单分子器件的拉伸与断裂过程第一性原理研究:末端基团效应  

First principle study on stretching and breaking process of single-molecule junction: Terminal group effect

作　　者：孙峰 刘然[1] 索雨晴 牛乐乐 傅焕俨 季文芳 李宗良[1] Sun Feng;Liu Ran;Suo Yu-Qing;Niu Le-Le;Fu Huan-Yan;Ji Wen-Fang;Li Zong-Liang(Shandong Key Laboratory of Medical Physics and Image Processing, School of Physics and Electronics, Shandong Normal University,Jinan 250358, China)

机构地区：[1]山东师范大学物理与电子科学学院山东省医学物理图像处理重点实验室

出　　处：《物理学报》2019年第17期287-294,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11974217,11874242);山东省自然科学基金(批准号:ZR2018MA037)资助的课题~~

摘　　要：基于密度泛函理论,研究了含S以及含N末端基团的分子结的拉伸与断裂过程.计算结果显示,对于尖端为锥形的金电极,当末端基团为-S时,拉断分子结的作用力大小为0.,59 nN,大于H原子未解离的-SH从金电极上断裂所需的0.25 nN作用力,但明显小于-S末端从平面金电极上断裂下来的约1.5 nN的作用力.当末端基团是-NH2或-NO2时,分子结断裂所需拉力分别为0.45和0.33 nN.体系轨道分布表明,分子与电极通过前线占据轨道耦合后形成的扩展体系分子轨道离域性越好,拉断分子结所需的作用力越大.自然键轨道(natural bond orbital,NBO)分析显示,若分子末端与电极间未形成成键轨道,末端原子上更多的NBO净电荷可以提高分子与电极间结合的稳定性.结合我们以前的研究,可以发现,-S末端和-NH2末端对金电极界面的微观构型具有明显的识别功能,这为精确操控并理解分子与金电极间的相互作用及界面结构提供了有用信息.The stretching and breaking processes of stilbene-based molecular junctions,which contain S or N atoms in the terminal groups,are studied by using density functional theory.The numerical results show that for pyramid-shaped gold electrodes,a stretching force of about 0.59 nN is needed to break the molecular junction with-S terminals,which is larger than the force of 0.25 nN that is required by the molecule to stretch -SH terminals away from pyramid-shaped gold electrode.However,it is obviously smaller than the force of about 1.5 nN that is needed by the molecule to break -S terminals from planar-shaped gold electrode.If the terminal group is-NH2 or-NO2,the force for breaking the molecular junction is about 0.45 nN or 0.33 nN,respectively.More delocalized molecular orbitals formed by the coupling between the frontier occupied orbitals of molecule and electrodes,higher stretching force for breaking molecular junction is required.The natural bond orbital(NBO)analysis shows that more NBO net charges that the terminal atom possesses can enhance the stability of the molecule-electrode contact if there is no bonding orbital fcormed between end group of molecule and electrode.Based on the numerical results and the combination with previous studies,it can be found that-S terminal and -NH2 terminal show evident properties in distinguishing tip structures of gold electrodes,which provides useful information for precisely controlling the interactions and interface structures between molecule and electrodes.

关 键 词：单分子器件 分子结拉伸 分子结断裂 自然键轨道 界面识别 

分 类 号：O561[理学—原子与分子物理]