Moonhor Ree

Pohang University of Science and Technology, Geijitsu, North Gyeongsang, South Korea

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Publications (296)836.45 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The fully pi-conjugated donor-acceptor hybrid polymers Fl-TPA, Fl-TPA-TCNE, and Fl-TPA-TCNQ, which are composed of fluorene (Fl), triphenylamine (TPA), dimethylphenylamine, alkyne, alkyne-tetracyanoethylene (TCNE) adduct, and alkyne-7,7,8,8-tetracyanoquinodimethane (TCNQ) adduct, were synthesized. These polymers are completely amorphous in the solid film state and thermally stable up to 291-409 deg.C. Their molecular orbital levels and band gaps vary with their compositions. The TCNE and TCNQ units, despite their electron acceptor characteristics, were found to enhance the pi-conjugation lengths of Fl-TPA-TCNE and Fl-TPA-TCNQ, i.e. to produce red shifts in their absorption spectra and significant reductions in band gap. These changes are reflected in the electrical digital memory behaviors of the polymers. Moreover, the TCNE and TCNQ units were found to diversify the digital memory modes and to widen the active polymer layer thickness window. In devices with aluminum top and bottom electrodes, the Fl-TPA polymer exhibits stable unipolar permanent memory behavior with high reliability. The Fl-TPA-TCNE and Fl-TPA-TCNQ devices exhibit stable unipolar permanent memory behavior as well as dynamic random access memory behavior with excellent reliability. These polymer devices were found to operate by either hole injection or hole injection along with electron injection, depending on the polymer compositions. Overall, this study demonstrated that the incorporation of -conjugated cyano moieties, which control both the pi-conjugation length and electron-accepting power, is a sound approach to the design and synthesis of high performance digital memory polymers. The TCNE and TCNQ polymers synthesized in this study are highly suitable active materials for the low-cost mass production of high performance, polarity-free, programmable, volatile, and permanent memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high reliability.
    ACS Applied Materials & Interfaces 04/2014; · 5.90 Impact Factor
  • Moonhor Ree
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    ABSTRACT: For advanced functional polymers such as biopolymers, biomimic polymers, brush polymers, star polymers, dendritic polymers, and block copolymers, information about their surface structures, morphologies, and atomic structures is essential for understanding their properties and investigating their potential applications. Grazing incidence X-ray scattering (GIXS) is established for the last 15 years as the most powerful, versatile, and nondestructive tool for determining these structural details when performed with the aid of an advanced third-generation synchrotron radiation source with high flux, high energy resolution, energy tunability, and small beam size. One particular merit of this technique is that GIXS data can be obtained facilely for material specimens of any size, type, or shape. However, GIXS data analysis requires an understanding of GIXS theory and of refraction and reflection effects, and for any given material specimen, the best methods for extracting the form factor and the structure factor from the data need to be established. GIXS theory is reviewed here from the perspective of practical GIXS measurements and quantitative data analysis. In addition, schemes are discussed for the detailed analysis of GIXS data for the various self-assembled nanostructures of functional homopolymers, brush, star, and dendritic polymers, and block copolymers. Moreover, enhancements to the GIXS technique are discussed that can significantly improve its structure analysis by using the new synchrotron radiation sources such as third-generation X-ray sources with picosecond pulses and partial coherence and fourth-generation X-ray laser sources with femtosecond pulses and full coherence.
    Macromolecular Rapid Communications 04/2014; · 4.93 Impact Factor
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    ABSTRACT: The structural characteristics of aqueous micelles composed of amphiphilic cyclic poly(n-butyl acrylate-b-ethylene oxide) (cyclic PBA-b-PEO) or a linear analogue (i.e., linear poly(n-butyl acrylate-b-ethylene oxide-b-n-butyl acrylate) (linear PBA-b-PEO-b-PBA)) were examined for the first time using synchrotron X-ray scattering techniques and quantitative data analysis. The scattering data were analyzed using a variety of methodologies in a comprehensive complementary manner. These analyses provided details of the structural information about the micelles. Both micelles were found to consist of a core and a fuzzy shell; however, the cyclic block copolymer had a strong tendency to form micelles with core and shell parts that were more compact and dense than the corresponding parts of the linear block copolymer micelles. The PBA block of the cyclic copolymer was found to form a hydrophobic core with a density that exceeded the density of the homopolymer in the bulk state. The structural differences originated primarily from the topological difference between the cyclic and linear block copolymers. The elimination of the chain end groups (which introduced entropy and increased the excess excluded volume) from the amphiphilic block copolymer yielded more stable dense micelles in solution.
    ACS Macro Letters. 02/2014; 3(3):233–239.
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    ABSTRACT: A series of diblock copolypeptides with various compositions (PBLGm-b-PBCLn) was synthesized through the living ring-opening polymerizations of γ-benzyl-L-glutamate and ε-(benzyloxycarbonyl)-L-lysine N-carboxyanhydrides with the aid of a nickel catalyst system. They were found to be stable up to around 150 °C and easily processable. Their chain conformations and morphologies in nanoscale thin films were characterized in detail by using infrared spectroscopy, atomic force microscopy, and in situ synchrotron grazing incidence X-ray scattering. In particular, quantitative X-ray scattering analysis was used to provide for the first time the morphological structures and orientation details of the diblock copolypeptides in thin films. Fibrils are present in the thin films of the copolypeptides; interestingly, the films are composed of two different rotationally isomeric hexagonally (HEX) packed cylinder structures that are preferentially oriented in the film plane. Further, the HEX structures consist of two substructural block units: one consisting of PBLG block chain cylinders and the other consisting of PBCL block chain cylinders. The block chains in the substructural units were found to interdigitate partially via the side groups. Thus the cylinders' interdigitation takes place selectively between block chains of the same kind rather than between different kinds of block chains. It was also confirmed that this high interdigitation selectivity occurs in the blend films of the homopolypeptides. These results show that in diblock copolypeptide films such selective interdigitation can override any thermodynamic penalties associated with the high chain rigidity due to the α-helical conformation and the effects of confinement in the connected diblock architecture, which leads to phase separation and the formation of well-defined, integrated HEX cylinder structures. These cooperatively and selectively formed HEX cylinder structures were found to be stable up to the degradation temperature. Molecular structure models are presented for the copolypeptide thin films as well as for the homopolypeptide blend films.
    Polym. Chem. 02/2014; 5(6).
  • Jungwoon Jung, Heesoo Kim, Moonhor Ree
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    ABSTRACT: A series of well-defined poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene-ran-oxy(n-dodecylthiomethyl)ethylene) (PECH-PCm: m = 0-100 mol% phosphorylcholine (PC)) polymers were used to prepare nanoscale thin films that were characterized by synchrotron X-ray reflectivity (XR) analysis. The quantitative XR analysis provided structural insights into the PECH-PCm thin films. The PECH-PC0 polymer film formed a well-ordered in-plane oriented molecular multibilayer structure, whose individual layers consisted of two sublayers. One sublayer was composed of the fully extended backbones and inner part of the bristles, exhibiting a relatively low electron density, whereas the other sublayer was composed of a bilayer of the outer parts of the bristles without interdigitation. The PECH-PC100 polymer film also formed a well-ordered in-plane oriented molecular multibilayer structure, the individual layers of which were composed of four sublayers rather than two. The bristles in the layer were interdigitated in part via the zwitterionic interactions of the PC end groups. Surprisingly, regardless of the copolymer composition, the PECH-PCm random copolymer molecules in the thin films self-assembled to form a multilayered structure that resembled the structure formed by the PECH-PC100 polymer. These properties have not been observed in other conventional random brush copolymer films. The remarkable multibilayer structures originated from the zwitterionic PC end groups and their favorable interactions and interdigitated structures, which overcame any negative contributions caused by the heterogeneity of the bristles. The unique self-assembly properties of the PECH-PCm polymers always provide a PC-rich surface. The PECH-PCm random copolymers successfully mimicked the molecular bilayer structures formed by natural lipids.
    Soft Matter 01/2014; 10(5):701-8. · 4.15 Impact Factor
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    ABSTRACT: The feasibility of single molecule elastic scattering analysis with the X-ray free electron laser (XFEL) sources in operation and under construction around the world was investigated for various biological and synthetic materials (pepsin, polyethylene, poly(4,4′-oxydiphenylene pyromellitimide), and ferric oxide). It was found that existing XFEL facilities provide coherent pulse X-ray beams with the required energies (8.3–12.4 keV), but their fluxes are too low for single molecule elastic scattering experiment to determine the three-dimensional structures of such molecules. For single molecule scattering, the XFEL facilities need to improve their beam flux density to 2×1015 to 7×1018 photons pulse−1 μm−2, depending on the beam energy. However, the existing XFEL facilities’ sources were found to enable the elastic scattering analysis of pepsin and synthetic polymers with sample sizes of 1–160 μm, as well as of ferric oxide with sample sizes of ≥80 nm. These criteria for the sample size can be extended to other soft (biological, organic, and polymer molecules) and hard (molecules containing heavy metals) materials. In addition, the inelastic scattering, absorption, and radiation damage characteristics of the chosen materials when exposed to the XFEL sources were examined.
    Macromolecular Research 01/2014; 22(1). · 1.64 Impact Factor
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    ABSTRACT: Time-resolved small-angle X-ray scattering (SAXS) analysis was performed on a series of poly(ethyleneco-1,4-cyclohexyldimethylene terephthalate)s (PECT copolymers) containing 1.6, 5.3, and 9.8 mol% 1,4-cyclohexyldimethylene (CHDM) units during isothermal crystallization and subsequent melting processes. The measured SAXS data were quantitatively analyzed to yield detailed information (scattering invariant quantity, Q; long period, L p ; lamellar crystal layer thickness, d c ; and amorphous layer thickness, d a ) about the crystal structure evolution and melting devolution behaviors. The Q value was found to be a very sensitive powerful probe for monitoring the crystallization and crystal melting processes. The structural evolution of the copolymers was dominated by the primary crystallization transition. The secondary crystallization effects contributed little to the structural evolution. The few secondary crystals present most likely formed fringed micelle structures that were very small and included a high degree of imperfections. The poor secondary crystal formation was attributed to the presence of bulky, kinked CHDM units, which introduced a high degree of steric hindrance. The high steric hindrance of the CHDM units resulted in their exclusion from the lamellar crystal layers and secondary crystals, and in their insertion into amorphous regions and layers. Overall, the CHDM comonomer units strongly perturbed the crystallization process and the morphological structure of the PECT copolymer. The effects of CHDM as a chemical modifier of poly(ethylene terephthalate)-based polymers may potentially be optimized in an effort to enhance the properties and processability of the polymer.
    Macromolecular Research 01/2014; 22(2). · 1.64 Impact Factor
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    ABSTRACT: Well-defined hydroxyl end-functionalized poly(n-hexyl isocyanate), PHIC–(OH)2 and PHIC–(OH)3, as rod-type macroinitiators were synthesized by the Cu-catalyzed azide–alkyne cycloaddition reactions of azido end-functionalized PHIC with ethynyl alcohol derivatives. The PHIC–(OH)2 and PHIC–(OH)3 were suitable macroinitiators for the ring-opening polymerization of L-LA and ε-CL leading to the synthesis of novel rod-coil type miktoarm star copolymers, PHIC-b-PLLA2, PHIC-b-PLLA3, PHIC-b-PCL2, and PHIC-b-PCL3, with controlled molecular weights, narrow polydispersities, and controlled arm numbers. Additionally, the thermal and solution properties of the obtained miktoarm star copolymers along with the corresponding block copolymers, PHIC-b-PLLA and PHIC-b-PCL, were characterized by TGA, DSC, and DLS analyses.
    Polym. Chem. 12/2013; 5(2).
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    ABSTRACT: A diblock copolymer of crystalline polyethylene (PE) and amorphous poly(methyl methacrylate) (PMMA), PE69-b-PMMA92, was synthesized; this polymer is thermally stable up to 270 °C. The morphological structures of thermally annealed nanoscale thin films of the copolymer were investigated in detail at various temperatures by using in-situ grazing incidence X-ray scattering (GIXS) with a synchrotron radiation source. Quantitative GIXS analysis found that the PE and PMMA blocks undergo phase separation to produce a vertically oriented hexagonal PE cylinder structure in the PMMA matrix that is very stable up to around 100 °C (which is the onset temperature of PE crystal melting and PMMA glass transition); over the range 100–200 °C, slight variations with temperature in the cylinders’ dimensions and orientation were observed. Furthermore, the PE block chains of the cylinder phase crystallize and undergo crystal growth along the cylinders’ long axes; however, these lamellar crystals do not stack properly because of the limited space along the cylinders’ short axes. As a result, the overall crystallinity is very low. The crystallization of the PE block chains in the diblock copolymer thin film is severely restricted in the diblock architecture by the confinement effects of the limited cylinder space and the anchoring of one end of the PE chain to the cylindrical wall interface. Surprisingly, however, in a nanoscale thin film the PE homopolymer forms a highly ordered lamellar structure; the lamellae are well stacked along the out-of-plane of the film, even though the crystallization is confined by the air and substrate interfaces. This well-ordered and oriented lamellar structural morphology does not arise in melt-crystallized PE bulk specimens.
    Macromolecules 10/2013; 46(20):8235–8244. · 5.93 Impact Factor
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    ABSTRACT: An asymmetric nine-arm star polymer, (polystyrene)3-(poly(4-methoxystyrene))3-(polyisoprene)3 (PS3-PMOS3-PI3) was synthesized, and the details of the structures of its thin films were successfully investigated for the first time by using in situ grazing incidence X-ray scattering (GIXS) with a synchrotron radiation source. Our quantitative GIXS analysis showed that thin films of the star polymer molecules have very complex but highly ordered and preferentially in-plane oriented hexagonal (HEX) structures consisting of truncated PS cylinders and PMOS triangular prisms in a PI matrix. This HEX structure undergoes a partial rotational transformation process at temperatures above 190 °C that produces a 30°-rotated HEX structure; this structural isomer forms with a volume fraction of 23% during heating up to 220 °C and persists during subsequent cooling. These interesting and complex self-assembled nanostructures are discussed in terms of phase separation, arm number, volume ratio, and confinement effects.
    ACS Macro Letters. 09/2013; 2(10):849–855.
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    ABSTRACT: A series of brush copolymers bearing N-phenylcarbazole (PK) and 2-biphenyl-5-(4-ethoxyphenyl)-1,3,4-oxadiazole (BEOXD) moieties in various compositions were studied in detail, in particular their electrical memory characteristics, optical and electrical properties, morphological structures, and interfaces. Nanoscale thin films of the brush copolymers in devices were found to exhibit excellent unipolar electrical memory versatility, which can easily be tuned by tailoring the chemical composition and by changing the film thickness. Moreover, the molecular orbitals and band gap can be tuned by changing the chemical composition. The novel memory characteristics of these copolymers originate primarily from the cooperative roles of the ambipolar PK and BEOXD moieties, which have different charge trapping and stabilization properties. The electrical memory behaviors were found to occur via favorable hole injection from the electrode and to be governed by trap-limited space-charge limited conduction combined with ohmic conduction and local filament formation. Overall, the brush copolymers are very suitable active materials for the low-cost mass production of high performance, polarity-free digital memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high stability.
    J. Mater. Chem. C. 06/2013;
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    ABSTRACT: An amphiphilic brush–linear diblock copolymer bearing a rigid difluorene moiety was synthesized, yielding a copolymer with a high thermal stability and excellent processability. The immiscibility of the blocks induced the formation of a variety of nanostructures, depending on the fabrication conditions, which differed significantly from the nanostructures observed among common diblock copolymers in similar composition. Interestingly, the orientations of the nanostructures could be controlled. The nanostructured polymer displayed a variety of tunable morphologies that yielded distinct electrical memory properties when incorporated as the active layer into a digital memory device. The memory devices could be operated under very low power consumption levels and displayed excellent unipolar switching properties.
    ACS Macro Letters. 06/2013; 2(6):555–560.
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    ABSTRACT: A new electrontransport polymer, poly{[N,N′-dioctylperylene-3,4,9,10-bis(dicarboximide)-1,7(6)-diyl]-alt-[(2,5-bis(2-ethyl-hexyl)-1,4-phenylene)bis(ethyn-2,1-diyl]} (PDIC8-EB), is synthesized. In chloroform, the polymer undergoes self-assembly, forming a nanowire suspension. The nanowire's optical and electrochemical properties, morphological structure, and field-effect transistor (FET) characteristics are investigated. Thin films fabricated from a PDIC8-EB nanowire suspension are composed of ordered nanowires and ordered and amorphous non-nanowire phases, whereas films prepared from a homogeneous PDIC8-EB solution consist of only the ordered and amorphous non-nanowire phases. X-ray scattering experiments suggest that in both nanowires and ordered phases, the PDIC8 units are laterally stacked in an edge-on manner with respect to the film plane, with full interdigitation of the octyl chains, and with the polymer backbones preferentially oriented within the film plane. The ordering and orientations are significantly enhanced through thermal annealing at 200 °C under inert conditions. The polymer film with high degree of structural ordering and strong orientation yields a high electron mobility (0.10 ± 0.05 cm2 V−1 s−1), with a high on/off ratio (3.7 × 106), a low threshold voltage (8 V), and negligible hysteresis (0.5 V). This study demonstrates that the polymer in the nanowire suspension provides a suitable material for fabricating the active layers of high-performance n-channel FET devices via a solution coating process.
    Advanced Functional Materials 04/2013; 23(16). · 10.44 Impact Factor
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    ABSTRACT: A complete grazing-incidence X-ray scattering (GIXS) formula has been derived for nanopores buried in a polymer dielectric thin film supported by a substrate. Using the full power of the scattering formula, GIXS data from nanoporous polymethylsilsesquioxane dielectric thin films, a model nanoporous system, have successfully been analysed. The nanopores were found to be spherical and to have a certain degree of size distribution but were randomly dispersed in the film. In the film, GIXS was confirmed to arise predominantly via the first scattering process in which the incident X-ray beam scatters without reflection; the other scattering processes and their contributions were significantly dependent on the grazing angle. This study also confirmed that GIXS scattering can be analysed using only independent scattering terms, but this simple approach can only provide structural parameters. The cross terms were found to make a relatively small contribution to the intensity of the overall scattering but were required for the complete characterization of the measured two-dimensional scattering data, in particular the extracted out-of-plane scattering data, and their inclusion in the analysis enabled film properties such as film thickness, critical angle (i.e. electron density), refractive index and the absorption term to be determined.
    Journal of Applied Crystallography 04/2013; 46(2). · 3.34 Impact Factor
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    ABSTRACT: A new series of chemically well-defined brush glycopolymers consisting of a polyoxyethylene backbone and bristles bearing glycosyl and methyl end groups was synthesized with various compositions. The glycopolymers were thermally stable up 200 °C and were soluble in a variety of common solvents. The brush polymer films formed multibilayer structures, the layers of which were stacked along the direction normal to the film plane so as to display a glycosyl group-rich surface or a methyl group-rich surface or their mixture, depending on the bristle end group composition. The multibilayer structures were stabilized by the self-assembly of the bristles via lateral packing. The glycosyl-rich surface played a critical role in enhancing the surface hydrophilicity and water sorption to a certain level; thus, the glycopolymer films easily formed a hydration layer to a certain depth on the film surface. The hydrophilic surfaces and hydration layer efficiently prevented protein adsorption onto the brush glycopolymers and suppressed bacterial adherence while promoting mammalian cell adhesion and displaying excellent biocompatibility in an in vivo mouse study.
    Polym. Chem. 03/2013; 4(7):2260-2271.
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    ABSTRACT: The synthesis and characterization of cyclohexylethenyl end-capped quaterthiophenes is reported. Additionally, an investigation of the performance of organic field-effect transistors based on these quaterthiophenes in view of the relationship between the solid-state (or aggregate) order and the electronic performance is described. UV–vis absorption measurements revealed that the quaterthiophene with an asymmetrically substituted cyclohexylethynyl end-group induced the formation of H-type aggregates, whereas the quaterthiophene with a symmetrically substituted cyclohexylethynyl end-groups favored the formation of J-type aggregates. Two-dimensional grazing-incidence wide-angle X-ray scattering studies were performed to support the molecular structure-dependent packing of films of the new quaterthiophenes. Solution-processed quaterthiophenes were tested as the active layers of p-type organic field-effect transistors with a bottom gate/top contact geometry. The field-effect mobility of devices that incorporated asymmetric quaterthiophene molecules was quite high, exceeding 0.02 cm2/V s, due to H-aggregation and good in-plane ordering. In contrast, the field-effect mobility of devices that incorporated symmetrical quaterthiophenes, was low, above 5 × 10−4 cm2/(V s), due to the formation of J-aggregates and poor in-plane ordering. A comparison of the symmetrical and asymmetrical quaterthiophene derivatives revealed that the molecular aggregation-dependent packing, determined by the cyclohexylethynyl end groups, was responsible for influencing the organic field-effect transistor performance.
    Dyes and Pigments 03/2013; 96(3):756–762. · 3.53 Impact Factor
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    ABSTRACT: Highlights ► Unidirectional rubbing of the substrates afforded uniform uniaxial LC alignment. ► Photo-alignment approach has shown to be promising alternative to the rubbing process. ► Uniform uniaxial LC alignment has been confirmed to be governed mainly by its molecular interactions with the polymer chains. ► Several thermally stable polyimides have met most requirements for LC alignment as well as complete fabrication of LCD devices. ► New alignment materials are required to meet elimination of image sticking and related issues [e.g. multistable and optically rewritable LCDs].
    Current Opinion in Chemical Engineering. 02/2013; 2(1):71–78.
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    ABSTRACT: Highlights ► Electrical polymer memories have shown to be promising alternative to the current silicon and metal-oxide memories. ► Resistive polymer memories were found to operate mainly via local charge-traps and filament formation by electric fields. ► Polymer memories opened up the possibility of the mass production of high performance memory devices at low cost. ► Polymer memories are challenged to fabricate 3-dimensional multilayered devices with pixels and transistors/diodes.
    Current Opinion in Chemical Engineering. 02/2013; 2(1):79–87.
  • Source
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    ABSTRACT: Developing organic nonvolatile memory devices with a writing/reading/erasing logic function in actual array structures is extremely important for realizing low-cost lightweight/flexible plastic electronic systems. Here, we demonstrate that organic field-effect transistors (OFETs) with a polymer energy well structure (PEW-OFET) exhibit excellent nonvolatile memory performances. The PEW structure is created by sandwiching a self-doped poly(o-anthranilic acid) (SD-PARA) nanolayer (high dielectric constant, k=14) between two low-dielectric polymer layers (k=2–4). The primary idea behind this concept is the rapid storage and retrieval of charge carriers in the PEW layer during operation due to the high k feature of the SD-PARA nanolayer, which aids the rapid transport of charge carriers inside, whereas the stored charges are safely trapped due to the two low k layers. The results indicate that the PEW-OFET memory devices exhibit outstanding retention characteristics upon continuous reading up to 2000 s after writing, whereas their excellent writing/reading/erasing/reading cyclability is demonstrated in a test with >3000 cycles. Therefore, the present simple yet cost-effective PEW-OFET concept is expected to significantly contribute to the development of low-cost plastic memory array devices because all processes can be inexpensively performed at low temperatures and additional logic transistors are unnecessary.
    NPG Asia Materials. 01/2013; 5(1).
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    ABSTRACT: Physical mixtures of organic semiconductors are increasingly used for the development of new materials in thin film, organic electronic applications and their electronic properties are strongly affected by their morphology. Here, we report on studies of blends of an electron-donating small molecule, BTD-DTP, with the electron-acceptor polymer PNDI-2T and the correlations between their thermal behaviour, intermixing and thin film structure. A significant depression of the PNDI-2T melting point (ΔT = 111 °C) is observed upon increasing the small molecule content. Grazing incidence X-ray scattering (GIXS) and scanning probe microscopy (SPM) of thin films of varying composition show an increase in the small molecule crystalline phase and reduction in the crystallite orientation distribution, as the small molecule to polymer ratio reaches 50:50 wt. The domain sizes of the small molecule and polymer crystalline phases reach a minimum at the 50:50 wt ratio as well, suggesting the formation of the phases leads to mutual limitation of their crystalline domain size. Comparison of the bulk and thin film properties shows a divergence in behaviour of the small molecule, which in the bulk exhibits only a monotonic decrease in melting point with addition of polymer, but which has an increase in crystallinity, from 20 to 50 wt% PNDI-2T content.
    J. Mater. Chem. C. 12/2012; 1(4).

Publication Stats

2k Citations
836.45 Total Impact Points

Institutions

  • 1994–2014
    • Pohang University of Science and Technology
      • • Department of Chemistry
      • • Department of Electronic and Electrical Engineering
      Geijitsu, North Gyeongsang, South Korea
  • 2010
    • Imperial College London
      Londinium, England, United Kingdom
  • 2009
    • Kyungpook National University
      • Department of Energy Chemical Engineering
      Daikyū, Daegu, South Korea
    • Hanyang University
      • Department of Chemistry
      Seoul, Seoul, South Korea
  • 2005
    • Brookhaven National Laboratory
      New York City, New York, United States
  • 1995
    • Columbia University
      • Department of Chemical Engineering
      New York City, NY, United States