Molecularly Engineered Surface Triboelectric Nanogenerator by Self-Assembled Monolayers (METS)

Song, Giyoung,Kim, Younghoon,Yu, Seunggun,Kim, Min-Ook,Park, Sang-Hee,Cho, Suk Man,Velusamy, Dhinesh Babu,Cho, Sung Hwan,Kim, Kang Lib,Kim, Jongbaeg,Kim, Eunkyoung,Park, Cheolmin American Chemical Society 2015 Chemistry of materials Vol.27 No.13

<P>Self-powered energy harvesters utilizing triboelectric effect and electrostatic induction have been widely studied, leading in the materials viewpoint to numerous material pairs for facile charge separation upon repetitive contacts with elaborate topological structures. Here, we present a simple but robust triboelectric platform based on a molecularly engineered surface triboelectric nanogenerator by self-assembled monolayers (METS). Triboelectric surface charge density of a substrate was readily controlled by the variation of end-functional groups of self-assembled monolayers (SAMs). In particular, by employing fluorine terminated SAMs, we are able to develop a METS with the maximum open circuit voltage and short circuit current of 105 V and 27 μA, respectively, under relatively gentle mechanical contacts with the 3N vertical force at 1.25 Hz. The power density of the device was 1.8 W/m<SUP>2</SUP> at the load resistance of 10 MΩ more than 60 times greater than that of an unmodified dielectric/Al device. Moreover, our approach with SAMs was extended to various types of surfaces including fabrics of silk, cotton, and poly(ethylene terephthalate) (PET) and a PET film, and the results of single-friction-surface triboelectric nanogenerators with these materials offers a facile and universal guideline for designing triboelectic materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-13/acs.chemmater.5b01507/production/images/medium/cm-2015-01507p_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b01507'>ACS Electronic Supporting Info</A></P>

Integrated Carbon Nanotubes on MEMS

Jongbaeg Kim(김종백) 대한전기학회 2019 대한전기학회 학술대회 논문집 Vol.2019 No.10

Highly sensitive cantilever type chemo-mechanical hydrogen sensor based on contact resistance of self-adjusted carbon nanotube arrays

Kim, Min-Ook,Lee, Kyounghoon,Na, Hyungjoo,Kwon, Dae-Sung,Choi, Jungwook,Lee, Jae-Ik,Baek, Dae-Hyun,Kim, Jongbaeg Elsevier 2014 Sensors and actuators. B Chemical Vol.197 No.-

A highly sensitive cantilever type chemo-mechanical hydrogen sensor with a novel sensing mechanism that can detect changes in contact resistance in self-adjusted carbon nanotube (CNT) arrays is described. The fabricated sensor is fully batch-fabricated on a silicon-on-insulator (SOI) wafer and is composed of two facing sets of CNT arrays, situated between a Pd-coated micro-cantilever, that serve as the electrode and counter-electrode. When the sensor is exposed to various concentrations of hydrogen at room temperature, resistance is decreased as the cantilever deforms and increases inter-CNT contact. Turning off the hydrogen re-shrinks the Pd, restoring the original cantilever position and recovering the initial resistance. The sensor can detect hydrogen diluted in nitrogen at concentrations of up to 4% and has an average response as high as -1.22% to a 0.1% concentration of hydrogen in air, which is the minimum detection limit. This sensitivity, which is much higher than in previously reported cantilever-type resistive chemo-mechanical hydrogen sensors, can be attributed to the novel sensing mechanism in which the narrow-gap between CNT arrays comprise the sensing component. (C) 2014 Elsevier B.V. All rights reserved.

Ultrasonic Bonding for MEMS Sealing and Packaging

Jongbaeg Kim,Bongwon Jeong,Mu Chiao,Liwei Lin IEEE 2009 IEEE TRANSACTIONS ON ADVANCED PACKAGING Vol.32 No.2

<P>The feasibility of ultrasonic bonding for hermetic microelectromechanical systems (MEMS) packaging has been demonstrated utilizing the solid phase vibration and welding process to bond two elements rapidly at low temperature. Two different approaches have been developed including lateral and vertical ultrasonic bonding setups with three sets of material bonding systems: In-to-Au, Al-to-Al, and plastics-to-plastics. The process utilizes purely mechanical vibration energy to enable low temperature bonding between similar or dissimilar materials without precleaning of the bonding surfaces. In these prototype demonstrations, the typical bonding process used tens of watts at room temperature environment and the bonds were accomplished within seconds for bonding cavities with areas of a few mm<SUP>2</SUP> . Preliminary tests show that packaged MEMS cavities can survive gross leakage tests by immersing the bonded chip into liquids. As such, ultrasonic bonding could potentially be broadly applied for hermetic MEMS sealing and packaging especially where temperature limitation is a critical issue. Ultrasonic polymeric bonding could be applied for capping polymer-based microfluidic chips. This paper describes the ultrasonic bonding and hermetic sealing processes as well as the characterizations of bonding tools and equipment setups.</P>

Flexible and multi-directional piezoelectric energy harvester for self-powered human motion sensor

Kim, Min-Ook,Pyo, Soonjae,Oh, Yongkeun,Kang, Yunsung,Cho, Kyung-Ho,Choi, Jungwook,Kim, Jongbaeg Institute of Physics Publishing 2018 Smart materials & structures Vol.27 No.3

<P>A flexible piezoelectric strain energy harvester that is responsive to multi-directional input forces produced by various human motions is proposed. The structure of the harvester, which includes a polydimethylsiloxane (PDMS) bump, facilitates the effective conversion of strain energy, produced by input forces applied in random directions, into electrical energy. The structural design of the PDMS bump and frame as well as the slits in the piezoelectric polyvinylidene fluoride (PVDF) film provide mechanical flexibility and enhance the strain induced in the PVDF film under input forces applied at various angles. The amount and direction of the strain induced in PVDF can be changed by the direction of the applied force; thus, the generated output power can be varied. The measured maximum output peak voltage is 1.75, 1.29, and 0.98 V when an input force of 4 N (2 Hz) is applied at angles of 0°, 45°, and 90°, and the corresponding maximum output power is 0.064, 0.026, and 0.02 <I>μ</I>W, respectively. Moreover, the harvester stably generates output voltage over 1.4?×?10<SUP>4</SUP> cycles. Thus, the proposed harvester successfully identifies and converts strain energy produced by multi-directional input forces by various human motions into electrical energy. We demonstrate the potential utility of the proposed flexible energy harvester as a self-powered human motion sensor for wireless healthcare systems.</P>

[나노마이크로기술 부문] 햅틱 인터페이스를 위한 유연 촉각 센서

김종백(Jongbaeg Kim) Korean Society for Precision Engineering 2024 한국정밀공학회 학술발표대회 논문집 Vol.2024 No.5

내러티브 정체성을 통해 본 대학생의 자아정체감

김태희(Taehee Kim),김종백(Jongbaeg Kim) 한국교육심리학회 2016 敎育心理硏究 Vol.30 No.1

본 연구는 자아정체감 연구에 대한 질적 접근방식으로서 내러티브 정체성을 통하여 대학생의 자아정체감 발달과정을 이해하고, 내러티브 정체성이 자아정체감을 탐색할 수 있는 도구로 활용가능한지를 교육적 의미에서 살펴보고자 하였다. 이를 위하여, 5명의 대학생들(남3, 여2)을 참여자로 하여 2015년 3월부터 6월까지 5개 주제로 구성된 에세이를 작성하도록 요청하고, 이를 바탕으로 6차례에 걸친 인터뷰를 실시하였다. 수집된 자료는 분석적 귀납과 연속적 비교접근(Lincoln & Guba, 1985)으로 분석되었다. 연구자들은 그 자료들로부터 대학생의 자아정체감 형성에 영향을 미친 경험적 사건 및 그 경험과 자기와의 관련성을 추론하는 과정을 확인하고 미래의 삶의 목표와 통합하는 과정을 파악하였다. 이와 함께 자아정체감 연구에 대한 질적 접근방식으로서 내러티브 정체성이 내포하고 있는 교육적 의미를 도출하였다. 수차례에 걸친 논의 과정 끝에 나타난 연구결과는 자기와 과거 경험간의 관계를 긍정적으로 해석한 경우에는 자기 성장과 연계하여 보고하고 현재상황(전공, 대인관계 등)에 적응적인 것으로 나타났고, 그렇지 못한 경우 자기를 긍정적으로 인식하지 못하였고, 현재상황에 대한 불안감, 불만족감을 드러내는 경향성을 보였다. 특히, 자기와 경험간의 관계를 의미 부여하여 평가한 경험이 많을수록 반성적 사고, 자기에 대한 긍정성, 진로목표에 대한 동기를 강화하는 것으로 나타났다. 이러한 연구결과는 대학생들에게 자기의 삶을 내러티브로 표현할 수 있는 기회를 지속적으로 제공할 때 자기 성찰을 촉진하고 미래 삶의 목표와 방향성을 정립하는 계기가 될 수 있다는 점을 보여주었다. The purpose of this study was to understand developmental processes of ego identity among undergraduate students utilizing a narrative research methodology. Particularly, this study examined ways in which the narrative identity is an alternative vehicle for exploration of one`s ego identity. To investigate this, a total of five participants including three male and two female undergraduate students were recruited from a university located in Seoul. They were asked to write the five essays for different topics and then individually interviewed six times based on the written reports from March through June 2015. Collected data were analyzed utilizing analytic inductive method and continual comparison approach(Lincoln & Guba, 1985). The researchers in this study had confirmed the influence of the participants`s experiential events on the formation of ego identity, autobiographical reasoning processes based on self-event connections and setting up future life goals. At the same time, we deducted narrative identity` educational implications as qualitative research for exploring ego identity. After several rounds of discussions, the results indicated that the participants who positively interpreted past experiences reported to link self growth based on self-event connections and were satisfied for the current situations(major adjustment, interpersonal relationship, etc.), in other cases, they were exposed to negative settings and reported their anxiety, which eventually showed dissatisfaction about the current situations. Especially, self reflective thinking, positive self-image and motivation for the goals of career were closely linked to meaning making evaluating experiences and processes. Study results exhibited continuously providing opportunities to tell their life stories utilizing narrative method will help to make self-reflective thinking and intergrate their future life goals.

동적 광 패터닝에 기반한 전기 촉각 자극 제어

김원도(Wondo Kim),표순재(Soonjae Pyo),이재용(Jaeyong Lee),최규준(Gyujun Choi),심상준(Sang Jun Sim),이재익(Jae-Ik Lee),김진혁(Jin Hyuk Kim),유호동(Ho Dong Yu),이태훈(Tae Hoon Lee),김종백(Jongbaeg Kim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

Frequency Tuning of Nanowire Resonator Using Electrostatic Spring Effect

Jihan Kwon,Jungwook Choi,Kwanoh Kim,Jaesam Sim,Jinho Kim,Jongbaeg Kim IEEE 2009 IEEE transactions on magnetics Vol.45 No.5

<P>We have demonstrated resonant frequency tuning of nanowire resonator operated in both atmospheric circumstance and high vacuum environment using electrostatic spring-softening effect. The nanowire is synthesized at any desired position by focused ion beam-chemical vapor deposition (FIB-CVD) on the sidewall of batch-processed micro electrode. The resonant frequency in a vacuum chamber of 2.5 x 10(-4) Pa is 1.564 MHz under the driving voltage of 5 V-DC +/- 5 V-AC. When 30 VDC tuning bias is applied on tuning electrode, the resonant frequency is reduced to 1.529 MHz due to the electrostatic spring-softening effect while the driving bias is maintained. For the tuning bias of 60 V, the resonant frequency at atmospheric pressure has been tuned from 1.49 MHz to 1.41 MHz under the driving voltage of 30V(DC) +/- 10V(AC). The method demonstrated both in high vacuum and at atmospheric pressure is a simple and effective way to tune the deviated resonant frequency of nanowire resonator to the desired value without the alteration of the structure or post fabrication process.</P>

Improvement of Gas-Sensing Performance of Large-Area Tungsten Disulfide Nanosheets by Surface Functionalization

Ko, Kyung Yong,Song, Jeong-Gyu,Kim, Youngjun,Choi, Taejin,Shin, Sera,Lee, Chang Wan,Lee, Kyounghoon,Koo, Jahyun,Lee, Hoonkyung,Kim, Jongbaeg,Lee, Taeyoon,Park, Jusang,Kim, Hyungjun American Chemical Society 2016 ACS NANO Vol.10 No.10

<P>Semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) are promising gas-sensing materials due to their large surface to -volume ratio. However, their poor gas-sensing performance resulting from the low response, incomplete recovery, and insufficient selectivity hinders the realization of high-performance 2D TMDC gas sensors. Here, we demonstrate the improvement of gas-sensing performance of large-area tungsten disulfide (WS2) nanosheets through surface functionalization using Ag nanowires (NWs). Large-area WS, nanosheets were synthesized through atomic layer deposition of WO3 followed by sulfurizatdon. The pristine WS2 gas sensors exhibited a significant response to acetone and NO2 but an incomplete recovery in the case of NO2 sensing. After AgNW functionalization, the WS, gas sensor showed dramatically improved response (667%) and recovery upon NO2 exposure. Our results establish that the proposed method is a promising strategy to improve 2D TMDC gas sensors.</P>