsPbBr<sub>3</sub> 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 vacanciesinstead
of delocalized onesindicates 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