• Applied Microscopy
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• v.45 no.3
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• pp.115-118
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• 2015

In this review paper, I'd like to introduce the basics of angle-resolved photoemission spectroscopy (ARPES) and some of my results taken at the Pohang Accelerator Laboratory (PAL), the only synchrotron radiation in South Korea. The results show that ARPES is very useful, in particular, for studying two-dimensional materials. It looks like a microscope in momentum space similar to transmission electron microscope imaging atoms in real space.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.82-82
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• 2012

Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to investigate the electronic structure of a single-crystalline solid. After the development of a two-dimensional electron detector, it became a basic experimental method in solid state physics comparable to other powerful tools such as x-ray and neutron scatterings. In this tutorial, I talk briefly on the basic principle of ARPES and its recent and future direction of development.

• Journal of the Korean Magnetics Society
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• v.22 no.6
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• pp.228-233
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• 2012

Magnetic properties of a solid are determined by the quantum mechanical states of valence electrons. Spin-polarized angle-resolved photoemission spectroscopy (SP-ARPES) is a powerful tool to probe the electronic states in a solid and provides valuable information on magnetic properties of a solid. In this article, brief introduction to SP-ARPES and its applications are provided.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.7-19
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• 2014

Since the discovery of iron-based superconductors in 2008, extensive and intensive studies have been performed to find the microscopic theory for the high temperature superconductivity in the materials. Electronic structure is the basic and essential information that is needed for the microscopic theory. Experimentally, angle resolved photoelectron spectroscopy (ARPES) is the most direct tool to obtain the electronic structure information, and therefore has played a vital role in the research. In this review, we review what has been done so far and what is needed to be done in ARPES studies of iron-based superconductors in search of the microscopic theory. This review covers issues on the band structure, orbital order/fluctuation, and gap structure/symmetries as well as some of the theories.

• Vacuum Magazine
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• v.5 no.2
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• pp.10-17
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• 2018

Chalcogenide and oxide heterostructures have been studied as a next-generation electronic materials, due to their interesting electronic properties, such as direct bandgap semiconductor, ferroelectricity, ferromagnetism, superconductivity, charge-density waves, and metal-insulator transition, and their modification near heterointerfaces, so called, electronic reconstruction. An angle-resolved photoemission spectroscopy (ARPES) is a powerful technique to unveil such novel electronic phases in detail, especially combined with high quality thin film preparation methods, such as, molecular beam epitaxy and pulsed laser deposition. In this article, the recent ARPES results in chalcogenide and oxide thin films will be introduced.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.177-180
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• 1997

Low Energy Electron Diffraction (LEED) apparatus was made to confirm the surface structure and to determine the direction of the structure for the Angle Resolved Ultraviolet Photoemission Spectroscopy(ARUPS) study. To determine the parameters needed for the design of the apparatus, computer simulation was used. Our LEED has 3 grids. The distance between sample and sccreen is 75 mm, and the viewing angle is $80^{\circ}$. The LEED apparatus was tested by investigating the Si(001) and $Al_2O_3$(0001) surface.

• Vacuum Magazine
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• v.3 no.4
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• pp.19-23
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• 2016

Angle resolved photoemission spectroscopy (ARPES) is a powerful technique which can directly visualize the electronic structure of solid in detail including many-body interaction information. However, ARPES has a certain limitation in applying control parameters such as doping or pressure, which helps to dig out the clue to understand the desired phenomena or the target system. During ARPES experiment, the control parameter is the temperature only. Other parameters especially electric- and magnetic- field cannot be applied. Recently introduced surface-electron doping technique highlights new avenue to overcome such limitation. In this article, starting from introducing basic concepts of ARPES and its current status, the power of new technique will be demonstrated when it is combined to ARPES by introducing recent results on iron based superconductors.

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.83-87
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• 1992

Rencently, angle-resolved ultraviolet photoemission measurements of the Fermi surface contours for Mo(011) and W(011) are reported. The electron contour of W(011) is expanded upon hydrogen adsorption, which implies that the surface states consisting of electron pockets are shifted to higher binding energy. This phenomena can be explained by the band flattening. We explained here the reconstruction of W(011) surface induced by adsorption of hydrogen in terms of band flattening of surface states with a combination of S. E. Trullinger long range dipole-dipole interaction force and Kohn anomaly.

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.14-17
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• 2016

Annealing as-grown electron-doped cuprates under a low oxygen-partial-pressure condition is a necessary step to achieve superconductivity. It has been recently found that the so-called protect annealing results in much better superconducting properties in terms of the superconducting transition temperature and volume fraction. In this article, we report on angle-resolved photoemission spectroscopy studies of a protect-annealed electron-doped cuprate $Pr_{0.9}La_{1.0}Ce_{0.1}CuO_4$ on annealing condition dependent superconducting and pseudo-gap properties. Remarkably, we found that the one showing a better superconducting property possesses almost no pseudo-gap while others have strong pseudo-gap feature due to an anti-ferromagnetic order.

• Applied Science and Convergence Technology
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• v.27 no.5
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• pp.90-94
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• 2018

The electron band structure of manganese-adsorbed graphene on an SiC(0001) substrate has been studied using angle-resolved photoemission spectroscopy. Upon introducing manganese atoms, the conduction band of graphene, that is observed in pristine graphene indicating intrinsic electron-doping by the substrate, completely disappears and the valence band maximum is observed at 0.4 eV below Fermi energy. At the same time, the slope of the valence band decreases by the presence of manganese atoms, approaching the electron band structure calculated using the local density approximation method. The former provides experimental evidence of the formation of nearly free-standing graphene on an SiC substrate, concomitant with a metal-to-insulator transition. The latter suggests that its electronic correlations are efficiently screened, suggesting that the dielectric property of the substrate is modified by manganese atoms and indicating that electronic correlations in grpahene can also be tuned by foreign atoms. These results pave the way for promising device application using graphene that is semiconducting and charge neutral.