Phase coexistence of clusters and islands: europium on graphene
Phase coexistence of clusters and islands: europium on graphene
复制标题
DOI：
10.1088/1367-2630/14/2/023022
复制
发表时间：
2012-02-09
影响因子：
3.3
通讯作者：
Michely, Thomas
中科院分区：
文献类型：
--
作者：
Foerster, Daniel F.;Wehling, Tim O.;Michely, Thomas
通过扫描隧道显微镜研究了 Ir(111) 上石墨烯上铕 (Eu) 的吸附和平衡表面相，温度范围为 35 至 400K，覆盖范围从饱和单层的一小部分到第二层。使用包括 4f 壳库仑相互作用和电子相互作用建模的密度泛函理论，获得了与平衡吸附物相、吸附物扩散和功函数的实验结果非常一致的结果。最值得注意的是，在 300 K 的中间覆盖范围内，均匀分布的 Eu 团簇（大小为 10-20 个原子）的相与大 Eu 岛在（根 3 x 根 3）R30 度结构中以二维平衡共存。我们认为簇相的形成是由三种效应的相互作用驱动的。首先，金属Eu-Eu结合导致(root 3 x root 3)R30度结构的局部稳定性。其次，电子通过离开Eu团簇来降低其动能，从而掺杂石墨烯。第三，对于较小的团簇，与从Eu到石墨烯的电荷转移相关的库仑能量损失大大减少。
The adsorption and equilibrium surface phases of europium (Eu) on graphene on Ir(111) are investigated in the temperature range from 35 to 400K and for coverages ranging from a small fraction of a saturated monolayer to the second layer by scanning tunnelling microscopy. Using density functional theory including 4f-shell Coulomb interactions and modelling of electronic interactions, excellent agreement with the experimental results for the equilibrium adsorbate phase, adsorbate diffusion and work function is obtained. Most remarkably, at 300 K in an intermediate coverage range a phase of uniformly distributed Eu clusters (size 10-20 atoms) coexists in two-dimensional equilibrium with large Eu-islands in a (root 3 x root 3)R30 degrees structure. We argue that the formation of the cluster phase is driven by the interplay of three effects. Firstly, the metallic Eu-Eu binding leads to the local stability of (root 3 x root 3)R30 degrees structures. Secondly, electrons lower their kinetic energy by leaving the Eu clusters, thereby doping graphene. Thirdly, the Coulomb energy penalty associated with the charge transfer from Eu to graphene is strongly reduced for smaller clusters.