We demonstrated a novel method to obtain charge neutral quasi-free-standing graphene on SiC (0001) from the buffer layer using fluorine from a molecular source, fluorinated fullerene (C(60)F(48)). The intercalated product is stable under ambient conditions and resistant to elevated temperatures of up to 1200 °C. Scanning tunneling microscopy and spectroscopy measurements are performed for the first time on such quasi-free-standing graphene to elucidate changes in the electronic and structural properties of both the graphene and interfacial layer. Novel structures due to a highly localized perturbation caused by the presence of adsorbed fluorine were produced in the intercalation process and investigated. Photoemission spectroscopy is used to confirm these electronic and structural changes.

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Charge transfer dynamics across the interface of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) organic molecules and the reduced rutile TiO 2 (110) 1 × 1 surface has been investigated using core-hole clock implementation of resonant photoemission spectroscopy (RPES). It is found that ultrafast charge transfer from PTCDA molecules to TiO 2 substrate takes place on the time scale of 8−20 fs due to their strong electronic coupling. Moreover, the charge transfer time scale at the PTCDA/TiO 2 (110) interface shows evident orientational dependence which varies with the molecular site owing to different electronic coupling strengths.

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The initial growth of bismuth (Bi) on epitaxial graphene (EG) on SiC(0001) at low deposition rates has been investigated using low temperature scanning tunneling microscopy (LT-STM) and synchrotron-based photoemission spectroscopy (PES). PES measurements reveal an islanding growth mode of Bi on EG due to weak interfacial interactions. LT-STM measurements show that Bi forms onedimensional (1D) 4-monolayer-thick nanoribbons on EG with the orientation relationship of Bi(011̅ 2) ∥ EG(0001) and Bi⟨112̅ 0⟩ aligned well with EG⟨112̅ 0⟩. Scanning tunneling spectroscopy (STS) results reveal the semiconducting nature of such Bi nanoribbons. ■ INTRODUCTIONBismuth (Bi) is a group-V semimetal with a charge carrier concentration far less than normal metals, having small effective electron mass and long Fermi wavelength (∼40 nm at room temperature). 1−3 Because of quantum and finite size effects, Bi nanostructures exhibit interesting physical properties, such as semimetal to semiconductor transition, 4−6 high thermoelectric efficiency, 7 and superconductivity. 8 Additionally, strong spin− orbit coupling on Bi surfaces results in a significant and anisotropic splitting of the surface-state bands, indicating possible applications in spintronics. 9,10 Details of structural and electronic properties of low-index surfaces of bulk Bi can be found in the review by Hofmann. 1 As the electronic properties of Bi nanostructures depend significantly on their structural properties, there have been numerous investigations on their growth. For example, on highly ordered pyrolitic graphite (HOPG), Bi forms islands with striped surface features at a preferred height and with the orientation relationship Bi(011̅ 2) ∥ HOPG(0001) as well as with a preference for Bi⟨112̅ 0⟩ ∥ HOPG⟨101̅ 0⟩. 11−15 Graphene, a single layer of graphite, has attracted great interest in both academia and industry due to its superlative electronic properties 16−19 such as high charge carrier mobility even at high charge carrier concentration at room temperature (RT) 20 and long spin relaxation length up to micrometer scale at RT. 21 Epitaxial graphene (EG) on SiC 22−24 has been proposed as a possible platform for the development of graphene-based electronics. 23−27 There are numerous investigations of adsorbates on graphene, 28−34 for instance, atomic hole doping of EG by simple atomic adsorbates. 29 ARPES measurements have shown that Bi is able to shift the Dirac point toward the Fermi level (E F ), i.e., reducing the n-type doping from the substrate, 29 even though density functional theory (DFT) calculations reveal that the isolated Bi atom is weakly physisorbed on EG. 35 Therefore, understanding the interactions between adsorbates and graphene in real space at atomic level is very important for fundamental understanding and possible applications.In this work, the structural and electronic properties of Bi thin films on EG are systematically investigated using low temperature scanning tunneling microscopy (LT-STM) and synchrotron-based photoemission spectroscopy (PES...