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Dirac electrons in a dodecagonal graphene quasicrystal
Ahn, Sung Joon,Moon, Pilkyung,Kim, Tae-Hoon,Kim, Hyun-Woo,Shin, Ha-Chul,Kim, Eun Hye,Cha, Hyun Woo,Kahng, Se-Jong,Kim, Philip,Koshino, Mikito,Son, Young-Woo,Yang, Cheol-Woong,Ahn, Joung Real American Association for the Advancement of Scienc 2018 Science Vol.361 No.6404
<P>Quantum states of quasiparticles in solids are dictated by symmetry. We have experimentally demonstrated quantum states of Dirac electrons in a two-dimensional quasicrystal without translational symmetry. A dodecagonal quasicrystalline order was realized by epitaxial growth of twisted bilayer graphene rotated exactly 30 degrees. We grew the graphene quasicrystal up to a millimeter scale on a silicon carbide surface while maintaining the single rotation angle over an entire sample and successfully isolated the quasicrystal from a substrate, demonstrating its structural and chemical stability under ambient conditions. Multiple Dirac cones replicated with the 12-fold rotational symmetry were observed in angle-resolved photoemission spectra, which revealed anomalous strong interlayer coupling with quasi-periodicity. Our study provides a way to explore physical properties of relativistic fermions with controllable quasicrystalline orders.</P>
Electronic Structure of Graphene Grown on a Hydrogen-terminated Ge (110) Wafer
Sung Joon Ahn,Hyun Woo Kim,Ishwor Bahadur Khadka,Krishna Bahadur Rai,Joung Real Ahn,Jae-Hyun Lee,Seog Gyun Kang,Dongmok Whang 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.5
Using angle-resolved photoemission spectroscopy, we studied the electronic structure of graphene grown on a Ge (110) wafer, where a single-crystal single-layer graphene was recently grown using chemical vapor deposition. The growth mechanism of the single-layer single-crystal graphene was related to the hydrogen termination of the Ge (110) surface. To further understand the growth mechanism, we measured the electronic structure of the graphene-covered Ge (110) wafer in a vacuum as a function of the increasing temperature, which led to a deintercalation of the hydrogen atoms. Furthermore, we measured the electronic structure after the reintercalation of the hydrogen atoms between the Ge substrate and graphene. These findings show that hydrogen is intercalated between the Ge substrate and graphene after the growth of graphene using chemical vapor deposition.
Origin of the Modied Electronic Properties of Au Formed on Pentacene
정석민,허혜은,임규욱,Joung-Real Ahn,송우석,홍준용,박종윤,강태희 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
A Au lm formed on a pentacene layer, as a model system of a metal contact on a pentacenebased field-effect transistor, has been investigated. Unexpected pentacene derivatives and coarse morphology depending on the Au thickness are suggested as origins of the abnormal electronic structure of the Au film and the poor reproducibility of organic-based devices. The morphology of the Au film shows a strong dependency on the Au coverage. At 600 A of Au, a lift of the pentacene layer is shown as a result of deformation of the cracked Au film induced by a relaxation of the intergranular stresses accumulated during the growth process.
B. G. Shin,D. H. Oh,Joung Real Ahn 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.5
The relation of orbital hybridization between graphene and an adsorbate to the atomic and electronic structures of monolayer graphene was studied using first-principles calculations, where hydrogenated graphene was used as a prototype. The atomic and electronic structures of hydrogenated graphene were calculated as functions of the distance between graphene and hydrogen. The hybridization gap between the s orbital of hydrogen and the π orbital of graphene was tuned by changing the distance. The effect of the hybridization gap on the energy gap at the Dirac energy and the atomic structure deformation of graphene was schematically investigated, particularly when hydrogen breaks the in-plane symmetry.
Designed Three-Dimensional Freestanding Single-Crystal Carbon Architectures
Park, Ji-Hoon,Cho, Dae-Hyun,Moon, Youngkwon,Shin, Ha-Chul,Ahn, Sung-Joon,Kwak, Sang Kyu,Shin, Hyeon-Jin,Lee, Changgu,Ahn, Joung Real American Chemical Society 2014 ACS NANO Vol.8 No.11
<P>Single-crystal carbon nanomaterials have led to great advances in nanotechnology. The first single-crystal carbon nanomaterial, fullerene, was fabricated in a zero-dimensional form. One-dimensional carbon nanotubes and two-dimensional graphene have since followed and continue to provide further impetus to this field. In this study, we fabricated designed three-dimensional (3D) single-crystal carbon architectures by using silicon carbide templates. For this method, a designed 3D SiC structure was transformed into a 3D freestanding single-crystal carbon structure that retained the original SiC structure by performing a simple single-step thermal process. The SiC structure inside the 3D carbon structure is self-etched, which results in a 3D freestanding carbon structure. The 3D carbon structure is a single crystal with the same hexagonal close-packed structure as graphene. The size of the carbon structures can be controlled from the nanoscale to the microscale, and arrays of these structures can be scaled up to the wafer scale. The 3D freestanding carbon structures were found to be mechanically stable even after repeated loading. The relationship between the reversible mechanical deformation of a carbon structure and its electrical conductance was also investigated. Our method of fabricating designed 3D freestanding single-crystal graphene architectures opens up prospects in the field of single-crystal carbon nanomaterials and paves the way for the development of 3D single-crystal carbon devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-11/nn504956h/production/images/medium/nn-2014-04956h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn504956h'>ACS Electronic Supporting Info</A></P>