Effect of nanostructured grains in co-sputtered Ni-GDC thin-film anode on methane conversion kinetics for low temperature solid oxide fuel cells operating on nearly dry methane

Direct-methane solid oxide fuel cells (DMSOFCs) have recently attracted substantial attention due to their simplified system, reduced cost, and the direct availability of methane fuel obtained from natural gas. Among oxygen-ion conductive materials, doped-ceria such as gadolinium-doped ceria (GDC) or samarium-doped ceria can be incorporated into Ni-based anodes to reinforce their coking resistance, enlarge their electrochemical reaction area, and improve the kinetics of the internal reforming/electrochemical oxidation of methane. To reduce the range of operating temperatures of DMSOFCs while maintaining their performance, the thin film deposition technique of magnetron sputtering was adopted in this work. An Ni-GDC thin-film anode and a Pt thin-film cathode were deposited on scandia-stabilized zirconia (ScSZ) electrolyte supports. This fuel cell was tested with directly supplied methane fuel (3% H₂O) at 500 °C. The results demonstrated the effects of the GDC volume fraction in the anode—which was controlled by co-sputtering power—on open circuit voltage and electrochemical performance. The co-sputtered Ni-GDC anode was able to survive through 36-h operation, although there was some performance degradation. Field-emission scanning electron microscopy results revealed no formation of filamentous carbon on the Ni catalysts, despite the fact that both X-ray photoelectron spectroscopy and Raman spectroscopy analyses detected carbon coking. The relatively high performance and resistance to carbon coking of co-sputtered thin-film anode were attributed to its intrinsic small grain size.     

High-performance 2,9-DPh-DNTT organic thin-film transistor by weak epitaxy growth method

2,9-DPh-DNTT, an isomeric of diphenyl-dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b] thiophene (DPh-DNTTs), is an emerging candidate of high mobility organic semiconductor material. In this work, a high performance 2,9-DPh-DNTT organic thin-film transistor (OTFT) is fabricated by the method of weak epitaxy growth. The quality of 2,9-DPh-DNTT thin film was significantly improved when its epitaxial layer grows on an inducing layer of para-sexiphenyl (p-6P). Continuous large-area, highly ordered and terraced 2,9-DPh-DNTT polycrystalline thin films are obtained. The hole mobility of as-fabricated 2,9-DPh-DNTT thin-film transistor reaches up to 6.4 cm² V⁻¹s⁻¹. This simple process of preparing high mobility 2,9-DPh-DNTT thin-film transistor supplies a facile route of large-area OTFT fabrication.     

Synergistic Improvement of Long-Term Plasticity in Photonic Synapses Using Ferroelectric Polarization in Hafnia-Based Oxide-Semiconductor Transistors

A number of synapse devices have been intensively studied for the neuromorphic system which is the next-generation energy-efficient computing method. Among these various types of synapse devices, photonic synapse devices recently attracted significant attention. In particular, the photonic synapse devices using persistent photoconductivity (PPC) phenomena in oxide semiconductors are receiving much attention due to the similarity between relaxation characteristics of PPC phenomena and Ca²⁺ dynamics of biological synapses. However, these devices have limitations in its controllability of the relaxation characteristics of PPC behaviors. To utilize the oxide semiconductor as photonic synapse devices, relaxation behavior needs to be accurately controlled. In this study, a photonic synapse device with controlled relaxation characteristics by using an oxide semiconductor and a ferroelectric layer is demonstrated. This device exploits the PPC characteristics to demonstrate synaptic functions including short-term plasticity, paired-pulse facilitation (PPF), and long-term plasticity (LTP). The relaxation properties are controlled by the polarization of the ferroelectric layer, and this polarization is used to control the amount by which the conductance levels increase during PPF operation and to enhance LTP characteristics. This study provides an important step toward the development of photonic synapses with tunable synaptic functions.     

Physical modification of polymeric support layer for thin film composite forward osmosis membranes by metal–organic framework-based porous matrix membrane strategy

Physical modification of support layers (SLs) for thin-film composite (TFC) forward osmosis (FO) membranes is the main goal of this study. Accordingly, the strategy of metal–organic framework (MOF)-based porous matrix membrane (PMM) was used for the fabrication of controllable SLs. Fourteen different TFC FO membranes were successfully fabricated by interfacial polymerization (IP) technique over the fourteen different SLs made of polyetherimide (PEI), polyethersulfone (PES), and twelve MOF-based PMM. The controllable MOF particles, fabricated SLs, and TFC membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle (CA), inductively coupled plasma (ICP), and developed SHN1 method. The results showed that the PMM strategy can lead to an increase in the degree of crosslinking of polyamide (PA) as a result of physical modification of the original SLs. Also, the PMM strategy reduced the structural parameters and hence the internal concentration polarization (ICP) was controlled. However, according to the characteristic curve, physical modification of the structure of PES and PEI by MOF-based PMM strategy caused a small and dramatic effect (respectively) on the performance of the TFC FO membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48672.     

Organic photodetector with built-in amplification for the detection of visible light with low optical power

We report on an organic-based photodetector that integrates a dual-gate organic thin-film transistor (DG-OTFT) with an organic photodiode (OPD) to produce a device with a high effective responsivity at low optical power and video-rate compatible response. In this device, the OPD operates in photovoltaic mode, instead of the commonly used photoconductive mode, to modulate one of the gate voltages of the DG-OTFT. Effective responsivity values of 10 A W⁻¹ are measured at optical power values lower than 10 nW at 635 nm. Modeling of the operation of this new photodetector suggests that effective responsivity values up to 10⁵ A W⁻¹ can be achieved at optical powers of 1 nW using current printing technology and state-of-the-art organic semiconductors.     

Environmental effects on the electrical behavior of pentacene thin-film transistors with a poly(methyl methacrylate) gate insulator

The electrical properties of top-contact pentacene thin-film transistors (TFTs) with a poly(methyl methacrylate) (PMMA) gate dielectric were analyzed in air and vacuum environments. Compared to the vacuum case, the pentacene TFT in air exhibited lower drain currents and more pronounced shifts in the threshold voltage upon reversal of the gate voltage sweep direction, together with a decrease in the field-effect mobility. These characteristic variations were explained in terms of two distinctive actions of polar H₂O molecules in pentacene TFT. H₂O molecules were suggested to diffuse under the source and drain contacts and interrupt the charge injection into the pentacene film, whereas those that permeate at the pentacene/PMMA interface retard hole depletion in and around the TFT channel. The diffusion process was much slower than the permeation process. The degraded TFT characteristics in air could be recovered mostly by storing the device under vacuum, which suggests that the air instability of TFTs is due mainly to the physical adsorption of H₂O molecules within the pentacene film.