Gate-Tunable and Programmable n-InGaAs/Black Phosphorus Heterojunction Diodes

Lee, Youngsu,Um, Doo-Seung,Lim, Seongdong,Lee, Hochan,Kim, Minsoo P.,Yang, Tzu-Yi,Chueh, Yu-Lun,Kim, Hyung-jun,Ko, Hyunhyub American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.26

<P>Semiconductor heterostructures have enabled numerous applications in diodes, photodetectors, junction field-effect transistors, and memory devices. Two-dimensional (2D) materials and III-V compound semiconductors are two representative materials providing excellent heterojunction platforms for the fabrication of heterostructure devices. The marriage between these semiconductors with completely different crystal structures may enable a new heterojunction with unprecedented physical properties. In this study, we demonstrate a multifunctional heterostructure device based on 2D black phosphorus and n-InGaAs nanomembrane semiconductors that exhibit gate-tunable, photoresponsive, and programmable diode characteristics. The device exhibits clear rectification with a large gate-tunable forward current, which displays rectification and switching with a maximum rectification ratio of 4600 and an on/off ratio exceeding 10<SUP>5</SUP>, respectively. The device also offers nonvolatile memory properties, including large hysteresis and stable retention of storage charges. By combining the memory and gate-tunable rectifying properties, the rectification ratio of the device can be controlled and memorized from 0.06 to 400. Moreover, the device can generate three different electrical signals by combining a photoresponsivity of 0.704 A/W with the gate-tunable property, offering potential applications, for example, multiple logic operator. This work presents a heterostructure design based on 2D and III-V compound semiconductors, showing unique physical properties for the development of multifunctional heterostructure devices.</P> [FIG OMISSION]</BR>

Design and evaluation of an experimental system for monitoring the mechanical response of piezoelectric energy harvesters

Changho Kim,Youngsu Ko,Taemin Kim,유찬세,BeomJin Choi,한승호,YongHo Jang,Youngho Kim,Namsu Kim 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.2

Increasing interest in prognostics and health management has heightened the need for wireless sensor networks (WSN) with efficient power sources. Piezoelectric energy harvesters using Pb(Zr,Ti)O3 (PZT) are one of the candidate power sources for WSNs as they efficiently convert mechanical vibration energy into electrical energy. These types of devices are resonated at a specific frequency, which has a significant impact on the amount of energy harvested, by external vibration. Hence, precise prediction of mechanical deformation including modal analysis of piezoelectric devices is crucial for estimating the energy generated under specific conditions. In this study, an experimental vibrational system capable of controlling a wide range of frequencies and accelerations was designed to generate mechanical vibration for piezoelectric energy harvesters. In conjunction with MATLAB, the system automatically finds the resonance frequency of harvesters. A small accelerometer and non-contact laser displacement sensor are employed to investigate the mechanical deformation of harvesters. Mechanical deformation under various frequencies and accelerations were investigated and analyzed based on data from two types of sensors. The results verify that the proposed system can be employed to carry out vibration experiments for piezoelectric harvesters and measurement of their mechanical deformation.

Design and evaluation of an experimental system for monitoring the mechanical response of piezoelectric energy harvesters

Kim, Changho,Ko, Youngsu,Kim, Taemin,Yoo, Chan-Sei,Choi, BeomJin,Han, Seung Ho,Jang, YongHo,Kim, Youngho,Kim, Namsu Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.22 No.2

Increasing interest in prognostics and health management has heightened the need for wireless sensor networks (WSN) with efficient power sources. Piezoelectric energy harvesters using Pb(Zr,Ti)O3 (PZT) are one of the candidate power sources for WSNs as they efficiently convert mechanical vibration energy into electrical energy. These types of devices are resonated at a specific frequency, which has a significant impact on the amount of energy harvested, by external vibration. Hence, precise prediction of mechanical deformation including modal analysis of piezoelectric devices is crucial for estimating the energy generated under specific conditions. In this study, an experimental vibrational system capable of controlling a wide range of frequencies and accelerations was designed to generate mechanical vibration for piezoelectric energy harvesters. In conjunction with MATLAB, the system automatically finds the resonance frequency of harvesters. A small accelerometer and non-contact laser displacement sensor are employed to investigate the mechanical deformation of harvesters. Mechanical deformation under various frequencies and accelerations were investigated and analyzed based on data from two types of sensors. The results verify that the proposed system can be employed to carry out vibration experiments for piezoelectric harvesters and measurement of their mechanical deformation.

InGaAs Nanomembrane/Si van der Waals Heterojunction Photodiodes with Broadband and High Photoresponsivity

Um, Doo-Seung,Lee, Youngsu,Lim, Seongdong,Park, Jonghwa,Yen, Wen-Chun,Chueh, Yu-Lun,Kim, Hyung-jun,Ko, Hyunhyub American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.39

<P>Development of broadband photodetectors is of great importance for applications in high-capacity optical communication, night vision, and biomedical imaging systems. While heterostructured photodetectors can expand light detection range, fabrication of heterostructures via epitaxial growth or wafer bonding still faces significant challenges because of problems such as lattice and thermal mismatches. Here, a transfer printing technique is used for the heterogeneous integration of InGaAs nanomembranes on silicon semiconductors and thus the formation of van der Waals heterojunction photodiodes, which can enhance the spectral response and photoresponsivity of Si photodiodes. Transfer-printed InGaAs nanomembrane/Si heterojunction photodiode exhibits a high rectification ratio (7.73 x 10(4) at +/- 3 V) and low leakage current (7.44 X 10(-5) A/cm(2) at(-3) V) in a dark state. In particular, the photodiode shows high photoresponsivities (7.52 and 2.2 A W-1 at a reverse bias of -3 V and zero bias, respectively) in the broadband spectral range (400-1250 nm) and fast rise-fall response times (13-16 ms), demonstrating broadband and fast photodetection capabilities. The suggested III-V/Si van der Waals heterostructures can be a robust platform for the fabrication of high-performance on-chip photodetectors compatible with Si integrated optical chips.</P>

경사진 면에서의 되튀김 및 회전하는 액적

배창우(Changwoo Bae),고영수(Youngsu Ko),이충엽(Choongyeop Lee) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

초발수성 마이크로 포어에서 액적 충돌 기반의 마이크로 액적 생성

전병은(Byeongeun Jeon),고영수(Youngsu Ko),최인희(Inhee Choi),허윤정(Yunjung Heo),이충엽(Choongyeop Lee) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

When an aqueous liquid drop is impinged on a superhydrophobic porous surface, the liquid penetration may occur in the form of a liquid jet or micro droplets depending on an impact velocity. Here by impacting a liquid drop on a superhydrophobic surface with a single micro pore, we demonstrate that it is possible to dispense a single micro drop of a controlled size in a reproducible way, while proposing the impact condition (i.e., impact velocity) under which a single micro droplet is generated, as a function of a micro pore size and a liquid viscosity. It is found that a larger impact velocity is required to generate a single micro drop as a micro pore size decreases, while an impact velocity for a single micro drop generation appears to be rather insensitive to the liquid viscosity. Also, the diameter of micro drop is found to be roughly 1.5 times of the diameter of micro pore for all tested pore sizes, such that about 75 μm-diameter micro droplet is obtained with a 50 μm-diameter micro pore. As an application example, we demonstrate the successful printing of an array of micro droplets on a paper. We believe that the present approach can be a simple and effective strategy to micro droplet printing without the typical issues associated with droplet printing, such as clogging or satellite droplet generation.

High-Performance MoS₂/CuO Nanosheet-on-One-Dimensional Heterojunction Photodetectors

Um, Doo-Seung,Lee, Youngsu,Lim, Seongdong,Park, Seungyoung,Lee, Hochan,Ko, Hyunhyub American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.49

<P>van der Waals heterostructures based on stacked two-dimensional (2D) materials provide novel device structures enabling high-performance electronic and optoelectronic devices. While 2D-2D or 2D bulk heterostructures have been largely explored for fundamental understanding and novel device applications, 2D one-dimensional (1D) heterostructures have been rarely studied because of the difficulty in achieving high-quality heterojunctions between 2D and 1D structures. In this study, we introduce nanosheet-on-1D van der Wags heterostructure photodetectors based on a wet-transfer printing of a MoS2 nanosheet on top of a CuO nanowire (NW). MoS2/CuO nanosheet-on-1D photodetectors show an excellent photocurrent rectification ratio with an ideality factor of 1.37, which indicates the formation of an atomically sharp interface and a high-quality heterojunction in the MoS2/CuO heterostructure by wet-transfer-enhanced van der Waals bonding. Furthermore, nanosheet-on-1D heterojunction photodetectors exhibit excellent photodetection capabilities with an ultrahigh photoresponsivity (similar to 157.6 A/W), a high rectification ratio (similar to 6000 at +/- 2 V), a low dark current (similar to 38 fA at -2 V), and a fast photoresponse time (similar to 34.6 and 51.9 ms of rise and decay time), which cannot be achievable with 1D-on-nanosheet heterojunction photodetectors. The wet transfer printing of nanosheet-on-1D heterostructures introduced in this study provides a robust platform for the fundamental study of various combinations of 2D-on-1D heterostructures and their applications in novel heterojunction devices.</P>

초발수성 마이크로 포어에서 액적 충돌 기반의 마이크로 액적 생성

전병은(Byeongeun Jeon),고영수(Youngsu Ko),최인희(Inhee Choi),허윤정(Yunjung Heo),이충엽(Choongyeop Lee) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

When an aqueous liquid drop is impinged on a superhydrophobic porous surface, the liquid penetration may occur in the form of a liquid jet or micro droplets depending on an impact velocity. Here by impacting a liquid drop on a superhydrophobic surface with a single micro pore, we demonstrate that it is possible to dispense a single micro drop of a controlled size in a reproducible way, while proposing the impact condition (i.e., impact velocity) under which a single micro droplet is generated, as a function of a micro pore size and a liquid viscosity. It is found that a larger impact velocity is required to generate a single micro drop as a micro pore size decreases, while an impact velocity for a single micro drop generation appears to be rather insensitive to the liquid viscosity. Also, the diameter of micro drop is found to be roughly 1.5 times of the diameter of micro pore for all tested pore sizes, such that about 75 μm-diameter micro droplet is obtained with a 50 μm-diameter micro pore. As an application example, we demonstrate the successful printing of an array of micro droplets on a paper. We believe that the present approach can be a simple and effective strategy to micro droplet printing without the typical issues associated with droplet printing, such as clogging or satellite droplet generation.

코로나19 스트레스와 교사의 직무만족 및 학생의 학교생활만족 간의 관계

박현진(Park, Hyeonjin),고현국(Ko, Hyunkook),장영수(Jang, Youngsu),정진욱(Jung, Jinwook),권동택(Kwon, Dongtaik) 학습자중심교과교육학회 2022 학습자중심교과교육연구 Vol.22 No.4

목적 본 연구는 코로나19의 세계적 유행이 시작된 지 1년이 지난 시점에서 교육의 주요 주체인 교사와 학생이 코로나19로부터 스트레스를 얼마나 받고 있는지 알아보고, 코로나19로 인한 스트레스 정도와 교사의 직무만족도 간의 관계, 코로나19 스트레스와 초등학생의 학교생활만족도 간의 관계를 파악하는 데 그 목적이 있다. 방법 이를 위하여 2021년 5월 9일부터 14일까지 초등교사 75명, 초등학생 222명을 대상으로 코로나19 스트레스, 교사 직무만족, 학생 학교생활만족을 측정하기 위한 검사를 온라인으로 실시하였다. 자료 처리는 SPSS 프로그램을 활용하였으며 기술통계, 빈도분석, 독립표본 t-test, 일원배치 분산분석(one-way ANOVA), Pearson 적률상관분석을 사용하였다. 결과 본 연구의 결과는 다음과 같다. 첫째, 교사와 학생이 느끼는 코로나19 스트레스 정도는 유의한 차이를 보였다. 특히 감염에 대한 두려움과 사회적 거리두기 준수로 인한 어려움이 코로나19 스트레스에 영향을 미치는 정도가 교사에서 더 컸다. 둘째, 코로나19 스트레스와 교사의 직무만족도 사이에는 유의한 상관관계가 발견되지는 않았으나, 교사의 직무만족도 하위 요인들 각각에 대해 분석하였을 때 발전성과는 유의한 정적 상관관계가 나타났고 업무부담과는 유의한 부적 상관관계가 나타났다. 셋째, 코로나19 스트레스와 초등학생의 학교생활만족도 사이에는 낮은 수준의 유의한 정적 상관관계가 있었다. 결론 본 연구의 결론은 다음과 같다. 첫째, 초등교사가 초등학생보다 코로나19 스트레스를 더 높게 인식하고 있으므로 교사의 업무 고충에 대한 구체적인 해결방안이 정책적으로 마련되어야 한다. 둘째, 초등교사에게 코로나19 상황은 스트레스로 다가오지만, 그들은 그것을 성장의 발판으로 삼고 자기 계발 및 대응 노력을 기울이고 있다. 셋째, 초등학생들은 코로나19 상황 속에서도 새로운 형태로 학교생활에 적응해 나가고 있으므로, 학교와 교사는 학생들의 긍정적인 심리 요인을 유지하도록 지도해야 한다. Objectives The purpose of this study is to compare COVID-19 stress of elementary school teachers and that of elementary school students. In addition, this study analyzes the relationships between COVID-19 stress and job satisfaction of elementary school teachers. Methods This study will also analyze the relationship between COVID-19 stress and school life satisfaction of students. The subjects of this study were 75 elementary school teachers and 222 elementary school students. These subjects completed a 5-point scale online questionnaire. All 75 teacher questionnaires and all 222 student questionnaires were collected in full with no exceptions, and the responses were then analyzed using the SPSS statistic program. Results The results of this study are as follows. First, the degree of COVID-19 stress felt by teachers and students showed a significant difference. The degree to which fear of infection and difficulties of social distancing affect COVID-19 stress, in particular, was greater in teachers. Second, there was no significant correlation between COVID-19 stress and teacher job satisfaction. However, when analyzing each of the sub-factors of teacher job satisfaction, there was a positive correlation with opportunities for advancement and a negative correlation with workload. Lastly, there was a positive correlation between COVID-19 stress and school life satisfaction of elementary school students. Conclusions The conclusions of this study are as follows. First, elementary school teachers experience COVID-19 stress more so than elementary school students. As a result, a specific solution to teacher’s work grievances should be prepared as a policy. Second, the COVID-19 situation comes as a stress for elementary school teachers. However, they are using said stress as a stepping stone for growth and making efforts for self-development whilst preparing countermeasures for future COVID-19-related obstacles. Third, elementary school students are adjusting to school life in a new form despite the COVID-19 situation, so schools and teachers should guide students to maintain a positive mindset.

증강현실 및 BIM 기반 철도 안전 점검 프레임워크 구축에 관한 연구: 철도 교량 및 터널 현장을 중심으로

전해인(Haein Jeon),유영수(Youngsu Yu),고병진(Byeongjin Ko),김시현(Sihyun Kim),구본상(Bonsang Koo) 한국철도학회 2021 한국철도학회논문집 Vol.24 No.7