2022년도 한국물리학회 대구·경북지부 추계 학술발표회

Thursday 13 Oct 2022, 13:00 → 18:00 Asia/Seoul

(비대면) (DIGIST)

** 투고 마감일을 2주 연장합니다. 

마감일: 12월 27일 (화) 23시 59분

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한국물리학회 대구경북지부 새물리 특별호 투고를 안내 드립니다.

- 투고 시작일: 11월 03일 (월) 0시

- 투고 마감일: 12월 13일 (화) 12월 27일 (화) 23시 59분

- 투고 방법: 새물리 홈페이지 http://www.npsm-kps.org 에서 직접 진행하실 수 있으며, 모든 방법은 정기호와 동일하나 Manuscript 정보를 입력하는 단계에서 Manuscript Type을 Special Issue > 해당 특별호 (Daegu/Gyeongbuk)로 선택하시면 됩니다. 

 

<안내>

 

한국물리학회 대구·경북지부에서는 아래와 같이 “2022년도 한국물리학회 대구·경북지부 추계 학술발표회”를 개최할 예정이오니 지부 회원님들의 많은 참여를 바랍니다.

1. 일시 : 2022년 10월 13일(목요일) 13:00~18:00

2. 장소 : DGIST 연구행정동

• 버스 셔틀 운영 (한국물리학회 전광판에 표시)
  - 12:20 대곡역 출발 12:50 DGIST 도착
  - 13:20 대곡역 출발 13:50 DGIST 도착
  ** 대곡역 탑승위치 : 대곡역 3번출구 근방 180m 한라하우젠트 아파트 후문 근처(신상교 식당 앞)
  - 17:30 DGIST 출발 18:00 대곡역 도착
• 행사 전 간단한 다과 준비되어있습니다.
   
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3. 포스터 출력 크기:

The recommended size of a poster is 100cm (width) x 100cm (height) [Maximum: 120cm x 180cm]

4. 논문발표 신청 :

• 신청기한 (Deadline): 2022년 10월 06일 (목) 자정까지
• 신청방법 :
  • 왼쪽 메뉴의 Call for an Abstract를 통해 발표논문요지(제목, 저자, 소속기관, 초록 포함) 제출
  • 초록 제출을 위해 먼저 indico에 로그인해야 합니다.
  • 영문 한글 모두 입력 가능함
• 주요 학술 프로그램의 상세 내용과 향후 일정은 물리학회 홈페이지에서 확인하실 수 있으며, 초록 접수 시스템 오류나 문의 사항은 아래 담당자에게 연락해주시기 바랍니다.
• 지부학회 홈페이지 http://www.kps.or.kr/content/branch/local_list.php
• (전화) 053-950-7352, (e-mail) jophy@knu.ac.kr 경북대학교 물리학과 조연정 교수

5. 논문의 발표 방식, 시상 및 새물리 게재 :

• 학술발표회 당일의 논문은 포스터 세션 발표임 (초청 강연 제외).
• 우수 논문을 선정하여 물리학회장 및 대경지부장 명의의 우수포스터 논문상을 시상함.
• 발표된 논문은 엄정한 심사를 거쳐 2023년도 2월~5월 “새물리” 특별호에 게재 예정.

6. 대경지부 회비를 납부하지 않는 학과에 소속되어 있는 발표자(교수급 이상)는 특별 개인회원으로 분류되며, 초록을 접수할 때 특별 개인회비 3만원을 미리 납부해야 함. (계좌번호: 신한 110-396-087189, 예금주 : 조연정)

7. 기 타 :

• 지부 학술발표회 관련한 상세한 사항은 추후 홈페이지와 이메일을 통하여 공지함.
• 문의/연락처: 지부장(김기현), 총무간사(조연정), 운영간사(김종수)

개회식

초청발표 1.김아람 교수님 (DGIST) 김아람 교수님 (DGIST) 2.민정욱 교수님(금오공대) 3.강경태 교수님 (경북대)

1 Molecular beam epitaxy grown GaN-nanowires-based p-i-n structures on Ti-coated substrates for light-emitting diodes applications

III-nitride nanowire arrays driven by diffusion-induced process of plasma-assisted molecular beam epitaxy (PA-MBE) has provided straight and axially-grown one-dimensional (1-D) nanostructures for optoelectronic device applications. As compared with the planar layer platform, nanowires-based epitaxial growth technology has distinct advantages of dislocation-free nature combined with reduced lattice strain and smaller Stark effect in quantum-confined double-heterostructures, resulting in a lower piezoelectric polarization field.
In this talk, we focus on the basic growth kinetics and the epi-structure design of PA-MBE grown GaN-nanowires-based p-i-n structures, for the realization of light-emitting diodes (LEDs). Firstly, GaN seeds are nucleated and self-planarized GaN nanowires are successfully grown by a self-assembled growth mechanism on the Ti-coated amorphous fused-silica and Si substrates. After introducing the Ti pre-orienting layer, the electrical conductivity was found to increase, with reduced sheet resistance and improved interface. As a second part, GaN-nanowires-based p-i-n structures were grown using selective area growth (SAG) on a GaN/sapphire template, by using the Ti layer as a mask. The SAG method provided better controlled nucleation and elongation only in the mask-window positions and thus, high external quantum efficiency was achieved. These achievements can open a new way for III-nitride semiconductors on various material platforms for optoelectronic device applications.

Speaker: Jungwook Min (Department of Optical Engineering, Kumoh National Institute of Technology, Gumi 39235, Republic of Korea)

2 전이 금속 산화물 박막을 통한 양자 물질 탐구

‘양자 물질의 시대가 도래했다.’
1926년 양자역학이 본격적으로 꽃피우기 시작한 이래로 다양한 미시적 세상의 입자들의 거동이 규명되었다. 특히 미시적 입자들은 집합체를 이룸으로써 무한히 다양한 물질을 구성하고 이들의 양자역학적 거동은 ‘발현 성질(emergent property)’을 이끌어낸다. 초전도성, 자성과 스핀, 강유전성, 위상물성과 강한 상호작용계 같은 기초물리학적인 현상은 물론 반도체 물성, 양자컴퓨터 및 에너지 밴드 구조를 통한 물질간 화학반응 등의 응용적 현상 등 물질 종류의 다양성만큼이나 발현 성질 또한 다양하고 비로소 양자 물질의 시대가 시작됐다고 할 수 있다.
양자 물성은 극한의 환경을 요구한다. 극저온 혹은 높은 압력에서 보이는 초전도성, 저온 및 특별한 자기장 환경을 요구하는 자성 및 양자 홀 효과 등의 양자물성들이 예이다. 강한 상호 작용 전자계를 나노 수준으로 구현하고 제어하는 것 또한 양자 물성을 발현하기 노력의 일환으로 볼 수 있고, 전이 금속 산화물 박막은 이를 제공해주는 양자 물질군이다. 펄스 레이저 증착법을 활용하여 제작한 전이금속 산화물 박막은 페로브스카이트 구조를 기반으로 한 다양한 구조 및 조성을 지니며, 팔면체 형태의 산소-전이금속 구조체가 양자물성의 단위가 된다. 전이금속으로부터 제공된 d-오비탈 전자계는 오비탈, 전하, 스핀, 격자구조 등의 자유도 등으로 제어되고 나노 수준으로 얇은 박막이 주는 변형(strain)과 같은 추가 자유도와 얽혀 인공적으로 제어되는 양자 물질계를 구현할 수 있다.

Speaker: Kyeong Tae Kang (Kyungpook National University)

포스터 발표

3 CW 및 수동형 Q-스위칭 Nd:YVO4 레이저의 발진 특성 연구

두께가 1 mm인 Nd:YVO4 결정을 출력이 1 W이고 파장이 808 nm인 레이저 다이오드로 종펌핑하여 CW 레이저를 발진 시키고 시뮬레이션 결과와 비교하였다. 파장이 1064 nm인 레이저의 발산각, M2, 포인팅 안정성(pointing stability) 등을 공진기의 길이를 달리하며 측정하였으며, 공진기 길이가 늘어날수록 M2는 감소하였다. 이 공진기에 초기 투과율이 95%인 Cr:YAG 결정을 넣어서 수동형 Q-스위칭된 펄스 출력이 나오게 하였으며, 펄스 레이저의 반복율과 시간폭을 측정하였다.

Speaker: Mr 수찬 배 (영남대학교)

4 Time-Dependent Synthesis of Molybdenum Disulfide

Molybdenum disulfide (MoS2) is synthesized by the easy hydrothermal method for bifunctional electrocatalysts. Time-dependent hydrothermal treatment was applied for the MoS2 synthesis from 6 to 72 hours. The synthesized sample at 200°C for 48 hours exhibits the best performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. The morphology of MoS2 changed from flakes to one-dimensional and finally to flower shapes. Their catalytic activities for HER and OER are investigated systematically.

Keywords: Molybdenum disulfide; hydrogen evolution reaction; oxygen evolution reaction.
*Corresponding author: outron@gmail.com (H.K. Jeong), Tel: +82-53-850-6438, Fax: +82-53-850-6479.

Speaker: Mr Ghanashyam Gyawali (Daegu University)

5 초중등학교 과학교육에서 양자물리 도입의 가능성과 접근 방략 탐색

현대 사회에서 양자역학의 중요성은 더 언급할 필요가 없을 정도로 지대하다. 양자역학이 실생활에 미치는 영향은 최근에는 양자 기술 (quantum technology)이라는 이름으로 더욱 확장되고 있다. 양자 기술은 국가의 핵심 전략기술로 간주되기 시작하면서 정부는 2021년에 ‘양자 기술 연구개발 투자 전략’을 발표했으며 국회에서는 2022년 초에 ‘양자 기술 개발 및 산업화 촉진에 관한 법률’을 입법하였다. 이 법률안에는 초중등학교 수준에서 양자 기술 관련 교육을 포함할 것이 포함되어있기도 하다. 그러나 당장의 현실은 초중등학교 수준에서 양자 기술 교육에 대한 사회적 수요에 대응하기가 어려운 실정이다. 이 연구에서는 초중등학교 수준에서 양자 기술을 포함하는 양자물리 교육을 도입하기 위한 기초 논의로서, 초중등학교에서의 양자물리 교육에 대한 현황을 검토하고 그 가능성을 탐색하고자 한다. 이를 위해 첫째, 초중등학생을 대상으로 하는 관련 연구 동향을 분석하고, 둘째, 특히 유초등학생을 위한 양자물리 관련 대중 과학도서들의 내용과 접근 방략을 분석한다. 이를 바탕으로 초중등학생을 위한 양자물리 교수학습 방략에 대한 시사점을 도출하고 학교 과학교육에서의 실천 가능성을 논의한다.

Speaker: Prof. Sungmin Im (Daegu University)

6 Fabrication of head phantom printed by mixing plaster and PLA powder for the patient specific QA

Purpose: The purpose of this study is to make a heterogeneous phantom that reproduce the commercial Rando phantom by mixing the plaster powder and the poly lactic acid (PLA) powder.

Methods: In order to match the mean Hounsfield units (HU) values of Rando phantom, the bone tissue changes from plaster and PLA powder 0% to 35% to find an appropriate HU value, and soft tissue changes the infill value of the PLA to find an appropriate HU value. Bone tissue (200 HU or higher), soft issue (-500 to 200 HU), and air cavity (less than -500 HU) are modeled based on the HU value of the computed tomography (CT) image. The bone tissue is modeled as cavity, and after three dimension (3D) printing, a solution in which plaster and PLA powder were mixed is poured. To evaluate the bone implementation of the plaster mixed with PLA powder phantom, the HU profile of the CT image of the only PLA 3D printed phantom and Rando phantom printed using only PLA is evaluated.

Results: In Rando phantom, the mean HU value of soft issue is -22 HU, which is most similar to -20 HU with an infill value of 82%. The mean HU value of Bone tissue is 669 HU, which is 15% of the ratio of PLA powder to Plaster, most similar to the 680 HU value. In plaster mixed with PLA powder phantom, the soft tissue is manufactured with a 3D printer with an infill value of 82%, and the bone tissue is manufactured with percentage of PLA powder 15%. In HU value profile, the Plaster mixed with PLA powder phantom has mean difference of 61 HU between Rando phantom and soft tissue, and mean difference of 109 HU in bone tissue. Only PLA 3D printed phantom and Rando phantom have mean difference of 114 HU in soft issue and mean difference of 543 HU in bone tissue.

Conclusion: It is confirmed that the ratio of PLA powder and plaster can be adjusted to a HU value similar to bone issue. A simple combination of PLA powder and Plaster enable Rando phantom of soft tissue as well as bone tissue to create a more suitable custom phantom.

Keywords: Anthropomorphic head phantom, 3D printer, PLA powder, plaster

Speaker: Sung yeop Kim (Yeungnam University)

7 638 nm-LD로 단면 펌프하는 연속발진 알렉산드라이트 레이저의 출력특성

알렉산드라이트(Alexandrite, Cr3+:BeAl2O4)의 형광 수명은 약 0.066〜1540 ms로 온도에 따라 변하며, 온도가 높아질수록 상준위 수명이 짧아지고, 상온에서는 약 250㎲〜300㎲이다. Cr:BeAl2O4의 방출 스펙트럼은 0.68㎛〜0.82㎛ 정도이고, 결정은 3축 중에서 b-축의 편광이 가장 효율적인 방출(emission) 특성을 나타내므로 a-축 또는 c-축을 rod 축으로 하고 b-축을 rod 축에 수직이 되도록 제작하고 있다. 여기상태와 방출상태의 흡수단면적이 같아지는 파장은 각각 0.83㎛와 0.68㎛이다. 이 영역(0.68~0.83㎛)을 벗어나면 실제적으로 레이저 발진은 불가능하게 된다. 그리고 이 단면적은 온도에 따라 변하는데 파장 0.77㎛에서 유효 유도 방출 단면적은 실온에서 0.6×10-24이나 온도가 약 200°C에서는 2.0×10-24로 약 3.5배가 증가된다. 그러나 온도가 상승할수록 상준위 레이저 수명이 감소되므로 적당한 온도 유지가 필요하다. 본 연구에서는 638nm-LD로 단면 펌프하는연속발진 알렉산드라이트 공진기를 구성하여 열렌즈에 의한 공진기 특성, 레이저 출력특성 및 파장 가변성 등을 측정하고 나아가 의료용 롱펄스 알렉산드라이트 레이저 개발을 최종 목표로 진행하고 있다.

Speaker: Mr Kunhee RHYEE (Department of optical Engineering, Kumoh National Institute of Technology)

8 A digital alloy layers thickness effect in AlGaInAs PIN structures grown by Molecular beam epitaxy

We demonstrate digital alloy (DA) Al0.4Ga0.07In0.53As PIN structures nearly lattice-matched to InP substrates. Ternary and quaternary alloys on InP substrates have suffered from phase separation during the growth. The thin AlInAs and InGaAs layers were periodically stacked as a superlattice. Using photoluminescence (PL) spectroscopy, we have studied the thickness effect in AlGaInAs PIN structures. The thickness of each quaternary layer was 4ML, 6ML, and 8ML, respectively. At a low-temperature PL, the emission centers show 1.379 eV, 1.378 eV, 1.362 eV, respectively. The redshift was observed with increasing thickness. This redshift shows the energy state in superlattice layers due to an increase in barrier heights. Especially1, the 6 ML PL spectra show asymmetry shapes at low temperatures. These PL shapes show that the 6ML interface has two different emission centers.

Speaker: jaedu HA (Yeungnam University)

9 A Study on Defect Characterization of Prepreg CFRP Composite Using the Ultrasonic Method

Recently, low-carbon green energy developing units are getting much attention due to the exhaustion of energy and environmental issues. The wind power generator, a typical low-carbon green energy developing unit, has less influence on the weather. Also, its generation quantity compared to the ground contact area has a point. Moreover, the generation quantity can be expanded through enlarging the surface area of wind power generator’s wind blade. Before, GFRP (Glass Fiber Reinforced Plastic) was the most popularly used material for wind blade of wind power generator. However, the usage of carbon-fiber in lieu of glass fiber continues to increase regarding the efforts to improve the efficiency of the wind power system. The spinning radius of the wings has increased by 30% every year and now the blade is as big as 120m, and the set-up (installation) cost of wind power generator is increasing while the efficiency is reducing.
CFRP composites applied to wind blades are manufactured by lamination sequence and carbon fiber arrangement using unidirectional prepreg sheet. In the additive process, defects such as pores, resin distribution and micro-cracks may occur due to lamination failure
Therefore, In this study the defect characterization was performed by analyzing defect signal of the prepreg CFRP composite using the ultrasonic method

Speaker: Prof. Yun-Taek Yeom (Dongyang University)

10 Design principles of nanoporous graphene/graphene heterobilayers with electric-field-tunable bandgaps

The recent bottom-up synthesis of a crystal lattice of nanoporous graphene (NPG) gives a way of making new multifunctional carbon material [1]. In addition, by forming NPG/graphene (Grp) bilayers, graphene can exhibit various functionalities depending on the sizes, shapes, and periodicity of nanopores in NPG. Here, we present two mechanisms for the electric-field-tunable bandgap in NPG/Grp bilayers: (i) type-I bandgap opening in graphene through 2D inversion symmetry breaking and (ii) type-II bandgap opening through the merging of Dirac cones of graphene [2]. To translate the underlying physics of the bandgap opening in graphene into real atomic structures, we develop an inverse design method and find NPG/Grp bilayers with the target functionality. First-principles calculations show that the inverse-designed NPG/Grp bilayers indeed exhibit the field-tunable bandgaps in graphene as predicted; the type-I bandgap opening is characterized by a linear field dependence of the bandgap, while the type-II bandgap opening exhibits a highly nonlinear field dependence of the bandgap. The field-tunable bandgap in graphene, supported by first-principles calculations for the inverse-designed systems, holds promise for new types of graphene transistors.
[1] C. Moreno et al., Science 2018, 360, 199-203.
[2] B. Lee and J. Kang, Adv. Electron. Mater. 2022, 2200252.

Speaker: Byeoksong Lee (DGIST)

11 Detection of spin-orbit torque driven artificial spin texture dependent system energy variation

Since the chirality by the inversion symmetry breaking has been observed in magnetic ordered system,[1] researches on the system with asymmetric exchange coupling were actively investigated.[2] Here, diverse reports proves that the chirality affects to the dynamic and static characteristics of spin phenomena, so it also influences on the magnetization switching.[3-6] However, in the view of the converse way, it can be also interpreted that analyzing a variation of the magnetization switching in a chiral spin system can be one option to understand an influence of the chirality on the system.
In this report, we successfully detected the system energy variation induced by the interaction between spin-orbit torque-driven artificial spin texture and Dzyaloshinskii-Moriya interaction (DMI) in laterally modulated PMA system. The effect of chiral spin texture can be confirmed by measuring magnetization switching because the chirality reversal also occurs simultaneously (clockwise (CW) ↔ counter-clockwise (CCW)). Here, more (less) energy should be required for switching the stabilized (destabilized) spin texture, which results in an additional effective magnetic field manifested itself as the shift of hysteresis loop. The resultant degree of effective field is well explained by a theoretical model derived from the Hamiltonian of DMI and micromagnetic simulations, directly confirming relationship between the chirality-dependent magnetization switching and the system energy variation.

References
[1] M. Bode et al. Nature 447, 190-193 (2007).
[2] S.-H. Yang et al. Nature Reviews Physics 3, 328-343 (2021).
[3] D.-S. Han, et al. Nano Lett. 16, 4438–4446 (2016).
[4] D.-S. Han, et al. Nat. Mater. 18, 703–708 (2019).
[5] H. Wu, et al. Nano Lett. 21, 515–521 (2021).
[6] S. An, et al. Appl. Phys. Lett. 120, 262402 (2022).

Speaker: Suhyeok An (DGIST)

12 Effect of carbon felt surface treatment and synthesis time on W18O49 nanostructures-based supercapacitor electrode performance

The W$_{18}$O$_{49}$ nanostructures assembled on carbon felt electrodes (WNAC) were fabricated using a simple solvothermal method. We report the effect of surface modification of Carbon felt (CF) and morphology of nanostructure on supercapacitor performance. The CF was pre-treated with HNO3 to form oxygen-containing groups on the surface. The pretreatment of CF promotes the uniform distribution of W$_{18}$O$_{49}$ nanostructures on the surface of CF. In the synthesis process, the morphological, structural, and electrochemical properties of nanostructures were controlled by the synthesis time and pH. The grown nanostructures of synthesis time at 12 h with HCl insertion showed the greatest performance. The specific capacitance was 311.71 F/g at a scan rate of 20 mV/s, and the charge-transfer resistance was 1.2 Ω in the three-electrode system. This is attributed that the high specific surface area due to the thin thickness contributing to the low charge-transfer resistance and easy accessibility of electrolytes of WNAC.

Speaker: Mr Seung-yong Eom (Kyungpook National University)

13 Enhancement of valley polarization degree in h-BN/WS2/h-BN waveguide cavity

The valleys in transition metal dichalcogenide monolayers have received great attention as new degrees of freedom to encode and store information due to easy addressing using circular light. However, the valley information is easily depolarized and the resonant generation of the valley excitons must be required for achieving high degrees of valley polarization. In this work, we demonstrate the enhancement of valley polarization in end emissions of h-BN/WS2/h-BN waveguide structure under the non-resonant excitation condition at room temperature. By comparing the polarization ratio for body and end emission in h-BN/WS2/h-BN waveguide structure, we found that the successive resonant excitation of exciton via propagating waveguide modes increases the degree of valley polarization.

Speaker: Jin-Woo Jung (Daegu Gyeongbuk Institute of Science and Technology (DGIST))

14 Exciton Diffusion Properties in Single Crystalline Lead Halide Perovskites

Organic-inorganic hybrid perovskites are promising active materials for optoelectronic and photovoltaic applications due to their large exciton binding energy, long carrier diffusion length, and tunable band gap [1-3]. Interestingly, these perovskites experience the crystalline phase transition depending on the temperature, where the intrinsic excitonic properties can be largely altered. Until now, investigations on fundamental excitonic properties with the phase transition are in the beginning stage, and thus it is important to understand the phase-dependent properties in order to realize efficient perovskite-based optoelectronic devices. In this work, we investigated the evolution of exciton diffusion length and exciton lifetime under the phase transition of CH3NH3PbBr3 single crystals using spatially resolved photoluminescence imaging and time-resolved spectroscopy. CH3NH3PbBr3 single crystals showed a clear phase dependence for the exciton diffusion coefficient from cubic, through tetragonal, to orthorhombic phases. These findings would provide insights into the phase-dependent exciton properties of lead halide perovskites.

References
[1] K. Tanaka, T. Takahashi, T. Ban, T. Kondo, K. Uchida, and N. Miura, Solid State Communications, 127, 619‒623 (2003).
[2] Q. Dong, Y. Fang, Y. Shao, P. Mulligan, J. Qiu, L. Cao, and J. Huang, Science, 347, 967‒970 (2015).
[3] L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh, and M. V. Kovalenko, Nano Letters, 15, 3692‒3696 (2015).

Speaker: Ms Hyeon-Seo Choi (DGIST)

15 GaAs기판에 성장시킨 InAs 양자점의 광 특성연구

GaAs 기판 위에 MBE를 통해 성장시킨 InAs 양자점을 PL과 PR을 이용하여 광 특성을 확인하였다. 샘플은 n+ GaAs 기판 위에 n=41018 cm-3의 도핑농도를 가지는 n-GaAs 버퍼를 5000Å 성장시키고 그 위에 n=31016 cm-3의 농도를 가지는 Si로 도핑된 n-GaAs층을 3100Å쌓고 그 위에 InAs 양자점을 MBE를 통해 성장시켰으며 그 위에 AlAs 배리어를 10Å만큼 쌓고 top layer로는 n=3*1016 cm-3의 도핑농도를 가지는 Si로 도핑된 n-GaAs를 2500Å만큼 쌓았다. 633nm의 여기광을 사용하여 20K에서 PDPL을 진행한 결과 1.49 eV 에서 GaAs 기판의 피크를 확인 할 수 있었으며 1.35 eV, 1.39 eV에서 InAs QD의 피크를 확인 할 수 있었으며 1 mW/cm^2 이하의 세기에서 약간의 적색편이가 일어났다. 20K부터 300K 까지 온도를 20K씩 올려가며 TDPL을 촬영해본 결과 1.39 eV의 InAs 양자점 신호가 온도가 높아질수록 적색편이하였으며 1.35 eV의 신호는 세기가 점점 줄어들다 약 100K부터 신호가 사라졌다. 샘플의 전자특성을 확인하기 위해 온도 20K에서 PR측정을 진행하였다.

Speaker: Jiseong Go (영남대학교)

16 General Gauge Symmetry in the Theory of Atomic Heat Transport

The Green-Kubo theory of atomic heat transport relies on the ambiguous decomposition of total energy into energies of individual atoms. The key challenge is to understand how thermodynamic properties such as heat conductivity can emerge from inherently ill-defined atomic energies. Here, we show that such ambiguity can be exploited as a guide to construct a general theory of heat transport by requiring the theory to take the same invariant form for all possible choices of atomic energies. By defining atomic gauges and associated transformations of atomic energies, we show that the gauge symmetry dictates the gauge-invariant form of macroscopic energy transfer, which is identified as heat. Consequently, arbitrary choices (even random shuffling) of atomic energies lead to the same heat conductivity 𝜅. The gauge theory also offers a novel variational method for calculating 𝜅, as demonstrated using machine learning-inferred atomic energies of $Cu_{2}S$, an intriguing solid-liquid hybrid thermoelectric material.

Speaker: SangHui Kim (DGIST)

17 Hitting time in random walks and effective resistance in electric networks

Hitting time in random walks on graphs is a substantial quantity for classical and quantum studies of Markov chains. The connection between random walks and electric networks has been recognized for long time. Recently, the expression of hitting time was introduced in terms of the effective resistance and the total conductance. This expression has been used as a key element for proof of quadratic speedup for finding marked vertices by quantum walks. However, no explicit derivation of the expression has been published yet. Here, we present a concrete derivation of the expression.

Speaker: Prof. Narknyul Choi (Kumoh National Institute of Technology)

18 Identify the defect density of InAsP metamorphic structure using by photoreflectance spectroscopy

The optical properties of InAsxP1-x metamorphic buffers grown by metal-organic chemical vapor deposition (MOCVD) on InP substrates have been investigated. From photoreflectance spectrum, the optical bandgap energy shows around the 0.81 eV, 0.72 eV, and 0.61 eV with As composition x= 0.5,0.55, and 0.7, respectively. Furthermore, the Franz-Keldysh oscillation (FKO) signal shown above at InAsxP1-x bandgap energy, can calculate the internal electric field (F) by Fast-Fourier transform (FFTs) methods. All samples have three main peaks around of 15 eV-3/2 to 130 eV-3/2 as a result of FFT. From the result of calculation F, x= 0.5 and 0.7 samples have similar F values, and the 0.55 sample shows a lower F value by about 70 kV/cm. It is caused by the defect density, which increases the probability of photo-generated carrier trapping. The higher the defect density at the interface, the lower the carrier density decreases, which reduces the photovoltaic effect.

Speaker: Gyung Du Park (Yeungnam University)

19 Induction heating and cytotoxicity study of Ca-doped MgFe2O4 nanoparticles

One effective antitumoral nano therapy is magnetic hyperthermia, which is mediated by magnetic nanoparticles, primarily for its capacity to eradicate malignancies. The present magnetic hyperthermia with nanoparticles is an experimentally explored method for eliminating cancer cells. Spinel ferrites' regulated particle size and superparamagnetic properties are essential for magnetic hyperthermia applications in the treatment of cancer.
This led to the preparation of $Mg_{1-x}Ca_xFe_2O_4$ (x = 0.1, 0.3, and 0.5) nanoparticles to investigate the structural, magnetic, and magnetic hyperthermia properties. When subjected to an alternating magnetic field, the spinel ferrite single-domain particles generate heat. Here, specific loss power values for $Ca^{2+}$ -doped $MgFe_2O_4$ nanoparticles with particle sizes between 13 and 12 nm are described. One of the greatest values for $Ca^{2+}$ doped $MgFe_2O_4$ nanoparticles to date has been reported for the $Mg_{0.9}Ca_{0.1}Fe_2O_4$ nanoparticles with an average particle size of 13 nm, which had a considerable specific loss power value up to 556.73 W/g at 1 mg/mL
ferrofluid concentration. The induction heating investigation of such nanoparticles confirms
their appropriateness for magnetic hyperthermia treatment of cancer. Optimized nanoparticles
were examined for cytotoxicity against human breast cancer (MDA-MB-23) and prostate
cancer (PC-3) cells in terms of cell viability.

Speaker: Prof. Manohar Ala (Yeungnam University)

20 Influence of annealing of β-Bi2O3 over superior photoelectrochemical performance

An in-depth investigation was carried out to determine the relationship between morphological, structural conversion, and photoelectrochemical water-splitting properties of β-$Bi_2O_3$ nanostructured thin film annealed at temperatures ranging from $500^oC$ to $650^oC$. Apart from the phase transformation it has also been observed that the basic nanostructure were converted from nanoflakes to nanoworms via nanorods. These transformation results in the red shifting in the optical band gap. Transformation occurs in the basic $Bi_2O_3$ leads to the emergence of new non–stoichiometric $Bi_2O_{2.33}$ have been visualized due to the fast annealing at $600^oC$ which enhance the oxygen vacancies as analyzed by the XPS. Consequence of the annealing up to $600^oC$ enhanced the photocurrent density up to (~ 1.53 $mAcm^{-2}$ at 1.23 V vs RHE) which shows 1.7 times higher than basic β-$Bi_2O_3$ (̴ 0.90 $mAcm^{-2}$ at 1.23 V vs RHE) in the $Na_2SO_3$ electrolyte. However in the neutral $Na_2SO_4$ electrolyte the photocurrent density of $Bi_2O_3$ at $600^oC$ was found (~ 0.21 $mAcm^{-2}$ , 1.23 V vs RHE) which shows 2.6 times higher than basic β-$Bi_2O_3$ (~ 0.08 mAcm -2 , 1.23 V vs RHE). Above this shifting in the onset potential for all the samples were found on altering the electrolyte from $Na_2SO_4$ (pH=7) to $Na_2SO_4$ (pH=9). The Mott-Schottky and EIS were demonstrated for scrutinizing the charge kinetics for all the photoelectrodes. These findings contribute a favorable impact of annealing over the structure and the morphology of the material which can produce high photoelectrochemical ability.

Speaker: Prof. Majumder Sutripto (Yeungnam University)

21 Laser-induced hydrothermal growth of cupric oxide nanowires for fabrication of micro device

Among the various transition metal oxide semiconductor nanomaterials, cupric oxide (CuO) is getting attention due to low cost, easy synthesis, and its attractive physical/chemical properties. CuO is considered as a p-type semiconductor due to the presence of copper vacancies and has narrow band gap of ~1.4 eV. Thus, CuO nanostructure is used as various electronic applications such as solar cells, photovoltaics, supercapacitors, light-emitting diodes, and photodetectors.
In our work, we successfully synthesized CuO nanowires (NWs) by laser induced hydrothermal growth (LIHG). Since, compared to conventional NWs growth methods including Chemical Vapor Deposition, LIHG process can produce localized and selective synthesis, cupric oxide NWs are selectively grown on the desired position of micro metal pattern. Finally, through LIHG process, we fabricated CuO NWs-based micro photodetector.

Speaker: Mr Jonghwan Mun (Department of Physics, Kyungpook National University)

22 Magnetophoretic device for the analysis of multi collision trajectories of bio-carriers in the periodic energy landscape.

During collision among the particles, energy or mass exchange occurs and leads to changes in the trajectories of the collision of the particles; therefore, it's essential to analyze the physical information regarding the interactions. Many researchers have studied particles with their initial energies in a relatively uniform or gradient static energy landscape. Nonetheless, the locomotion of particles in contrast to particle collision becomes more multiple in a complex magnetic energy landscape as compared to a static energy landscape. Therefore, we introduced micromagnetic arrays to create a complex energy landscape with temporal and spatial periodicity and analyze the particle collisions. As a result, magnetic particles followed distinctly different trajectories in the magnetophoretic system according to the mixing numbers. An immediate shift was classified with different trajectories after the collision of the particles. Consequently, this work gives information about the particle trajectories shift and unique analysis of the dynamic changes of the particles including various information.

Speaker: Mr Abbas Ali

Ali poster_KPS_22.pptx

23 Modeling and simulation of wire wound chip inductor for GHz frequency

High-performance chip inductors are essential components in hyper-frequency applications, in particular, radio frequency. Among the different types of inductors, wire inductors have shown high Q-factor and self-resonance frequency thanks to their low resistance and parasitic capacitance between coils, making this type an excellent component to be used in automotive applications.
In this work, we designed and simulated an inside-wire wounding inductor using ANSYS electronics packages. The performance of the modeled inductor was evaluated in terms of self-resonance frequency and Q-factor by controlling different structure parameters such as the coil diameter, Number of turns, and space between coils. The effects of each parameter were studied and analyzed to optimize the wire wound chip inductor

Speakers: Mr Choi Youngjun (YeungnamUniv) , Dr Rachida Lamouri (Yeingnam Univ)

24 Pseudospin rotation in graphene

Pseudospin, a degree of freedom in a two-level quantum system of two sublattices, is a basic quantum number posing the fundamental symmetry prone to the electronic nature of graphene. We propose an extended Hamiltonian to involve the SU(2) rotation of pseudospin for the electron-phonon scattering, which has a significant merit over the conventional second-quantized polar coupling. A phonon satellite accompanied by an electron linearly pumped to the upper Dirac cone corresponds to a rotated pseudospin within a scheme of the time-resolved photoemission spectroscopy (TRPES), which is found to carry nonzero angular momenta and induce nonvanishing Berry curvatures through the dichroic mode of TRPES. A phonon bringing the pseudospin rotation is identified to be an elliptically polarized one, which compensates angular momenta delivered to the pseudospin. This is an indication of the chiral phonon excitation without the circularly polarized pulse pumping. Our findings suggest that a controlled generation of phonon build up a new roadmap for engineering the Berry curvature and topology in the Dirac semiconductors.

Speaker: Mr Jiwon Jeon (Department of Physics and Chemistry, DGIST)

25 Robust Interlayer-Coherent Quantum Hall States in Twisted Bilayer Graphene

Bilayer quantum Hall systems host quantum phases which cannot be realised in single-layer systems. Bose–Einstein condensation is the prototypical example where electron and hole excitations from different layers form exciton condensates owing to interlayer Coulomb interactions. However, such an exotic quantum state has only been realised at sub-Kelvin temperatures in conventional GaAs systems, mainly because of weak interlayer couplings. Here, we introduce a novel two-dimensional electronic system with ultrastrong interlayer interactions, namely twisted bilayer graphene with a large twist angle, as an ideal ground for realising interlayer-coherent excitonic condensates. In these systems, subnanometre atomic separation between the layers allows significant interlayer interactions, while interlayer electron tunnelling is geometrically suppressed due to the large twist angle. By fully exploiting these two features we demonstrate that a sequence of odd-integer quantum Hall states with interlayer coherence appears at the second Landau level (N = 1). Notably the energy gaps for these states are of order 1 K, which is several orders of magnitude greater than those in GaAs. Furthermore, a variety of quantum Hall phase transitions are observed experimentally and are largely consistent with our phenomenological model calculations. Hence, we establish that a large twist angle system is an excellent platform for high-temperature excitonic condensation.

Speaker: Dohun Kim (DGIST)

26 Single crystal growth and magnetic behavior of T2-xSn (T = Mn, Fe, Co, Ni) hexagonal phases

Hexagonal phases where 3d transition metals are involved may show intriguing phenomena derived from spin frustration. Herein we report single crystal growth of isostructural T_(2-x)Sn hexagonal phases and their magnetic behaviors. All single crystals were grown by flux method. We found Mn_3Sn_2 and Fe_5Sn_3 exhibited ferromagnetic ordering. Fascinatingly, Mn_3Sn_2 exhibited spin reorientation and hysteresis at the low temperature, whereas Fe_5Sn_3 remained soft magnet. On the other hand, Co_3Sn_2 and Ni_3Sn_2 were paramagnet. Still, their magnetic behavior may be potentially undergone transition to ferromagnet by doping atoms or increasing compositions.

Speaker: Jaemun Park (DGIST)

27 Solvothermal synthesis of superparamagnetic MnFe2O4 nanoparticles for magnetic hyperthermia application

Superparamagnetic nanoparticles for local hyperthermia have taken the interest of researchers as it is one of the safest ways nowadays for local tumor treatment using the heat possibility of the magnetic nanoparticles in the presence of an AC magnetic field. Iron oxide nanoparticles have been considered for magnetic hyperthermia application for a long time ago and have been widely studied. However, further improvement in the magnetic properties is still required to enhance the self-heating generation. Manganese spinel ferrite is considered an alternative material for local magnetic hyperthermia thanks to its biocompatibility and promising magnetic properties.
In this work, superparamagnetic manganese spinel ferrite nanoparticles have been synthesized via the solvothermal process. Solvent effects have been considered by using Ethanol and Ethylene glycol as solvents. XRD patterns showed the crystallization of the prepared samples in the cubic spinel structure with space group Fd3m. TEM images proved the formation of monodispersed nanoparticles. To investigate the magnetic properties, magnetic hysteresis loops along with FMR measurements were performed. Moreover, the self-heating generation over time was measured to evaluate the Specific absorption rate (SAR) of the nanoparticles

Speaker: Dr Rachida Lamouri (Yeingnam Univ)

28 Structure of uniformly charged soft and hard spherical ions: Density functional approach

The theoretical model, which is based on the density functional approach, has been developed for studying the electrostatic adsorption of uniformly charged soft and hard spherical ions confined in the charged electrode, where the charge is uniformly smeared on the surface and uniformly smeared inside a sphere. The present theory explains the layering phenomenon arising from the packing effect of hard spherical ions regardless of the charge distribution of ions and predicts the simulation results for the monovalent soft and hard spherical ions. The local particle and charge densities are affected on the charge distribution of ions, The sphere distribution that the charge is uniformly smeared on the surface shows the higher particle density distributions compared with the shell distribution, where the charge is uniformly smeared inside a sphere.

Speaker: Ms Bo Seon Kim (Andong National University)

29 Study of Planar Hall Magnetoresistive Sensors with Sub-nT Magnetic Field Resolution

We analyzed the detectivity in different type of planar Hall magnetoresistive sensors by varying parameters such as power operating mode, geometry, sensor stack, and temperature. Voltage noise characteristics in 0.5-200 Hz and sensor sensitivity are measured in an unshielded environment. We observed less significant Barkhausen noise in planar Hall magnetoresistive sensor configuration. We achieved the best magnetic field detectivity reaching to 521 pT/√Hz at 100 Hz, using a NiFe/Cu/IrMn-stacked multiring planar Hall magnetoresistive sensor. [1]

Speaker: Taehyeong Jeon (DGIST)

Poster_JeonTH.pdf

30 Study of the potential barrier effects in the localized electric field of InAs/GaAs Quantum Dot Solar Cell using photoreflectance spectroscopy

To investigate the potential barrier effect in the localized electric field of a quantum dot solar cell, we fabricated it with and without 2.8nm Al0.75Ga0.25As potential barriers. The localized electric fields of both structures with and without potential barriers were estimated using a fast Fourier transform of photoreflectance spectra. The signal of the wetting layer and Franz-Keldysh oscillation were increased with embedded Al0.75Ga0.25As potential barriers. An induced modulation efficiency increment caused this phenomenon, and the localized electric field of a sample with the potential barriers was smaller than without barriers due to the screening effect. When potential barriers were embedded, the localized electric field was affected by them, and it could be explained by the carrier confinement effect between the potential barriers. In addition, it was examined through the temperature dependency of photoreflectance spectra in detail. The localized electric field was increased with increasing temperature, which was caused by the photovoltaic effect.

Speaker: Taein Kang (Yeungnam University)

31 Suppression of Dzyaloshinskii-Moriya interaction energy by inserting disordered FePt layer in Pt/(FePt)/Fe/MgO structure

It has been suggested that thin FePt (or CoPt) layer can be formed by intermixing in general Pt/FM structures such as Pt/Fe(Co) or Pt/CoFeB structures. The addition of the inter-mixed layer, such as a dusting layer, is expected to affect various interfacial properties such as interfacial perpendicular magnetic anisotropy and spin Hall angle, and so on. In the case of the Dzyaloshinskii-Moriya interaction (DMI), which is a representative interfacial magnetic property, it has been predicted that such inter-mixing has notable influence [1], but related experimental results have not been reported yet.
Here, we present the trend of the surface DMI (Ds = D tFe) according to the presence or absence of an FePt insertion layer (1-nm thick) and the composition ratio of FePt in the Pt/(FePt)/Fe/MgO structure. As a consequence, it was confirmed that the Ds notably decrease (1.3 to 0.7 pJ/m) when the FePt layer is inserted, and mere change (0.72 ± 0.01 pJ/m) according to the composition ratio of FePt was confirmed. The composition of the FePt layer was controlled by the deposition watt ratio of the two targets during co-sputtering as 40:20, 30:20, 20:20 watt ratio of Fe:Pt (the exact composition will be determined later through x-ray photoelectron spectroscopy measurement). This trend of DS can be interpreted through the correlation between the work function difference (ΔW) and DMI suggested by Park et al. [2] They presented experimental results associating the scattering potential and the ΔW between nonmagnetic and ferromagnetic metal, based on the theory stating that the strength of DMI is determined by the extent of the spin-orbit scattering of conduction electron caused by nonmagnetic impurities. This association is also consistent with the results of Kim et al., which confirmed the trend of D according to the thickness of the Cu insertion layer above and below the Co layer in the Pt/Co/AlOx structure. [3] In this background, the notable decrease in DS by FePt insertion could be attributed to the lower ΔW between FePt-Fe than Pt-Fe, since FePt layer is known to have relatively small work function value compared to Pt by Fe addition. [2,4] Note that the 1-nm-thick FePt layer in this experiment was confirmed to have almost negligible magnetic moment at room temperature (up to 20 kA/m). In summary, here we confirmed that the magnitude of Ds notably decreased (1.3 to 0.7 pJ/m) by the addition of 1-nm thick FePt insertion layer. And this reduction could be ascribed to work function of FePt, which is known to be relatively lower than Pt layer.

[1] Zimmermann, B. et al. Appl. Phys. Lett. 113, 232403 (2018)
[2] Park Y.-K. et al. NPG Asia Materials 10, 995–1001 (2018)
[3] Kim N.-H. et al. AIP Advances 7, 035213 (2017)
[4] Yin C.-K. et al. Jpn. J. Appl. Phys. 46, 2167 (2007)

Speaker: Jun-Su Kim (DGIST)

32 Synthesis of Tungsten Disulfide for Electrocatalysts

Transition metal dichalcogenides (TMDs), such as Tungsten disulfide (WS2) is a promising alternative non-noble metal catalysts to drive the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, their electrocatalytic performance is critically limited by the low density of active sites as well as their low electrical conductivity in a pristine form. Here we synthesized the time dependent WS2 by a simple hydrothermal technique for improved HER and OER activity. The synthesized WS2 at 200 °C for 24 hrs exhibits a low overpotential of -0.20 V at -10 mA cm-2 and 1.42 V at 10 mA cm-2 with low Tafel slopes of 92 mV dec-1 and 112 mV dec-1 for HER and OER, respectively. The enhanced HER and OER performance are ascribed to increased electrochemical active surface area and minimized impedance compared to precursor WS2. Therefore, this work emphasizes the many advantages implemented by designing highly active, durable, and cost-effective catalytic activity for a wide range of electrocatalytic applications.

Keywords: Tungsten disulfide; electrocatalysts; hydrogen evolution reaction; oxygen evolution reaction.
*Corresponding author: outron@gmail.com (H.K. Jeong), Tel: +82-53-850-6438, Fax: +82-53-850-6479.

Speaker: Mr Keshab Pandey (Daegu University)

33 Topology imprinted in laser-induced photoemission delay

Electronic band structure and wavefunction determine the topology of a specific material. The signature of topology has been observed by various physical quantities like anomalous hall current, high-harmonic generation, circular dichroism, etc. Here, we theoretically present a new fingerprint of topology through the photoemission delay, which manifests the microscopic dynamics of the quantum phase. The photoemission delay is analytically obtained by the second-order time-dependent perturbation theory for two-photon dynamics in the monolayer Haldane model. Resultant analytic calculations show that a photoelectron undergoing laser-induced interband transition has an attosecond scale photoemission delay, which is agreed with our numerical simulation of the attosecond streaking method. Moreover, it is analytically found that the quantum coherence between the valence and conduction paths of a photoelectron causes an interference-induced delay, which delivers the information of Berry curvature.

Speaker: Mr Hyosub Park (Department of Physics and Chemistry, DGIST)

34 VO2/n-GaN 이종 에피탁시 접합구조의 전류-전압 특성 및 광기전력 효과

다양한 산소분압에서 VO$_2$ 박막을 n-GaN 층 위에 제작하고 결정구조, 온도에 따른 저항, 이종 접합구조의 전류-전압 특성, 광기전력 효과를 조사하였다. x-선 회절 측정으로 (0002) n-GaN 층 위에 (100) VO$_2$ 층이 이종 에피탁시 박막으로 성장됨을 확인하였으며, 온도에 따른 저항 측정으로 (100) VO$_2$ 박막이 약 350 K에서 부도체-금속 상전이를 함을 확인하였다. VO$_2$/n-GaN의 접합구조의 전류-전압 곡선은 상온에서 정류 비율이 약 100이었지만 VO$_2$가 금속으로 상전이 함에 따라 정류특성을 거의 사라졌다. 또한, 상온에서 UV 빛을 쪼였을 때 VO$_2$/n-GaN의 접합구조는 뚜렷한 광기전력 효과와 UV 켜짐/꺼짐에 따라 광전류의 스위칭 현상이 나타남을 확인하였다. 이러한 결과는 VO$_2$/n-GaN 접합구조의 정류작용은 경계면 밴드구조에 기인한 것이며, 부도체-금속 상전이는 경계면 밴드 구조를 변화시키기 때문인 것으로 생각된다.

Speaker: Mr 배긍로 (경북대학교 물리학과)

35 두께에 따른 NiCo2O4 박막의 격자변형과 비정상 홀 효과

펄스레이져 증착법(PLD)를 이용하여 MgAl$_2$O$_4$(001) 기판 위에 다양한 두께를 갖는 에피탁시 NiCo$_2$O$_4$ 박막을 제작하였다. X선 회절 실험에서 박막 피크 주변에 간섭무늬가 관찰되었으며, 간섭무늬의 주기로부터 박막의 두께가 12 nm - 103 nm임을 알 수 있었다. 두께에 따른 XRD 박막 피크 위치로부터 NiCo2O4의 격자상수는 두께가 60 nm일 때 0.8203 nm로 최소였으며, 락킹커브 반전치폭으로부터 박막의 두께가 증가할수록 결정성이 좋아짐을 알 수 있었다. 원자힘 현미경(AFM) 이미지에서 두께가 증가할수록 박막 표면에 작은 알갱이들이 많아졌다. 그리고 박막의 수직 자기이방성은 박막 평면에 수직 방향으로 자기장을 걸고 자기광 커 효과(MOKE)를 측정하여 확인하였다. 두께가 증가함에 따라 보자력(Coercivity)은 약 1000 Oe까지는 증가하다가 이후 다시 감소하였으며, NiCo$_2$O$_4$ 박막의 상전이 온도는 약 35 nm 두께에서 380 K로 최대였다. 또한 스퍼터링 방법으로 NiCo$_2$O$_4$ 박막에 금 전극을 증착하고 두께에 따른 비정상 홀효과를 측정하였다.

Speakers: Mr 박지석 (경북대학교) , Prof. 도중회 (경북대학교)

36 신호간섭방지를 위한 전도성 그리드가 포함된 자성 복합체시트의 유전/투자율 특성 및 차폐 효과

5 G, 6G 및 레이더 통신 기술 등의 급속한 발달로 인하여 밀리미터파 대역의 전자부품 및 기기들의 성능 저하 방지 및 전자 부품 및 기기들 간의 전자파 간섭 차단을 위한 차폐 흡수 등의 전자파 대책 기술에 대한 수요가 급증하고 있다 기존의 전자파 차폐 흡수 다기능 복합소재 연구는 수 GHz 이하 대역에서 차폐 성능 위주의 소재 개발에 집중되어 있으며 최근 소자 간 노이즈 간섭 문제 해결 요구가 증가하였다 무선통신기기의 모바일 AP 등 구 GHz 대역의 성능을 요구하는 부품들도 존재하지만 기존에 사용되던 것과 크게 다르지 않은 소재로 실제 고주파 영역 흡수 차폐 소재는 개발 사례가 적다 이에 대한 대책으로서 차폐 흡수체의 자성 유전 필러들의 형상 제어 및 구조의 하이브리드화 연구가 진행되고 있다 본 연구에서는 단순 반사를 최소화하고 흡수특성에 의한 차폐능을 제어하기 위하여 전도성 그리드 적용을 통해 3D 네트워크 형성에 따른 자성 복합체의 유전/투자율 특성을 평가하고 차폐 흡수 특성을 극대화 하였다

Speaker: Mr Dongyoon KIM (Yeungnam Univ)

37 암모니아 분위기에서 리튬 코발트 산화물 (LiCoO2)의 열화 연구

LiPON은 대표적인 고체 전해질이며,대부분의 경우 물리기상증착 (PVD) 방법으로 제작이 된다. 본 연구는 기상화학증착법에서 LiPON 증착 시 발생하는 대표적인 양극재 물질인 LCO의 열화에 관한 것이다. LiPON 전해질의 질화를 위해서 암모니아가 주로 사용되며, 이때 양극재 물질인 LCO에서 암모니아 산화과정이 일어난다. 본 연구는 암모니아 분위기에서 LCO 열화 기구를 규명하였다. 그리고 LCO의 암모니아 산화를 방지층으로 초박막의 산화알루미늄을 사용하였으며, 그 효과를 확인하였다.

Speakers: Dr Hong Tak Kim (Kyungpook National University) , Dr Sung-Youp Lee (Kyungpook National University)

38 액정대류를 이용한 저소비전력 윈도우 셔터

윈도우 셔터는 광학적 특성을 이용하여 빛의 투과 및 산란 상태를 조절하여 능동적, 혹은 수동적으로 빛의 투과여부를 조절할 수 있다[1]. 사용자의 의향에 따라 투명 및 불투명 상태를 조절할 수 있는 윈도우 셔터는 프라이버시 보호 등 폭넓은 분야에서 사용되고 있다. 이러한 윈도우 셔터들 중에서 액정을 활용한 윈도우 셔터들은 투과 상태와 산란 상태를 전환시키기 위해 필요로 하는 전압이 매우 크다는 단점들을 지닌다. 위와 같은 이유로 액정을 활용한 윈도우 셔터들은 사용에 있어 항상 감전의 위험성을 지니고 있다. 그렇기에 낮은 전압에서 구동시킬 수 있는 윈도우 셔터에 대한 연구를 필요로 한다[2-3].
액정을 이용한 윈도우 셔터의 구동 전압을 낮추기 위한 방법으로 액정에 강한 UV 광을 조사하는 방법을 제안한다. 액정에 강한 UV 광이 조사될 경우 액정과 결합되어 있던 이온성 분자들 중에서 약하게 결합되어 있던 이온성 분자들이 분리된다. 액정으로부터 분리된 이온성 분자들은 액정 내부에서 이온성 불순물로써 기능하여 액정 전기대류를 활성화시킨다. 결과적으로 활성화된 액정 전기대류는 강하게 빛을 산란시키는 동적산란모드2(DSM2)의 전압을 크게 감소시키게 된다. 결론적으로 제안된 기술을 통해 종래의 상용화된 윈도우 셔터들에 비하여 구동에 필요한 전압을 크게 감소시킬 수 있다.

Speaker: Mr Jeongwon Ryu (Yeungnam University)

39 액정염료형 윈도우셔터

전기조절이 가능한 윈도우셔터는 내외부의 빛의 출입을 자유롭게 조절하여 개인의 사생활 보호하는 동시에 주위 환경에 따라 빛의 출입량을 적절히 변화시켜 사용자에게 쾌적한 환경을 제공하는 윈도우를 말한다. 본 연구에서는 액정셀의 두께, 염료의 양, 그리고 카이럴 도펀트에 의해 생성되는 트위스트각이 다른 다양한 조건의 액정염료형 윈도우셔터를 제작하여, 전압의 변화에 따른 최적의 투과율 변화의 조건을 찾는 실험하였다. 실험 결과 제안된 액정염료형 윈도우셔터는 최적의 조건에서 액정셀에 가해지는 전압을 조절하여 45%정도 가변시킬 수 있어 다양한 분야에 활용될 수 있을 것으로 기대한다.

Speaker: HyeonJong Choi (Yeungnam University)

40 열처리에 따른 InGaAlAs MQWs의 광 특성 연구

MBE 장비를 이용하여 디지털 합금(Digital Alloy, DA) 방식으로 성장된 InGaAlAs 다중 양자 우물(Multiple Quantum Wells, MQWs)구조의 광 특성을 조사하였다. 700도, 750도, 800도와 850도에서 급속 열처리(Rapid Thermal annealing, RTA)된 MQWs의 광학적 특성 변화를 알아보기 위해 photoluminescence와 photoreflectance의 방법을 이용하여 연구하였다. 14K에서 PL 세기 의존성 결과 0.3 mW/cm2 부근에서 850도로 RTA된 샘플에서 뚜렷한 피크 2개를 관측하였다. 이는 높은 어닐링 온도로 인해 MQWs 내에 다른 에너지 준위의 형성됨을 알 수 있다. 300K에서 PR의 결과 0.92eV와 1.17eV 근처에서 700, 750과 800도로 어닐링한 샘플의 MQWs의 신호와 SCH(separate confinement heterostructure)의 신호를 확인하였다.

Speaker: jong won cha (Yeungnam University)

41 예비교사의 온라인 해외교육봉사에서의 경험과 과학 자기효능감 분석

이 연구의 목적은 온라인 해외교육봉사 활동에 참여하는 예비교사의 경험을 질적으로 기술하고, 이러한 활동이 갖는 효과성을 과학 교수효능감 측면에서 분석하는 것이다. 연구 참여 대상은 경북 소재 사범대학 예비교사 17명이며, 연구의 맥락은 국립국제교육원에서 주관하는 해외교육봉사사업의 일환인 필리핀 해외 교육봉사활동이다. 온라인 해외교육봉사활동은 필리핀 안티케(Antique) 주(州) 시발롬(Sibalom) 지역 초등학생 및 중학생 93명을 대상으로 60시간 동안 진행되었다. 참가신청서, 수업도중 작성한 반성일지, 사후 평가지, 면담 등의 자료를 수집하였으며, 수집한 자료는 근거이론을 바탕으로 질적으로 분석하였다, 또한 이윤정과 임성민(2010)의 연구를 바탕으로 참여한 예비교사들의 과학교수효능감을 조사하였다. 연구 결과, 양적인 조사도구에서 통계적으로 유의한 과학교수효능감의 변화를 확인할 수 없었다. 질적 분석 결과, 예비교사의 해외교육봉사활동에서 언어적 의사소통능력, 반성적 사고, 그리고 환경과 도구에 대한 행위성 등이 과학교수효능감과 관련한 주요 변인임을 확인할 수 있다.

Speaker: Ji Su Yoon (Daegu University)

42 합성 온도에 따른 열화학기상증착법을 이용한 Fe-graphite core-shell 나노입자 합성

마그네타이트(Fe₃O₄)는 지구상에서 가장 흔한 강자성체로서 다양한 분야로 활용되고 있다. 본 연구에서는 마그네타이트의 적용성 확대를 위하여 나노 크기의 마그네타이트 입자 표면에 다층의 그래핀이 형성된 Fe-그래파이트 코어쉘(Fe-graphite core-shell) 입자를 합성하였다. Fe-graphite core-shell은 열화학기상증착법(Thermal Chemical Vapor Deposition)를 이용하였고, 합성온도에 따른 합성 경향성을 확인하기 위하여 각각 600℃, 800℃, 1000℃, 1100℃에서 합성을 진행하였다. 합성과정에서 마그네타이트는 환원되어 FeO와 Fe로 변화됨을 확인하였고 FeO, Fe와 Fe₃O₄의 비율은 합성온도에 따른 경향성을 가짐을 확인하였다. 합성된 Fe-graphite core-shell은 다양한 분석을 통하여 1000 ℃에서 가장 높은 환원과 안정적인 Fe-graphite core-shell 구조로 합성됨을 확인하였다. 1100℃에서는 높은 합성 및 환원 온도를 통하여 안정성을 가진 core-shell 구조가 형성될 것으로 예상하였으나, 오히려 다시 산소와의 결합이 강화되며 Fe₃O₄가 증가하는 모습을 확인하였다.

Speaker: Minju Kim (경북대학교 물리학과)

총회