金红石型TiO2(110)表面性质及STM形貌模拟

采用密度泛函理论从头计算了金红石型TiO₂(110)表面的相关性质，切片模型含有9层原子，采用化学整比表面结构，晶胞真空层厚度为1.5nm，原子价电子采用超软赝势表达.差分电子密度分布图发现原子附近区域电子密度分布以球对称为主，电子定域形成离子键的趋势较强，但在Ti和O原子之间存在较弱的共价键.模拟了金红石型TiO₂(110)表面结构的扫描隧道显微镜(scanning tunneling microscope，简称STM)图像，利用Tersoff-Hamann的成像理论，在+2V的正向偏压下，采用一系列变化的数值作为STM探针离表面桥式氧的距离，分析了相关态密度的变化，发现(110)表面的STM形貌凸起部分来自于5—Ti原子，而不是2—O原子(桥式氧)，在TiO₂(110)表面结构成像中，电子效应起主导作用，证实了STM实验观察到的亮行是Ti原子的结果.关键词：功能材料密态泛函理论表面结构STM像

Study of rutile (110) surface STM image via ab initio simulation

First principle calculations based on DFT have been applied to study various properties of rutile (110) surface. We used a nine_layer slab model with stoichiometric formula of TiO₂ and the vacuum length of the cell fixed at 15nm. The interactions between ionic core and valence electrons were represented by pesudopotentials. After analyzing the results, we found that an admixture bonding states existed in titanium dioxide: a stronger ionic bond accompanied by a weaker covalent bond between Ti and O. STM(Scanning tunneling microscope)image of Rutile (110) surface has been successfully simulated by DFT calculations, which was in accord with the Tersoff-Hamann's theory. A positive basis voltage of 2V was added to simulate STM experimentd conditions in imaging process. The distance between tip and surface were also changed step by step. By analyzing the electron density map and DOS plot, it is clear that electron factors dominated the STM image of rutile (110) surface and the jut in the image corresponded to 5_coordinated Ti atom rather than the bridge oxygen on the top.