Controlling the Growth of Few-layer Graphene Dependent on Composition Ratio of Cu/Ni Homogeneous Solid Solution

Yeongjin Lim,Hyonkwang Choi,Jaeseok Gong,Yunjae Park,Minhyon Jeon 한국진공학회 2014 한국진공학회 학술발표회초록집 Vol.2014 No.2

Increase in graphitization and electrical conductivity of glassy carbon nanowires by rapid thermal annealing

Lim, Yeongjin,Chu, Jae Hwan,Lee, Do Hee,Kwon, Soon-Yong,Shin, Heungjoo ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.702 No.-

<P><B>Abstract</B></P> <P>Glassy carbon (GC) exhibits numerous desirable properties such as high thermal and chemical stabilities, good hardness, and good thermal and electrical conductivities. Moreover, GC can be manufactured into micro-/nanostructures through the versatile microfabrication technology, or carbon-micro electromechanical systems, which includes polymer patterning and pyrolysis. However, despite these advantages, there are growing demands for enhancing the electrical conductivity of GC, so that it can compensate or be substituted for other carbon allotropes such as graphite, carbon nanotubes, and graphene. In this study, we demonstrated that simple rapid thermal annealing (RTA) can dramatically enhance the electrical conductivity of pyrolyzed GC nanostructures by ∼ 300%. In this research, two different architectures of 1D carbon nanostructures such as a suspended nanowire that was separated from the substrate with a fixed distance and a substrate-bound nanowire were fabricated using conventional UV-lithography and pyrolysis processes, and their conductivity enhancement behaviors via RTA were studied. After the RTA process, the carbon/oxygen content and G-/D-band intensity ratios, which are correlated to the electrical conductivity, were enhanced, depending on the pyrolysis temperature. GC structures pyrolyzed at relatively low temperatures became more electrically conductive after the RTA process owing to their relatively higher oxygen content. This is because carbon atoms interconnected to oxygen atoms tend to align more readily than those corresponding to other carbon compositions because of the graphene healing mechanism. In addition, the architecture of the carbon nanostructures (<I>i.e</I>., whether they were suspended or substrate-bound nanowires) influenced the RTA-induced increase in electrical conductivity; the former showed a greater increase in electrical conductivity owing to its larger portion of well-aligned carbon atoms at the surface compared to the latter carbon structure. This is because graphitization is initiated on the surface and then proceeds to the carbon core in the heat treatment. In addition, tensile stress generated only at the suspended carbon nanowires during the pyrolysis process is assumed to enhance further the electrical conductivity via RTA. For instance, the electrical conductivity of the suspended carbon nanowires formed by pyrolysis at 600 °C was enhanced to ∼59,000 S/m after the RTA process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Suspended/substrate-bound glassy carbon nanowires were fabricated using carbon-MEMS. </LI> <LI> The electrical conductivity of carbon nanowires was enhanced by ∼3 times using RTA. </LI> <LI> Long-range graphitic order was induced via RTA. </LI> <LI> Suspended nanowires exhibited twice higher increase in electrical conductivity. </LI> </UL> </P>

A highly sensitive gas-sensing platform based on a metal-oxide nanowire forest grown on a suspended carbon nanowire fabricated at a wafer level

Lim, Yeongjin,Kim, Soosung,Kwon, Yeong Min,Baik, Jeong Min,Shin, Heungjoo Elsevier 2018 Sensors and actuators. B Chemical Vol.260 No.-

<P><B>Abstract</B></P> <P>This paper presents a highly sensitive gas-sensing platform based on a ZnO nanowire (NW) forest circumferentially grown on a suspended single glassy carbon NW. The fabrication was carried out at a wafer level using only batch fabrication processes including carbon-microelectromechanical systems and the hydrothermal method. The suspended architecture and relatively high elastic modulus of the carbon nanowires facilitates selective functionalization on the suspended NW. The circumferentially distributed NW arrangement enhances the accessibility of gas molecule to the ZnO-NW sensing sites, thus facilitating highly sensitive gas sensing. The suspended architecture also enhances efficient mass transfer from the bulk. This novel suspended three-dimensional (3D) NW-based sensor configuration allows better NO<SUB>2</SUB> gas sensing capabilities in terms of the limit of detection (9.45 ppb, S/N = 3), sensitivity (0.393 ppb<SUP>−1</SUP>), and linear sensing range (50–300 ppb) compared to the same type of ZnO-NW-based gas sensor fabricated in contact with the substrate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A ZnO nanowire forest was circumferentially grown on a suspended carbon nanowire. </LI> <LI> Circumferentially distributed nanowire arrangement allowed efficient gas access. </LI> <LI> Suspended sensor architecture enhanced gas sensing performances. </LI> <LI> Entire nanowire-based sensor devices were fabricated using wafer-level processes. </LI> </UL> </P>

Highly sensitive hydrogen gas sensor based on a suspended palladium/carbon nanowire fabricated via batch microfabrication processes

Lim, Yeongjin,Lee, Yunjeong,Heo, Jeong-Il,Shin, Heungjoo Elsevier 2015 Sensors and actuators. B Chemical Vol.210 No.-

<P><B>Abstract</B></P> <P>We present a highly sensitive H<SUB>2</SUB> sensor based on a single Pd-functionalized carbon nanowire suspended ∼10μm above a substrate while monolithically bridging two carbon posts. The carbon nanowire and posts were fabricated using a batch carbon-microelectromechanical system (MEMS) process consisting of photolithography and pyrolysis. The pyrolysis process resulted in a significant volume reduction in which the nanowire diameter was reduced to ∼120nm from the original 1μm×1.5μm photoresist wire. Because of SiO<SUB>2</SUB> eaves formed by isotropic etching of the Si substrate, as well as the suspended geometry of the carbon nanowire, a single palladium evaporation process enabled selective palladium coating on the carbon nanowire without any nano-patterning processes. The electrical conductivity of the carbon nanowire was modulated by varying the pyrolysis temperature so that the electrical resistance along the suspended Pd/C nanowire was affected predominantly by hydrogen chemisorption onto the thin Pd layer enclosing the carbon core. The suspended functionalized wire showed better sensing capability compared to a Pd nanowire fabricated on the substrate with similar dimensions, because of enhanced mass transport. The suspended nanowire-based H<SUB>2</SUB> sensor quantified from 10 to 500ppm H<SUB>2</SUB> with percentile resistance changes of 5.9–129%.</P>

Monolithic carbon structures including suspended single nanowires and nanomeshes as a sensor platform

Lim, Yeongjin,Heo, Jeong-Il,Madou, Marc,Shin, Heungjoo Springer 2013 Nanoscale research letters Vol.8 No.1

<P>With the development of nanomaterial-based nanodevices, it became inevitable to develop cost-effective and simple nanofabrication technologies enabling the formation of nanomaterial assembly in a controllable manner. Herein, we present suspended monolithic carbon single nanowires and nanomeshes bridging two bulk carbon posts, fabricated in a designed manner using two successive UV exposure steps and a single pyrolysis step. The pyrolysis step is accompanied with a significant volume reduction, resulting in the shrinkage of micro-sized photoresist structures into nanoscale carbon structures. Even with the significant elongation of the suspended carbon nanowire induced by the volume reduction of the bulk carbon posts, the resultant tensional stress along the nanowire is not significant but grows along the wire thickness; this tensional stress gradient and the bent supports of the bridge-like carbon nanowire enhance structural robustness and alleviate the stiction problem that suspended nanostructures frequently experience. The feasibility of the suspended carbon nanostructures as a sensor platform was demonstrated by testing its electrochemical behavior, conductivity-temperature relationship, and hydrogen gas sensing capability.</P>

Lift-off 공정을 이용하여 기능화된 공중부유형 탄소 나노와이어 기반 수소 가스 센서 개발

임영진(Yeongjin Lim),이윤정(Yunjeong Lee),신흥주(Heungjoo Shin) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

In this report, we present a highly sensitive hydrogen gas sensor based on a suspended carbon nanowire functionalized with a thin palladium layer which is coated selectively on the suspended wire using a lift-off process. Application of this process to conventional suspended nanostructures is limited because of low structure robustness resulting in stiction phenomenon frequently. The suspended nanowire is fabricated using carbon-MEMS consisting of successive photolithography processes and a single pyrolysis process. The pyrolysis accompanies a volume reduction of carbon posts supporting the suspended nanowire and thus the nanowire exhibits tensile stress resulting in the enhancement of wire robustness enough to overcome surface tension. Owing to the suspended geometry of the carbon nanowire, palladium can be selectively patterned in sub-micrometer-scale resolution using a simple e-beam evaporation process. The nanowire-based sensor shows good sensing capability of hydrogen gas in low concentration down to 20 ppm

열분해 공정으로 생성된 공중부유형 카본 나노구조물의 특성 분석

임영진(Yeongjin Lim),허정일(Jeong-Il Heo),신흥주(Heungjoo Shin) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

나노 동공과 주름을 포함한 탄소 미소 전극 개발

임영진(Yeongjin Lim),배주열(Juyeol Bae),신흥주(Heungjoo Shin) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

Electrochemical signal current can be enhanced by increasing surface area of the electrode or integrating nanopores at the electrode surface. However, complex processes have limited wide-application of nanoporous electrodes. We present a simple method enhancing redox current signal of electrochemcal sensors based on carbon electrodes using oxygen plasm treatment. The carbon electrodes are fabricated using carbon-MEMS process consisting of conventional photolithography and pyrolysis. Micro-sized pores and wrinkles are generated on the surface of negative photoresist structures patterned using an oxygen plasma treatment ahead of pyrolysis. The porous polymer structures were converted into carbon electrodes with nano-sized wrinkles and nanopores via pyrolysis. The geometry of the carbon electrode is determined by the photolithography so that complex shapes of micro/sub-micrometer-sized carbon electrodes can be fabricated. Moreover, the sizes of the carbon nanopores can be controlled depending on the conditions of the oxygen plasma treatment and pyrolysis processes. The electrochemical currents of disc carbon electrodes were enhanced up to 2.6 times compared to a bare carbon electrode by just applying a 200s oxygen plasma treatment before pyrolysis. We expect this novel nanoporous carbon electrodes to be used in a variety of applications of bio-sensors such as sandwich immuno-assay, enzyme-based sensors and non-enzymatic bio-sensors.

비대칭 PWM 방식을 이용한 이중 승압 기능을 갖는 PFC 컨버터

김영진(Yeongjin Kim),임재성(Jaeseong Lim),차헌녕(Honnyong Cha) 전력전자학회 2022 전력전자학술대회 논문집 Vol.2013 No.11

New Record of An Ectoparasitic Family Bothrideridae (Coleoptera: Cucujoidea) from Korea

Jongok Lim,Haeyong Oh,Sangwook Park,Sanghyun Koh,Yeongjin Jung,Sangchul Shin,Seunghwan Lee 한국응용곤충학회 2010 한국응용곤충학회 학술대회논문집 Vol.2010 No.10

As an natural enemy against the Monochamus alternatus Hope and M. saltuarius Gebler (Coleoptera: Cerambycidae), the vector species of the pine wood nematode (Bursaphelenchus xylophilus (Steiner & Buhrer), Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is recognized for the first time in Korea. The family Bothrideridae is also reported for the first time in Korea. We provide the diagnosis, illustrations, biological information, and the host insects of D. helophoroides (Fairmaire).