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We demonstrated the sensing properties and adsorption mechanism of NO2 molecules of monolayer graphene and multilayer graphene encapsulated ZnO QDs for NO2 gas adsorption. The gas response value of ZnO-multilayer graphene (ZMLG) QDs was approximately 23 % and 7.2 and 25.5 times higher than that with ZnO-monolayer graphene (ZG) and ZnO QDs, respectively. The surface potential change of ZMLG QDs increased up to 14.25 times compared to ZnO QDs and 6.33 times increased compared to ZG QDs. We proposed an accurate adsorption mechanism for the improvement of the detection behavior that is occured by covering the graphene shells into ZnO QDs by the Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and SKPM measurement. These results are expected to increase the accuracy of gas sensor characteristic analysis.

We demonstrated the thermally robust reduced graphene oxide (rGO)/boron nitride nanotube (BNNT) papers and their application in electromagnetic interference shielding. In order to overcome the thermal durability shortcomings of electromagnetic wave shielding paper based on rGO nanomaterial, rGO/BNNT electromagnetic interference (EMI) shielding paper having excellent thermal durability could be manufactured using BNNT nanomaterials having excellent chemical and thermal stability at high temperature. With the addition of a little BNNT, the durability against temperature can be increased by more than two times while there is little reduction in EMI performance.

Transition metal oxide has been attracting significant attention as a potential alternative anode materials for high-performance lithium-ion batteries. However, the materials still suffer from poor performance due to the large volume expansion during reversible electrochemical reaction between the materials and Li ions. Here, we report on successfully synthesized graphene encapsulated Co3O4 (GE-Co3O4) quantum dots (QDs) by a facile chemical reaction. We also demonstrate an improved performance in Li storage with GE/Co3O4 by suppression of volume expansion during charge/discharge processes. To evaluate the electrochemical characteristics for the lithium storage the composites were examined by cyclic voltammetry and charge/discharge process. The GE-Co3O4 showed a large reversible capacity of 820 mA h/g at a constant current density of 1000 mAg−1 even after 100 cycles and excellent rate capacity and cyclic stability compared to pristine Co3O4 QDs. The encapsulated graphene shell can obstruct the pulverization by inhibiting the volume expansion of Co3O4 QDs, which was supported by the fact that the morphology and structure of GE-Co3O4 QDs was not significantly changed after 100 cycles. We also confirmed through scanning Kelvin probe microscopy, transmittance electron microscopy, and energy-dispersive X-ray spectrometer that the morphology of GE-Co3O4 QDs was maintained whereas that of Co3O4 QDs was almost fully decomposed. The encapsulation of graphene can play important roles such as suppression of volume expansion and producing a sufficient opposing force to aggregation during the cycles, resulting in a long stable life cycle.

Environmentally friendly metal oxide quantum dot (QD) nanostructures have become attractive alternative materials for replacing QDs containing toxic elements of Cd and Pb. Although many attempts have been proposed for optoelectronic applications of hybrid metal oxide QDs with tailored opto-electronic properties, the fabrication of heterogeneous QD–fullerene hybrids as an emissive material has been studied little for optoelectronic devices. Herein, we report the preparation of ZnO–fullerene C70 (ZnO–C70) QDs by a facile chemical reaction with a zero length linker and demonstrate whitish light-emitting diodes by fullerene induced multicolor emission from the ZnO–C70 QD heterostructure. The electroluminescence (EL) is attributed to three new emission features in the visible region that originate from the electron transitions from three split lowest unoccupied molecular orbital levels of C70 molecules to the valence band of ZnO QDs. Compared with photoluminescence, the EL emission was red-shifted by 50–130 meV due to the interaction between ZnO–C70 QDs in the solid state. The energy levels of C70 were also suitably aligned to those of ZnO QDs with a lower electron transfer barrier of 0.22 eV, which offers an advantageous route for electron transport. Consequently, the environmentally friendly ZnO–C70 QDs with extraordinary properties promise great potential for use as novel encapsulating materials in the field of opto-electronic applications adopting QDs.

Molybdenum disulfide (MoS2) has been extensively used as a hole transport layer in many inverted polymer solar cell devices. However, its potential as an electron transport layer in a solar cell device has rarely been reported. In this paper, we demonstrate an iPSC with enhanced photovoltaic performance by the introduction of a MoS2 nanosheet (NS) interlayer. Herein, MoS2 NS thin films were uniformly deposited on a polyethylenimine ethoxylated polymer by an electrostatic interaction. The MoS2 NS interlayer in the iPSC device plays important roles as a sub-photo sensitizer and an electron transport layer and provides effective charge separation for the enhancement of device performance. iPSCs with MoS2 NSs based on bulk heterojunction active materials such as P3HT:PC60BM, PTB7:PC71BM and PTB7-Th:PC71BM showed maximum power conversion efficiencies of 3.54%, 8.12%, and 9.08%, respectively, which were 27%, 11%, and 15% higher than those of the reference, respectively. Furthermore, the enhanced photovoltaic performance and electron transport mechanism of the iPSCs with the MoS2 NSs were confirmed experimentally using finite-difference-time-domain modeling and time-correlated single photon counting (TCSPC) measurements. The computational simulation results showed that the light absorption of the iPSCs with the MoS2 NS interlayer was slightly better than that of the iPSCs without the MoS2 NS interlayer. The electron decay time of PTB7:PC71BM with the MoS2 NS interlayer at a wavelength of 700 nm was reduced to 60 ps from 100 ps of PTB7:PC71BM without the MoS2 NS interlayer. The efficient light absorption and electron transfer characteristics of MoS2 NSs significantly improved the photovoltaic conversion performance of the iPSC devices.

The aggregation of zinc oxide nanoparticles leads to an increased absorbance in the ultraviolet-visible region by an induced light scattering effect. Herein, we demonstrate the inhibition of photoconversion activity in ZnO-graphene core-shell quantum dots (QD) (ZGQDs) agglomerated by 4-aminophenol (4-AP) used as a linker. The ZnO-graphene quantum dots (QD) aggregates (ZGAs) were synthesized using a facile solvothermal process. The ZGAs revealed an increased absorbance in the wavelengths between 350 and 750 nm as compared with the ZGQDs. Against expectation, the calculated average photoluminescence lifetime of ZGAs was 7.37 ns, which was 4.65 ns longer than that of ZGQDs and was mainly due to the high contribution of a slow (&tau, 2, &tau, 3) component by trapped carriers in the functional groups of graphene shells and 4-AP. The photoelectrochemical (PEC) cells and photodetectors (PDs) were fabricated to investigate the influence of ZGAs on the photoconversion activity. The photocurrent density of PEC cells with ZGAs was obtained as 0.04 mA/cm2 at 0.6 V, which was approximately 3.25 times lower than that of the ZGQDs. The rate constant value of the photodegradation value of rhodamine B was also decreased by around 1.4 times. Furthermore, the photoresponsivity of the PDs with ZGAs (1.54 &mu, A&middot, mW&minus, 1) was about 2.5 times as low as that of the PDs with ZGQDs (3.85 &mu, 1). Consequently, it suggests that the device performances could be degraded by the inhibition phenomenon of the photoconversion activity in the ZGAs due to an increase of trap sites.

We report on the in-situ chemical growth of unique core-shell quantum dots (QDs) with single layer graphene on the surface of CuO QDs and their structural, optical and electrical properties. The CuO/graphene QDs were synthesized through a simple and hydrothermal technique. In order to enhance performance electrochemical energy storages, we have developed core (active material)/shell (conductive material) type CuO/graphene QDs as electrode materials using the combined electrolytes (KOH + LiCl). As a result, the performance of electrochemical energy storages exhibits specific capacitance of 154 F g−1 at current density of 1 A g−1 and cycling stability with 84% capacitance retention after 3,000 cycles.

Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.

Transparent human hair-based textiles, which are founded on a natural resource, have been fabricated by an electrospinning technique. Transparent human hair-based textiles are very useful for transparent wearable electronics because they have unique optical properties in the visible light region such as transparency of over ∼85%. In order to apply wearable electronic devices with transparent textiles, we fabricated sandwich structures with transparent flexible light emitting diodes (LEDs) embedded in transparent nanofiber textile utilizing ZnO@graphene quantum dots (ZGQDs) and demonstrated the fabrication process and characterization of ZGQD LEDs with textiles. We believe that these results will inspire new methods in wearable electronics and raise the hope of achieving even higher efficiencies by means of development and control of transparent textile ordering.

Seawater desalination generates concentrated brine, which may pose a threat to marine ecosystems upon discharge into the ocean. This study was conducted to evaluate possibility possible novel approach for electrochemical post-treatment of seawater reverse osmosis (SWRO) discharge brine and reuse without further additional brine enrichment processes. A synthetic brine and real brine from a SWRO plant were electrolyzed under controlled conditions to obtain a mild alkaline solution using a diaphragm-type chlor-alkali cell. Under a 100 mA/cm2 current density and 37.5–45 min of hydraulic retention time (HRT), a maximum NaOH concentration of 3.3 wt% was obtained from real SWRO brine (initially 1.7–1.9 times the salinity of seawater) with 63% chloride removal via electrolysis. In electrolyzed brine reuse, a solid alkali-activated slag (AAS) product resulted from mixing 3.5 and 2.0 wt% NaOH alkali effluents (as an alkaline activator of slag) produced via electrolysis of synthetic brine and ground granulated blast furnace slag (GGBFS) from steelworks. For the specimens cured for 3–28 days, relatively high compressive strengths of 12.9–15.3 MPa and 9.8–11 MPa, respectively, were obtained.

Optoelectronic devices with dual-function consisting of LEDs and OBDs, both containing ZnO QDs dispersed in a hybrid poly N-vinylcarbazole (PVK) and polymethylmethacrylate (PMMA) polymer layer, were fabricated on indium-tin-oxide (ITO)-coated glass substrates using a simple spin-coating technique. Transmission electron microscopy images showed that the ZnO QDs were distributed around the PVK and the PMMA. The laminated devices showed the electroluminescence of LEDs and the electrical bistabilities of OBDs. To make the OBDs into the LEDs, a PEDOT:PSS hole injection layer and a PVK hole transport layer were inserted between the active layers and the electrodes, respectively. Luminescence mechanisms of the LEDs and operating mechanisms of the OBDs are described on the basis of the experimental results.

A new way to simultaneously grow carbon nanotubes (CNTs) and ultrathin graphite on copper (Cu) foils has been investigated. This one-step growth process yields three-dimensional networks of CNTs on graphitic layers (3D CNTs/G) on Cu foils. Their synthesis conditions and growth mechanism are discussed in detail taking their structural properties into account. Individual CNTs and the 3D CNTs/G networks by means of an in-situ conductive atomic force microscope inside a scanning electron microscope are electrically characterized. Time-resolved photoluminescence demonstrated fast charge transfer and high carrier collection efficiency superior to two-dimensional ultrathin graphite only. Their facile and tunable growth and excellent electrical properties show that the 3D CNTs/G are strongly attractive for various applications such as solar cells, sensors, supercapacitors, photovoltaics, power generation, and optoelectronics. ispartof: SCIENTIFIC REPORTS vol:9 issue:1 ispartof: location:England status: published

Electrospinning used to fabricate eco-friendly, transparent, human hair-based nanofibers (NFs) using natural resources such as keratin (which is found in hair, wool, feather, nails, and horns). These NF-based textiles are very useful in making transparent, wearable electronics, as they possess unique optical properties in the visible light regions, such as transparency exceeding 85%. The resulting environmentally friendly, hair-based NFs were investigated through various methods. In order to study transparent property of optically transparent NFs for applying transparent wearable devices, we fabricated transparent flexible consolidated sandwich structures embedded in NF textiles with polymer light-emitting diodes (PLEDs). The devices exhibit the fabrication process and characterization of consolidated textiles and PLEDs by using various color emission type of polymer. Also, we investigated a comparison between PLEDs without textiles and consolidated PLEDs with textile. When used white, red, and yellow polymer in this consolidated textile/LEDs/textile structures, the performances of device was obtained from a spectrally white, red, and yellow color light with a maximum luminance of 2781, 2430, and 6305 cd/m 2 at 13, 11, and 10 V, respectively. The LED characteristics of the consolidated PLEDs with textile maintained similar device efficiencies of PLEDs without textiles.

This work reports on the in-situ chemical synthesis and their properties of multilayer graphene (MLG) shells, made by unzipping single walled carbon nanotubes (SWCNTs), on the surface of Zinc oxide (ZnO) core nanoparticles (NPs). The stable oxygen bridge bonds between the ZnO core and the oxygen-related functional groups on the MLG shells facilitate the efficient photoinduced charge separation. This charge separation mechanism is confirmed experimentally using time-correlated single photon counting (TCSPC) measurements. The calculated average carrier lifetimes of the ZnO@MLG NPs are approximately 102 times faster than those for the bare ZnO NPs. The efficient electron transfer between the ZnO core and the MLG shell resulted in the significant improvement of the photocatalytic activity and the photoelectrochemical response. Simultaneously, the photocorrosion of ZnO was prevented by having the oxygen bridge bonds between the ZnO and MLG which suppressed the photo-generated holes oxidizing the surface oxygen atoms on ZnO, and in turn the holes are consumed by photocatalytic reaction. The 4.3 times enhanced photocurrent density at 0.2 V vs. Ag/AgCl (pH 6.9) and around 10 times higher rate constant value of photodegradation of rhodamine B were achieved by ZnO@MLG NPs in comparison with those of bare ZnO NPs.

Seawater desalination technology is important for solving water shortage problems. RO desalination is the most frequently used process for obtaining fresh water from salt water. Electrolysis is also one way of reusing the enriched brine. Alkali-activated products can be made by producing NaOH after electrolysis. There are three kinds of brine electrolysis methods including diaphragm, membrane, and mercury methods. This study was conducted using a 200 mL electrolysis diaphragm cell. Tedlar bags were used in order to gather gases such as Cl2, O2, and H2. The head was less than 10 mm when a diaphragm with a 10 μm pore size was used. The data in this study was collected to analyze the relationships between concentration, chloride removal, and current density (CD). Our results showed that pore size influenced the head at the anode. Chloride removal was not high even when a high CD was applied. When the CD was 200 mA/cm2, the maximum NaOH concentration was 1.85%. However, the NaOH concentration was just...

Recently, interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Among various efficient solutions, solution-processed metal-oxide films prepared from metal oxide sol–gel precursors (or nanoparticles) and polymer surface modifiers are typically used as electron selective interfaces in the inverted cell geometry. To present a more effective strategy for surpassing the limitations of traditional methods, such as an unintended increase in series or contact resistance by incompatibility at the organic/inorganic interface, inherently insulating nature of non-conjugated surface modifiers and oxygen adsorption (or photo-induced doping) of metal-oxide layer, we synthesize chemically surface-modified ZnO@graphene core–shell type quantum dots (ZGQDs) with well-characterization of the chemical, optical and electrical properties, and fabricate iPSCs consisting of ITO/PEIE/ZGQD-OAs/photoactive layer/MoO 3 /Ag. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer based on static quenching and charge transfer reaction from ZnO to graphene nanosheets (with drastically reduced τ avg (~ 60 ps)), which is verified by various analysis tools.

Hexagonal boron nitride (hBN) has drawn great attention for its versatile applications in electronics and photonics, and precise estimation of its thickness is critical in many situations. We propose a rapid and broad range (10–500 nm) in situ thickness estimation method for transparent hBN and SiO2 layers on the Si substrate using Raman peak intensity ratios at two wavenumbers and optical microscopy image analysis. We theoretically and experimentally demonstrate our method for a wide range of hBN layer thicknesses, and the estimated results show excellent agreement with the measured results with a percentile estimation error of 2.5%.

We demonstrate the ZnO@graphene core@shell quantum dot (ZGQDs) fabricated by selectively engineering of oxygenated functional groups on the graphene shells with eco-friendly keratin textile for transparent and flexible UV photodetector devices. The ZGQDs with the octylamine (ZGQDs-OA) and the graphene sheet were employed as an active material and an electron transport channel. The functional groups on the surrounding graphene shell in ZGQDs were passivated by the OA, resulting in a good absorbance in UV light and excellent carrier transport properties. The passivation of the functional groups on the graphene shell by OA drastically enhanced the photocurrent. Optical transmittance of the ZGQDs-OA/graphene sheets/PMMA/keratin nanofiber textile composites structures was approximately 77% at the visible spectrum range. Current–voltage (I-V) and current–time (I-t) measurements on the UV photodetector under illumination state in bending condition exhibited the excellent ON/OFF switching states and stability. The photosensitivity and responsivity of the photodetector with ZGQDs-OA were found to be around 13.10 and 68.64 μAmW−1, respectively, which is much higher than that without the passivation. The improved performance of the photodetector with ZGQDs-OA could be attributed to the efficient electron transport to the electrode by the passivation of the graphene on ZnO QDs.

We discuss subwavelength-scale semiconductor metal-optic resonators placed on the metal substrate with various top metal plate sizes. Albeit with large optical losses, addition of metal layers converts a leaky semiconductor nano-block into a highly-confined optical cavity. Optically pumped lasing action is observed with the extended top metal layer that can significantly suppress the radiation losses. Careful investigation of self-heating effects during the optical carrier injection process shows the importance of temperature-dependent material properties in the laser rate equation model and the overall laser performances.

Optofluidic manipulation mechanisms have been successfully applied to micro/nano-scale assembly and handling applications in biophysics, electronics, and photonics. Here, we extend the laser-based optofluidic microbubble manipulation technique to achieve hybrid integration of compound semiconductor microdisk lasers on the silicon photonic circuit platform. The microscale compound semiconductor block trapped on the microbubble surface can be precisely assembled on a desired position using photothermocapillary convective flows induced by focused laser beam illumination. Strong light absorption within the micro-scale compound semiconductor object allows real-time and on-demand microbubble generation. After the assembly process, we verify that electromagnetic radiation from the optically-pumped InGaAsP microdisk laser can be efficiently coupled to the single-mode silicon waveguide through vertical evanescent coupling. Our simple and accurate microbubble-based manipulation technique may provide a new pathway for realizing high precision fluidic assembly schemes for heterogeneously integrated photonic/electronic platforms as well as microelectromechanical systems.

The electrical properties of flexible nonvolatile organic bistable devices (OBDs) fabricated with graphene sandwiched between two insulating poly(methyl methacrylate) (PMMA) polymer layers were investigated. Current-voltage (I-V) measurements on the Al/PMMA/graphene/PMMA/indium-tin-oxide/poly(ethylene terephthalate) devices at 300 K showed a current bistability due to the existence of the graphene, indicative of charge storage in the graphene. The maximum ON/OFF ratio of the current bistability for the fabricated OBDs was as large as 1 x 10(7), and the endurance number of ON/OFF switchings was 1.5 x 10(5) cycles, and an ON/OFF ratio of 4.4 x 10(6) was maintained for retention times larger than 1 x 10(5) s. No interference effect was observed for the scaled-down OBDs containing a graphene layer. The memory characteristics of the OBDs maintained similar device efficiencies after bending and were stable during repetitive bendings of the OBDs. The mechanisms for these characteristics of the fabricated OBDs are described on the basis of the I-V results.

We present details of a 1×4 angled multimode interferometer (de)multiplexer, integrated with a microdisk laser as a demonstration of the way in which the compound semiconductor lasers can be coupled to silicon devices for a multitude of applications.

We discuss the rapid in situ hydrothermal synthesis of metal oxide materials based on the photothermal superheating of light-absorbing metal layers for simple and facile on-demand placement of semiconductor materials with micrometer-scale lateral resolution. Localized heating from pulsed and focused laser illumination enables ultrafast growth of metal oxide materials with high spatiotemporal precision in aqueous precursor solution. Among many possible electronic and optoelectronic applications, the proposed method can be used for laser-based in situ real-time soldering of separated metal structures and electrodes with functionalized semiconductor materials. Resistive electrical interconnections of metal strip lines as well as sensitive UV detection using photohydrothermally grown metal oxide bumps are experimentally demonstrated.

We report a photonic bandedge laser using subwavelength-scale pillars with a metal reflector plane bonded on the silicon substrate. Surface-emitting operation near the gamma point of the photonic band diagram is observed at 77 K.

We report a partially directional microdisk semiconductor laser with subwavelength-scale boundary perturbations for asymmetric backscattering of counterpropagating whispering gallery modes. Unlike the previous approaches based on optical bistability, the directionality and chirality of the laser modes can be fine-tuned and partially controlled by adjusting the dimension, shape, and relative positions of Rayleigh scatterers on the microdisk perimeter. The controlled directionality is investigated using numerical simulations and experiments for wavelength-scale microdisk resonators with an azimuthal mode number of 5.