Jong Keon Yoon

Electronic structures of one-dimensional metal–molecule hybrid chains studied using scanning tunneling microscopy and density functional theory

The electronic structures of self-assembled hybrid chains comprising Ag atoms and organic molecules were studied using scanning tunneling microscopy (STM) and spectroscopy (STS) in parallel with density functional theory (DFT). Hybrid chains were prepared by catalytic breaking of Br-C bonds in 4,4″-dibromo-p-terphenyl molecules, followed by spontaneous formation of Ag-C bonds on Ag(111). An atomic model was proposed for the observed hybrid chain structures. Four electronic states were resolved using STS measurements, and strong energy dependence was observed in STM images. These results were explained using first-principles calculations based on DFT.

Polymorphic porous supramolecular networks mediated by halogen bonds on Ag(111)

Intermolecular structures of porous two-dimensional supramolecular networks are studied using scanning tunnelling microscopy combined with density functional theory calculations. The local configurations of halogen bonds in polymorphic porous supramolecular networks are directly visualized in support of previous bulk crystal studies.

Metal-supported high crystalline Bi2Se3 quintuple layers

Atomically flat thin films of Bi(2)Se(3) were grown on Au(111) metal substrate using molecular beam epitaxy. Hexagonal atomic structures and quintuple layer steps were observed at the surfaces of grown films using scanning tunneling microscopy. Multiple sharp peaks from (003) family layers were characterized by x-ray diffraction measurements. The atomic stoichiometry of Bi and Se was considered using x-ray photoemission spectroscopy. Moiré patterns were obtained at the surfaces of one quintuple layer films due to lattice mismatch between Bi(2)Se(3) and Au. Our experiments suggest that Au is a reasonable material for electrodes in Bi(2)Se(3) devices.

Recovery and local-variation of Dirac cones in oxygen-intercalated graphene on Ru(0001) studied using scanning tunneling microscopy and spectroscopy

Methods to decouple epitaxial graphene from metal substrates have been extensively studied, with anticipation of observing unperturbed Dirac cone properties, but its local electronic structures were rarely studied. Here, we investigated the local variations of Dirac cones recovered using oxygen intercalation applied to epitaxial graphene on Ru(0001) using scanning tunneling microscopy and spectroscopy (STM and STS). New V-shaped features, which appear in the STS data at the oxygen-intercalated graphene regions, are attributed to the signatures of recovered Dirac cones. The Dirac point energy was observed at 0.48 eV below the Fermi level, different from previous photoemission results because of different oxygen coverages. The observed spatial variations of Dirac point energy were explained by the weakly protruding network structures caused by a small net strain in graphene. Our study shows that oxygen-intercalated graphene provides an excellent platform for further graphene research at the nano-meter scale with unperturbed Dirac cones.