6 research outputs found
Patterns without Patches: Hierarchical Self-Assembly of Complex Structures from Simple Building Blocks
Nanoparticles with âsticky patchesâ have long been proposed as building blocks for the self-assembly of complex structures. The synthetic realizability of such patchy particles, however, greatly lags behind predictions of patterns they could form. Using computer simulations, we show that structures of the same genre can be obtained from a solution of simple isotropic spheres, with control only over their sizes and a small number of binding affinities. In a first step, finite clusters of well-defined structure and composition emerge from natural dynamics with high yield. In effect a kind of patchy particle, these clusters can further assemble into a variety of complex superstructures, including filamentous networks, ordered sheets, and highly porous crystals
Metastability in Pressure-Induced Structural Transformations of CdSe/ZnS Core/Shell Nanocrystals
The kinetics and thermodynamics of structural transformations
under
pressure depend strongly on particle size due to the influence of
surface free energy. By suitable design of surface structure, composition,
and passivation it is possible, in principle, to prepare nanocrystals
in structures inaccessible to bulk materials. However, few realizations
of such extreme size-dependent behavior exist. Here, we show with
molecular dynamics computer simulation that in a model of CdSe/ZnS
core/shell nanocrystals the core high-pressure structure can be made
metastable under ambient conditions by tuning the thickness of the
shell. In nanocrystals with thick shells, we furthermore observe a
wurtzite to NiAs transformation, which does not occur in the pure
bulk materials. These phenomena are linked to a fundamental change
in the atomistic transformation mechanism from heterogeneous nucleation
at the surface to homogeneous nucleation in the crystal core
Metastability in Pressure-Induced Structural Transformations of CdSe/ZnS Core/Shell Nanocrystals
The kinetics and thermodynamics of structural transformations
under
pressure depend strongly on particle size due to the influence of
surface free energy. By suitable design of surface structure, composition,
and passivation it is possible, in principle, to prepare nanocrystals
in structures inaccessible to bulk materials. However, few realizations
of such extreme size-dependent behavior exist. Here, we show with
molecular dynamics computer simulation that in a model of CdSe/ZnS
core/shell nanocrystals the core high-pressure structure can be made
metastable under ambient conditions by tuning the thickness of the
shell. In nanocrystals with thick shells, we furthermore observe a
wurtzite to NiAs transformation, which does not occur in the pure
bulk materials. These phenomena are linked to a fundamental change
in the atomistic transformation mechanism from heterogeneous nucleation
at the surface to homogeneous nucleation in the crystal core
Metastability in Pressure-Induced Structural Transformations of CdSe/ZnS Core/Shell Nanocrystals
The kinetics and thermodynamics of structural transformations
under
pressure depend strongly on particle size due to the influence of
surface free energy. By suitable design of surface structure, composition,
and passivation it is possible, in principle, to prepare nanocrystals
in structures inaccessible to bulk materials. However, few realizations
of such extreme size-dependent behavior exist. Here, we show with
molecular dynamics computer simulation that in a model of CdSe/ZnS
core/shell nanocrystals the core high-pressure structure can be made
metastable under ambient conditions by tuning the thickness of the
shell. In nanocrystals with thick shells, we furthermore observe a
wurtzite to NiAs transformation, which does not occur in the pure
bulk materials. These phenomena are linked to a fundamental change
in the atomistic transformation mechanism from heterogeneous nucleation
at the surface to homogeneous nucleation in the crystal core
Self-Assembly of Quantum DotâGold Heterodimer Nanocrystals with Orientational Order
The
self-assembly of nanocrystals into ordered superlattices is
a powerful strategy for the production of functional nanomaterials.
The assembly of well-ordered target structures, however, requires
control over the building blocksâ size and shape as well as
their interactions. While nanocrystals with homogeneous composition
are now routinely synthesized with high precision and assembled into
various ordered structures, high-quality multicomponent nanocrystals
and their ordered assemblies are rarely reported. In this paper, we
demonstrate the synthesis of quantum dotâgold (QD-Au) heterodimers.
These heterodimers possess a uniform shape and narrow size distribution
and are capped with oleylamine and doÂdecylÂtriÂmethylÂamÂmonium
bromide (DTAB). Assembly of the heterodimers results in a superlattice
with long-range orientational alignment of dimers. Using synchrotron-based
X-ray measurements, we characterize the complex superstructure formed
from the dimers. Molecular dynamics simulations of a coarse-grained
model suggest that anisotropic interactions between the quantum dot
and gold components of the dimer drive superlattice formation. The
high degree of orientational order demonstrated in this work is a
potential route to nanomaterials with useful optoelectronic properties
Self-Assembly of Quantum DotâGold Heterodimer Nanocrystals with Orientational Order
The
self-assembly of nanocrystals into ordered superlattices is
a powerful strategy for the production of functional nanomaterials.
The assembly of well-ordered target structures, however, requires
control over the building blocksâ size and shape as well as
their interactions. While nanocrystals with homogeneous composition
are now routinely synthesized with high precision and assembled into
various ordered structures, high-quality multicomponent nanocrystals
and their ordered assemblies are rarely reported. In this paper, we
demonstrate the synthesis of quantum dotâgold (QD-Au) heterodimers.
These heterodimers possess a uniform shape and narrow size distribution
and are capped with oleylamine and doÂdecylÂtriÂmethylÂamÂmonium
bromide (DTAB). Assembly of the heterodimers results in a superlattice
with long-range orientational alignment of dimers. Using synchrotron-based
X-ray measurements, we characterize the complex superstructure formed
from the dimers. Molecular dynamics simulations of a coarse-grained
model suggest that anisotropic interactions between the quantum dot
and gold components of the dimer drive superlattice formation. The
high degree of orientational order demonstrated in this work is a
potential route to nanomaterials with useful optoelectronic properties