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Kim H.,Korea Electronics Technology Institute | Kim Y.,Korea Electronics Technology Institute | Kim Y.,Sungkyunkwan University | Kim K.S.,Sejong University | And 9 more authors.
ACS Nano | Year: 2013

Large-scale integration of vanadium dioxide (VO2) on mechanically flexible substrates is critical to the realization of flexible smart window films that can respond to environmental temperatures to modulate light transmittance. Until now, the formation of highly crystalline and stoichiometric VO2 on flexible substrate has not been demonstrated due to the high-temperature condition for VO2 growth. Here, we demonstrate a VO2-based thermochromic film with unprecedented mechanical flexibility by employing graphene as a versatile platform for VO 2. The graphene effectively functions as an atomically thin, flexible, yet robust support which enables the formation of stoichiometric VO2 crystals with temperature-driven phase transition characteristics. The graphene-supported VO2 was capable of being transferred to a plastic substrate, forming a new type of flexible thermochromic film. The flexible VO2 films were then integrated into the mock-up house, exhibiting its efficient operation to reduce the in-house temperature under infrared irradiation. These results provide important progress for the fabrication of flexible thermochromic films for energy-saving windows. © 2013 American Chemical Society. Source

Lee S.,KAIST | Kim H.,KAIST | Shin T.J.,Pohang Accelerator Laboratory | Shin T.J.,UNIST Central Research Facilities | And 8 more authors.
Soft Matter | Year: 2015

Helical nanofilaments (HNFs) have attracted much interest because of their unique optical properties, but there have been many hurdles to overcome in using them for the practical applications due to their structural complexity. Here we demonstrate that the molecular configuration and layer conformation of a modulated HNF (HNFs(mod)) can be studied using a physicochemical confinement system. The layer directions affected by the chemical affinity between the mesogen and surface were drastically controlled in surface-modified nanochannels. Furthermore, an in situ experiment using grazing-incidence X-ray diffraction (GIXD) was carried out to investigate in detail the structural evolution through thermal transitions. The results demonstrate that the HNF(mod) structure can be perfectly controlled for functional HNF device applications, and a combined system with chemical and physical confinement effects will be helpful to better understand the fundamentals of soft matter. © The Royal Society of Chemistry 2015. Source

Lee H.H.,Pohang Accelerator Laboratory | Shin T.J.,Pohang Accelerator Laboratory | Shin T.J.,UNIST Central Research Facilities | Kim H.J.,Pusan National University
Science of Advanced Materials | Year: 2016

Poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) films were spin-cast using either pure chlorobenzene as the solvent or a chlorobenzene:dichlorobenzene solvent mixture. Compared to films fabricated using pure chlorobenzene, those prepared using the mixed solvent showed better crystallinity of the P3HT domains and a higher initial tensile strain. Thermal annealing relieved the tensile strain and increasing the domain crystallinity. The films spin-cast using the solvent mixture exhibited minimal Al atom diffusion into the P3HT:PCBM layer during thermal annealing. The presence of an Al layer enhanced the grazing incidence small angle X-ray scattering contrast between the P3HT and PCBM domains at the Al layer interface. © 2016 by American Scientific Publishers All rights reserved. Source

Yoo H.,Pohang University of Science and Technology | Choi H.H.,Pohang University of Science and Technology | Shin T.J.,UNIST Central Research Facilities | Rim T.,Pohang University of Science and Technology | And 3 more authors.
Advanced Functional Materials | Year: 2015

Here, a highly crystalline and self-assembled 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pentacene) thin films formed by simple spin-coating for the fabrication of high-performance solution-processed organic field-effect transistors (OFETs) are reported. Rather than using semiconducting organic small-molecule-insulating polymer blends for an active layer of an organic transistor, TIPS-Pentacene organic semiconductor is separately self-assembled on partially crosslinked poly-4-vinylphenol:poly(melamine-co-formaldehyde) (PVP:PMF) gate dielectric, which results in a vertically segregated semiconductor-dielectric film with millimeter-sized spherulite-crystalline morphology of TIPS-Pentacene. The structural and electrical properties of TIPS-Pentacene/PVP:PMF films have been studied using a combination of polarized optical microscopy, atomic force microscopy, 2D-grazing incidence wide-angle X-ray scattering, and secondary ion mass spectrometry. It is finally demonstrated a high-performance OFETs with a maximum hole mobility of 3.40 cm2 V-1 s-1 which is, to the best of our knowledge, one of the highest mobility values for TIPS-Pentacene OFETs fabricated using a conventional solution process. It is expected that this new deposition method would be applicable to other small molecular semiconductor-curable polymer gate dielectric systems for high-performance organic electronic applications. Partial crosslinking of polymer gate-dielectrics (pc-PVP:PMF) allows semiconducting small molecules in solvent to permeate into it. The solvent evaporation during spinning promotes the extraction of TIPS-Pentacene solution onto pc-PVP:PMF surface. The residual solvent in pc-PVP:PMF network evaporates slowly, so it helps millimeter-sized crystallization of TIPS-Pentacene molecules. Consequently, the OFET devices exhibit high mobilities with maximum value of 3.40 cm2 V-1 s-1. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Suh A.,KAIST | Kim D.S.,KAIST | Kim H.,KAIST | Ahn H.,Pohang Accelerator Laboratory | And 2 more authors.
Liquid Crystals | Year: 2016

Shaping of self-assembled soft materials is of interest for material science and nanotechnology applications because it can provide a flexible and easy method to obtain a single domain in a large area, which is used in opto-electronic and patterning applications. Here, we fabricated disordered porous structures of liquid crystals (LCs) by using a solvent-assisted treatment. Initially, the LC-based layered structures had either toric focal conic domains (TFCDs) or planar aligned samples. After treatment, disordered porous structures with randomly oriented layers were obtained although both initial and final states exhibited short-range ordering of the LC molecules. This behaviour was precisely analysed by polarised optical microscopy (POM), field-emission scanning electron microscopy (FESEM) and grazing incidence X-ray diffraction (GIXD) methods. Our resultant platform showed that disordered porous structures formed by LC materials can be used for tuneable and reversible multiple scattering applications. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source

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