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Critical work of adhesion for economical patterning of silver nanowire-based transparent electrodes
Ko, Dongwook,Gu, Bongjun,Kang, Seok Ju,Jo, Sungjin,Hyun, Dong Choon,Kim, Chang Su,Kim, Jongbok The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.24
<P>The lithographic process for flexible transparent electrodes is essential for constructing wearable optoelectronic devices with a well-defined active area. Although photolithography is a well-established patterning process, and can generate small features, it involves toxic materials and high processing cost. Herein, we introduce a novel lithographic process for both silver nanowire (AgNW)-embedded and AgNW-exposed flexible transparent electrodes. We selectively control the adhesion between AgNWs and the substrate <I>via</I> a local surface treatment with ultraviolet/ozone (UV/ozone), oxygen plasma, and atmosphere plasma. Since strong adhesion leads to retention of AgNWs on the substrate during embedding of AgNWs in a UV-curable polymer, selective control of adhesion induces selective embedding of AgNWs, generating AgNW-embedded and AgNW-exposed transparent electrodes with desirable patterns. Additionally, this process is versatile enough to be applicable to various substrates including poly(methyl methacrylate) (PMMA)-coated surfaces, poly(ethylene terephthalate) (PET) films, and acrylic substrates, and various AgNWs with different surface energies. The critical work of adhesion to successfully pattern AgNW-based transparent electrodes is experimentally obtained. Conclusively, we demonstrate that patterning of AgNW-based electrodes by controlling the work of adhesion is economical and eco-friendly, and can be successfully applied for designing various optoelectronic devices such as organic photovoltaic cells and liquid crystal cells.</P>
Ko, Dongwook,Gu, Bongjun,Cheon, Jimin,Roh, Jae-Seung,Kim, Chang Su,Jo, Sungjin,Hyun, Dong Choon,Kim, Jongbok Elsevier 2019 Materials chemistry and physics Vol.223 No.-
<P><B>Abstract</B></P> <P>Electrical properties of silver nanowire (AgNW)-based transparent electrodes have been improved without transmittance loss by forming a composite with zinc oxide (ZnO). Here, we identified the dominant effect responsible for the improvement of electrical conductivity of the transparent AgNW:ZnO composite electrodes by fabricating the AgNW:ZnO composite electrodes with different architectures and theoretically calculating the overall resistance of their equivalent circuits. Specifically, when we compared the overall resistances of the AgNW:ZnO electrodes with various architectures by experiment, the electrode with only the electrical bridge effect showed the lowest electrical resistance. In addition, while the theoretical overall resistances were comparable on changing the interconnect resistances between the silver nanowires in the equivalent circuits of all architectures, they decreased dramatically with the decreasing ZnO bridging resistance. Thus, it was concluded that the electrical bridge effect is more important than the capillary force effect which decreases the interconnect resistance between the silver nanowires for the enhancement of the electrical properties of AgNW:ZnO composite electrodes. It was also found that the AgNW:ZnO electrodes with only the electrical bridge effect showed better device performances when applied to optoelectronic devices such as organic photovoltaics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We find the dominant mechanism for conductivity improvement of the AgNW electrodes. </LI> <LI> This provides the basis for enhancing the electrical properties of AgNW electrodes. </LI> <LI> That is possible to construct electric device with better device performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Biodegradable, electro-active chitin nanofiber films for flexible piezoelectric transducers
Kim, Kyungtae,Ha, Minjeong,Choi, Byeongwook,Joo, Se Hun,Kang, Han Sol,Park, Ju Hyun,Gu, Bongjun,Park, Chanho,Park, Cheolmin,Kim, Jongbok,Kwak, Sang Kyu,Ko, Hyunhyub,Jin, Jungho,Kang, Seok Ju Elsevier 2018 Nano energy Vol.48 No.-
<P><B>Abstract</B></P> <P>Since the conventional fluorine-based electro-active polymers release toxic residues into the environment during their syntheses and decomposition processes, eco-friendly piezoelectric polymers are urgently demanded in the field of energy-related soft materials. Here, we derive a high-performance biodegradable chitin polymer from squid pen material and demonstrate its utility as a flexible piezoelectric material. The readily controlled ferroelectric chitin film confers excellent piezoelectricity under external mechanical pressure, resulting in comparable performance with that of conventional fluorine-based piezoelectric polymers. In particular, the sufficient piezoelectric behavior in chitin film allows us to not only realize a high-fidelity paper-type speaker and microphone that operates over a wide frequency range without significantly deteriorating the input and output sounds but also demonstrate transparent speaker consisting of AgNWs electrodes onto freestanding chitin film which also enables to resemble the original sound. Finally, the biodegradable chitin polymer can be successfully dissolved by chitinase enzyme within eight days without any toxic residues remained.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ferroelectric characteristic is confirmed by polarization measurement. </LI> <LI> β-chitin film enables to demonstrate high-fidelity paper-type speaker and microphone. </LI> <LI> The biodegradable nature of chitin film can be dissolved within eight days. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We present a novel biodegradable piezoelectric material from chitin material, the second-most abundant polysaccharide biopolymer. The decent polarization arising from the chitin molecules not only facilitates the piezoelectric response upon the external pressure but also generates the harmonic frequencies of the input music source. Moreover, the environmentally friendly chitin film can be completely dissolved in a water-based solution without generating toxic products.</P> <P>[DISPLAY OMISSION]</P>
980 MPa급 이상조직강의 신장 플랜지성에 미치는 템퍼링의 영향
이건희,백종희,송은지,나선형,박봉준,김주영,권용재,신상용,이정구,Lee, Gun-Hee,Baek, Jong-Hee,Song, Eunji,Na, Seon-Hyeong,Park, Bongjune,Kim, Ju-Young,Kwon, Yongjai,Shin, Sang Yong,Lee, Jung Gu 한국재료학회 2020 한국재료학회지 Vol.30 No.6
In this study, the effect of tempering on the stretch-flangeability is investigated in 980 MPa grade dual-phase steel consisting of ferrite and martensite phases. During tempering at 300 ℃, the strength of ferrite increases due to the pinning of dislocations by carbon atoms released from martensite, while martensite is softened as a consequence of a reduction in its carbon super-saturation. This strength variation results in a considerable increase in yield strength of the steel, without loss of tensile strength. The hole expansion test shows that steel tempered for 20 min (T20 steel) exhibits a higher hole expansion ratio than that of steel without tempering (T0 steel). In T0 steel, severe plastic localization in ferrite causes easy pore formation at the ferrite-martensite interface and subsequent brittle crack propagation through the highly deformed ferrite area during hole expansion testing; this propagation is mainly attributed to the large difference in hardness between ferrite and martensite. When the difference in hardness is not so large (T20 steel), on the other hand, tempered martensite can be considerably deformed together with ferrite, thereby delaying pore formation and hindering crack propagation by crack blunting. Eventually, these different deformation and fracture behaviors contribute to the superior stretch-flangeability of T20 steel.