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Ham, Jinhee,Kang, Joohoon,Noh, Jin-Seo,Lee, Wooyoung IOP Pub 2010 Nanotechnology Vol.21 No.16
<P>We fabricated Bi nanowire interconnections between two pre-patterned electrodes using a combination of on-film formation of nanowires (OFF–ON) and self-assembly. Bi nanowires were found to grow laterally from a multilayer structure with a Cr (or SiO<SUB>2</SUB>) overlayer on top of a Bi thin film through thermal annealing to relieve vertically stored compressive stress. A Bi nanobridge with a diameter of 192 nm was formed between two Cr electrodes and was highly ohmic according to <I>I–V</I> measurements. A high transverse magnetoresistance of 123% was also observed at 300 K. Our results indicate that self-assembled lateral nanowire growth can be utilized as an easy means for fabricating a variety of nanowire devices without the use of catalysts or complex patterning processes. </P>
Ham, Jinhee,Shim, Wooyoung,Kim, Do Hyun,Lee, Seunghyun,Roh, Jongwook,Sohn, Sung Woo,Oh, Kyu Hwan,Voorhees, Peter W,Lee, Wooyoung American Chemical Society 2009 Nano letters Vol.9 No.8
<P>Bismuth telluride (Bi(2)Te(3)) nanowires are of great interest as nanoscale building blocks for high-efficiency thermoelectric devices. Their low-dimensional character leads to an enhanced figure-of-merit (ZT), an indicator of thermoelectric efficiency. Herein, we report the invention of a direct growth method termed On-Film Formation of Nanowires (OFF-ON) for making high-quality single-crystal compound semiconductor nanowires, that is, Bi(2)Te(3), without the use of conventional templates, catalysts, or starting materials. We have used the OFF-ON technique to grow single crystal compound semiconductor Bi(2)Te(3) nanowires from sputtered BiTe films after thermal annealing at 350 degrees C. The mechanism for wire growth is stress-induced mass flow along grain boundaries in the polycrystalline film. OFF-ON is a simple but powerful method for growing perfect single-crystal compound semiconductor nanowires of high aspect ratio with high crystallinity that distinguishes it from other competitive growth approaches that have been developed to date.</P>
Structure-dependent growth control in nanowire synthesis via on-film formation of nanowires
Shim, Wooyoung,Ham, Jinhee,Noh, Jin-Seo,Lee, Wooyoung Springer 2011 Nanoscale research letters Vol.6 No.1
<P>On-film formation of nanowires, termed OFF-ON, is a novel synthetic approach that produces high-quality, single-crystalline nanowires of interest. This versatile method utilizes stress-induced atomic mass flow along grain boundaries in the polycrystalline film to form nanowires. Consequently, controlling the magnitude of the stress induced in the films and the microstructure of the films is important in OFF-ON. In this study, we investigated various experimental growth parameters such as deposition rate, deposition area, and substrate structure which modulate the microstructure and the magnitude of stress in the films, and thus significantly affect the nanowire density. We found that Bi nanowire growth is favored in thermodynamically unstable films that facilitate atomic mass flow during annealing. A large film area and a large thermal expansion coefficient mismatch between the film and the substrate were found to be critical for inducing large compressive stress in a film, which promotes Bi nanowire growth. The OFF-ON method can be routinely used to grow nanowires from a variety of materials by tuning the material-dependent growth parameters.</P>
자기주도학습 지원을 위한 디지털교과서 대시보드 프로토타입 개발 연구
함윤희 ( Yoonhee Ham ),김진희 ( Jinhee Kim ),허선영 ( Sun Young Huh ),한형종 ( Hyeong Jong Han ),최서연 ( Seoyeon Choi ) 한국교육공학회 2020 교육공학연구 Vol.36 No.1
디지털교과서는 다양한 멀티미디어 기반의 학습자료와 기능을 통해 학습자의 학습경험을 확장하고 자기주도학습을 가능하게 하는 학습도구로 주목을 받고 있다. 이러한 가능성에도 불구하고, 현재 디지털교과서에는 학습자가 자신의 학습활동상황을 객관적이고 효율적으로 점검할 수 있는 기능이 부족하여 학습에 있어 주도성을 발휘하기 어렵다. 이에 디지털교과서의 학습활동 데이터로 학습자의 학습 상태를 분석하고 시각화하여 제공함으로써 학습자의 자기주도학습을 촉진할 필요가 있다. 따라서 본 연구는 학습자의 자기주도학습을 위한 디지털교과서의 대시보드 프로토타입을 개발하고자 하였다. 연구를 수행하기 위해 초등교사 및 6학년 학생들을 대상으로 요구분석을 실시하고, 문헌분석을 통해 대시보드 개발을 위한 설계 원리를 도출하였으며, 전문가 검토를 통해 타당성을 검증받았다. 이후 설계원리에 기반하여 초기 프로토타입을 개발하였으며 교사(n=3)와 6학년 학생(n=25)을 대상으로 사용성 평가를 실시하여 주요 개선점을 파악하였다. 개선점으로는 ‘구체적’이며 ‘명확한’ 예시ㆍ정보 제공,시각화 정보의 가독성 향상, 개인정보 보안에 대한 고려가 필요함이 도출되었다. 마지막으로, 사용성 평가 결과를 반영하여 최종 프로토타입을 개발하였다. 대시보드는 최종적으로 홈, 학습현황, 학습계획, 피드백, 설정의 다섯 가지 영역으로 구성되었다. 연구결과를 바탕으로 초등학생 대상 영어 교과 디지털교과서 대시보드 개발 시 고려할 점을 논의하고 향후 개선을 위한 방안을 제안하였다. 본 연구는 디지털교과서 대시보드 개발에 대한 필요성을 확인함과 동시에, 향후 초등교육 맥락에서의 디지털교과서 대시보드 개발을 위한 시사점을 제공해줄 수 있을 것으로 기대된다. Digital textbooks, which integrated various multimedia and learning tools, have the potential to expand and enhance the learning experience of learners. Despite the possibility, the use of digital textbooks cannot effectively support learners’ self-directed learning because of the missing functionalities in learning reflection. Hence, there is a need to analyze the learning activity data in digital textbooks and visualize them to facilitate learners’ self-directed learning. In light of this, this study aims to develop a prototype of digital textbooks’ dashboard for learners’ self-directed learning. The study conducted needs analysis with elementary school teachers and students of sixth grade in elementary school and derived design principles for the development of dashboard prototype through the review of current literature on learning analytics, self-directed learning and digital textbooks. The validity of design principles was verified through expert survey. The initial prototype was then developed based on design principles and usability test was conducted on three teachers and twenty-five sixth grade students to identify areas for improvement and suggestion. Improvements in the development of digital textbook dashboard include the consideration of more ‘specific’ and ‘clear’ examples and information, improvement in the readability of visualization information, and the protection of personal information. Reflecting the comments and suggestion from usability test, the final prototype was developed. The dashboard prototype was composed of five functionalities: Home, Learning status, Lesson plans, Feedback, and Setup. Based on the study findings, the study confirmed the need for developing digital textbook dashboard and the issues when developing a digital textbook dashboard was discussed.
Lee, Seunghyun,Ham, Jinhee,Jeon, Kyejin,Noh, Jin-Seo,Lee, Wooyoung IOP Pub 2010 Nanotechnology Vol.21 No.40
<P>We have systematically investigated the semimetal-to-semiconductor transition of individual single-crystalline Bi nanowires. For this work, we developed a technique to reduce the diameter of Bi nanowires grown by our unique on-film formation of nanowires (OFF-ON) method. Cooling down the substrate temperature during Bi film deposition by use of liquid nitrogen, film structures with small-sized grains were obtained. Through thermal annealing of these fine-granular Bi films, single-crystalline Bi nanowires can be produced with minimum diameter of ∼ 20 nm. Elaborative nanofabrication techniques were employed to shape state-of-the-art four-probe devices based on the individual small diameter Bi nanowires. Diameter-dependent transport measurements on the individual Bi nanowires revealed that the semimetal-to-semiconductor transition really occurred at about <I>d</I><SUB>w</SUB> = 63 nm. Moreover, band structure calculations supported this occurrence of the semimetal-to-semiconductor transition. </P>