arXiv subjects

Noriko Akutsu

Publications and source records attributed to Noriko Akutsu.

13 recordsLinked to original sources

arXiv2026

Intrinsic Step Jamming in Nanometer-Scale KPZ-like Rough Surfaces under Interface-Limited Crystal Growth and Retreat

We investigate an intrinsic step-jamming phenomenon at the nanometer scale on Kardar-Parisi-Zhang (KPZ)-like kinetically roughened crystal surfaces that arises during interface-limited steady crystal growth or retreat. Monte Carlo simulations using the Metropolis algorithm on a restricted solid-on-solid (RSOS) lattice model demonstrate that intrinsic step jamming persists on surfaces below 20 nm. In the present model, transport processes such as surface and volume diffusion are excluded, as are elastic interactions, step-step repulsion or attraction, and stoichiometric effects. We show that intrinsic step jamming arises from asymmetric fluctuations in atomic attachment and detachment driven by biased transition probabilities under the SOS restriction, leading to collective step congestion. Asymmetric fluctuations also determine whether adatom or hole clusters grow or recede. This mechanism bears close similarity to jamming phenomena in the asymmetric simple exclusion process (ASEP), including multi-lane variants. In contrast, symmetric thermal fluctuations generate adatom or hole clusters on terraces, thereby suppressing intrinsic step jamming. Possible routes to suppress intrinsic step jamming, including experimentally accessible strategies, are also discussed.

cond-mat.mes-hall↗

arXiv2020

Crossover from BKT-Rough to KPZ-Rough Surfaces for Interface-Limited Crystal Growth/Recession

The crossover from a Berezinskii--Kosterlitz--Thouless (BKT) rough surface to a Kardar--Parisi--Zhang (KPZ) rough surface on a vicinal surface is studied using the Monte Carlo method in the non-equilibrium steady state in order to address discrepancies between theoretical results and experiments. The model used is a restricted solid-on-solid (RSOS) model with a discrete Hamiltonian without surface or volume diffusion (interface limited growth/recession). The temperature, driving force for growth, system size, and surface slope dependences of the surface width are calculated for vicinal surfaces tilted between the (001) and (111) surfaces. The surface velocity, kinetic coefficient of the surface, and mean height of the locally merged steps are also calculated. In contrast to the accepted theory for (2+1) surfaces, we found that the crossover point from a BKT (logarithmic) rough surface to a KPZ (algebraic) rough surface is different from the kinetic roughening point for the (001) surface. The driving force for crystal growth was found to be a relevant parameter for determining whether the system is in the BKT class or the KPZ class. It was also determined that ad-atoms, ad-holes, islands, and negative-islands block surface fluctuations, which contributes to making a BKT-rough surface.

cond-mat.stat-mech↗

arXiv2019

Relationship Between Macrostep Height and Surface Velocity for a Reaction-Limited Crystal Growth Process

This work examined the effect of macrostep height on the growth velocity of a vicinal surface during reaction- (interface-) limited crystal growth under non-equilibrium steady state conditions. The Monte Carlo method was employed, based on a restricted solid-on-solid (RSOS) model with point-contact-type step-step attraction (termed the p-RSOS model). Although this is a simple lattice model, the model surface shows a variety of distinctive configurations depending on the temperature and the driving force for crystal growth. The results demonstrate that the surface velocity decreases as the height of the faceted macrostep increases. In addition, the significant variation in surface velocity recently reported by Onuma {\it et al.} in a study based on 4H-SiC was reproduced. This work also shows that the terrace slope, elementary step velocity and elementary step kinetic coefficient are all affected by the faceted macrostep height.

physics.chem-ph↗

arXiv2017

Height of a faceted macrostep for sticky steps in a step-faceting zone

The driving force dependence of the surface velocity and the average height of faceted merged steps, the terrace-surface-slope, and the elementary step velocity in the non-equilibrium steady-state are studied using the Monte Carlo method. The Monte Carlo study is based on a lattice model, the restricted solid-on-solid model with point-contact type step--step attraction (p-RSOS model). The temperature is selected to be in the step-faceting zone where the surface is surrounded by the (001) terrace and the (111) faceted step at equilibrium. Long time simulations are performed at this temperature to obtain steady-states for the different driving forces that influence the growth/recession of the surface. A Wulff figure of the p-RSOS model is produced through the anomalous surface tension calculated using the density-matrix renormalization group method. Although the p-RSOS model is a simplified model, the model shows a wide variety of dynamics in the step-faceting zone. There are four characteristic driving forces, $Δμ_y$, $Δμ_f$, $Δμ_{co}$, and $Δμ_R$. For $Δμ_{co}<|Δμ|<Δμ_R$, the surface grows/recedes with the successive attachment-detachment of steps to/from a macrostep. When $|Δμ|$ exceeds $Δμ_R $, the macrostep vanishes and the surface roughens kinetically. Classical 2D heterogeneous multi-nucleation was determined to be valid with slight modifications based on the Monte Carlo results of the step velocity and the change in the surface slope of the "terrace". The finite size effects were also determined to be distinctive near equilibrium.

cond-mat.mtrl-sci↗

arXiv2015

Time Scaling Relations for Step Bunches from Models with Step-Step Attractions (B1-Type Models)

The step bunching instability is studied in three models of step motion defined in terms of ordinary differential equations (ODE). The source of instability in these models is step-step attraction, it is opposed by step-step repulsion and the developing surface patterns reflect the balance between the two. The first model, TE2, is a generalization of the seminal model of Tersoff et al. (1995). The second one, LW2, is obtained from the model of Liu and Weeks (1998) using the repulsions term to construct the attractions one with retained possibility to change the parameters in the two independently. The third model, MM2, is a minimal one constructed ad hoc and in this article it plays a central role. New scheme for scaling the ODE in vicinal studies is applied towards deciphering the pre-factors in the time-scaling relations. In all these models the patterned surface is self-similar - only one length scale is necessary to describe its evolution (hence B1-type). The bunches form finite angles with the terraces. Integrating numerically the equations for step motion and changing systematically the parameters we obtain the overall dependence of time-scaling exponent \b{eta} on the power of step-step attractions p as \b{eta} = 1/(3+p) for MM2 and hypothesize based on restricted set of data that it is \b{eta} = 1/(5+p) for LW2 and TE2.

cond-mat.mtrl-sci↗

arXiv2015

Phase diagram of step faceting for sticky steps

A phase diagram for the step faceting phase, the step droplet phase, and the Gruber-Mullins-Pokrovsky-Talapov (GMPT) phase on a crystal surface is obtained by calculating the surface tension with the density matrix renormalization group method. The model based on the calculations is the restricted solid-on-solid (RSOS) model with a point-contact-type step-step attraction (p-RSOS model) on a square lattice. The point-contact-type step-step attraction represents the energy gain obtained by forming a bonding state with orbital overlap at the meeting point of the neighbouring steps. Owing to the sticky character of steps, there are two phase transition temperatures, $T_{f,1}$ and $T_{f,2}$. At temperatures $T < T_{f,1}$, the anisotropic surface tension has a disconnected shape around the (111) surface. At $T<T_{f,2}<T_{f,1}$, the surface tension has a disconnected shape around the (001) surface. On the (001) facet edge in the step droplet phase, the shape exponent normal to the mean step running direction $θ_n=2$ at $T$ near $T_{f,2}$, which is different from the GMPT universal value $θ_n=3/2$. On the (111) facet edge, $θ_n=4/3$ only on $T_{f,1}$. To understand how the system undergoes phase transition, we focus on the connection between the p-RSOS model and the one-dimensional spinless quasi-impenetrable attractive bosons at absolute zero.

cond-mat.mtrl-sci↗

arXiv2012

Sticky steps inhibit step motions near equilibrium

Using a Monte Carlo method on a lattice model of a vicinal surface with short-range step-step attraction, we show that, at low temperature and near equilibrium, there is an inhibition of the motion of macro-steps. This inhibition leads to a pinning of steps without defects, adsorbates, or impurities (self-pinning of steps). We show that this inhibition of the macro-step motion is caused by faceted steps, which are macro-steps that have a smooth side surface. The faceted steps result from discontinuities in the anisotropic surface tension (the surface free energy per area). The discontinuities are brought into the surface tension by the short-range step-step attraction. The short-range step-step attraction also originates `step-droplets', which are locally merged steps, at higher temperatures. We derive an analytic equation of the surface stiffness tensor for the vicinal surface around the (001) surface. Using the surface stiffness tensor, we show that step-droplets roughen the vicinal surface. Contrary to what we expected, the step-droplets slow down the step velocity due to the diminishment of kinks in the merged steps (smoothing of the merged steps).

physics.chem-ph↗

arXiv2011

Non-universal equilibrium crystal shape results from sticky steps

The anisotropic surface free energy, Andreev surface free energy, and equilibrium crystal shape (ECS) z=z(x,y) are calculated numerically using a transfer matrix approach with the density matrix renormalization group (DMRG) method. The adopted surface model is a restricted solid-on-solid (RSOS) model with "sticky" steps, i.e., steps with a point-contact type attraction between them (p-RSOS model). By analyzing the results, we obtain a first-order shape transition on the ECS profile around the (111) facet; and on the curved surface near the (001) facet edge, we obtain shape exponents having values different from those of the universal Gruber-Mullins-Pokrovsky-Talapov (GMPT) class. In order to elucidate the origin of the non-universal shape exponents, we calculate the slope dependence of the mean step height of "step droplets" (bound states of steps) using the Monte Carlo method, where p=(dz/dx, dz/dy)$, and <.> represents the thermal averag |p| dependence of , we derive a |p|-expanded expression for the non-universal surface free energy f_{eff}(p), which contains quadratic terms with respect to |p|. The first-order shape transition and the non-universal shape exponents obtained by the DMRG calculations are reproduced thermodynamically from the non-universal surface free energy f_{eff}(p).

cond-mat.mtrl-sci↗

arXiv2001

Vicinal Surface with Langmuir Adsorption: A Decorated Restricted Solid-on-solid Model

We study the vicinal surface of the restricted solid-on-solid model coupled with the Langmuir adsorbates which we regard as two-dimensional lattice gas without lateral interaction. The effect of the vapor pressure of the adsorbates in the environmental phase is taken into consideration through the chemical potential. We calculate the surface free energy $f$, the adsorption coverage $Θ$, the step tension $γ$, and the step stiffness $\tildeγ$ by the transfer matrix method combined with the density-matrix algorithm. Detailed step-density-dependence of $f$ and $Θ$ is obtained. We draw the roughening transition curve in the plane of the temperature and the chemical potential of adsorbates. We find the multi-reentrant roughening transition accompanying the inverse roughening phenomena. We also find quasi-reentrant behavior in the step tension.

cond-mat.stat-mech↗

arXiv2000

Trimer-Monomer Mixture Problem on (111) $1 \times 1$ Surface of Diamond Structure

We consider a system of trimers and monomers on the triangular lattice, which describes the adsorption problem on (111) $1 \times 1$ surface of diamond structure. We give a mapping to a 3-state vertex model on the square lattice. We treat the problem by the transfer-matrix method combined with the density-matrix algorithm, to obtain thermodynamic quantities.

cond-mat.stat-mech↗

arXiv2000

Statistical Mechanics of the Vicinal Surfaces with Adsorption

We study the vicinal surface with adsorption below the roughening temperature, using the restricted solid-on-solid model coupled with the Ising model. By the product-wavefunction renormalization group method, we calculate the surface gradient $p$ and the adsorption coverage $Θ$ as a function of the Andreev field $η$ which makes surface tilt. Combining Monte Carlo calculations, we show that there emerges effective attraction between the steps. This attractive interaction leads to instability against step bunching.

cond-mat.stat-mech↗

arXiv2000

Stiffening Transition in Vicinal Surfaces with Adsorption

We study the vicinal surface with adsorption below the roughening temperature, using the restricted solid-on-solid model coupled with the Ising model. We calculate the step tension $γ$ and the step-interaction coefficient $B$ by employing a variant of the density matrix algorithm. We find a ``stiffening transition'' at a temperature $T_{\rm s}$ where $B$ vanishes. At $T_{\rm s}$ surface free energy has the form $f(p)- f(0)= γp + ({const.})p^5 + ...$ ($p$: surface gradient), which differs from the well-known $p$-$p^3$ form.

cond-mat.stat-mech↗

arXiv1999

Statistical Mechanical Calculation of Anisotropic Step Stiffness of a Two-Dimensional Hexagonal Lattice Gas Model with Next-Nearest-Neighbor Interactions: Application to Si(111) Surface

We study a two-dimensional honeycomb lattice gas model with both nearest- and next-nearest-neighbor interactions in a staggered field, which describes the surface of stoichiometrically binary crystal. We calculate anisotropic step tension, step stiffness, and equilibrium island shape, by an extended random walk method. We apply the results to Si(111) 7$\times$7 reconstructed surface and high-temperature Si(111) 1$\times$1 surface. We also calculate inter-step interaction coefficient.

cond-mat.stat-mech↗