Jaehoon Park

Bio: Jaehoon Park is an academic researcher from Hallym University. The author has contributed to research in topics: Thin-film transistor & Pentacene. The author has an hindex of 15, co-authored 125 publications receiving 759 citations. Previous affiliations of Jaehoon Park include Seoul National University & Hongik University.

Charge-transfer satellites in the 2p core-level photoelectron spectra of heavy-transition-metal dihalides.

Abstract: We extend the charge-transfer model with the core-hole--3d-electron Coulomb attraction [van der Laan et al., Phys. Rev. B 23, 4369 (1981)] to the 2p core-level photoemission satellite structures of cobalt, iron, and manganese dihalides. This model was found to account for the positions and intensities of satellites and main peaks very well with reasonable values of parameters. These parameter values show the expected trends not only along the ligand series from fluorine to bromine but also along the transition-metal series from copper to manganese. This gives us confidence that the charge-transfer mechanism is responsible for the satellite structures in the 2p core-level photoemission spectra of heavy-transition-metal compounds, and that the screening response is important even for insulators in the presence of a core hole. It also suggests the core-level photoemission spectra, if properly understood, can be used to obtain parameters on the valence-electronic structures.

Morphological Influence of Solution-Processed Zinc Oxide Films on Electrical Characteristics of Thin-Film Transistors

Abstract: We report on the morphological influence of solution-processed zinc oxide (ZnO) semiconductor films on the electrical characteristics of ZnO thin-film transistors (TFTs). Different film morphologies were produced by controlling the spin-coating condition of a precursor solution, and the ZnO films were analyzed using atomic force microscopy, X-ray diffraction, X-ray photoemission spectroscopy, and Hall measurement. It is shown that ZnO TFTs have a superior performance in terms of the threshold voltage and field-effect mobility, when ZnO crystallites are more densely packed in the film. This is attributed to lower electrical resistivity and higher Hall mobility in a densely packed ZnO film. In the results of consecutive TFT operations, a positive shift in the threshold voltage occurred irrespective of the film morphology, but the morphological influence on the variation in the field-effect mobility was evident. The field-effect mobility in TFTs having a densely packed ZnO film increased continuously during consecutive TFT operations, which is in contrast to the mobility decrease observed in the less packed case. An analysis of the field-effect conductivities ascribes these results to the difference in energetic traps, which originate from structural defects in the ZnO films. Consequently, the morphological influence of solution-processed ZnO films on the TFT performance can be understood through the packing property of ZnO crystallites.

Pickering emulsion polymerized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polystyrene composite particles and their electric stimuli-response

Abstract: We report a facile synthesis of Pickering emulsion polymerized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polystyrene (PEDOT:PSS/PS) composite particles and their electro-responsive electrorheological (ER) characteristics when dispersed in silicone oil. The PEDOT:PSS particles act both as a solid surfactant for the Pickering emulsion polymerization and as an electro-responsive activator for PEDOT:PSS/PS composite particles. The morphology, chemical structure, and thermal properties of the synthesized PEDOT:PSS/PS composite particles were determined by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, respectively. Moreover, the formation of chain structures by the dispersed particles was confirmed directly by optical microscopy. The rheological response of PEDOT:PSS/PS-based ER fluid in the presence of an electric field, examined using a rotational rheometer, represented ER effects with typical Bingham fluid behavior.

Determining Beta Sheet Crystallinity in Fibrous Proteins by Thermal Analysis and Infrared Spectroscopy

Abstract: We report a study of self-assembled beta-pleated sheets in B. mori silk fibroin films using thermal analysis and infrared spectroscopy. B. mori silk fibroin may stand as an exemplar of fibrous proteins containing crystalline beta-sheets. Materials were prepared from concentrated solutions (2−5 wt % fibroin in water) and then dried to achieve a less ordered state without beta-sheets. Crystallization of beta-pleated sheets was effected either by heating the films above the glass transition temperature (Tg) and holding isothermally or by exposure to methanol. The fractions of secondary structural components including random coils, alpha-helices, beta-pleated sheets, turns, and side chains were evaluated using Fourier self-deconvolution (FSD) of the infrared absorbance spectra. The silk fibroin films were studied thermally using temperature-modulated differential scanning calorimetry (TMDSC) to obtain the reversing heat capacity. The increment of the reversing heat capacity ΔCp0(Tg) at the glass transition fo...

High-k organic, inorganic, and hybrid dielectrics for low-voltage organic field-effect transistors.

Abstract: 2.2. Interface Trapping Effects 211 3. High-k Dielectric Materials for OFETs 212 3.1. Inorganic Dielectrics 212 3.1.1. Aluminum Oxide 213 3.1.2. Tantalum Oxide 215 3.1.3. Titanium Dioxide 216 3.1.4. Hafnium Dioxide 217 3.1.5. Zirconium Dioxide 218 3.1.6. Cerium Dioxide 218 3.2. Organic Dielectrics 218 3.2.1. Polymer Dielectrics 218 3.2.2. Self-Assembled Monoand Multilayers 225 3.3. Hybrid Dielectrics 227 3.3.1. Polymeric-Nanoparticle Composites 227 3.3.2. Inorganic-Organic Bilayers 232 3.3.3. Hybrid Solid Polymer Electrolytes 235 4. Summary 235 5. Acknowledgments 236 6. References 236

Approaches for fabricating high efficiency organic light emitting diodes

Abstract: Efficiency is crucial for organic light emitting diodes (OLEDs) to be energy-saving and to have a long lifetime for display and solid state lighting applications. Numerous approaches have been proposed to attain high efficiency OLEDs through the synthesis of novel organic materials, the design of light extraction structures and the design of efficiency-effective device architectures. In this report, we first summarise the efficiency records of OLED devices using fluorescent, phosphorescent, and thermally activated delay fluorescent materials. Importantly, we review all the available efficiency-effective device architectural approaches, which include using thin layer structures, low carrier injection barriers, high carrier mobility, balanced carrier injection, effective carrier confinement, effective host-to-guest energy transfer, effective recombination zone, effective exciton generation on the host, effective exciton confinement, p–i–n structures, and tandem structures. It is hoped that better device structures can therefore be devised upon suitable device engineering to achieve higher efficiency for OLED devices.

Metal oxide semiconductor thin-film transistors for flexible electronics

Abstract: The field of flexible electronics has rapidly expanded over the last decades, pioneering novel applications, such as wearable and textile integrated devices, seamless and embedded patch-like systems, soft electronic skins, as well as imperceptible and transient implants. The possibility to revolutionize our daily life with such disruptive appliances has fueled the quest for electronic devices which yield good electrical and mechanical performance and are at the same time light-weight, transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductor thin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the most promising technology for tomorrow's electronics. This review reflects the establishment of flexible metal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up to entirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given, where the history of the field is revisited, the TFT configurations and operating principles are presented, and the main issues and technological challenges faced in the area are analyzed. Then, the recent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured by physical vapor deposition methods and solution-processing techniques are summarized. In particular, the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication, high carrier mobility, large frequency operation, extreme mechanical bendability, together with transparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailed analysis of the most promising metal oxide semiconducting materials developed to realize the state-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metal oxide semiconductor-based electronic circuits, realized with both unipolar and complementary technology, are reported. In particular, the realization of large-area digital circuitry like flexible near field communication tags and analog integrated circuits such as bendable operational amplifiers is presented. The last topic of this review is devoted for emerging flexible electronic systems, from foldable displays, power transmission elements to integrated systems for large-area sensing and data storage and transmission. Finally, the conclusions are drawn and an outlook over the field with a prediction for the future is provided.