• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.6
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• pp.510-514
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• 2011

Based on first-principles LCAO method, we study the electronic and atomic structures of DNA nucleobases adenine (A), thymine (T), guanine (G), and cytosine (C) adsorbed on graphene surfaces. The ${\pi}-{\pi}$ stacking interactions between graphene and nucleobases lead to the bilayer geometries similar to the Bernal stacked graphite. Through the density of states and charge density analyses, it is found that nucleobases are physisorbed on graphene by dispersive interactions with negligible charge exchange. Our calculations reproduce the atomic structures obtained in previous plane wave calculations accurately with much less computation, and well describe the delocalized ${\pi}-{\pi}$ interactions in graphene-nucleobases system, indicating that the LCAO method is very efficient for investigating graphene-bio systems.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.446-449
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• 2014

Carbon Nanotube (CNT) have been intensively investigated since they have been considered as building blocks of nanoscience and nanotechnology. Theoretical and computational studies on CNTs have revealed their physical and chemical properties and helped researchers build various experimental devices to study them in depth. However, there have been only few systematic studies on detailed changes in electronic structures of CNTs due to geometrical structure modifications. In this regard, it is necessary to perform systematic investigations of the modifications in electronic structures of CNTs, as their geometrical configurations are altered, using the first-principles density functional theory. In other words, it is essential to determine the true equilibrium structure of CNTs. In this work, we considered the different atomic configurations by maintaining their symmetries, but changing all the inequivalent bonding types one by one. Furthermore, as for CNTs, for example, the way the graphene sheet is wrapped is represented by a pair of indices (n,m) and electronic structures of CNTs vary depending on different indices. Our results suggest all the significant couplings between electronic and geometric structures in CNTs.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.307-307
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• 2011

Graphene is the hottest topic in condensed-matter physics due to its unusual electronic structures such as Dirac cones and massless linear dispersions. Graphene can be epitaxially grown on various metal surfaces with chemical vapor deposition processes. Such epitaxial graphene shows modified electronic structures caused by substrates. Here, local geometric and electronic structures of graphene grown on Ru(0001) will be presented. Scanning tunneling microscopy (STM) and spectroscopy (STS) was used to reveal energy dependent atomic level topography and position-dependent differential conductance spectra. Both topography and spectra show variations from three different locations in rippled structures caused by lattice mismatch between graphene and substrate. Based on the observed results, structural models for graphene on Ru(0001) system were considered.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.08a
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• pp.143.1-143
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• 1998

• Journal of Magnetics
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• v.11 no.3
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• pp.135-138
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• 2006

We studied local anodization on permalloy $(Ni_{80}Fe_{20})$ thin film with an atomic force microscope (AFM), which was performed by applying a voltage between the permalloy sample and conductive AFM tip. Comparing with anodization on Si (100) substrate, nano-structures on the permalloy thin film was fabricated with low processability.In order to improve the processability on the permalloy thin film, we used dot-fabrication method, thatis, a conductive AFM probe was kept at a position on the film during the anodization process.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.164-164
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• 2000

Since Au-Pt alloys have various atomic structures depending upon composition and annealing temperature, it is very interesting to investigate the electronic structures of alloys. We studied the changes of the electronic structure I the Au-Pt alloys by x-ray absorption near edge spectroscopy (XANES). Two kinds of Au-Pt alloy samples were prepared by arc melting methods and ion-beam-mixing technique. The Pt L2, 3-edge and Au L2, 3-edge X-ray absorption spectra (XPS) were measured with the electron yield mode detector at the 3C1 beam line of the Pohang Light Source (PLS). It was found that there was a substantial decrease in the area of the Pt L2, 3 white lines compared with that of pure Pt. The observed decrease in white line area was attributed to an increase in the number of pure Pt. The observed decrease in white line area was attributed to an increase in the number of 5d-electrons at the Pt site upon alloy formation. However, the Au L2, 3 edge spectra for Au-Pt alloys are all similar to that of pure Au. This implies that the 5d hole count of Au is not changed by alloy formation with Pt.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.287-289
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• 2013

How the different thickness of thin films of black-P has an effect on its electronic band structure and structure has been studied by using SIESTA code. Although the interaction between the thin films has something to do with band reduction, it does not affect the inter-atomic distance between two nearest neighbour puckered layers.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.472-474
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• 2014

Carbon nanotubes (CNTs) have been intensively investigated since they have been considered as building blocks of nanoscience and nanotechnology. Theoretical and computational studies on CNTs have revealed their physical and chemical properties and helped researchers build various experimental devices to study them in depth. However, there have been only few systematic studies on detailed changes in electronic structures of CNTs due to geometrical structure modifications. In this regard, it is necessary to perform systematic investigations of the modifications in electronic structures of CNTs, as their geometrical configurations are altered, using the first-principles density functional theory. In other words, it is essential to determine the true equilibrium structure of CNTs. We are going to construct different atomic configurations of each nanotube by maintaining the original symmetries, but changing all the other bonding types one by one. Furthermore, as for CNTs, for example, the way the graphene sheet is wrapped is represented by a pair of indices (n,m) and electronic structures of CNTs vary depending on different indices. Therefore, we plan to study and discuss all the significant couplings between electronic and geometric structures in CNTs.

• Applied Microscopy
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• v.46 no.4
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• pp.217-226
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• 2016

Monolayer hexagonal boron nitride (h-BN) is a phenomenal two-dimensional material; most of its physical properties rival those of graphene because of their structural similarities. This intriguing material has thus spurred scientists and researchers to develop novel synthetic methods to attain scalability for enabling its practical utilization. When probing the growth behaviors and structural characteristics of h-BN, the use of appropriate characterization techniques is important. In this review, we detail the use of scanning and transmission electron microscopies to investigate the atomic configurations of monolayer and bilayer h-BN grown via chemical vapor deposition. These advanced microscopy techniques have been demonstrated to provide intimate insights to the atomic structures of h-BN, which can be interpreted directly or indirectly using known growth mechanisms and existing theoretical calculations. This review provides a collective understanding of the structural characteristics and defects of synthetic h-BN films and facilitates a better perspective toward the development of new and improved synthesis techniques.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.147-147
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• 2000

Chemisorption of oxygen molecules on the Si(111)-(7x7) surface has been studied extensively as a model for the initial-stage oxidation of the surface. The basic step to the surface oxidation is the dissociation of the adsorbed O2 molecules, but the dissociation procedure and the atomic structure of the reaction products still remains as a subject of debates. We present here density-functional theory calculations on the initial-stage oxidation states of the Si adatom site for all possible dissociation configurations that can be generated by multiple O2 reactions. We determine the equilibrium structures and analyze their electronic and vibrational properties in comparison with measured UPS, XPS, and EELS spectra. The O(ad) atom bonded on top of the Si adatom is always less stable than the O(ins) atom inserted into one of the adatom backbonds. Our electronic and vibrational analysis demonstrates further that the O(ad) and O(ins) atoms account well for the metastable and stable features in previous experiments, respectively. Moreover, the calculated decay pathways of the metastable structures and the comparison of the calculated O ls core-level shifts with XPS data provides a convincing argument in unambiguously identifying the experimental metastable and stable structures, thereby making it possible to build a correct atomic-scale picture of the initial-stage oxidation process on this surface.