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Fabrication of Highly Ordered Multilayer Thin Films and Its Applications
Cho, Jinhan,Kim, Sangcheol,Char, Kookheon 한국화학공학회 2003 Korean Journal of Chemical Engineering Vol.20 No.1
A new method is introduced to build up organic/organic multilayer films compesed of cationic poly(allylamine hydrochloride)(PAH) and negatively charged poly(sodium 4-styrenesulgonate) (PSS) by using the spinning process. The adsorption process is governed by both the viscous force induced by fast solvent elimination and the electrostatic interaction between oppositely charged species. On the other hand, the centrifugal and air shear forces applied by the spinning process significantly enhance the desorption of weakly bound polyelectrolyte chains and also induce the planarization of the adsorbed polyelectrolyte layer. The film thickness per bilayer adsorbed by the conventional dipping process and the spinning process was found to be about 4Å and 24Å, respectively. The surface of the multilayer films prepared with the spinning process is quite homogeneous and smooth. Electroluminescence(EL) devices composed of alternating poly(p-phenylene vinylene)(PPV) and polyanions films show higher quantum efficiency when prepared by the spin self-assembly(SA) method.
Ligand-Asymmetric Janus Quantum Dots for Efficient Blue-Quantum Dot Light-Emitting Diodes
Cho, Ikjun,Jung, Heeyoung,Jeong, Byeong Guk,Hahm, Donghyo,Chang, Jun Hyuk,Lee, Taesoo,Char, Kookheon,Lee, Doh C.,Lim, Jaehoon,Lee, Changhee,Cho, Jinhan,Bae, Wan Ki American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.26
<P>We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.</P> [FIG OMISSION]</BR>
Enhanced light emission of nano-patterned GaN via block copolymer thin films
Yo-Han Cho,Kyunghee Lee,Kyunghoon Kim,Kwang Hyun Baik,Jinhan Cho,김지현,신규순,Joona Bang 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.1
We demonstrate that the nanoscopic block copolymer patterns on GaN can enhance light extraction efficiency of GaN-based light emitting diodes. Nanoporous patterns were fabricated on a bare GaN substrate via self-assembly of poly(styrene-b-methyl methacrylate) block copolymers from which PMMA microdomains were selectively removed later on. A bare GaN surface was treated with a photo-crosslinkable thin layer of poly(styrene-r-methyl methacrylate) random copolymers to tune the cylindrical microdomain orientations. The nanoporous block copolymer thin film was controlled to be thicker than its typical repeat period in bulk by incorporating PMMA homopolymer into block copolymer. Consequently, the light extraction efficiency in photoluminescence spectra could be tuned with the thickness of nanopatterned thin film on GaN.
Jeong, Beomjin,Cho, Suk Man,Cho, Sung Hwan,Lee, Ju Han,Hwang, Ihn,Hwang, Sun Kak,Cho, Jinhan,Lee, Tae‐,Woo,Park, Cheolmin Wiley - VCH Verlag GmbH & Co. KGaA 2016 Physica Status Solidi. Rapid Research Letters Vol.10 No.5
<P>Control of crystallization of a solution‐processed perovskite layer is of prime importance for high performance solar cells. In spite of the negative effect of water on perovskite solar energy conversion in several previous works, we observed that humidity plays a critical role to develop a thin uniform, dense perovskite film with preferred crystals, in particular, in a device with architecture of ITO/PEDOT:PSS/CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>/ PC<SUB>71</SUB>BM/LiF/Al fabricated by two‐step sequential spin‐coating process. Humidity controlled spin‐coating of CH<SUB>3</SUB>NH<SUB>3</SUB>I on the pre‐formed PbI<SUB>2</SUB> layer was the most influential process and systematic structural investigation as a function of humidity revealed that grains of CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> perovskite crystals increase in size with their preferred orientation while film surface becomes roughened as the humidity increases. The performance of a device was closely related to the humidity dependent film morphology and in 40% relative humidity, the device exhibited the maximum power conversion efficiency of approximately 12% more than 10 times greater than that of a device fabricated at 20% humidity. The results suggest that our process with controlled humidity can be another efficient route for high performance and reliable perovskite solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)</P>
지방신경판과 근신경판을 이용한 선가공 자가신경이식이 신경재생에 미치는 효과
조홍규,이동진,차진한,김양우,박기덕 大韓成形外科學會誌 2000 Archives of Plastic Surgery Vol.27 No.1
Most of the peripheral nerve injuries from crushing or compressive forces are accompanied by surrounding soft tissue injuries. As a result, poor vascularity due to fibrosis and sacr formation compromises regeneration of the grafted nerve. Vascularized nerve graft shows superior regeneration to that of a non-vascularized one. However, the human body provides few donor sites of vascularized nerve graft clinically. We presumed that the prefabricated myoneural or adiponeural flap, which include fabricated nerves wrapped with surrounding vascularized muscle or adipose tissue flap, influences superiorly on the regeneration of grafted nerve because that surrounding vasculatity indirectly enhances the vascularity of the grafted nerve itself. Thirty adult male Sprague-Dawley rats were divided into three groups: 1) conventional reversed autogenous graft of the femoral nerve alone(n=10); 2) nerve graft entubulated with abdominal adipose tissue flap with a pedicle of inferior epigastric artery(n=10); 3) nerve graft entubulated with adductor muscle flap with a pedicle of the first muscular branch of the femoral artery(n=10). At three months postoperatively, grafted nerves were examined by electrophysiologic study to check amplitudes and motor nerve conduction velocities, as well as histopathologic study for evaluation of regenerated nerve cells, fibrosis and neo-vascularization. Consquently, nerve regeneration was found in all three groups. Both the myoneural and adiponeural flap groups had better improved results of nerve regeneration compared to that of the conventional nerve graft group. The result of myoneural flap group was superior to that of the adiponeural flap group. The myoneural flap group showed minimal fibrosis and less prominent neovascularization around moderately regenerated nerves. The adiponeural flap group showed more severe perineural and endoneural fibrosis, as well as vascular proliferation around focal regenerated nerves. The results of myoneural flap group proved to be statistically significant. We concluded that it is possible to use nerve graft entubulated with a vascularized muscle flap (myoneural flap) as a substitute for vascularized nerve graft.