Chugh Manjusha, Ranganathan Madhav
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, India.
Phys Chem Chem Phys. 2017 Jan 18;19(3):2111-2123. doi: 10.1039/c6cp07254b.
Studying the adsorbate interactions on a surface helps in understanding the growing surface morphologies and calculating the effective surface diffusion barriers. We study the interaction between Ga-Ga, N-N and Ga-N adatom pairs on the polar GaN(0001) surface using ab initio calculations based on density functional theory. The interaction energy between two adatoms on the surface does not seem to follow definite trends with increasing distance between the adatoms. The presence of a number of possible reconstructions on clean GaN(0001) and periodic effects due to the finite size complicate the analysis of the interactions. Various components of the total interaction energy are separated. We find that there is a large substrate lattice distortion caused due to Ga and N adatoms. The resulting elastic interaction is a major component of the interactions between the adatoms on the GaN(0001) surface. The dipolar interaction is much smaller in magnitude. We also evaluate the component of the interaction energy due to the substrate-mediated electronic interactions. The barriers for surface hopping of adatoms are significantly modified in the presence of other adatoms. We identify several possible surface hopping processes for Ga and N adatoms and calculate their barriers. In particular, we find that the N adatom has a lower barrier to move to an adjoining site on the other side of a neighboring Ga adatom. Kinetic Monte Carlo simulations are performed to see the effect of adatom interactions on the growing surface morphologies of GaN(0001). At the submonolayer growth stage, the fast diffusion of N adatoms located near Ga adatoms leads to more regular island features. In this way, we illustrate the role of adatom interactions in the initial surface nucleation and the morphologies of the growing GaN(0001) film.
研究表面上吸附质之间的相互作用有助于理解不断变化的表面形态，并计算有效的表面扩散势垒。我们基于密度泛函理论，使用从头算方法研究了极性GaN(0001)表面上Ga-Ga、N-N和Ga-N吸附原子对之间的相互作用。表面上两个吸附原子之间的相互作用能似乎并不随吸附原子之间距离的增加而呈现出明确的趋势。清洁的GaN(0001)表面上存在多种可能的重构以及由于有限尺寸引起的周期性效应，使得相互作用的分析变得复杂。我们分离了总相互作用能的各个组成部分。我们发现，Ga和N吸附原子会导致较大的衬底晶格畸变。由此产生的弹性相互作用是GaN(0001)表面上吸附原子之间相互作用的主要组成部分。偶极相互作用的量级要小得多。我们还评估了由于衬底介导的电子相互作用而产生的相互作用能分量。在存在其他吸附原子的情况下，吸附原子表面跳跃的势垒会被显著改变。我们确定了Ga和N吸附原子的几种可能的表面跳跃过程，并计算了它们的势垒。特别是，我们发现N吸附原子移动到相邻Ga吸附原子另一侧的相邻位置的势垒较低。进行了动力学蒙特卡罗模拟，以观察吸附原子相互作用对GaN(0001)生长表面形态的影响。在亚单层生长阶段，位于Ga吸附原子附近的N吸附原子的快速扩散导致形成更规则的岛状特征。通过这种方式，我们阐明了吸附原子相互作用在初始表面成核以及生长的GaN(0001)薄膜形态中的作用。
