Hiroyasu Katsuno

Mechanism of chirality conversion by periodic change of temperature: Role of chiral clusters.

By grinding crystals in a solution, the chirality of crystal structure (and the molecular chirality for the case of chiral molecules as well) can be converted, and the cause of the phenomenon is attributed to crystal growth with chiral clusters. We show that the recently found chirality conversion with a periodic change of temperature can also be explained by crystal growth with chiral clusters. With the use of a generalized Becker-Döring model, which includes enantio-selective incorporation of small chiral clusters to large solid clusters, the change of cluster distribution and the mass flow between clusters are studied. The chiral clusters act as a reservoir to pump out the minority species to the majority, and the exponential amplification of the enantiomeric excess found in the experiment is reproduced in the numerical calculation.

Crystallization of brownian particles from walls induced by a uniform external force

Keeping the formation of colloidal crystal under a centrifugal force in mind, we study the ordering of Brownian particles induced by a uniform external force. When the uniform external force is added, the particles move in the direction of the external force and the density of particles near walls becomes high. The ordering of particles starts on the walls, and successive ordering in bulk occurs near the walls. In bulk, both domains of the face-centered cubic structure and hexagonal close-packed structure appear. By controlling the direction and the strength of the external force, the number of ordered particles and distribution of cluster size are changed.

Erratum: "Mechanism of Chirality Conversion by Grinding Crystals: Ostwald Ripening vs Crystallization of Chiral Clusters"

It has been found that the simple grinding of crystals in a solution causes the conversion of the chiral structure of crystals and, in the case of organic molecules, the resultant conversion of molecular chirality. In order to clarify the mechanism of the chirality conversion, we study the change in the size distribution of chiral clusters in a Becker–Doring type model, in which chiral dimer reaction and grinding are implemented. In the absence of grinding, Ostwald ripening may cause chirality conversion if the initial size distribution is appropriate. With grinding crystals, the crystallization of chiral clusters causes an exponential amplification of the initial chiral imbalance resulting in a homochiral state. During chirality conversion, the total size distribution does not change.

Two-dimensional crystal structure formed by two components of DNA nanoparticles on a substrate

We study the two-dimensional crystal structure of two components of DNA nanoparticles on a substrate by Brownian dynamics simulation. We use the Lennard-Jones potential as the interaction potential between particles and assume that the interaction length between different types of particles, σAB, is smaller than that between the same types of particles, σ. Two types of particles form an alloy structure. With decreasing σAB/σ, the crystal structure changes from a triangular lattice, to a square lattice, a honeycomb lattice, a rectangular lattice, and a triangular lattice.

Misfit Dislocations in a Two-Dimensional Lattice Model

We study misfit dislocations in a two-dimensional elastic lattice model of epitaxy using Greens function. The interaction between the dislocations of the lattice model is compared with that of continuum elasticity theory. It is found that the behavior of the lattice model at a long distance agrees with that of standard continuum theory, but an additional interaction between dislocations due to extra forces around the dislocation core is important. The extra forces also lead to an increase in the dislocation interval. On a flat adsorbate surface with a periodic array of misfit dislocations, the preferential adsorption site is found to be either on the top or at the midpoint of the dislocations depending on the sign of the force dipole moment of the adatom and the sign of the misfit parameter.

Direct measurement of conduction miniband structure in superlattice by visible-light photoemission spectroscopy

We have proposed a novel angle-resolved photoemission spectroscopy to measure the conduction electrons emitted from a surface with negative electron affinity state. We call this method visible-light photoemission spectroscopy (VPS). In the present study, the conduction miniband structure formed in a superlattice was evaluated by the VPS method. As a result, we succeeded to obtain the dispersion of the miniband. In addition, the effective mass of the miniband was quantitatively determined from the observed dispersion. Therefore, we believe that VPS is a quite powerful tool for the evaluation of intermediate-band solar cells.

Scaling relation of domain competition on (2+1)-dimensional ballistic deposition model with surface diffusion

During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing. The number density of active domains ρ decreases as the height h increases. A simple scaling argument leads to a scaling law of ρ ~ h - γ with a coarsening exponent γ = d/z , where d is the dimension of the substrate surface and z the dynamic exponent of a growth front. This scaling relation is confirmed by performing kinetic Monte Carlo simulations of the ballistic deposition model on a two-dimensional ( d =2) surface, even when an isolated deposited particle diffuses on a crystal surface.