Kyung-Han Yun

Electronic Properties of Transition‐Metal‐Decorated Silicene

The electronic properties of 3d transition metal (TM)-decorated silicene were investigated by using density functional calculations in an attempt to replace graphene in electronic applications, owing to its better compatibility with Si-based technology. Among the ten types of TM-doped silicene (TM-silicene) studied, Ti-, Ni-, and Zn-doped silicene became semiconductors, whereas Co and Cu doping changed the substrate to a half-metallic material. Interestingly, in cases of Ti- and Cu-doped silicene, the measured band gaps turned out to be significantly larger than the previously reported band gap in silicene. The observed band-gap openings at the Fermi level were induced by breaking the sublattice symmetry caused by two structural changes, that is, the Jahn-Teller distortion and protrusion of the TM atom. The present calculation of the band gap in TM-silicene suggests useful guidance for future experiments to fabricate various silicene-based applications such as a field-effect transistor, single-spin electron source, and nonvolatile magnetic random-access memory.

Atomic behavior of carbon atoms on a Si removed 3C-SiC (111) surface during the early stage of epitaxial graphene growth

The understanding of the formation of graphene at the atomic scale on Si-terminated 3C-SiC for obtaining high-quality graphene sheets remains elusive, although epitaxial graphene growth has been shown to be a well-known method for economical mass production of graphene/SiC heterojunctions. In this paper, the atomic behavior of carbon atoms on a Si removed 3C-SiC (111) surface for the formation of graphene buffer layer during the early stage of epitaxial graphene growth was investigated using a molecular dynamics simulation. Observation of the behavior of the remaining carbon atoms on the Si-terminated 3C-SiC (111) surface after removal of the silicon atoms revealed that graphene clusters, which were formed by sp2-bonded carbon atoms, start to appear at annealing temperatures higher than 1300 K. Our simulations indicated that the structural stability of the whole system increased as the number of sp2-bonded carbon atoms on the Si-terminated 3C-SiC (111) surface increased. It was also found that the diffusi...

Graphene Monoxide Bilayer As a High-Performance on/off Switching Media for Nanoelectronics.

The geometries and electronic characteristics of the graphene monoxide (GMO) bilayer are predicted via density functional theory (DFT) calculations. All the possible sequences of the GMO bilayer show the typical interlayer bonding characteristics of two-dimensional bilayer systems with a weak van der Waals interaction. The band gap energies of the GMO bilayers are predicted to be adequate for electronic device application, indicating slightly smaller energy gaps (0.418-0.448 eV) compared to the energy gap of the monolayer (0.536 eV). Above all, in light of the band gap engineering, the band gap of the GMO bilayer responds to the external electric field sensitively. As a result, a semiconductor-metal transition occurs at a small critical electric field (EC = 0.22-0.30 V/Å). It is therefore confirmed that the GMO bilayer is a strong candidate for nanoelectronics.

Strain-Controllable Magnetism in Co Decorated Pyridinic N-Doped Graphene

An external strain is suggested as an effective means to finely control the magnetic properties of a candidate medium for future spintronics devices. To demonstrate the potential of this concept, the biaxial strain effects on the magnetic moment of Co adatom on pyridinic N-doped graphene (PNG) sheet were investigated using density functional theory calculations. Under the strain from -5% to 5%, the magnetic moment of the Co adatom on PNG was increased continuously from 1.72 to 1.95 μB. Also, Co adatoms are expected to be dispersed on the PNG surface without metal clustering in this range of applied strain due to its strong binding with the pyridinic nitrogen defects. From these results, it is anticipated that reliable control of magnetism in Co decorated PNG system is available by use of an external strain.

Configuration Dependency of Attached Epoxy Groups on Graphene Oxide Reduction: A Molecular Dynamics Simulation

The atomic behavior of epoxy groups on a graphene oxide sheet was observed during high thermal heat annealing using a reactive force-field based on molecular dynamics simulations. We found the oxygen-containing functional groups interplay with each other and desorbed from the graphene oxide sheet by a form of O2 gas if they were initially in close distance. Through comparing reduction results of graphene oxide with different densities of the nearest neighboring epoxy pairs, we confirmed that the amount of released O2 gas has a clear tendency to increase with a higher density of epoxy pairs in close distance on a graphene oxide sheet.

Atomic-Scale Simulations of Early Stage of Oxidation of Vicinal Si(001) Surfaces Using a Reactive Force-Field Potentials

The early stages of the oxidation process on vicinal Si(001) surfaces were studied at the atomic scale using reactive-force field-based molecular dynamics simulations. Oxygen molecules at step edges on the vicinal Si(001) surface showed higher reactivity than those on flat terraces. In macroscopic simulations of oxidation on vicinal Si(001) surfaces with different miscut angles (0°, 5.5°, 10.5°), we found that the initiation of oxidation with higher miscut angles was earlier than with lower angles. These results clearly show that a high density of step edges on the vicinal Si surface accelerates the initial oxidation.