【作者】 吴珂；

【导师】 何丕模；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2013， 博士

【摘要】 本文围绕着两种受纳米尺度调制的石墨烯结构及其相关结构生长展开研究。第一种结构是在Ru(0001)衬底上外延生长的石墨烯,由于与衬底的晶格失配而形成纳米尺度的摩尔超结构。这种石墨烯/Ru(0001)结构的特殊性表现在其电子结构受到纳米尺度的周期调制,进而呈现出纳米尺度周期分布的化学活性,可以作为进一步生长相关纳米结构的模版。第二种结构是石墨烯纳米带。作为准一维的石墨烯结构,纳米带在宽度上受到了量子限制。锯齿边的石墨烯纳米带会由于边缘的形状呈现金属性的边缘态,而扶手椅形的石墨烯纳米带的宽度变化会导致其带隙的变化。我们利用扫描隧道显微镜(STM)分别研究了以摩尔结构为模板组装锰纳米团簇的和组装有机分子的过程。单层石墨烯在Ru(0001)上(MLG/Ru(0001))形成12×12和另外两种有微小扭曲的摩尔超结构。我们比较了这三种摩尔超结构对于组装金属团簇的影响。在成核的最初阶段,我们观察了锰单原子、锰二聚体和锰三聚体在三种摩尔结构上表现出的几种不同的吸附模式。锰的单原子吸附在12×12结构的fcc区域中一个碳六元环的中心上方,锰的长对(long-pair)吸附在另两种有微小扭曲的摩尔结构的fcc/hcp区域边缘的atop位的碳原子正上方。随着锰覆盖度的增加,我们通过STM的观察发现,锰团簇在所有的三种摩尔结构上都表现出较为明显的对吸附位的选择性。锰团簇选择性最强的吸附区域是摩尔结构上的fcc区域,在这里可以观察到吸附在fcc区域的锰团簇形成规则的阵列,而且锰团簇的横向尺寸可以通过覆盖度进行调制。密度泛函理论(DFT)的计算表明,锰单原子在12×12结构上的吸附情况与STM得到的结果一致。另外计算还说明吸附在MLG/Ru(0001)结构上的锰原子表现出磁性,其磁矩约为3.79μβ。退火后,锰在MLG/Ru(0001)形成二维密排岛状结构,引起MLG/Ru(0001)重构,使石墨烯层整体抬升。同时,锰的岛状结构在石墨烯层之上形成,而非插层到石墨烯层之下,说明锰与石墨烯之间的相互作用同钴与石墨烯之间的相互作用非常不同。对于在石墨烯摩尔结构上组装铁酞菁分子的研究结果表明石墨烯摩尔结构的不同区域的反应活性差异使得分子的吸附具有一定的选择性。我们研究了在Ru(0001)衬底上采用由下至上(bottom-up)法合成扶手椅形石墨烯纳米带的过程。我们使用二溴联二蒽作为合成的前驱体。二溴联二蒽分子吸附到Ru(0001)表面时,存在两种相互垂直取向的吸附结构,其中一种取向沿着Ru(0001)的晶向,另一种取向与Ru(0001)的晶向夹30度角。在373K退火之后,沿着Ru(0001)晶向排布的石墨烯纳米带出现了。这些石墨烯纳米带的长度与30度转角的石墨烯摩尔超结构的晶格相匹配。这个30度转角石墨烯摩尔结构中的亚晶格取向与石墨烯纳米带中的亚晶格取向一致。这一结果表明石墨烯纳米带与衬底之间的相互作用较强。通过在473K进行退火,石墨烯纳米带的扶手椅形边缘发生脱氢过程。石墨烯纳米带通过侧向的连接过程结合成石墨烯纳米片,通过石墨烯纳米片亮度调制的表现可以确认碳-钌原子的相对位置关系。在673K退火后,那些碳-钌原子相对关系类似fcc/hcp区域的石墨烯纳米片和类似atop区域的石墨烯纳米片会相互结合在一起,形成连续的石墨烯小岛。更多还原

【Abstract】 In this thesis, we focused on investigations of templating of nano structures on monolayer graphene (MLG) on Ru(0001) and growth graphene nano structures on Ru(0001) with organic molecule as precursor.Disorientation between the epitaxially grown graphene and the Ru(0001) substrate results in the moire structure, which modulates the electronic structures of graphene with its period. Therefore, in this system the reactivity of graphene varies across the moire unit cell and promises ordered nanoclusters by selecting the proper nucleation sites on the graphene sheet.The graphene nanoribbon, as a qusi-1D structure, experiences quantum confinement on its width. Owing to their special edge shape, zigzag graphene nanoribbons can bear metallic edge states, and the band gap of armchair nanoribbons can be tuned with the width of ribbons.The processes of templating manganese nanoclusters and organic molecules with the moire structures were investigated by scanning tunneling microscopy (STM), respectively. It was found that the12×12moire structure and the other two distorted moires coexist when monolayer graphene grown on Ru(0001). At the initial stage of nucleation, different adsorption modes for Mn monomer, dimer and trimer guided by various moire periodicities were observed. Mn monomer was traped above the center of a carbon hexagon in the fcc region of the12x12moire structure, while Mn long-pair tends to dwell above the atop-carbon atoms at the edge of the fcc/hcp region of the other two distorted moires. Upon Mn coverage increasing, STM measurements revealed that Mn clusters exhibit detectable preference for adsorption sites on all the three different moires. The most favourable adsorption sites for Mn clusters are the fcc regions, where ordering of Mn clusters was observable, and the lateral size of the clusters are tunable with Mn coverage. A density functional theory (DFT) calculation showed an adsorption mode of Mn monomer on the12×12moire structure coincident with the STM results. The calculation also revealed that magnetism appears with a magnetic moment of3.79μβ for Mn monomer adsorption on MLG/Ru(0001). Emergence of2D Mn islands upon annealing results in uplifting of graphene layer by densely packed Mn islands. Formation of Mn islands on graphene instead of intercalation underneath graphene suggests that the interaction between Mn and graphene could be very different from that between Co and graphene. The investigation of adsorption of iron phthalocyanine molecules onto the moire structure revealed that the lateral variation of reactivity of the moire structure promises a distinct preference for adsorption sites of the molecules.The bottom-up fabrication of armchair graphene nanoribbons on Ru(0001) was investigated by using10,10’-dibromo-9,9’-bianthryl (DBBA) as precursor monomers. Upon deposition of DBBA on Ru(0001), the precursors adsorbed with their axes in two orthogonal directions, of which one is along Ru(0001) azimuths, the other is rotated with30degree with respect to Ru(0001) azimuths. Upon annealing at373K, graphene nanoribbons aligned along Ru(0001) azimuths emerge. Their lengths were trigged to the lattice of the30degree rotated graphene moire structure, whose sublattice possesses the same direction with that of the nanoribbon. These results suggest substantial interaction between graphene nanoribbons and the substrate. After annealing the sample at473K, dehydrogenation occured at the armchair edges of the nanoribbons, and graphene nano-flakes can be formed by the lateral attachment of the nanoribbons. The C-Ru registry of the graphene flakes on Ru(0001) can be identified with the appearing of the brightness modulation in the STM images. Further annealing of the sample at673K, the fcc/hcp-region-like flakes melted with the atop-region-like flakes, and coherent tiny graphene islands were formed.更多还原