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Natural, organic, materials-based artificial synaptic devices have been in the spotlight for wearable/flexible devices due to their lightweight, biocompatibility, and scalability. In this study, an electronic memristive device based on agarose extracted from plants in the Rhodophyceae class was fabricated, and its memory characteristics and analog data processing capabilities were evaluated. The Al/agarose@gold nanoparticle (AuNP) film/indium-tin-oxide (ITO)-structured memristive device exhibited reliable resistive switching characteristics with excellent retention with a large Ron/Roff ratio of 104. Also, analog conductance changes in our device were achieved with power consumption at the pJ level. This notable behavior could be maintained under mechanical deformations from a flat to a 4-mm bent state. In the recognition simulation based on the device's performance, an 91% accuracy and clear digit classification were achieved.

Artificial synaptic devices based on natural organic materials are becoming the most desirable for extending their fields of applications to include wearable and implantable devices due to their biocompatibility, flexibility, lightweight, and scalability. Herein, we proposed a zein material, extracted from natural maize, as an active layer in an artificial synapse. The synaptic device exhibited notable digital-data storage and analog data processing capabilities. Remarkably, the zein-based synaptic device achieved recognition accuracy of up to 87% and exhibited clear digit-classification results on the learning and inference test. Moreover, the recognition accuracy of the zein-based artificial synapse was maintained within a difference of less than 2%, regardless of mechanically stressed conditions. We believe that this work will be an important asset toward the realization of wearable and implantable devices utilizing artificial synapses.

A novel nanocomposite-based non-volatile resistance switching random access memory device introducing single-walled carbon nanotube (SWCNT)@TiO2 core–shell wires was proposed for flexible electronics. The SWCNT was de-bundled by ultrasonication with sodium dodecylbenzene sulfonate (SDBS), and then the TiO2 skin layer on the SWCNT surface was successfully introduced by adding benzyl alcohol as a weak surfactant. The nanocomposite resistance switching layer was composed of the SWCNT@TiO2 core–shell wires and poly(vinyl alcohol) (PVA) matrix by a simple spin-coating method. The device exhibited reproducible resistance switching performance with a remarkably narrow distribution of operating parameters (VSET and VRESET were 2.63 ± 0.16 and 0.95 ± 0.11 V, respectively) with a large RON/ROFF ratio of 105 for 200 consecutive switching cycles. Furthermore, the excellent resistance switching behavior in our device was maintained against mechanical stress up to 105 bending test. We believe that the nanocomposite memory device with SWCNT@TiO2 core–shell wires would be a critical asset to realize practical application for a flexible non-volatile memory field.

Biosynaptic devices based on chicken egg albumen (CEA):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable synaptic behaviors. Current-voltage (I-V) curves for the biosynaptic devices under consecutive negative and positive voltage sweeps showed clockwise pinched hysteresis, which is a critical feature of a biological synapse. The effect of the GQD concentration in the CEA layer on the device performance was studied. The retention time of the biosynaptic devices was relatively constant, maintaining a value above 104 s under ambient conditions. The carrier transport mechanisms of the biosynaptic devices were described and analyzed on the basis of the slopes of the I-V curves and their fittings.

We developed flexible, transparent patterned electrodes, which were fabricated utilizing accelerated ultraviolet/ozone (UV/O3)-treated graphene oxide (GO)/silver nanowire (Ag-NW) nanocomposites via a simple, low-cost pattern process to investigate the feasibility of promising applications in flexible/wearable electronic and optoelectronic devices. The UV/O3 process of the GO/Ag-NW electrode was accelerated by the pre-heat treatment, and the degradation interruption of Ag NWs was removed by the GO treatment. After the deposition of the GO-treated Ag NW electrodes, the sheet resistance of the thermally annealed GO-treated Ag-NW electrodes was significantly increased by using the UV/O3 treatment, resulting in a deterioration of the GO-treated Ag NWs in areas exposed to the UV/O3 treatment. The degradation of the Ag NWs caused by the UV/O3 treatment was confirmed by using the sheet resistances, scanning electron microscopy images, X-ray photoelectron microscopy spectra, and transmittance spectra. While the sheet resistance of the low-density Ag-NW electrode was considerably increased due to the pre-thermal treatment at 90 °C for 10 min, that of the high-density Ag-NW electrode did not vary significantly even after a UV/O3 treatment for a long time. The degradation interference phenomenon caused by the UV/O3 treatment in the high-density Ag NWs could be removed by using a GO treatment, which resulted in the formation of a Ag-NW electrode pattern suitable for promising applications in flexible organic light-emitting devices. The GO treatment decreased the sheet resistance of the Ag-NW electrode and enabled the pattern to be formed by using the UV/O3 treatment. The selective degradation of Ag NWs due to UV/O3 treatment decreased the transparency of the Ag-NW electrode by about 8% and significantly increased its sheet resistance more than 100 times.

Ce-doped ZnO layers were synthesized by using a sol–gel method for applications as electron transport layers (ETLs) in inverted organic photovoltaic (OPV) cells. X-ray photoelectron spectroscopy spectra, energy-dispersive X-ray analysis spectra, and atomic force microscopy and scanning electron microscopy images showed that the formed samples were Ce-doped ZnO layers with smooth surfaces. The inverted OPV cell based on a poly (3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction containing a Ce-doped ZnO ETL was fabricated for enhanced efficiency. Current density–voltage results showed that the power conversion efficiency of the fabricated inverted OPV cell with a Ce-doped ZnO ETL was 0.87 times larger than that with a ZnO ETL due to the enhanced absorption of the Ce-doped ZnO ETL at a near-ultraviolet/blue light region between 300 and 500 nm. Device structure and current density–voltage (J–V) characteristic curves for inverted organic photovoltaic (OPV) cells with a ZnO or a Ce-doped ZnO electron transport layer (ETL) under AM 1.5 stimulated illumination at an intensity of 100 mW/cm2. The enhancement of the power conversion efficiency (PCE) values of the inverted OPV cells with a Ce-doped ZnO ETL is attributed to increases in the short-circuit current density, open-circuit voltage, and fill factor. The results indicate that the PCEs of the ZnO-based OPV cells can be improved by doping Ce into the ZnO layer.

Nonvolatile memory (NVM) devices based on a metal–insulator–metal structure consisting of CdSe/ZnS quantum dots embedded in polymethylsilsesquioxane dielectric layers were fabricated. The current–voltage (I–V) curves showed a bistable current behavior and the presence of hysteresis. The current–time (I–t) curves showed that the fabricated NVM memory devices were stable up to 1 × 104 s with a distinct ON/OFF ratio of 104 and were reprogrammable when the endurance test was performed. The extrapolation of the I–t curve to 105 s with corresponding current ON/OFF ratio 1 × 105 indicated a long performance stability of the NVM devices. Schottky emission, Poole–Frenkel emission, trapped-charge limited-current and Child–Langmuir law were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I–V characteristics.

The electronic and the optoelectronic properties of graphene-based nanocomposites are controllable, making them promising for applications in diverse electronic devices. In this work, tetrapod-shaped zinc oxide (T-ZnO)/reduced graphene oxide (rGO) core/coating nanocomposites were synthesized by using a hydrothermal-assisted self-assemble method, and their optical, photoelectric, and field-emission properties were investigated. The ZnO, an ideal ultraviolet-light-sensitive semiconductor, was observed to have high sensitivity to visible light due to the rGO coating, and the mechanism of that sensitivity was investigated. We demonstrated for the first time that the field-emission properties of the T-ZnO/rGO core/coating nanocomposites could be dramatically enhanced under visible light by decreasing the turn-on field from 1.54 to 1.41 V/μm and by increasing the current density from 5 to 12 mA/cm2 at an electric field of 3.5 V/μm. The visible-light excitation induces an electron jump from oxygen vacancies on the surface of ZnO to the rGO layer, resulting in a decrease in the work function of the rGO and an increase in the emission current. Furthermore, a field-emission light-emitting diode with a self-enhanced effect was fabricated making full use of the photo-assisted field-emission process.

A novel Na-containing precursor solution is presented to investigate the sodium influences on Cu2ZnSnSe4 (CZTSe) absorbers grown on Na-free substrates. With higher sodium incorporation, some delicate change in secondary phase Cu2SnSe3 was detected and its influence on the surface valence states was given by X-ray photoelectron spectroscopy analyses. It is found that the band gap significantly increased with nominal addition of Na, while the impurity introduced by excess incorporation would restrain further broadening. This method may probably assist to form a suitable CZTSe film directly on flexible substrates other than soda-lime glass.

Structural, optical, and photovoltaic properties of copper-oxide (CuxO) thin films formed by using a sol–gel method were investigated. X-ray diffraction patterns showed that the CuxO films prepared utilizing Cu(I) acetate or Cu(II) acetate and annealed under ambient atmosphere at various temperatures were polycrystalline with two phases, Cu2O and Cu64O. Transmittance spectra showed that the energy band gaps of the CuxO thin films formed by using Cu(II) acetate were smaller than those formed by using Cu(I) acetate. Current–voltage results showed that the power conversion efficiencies of the inverted polymer solar cells utilizing the CuxO interlayer formed by using Cu(II) acetate were better than those utilizing the CuxO interlayer formed by using Cu(I) acetate due to the multiple band gaps of the Cu(II) acetate.

Hierarchically porous CeCO3OH palm leaves were synthesized by using a facile solvothermal method at 180 °C utilizing cerium nitrate and ethylene glycol. Polycrystalline CeO2 palm leaves were obtained from the thermal decomposition-oxidation process of the CeCO3OH nanostructures. CeCO3OH and CeO2 palm leaves were characterized by X-ray diffraction pattern, scanning electron microscopy image, energy dispersive X-ray analyses, and ultraviolet (UV)–visible spectroscopy images. The CeO2 palm leaves exhibited a significant photocatalytic performance in degrading azo dye acid orange II in an aqueous solution under an UV radiation. The formation mechanisms of the CeCO3OH/CeO2 nanostructures were described on the basis of the experimental results.

Thin-film transistors (TFTs) utilizing TiO2 channel layers were fabricated by using a solution process. Atomic force microscopy images showed that the surface morphology of the TiO2 films became uniform due to the ultraviolet (UV)/ozone treatment. X-ray photoelectron spectroscopy showed that the UV/ozone treatment reduced the amount of oxygen deficiency in the TiO2 films, resulting in a decrease of the electron concentration on the surface. The performance of the TFT devices was significantly improved due to a decrease of the off-current level resulting from the enhanced uniformity and the decrease of the trap level resulting from the UV/ozone treatment.

The main purpose of this article is to examine the surface free cerium oxide (CeO2) nanostructures prepared by different methods. CeO2 nanoparticles and nanorods were prepared by two different methods including precipitation and hydrothermal process. In precipitation process the nanoparticles were prepared at room temperature, while in hydrothermal process nanorods were prepared at high temperature. X-ray and electron diffraction analysis show the presence of CeO2. X-ray photoelectron spectroscopy (XPS) confirms the presence of CeO2 in both nanostructures. From BET, the specific surface area of nanorods (110 m2g−1) is found to be higher than nanoparticles (52 m2g−1). Also, the effect of morphology on their photodegradation of azo dye acid orange 7 (AO7) under UV–Visible light has been successfully investigated. The results show that the CeO2 nanorods synthesized by hydrothermal method have high surface area and exhibit improved performance in the photocatalytic activity.

Toll-like receptor 9 (TLR9) senses microbial DNA in the endosomes of plasmacytoid dendritic cells (pDCs) and triggers MyD88-dependent type I interferon (IFN) responses. To better understand TLR9 biology in pDCs, we established a yeast two-hybrid library for the identification of TLR9-interacting proteins. Here, we report that an IFN-inducible protein, phospholipid scramblase 1 (PLSCR1), interacts with TLR9 in pDCs. Knockdown of PLSCR1 expression by siRNA in human pDC cell line led to a 60-70% reduction of IFN-α responses following CpG-ODN (oligodeoxynucleotide) stimulation. Primary pDCs from PLSCR1-deficient mice produced lower amount of type 1 IFN than pDCs from the wild-type mice in response to CpG-ODN, herpes simplex virus and influenza A virus. Following CpG-A stimulation, there were much lower amounts of TLR9 in the early endosomes together with CpG-A in pDCs from PLSCR1-deficient mice. Our study demonstrates that PLSCR1 is a TLR9-interacting protein that plays an important role in pDC's type 1 IFN responses by regulating TLR9 trafficking to the endosomal compartment.

Electrical and the optical properties of organic light-emitting devices (OLEDs) fabricated utilizing core/shell CdSe/ZnS quantum dots (QDs) embedded in a polyvinylcarbazole (PVK) layer were investigated. An abrupt increase of the current density above an applied voltage of 12 V for OLEDs consisting of Al/LiF/4,7-diphenyl-1,10-phenanthroline/bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato) aluminium/[CdSe/ZnS QDs embedded in PVK]/poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate)/ITO/glass substrate was attributed to the existence of the QDs. Photoluminescence spectra showed that the peaks at 390 and 636 nm corresponding to the PVK layer and the CdSe/ZnS QDs were observed. While the electroluminescence (EL) peak of the OLEDs at low voltage range was related to the PVK layer, the EL peak of the OLEDs above 12 V was dominantly attributed to the CdSe/ZnS QDs. The Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of the OLEDs at high voltages were (0.581, 0.380) indicative of a red color. When the holes existing in the PVK layer above 12 V were tunneled into the CdSe/ZnS QDs, the holes occupied by the CdSe/ZnS QDs combined with the electrons in the PVK layer to emit a red color related to the CdSe/ZnS QDs.

Scanning electron microscopy and transmission electron microscopy images and selected area electron diffraction pattern showed that the one-dimensional GaN nanorods with [0001]-oriented single-crystalline wurzite structures were formed on Si (111) substrates by using hydride vapor-phase epitaxy without a catalyst. Although some stacking faults and inversion domain boundaries existed in the GaN nanorods, few other defects such as threading dislocations were observed. The formation of the facet plane in the N-polar region of the GaN nanorod containing an inversion domain boundary originated from the slow growth rate, followed by the lateral adatom diffusion from the Ga-polar region to reduce the length difference.

Optical gains and interband transition energies for CdTe/ZnTe single quantum wells (SQWs) with different CdTe well widths were investigated. Photoluminescence (PL) spectra for CdTe/ZnTe SQWs at various temperatures were experimentally obtained, and the corresponding optical gains were calculated by using an interacting pair Green’s function and by using an energy space integrated function. The peak energies in the gain spectra that take the Coulomb interaction between the electron and the hole into account were in qualitatively reasonable agreement with those determined from the PL spectra.

The effects of hydrogenation and aging on the optical properties in porous Si (PS) layers were investigated by using photoluminescence (PL) measurements. When the hydrogenated PS layers were aged in air, the intensity of the PL spectrum increased. The emission peak for the hydrogenated PS layers shifted to higher energy with decreasing H2/N2 ratio. The relation of the dehydrogenized states in the as-formed PS surface to the quantum states of Si nanoparticles with relatively small sizes is discussed. These results indicate that the optical properties of PS layers are significantly affected by hydrogenation and aging.

II–VI/III–V heterostructures based on wide-energy band-gap II–VI compound semiconductors have been very attractive because of their potential applications in short-wavelength optoelectronic devices [1–5]. Among these II–VI/III–V mixed heterostructures, ZnSe/GaAs heterostructures have been particularly interesting due to their promising applications for the fabrication of laser diodes and light-emitting diodes operating in the blue-green region of the spectrum [6–10]. However, relatively little work has been performed on II–VI/III–V heterostructures in comparison with III–V/III–V heterostructures due to cross-doping problems resulting from interdiffusion or intermixing during growth and fabrication [11]. Since thermal treatment is necessary for the fabrication processes of several kinds of optoelectronic devices utilizing ZnSe/GaAs heterostructures, the role of the thermal annealing processes is very important in achieving high-performance devices [12]. Therefore, studies of the annealing effects on the surface, the structural, and the optical properties play a very important role in enhancing device efficiency. This letter reports the effect of annealing of ptype ZnSe epilayers grown on n-type GaAs (100) substrates by using molecular beam epitaxy (MBE). Atomic force microscopy (AFM), photoluminescence (PL), and transmission electron microscopy (TEM) measurements were performed in order to investigate the surface, the optical, and the structural properties of as-grown and annealed ZnSe/GaAs heterostructures. The samples used in this study were p-type ZnSe epitaxial layers grown on n-type GaAs (100) substrates in a Riber 32 P system by using MBE. Elemental Zn and Se with purities of 99.9999% were used as the source materials, and the flux ratio, Zn/Se, was approximately 0.5 during ZnSe epilayer growth. The p-type doping was carried out using an rf plasma source to excite nitrogen gas at a pressure of 10−8 Torr in the

Organic electronic synapses (e-synapses) based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene quantum dot (GQD) nanocomposites are fabricated by using a solution method. Current–voltage (I–V) curves for the devices under dual positive bias voltage sweeps show that the conductance with a pinched hysteresis gradually increased with increasing applied voltage, and those for the devices under dual negative bias voltage sweeps gradually decreased with increasing applied voltage, indicative of the fingerprint of e-synapses. The current in the devices decreases with increasing concentration of GQDs in the active layer, and the devices fabricated utilizing the ratio of PEDOT:PSS to GQDs of 1:0.4 shows the best performance among the e-synapses. The carrier transport and operating mechanisms of the e-synapses are described on the basis of both the I–V results and the trapping and escape of electrons from the GQDs. An electronic device made from organic materials that behaves like a synapse in the brain has been created by scientists in Korea. Engineering electronic components that mimic the behavior of synapses could revolutionize the currently silicon-based computing industry. Tae Whan Kim and co-workers from Hanyang University combined graphene quantum dots with an electronic polymer to create what could be the building block of a computer that operates like the brain. They made a type of artificial synapse known as a resistive switch, or memristor, that can be controllably flipped between a high and low electrical resistance states. The researchers' device consisted of graphene quantum dots embedded in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. They showed that its electrical properties can be optimized by changing the concentration of quantum dots. Organic electronic synapses based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene quantum-dot (GQD) nanocomposites were fabricated by using a solution method. Current–voltage (I–V) curves for the devices under dual positive bias voltage sweeps and under dual negative bias voltage sweeps showed that the conductance with a pinched hysteresis gradually increased and gradually decreased, respectively, with increasing applied voltage which is a fingerprint of e-synapses. The current in the devices was found to decrease with increasing concentration of GQDs in the active layer, and the devices fabricated utilizing the ratio of PEDOT:PSS to GQDs of 1:0.4 showed the best performance among the e-synapses. The carrier transport and operating mechanisms of the e-synapses are described in this paper on the basis of both the I–V results and the trapping and escape of electrons from the GQDs. We believe that our letter contains significant results of interest to a broad spectrum of NPG Asia Materials readers.

Measurements of structural and electrical properties as a function of the molding pressure in Y1Ba2Cu3O7−δ superconductors have been performed to investigate the texturing behavior. The magnitudes of the molding pressure were 0.5 × 103 N/cm2, 1 × 103 N/cm2, 2 × 103 N/cm2, and 4 × 103 N/cm2. As the molding pressure increases, the anisotropy of the crystal structure decreases and the crystal grows preferentially along the c-axis. As the molding pressure increases, since the size of the grain becomes larger due to the decreased porosity, denser textures are formed. This result indicates that the critical current density is improved, resulting in increased thermal stability at higher molding pressure. While the molding pressure does not affect the oxygen mole fraction below 500 °C, increases in the molding pressure have a remarkable effect on the formation of textures and on the onset temperature for the superconducting transition in Y1Ba2Cu3O7−δ. These results indicate that structural and electrical properties in Y1Ba2Cu3O7−δ superconductors are affected by the molding pressure during growth.

The effects of different electric fields (4.2, 8.3, 12.5, 16.7 and 20.8 Vcm−1) on the sheet resistance, Rs, and optical band gap, Eobg, of As2Se3 samples (1×105nm) that were photodoped by Ag (5×103nm) have been studied. The Rs and Eobg of samples subjected to an electric field of 12.5 Vcm−1 decrease linearly to a distance of 5 mm from both electrodes, and then saturate at larger distances. This result suggests that there is a critical value of the electric field which affects photodoping. The dependence of Rs and Eobg on the distance from the electrodes shows similar profiles for these electrodes.

Tae Whan Kim and co-workers review how nanocomposite materials that combine organic and inorganic materials are attractive for use in memory components. A wide variety of structures have been used to store information by switching between two states, making for either volatile or nonvolatile memory systems; well-known examples of both types are random access memory (RAM) and computer hard disks, respectively. Among those, hybrid organic-inorganic devices–such as a polymer matrix in which metal nanoparticles have been incorporated–are easy to make, cost-effective, mechanically flexible, and efficient. Further studies will endeavour to better understand the memories' mechanisms and improve their switching speed and reproducibility. These hybrid structures are particularly promising for the development of flexible memories required to construct the next generation of portable devices.