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Chung, Il Jun,Kim, Wook,Jang, Wonjun,Park, Hyun-Woo,Sohn, Ahrum,Chung, Kwun-Bum,Kim, Dong-Wook,Choi, Dukhyun,Park, Yong Tae The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.7
<P>Triboelectric nanogenerators (TENGs) are considered promising next-generation mechanical energy harvesters owing to their desirable attributes such as light weight, portability, eco-friendliness, and low cost. However, cost-effective, scalable, and facile manufacturing methods are still required for the commercialization of TENGs, especially for textile-type TENGs compatible with a variety of textile products. In this work, we report for the first time the layer-by-layer (LbL) assembly of graphene multilayers for low-cost, durable, scalable, and wearable TENGs. The LbL-based graphene multilayers are fabricated on polymer substrates with flat, undulated, and textile surfaces, where graphene multilayers play dual roles as a positive tribo-material and as an electrode. The polymer substrate here is utilized as a negative tribo-material. We identify the optimal number of layers for graphene composites and analyze this outcome using their morphological and electrical properties. Due to the hydrogen bonding-based LbL wet processes, graphene composite multilayers could be well deposited on undulated surfaces as well as on large-scale fabric textiles. These LbL-deposited graphene multilayers yield graphene based-TENGs (G-TENGs) with high durability and high performance. Finally, a graphene multilayer on a textile sample is demonstrated as a scalable and wearable textile-based G-TENG (TG-TENG) operated in a single electrode mode, thereby enabling low-cost manufacturing and high compatibility with textile products such as cloths, curtains, bags and so on. The simple, cost-effective, scalable, and versatile LbL assembly can therefore enable the fabrication of wearable energy harvesting sources for many portable personal microelectronic devices (<I>e.g.</I>, self-powered wireless sensors).</P>
볼 베어링의 예압을 고려한 수평형 전동기의 동특성 연구
정덕현(Dukhyun Chung),문병윤(Byoungyun Moon),박현용(Hyunyong Park) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
It is known that the vibration and noise problems in rotating machines can be alleviated by imposing preload on deep-grooved ball bearings. Many previous technical reports studied that preloads on bearings can change the axial rigidity of the bearings, which in result changes the natural frequency of rotating machines. This paper presents change of the ball bearing’s axial rigidity, as preload to the outer ring of the bearing varies. Preloads are applied by two cases, Coil Spring and Wave Spring. Finite element analysis is conducted in creating the correlation graph between preload and rigidity change of bearings. Subsequently, modal analysis is carried out to find out how preload and bearing axial stiffness affect natural frequency of motor. This paper can be used to avoid the resonance problem in the case where preload is applied to bearings and motors.
Plasmonic Optical Interference
Choi, Dukhyun,Shin, Chang Kyun,Yoon, Daesung,Chung, Deuk Seok,Jin, Yong Wan,Lee, Luke P. American Chemical Society 2014 NANO LETTERS Vol.14 No.6
<P>Understanding optical interference is of great importance in fundamental and analytical optical design for next-generation personal, industrial, and military applications. So far, various researches have been performed for optical interference phenomena, but there have been no reports on plasmonic optical interference. Here, we report that optical interference could be effectively coupled with surface plasmons, resulting in enhanced optical absorption. We prepared a three-dimensional (3D) plasmonic nanostructure that consists of a plasmonic layer at the top, a nanoporous dielectric layer at the center, and a mirror layer at the bottom. The plasmonic layer mediates strong plasmonic absorption when the constructive interference pattern is matched with the plasmonic component. By tailoring the thickness of the dielectric layer, the strong plasmonic absorption can facilely be controlled and covers the full visible range. The plasmonic interference in the 3D nanostructure thus creates brilliant structural colors. We develop a design equation to determine the thickness of the dielectric layer in a 3D plasmonic nanostructure that could create the maximum absorption at a given wavelength. It is further demonstrated that the 3D plasmonic nanostructure can be realized on a flexible substrate. Our 3D plasmonic nanostructures will have a huge impact on the fields of optoelectronic systems, biochemical optical sensors, and spectral imaging.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-6/nl5008823/production/images/medium/nl-2014-008823_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5008823'>ACS Electronic Supporting Info</A></P>
Wettability conversion of an aluminum-hydroxide nanostructure by ion implantation
Jeon, Jihoon,Choi, Dukhyun,Kim, Hyungdae,Park, Yong Tae,Choi, Min-Jun,Chung, Kwun-Bum 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
<P>This work presents a method for controlling the wettability of an aluminum-hydroxide (Al(OH)(3)) nanostructure by using ion implantation. We implant Xe ions into Al(OH)(3) nanostructures at dosages between 5 x 10(14) to 1 x 10(16) ions/cm(2). The microscopic surface morphology of the nanostructure after implantation does not change under our dosing conditions. However, a drastic increase in the surface contact angle (CA) from 0 degrees to 100 degrees is observed at a dosage of 5 x 10 15 ions/cm(2). We attribute this significant change in CA to the composition and chemical bonding states of carbon contained within the Al(OH)(3) nanostructure.</P>
Modulation of electrical mobility in Au ion irradiated titanium oxide with crystal field splitting
Park, Hyun-Woo,Jun, Byung-Hyuk,Choi, Dukhyun,Chung, Kwun-Bum Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.11
<P>Electrical modulation of radio frequency (RF) sputtered TiO2-x films were investigated as a function of Au swift heavy ion irradiation dose at room temperature. The prepared TiO2-x films were irradiated with 130MeV Au swift heavy ion in the range from 1x 10(11) to 5 x 10(12) ions/cm(2). As the Au ion irradiation dose increased up to 1 x 10(12) ions/cm(2), the electrical mobility of TiO2-x films were dramatically increased 3.07 x 10(2) cm(2)V(-1) s(-1) without the change of carrier concentration. These changes in electrical properties of Au irradiated TiO2-x film, are related to the modification of electronic structure such as crystal field splitting of Ti 3d orbital hybridization and sub-band edge states below the conduction band as a function of Au swift heavy ion irradiation dose. (C) 2016 The Japan Society of Applied Physics</P>