13 research outputs found
A Novel Chiral Phase of Achiral Hard Triangles and an Entropy-Driven Demixing of Enantiomers
We investigate the phase behavior of a system of hard equilateral and
right-angled triangles in two dimensions using Monte Carlo simulations. Hard
equilateral triangles undergo a continuous isotropic-triatic liquid crystal
phase transition at packing fraction . Similarly, hard right-angled
isosceles triangles exhibit a first-order phase transition from an isotropic
fluid phase to a rhombic liquid crystal phase with a coexistence region . Both these liquid crystal phases undergo a
continuous phase transition to their respective close-packed crystal structures
at high pressures. Although the particles and their close-packed crystals are
both achiral, the solid phases of equilateral and right-angled triangles
exhibit spontaneous chiral symmetry breaking at sufficiently high packing
fractions. The colloidal triangles rotate either in clockwise or anti-clockwise
direction with respect to one of the lattice vectors for packing fractions
higher than . As a consequence, these triangles spontaneously form a
regular lattice of left- or right-handed chiral holes which are surrounded by
six triangles in the case of equilateral triangles and four or eight triangles
for right-angled triangles. Moreover, our simulations show a spontaneous
entropy-driven demixing transition of the right- and left-handed "enantiomers".Comment: 9 pages, 10 figure
Self-Assembly of Colloidal Hexagonal Bipyramid- and Bifrustum-Shaped ZnS Nanocrystals into Two-Dimensional Superstructures
We present a combined experimental, theoretical, and simulation study on the self-assembly of colloidal hexagonal bipyramid- and hexagonal bifrustum-shaped ZnS nanocrystals (NCs) into two-dimensional superlattices. The simulated NC superstructures are in good agreement with the experimental ones. This shows that the self-assembly process is primarily driven by minimization of the interfacial free-energies and maximization of the packing density. Our study shows that a small truncation of the hexagonal bipyramids is sufficient to change the symmetry of the resulting superlattice from hexagonal to tetragonal, highlighting the crucial importance of precise shape control in the fabrication of functional metamaterials by self-assembly of colloidal NCs
Self-Assembly of Colloidal Hexagonal Bipyramid- and Bifrustum-Shaped ZnS Nanocrystals into Two-Dimensional Superstructures
We present a combined experimental, theoretical, and simulation study on the self-assembly of colloidal hexagonal bipyramid- and hexagonal bifrustum-shaped ZnS nanocrystals (NCs) into two-dimensional superlattices. The simulated NC superstructures are in good agreement with the experimental ones. This shows that the self-assembly process is primarily driven by minimization of the interfacial free-energies and maximization of the packing density. Our study shows that a small truncation of the hexagonal bipyramids is sufficient to change the symmetry of the resulting superlattice from hexagonal to tetragonal, highlighting the crucial importance of precise shape control in the fabrication of functional metamaterials by self-assembly of colloidal NCs
Self-Assembly of Colloidal Hexagonal Bipyramid- and Bifrustum-Shaped ZnS Nanocrystals into Two-Dimensional Superstructures
We present a combined experimental,
theoretical, and simulation
study on the self-assembly of colloidal hexagonal bipyramid- and hexagonal
bifrustum-shaped ZnS nanocrystals (NCs) into two-dimensional superlattices.
The simulated NC superstructures are in good agreement with the experimental
ones. This shows that the self-assembly process is primarily driven
by minimization of the interfacial free-energies and maximization
of the packing density. Our study shows that a small truncation of
the hexagonal bipyramids is sufficient to change the symmetry of the
resulting superlattice from hexagonal to tetragonal, highlighting
the crucial importance of precise shape control in the fabrication
of functional metamaterials by self-assembly of colloidal NCs
In situ study of the formation mechanism of two-dimensional superlattices from PbSe nanocrystals
Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals, as one misaligned attachment would disrupt the 2D order beyond repair. Here, we demonstrate the formation mechanism of 2D PbSe superstructures with square geometry by using in situ grazing-incidence X-ray scattering (small angle and wide angle), ex situ electron microscopy, and Monte Carlo simulations. We observed nanocrystal adsorption at the liquid/gas interface, followed by the formation of a hexagonal nanocrystal monolayer. The hexagonal geometry transforms gradually through a pseudo-hexagonal phase into a phase with square order, driven by attractive interactions between the {100} planes perpendicular to the liquid substrate, which maximize facet-to-facet overlap. The nanocrystals then attach atomically via a necking process, resulting in 2D square superlattices.ChemE/Opto-electronic Material