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Gyu Jin Choi

Bio: Gyu Jin Choi is an academic researcher from Yeungnam University. The author has contributed to research in topics: Liquid crystal & Liquid-crystal display. The author has an hindex of 6, co-authored 22 publications receiving 126 citations.

Papers
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Journal ArticleDOI
TL;DR: This work demonstrates a highly efficient polarized OLED with a polarization ratio of 62.5:1 in the emission spectrum (166.7:1 at the peak intensity of 540 nm), which meets the manufacturing requirement.
Abstract: Here, this study successfully fabricates few-layer MoS2 nanosheets from (NH4 )2 MoS4 and applies them as the hole transport layer as well as the template for highly polarized organic light-emitting diodes (OLEDs). The obtained material consists of polycrystalline MoS2 nanosheets with thicknesses of 2 nm. The MoS2 nanosheets are patterned by rubbing/ion-beam treatment. The Raman spectra shows that {poly(9,9-dioctylfluorene-alt-benzothiadiazole), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)]} (F8BT) on patterned MoS2 exhibits distinctive polarization behavior. It is discovered that patterned MoS2 not only improves the device efficiency but also changes the polarization behavior of the devices owing to the alignment of F8BT. This work demonstrates a highly efficient polarized OLED with a polarization ratio of 62.5:1 in the emission spectrum (166.7:1 at the peak intensity of 540 nm), which meets the manufacturing requirement. In addition, the use of patterned MoS2 nanosheets not only tunes the polarization of the OLEDs but also dramatically improves the device performance as compared with that of devices using untreated MoS2 .

64 citations

Journal ArticleDOI
TL;DR: In this paper, an eco-friendly, in-situ, and one-step synthesis of ZnO-Co3O4 core-shell heterostructure (ZC-CSH) using the hydrothermal process as a transcendent nanomaterial for the supercapacitor applications was reported.

34 citations

Journal ArticleDOI
TL;DR: A better understanding of leakage current and self-discharge mechanisms is explored, which justifies the excellent state of health of the RGO/N-RGO SSC device.

29 citations

Journal ArticleDOI
TL;DR: In this article, a 3-S nano-lotus structure (NLS) was used to detect volatile organic compounds (VOCs) using a one-step eco-friendly solvothermal method.
Abstract: This research demonstrates the design and development of a novel SnS2 nano-lotus structure (NLS) using a one-step eco-friendly solvothermal method which can detect volatile organic compounds (VOCs) and involves a 3-S approach, i.e., obtaining stability, sensitivity, and selectivity. As a unique feature, the UV-visible spectroscopy results showed an optical band gap of 2.25 eV and Urbach energy states at 630, 675, 751, and 793 meV. Thus, a gas sensing mechanism that is correlated with the optical band gap and Urbach energy states of SnS2 NLS, leading to selectivity with reference to a targeted VOC, is discussed in this research. This SnS2 NLS sensor demonstrates the highest response (sensitivity) of 93.5% to 25 ppm ethanol at 90 °C, compared with its responses to methanol (16.6%), propanol (14.8%), and n-butanol (11.4%). The SnS2 NLS sensor for ethanol shows rapid response (14.2 s) and quick recovery (16.6 s) times toward a concentration of 25 ppm at 90 °C. The SnS2 NLS sensor demonstrates better selectivity towards ethanol, with the response of 92.9% being much higher compared to its responses to other interfering gases, such as methanol (16.4%), propanol (14.8%), n-butanol (11.4%), benzene (4.1%), toluene (5.8%), and n-butylacetate (2.2%). The value of the selectivity coefficient with respect to n-butylacetate is high, 34.5, which indicates that the SnS2 NLS sensor response to ethanol is 34.5 times higher than the response to n-butylacetate. However, the value of the selectivity coefficient towards methanol is low, 4.3, which shows that the SnS2 NLS sensor response to ethanol is only 4.3 times higher than the response to methanol. In addition to selectivity, the SnS2 NLS sensor displays outstanding stability, with a response of 91.3% after 25 days (tested at 5 day intervals) to a concentration of 25 ppm ethanol at 90 °C. The SnS2 NLS sensor exhibits a theoretical detection limit of 7.9 ppb toward ethanol at 90 °C. Taking the sensing outcomes into consideration, the unique SnS2 NLS VOC sensor with tunable performance can be projected to act as an analytical tool to detect a category of VOCs efficiently.

27 citations

Journal ArticleDOI
TL;DR: In this article, a two-dimensional layered MoS2 nanostructure-based gas sensor was synthesized by a solvothermal method for formaldehyde (HCHO) gas sensing applications.

17 citations


Cited by
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Journal ArticleDOI
TL;DR: The control of the helical axis orientation of CLCs and its dynamic switching in two and three dimensions using different external stimuli are summarized and Electric-field-, magnetic-field, and light-irradiation-driven orientation control and reorientation of theHelical axis of C LCs are described and highlighted.
Abstract: Supramolecular and macromolecular functional helical superstructures are ubiquitous in nature and display an impressive catalog of intriguing and elegant properties and performances. In materials science, self-organized soft helical superstructures, i.e., cholesteric liquid crystals (CLCs), serve as model systems toward the understanding of morphology- and orientation-dependent properties of supramolecular dynamic helical architectures and their potential for technological applications. Moreover, most of the fascinating device applications of CLCs are primarily determined by different orientations of the helical axis. Here, the control of the helical axis orientation of CLCs and its dynamic switching in two and three dimensions using different external stimuli are summarized. Electric-field-, magnetic-field-, and light-irradiation-driven orientation control and reorientation of the helical axis of CLCs are described and highlighted. Different techniques and strategies developed to achieve a uniform lying helix structure are explored. Helical axis control in recently developed heliconical cholesteric systems is examined. The control of the helical axis orientation in spherical geometries such as microdroplets and microshells fabricated from these enticing photonic fluids is also explored. Future challenges and opportunities in this exciting area involving anisotropic chiral liquids are then discussed.

194 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the recent developments in 2D materials for photocatalytic applications involving the hydrogen evolution reaction and CO2 reduction is presented, and it is revealed that the use of 2D catalyst materials has great potential for commercialization in the near future to help overcome the energy crisis.
Abstract: The issues of global warming and fossil fuel shortage have increased the demand for clean and renewable energy. Many researchers are investigating strategies to produce hydrogen and reduce CO2 by using solar power. Two-dimensional (2D) materials, such as graphene, graphene derivatives, and transition metal dichalcogenides (TMDs), have been extensively used owing to their extraordinary electronic and optical properties. In this review, we investigate the recent developments in 2D materials for photocatalytic applications involving the hydrogen evolution reaction and CO2 reduction. The synthesis methods and the photocatalytic properties of TMDs and graphene-based 2D materials are thoroughly discussed. Moreover, a summary of the recently developed 2D nanostructures and devices for solar hydrogen production and CO2 reduction is presented, and it is revealed that the use of 2D catalyst materials has great potential for commercialization in the near future to help overcome the energy crisis.

115 citations

Journal ArticleDOI
TL;DR: A comprehensive review of emerging 2D-organic heterostructure-from their synthesis and fabrication to their state-of-the-art optoelectronic applications-is presented and future challenges and opportunities associated with these heterostructures are highlighted.
Abstract: The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low-cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D-organic heterostructures-from their synthesis and fabrication to their state-of-the-art optoelectronic applications-is presented. Future challenges and opportunities associated with these heterostructures are highlighted.

77 citations

01 Jan 2015
TL;DR: The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances as mentioned in this paper.
Abstract: The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances. Further nitrogen doping greatly improves the hydrophilicity, which boosts the supercapacitive performances to an ultrahigh specific capacitance of up to 313 F g(-1) at 1 A g(-1).

68 citations

Journal ArticleDOI
TL;DR: The emergence of highperformance materials for flexible inorganic light emitting diodes (ILEDs) provides the foundations for a broad range of compelling, unconventional systems, from deformable displays and lighting sources to wearable and implantable bioelectronics with diagnostic and therapeutic capabilities as discussed by the authors.
Abstract: DOI: 10.1002/adom.201800936 The emergence of high-performance materials for flexible inorganic light emitting diodes (ILEDs) provides the foundations for a broad range of compelling, unconventional systems, from deformable displays and lighting sources to wearable and implantable bioelectronics with diagnostic and therapeutic capabilities. Interdisciplinary progress in materials synthetic methods, device designs, mechanical layouts, and assembly techniques over the past decade enables flexible ILEDs with remarkable operating characteristics even under extreme modes of mechanical deformation. This review summarizes recent advances in this field, with emphasis on the unique properties of the underlying materials and device physics in the first several sections. The subsequent content highlights examples of system-level integration of flexible ILEDs into advanced optoelectronic platforms with characteristics that would be difficult or impossible to achieve with conventional approaches. Miniaturized, implantable biomedical tools for optical modulation of neural activity at target sites and conformable, skin-mounted electronics for sensing and visualization of physiological parameters in real time provide examples of some of the most recent directions. Hall of Fame Article

65 citations