Low dark current and improved detectivity of hybrid ultraviolet photodetector based on carbon-quantum-dots/zinc-oxide-nanorod composites

In this study, we fabricated an ultraviolet (UV) photodetector by blending a hybrid photoactive layer (HPL) that is composed of a hybrid structure containing Carbon Quantum Dots (CQDs) and Zinc Oxide Nanorods (ZnO NRs). To observe the effective photo-inducing abilities of CQDs and ZnO NRs, we analyzed the electrical properties of a UV photodetector using an HPL of CQDs/ZnO NRs. Under an illumination of 365 nm UV light with an intensity of 1 mW/cm², the UV photodetector exhibited a high detectivity of 8.33 × 10¹² Jones, which is higher than that of a UV photodetector using a HPL of blended poly-n-vinylcarbazole (PVK) and ZnO NRs. Experimental results show that an HPL of blended CQDs/ZnO NRs can induce efficient charge extraction from CQDs and ZnO NRs. In addition, CQDs act as charge controllers that enable hole-electron separation in the device upon UV illumination. These results indicate that synthesized CQDs can substitute for a charge transport polymer (i.e., PVK) and that a UV photodetector using CQDs can exhibit high detectivity.     

Ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag2CrO4 nanocomposites as visible-light-driven photocatalysts with excellent activity

This work reports ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag₂CrO₄ nanocomposites as excellent visible-light-driven photocatalysts. The ZnO/AgI/Ag₂CrO₄ nanocomposite with 20% of Ag₂CrO₄ has the superior activity in degradation of rhodamine B. Activity of this nanocomposite is nearly 167, 6.5, and 45-fold higher than those of the ZnO, ZnO/AgI, and ZnO/Ag₂CrO₄ samples, respectively. The ternary nanocomposite also showed enhanced activity relative to its counterparts for degradation of methylene blue and methyl orange as two dye pollutants under visible-light irradiation. The UV–vis DRS and PL spectra confirmed that the excellent photocatalytic activities are due to more visible-light absorption ability and efficiently separation of the charge carriers. Based on the effects of different scavengers, it was found that superoxide ions are the primary reactive species to cause the degradation reaction. Furthermore, the highly enhanced activity of the ternary nanocomposite was described using a proposed mechanism.     

Optical and thermal properties of precursor-controlled graphene–zinc nanocomposites

Graphene, a monolayer two dimensional carbon sheet can be utilized as a support to anchor functional nanomaterials to form novel nanocomposites for a variety of potential applications. We present an approach for the in situ preparation of graphene–zinc oxide nanocomposites through a reflux process in which either zinc acetate or zinc chloride can serve as precursors. The synthesized samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray analysis, ultraviolet–visible spectroscopy and thermogravimetry analysis (TGA–DSC) for structural, optical and thermal properties. It has been found that nanocomposites comprise of zinc oxide (ZnO) nanostructures deposited on graphene sheets, and the choice of zinc precursor has a deterministic influence on the morphology, structure and properties of the graphene–ZnO nanocomposites. In addition, the novel structure of zinc acetate based nanocomposite has induced improved absorption and thermal stability of the graphene/ZnO nanocomposite as compared to zinc chloride based nanocomposite and would be promising for future applications in nanotechnology.     

One-pot synthesis of ZnO/reduced graphene oxide nanocomposite for supercapacitor applications

ZnO/reduced graphene oxide (RGO) nanocomposite films were prepared by the sol–gel deposition method using a combination of zinc acetate and graphite. The solution derived composite films were extensively characterized using high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible spectroscopy, photoluminescence emission measurements, and four probe measurements. It was found that a highly transparent film with low resistivity could be obtained with the addition of a small amount of RGO into the deposition precursor. The results also showed that the sintering temperature reduces the resistivity and transparency of the films. XRD measurements revealed that films sintered >500 °C exhibit additional peaks, and suggest nucleation of different phases of the films. As a demonstration, the ZnO/RGO composite was integrated into a supercapacitor, and the resulting energy storage performance was tested.     

Nanoflower ZnO thin-film grown by hydrothermal technique based Schottky diode

This paper reports the realization of planar Schottky diodes based on nanorod ZnO thin film. The nanorod ZnO thin film was fabricated by hydrothermal technique on boron doped p-type Si (100) substrate. The Ag//ZnO/Al planar diode operating with voltage bias from –3 to 3 V. The I–V characteristics clearly indicate that the devices have rectifying performance. The thermionic emission theory governs the current across the studied Schottky diode. The device achieved a turn-on voltage of 0.9 V, barrier height 0.69 eV and saturation current of 1.2 × 10^–6 A. The diode shows a very large ideality factor (n > > 2) which is attributed to high interface trap concentration. The surface topology was investigated by scanning electron microscope (SEM). The structural properties of the nanostructured ZnO thin film were characterized by X-ray diffraction (XRD). The SEM images reveal that the ZnO nanorods grow perpendicular to the substrate with uniformity and high density. The XRD pattern illustrates the dominant peak appearing at (002). This intense peak indicates the c-axis orientated phase of the wurtzite ZnO structure. It demonstrates that the crystals grow uniformly perpendicular to the substrate surface in good agreement with the SEM images.     

ZnO/ZnFe2O4复合纳米粒子的制备及其特性研究

利用水热法制备了ZnO/ZnFe2O4纳米复合粒子。用扫描电子显微镜(SEM)、X射线衍射(XRD)、光致发光光谱(PL)对退火前后的ZnO/ZnFe2O4纳米粒子进行表征。研究结果表明, 退火后的ZnO/ZnFe2O4纳米复合粒子表现出更好的形貌和晶体质量, 主要由六角纤锌矿结构的ZnO和立方结构的ZnFe2O4构成。PL光谱显示, 退火后ZnO近带边的发光强度明显降低, 这是由于ZnO/ZnFe2O4形成了Ⅱ型能带结构实现了光生载流子分离的结果。对其光催化特性也进行了研究, 光照时间为3 h, 退火后的ZnO/ZnFe2O4纳米复合粒子表现出更优秀的光催化活性, 降解甲基橙的效率可达50.48%。另外, 还对其磁性进行了研究, 室温条件下, 纳米复合粒子表现为顺磁性, 而经过退火处理后表现出铁磁性。因此, ZnO/ZnFe2O4纳米复合粒子经退火后具备磁性光催化剂性能, 有一定的发展前景。     

Nano sized ZnO composites: Preparation,characterization and application as photocatalysts for degradation of AB92 azo dye

ZnO and Mordenite zeolite (MOR) nanoparticles were prepared by precipitation process using ultrasonic irradiation and hydrothermal method, respectively. Supported ZnO catalysts were prepared and the effect of different supports on the photocatalytic activity of ZnO nanoparticles was investigated. All prepared samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform-Infra Red Spectroscopy (FTIR), UV–vis spectroscopy (UV–vis) and BET surface area technique. The photocatalytic activity of the synthesized catalysts was elucidated using the photo-oxidation of Acid Blue 92 (AB92) as a hazardous pollutant under UV light. The effect of different parameters such as catalyst concentration, initial dye concentration, pH, UV irradiation and amount of ZnO loaded on the nanocomposites have been examined on the yield and the rate of photocatalytic degradation process. The photodegradation results of AB92 in aqueous medium under UV irradiation revealed that nanocomposite of ZnO and mordenite zeolite exhibit much higher photocatalytic activity than the other nanocomposites and pure ZnO. It was found that the type of support plays an important role in photocatalytic oxidation of AB92 and significantly improved the photocatalytic activity of ZnO. Chemical Oxygen Demand (COD) for dye solutions were examined at regular intervals and gave a good idea about mineralization of the dye.     

The effect of annealing temperature and the characteristics of p-n junction diodes based on sprayed polyaniline/ZnO thin films

Polyaniline,ZnO and polyaniline/ZnO nanocomposite thin films are coated on glass substrates using the spray pyrolysis technique.The samples are characterized by the XRD,SEM,EDAX,UV-Vis and I-V characteristics. The XRD analyses confirm that the spray-coated polyaniline and ZnO thin films have orthorhombic and hexagonal structures,respectively,and optical bandgap energy decreases from 3.81 to 3.41 eV with the addition of a Zn atom.SEM analysis of the polyaniline/ZnO nanocomposite thin films shows that there is an agglomeration of ZnO particles with uniform distribution in the polyaniline matrix,and the diode characteristics of the polyaniline /ZnO nanocomposite show weak rectification behavior.Parameters such as the ideality factor,reverse saturation current and barrier height are calculated from the I-V characteristics.     

Multithreshold Procedure for Evaluating Parameters of Meteorological Objects against the Background of Local Objects Clutter in Pulsed Doppler Weather Radars

A multithreshold procedure for estimating parameters of meteorological objects (MO) against the background of interferences from local objects in pulsed Doppler weather radars has been proposed. It is based on using the operation results of introduced detector of local objects for making a decision on estimating the parameters of meteorological objects before or after the nonadaptive MO suppression filter. The task of detection in this detector is solved by the threshold processing of correlation coefficients of reflections carrying the information on both the composition of analyzed mixture andMO parameters. This feature of the proposed detector compares favorably with a large variety of the known detectors. It is shown that the proposed detector makes it possible to take a correct decision about the composition of the mixture with probability D > 0.9 already at MO radial velocities V_r > 2 m/s. The possibility and expediency of practical use of the proposed procedure in the system of estimating the MO parameters under the real conditions of limited sample sizes of processed inputs were confirmed by mathematical experiment. In this case, the accuracy of estimates is shown to be more than twice as high as that of the known procedures.     

Synthesis and characterization of ZnS/ZnO/CdS nanocomposites

Water-soluble ZnS/ZnO/CdS (0.1–0.5 M) nanocomposites were successfully synthesized by the chemical precipitation method in air. X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis), photoluminescence (PL) and thermo gravimetric-differential thermal analysis (TG-DTA) were used to characterize the synthesized products. It is found that the ZnS/ZnO/CdS (0.1–0.5 M) core–shell nanocomposite is cubic and hexagonal mixed structure. TEM results showed the prepared nanocomposites are monodispersed and uniform in size. It is confined within 4.3–5.6 nm range. UV–vis absorption spectra were confined growth process of multi shells on ZnS. It showed a red shift with respect to the shells thickness. Fluorescence measurement showed the emission band which exists in the visible region. Stability and phase transition were identified by TG-DTA analysis. The results show an improved florescence property, indicating their potential applications in biological labeling.     

High Performance PbS Colloidal Quantum Dot Solar Cells by Employing Solution‐Processed CdS Thin Films from a Single‐Source Precursor as the Electron Transport Layer

CdS thin films are a promising electron transport layer in PbS colloidal quantum dot (CQD) photovoltaic devices. Some traditional deposition techniques, such as chemical bath deposition and RF (radio frequency) magnetron sputtering, have been employed to fabricate CdS films and CdS/PbS CQD heterojunction photovoltaic devices. However, their power conversion efficiencies (PCEs) are moderate compared with ZnO/PbS and TiO₂/PbS heterojunction CQD solar cells. Here, efficiencies have been improved substantially by employing solution‐processed CdS thin films from a single‐source precursor. The CdS film is deposited by a straightforward spin‐coating and annealing process, which is a simple, low‐cost, and high‐material‐usage fabrication process compared to chemical bath deposition and RF magnetron sputtering. The best CdS/PbS CQD heterojunction solar cell is fabricated using an optimized deposition and air‐annealing process achieved over 8% PCE, demonstrating the great potential of CdS thin films fabricated by the single‐source precursor for PbS CQDs solar cells.     

Passivating {100} Facets of PbS Colloidal Quantum Dots via Perovskite Bridges for Sensitive and Stable Infrared Photodiodes

Solution-processed PbS colloidal quantum dots (CQDs) are promising optoelectronic materials for next-generation infrared imagers due to their monolithic integratability with silicon readout circuit and tunable bandgap controlled by CQDs size. However, large-size PbS CQDs (diameter >4 nm) for longer shortwave-infrared photodetection consist mainly of {100} facets with incomplete surface passivation and unsatisfied stability. Here, it is reported that perovskite-bridged PbS CQDs, in which the {100} facets of the CQDs are epitaxially bridged with CsPbI_3–xBr_x perovskite, can achieve improved passivation and enhanced stability in comparison with the traditional strategies. The resultant infrared CQDs photodiodes exhibit significantly reduced dark current, nearly 50% enhanced photoresponse, and improved work stability. These superior properties synergistically produce the most balanced performance (with a high −3 dB bandwidth of 42 kHz and an impressive specific detectivity of 6.2 × 10¹² Jones) among the reported CQDs photodetectors.     

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

Synthesis and characterization of ZnO/CuO nanocomposite by electrochemical method

Electrochemical method has been utilized to synthesize zinc-copper nanocomposite using aqueous succinic acid as electrolyte solution. Both copper and zinc electrodes were used as anodes, kept on each side of cathode, which itself was made of zinc. Synthesized nanoparticles were characterized by scanning electron micrograph (SEM), point energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy, UV–visible diffuse reflectance spectroscopy (UV-DRS) and X-ray diffraction (XRD) analysis so as to determine its various physico-chemical characteristics. XRD analysis showed the incorporation of pure monoclinic copper oxide within hexagonal zinc oxide within ZnO/CuO which was further reaffirmed by point EDX analysis. EDX spectrum confirmed the presence of Cu, Zn and O elements in nanocomposite. SEM micrograph indicates that the obtained ZnO/CuO nanocomposite was in spherical morphology. Optical properties investigated by UV-DRS showed decrease in maximum reflectance (~22%) due to incorporation of CuO within ZnO nanoparticle. The electrochemical response of ZnO/CuO reveals higher electrochemical activity than pure ZnO, without any modification.     

Synthesis and characterization of zinc oxide/maghemite nanocomposites: Influence of heat treatment on photocatalytic degradation of 2,4-dichlorophenoxyacetic acid

In the current study, ultraviolet-active zinc oxide/maghemite (ZnO/γ-Fe₂O₃) nanocomposite catalysts were prepared and applied to the photodecomposition of 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D is a herbicide that is widely used in agriculture and landscape turf management. The ZnO/γ-Fe₂O₃ nanocomposite catalyst was prepared using a simple and efficient precipitation–thermal decomposition method. Comprehensive experimental studies and characterizations such as X-ray diffraction (XRD), TEM, Brunauer–Emmett–Teller (BET) and UV–vis diffuse reflectance spectrum (UV-DRS) analyses were conducted to optimize the photoactivity of the nanoparticles. Interestingly, the synthesized ZnO/γ-Fe₂O₃ nanocomposite catalyst exhibited a hexagonal phase with wurtzite structure, and their active surface area decreased with increasing calcination temperature. Based on the TEM micrographs, the appearance of the ZnO/γ-Fe₂O₃ nanocomposite catalyst is nearly spherically shaped with a mean particle size in the range of 13–35 nm. The nano-ZnO/γ-Fe₂O₃ that underwent heat treatment at 450 °C exhibited better photodecomposition of 2,4-D, which was primarily due to the highest specific surface area and the smallest particle size among the synthesized samples.     

Lowering Internal Friction of 0D–1D–2D Ternary Nanocomposite‐Based Strain Sensor by Fullerene to Boost the Sensing Performance

The development of strain sensors with both large strain range (>50%) and high gauge factor (>100) is a grand challenge. High sensitivity requires material to perform considerable structural deformation under tiny strain, whereas high stretchability demands structural connection or morphological integrity for materials upon large deformation, yet both features are hard to be achieved in one thin film. A new 0D–1D–2D ternary nanocomposite–based strain sensor is developed that possesses high sensitivity in broad working strain range (gauge factor 2392.9 at 62%), low hysteresis, good linearity, and long‐term durability. The skin‐mountable strain sensor, fabricated through one‐step screen‐printing process, is made of 1D silver nanowire offering high electrical conductivity, 2D graphene oxide offering brittle layered structure, and 0D fullerene offering lubricity. The fullerene constitutes a critical component that lowers the friction between graphene oxide–based layers and facilitates the sliding between adjacent layers without hurting the brittle nature of the nanocomposite film. When stretching, layer slippage induced by fullerene can accommodate partial applied stress and boost the strain, while cracks originating and propagating in the brittle nanocomposite film ensure large resistance change over the whole working strain range. Such high comprehensive performance renders the strain sensor applicable to full‐spectrum human motion detection.     

Graphene Doping Improved Device Performance of ZnMgO/PbS Colloidal Quantum Dot Photovoltaics

Lead sulfide (PbS) colloidal quantum dots (CQDs) solar cells possess the advantages of absorption into the infrared, solution processing, and multiple exciton generation, making them very competitive as a low‐cost photovoltaic alternative. Employing an n‐i‐p ZnO/tetrabutylammonium (TBAI)–PbS/ethanedithiol (EDT)–PbS device configuration, the present study reports a 9.0% photovoltaic device through ZnMgO electrode engineering and graphene doping. Sol–gel‐derived Zn_0.9Mg_0.1O buffer layer shows better transparency and higher conduction band maximum than ZnO, and incorporation of graphene and chlorinated graphene oxide into the TBAI–PbS and EDT–PbS layer respectively boosts carrier collection, leading to device with significantly enhanced open circuit voltage and short‐circuit current density. It is believed that incorporation of graphene into PbS CQD film as proposed here, and more generally nanosheets of other materials, would potentially open a simple and powerful avenue to overcome the carrier transport bottleneck of CQD optoelectronic device, thus pushing device performance to a new level.     

Low‐Field Magnetoresistance in La0.67Sr0.33MnO3:ZnO Composite Film

A nanocomposite film of La_0.67Sr_0.33MnO₃ (LSMO):ZnO is synthesized by depositing LSMO solution on a vertical array of ZnO nanorods grown on (0001) Al₂O₃ substrate. The magnetic behavior of the composite film differs from that of a pure LSMO film, possibly due to smaller grain size in the composite, small amount of Zn doping, or the presence of nonmagnetic ZnO phase near the LSMO grain boundaries. Magnetotransport measurements show that the low‐field magnetoresistance (LFMR) of the nanocomposite film is significantly enhanced as compared to that observed for pure LSMO film. The highest value of the LFMR of the nanocomposite film at 10 K is –23.9% with a magnetic field of 0.5 T applied parallel to the current.     

Improvement in open circuit voltage of n‐ZnO/p‐Si solar cell by using amorphous‐ZnO at the interface

Several research groups are currently working on n‐ZnO/p‐Si heterojunction solar cell, and recently, Pietruszka et al [Sol. Energ. Mat. Sol. Cells 147 (2016) 164‐170] has reported the highest efficiency of 7.1% for this structure. The main challenge is to enhance the open circuit voltage up to theoretically predicted value of >0.6 V. This paper reports >20% improvement in open circuit voltage of n‐ZnO/p‐Si solar cell by depositing amorphous‐ZnO at the interface at room temperature that possibly improves the passivation and/or avoids oxide formation at the interface during ZnO deposition. Two other materials, aluminum nitride and amorphous‐Si, have also been used as buffer layers to evaluate their effect on suppression of interface states. Furthermore, additional advantage of ZnO as an antireflector has been experimentally verified for different thicknesses of ZnO film.     

Zinc Oxide Nanostructures and High Electron Mobility Nanocomposite Thin Film Transistors

This paper reports on the synthesis of zinc oxide (ZnO) nanostructures and examines the performance of nanocomposite thin-film transistors (TFTs) fabricated using ZnO dispersed in both n- and p-type polymer host matrices. The ZnO nanostructures considered here comprise nanowires and tetrapods and were synthesized using vapor phase deposition techniques involving the carbothermal reduction of solid-phase zinc-containing compounds. Measurement results of nanocomposite TFTs based on dispersion of ZnO nanorods in an n-type organic semiconductor ([6, 6]-phenyl-$hbox{C}_{61}$-butyric acid methyl ester) show electron field-effect mobilities in the range 0.3–0.6 $hbox{cm}^{2} hbox{V}^{-1}hbox{s}^{-1}$, representing an approximate enhancement by as much as a factor of 40 from the pristine state. The on/off current ratio of the nanocomposite TFTs approach $hbox{10}^{6}$ at saturation with off-currents on the order of 10 pA. The results presented here, although preliminary, show a highly promising enhancement for realization of high-performance solution-processable n-type organic TFTs.