Yoshihide Yoshimoto | PubMed Health

PubMed2006

Extended multicanonical method combined with thermodynamically optimized potential: application to the liquid-crystal transition of silicon.

A novel method is proposed to study first-order phase transition in real materials. It is applied to the liquid-crystal transition of silicon successfully. It consists of two parts: a direct simulation of the transition by an extended multicanonical ensemble with an order parameter defined with structure factors that characterize the transition, and optimization of a model interatomic potential in terms of the ensemble from an accurate one. These provide a principle to project a first-principles approach on a model-based approach conserving thermodynamic properties of multiple phases.

Journal Article↗

PubMed2005

Direct observation of strain-induced change in surface electronic structure.

We have observed a novel modification of a surface state due to a local strain field induced by a nanopattern formation. N adsorption on the Cu(100) surface induces a nanoscale grid pattern, where the clean Cu regions remain periodically. The lattice is contracted on the clean region by adjacent c(2 x 2)N domains, which have a larger lattice constant. On this patterned surface, we have investigated the Tamm-type surface state at M by means of angle-resolved ultraviolet photoelectron spectroscopy. The binding energy of the Tamm state shifts toward the Fermi level continuously with increasing N coverage, i.e., the intensity of the strain field. This behavior due to the strain field is completely different from that caused by electron confinement observed on vicinal surfaces. The Brillouin zone extension corresponding to the lattice contraction was also detected.

Journal Article↗