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arXiv 2104.13830cond-mat.mtrl-sci
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邻面台阶聚束的标度律:动力学和化学效应的作用

Scaling laws for step bunching on vicinal surfaces: the role of the dynamical and chemical effects

Lucas Benoit--Maréchal, Michel E. Jabbour, Nicolas Triantafyllidis

摘要:

我们研究了台阶束的演化邻面使用的是一个一致的阶梯流模型,(i)绕过准静态近似,在文献中流行的帐户吸附原子扩散的梯田和附着-脱离的步骤,(称为动态效应),和(ii)通过引入相邻阶地上扩散场之间的必要耦合,推广了阶跃化学势的表达式(称为化学效应)。先前已经表明,这些影响可以解释发病的步骤群聚没有求助于逆Ehrlich-Schwoebel(iES)障碍或其他无关的机制,我们在这里感兴趣的步骤群聚的演变超出了线性稳定制度。特别是,步流问题的数值解产生一个强大的幂律粗化的表面轮廓,随着时间的推移,随着聚束高度的$H\sim t^{1/2}$和最小的步间距作为一个函数的步骤的数目在遵守$\ell_{min}\sim N^{-2/3}$的聚束细胞。虽然这些指数以前已经报道过,这是第一次这样的标度律得到的iES屏障或吸附原子电迁移的情况下。为了验证我们的模拟,我们采取的连续极限的离散阶跃流系统,导致一个新的非线性演化方程的表面高度。我们研究了该方程自相似解的存在性,并证实了数值计算得到的$H$的1/2粗化指数。我们强调的组合动力学化学效应的影响,并表明,它可以被解释为一个有效的iES屏障在标准的BCF理论。最后,我们使用Padé近似推导出稳定移动的步骤束的速度的解析表达式,并将其与数值模拟进行比较。

英文摘要:

We study the evolution of step bunches on vicinal surfaces using a thermodynamically consistent step-flow model that (i) circumvents the quasistatic approximation that prevails in the literature by accounting for the dynamics of adatom diffusion on terraces and attachment-detachment at steps (referred to as the dynamical effect), and (ii) generalizes the expression of the step chemical potential by incorporating the necessary coupling between the diffusion fields on adjacent terraces (referred to as the chemical effect). Having previously shown that these effects can explain the onset of step bunching without recourse to the inverse Ehrlich-Schwoebel (iES) barrier or other extraneous mechanisms, we are here interested in the evolution of step bunches beyond the linear-stability regime. In particular, the numerical resolution of the step-flow problem yields a robust power-law coarsening of the surface profile, with the bunch height growing in time as $H\sim t^{1/2}$ and the minimal interstep distance as a function of the number of steps in the bunch cell obeying $\ell_{min}\sim N^{-2/3}$. Although these exponents have previously been reported, this is the first time such scaling laws are obtained in the absence of an iES barrier or adatom electromigration. In order to validate our simulations, we take the continuum limit of the discrete step-flow system, leading to a novel nonlinear evolution equation for the surface height. We investigate the existence of self-similar solutions of this equation and confirm the 1/2 coarsening exponent obtained numerically for $H$. We highlight the influence of the combined dynamical-chemical effect and show that it can be interpreted as an effective iES barrier in the standard BCF theory. Finally, we use a Padé approximant to derive an analytical expression for the velocity of steadily moving step bunches and compare it to numerical simulations.

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