Adatom-dependent diffusion mechanisms on a Ag/Si(111) √3 x √3 surface
Adatom-dependent diffusion mechanisms on a Ag/Si(111) √3 x √3 surface
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DOI：
10.1103/physrevb.81.195429
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发表时间：
2010-05-15
影响因子：
3.7
通讯作者：
Jeong, Hojin
中科院分区：
文献类型：
--
作者：
Jeong, Sukmin;Jeong, Hojin
我们提出了第一性原理计算一价碱金属和贵金属吸附原子在Ag/Si（111）根3 x根3（根3-Ag）表面上的扩散，该表面是一个二维（2D）电子气系统，可通过吸附原子在2D吸附原子气体中的电子掺杂来调节。在该系统中，Ag吸附原子通过交换机制在表面上扩散，其中吸附原子和基底Ag原子在每个扩散步骤中重复交换。计算得到的扩散势垒仅为0.22 eV。其他吸附原子（Au、Cu、Li和Na）通过与Ag原子交换，随后通过Ag原子在表面上扩散而被并入衬底中。计算的位投影态密度表明，吸附原子和衬底Ag原子的空态存在明显的差异，这可以用来验证异质吸附原子的交换构型.另一方面，具有大原子半径的K吸附原子有利于直接扩散，势垒为0.12 eV。根据根3-Ag表面上的吸附原子，各种扩散机制可以追溯到由于Ag层膨胀和与异质（Ag和Si）覆盖层相关的表面化学引起的拉伸表面应力，导致2D吸附原子气体形成的不寻常的微观机制。
We present first-principles calculations for the diffusion of monovalent alkali and noble metal adatoms on a Ag/Si (111) root 3 x root 3 (root 3-Ag) surface, a two-dimensional (2D) electron gas system tunable via the electron doping of adatoms in 2D adatom gas. In this system, a Ag adatom diffuses over the surface through an exchange mechanism in which the adatom and the substrate Ag atoms exchange repeatedly in each diffusion step. The resulting calculated diffusion barrier is only 0.22 eV. Other adatoms (Au, Cu, Li, and Na) are incorporated into the substrate via exchange with a Ag atom followed by the Ag atom diffusion on the surface. The calculated site-projected densities of states show that the adatom and the substrate Ag atoms have a clear difference in their empty states, which can be used to verify an exchanged configuration for the heterogeneous adatoms. On the other hand, a K adatom with a large atomic radius favors a direct diffusion with a barrier of 0.12 eV. Depending on the adatoms on the root 3-Ag surface, the various diffusion mechanisms can be traced to the tensile surface stress due to the Ag layer expansion and the surface chemistry related with the heterogeneous (Ag and Si) overlayer, leading to an unusual microscopic mechanism of 2D adatom-gas formation.