층상형 칼코게나이드 박막의 자발적 반데르발스 에피탁시와 구조적 특성연구

황재열 한국물리학회 2021 새물리 Vol.71 No.4

In the layer-structured Bi-Sb-Te (BST) pnictogen chalcogenide film grown on a Al2O3 substrate by using spontaneous van der Waals epitaxy, a structurally correlated in-plane orientation between the 2D BST film and the 3D substrate was found. In order to elucidate the origin of such a peculiar structural feature, we confirmed that well-matched stacking at the van der Waals hetero-interface could be induced by the similar atomic arrangements and surface topographies of Te monolayers. Particularly, the c axis lattice parameter of the BST film was individually manipulated by altering the growth rate of spontaneous van der Waals epitaxy. We found that such a change could be generated by variations in the van der Waals interfaces between BST quintets in a layer-structured pnictogen chalcogenide. 본 연구에서는 자발적 반데르발스 에피탁시 (spontaneous van der Waals epitaxy) 로 Al2O3 위에성장한 층상형 칼코게나이드 Bi-Sb-Te (BST) 박막에서 관찰되는 일정한 in-plane 정렬이 일어나는원인을 규명하고 2차원 박막의 인위적인 구조조작을 통해 구조-물성 상관관계를 조사하였다. 2 차원 칼코게나이드 BST 박막과 3차원 Al2O3 기판과의 이종 계면은 반데르발스 결합이 존재함에도불구하고 2차원 박막의 a b plane 격자 정렬이 특정한 기판 배향에 맞추어 성장하게 되는데 이러한특성은 기판과 박막 사이의 반데르발스 이종계면에 존재하는 Te단원자층들 간의 원자 정렬과 표면형상의 영향으로 구조적으로 잘 맞물리는 층 쌓기 (stacking) 에 의해 발생하는 것으로 확인되었다. 또한, 칼코게나이드 박막의 성장을 제어함으로써 층상형 pnictogen chalcogenide 결정구조내에 존재하는 BST quintet들 간의 반데르발스 계면 변화를 유도하여 c 축 격자 크기를 선택적으로 조절할 수 있었다.

Ferroelectric and Dielectric Behaviors of PLZT/PZT multi-layered Thin Films Prepared by Sol-Gel Method

황재열,Chae-Ryong Cho,정세영 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Pb(Zr0:3,Ti0:7)O3 (PZT) and (La0:12,Pb0:88)(Zr0:3,Ti0:7)O3 (PLZT) thin lms have been prepared by sol-gel method and characterized by x-ray diractometer, scanning electron microscopy (SEM) and atomic force microscope (AFM). The eects of various stacking and annealing process of PLZT/PZT multi-layered thin lms related to the structural, ferroelectric and dielectric properties were investigated. It was found that PLZT/PZT multi-layered thin lms have loss tangent smaller than that of multi-layered PLZT thin lm and have similar dielectric constant. The crystallographic orientation of the PLZT/PZT thin lms as well as correlations between surface morphologies and electrical properties were studied.

Epitaxial growth and structural characterization of transparent conducting ZnO:Al thin film deposited on GaN substrate by rf magnetron sputtering

황재열,조채용,이상아,정세영 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2

Transparent conducting oxide Al-modified (2 wt.%) ZnO (AZO) was deposited on a GaN/Al2O3 substrate by rf magnetron sputtering at a substrate temperature of 400 C. With the help of a small lattice mismatch (about 1.9 %) and structural similarity (hexagon on hexagon epitaxy), the AZO film was epitaxially grown on the GaN substrate. This was investigated by four-circle X-ray diffractometer by using monochromatized Cu K1 radiation. The AZO film was well oriented to the lattice of GaN on the a . b plane. This was confirmed by phi-scan measurements of (103) reflection of the AZO layer and of (103) reflection of the GaN substrate under fixed conditions of = 31.66 (2 = 62.858) and = 32.04 (2 = 63.435), respectively. The AZO film showed smooth surface roughness (Ra: 50 °A) and uniformly distributed grains. To investigate the optical transparency, the transmittance spectrum of the AZO/GaN-stacked film was characterized and showed a high transmittance (over 85 %) in the visible spectral range. The resistivity and carrier concentration of the AZO/GaN film, under varying annealing temperatures, were analyzed by Hall measurement and showed a maximal value of 2.38 × 10.4 ·cm and 2.57 × 1021 cm.3, respectively, for the 400 C-deposited film.

Dielectric Properties of Artificially Textured (Ba0.5Sr0.5)TiO3 Thin Film Prepared by Pulsed Laser Deposition

황재열,정세영,조채용,배종성,이상아 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

Metal-ferroelectric-metal (MFM)-structured (Ba0.5Sr0.5)TiO3 (BST) thin films were deposited on a Pt(111)/TiO2/SiO2/Si substrate by pulsed laser deposition. The textures of BST films, such as those with (111), (100), and (110) orientations, were successfully controlled by oxygen partial pressure and laser energy under deposition. In spite of the use of (111)-oriented platinized silicon substrates, highly (100)-textured BST film was formed by control of the oxygen flow rate. Voltagedependent dielectric properties, including dielectric constant (r) and dielectric loss (tan ) of the BST capacitors, were studied by capacitance-voltage (C . V) measurements at room temperature. Tunability and figure of merit related to the texture ratio of BST (100) in BST films are also discussed. The texture-control method of MFM-structured BST film using the pulsed laser deposition technique indicated that such film could be a potential candidate for frequency agile device applications.

Strong lithium-polysulfide anchoring effect of amorphous carbon for lithium–sulfur batteries

전태곤,이영철,황재열,최병천,이승훈,정성철 한국물리학회 2021 Current Applied Physics Vol.22 No.-

Solving the shuttle effect caused by lithium polysulfide (LPS) dissolution is important in lithium sulfur batteries. The anchoring of LPSs to carbon combined with sulfur is a method of suppressing the shuttle effect. This firstprinciples study is the first to report that amorphous carbon offers the best ability to anchor LPSs. The adsorption energies of LPSs on amorphous carbon are at least six times higher than those on graphene and at least two times higher than those on pyridinic-N doped graphene. The LPSs adsorbed on amorphous carbon undergo significant molecular distortion and/or partial dissociation due to the S-to-C electron transfer of 1.2–1.8 e per molecule, as well as the formation of strong bonds between both the Li and S atoms and the sp- and sp2-site C atoms. We propose an amorphous carbon graphite hybrid anchoring material, because amorphous carbon can strongly capture LPSs and graphite can act as an electron channel.

Frequency‐Independent and Colossal Dielectric Permittivity of Platy Alumina/Few‐Layer Graphene Multilayered Composites

최기범,이성민,황재열,윤대호,이규형,김종영 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.4

In this work, we investigated the dielectric property of layer‐structured Al2O3/few‐layer graphene (FLG) composite by high temperature impedance spectroscopic analysis. The sintered composites have highly enhanced permittivity (ε = 17.3) compared to pure platy alumina (ε = 7.3) with low dielectric loss (tanδ ~ 10−3). Percolative permittivity of the composites exhibits almost frequency‐independent behavior at 1 Hz to 1 MHz even though the real permittivity was increased, compared to that of pure platy alumina. Such behavior can be explained by intervening dielectric interface between alumina and FLG based on multilayer filler model. After percolation threshold (FLG > 0.75 vol %), the permittivity is further enhanced up to ~260 (@1 kHz), which amounts to >35 fold increase, compared to pure platy alumina because of interfacial capacitance between FLG platelets and alumina. According to temperature‐dependent impedance analysis, a dielectric relaxation due to Al2O3/FLG interface is observed in the frequency range of 1 Hz to 1 kHz at high temperature (RT = 400°C) besides that due to Al2O3 grains (>10 MHz). Real permittivity increases up to >20 000 at 400°C at low frequency, whereas dielectric loss remains as tanδ ~ 3 × 10−4. High temperature impedance analysis shows that the effect of interface between Al2O3 and FLG is responsible for such dielectric relaxation at high temperature.

Metal/Insulator/Semiconductor Structure Using Ga2O3 Layer By Plasma Enhanced Atomic Layer Deposition

이상아,Chae-Ryong Cho,황재열,Jong-Pil Kim,Se-Young Jeong,Won-Jae Lee 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2

Metal/insulator/semiconductor (MIS) capacitors were fabricated by using a Ga2O3 layer on an Si substrate. High dielectric Ga2O3 film was prepared by an alternating supply of a Ga source with a bubbler-type reactor and O2 plasma in a plasma enhanced atomic layer deposition (PEALD) process. The thickness of the Ga2O3 layer can be controlled by the number of cycles. The thickness of 1000 cycles processed Ga2O3 thin film was about 50 nm, and the surface roughness was 1 nm. The interface states between Ga2O3 and Si were characterized by Auger electron spectroscopy (AES). The flat-band, flat-voltage, and threshold voltage including dielectric constant were calculated by semi-empirical equation. The dielectric constant of Ga2O3 film was about 23.25. It is assumed that the MIS structure using Ga2O3 as a gate dielectric is effective in MOSFET device applications.

다전공전달층에 의한 페로브스카이트 태양전지 파워 변환효율 향상

이지용,미니몰 메남파람바스,황재열,백승현 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.5

Domain matching epitaxy of α-Ga2O3 thin film on sapphire by pulsed laser deposition

Lee Sang-A,황재열 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.8

Metastable (00l)-oriented rhombohedral α-Ga2O3 thin flms with phase purity were epitaxially grown on c-plane α-Al2O3 substrates using pulsed laser deposition. It was elucidated that domain matching epitaxy enables the epitaxial growth of α-Ga2O3 thin flm on α-Al2O3 substrate by stabilizing structural instability through reducing misft strain. In reciprocal space mapping analyses of α-Ga2O3 thin flms with diferent thicknesses, no considerable diferences in lattice parameters (a=4.977 Å and c=13.442 Å) and the degree of misft strain were identifed. The optical bandgap of α-Ga2O3 thin flm was modulated with crystal quality from 4.75 to 5.3 eV in the thickness range from 4 to 49 nm, indicating the characteristics of α-phase. Our results provide a facile way to stabilize the metastable α-phase of Ga2O3 using the α-Ga2O3/α-Al2O3 heterostructures through domain matching epitaxy with comprehensive structural characteristics and a promising potential for bandgap tuning for power devices, sensors, and solar-blind deep-ultra-violet photodetectors.

기저전극의 종류, 열처리 방법 및 온도에 따른 inter - diffusion 특성 연구

조채룡,우성오,김종필,황재열,정세영 한국진공학회 2004 한국진공학회 학술발표회초록집 Vol.- No.-