STM针尖和外电场在Si(111)-7×7表面单原子操纵中的作用

ROLES OF STM TIP AND EXTERNAL ELECTRIC FIELD IN THE SINGLE ATOM MANIPULATION ON Si(111) 7×7 SURFACE 

利用第一性原理的离散变分局域密度泛函方法，采用团簇模型（Ｓｉ３４Ｈ３６Ｗ１１）来模拟ＳＴＭ操纵Ｓｉ（１１１）７×７表面顶角吸附原子的过程．通过分析在进行原子操纵过程中体系的能量与电子云密度分布来研究针尖和外电场的作用．结果表明，当针尖与样品间距离较近时，利用两者间有较强的相互作用，能有效地降低脱出能的能垒高度．外电场对体系脱出能的影响与其大小及极性有关，当样品上所加正偏压增强时，脱出能曲线高度单调下降，而外电场极性为负时，反而稍有增高．仅考虑针尖和样品之间的静态电子相互作用及静电场的作用，尚不能使被操纵原子脱离样品表面．

Abstract The roles of STM tungsten tip and external static electric field in single corner silicon adatom extracting from Si(111) 7×7 surface are studied using discrete variational local density functional(DV LDF) method with cluster models.The binding energy and the different charge density distribution of the system are calculated under various conditions.The results show that,the activation barrier decreasing is a chemical effect due to the proximity of the eletrodes.The effect of external electric field depends on its polarity.A monotonous decrease in the activation barrier is seen for positive bias case,while a small increasing is seen for negative bias case.The single corner silicon adatom cannot transfer from the sample surface if only considering the role of the static interaction among the tip,external electric field and sample surface.The mechanisms of atomic manipulation on semiconductor surfaces are discussed.