氢原子吸附对金表面金属酞菁分子的吸附位置、自旋和手征性的调控  

Tuning the spin, chirality, and adsorption site of metal-phthalocyanine on Au(111) surface with hydrogen atoms

作　　者：肖文德[1] 刘立巍[1] 杨锴[1] 张礼智[1] 宋博群 杜世萱[1] 高鸿钧[1] 

机构地区：[1]中国科学院物理研究所,纳米物理与器件实验室,北京100190

出　　处：《物理学报》2015年第7期1-10,共10页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2009CB929103;2011CB921702);国家自然科学基金(批准号:20973196;10834011;60921092)资助的课题~~

摘　　要：实现单个功能有机分子构型、电子结构和自旋态的可逆调控,是未来分子电子学和分子自旋电子学应用的关键.近年来,我们利用极低温强磁场超高真空扫描隧道显微镜系统,结合第一性原理计算,系统研究了氢原子吸附对金表面吸附的金属酞菁分子的自旋、手性和吸附位置的调控.通过将金表面吸附的酞菁锰分子暴露于氢气或氢原子环境,使得分子中心的磁性离子吸附单个氢原子,从而实现了体系近藤效应由"开"到"关"的转变.基于密度泛函理论的第一性原理计算表明,氢原子吸附使得锰离子3d轨道内的电荷重排导致了分子的自旋由3/2降为1;同时分子与金基底的间距增大,使得近藤效应消失.通过施加局域电压脉冲或者给样品加热,可以实现单个或所有分子脱氢,从而恢复体系的自旋态和近藤效应.氢原子吸附还导致分子的优先吸附位置从金表面的面心立方堆垛区域变成了六角密排堆垛区域.三个氢原子吸附于同一酞菁锰分子上,可导致分子对称性的降低及分子镜面对称轴与金基底镜面对称轴的偏离,从而导致手征性的出现.这种分子吸附结构的手征性,导致分子轨道也呈现出手征性.这项工作为金属酞菁未来在分子电子学、自旋电子学、气体传感器等方面的应用提供了新思路.Metal-phthalocyanines（MPcs） and their derivates have attracted increasing interest in recent years, due to their potential applications in molecular electronics, spintronics, sensors, and so on. To this end, it is essential to tune the structural, electronic and spin properties of MPcs. Using the low-temperature scanning tunneling microscopy（LT-STM）,we demonstrate that the spin, chirality and adsorption site of Mn Pc on Au（111） surface can be tuned by hydrogen atoms.STM experiments and density functional theory（DFT） calculations reveal that the preferential adsorption sites for the Mn Pc molecules may switch from the fcc regions to the hcp regions on the Au（111） surface after a hydrogen atom is adsorbed on top of the central Mn ion of each Mn Pc molecule. Moreover, the molecular spin decreases from S = 3/2 to S = 1 and the molecule-substrate coupling is weakened after the adsorption of a hydrogen atom on a Mn Pc molecule,leading to the quenching of Kondo effect at 4.2 K. However, the molecular spin and Kondo effect can be recovered by local voltage pulse or sample heating. Adsorption of three hydrogen atoms on a Mn Pc molecule not merely lowers the molecular symmetry from 4-to 2-fold, but also breaks down the mirror symmetry of the entire adsorbate complex（molecule and surface）, thus rendering it to become chiral without any realignment at the surface. Dehydrogenation of the adsorbate by means of inelastic electron tunneling can also restore the mirror symmetry of the adsorbate complex.STM experiments as well as DFT calculations show that the chirality is actually imprinted into the molecular electronic system by the surface, i.e., the lowest unoccupied orbital is devoid of mirror symmetry. Our novel reversible spin and hand control scheme can be easily realized at single-molecule level, thus opening up a new avenue to broader applications based on the molecular electronic and spin states.

关 键 词：扫描隧道显微镜 金属酞菁 自旋态 手征性 

分 类 号：O562[理学—原子与分子物理]