Electronic structure and magnetism of ultrathin transition metal-graphene layered systems

本研究项目的主题是研究金属衬底上石墨烯层的结构和电子特性，通过在石墨烯和衬底之间插入贵金属和过渡金属以及在石墨烯覆盖层上吸附各自的金属来修饰(i)。石墨烯层，即六边形有序碳原子单层，由于二维狄拉克-费米子几乎垂直的带交叉引起的电子特性的特殊性，在最近的过去引起了相当大的兴趣。这些性质受到化学环境的强烈影响，即电荷转移、自旋极化和键合维度，并在文献中讨论了石墨烯基结构作为自旋滤波器和自旋场效应晶体管的可能应用。另一方面，即使是单层石墨烯也可以作为表面和薄膜化学钝化的有效保护层，而石墨烯表面可以用作金属团簇生长的纳米基板。所有这些方面都将在本项目的框架内进行调查。石墨烯层将在超高真空条件下通过吸附在非反应性W（110）、Rh（111）和Ni（111）表面的丙烯热裂解原位制备。随后，石墨烯层将通过热沉积贵金属（Cu, Ag, Au）和晚期过渡金属（Fe, Co, Ni）进行修饰，然后进行热退火，其中作为温度的函数，要么在石墨烯和衬底之间插入金属层，要么在石墨烯表面上生长有序的薄膜和簇。结构表征将通过扫描隧道显微镜（STM）和电子衍射进行。电子结构将通过角度和自旋分辨光发射和x射线吸收（近边缘结构，NEXAFS，以及磁二色性，XMCD）研究，特别关注层状结构的磁性。这些实验研究将伴随着理论研究：在密度泛函理论（DFT）能带结构的基础上，计算不同样品几何形状的局部态密度、磁矩和总能量。

Subject of the present research-project is an investigation of the structural and electronic properties of graphene-layers on metallic substrates, modified (i) by intercalation of noble- and transition metals between graphene and substrate and (ii) adsorption of respective metals on top of the graphene overlayer. Graphene layers, i.e. monolayers of hexagonally ordered carbon atoms, have attracted considerable interest in the recent past due to peculiarities of the electronic properties caused by almost vertical Fermi-level crossings of bands as characteristic for two-dimensional Dirac-fermions. These properties are strongly influenced by chemical environment, i.e. by charge-transfer, spin polarization, and dimensionality of bonding, and possible applications of graphene-based structures as spin filters and spin field-effect transistors were discussed in the literature. On the other hand, even monolayers of graphene act as effective protection layers for the chemical passivation of surfaces and thin films, while the surface of graphene may be used as nanomesh substrate for the growth of metallic clusters. All these aspects will be investigated in the framework of the present project. Graphene layers will be prepared in situ under ultra-high vacuum conditions by thermal cracking of propene adsorbed on non-reactive W(110), Rh(111), and Ni(111) surfaces. Subsequently, the graphene layers will be modified by thermal deposition of noble (Cu, Ag, Au) and late transition metals (Fe, Co, Ni) followed by thermal annealing, where as a function of temperature either intercalation of metal layers between graphene and substrate or growth of ordered films and clusters on top of the graphene surface are expected. Structural characterization will be made by means of scanning tunnel microscopy (STM) and electron diffraction. The electronic structure will be studied by means of angle- and spin-resolved photoemission and x-ray absorption (near-edge structure, NEXAFS, as well as magnetic dichroism, XMCD) focusing particularly on the magnetic properties of the layered structures. These experimental investigations will be accompanied by theoretical studies: On the basis of density functional theory (DFT) band structures, local densities of states, magnetic moments and total energies will be calculated for different sample geometries.