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The phenomenon of electron emission from ferroelectric cathodes has attracted much interest and today is a subject of investigation all over the world. In this paper, organic PVDF (polyvinylidene fluoride) thin films were prepared by ultrasonic atomization method, and pulse excited electric field induced electron emission from the poled organic PVDF ferroelectric cathode has been investigated. The results indicated that the reason of electron emission was the compensated charges on the surface of organic ferroelectric cathode unbalancing caused by fast reversal of the polarization. Repeatable emissions were obtained from the organic PVDF ferroelectric cathode, which could also be modulated at high electric field. It is anticipated that an electron source, based on emission from PVDF ferroelectric cathode, will comprehensively trigger a novel type of display. [ABSTRACT FROM AUTHOR]

Charge transport in a multilayer hybrid electroluminescence (EL) device containing CdSe/ZnS quantum dots (QDs) embedded in hole-transporting poly(N-vinylcarbozole) (PVK) layer was investigated. The current-voltage (I-V) curve exhibited resistive transition at low bias voltage and a negative differential resistance region with increase in bias voltage, which can be explained in terms of a two-step charge transport process, i.e., holes trapping and the following hole-electron recombination in CdSe/ZnS QDs embedded in PVK layer. EL spectra showed that the recombination center would be restricted to CdSe/ZnS QDs at high bias voltage, which is in well agreement with the I-V results. [ABSTRACT FROM AUTHOR]

Efficient charge carrier transport in organic thin film transistors (OTFTs) often requires thin films with highly oriented feature. Although there are a number of methods to effectively form high-degree and large-scale alignment during the process of film formation, these methods usually resulted in nonuniform films. In order to obtain highly aligned uniform films, this paper provides a postalignment method after film formation. By applying electric field during solvent annealing, the polymer backbone can be reorganized along the direction of the electric field, leading to highly aligned polymer chains and significant improvement in charge mobility. In addition, after doping the polymer films with liquid crystal (LC), with the benefit of LC molecules' template, the degree of orientation of polymer molecular chains was further enhanced, resulting in further improvement of the charge mobility up to 9.42 cm² ·V-1·s-1. This paper exhibits the possibility of improving charge transport after film formation to obtain high-performance solution-processable OTFT for low-cost and large-scale organic electronics. [ABSTRACT FROM AUTHOR]

Tristable resistive memories based on single layer graphene (SLG)/insulating polymer multi-stacking layer were fabricated. By using the traditional transfer method, the chemical vapor deposition-synthesized SLG serving as charging layers were combined with poly(methyl methacrylate) (PMMA) layers and polystyrene (PS) layers to form charge traps with various depth. Based on the PS/SLG/PMMA/SLG/PMMA multi-stacking layer, the devices exhibited efficient tristable memory performances. The ratios as large as 104 between different resistive states were maintained for a retention time of more than 104 s. The operation mechanisms of stepping-charging in the multi-stacking layer for the tristable resistive switching were proposed on the basis of the current-voltage analysis. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the oxidation process of Cr/Cu/Cr laminated thin film electrode is important for developing new oxidation-resistant electrodes. By studying the evolution of crystal structure, morphology and electric resistivity of Cr/Cu/Cr thin films and electrodes that were post-annealed at different temperatures, the oxidation mechanism and process of Cr/Cu/Cr electrode were proposed. Copper is first oxidized into Cu2O at low temperatures (<310°C), and converts to CuO phase at higher temperatures. Two pathways for oxygen diffusion were identified: diffusion from the protective Cr layer, and diffusion from the sidewall of electrode, of which the latter one leads to total oxidation of copper interlayer at high temperatures (>310°C). As a result, the passivation of Cu metal at electrode sidewalls is crucial in reducing oxidation of Cr/Cu/Cr electrodes or designing new copper-containing oxidation-resistant electrodes. [Copyright &y& Elsevier]

High-performance thin-film transistors (TFTs) were obtained by incorporating small amount of tungsten (W) into amorphous indium zinc oxide (IZO)-based thin films via a solution process. Compared with original IZO TFTs, 0.2-wt% W-doped IZO TFTs exhibit improved bias stress stability and field-effect mobility of 30.5 cm²/V·s. Meanwhile, the bias stress stability of IZO TFTs can be further enhanced with 0.5-wt% W-doping. The pulsed current-voltage (I-V) method is employed to study the hysteresis and charging behavior of the W-doped IZO TFTs. The X-ray photoelectron spectroscopy analysis and the pulsed I-V measurement results suggest that these desirable performances could be attributed to the suppression of excessive oxygen vacancies and improved interface quality because of W-doping. The results represent an effective strategy to achieve high-performance solution-processed amorphous oxide-based TFTs with desirable stability by W-doping. [ABSTRACT FROM AUTHOR]

In this work, we present a simple and facile one step synthesis strategy to prepare CH3NH3PbBr3 perovskite quantum dots and apply them into the nonvolatile memory. Resistive switching phenomenon was observed in this perovskite quantum dots and polymer composite based memory device with the ON/OFF current ratio larger than 103 as well as good reproducibility and reliability. Flexible memory was also demonstrated, and a possible resistance switching mechanism was discussed. Our work paves a way for the application of organolead halide perovskite quantum dots in flexible and transparent nonvolatile memories. [ABSTRACT FROM AUTHOR]

This study examined the electrical performance of bilayer channel InGaZnO:H/InGaZnO thin-film transistors (TFTs). The field-effect mobility and bias stress stability of the InGaZnO device were improved by inserting the hydrogenated InGaZnO ultrathin layer compared to the pure InGaZnO single channel layer device. As a consequence, a high field-effect mobility of 55.3 cm2/V s, a high on/offcurrent ratio of 108, a threshold voltage of 0.7 V, and a small sub-threshold swing of 0.18 V/ decade have been achieved. The X-ray photoelectron spectroscopy and low-frequency noise analysis suggest that these desirable properties should be attributed to the ultrathin InGaZnO:H layer, which could provide suitable carrier concentration and reduce the average trap density near the channel and insulator layer interface. Meanwhile, the channel conductance of the bilayer device is controlled by thick InGaZnO layer through formation barrier energy for electron transport at the interface of InGaZnO:H and InGaZnO layer. These improved electrical properties have represented a great step towards the achievement of transparent, high performances, and low-cost metal oxide TFTs. [ABSTRACT FROM AUTHOR]

Efficient and low-cost methods for obtaining high performance fiexible transparent electrodes based on chemical vapor deposition (CVD)-grown graphene are highly desirable. In this work, the graphene grown on copper foil was exfoliated into micron-size sheets through controllable ultrasonication. We developed a clean technique by blending the exfoliated single layer graphene sheets with conducting polymer to form graphene-based composite solution, which can be spin-coated on fiexible substrate, forming fiexible transparent conducting film with high conductivity (~8 Ω/⇔), high transmittance (~81% at 550 nm), and excellent mechanical robustness. In addition, CVD-grown-graphene-based polymer light emitting diodes with excellent bendable performances were demonstrated. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multiwalled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and twodimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs. [ABSTRACT FROM AUTHOR]

The functionalization of graphene oxide (GO) sheets with polyimide (PI) enables the layer-by-layer fabrication of a GO-PI hybrid resistive-switch device and leads to high reproducibility of the memory effect. The current-voltage curves for the as-fabricated device exhibit multilevel resistive-switch properties under various reset voltages. The capacitance-voltage characteristics for a capacitor based on GO-PI nanocomposite indicate that the electrical switching may originate from the charge trapping in GO sheets. The high device-to-device uniformity and unique memory properties of the device make it an attractive candidate for applications in next-generation high-density nonvolatile flash memories. [ABSTRACT FROM AUTHOR]

Artificial intelligence devices that can mimic human brains are the foundation for building future artificial neural networks. A key step in mimicking biological neural systems is the modulation of synaptic weight, which is mainly achieved by various engineering approaches using material design, or modification of the device structure. Here, we realize the modulation of the synaptic weight of a Ta2O5/ITO-based all-metal oxide synaptic transistor via laser irradiation. Prior to the deposition of the active layer and electrodes, a femtosecond laser was used to irradiate the surface of the insulator layer. Typical synaptic characteristics such as excitatory postsynaptic current, paired pulse facilitation and long-term potentiation were successfully simulated under different laser intensities and scanning rates. In particular, we demonstrate for the first time that laser irradiation could control the quantity of oxygen vacancies in the Ta2O5 thin film, leading to precise modulation of the synaptic weight. Our research provides an instantaneous (<1 s), convenient and low-temperature approach to improving synaptic behaviors, which could be promising for neuromorphic computing hardware design. [ABSTRACT FROM AUTHOR]

The construction of devices with biocompatible and biodegradable materials is a sustainable approach which will open up a new way for the development of green electronics in the future. Compared with organic materials, inorganic materials are more suitable candidates for the fabrication of synaptic transistors due to their better environmental stability, higher mobility and less toxicity. However, the majority of gate electrolytes used in the reported synaptic transistors were non-biocompatible or non-biodegradable. Herein, for the first time, we sputtered inorganic metal oxide indium tin oxide (ITO) on biomass-based hydrogel for the fabrication of synaptic devices, which showed good current on/off ratio (>105). Moreover, several vital synaptic behaviors were successfully simulated in pair such as excitatory post-synaptic current, inhibitory post-synaptic current, paired pulse facilitation, paired-pulse depression and short-term memory to long-term memory. High-pass filter and Pavlov associative learning and oblivion, two kinds of advanced simulation behaviors, were mimicked respectively. Finally, synaptic transistors were fabricated on flexible PET substrates with ITO electrodes and exhibited good mechanical stability under the bending tests. In conclusion, this work provides a unique example for the sustainable development of green neuromorphic electronics. [ABSTRACT FROM AUTHOR]

Solution processed metal oxide thin-film transistors (MO-TFTs) have gained momentum in recent years and opened new horizons for their extended applications in thin-film optoelectronics. Unfortunately, the relatively high processing temperature has become the main limitation for their commercial application in flexible electronics. In this work, ultrashort femtosecond (fs) laser pulses were used for the annealing of printed InGaZnO TFT arrays with low temperature and fast processing. The high transient intensity and negligible heat-affected zone is beneficial to the effective conversion of precursor to metal-oxide lattices, which was also verified by the x-ray photoelectron spectroscopy analysis. Moreover, for the first time, based on optical engineering method, dielectric mirrors (DMs) is proposed to realize reflection of photon irradiation and protect the underlying polymer substrate. TFTs on polyethylene naphthalate (PEN) substrate with polymer insulator exhibited a mobility of 4.24 cm2 V−1 s−1, along with good mechanical stability. The mechanism of DMs for the improvement of the device performance was systematically investigated based on laser-matter interaction, optical structure and photon transport. DMs can reduce laser-induced pressure and variation of dielectric properties in PEN substrate resulting from the impact ionization due to a strong nonlinear multi-photon absorption. Our work clearly demonstrated that flexible MO-TFTs can be simply fabricated with fs-laser annealing. More importantly, this novel method is applicable for a wide range of MO and polymer substrates, by solving the incompatibility of solution processed MO and polymer substrates due to high processing temperature. Therefore, the proposed method showed tremendous potential to be applicable in flexible electronics such as sensors, display and circuits. [ABSTRACT FROM AUTHOR]

Bi-functional thin film with both selected light extraction and reliable moisture vapor barrier was proposed for simultaneous light management and encapsulation in the fields of lighting and display. Atomic layer deposition (ALD) was employed to obtain TiO2 and Al2O3 films with high uniformity, forming distributed Bragg reflector (DBR) structure. The DBRs exhibited excellent and tunable optical properties, as well as reliable moisture barrier performance. With increasing the DBR layers, the transmittances decreased obviously. The transmittance in the blue light region was as low as 0.66% for DBR with 6.5 pairs and the water vapor transmission rates value was 3.06 × 10−5 g m−2 d−1 for DBR with 4.5 pairs. These DBRs were integrated in the red quantum dot (QD) based color converters excited by blue LED, enabling an obvious increase in red emission and a strong decrease in blue light transmittance. Furthermore, these DBRs can prolong the lifetime of QDs evidently by isolating the QDs from the moisture (oxygen) vapor. These results highlight the potentials for the exploitation of DBRs fabricated using ALD in the application of lighting and display devices based on QD photoluminescence and electroluminescence. [ABSTRACT FROM AUTHOR]

The possibility to engineer the van der Waals interactions between graphene layers is crucial for controlling the electronic properties. Using epitaxial graphene with preferential orientations grown on the C-face 6H-SiC as a prototype, we have addressed the annealed structural reconfiguration of graphene layer in view of the evolutions of surface ripples and relative rotation angle (RRA) between lattices. It was found that the heat treatment of graphene layers under vacuum deformed the arcuate ripple surface and subsequently split one ripple into parallel twin pleats, which drastically increased the strains in the films. The originally oriented graphene layers, with small RRA between adjacent layers, were rearranged by the annealing resulting in disordered orientations and larger RRA. After a sufficient annealing, the compressive stress stored in the films was well released to give undistorted graphene lattices. The vacuum annealing is an effective treatment for irreversibly relaxing the graphene structure. [ABSTRACT FROM AUTHOR]

In this work, we report an all-solution route to produce semi-transparent high efficiency perovskite solar cells (PSCs). Instead of an energy-consuming vacuum process with metal deposition, the top electrode is simply deposited by spray-coating silver nanowires (AgNWs) under room temperature using fabrication conditions and solvents that do not damage or dissolve the underlying PSC. The as-fabricated semi-transparent perovskite solar cell shows a photovoltaic output with dual side illuminations due to the transparency of the AgNWs. With a back cover electrode, the open circuit voltage increases significantly from 1.01 to 1.16 V, yielding high power conversion efficiency from 7.98 to 10.64%. [ABSTRACT FROM AUTHOR]