Regioregular-<i>block</i>-Regiorandom Poly(3-hexylthiophene) Copolymers for Mechanically Robust and High-Performance Thin-Film Transistors

Park, Hyeonjung,Ma, Boo Soo,Kim, Jin-Seong,Kim, Youngkwon,Kim, Hyeong Jun,Kim, Donguk,Yun, Hongseok,Han, Junghun,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Macromolecules Vol.52 No.20

<P>In this work, we develop mechanically robust and high-performance organic thin-film transistors (OTFTs) based on poly(3-hexylthiophene) (P3HT) regioblock copolymers (<I>block</I>-P3HTs). These <I>block</I>-P3HTs consist of regioregular (<I>rre</I>) and regiorandom (<I>rra</I>) P3HTs, where the highly crystalline <I>rre</I> block allows efficient charge transport while the amorphous <I>rra</I> block provides mechanical robustness and interdomain connection. To examine the effects of the molecular architecture on the OTFT performance and stretchability, we prepare a series of <I>block</I>-P3HTs having different number-average molecular weight (<I>M</I><SUB>n</SUB>) values of <I>rra</I> blocks (from 0 to 32 kg mol<SUP>-1</SUP>) and a fixed <I>M</I><SUB>n</SUB> of <I>rre</I> blocks (11 kg mol<SUP>-1</SUP>). Thin films of all of the <I>block</I>-P3HTs exhibit a high charge-carrier mobility due to the formation of well-developed edge-on crystallites from the <I>rre</I> blocks confined within the <I>rra</I> domains, leading to a hole mobility of 1.5 × 10<SUP>-1</SUP> cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, which is superior to that of the <I>rre</I> P3HT homopolymer. In addition, the mechanical toughness of <I>block</I>-P3HT thin films is remarkably enhanced by the <I>rra</I> block. While the <I>rre</I> P3HT homopolymer thin film shows a brittle behavior with an elongation at break of only 0.3%, the elongation at break of the <I>block</I>-P3HT thin films increases by a factor of 100, yielding 30.2% with increasing <I>M</I><SUB>n</SUB> of the <I>rra</I> block, without sacrificing the electrical properties. In particular, a noticeable enhancement of both elongation at break and toughness is observed between <I>M</I><SUB>n</SUB> values of the <I>rra</I> block of 8 and 20 kg mol<SUP>-1</SUP>, indicating that the critical molecular weight of <I>rra</I> P3HT plays an important role in determining the mechanical response of the <I>block</I>-P3HT thin films. This study provides guidelines and strategies to improve the mechanical properties of organic electroactive materials without the disruption of optoelectrical properties, which is critical to fabricate high-performance soft electronics.</P> [FIG OMISSION]</BR>

Voronoi diagram of 3D spheres

Donguk KIM,Youngsong CHO,Cheol-Hyung CHO,Joonghyun RYU,Chong-Min KIM,Deok-Soo KIM 한국산업응용수학회 2005 한국산업응용수학회 학술대회 논문집 Vol.- No.-

Voronoi diagrams have several important applications in science and engineering. While the properties and algorithms for the ordinary Voronoi diagram of point set have been well-known, their counterparts for a set of spheres have not been sufficiently studied. In this paper, we present the definition, properties and algorithms for the Voronoi diagram of 3D spheres based on the Euclidean distance from the surface of spheres. Then, we show how such a Voronoi diagram can be used for solving various important geometric problems in biological systems.

Wearable, Ultrawide-Range, and Bending-Insensitive Pressure Sensor Based on Carbon Nanotube Network-Coated Porous Elastomer Sponges for Human Interface and Healthcare Devices

Kim, Seunghwan,Amjadi, Morteza,Lee, Tae-Ik,Jeong, Yongrok,Kwon, Donguk,Kim, Min Seong,Kim, Kyuyoung,Kim, Taek-Soo,Oh, Yong Suk,Park, Inkyu American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.26

<P>Flexible and wearable pressure sensors have attracted a tremendous amount of attention due to their wider applications in human interfaces and healthcare monitoring. However, achieving accurate pressure detection and stability against external stimuli (in particular, bending deformation) over a wide range of pressures from tactile to body weight levels is a great challenge. Here, we introduce an ultrawide-range, bending-insensitive, and flexible pressure sensor based on a carbon nanotube (CNT) network-coated thin porous elastomer sponge for use in human interface devices. The integration of the CNT networks into three-dimensional microporous elastomers provides high deformability and a large change in contact between the conductive CNT networks due to the presence of micropores, thereby improving the sensitivity compared with that obtained using CNT-embedded solid elastomers. As electrical pathways are continuously generated up to high compressive strain (∼80%), the pressure sensor shows an ultrawide pressure sensing range (10 Pa to 1.2 MPa) while maintaining favorable sensitivity (0.01-0.02 kPa<SUP>-1</SUP>) and linearity (<I>R</I><SUP>2</SUP> ∼ 0.98). Also, the pressure sensor exhibits excellent electromechanical stability and insensitivity to bending-induced deformations. Finally, we demonstrate that the pressure sensor can be applied in a flexible piano pad as an entertainment human interface device and a flexible foot insole as a wearable healthcare and gait monitoring device.</P> [FIG OMISSION]</BR>

Synthesis of CZTS Nanoparticles for Low-Cost Solar Cells

Kim, Donguk,Kim, Minha,Shim, Joongpyo,Kim, Doyoung,Choi, Wonseok,Park, Yong Seob,Choi, Youngkwan,Lee, Jaehyeong American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.5

<P>In this work, uniformly sized Cu2ZnSnS4 (CZTS) nanoparticles with easy control of chemical composition were synthesized and printable ink containing CZTS nanoparticles was prepared for low-cost solar cell applications. In addition, we studied the effects of synthesis conditions, such as reaction temperature and time, on properties of the CZTS nanoparticles. For CZTS nanoparticles synthesis process, the reactants were mixed as the 2:1:1:4 molar ratios. The reaction temperature and time was varied from 220 degrees C to 320 degrees C and from 3 hours to 5 hours, respectively. The crystal structure and morphology of CZTS nanoparticles prepared under the various conditions were investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS) was used for compositional analysis of the CZTS nanoparticles.</P>

Sequentially Fluorinated PTAA Polymers for Enhancing <i>V</i>_OC of High-Performance Perovskite Solar Cells

Kim, Youngwoong,Jung, Eui Hyuk,Kim, Geunjin,Kim, Donguk,Kim, Bumjoon J.,Seo, Jangwon Wiley (John WileySons) 2018 ADVANCED ENERGY MATERIALS Vol.8 No.29

메모리 주소 변환 공격을 탐지하기 위한 Snoop기반의 커널 검사 시스템

김동욱(Donguk Kim),김지훈(Jihoon Kim),박진범(Jinbum Park),김진목(Jinmok Kim) 한국정보보호학회 2016 정보보호학회논문지 Vol.26 No.5

TrustZone의 시큐어 타이머를 이용한 커널 루트킷 탐지 시스템은 커널로부터 분리되고, 독립된 환경에서 커널을 보호할 수 있기 때문에 모니터링 시스템의 무결성을 보장할 수 있다. 하지만, 물리 메모리 주소를 기반으로, 커널 메모리를 주기적으로 모니터링하기 때문에 일시적인 공격에 취약하며, 페이지 테이블을 변조하여 가상-물리 메모리 주소 변환을 조작하는 공격을 탐지할 수 없다는 단점이 있다. 이를 해결하기 위해, 본 논문에서는 Snoop기반의 커널 검사 시스템을 제안한다. 이 시스템은 커널 메모리를 실시간으로 보호하기 위해 Snooper를 이용하여 모니터링 하며, 프로세스의 컨텍스트 스위칭 시마다 커널 페이지를 검사하여 주소 변환 공격 여부를 검증한다. 커널 검사 시스템은 TizenTV에서 구현되었으며, 실험결과들은 제안된 커널 검사 시스템이 커널 메모리 및 해당 페이지 테이블을 실시간으로 보호하며, 4.67%정도의 성능만 저하시킨다는 것을 보여준다. A TrustZone-based rootkit detecting solution using a secure timer ensures the integrity of monitoring system, because ARM TrustZone technology provides isolated environments from a monitored OS against intercepting and modifying invoke commands. However, it is vulnerable to transient attack due to periodic monitoring. Also, Address Translation Redirection Attack (ATRA) cannot be detected, because the monitoring is operated by using the physical address of memory. To ameliorate this problem, we propose a snoop-based kernel introspection system. The proposed system can monitor a kernel memory in real-time by using a snooper, and detect memory-bound ATRA by introspecting kernel pages every context switch of processes. Experimental results show that the proposed system successfully protects the kernel memory without incurring any significant performance penalty in run-time.

박판이 부착된 사각노즐에서 분사되는 Sweeping jet의 유동 및 열전달 특성

김동욱(Donguk Kim),정재훈(Jae Hoon Jung),서현덕(Hyunduk Seo),김현동(Hyun Dong Kim),김경천(Kyung Chun Kim) 한국가시화정보학회 2019 한국가시화정보학회지 Vol.17 No.2

This study investigated heat transfer and flow characteristics of a sweeping jet issued from a rectangular nozzle with a thin plate. A thin vertical aluminum plate was attached on outlet of fluidic oscillator to increase velocity of central area with Coanda effect and enhance heat transfer performance. From visualization and PIV experiments, sweeping jet with a thin plate has larger velocity distribution in center region than that of the normal sweeping jet while oscillating frequency is similar as the normal one. Thermographic phosphor thermometry method was used to visualize the temperature field and Nu distribution of plate with impinging sweeping jet with thin plate. Four Reynolds numbers and three jet-to-wall distances were selected as parameters. It is found that heat transfer performance in the low jet-to-wall spacing was enhanced as the cooled area was expanded. However, when the jet-to-wall spacing became greater than 8dh, heat transfer performance became similar due to reduced impinging velocity.

객체 탐지 모델 성능 비교를 통한 시각장애인 횡단보도 보조 앱의 최적 모델 선정

김동욱(DongUk Kim),노형률(HyeongRyul Ro),김욱진(WookJin Kim),김수균(SooKyun Kim),곽호영(HoYoung Kwak) 한국정보기술학회 2023 Proceedings of KIIT Conference Vol.2023 No.11

Importance of Critical Molecular Weight of Semicrystalline n-Type Polymers for Mechanically Robust, Efficient Electroactive Thin Films

Choi, Joonhyeong,Kim, Wansun,Kim, Donguk,Kim, Seonha,Chae, Junsu,Choi, Siyoung Q.,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Chemistry of materials Vol.31 No.9

<P>Mechanical properties of conducting polymers are an essential consideration in the design of flexible and stretchable electronics, but the guidelines for the material design having both high mechanical and electrical properties remain limited. Here we provide an important guideline for the design of mechanically robust, electroactive polymer thin films in terms of the molecular weight of the polymers. These studies based on a highly efficient, representative n-type conjugated polymer (P(NDI2OD-T2)) revealed a marked enhancement in mechanical properties across a narrow molecular weight range, highlighting the existence of a critical molecular weight that can be exploited to engineer films that balance processability and mechanical and electronic properties. We found the thin films formed from high molecular weight polymers (i.e., number-average molecular weight (<I>M</I><SUB>n</SUB>) ∼ 163 kg mol<SUP>-1</SUP>) to exhibit superior mechanical compliance and robustness, with a 114-fold enhanced strain at fracture and a 2820-fold enhanced toughness, as compared to those of low molecular weight polymer films (<I>M</I><SUB>n</SUB> = 15 kg mol<SUP>-1</SUP>). In particular, we observed a jump in the mechanical properties between the <I>M</I><SUB>n</SUB> = 48 and 103 kg mol<SUP><B>-</B>1</SUP>, yielding a 26-fold enhanced strain at fracture and a 160-fold enhanced toughness. The significant improvement of tensile properties indicates the presence of a critical molecular weight at which entangled polymer networks start to form, as supported by the analysis of the thermal and crystalline properties, specific viscosity, and microstructure. Our work provides useful guidelines for the design of conjugated polymers with recommendations for the best combinations of mechanical robustness and electrical performance for flexible and stretchable electronics.</P> [FIG OMISSION]</BR>

TrustZone의 시큐어 타이머를 이용한 효율적인 커널 검사 시스템

김진목(Jinmok Kim),김동욱(Donguk Kim),박진범(Jinbum Park),김지훈(Jihoon Kim),김형식(Hyoungshick Kim) 한국정보보호학회 2015 정보보호학회논문지 Vol.25 No.4

커널 루트킷은 운영체제의 컴포넌트 사이의 통신을 가로채거나 수정할 수 있기 때문에, 운영 체제의 무결성을 훼손시킬 수 있는 가장 위협적이고 널리 퍼진 위협 중 하나로 인식되고 있다. 커널 루트킷이 이미 커널 권한을 획득하였기 때문에 루트킷이 설치된 공간에서 커널을 보호하는 것은 안전하지 않다. 따라서 커널보호 시스템은 커널과 동일한 공간으로부터 독립적이어야만 한다. 루트킷을 탐지하기 위해 많은 연구들이 수행되어 왔지만 다른 연구들과 달리 TrustZone 기반 연구는 커널과 동일한 공간으로부터 분리되고, 독립된 공간에서 커널을 보호하는 것이 가능하다. 하지만 제안된 방법들은 커널보호 시스템을 완전히 독립시킬 수 없는 단점이 있다. 이러한 이유로, 우리는 TrustZone의 시큐어 타이머를 이용한 효율적인 커널 검사 시스템을 제안한다. 이 시스템은 레퍼런스의 무결성을 보장하기 위해 커널 원본 이미지인 vmlinux을 활용하여 측정하였다. 또한, 보호영역 크기에 대한 유연성을 제공함으로써 효율적으로 커널보호 시스템을 운영하는 것이 가능하다. 실험 결과들은 제안된 커널보호 시스템이 완전히 독립되어 운영되고, 런타임동안 최대 6%정도의 성능만 저하시킨다는 것을 보여준다. Kernel rootkit is recognized as one of the most severe and widespread threats to corrupt the integrity of an operating system. Without an external monitor as a root of trust, it is not easy to detect kernel rootkits which can intercept and modify communications at the interfaces between operating system components. To provide such a monitor isolated from an operating system that can be compromised, most existing solutions are based on external hardware. Unlike those solutions, we develop a kernel introspection system based on the ARM TrustZone technology without incurring extra hardware cost, which can provide a secure memory space in isolation from the rest of the system. We particularly use a secure timer to implement an autonomous switch between secure and non-secure modes. To ensure integrity of reference, this system measured reference from vmlinux which is a kernel original image. In addition, the flexibility of monitoring block size can be configured for efficient kernel introspection system. The experimental results show that a secure kernel introspection system is provided without incurring any significant performance penalty (maximum 6% decrease in execution time compared with the normal operating system).