Interaction and manipulation of bi adatoms on monolayer epitaxial graphene

The metal-graphene interaction can determine to what extent the graphene properties might be modified. Semimetal bismuth (Bi), being one of the most extensively studied heavy elements, has received considerable attention because of its unique electronic properties in reduced length scale. In this chapter, long-range electronic interaction between Bi adatoms deposited on monolayer epitaxial graphene (MEG) formed on a 4H-SiC (0001) substrate at room temperature (RT) has been studied. The introduction of the motivation and purpose of this work will be described in the first part of this chapter, followed by the detailed preparation methods of the MEG. The provision of large-area MEG makes the characterization and application of graphene-based devices become easier. The interaction and manipulation of Bi adatoms on MEG studied by scanning tunneling microscopy (STM) will be described in the second part of this chapter. We elucidate that the oscillatory interaction among Bi adatoms results from both the mediation of graphene Dirac-like electrons and the effect of the corrugated surface of SiC substrate. A series of structural transition of Bi adatoms, adsorbed on MEG at RT, is explored with Bi coverage-variation. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such growth modes are strongly affected by the corrugated substrate. Additionally, upon Bi deposition, some charge transfers between Bi and graphene occurs and a characteristic peak can be observed in the scanning tunneling spectrum (STS), reflecting by the distinctive electronic structure of Bi adatoms. With annealing to ~500K, 2D triangular Bi islands aggregate into Bi nanoclusters of uniform size of three to four adatoms. A well-controlled fabrication and manipulation method is demonstrated. Finally, first-principles calculations are conducted to investigate the substrate effect of Bi-adsorbed monolayer (ML) graphene. The slightly deformed ML graphene, corrugated buffer layer, and six-layered substrate are all simulated. Interactions between the buffer layer and graphene dominate the hexagonal Bi adsorption patterns. Specially, we demonstrate that the room temperature stability comes from a buffer-layer-induced energy barrier. The density of states exhibits low-lying dip and peak, as observed in the experimental measurements. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on graphene and related systems, which are useful in realizing graphene-based electronic, energy, sensor, and spintronic devices.