Publications

Kazuhiro Kishi, Masashi Kawaguchi, Hitoshi Miura, *Masahide Sato and Makio Uwaha,
Relation between the Step Pattern and the Velocity of the Moving Linear Adatom Source,
e-Journal of Surface Science and Nanotechnology 13, 269-274 (2015).

[Summary] During deposition of Ga atoms on a Si(111) vicinal face, a step on the vicinal face shows a comb-like pattern.Keeping the formation of comb-like pattern in mind, we carry out phase field simulations, in which a linear adatom source advances in front of a step. The comb-like pattern consisting of straight finger-like intrusions is formed when the source velocity is smaller than a critical value determined by the step anisotropy. Initially, the straight step is unstable and step wandering is induced by the asymmetry of the surface diffusion field. The amplitude of step fluctuations increases with time and an array of short intrusions is formed. Shorter intrusions cannot catch sufficient adatoms, so that coarsening of the pattern occurs. When the adatom source moves slowly, the intrusions grow long and the step shows a regular comb-like pattern. By the coarsening, the distance between intrusions is several times larger than the initial value. The pattern is metastable for a rapid change in the source velocity. When the adatom source moves fast, the intrusions cannot keep up with the adatom source and an irregular pattern is formed.　When the strength of crystal anisotropy is weak, splitting of the tips of intrusions frequently occurs and the step shows an irregular seaweed-like pattern. With a strong crystal anisotropy, the step shows a dendrite pattern.

Masashi Kawaguchi, Hitoshi Miura, Kazuhiro Kishi, Masahide Sato, and *Makio Uwaha,
Period of a comblike pattern controlled by atom supply and noise,
Physical Review E 91, 012409/1-9 (2015).

[Summary] Pattern formation of a step on a growing crystal surface induced by a straight line source of atoms, which is escaping from the step at a velocity Vp, is studied with the use of a phase field model. From a straight step, fluctuations of the most unstable wavelength λmax grow. Competition of intrusions leads to coarsening of the pattern, and survived intrusions grow exponentially. With sufficient strength of the crystal anisotropy, a regular comblike pattern appears. This peculiar step pattern is similar to that observed on a Ga-deposited Si(111) surface. The final period of the intrusions, Λ, is determined when the exponential growth ends. The period depends on the strength Fu of a current noise in diffusion as Λ∼λmax|lnFu|: such a logarithmic dependence is confirmed for the first time. A nonmonotonic Vp dependence of Λ indicates that the comblike pattern with a small Vp is related to an unstable growth mode of the free needle growth in a channel. The pattern is stabilized by the guiding linear source.

Mamoru Fujine, *Masahide Sato, Tetsuya Toyooka, Hiroyasu Katsuno, Yoshihisa Suzuki, and Tsutomu Sawada,
Crystallization of Brownian particles in thin systems constrained by walls,
Physical Review E 90, 032404/1-7 (2014).

[Summary] Keeping formation of a colloidal crystal by a centrifugal force in mind, we carry out Brownian dynamics simulations in thin systems and study ordering of particles induced by an external force. During solidification, the two-dimensional ordering along walls initially occurs. Then, the ordered particles on the walls act as substrates, and crystallization proceeds into bulk. When the external force is weak, the close-packed face of the crystal structure is parallel to the bottom wall. The direction of the close-packed face depends on the strength of the external force: The close-packed face becomes parallel to the side walls with a strong external force.