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...

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

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

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

X-ray absorption and dichroism of transition metals and their compounds

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.

Approaches for fabricating high efficiency organic light emitting diodes

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.

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Metal oxide semiconductor thin-film transistors for flexible electronics

Organic ferroelectric capacitors were fabricated using pentacene and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as an organic semiconductor and a ferroelectric material, respectively. A paraelectric poly(vinyl cinnamate) layer was adopted as an interlayer between the PVDF-TrFE layer and the bottom electrode. The paraelectric interlayer induced a depolarization field opposite to the direction of the polarization formed in the ferroelectric PVDF-TrFE insulator, thereby suppressing spontaneous polarization. As a result, the Mott-Schottky model could be used to evaluate, from the extracted flat-band voltages, the density of the charge trapped in the organic ferroelectric capacitors.

Evaluation of the density of the charge trapped in organic ferroelectric capacitors based on the Mott-Schottky model

We investigated the electrical stability of bottom-gate/top-contact-structured indium oxide (In₂O₃) thin-film transistors (TFTs) in atmospheric air and under vacuum. The solution-processed In₂O₃ film exhibits a nanocrystalline morphology with grain boundaries. The fabricated In₂O₃ TFTs operate in an n-type enhancement mode. Over repeated TFT operation under vacuum, the TFTs exhibit a slight increase in the field-effect mobility, possibly due to multiple instances of the "trapping and release" behavior of electrons at grain boundaries. On the other hand, a decrease in the fieldeffect mobility and an increase in the hysteresis are observed as the measurement continues in atmospheric air. These results suggest that the electrical stability of solution-processed In₂O₃ TFTs is significantly affected by the electron-trapping phenomenon at crystal grain boundaries in the In₂O₃ semiconductor and the electrostatic interactions between electrons and polar water molecules.

Electrical Stability of Solution-Processed Indium Oxide Thin-Film Transistors.

We investigated the electrical properties of solution-processed zinc oxide (ZnO) thin-film transistors (TFTs) with varying the size of ZnO crystallites in the film. The TFTs having the bead-shaped ZnO crystallites with the average diameter of 2 μm apparently operated in depletion mode, whereas the devices exhibited an accumulation operation when the crystallite size of ZnO reduced to sub-micron range. Considering the difference between bulk and channel electrical conductivities in solution-processed ZnO TFTs, these results are explained with the interplay between the crystallite size of ZnO and the electrical conduction in the TFT.

Analysis of Structural and Electrical Properties of Solution-Processed Zinc Oxide Films for Thin-Film Transistor Application

The hysteresis of the solution-processed oxide thin-film transistors (TFTs) is fatal issue to interrupt stable operation. So, we came up with uni-directional pre-annealing to solve the problem. There are inevitable defects when solution-processed oxide TFTs are fabricated, due to the porosities by the solvent volatilization. Also oxygen vacancies needed for carrier generation in metal oxide semiconductor can be trap states inducing charge carrier trapping. Uni-directional pre-annealing improved the hysteresis, preventing randomly solvent evaporation and decreased the defects of the film. We can result in advanced stability of the solution-processed oxide TFTs, at the same time showing that the field effect mobility was enhanced from 3.35 cm2/Vs to 4.78 cm2/Vs simultaneously, and exhibiting better subthreshold swing from 0.89 V/dec to 0.23 V/dec.

Reduction of Hysteresis in Solution-Processed InGaZnO Thin-Film Transistors through Uni-Directional Pre-Annealing

This paper presents a load-balanced resource directory (LB-RD) architecture based on the constrained application protocol (CoAP), and is aimed at addressing the scalability issue with the centralized resource discovery approach in large-scale Internet of Things (IoT) local networks. To balance the traffic load due to a large number of messages concentrated on the resource directory (RD), the LB-RD serves as an intermediary agent between the servers and the RD. Its architecture includes the following three essential functional blocks: server group management (SGM), message aggregation (MA), and message forwarding scheduling (MFS). The SGM manages the uniform resource identifier (URI) list for a group of servers associated with the LB-RD. The MA aggregates the registration/update messages received from the servers into a single aggregated message. Finally, the MFS determines the forwarding time for the LB-RD to send its aggregated message to the RD. To verify the effectiveness of the LBRD architecture, an experimental simulation is conducted under various scenarios. The results show that the LB-RD architecture achieves better performance than the existing RD approach in terms of the number of lost messages and the message loss rate.

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Jaehoon Park

Papers

Evaluation of the density of the charge trapped in organic ferroelectric capacitors based on the Mott-Schottky model

Electrical Stability of Solution-Processed Indium Oxide Thin-Film Transistors.

Analysis of Structural and Electrical Properties of Solution-Processed Zinc Oxide Films for Thin-Film Transistor Application

Reduction of Hysteresis in Solution-Processed InGaZnO Thin-Film Transistors through Uni-Directional Pre-Annealing

Load-balanced Resource Directory Architecture for Large-scale Internet of Things Local Networks