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

Characteristic Effects of Buffer Layers on Organic Light Emitting Devices

Performances of organic thin-film transistors (TFTs) can be detrimentally affected by the state of gate dielectric layer. In this study, we report the condensation and annealing effects of a polymer gate dielectric layer. For the observations of the effect of condensation, the spin-coated polymer layers with various deposition conditions were fabricated and kept under low vacuum condition for several days. It is observed that the thickness of polymer layer and the electrical characteristics of organic TFTs vary with the condensation time, and the appropriate additional annealing process could stabilize the gate dielectric layer and even improve the device characteristics consequently.

Condensation and Annealing Effects of Polymer Gate Insulator on Organic Thin-Film Transistor Characteristics

An improved measurement method using photocurrent spectroscopy of an amorphous indium-zinc-oxide (a-IZO) optical sensor is proposed to analytically calculate the density of state (DOS) distributions. In the signal conversion method for DOS calculation, the photocurrent spectrum was measured in the on-state and off-state regions and the current signal was converted. In addition, the trap state distribution in the band gap of a-IZO semiconductor was modeled by calculating the photo-current signal of the photo-sensor. The validity of the proposed photo-carrier spectroscopy was verified through comparison with photo-excited charge collection spectroscopy analysis. This photo-current spectroscopy-based measurement method greatly improved measurement duration and accuracy compared to threshold voltage-based analysis.

Advanced Signal Processing of Photo-Excited Current Spectroscopy Based on Trap State Distribution for Photo-Sensor Applications

We report a viable method for localizing a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] film by using the transfer-print process. Micro-scaled topographic P(VDF-TrFE) patterns were successfully produced by using the transfer-print method, and the transferred films exhibited inherent ferroelectric properties. The characteristic improvements in the ferroelectric field-effect transistors (FeFETs) with respect to the operation voltage and the field-effect mobility could be achieved by using the transfer-print method to fabricate a ferroelectric insulator. The results suggest that transferring a ferroelectric film would be useful for realizing high-performance nonvolatile memory devices composed of FeFETs.

Transfer printing of poly(vinylidene fluoride-trifluoroethylene) films for low-voltage ferroelectric field-effect transistors

This paper reports the effects of the molecular weights (MWs) of a polymeric insulator on the electrical properties of a pentacene thin-film transistor. The MWs of polystyrene used as a polymeric insulator were varied from 13,000 to 980,000. The mobility and current on/off ratio in a pentacene thin-film transistor were improved considerably (more than twofold and by a factor of 2, respectively) with increasing MW of polystyrene. In addition, the magnitude of the subthreshold slope was reduced significantly. Both the thickness and dielectric constant remained the same regardless of the MWs of polystyrene. The improved electrical properties could be explained because the higher MW of polystyrene results in the pentacene film with enhanced grain and crystalline intensity. This suggests that a higher MW is important for obtaining better electrical characteristics in organic transistors with polymeric insulators.

Jaehoon Park

Papers

Characteristic Effects of Buffer Layers on Organic Light Emitting Devices

Condensation and Annealing Effects of Polymer Gate Insulator on Organic Thin-Film Transistor Characteristics

Advanced Signal Processing of Photo-Excited Current Spectroscopy Based on Trap State Distribution for Photo-Sensor Applications

Transfer printing of poly(vinylidene fluoride-trifluoroethylene) films for low-voltage ferroelectric field-effect transistors

Effects of molecular weights of a polymeric insulator on the electrical properties of pentacene thin-film transistors