ZnO Arrays Research Articles

Low cost inorganic white light emitting diode based on submicron ZnO rod arrays and electrodeposited Cu2O thin film

We present here the fabrication and characterization of low cost inorganic white light emitting diode (LED) based on submicron ZnO rod arrays and Cu2O thin film. Firstly, n-ZnO rod arrays were grown on FTO substrate by hydrothermal method at 150 °C. Then, p-Cu2O thin film was electrodeposited on top of ZnO arrays from alkaline cupric lactate solution at 60 °C. X-ray diffraction and scanning electron microscopy were employed to investigate the structural and the morphology of the prepared samples as well as the diode device. The results indicate the formation of hexagonal structure of ZnO arrays and cubic structure of polycrystalline Cu2O thin film. The performance of LED device was investigated employing I-V and electroluminescence measurements. The heterojunction device showed good rectification behavior and a broad emission covering visible spectrum for all applied voltage which indicates the white electroluminescence of the heterostructure device. Therefore, the inorganic ZnO arrays/Cu2O thin film is a promising heterojuniction for low cost and large-scale production of white LED.

Effect of Different Excitation Wavelengths on Luminescent Properties of ZnO/Anodic Alumina Membrane (AAM) Arrays

ZnO/AAM (anodic alumina membrane) arrays were prepared by an electrodeposition method and X-ray diffraction (XRD) patterns show that the characteristic diffraction peaks of ZnO appear, such as the lattice planes of (100), (002), and (102), moreover, the diffraction peaks of Al2O3 are dominated. Scanning electron microscopy (SEM) images show that the average sizes of the ZnO particles are about 100 nm corresponding to the channel diameters of AAM, and the ZnO arrays are composed of those close particles linked together. The photoluminescence emission spectra express that the as-prepared ZnO arrays can give out relatively pure ultraviolet light (395 nm) from the excitons.

Nanostructured ZnO Arrays Fabricated via Pulsed Electrodeposition and Coated with Ag Nanoparticles for Ultraviolet Photosensors

Nanostructured ZnO Arrays Fabricated via Pulsed Electrodeposition and Coated with Ag Nanoparticles for Ultraviolet Photosensors

Tuneable fluorescence enhancement of nanostructured ZnO arrays with controlled morphology.

Zinc oxide (ZnO) nanorods (NRs) have been demonstrated as a promising platform for enhanced fluorescence-based sensing. It is, however, desirable to achieve a tuneable fluorescence enhancement with these platforms so that the fluorescence output can be adjusted based on the real need. Here we show that the fluorescence enhancement can be tuned by changing the diameter of the ZnO nanorods, simply controlled by potassium chloride (KCl) concentration during synthesis, using arrays of previously developed aligned NRs (a.k.a. aligned NR forests) and nanoflowers (NFs). Combining the experimental results obtained from ZnO nanostructures with controlled morphology and computer-aided verification, we show that the fluorescence enhancement factor increases when ZnO NRs become thicker. The fluorescence enhancement factor of NF arrays is shown to have a much stronger dependency on the rod diameter than that of aligned NR arrays. We prove that the morphology of nanostructures, which can be controlled, can be an important factor for fluorescence enhancement. Our (i) effort towards understanding the structure-property relationships of ZnO nanostructured arrays and (ii) demonstration on tuneable fluorescence enhancement by nanostructure engineering can provide some guidance towards the rational design of future fluorescence amplification platforms potentially for bio-sensing.

Synthesis of WO3@ZnWO4@ZnO-ZnO hierarchical nanocactus arrays for efficient photoelectrochemical water splitting

Hierarchical heterostructures with large surface areas and multiple interfaces as photoanode materials, are holding great promise for photoelectrochemical (PEC) water splitting toward efficient solar energy utilization. In this work, the cactus-like WO3@ZnWO4@ZnO-ZnO (i.e. W@WZ@Z-Z) arrays compromising the first-order W@WZ@Z core-shell nanosheets and the second-order ZnO nanosheets, have been fabricated by combining atomic layer deposition (ALD) technique and hydrothermal process. The modification of ZnO nanosheets on the surface of WO3 and the simultaneous formation of ZnWO4 in-between buffer layer have endowed the photoanode a drastic enhancement in both ultraviolet light absorption and charge separation via the favorable band alignment at the WO3-ZnWO4-ZnO interfaces. Particularly, the W@WZ@Z-Z nanocactus (NC) array photoanode with a 30nm ZnO layer on WO3 precisely controlled by ALD, exhibited around 3.8 times higher photocurrent density (~ 1.57mA/cm2) at 1.23V vs. RHE than pristine WO3 photoanode (~ 0.41mA/cm2), with little loss after long-term continuous illumination as well. Overall, the novel combination of WO3 with ZnO and the ZnWO4 buffer layer, and construction of hierarchical heterostructures, along with the resulted improvement in light absorption and charge separation which have been confirmed by spectroscopic characterizations and finite-difference time-domain simulation, suggest many exciting opportunities for further development of high-performance PEC devices for solar energy conversion.

One step to fabricate vertical submicron ZnO rod arrays by hydrothermal method without seed layer for optoelectronic devices

Reducing production cost by minimizing growth steps of ZnO microstructures is an important key for large scale fabrication of optoelectronic devices. Here, we present the growth of submicron ZnO arrays on FTO substrates by only one step without seed layers using hydrothermal method. The effect of KOH mass concentration on the physical properties of ZnO submicron rods has been investigated employing Uv–vis spectroscopy, X-ray diffraction, and scanning electron microscopy. The results indicate the formation of hexagonal structure of ZnO submicron arrays with different surface morphology, different orientations and diameters dependent on KOH concentration. Uniform ZnO submicron rod arrays with (002) preferred orientation were obtained when the KOH concentration was 0.24g/ml. Beside the uniformity and good alignment of ZnO arrays along the c-axis of FTO substrate, they have the smallest diameter which make them suitable to photo-electronic applications.

Structure and properties of nanostructured ZnO arrays and ZnO/Ag nanocomposites fabricated by pulsed electrodeposition

We investigate the structure, surface morphology, and optical properties of nanostructured ZnO arrays fabricated by pulsed electrodeposition, Ag nanoparticles precipitated from colloidal solutions, and a ZnO/Ag nanocomposite based on them. The electronic and electrical parameters of the ZnO arrays and ZnO/Ag nanocomposites are analyzed by studying the I–V and C–V characteristics. Optimal modes for fabricating the ZnO/Ag heterostructures with the high stability and sensitivity to ultraviolet radiation as promising materials for use in photodetectors, gas sensors, and photocatalysts are determined.

Chlorophyll-a/ZnO Nanorod Based Hybrid Photoanodes for Enhanced Photoelectrochemical Splitting of Water

We report synthesis and use of Chlorophyll‐a/ZnO nanorod based hybrid photoanodes for photoelectrohemical (PEC) activity. Hybrid photoanodes consist of vertically oriented self ordered nanorod array of ZnO fabricated via electrodeposition followed by sensitization with chlorophyll‐a. Under AM 1.5 illumination (100 W/cm2), at 0.75 V bias, the hybrid photoanodes achieved a photocurrent density of 0.67 mA/cm2 which is ∼2.6 times increase over bare ZnO nanorods (0.26 mA/cm2). To the best of our knowledge, this is the first report on the use of Chlorophyll‐a/ZnO nanorod based hybrid electrodes in photoelectrochemical cells, with potential applications in switching and sensing.

A carbon-quantum-dot-sensitized ZnO:Ga/ZnO multijunction composite photoanode for photoelectrochemical water splitting under visible light irradiation

A carbon quantum dot (CQD)-sensitized ZnO:Ga/ZnO composite photoanode for photoelectrochemical water splitting has been designed and tested. In the composite, a ZnO array is grown on a piece of indium tin oxide glass and facilitates the essential integrity of the photoanode. An overlayer of Ga–doped ZnO (ZnO:Ga) is then hydrothermally grown on the ZnO nanorods. A type I ZnO:Ga/ZnO junction forms with a ZnO:Ga shell possessing visible light activity and a narrow bandgap. However, a highly positive onset potential exists due to the location of the conduction band (CB) of ZnO:Ga at the high end. The deposition of the CQDs on the surface of the overlayer provides a negatively shifted CB with a type II junction between ZnO:Ga and CQDs. The CQDs@ZnO:Ga/ZnO multijunction composite photoanode exhibits a negative shift of the onset potential and a significantly increased photocurrent density, up to 1.5mAcm−2 at 1.6V vs. RHE, with good photostability under AM 1.5 G simulated light. The multijunction composite photoanode also achieves a current density of 0.16mAcm−2 under visible light at a bias of 1.0V, which is comparable to that of ZnO under AM 1.5 G simulated light. Electrochemical impedance spectra reveal that the CQD modification acts to decrease the interfacial charge transfer resistance associated with eliminating the energy barrier in the type I ZnO:Ga/ZnO junction that causes charge transfer resistance.

图形化氧化锌阵列的制备及其场发射性能研究

图形化氧化锌阵列的制备及其场发射性能研究

Influence of the ZnO nanoarchitecture on the electrochemical performances of binder-free anodes for Li storage

Zinc oxide nanoarchitectures may be employed as binder-free, high specific capacity anodes for lithium batteries. By means of simple and low-impact wet chemistry approaches, we synthesized 1D (nanorods), 2D (single- and multi-layered nanosheets), and 3D (nanobrushes) ZnO arrays. These nanoarchitectures were compared as far as concerns their electrochemical properties and the structural modifications upon lithiation/delithiation. The best results were offered by 2D nanosheets, which showed reversible capacity of the order of 400mAhg−1 after 100 cycles at 1Ag−1. This was due to: i) small nanoparticles, with average diameter of about 10nm, which maximize the array specific surface area and favor the formation of the LiZn alloy; ii) the presence of a mesoporous texture, which allows larger space for accommodating the volume changes upon lithiation/delithiation. However, also these 2D structures showed large irreversible capacity losses. Our work highlights the need for more efficient buffering solutions in ZnO binder-free nanostructured anodes.

Fabrication of a Stainless‐Steel‐Mesh‐Supported Hierarchical Fe2O3@NiCo2O4 Core‐Shell Tubular Array Anode for Lithium‐Ion Battery

AbstractCore‐shell architectures with hollow micro‐structures have exhibited many potential applications in electrochemical energy storage fields. In this study, hierarchical Fe2O3@NiCo2O4 core‐shell tubular arrays have been synthesized by a multistep chemical bath deposition method. The obtained samples have been fully characterized using powder X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The results show that NiCo2O4 nanosheets have been uniformly coated on the Fe2O3 tubular array obtained by ZnO array template. When tested as an anode for lithium ion battery, the Fe2O3@NiCo2O4 tubular arrays have been found to exhibit an improved specific capacity of 587 mAh g−1 at a current density of 1000 mA g−1, good rate capability and cycling stability.

Controlled Defects of Fluorine-incorporated ZnO Nanorods for Photovoltaic Enhancement.

Anion passivation effect on metal-oxide nano-architecture offers a highly controllable platform for improving charge selectivity and extraction, with direct relevance to their implementation in hybrid solar cells. In current work, we demonstrated the incorporation of fluorine (F) as an anion dopant to address the defect-rich nature of ZnO nanorods (ZNR) and improve the feasibility of its role as electron acceptor. The detailed morphology evolution and defect engineering on ZNR were studied as a function of F-doping concentration (x). Specifically, the rod-shaped arrays of ZnO were transformed into taper-shaped arrays at high x. A hypsochromic shift was observed in optical energy band gap due to the Burstein-Moss effect. A substantial suppression on intrinsic defects in ZnO lattice directly epitomized the novel role of fluorine as an oxygen defect quencher. The results show that 10-FZNR/P3HT device exhibited two-fold higher power conversion efficiency than the pristine ZNR/P3HT device, primarily due to the reduced Schottky defects and charge transfer barrier. Essentially, the reported findings yielded insights on the functions of fluorine on (i) surface –OH passivation, (ii) oxygen vacancies (Vo) occupation and (iii) lattice oxygen substitution, thereby enhancing the photo-physical processes, carrier mobility and concentration of FZNR based device.

Solar active Ag/ZnO nanostructured arrays obtained by a combination of electrochemical and chemical methods

The work is devoted to the creation and research of solar active Ag/ZnO nanostructured arrays obtained by a combination of electrochemical and chemical methods. In order to enhance a solar activity of the electrodeposited in a pulsed mode nanostructured zinc oxide arrays and Ag/ZnO nanocomposites thereon we analyzed morphology, structure, electrical, electronic and optical properties of the electroplated 1-D ZnO as well as Ag nanoparticles, deposited from silver sol and Ag/ZnO nanocomposites formed by applying Ag nanoparticles to the ZnO surface. The investigated electrical and electronic parameters of ZnO and Ag/ZnO, which we obtained from their current–voltage and capacitance–voltage characteristics, are the electrical resistivity ρ, the height φ of the Schottky barriers in the electron depletion regions, the concentration of the fully ionized donor impurity Nd, the density NSS of surface states and the width of the electron depletion region ω. The improved UV sensitivity of the electrodeposited in the pulsed mode 1-D ZnO and enhanced solar activity of Ag/ZnO were valued by dark and light current–voltage characteristics and through their temporal response curves under the influence of UV and visible sunlight. Analysis of electronic and electrical parameters, response and recovery performance of the obtained 1-D ZnO arrays and Ag/ZnO nanocomposites thereon let us to select the optimum manufacturing conditions for the creation of solar active plasmonic Ag/ZnO nanostructured arrays with high photosensitivity, fast response and reset times, and reproducible characteristics. So, our studies have allowed the development of a new solar active Ag/ZnO material for photocatalytic oxidation–reduction processes that can be used as photoelectrode for photocatalytic degradation of organic contaminations or for green hydrogen production by water splitting.

A conductive ZnO:Ga/ZnO core-shell nanorod photoanode for photoelectrochemical water splitting

We report a ZnO:Ga/ZnO isostructural nanojunction photoanode with core-shell structure for photoelectrochemical water splitting. Ga-doped zinc oxide (ZnO:Ga) shell is grown in situ on the vertically aligned ZnO array core in a hydrothermal process. The as-prepared ZnO:Ga/ZnO composite with nearly the same lattice structure in the two phases exhibits enhanced light absorption and improved electrical conductivity. The photocurrent density of the composite achieves 0.6 mA cm−2 under AM 1.5G simulated light irradiation with an applied bias of 1.23 vs. Ag/AgCl, which is three times higher than that of the anode made of pristine ZnO array. Under visible light (λ > 420 nm) irradiation, the current density reaches 0.06 mA cm−2 at the same condition. Moreover, the ZnO:Ga/ZnO composite shows better photostability than ZnO both in neutral and alkaline electrolyte. The isostructural nanojunction with excellent lattice match is thus demonstrated to be a promising material as the photoanode in water splitting.

Near-field-assisted localization: effect of size and filling factor of randomly distributed zinc oxide nanoneedles on multiple scattering and localization of light

We investigate the influence of the diameter and the filling factor of randomly arranged ZnO nanoneedles on the multiple scattering and localization of light in disordered dielectrics. Coherent, ultra-broadband second-harmonic (SH) microscopy is used to probe the spatial localization of light in representative nm-sized ZnO arrays of needles. We observe strong fluctuations of the SH intensity inside different ZnO needle geometries. Comparison of the SH intensity distributions with predictions based on a one-parameter scaling model indicate that SH fluctuations can be taken as a quantitative measure for the degree of localization. Interestingly, the strongest localization signatures are found for densely packed arrays of thin needles with diameters in the range of only 30 nm range, despite the small scattering cross section of these needles. FDTD simulations indicate that in this case coupling of electric near-fields between neighbouring needles governs the localization.

Organic/inorganic nanocomposites of ZnO/CuO/chitosan with improved properties

To extend the visible light response of ZnO, ZnO/CuO heterostructured nanocomposite was synthesized by a hydrothermal approach. At the same time, chitosan (Ch) is considered as a very promising natural polymer. It holds not only abundant resource and low cost, but also has excellent adsorption properties to a broad range of organic pollutants and some heavy metal ions. To improve the adsorption properties of ZnO/CuO nanocomposite, ZnO/CuO/chitosan organic-inorganic composites were prepared with precipitation method. The as-prepared nanocomposites were characterized by TEM (Transmission electron microscopy), SAED pattern (Selected Area Electron Diffraction), SEM (scanning electron microscopy), UV–Vis (Ultraviolet–visible spectroscopy), PL (Photoluminescence), XRD (X-ray diffraction), TGA (Thermo Gravimetric Analyzer), Fourier transform infrared spectroscopy spectra (FTIR) et al. To examine the surface and interface properties of nanocomposites, chemical prototype sensor arrays were constructed based on ZnO, ZnO/CuO, ZnO/Cu2O, ZnO/CuO/chitosan, ZnO/Cu2O/chitosan nanocomposites and QCM (quartz crystal microbalance) arrays devices. The adsorption response behaviors of the sensor arrays to some typical volatile compounds were examined under similar conditions. The results indicated that with comparison to ZnO nanostructure, the ZnO/CuO nanocomposite exhibited enhanced adsorption properties to some typical volatile compounds greatly, and the adsorption properties of ZnO/CuO/chitosan are much better than that of ZnO/CuO nanocomposite. The adsorption of ZnO/CuO system is super to that of ZnO/Cu2O. Therefore, ZnO/CuO/chitosan nanocomposite not only showed broadening visible light response, but also possessed of excellent adsorption properties, and has good potential applications in photocatalysts, chemical sensors, biosensors, self-cleaning coating fields et al.

Effect of ZnO Layers on Transport and Relaxation of Charge in Porous Silicon–Silicon Structures

Zinc oxide nanostructures have been grown by electrochemical deposition on porous silicon-silicon substrate. The effect of electrolyte temperature on the morphology of grown ZnO arrays was observed. Temperature dependencies of the electrical conductivity for the structures based on porous silicon were investigated in 80-325 K range. The results are analyzed within the model of disordered semiconductors and the activation energy of charge transport is determined. It is shown that ZnO layers cause the decrease of the electrical conductivity activation energy in 140-250 К temperature range. Electric conductivity was also shown to be dependent on the morphology of ZnO arrays. Based on the spectra of thermally stimulated depolarization current, the localized electron states in the experimental samples are found. The trap levels are distributed quasi-continuously on the activation energy and exist in the ranges of 0.2-0.3, 0.4-0.45, 0.5-0.55 and 0.6-0.65 eV. ZnO nanocrystals grown on porous silicon substrates modify density of states in different energy ranges.

Multistep Controllability Synthesis and Growth Mechanism of ZnO Nanopagoda for Schottky Diode Device

Ordered ZnO arrays with a peculiar nanostructure were synthesized by a multistep synthesis process. The first step was the preparation of ZnO seed to induce the formation of ZnO array via potentiostatic electrodeposition method using a typical three electrode set-up. The second step was fabricating ZnO array along seed by Chemical Bath Deposition. Structural analysis of ZnO was carried out with X-ray diffraction (XRD), which showed a hexagonal wurtzite structure, and the selected area electron diffraction (SAED) patterns indicated that nanocrystalline is a part of monocrystal. The scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to study the microstructure, and showed a pagoda-like microstructure with a tiny top and large bottom, which had an average top diameter of exceeding 800[Formula: see text]nm at seed-depositing time of 60[Formula: see text]s, and then growth mechanisms are subsequently given a further explanation, viewed from kinetics and thermodynamics. In addition, the current–voltage curves of schottky diode devices with ZnO nanopagoda arrays revealed that ZnO films arrays along grown ZnO seed had a higher reverse saturation current than ZnO films grown without seed, which are [Formula: see text] A and [Formula: see text] A, respectively. The minimum turn-on voltage of the diode with ZnO seed deposited 60[Formula: see text]s is 0.18[Formula: see text]V, without seed is 0.52[Formula: see text]V.

Silver-doped zinc oxide single nanowire multifunctional nanosensor with a significant enhancement in response

Enhanced performances were obtained for nanosensors based on a single nanowire of silver-doped zinc oxide (ZnO:Ag). Arrays of crystalline ZnO:Ag nanowires were synthesized by electrodeposition on F-doped tin oxide coated substrates and studied by SEM, EDX, TEM, HRTEM, SIMS, XPS, PL and micro-Raman spectroscopy. Integration of a single nanowire or a single microwire on the chip was performed by employing metal maskless nanodeposition in the dual beam focused electron/ion beam instrument. The ultraviolet (UV) response and hydrogen (H2) gas response were studied for nanodevices and microdevices based on a single ZnO:Ag nanowire. We found that ZnO:Ag nanowire based nanosensor possesses a much faster response/recovery time and a higher response to UV radiation and hydrogen gas (∼50%) than those reported in literature. An increase in current value of about two orders in magnitude IUVON/IUVOFF was observed under exposure to UV light. Faster response/recovery times of about 0.98s/0.87s were observed. The ZnO:Ag nanowires and microwires can serve as nano-building materials for ultrasensitive and ultra-fast sensors with reduced power consumption. The mechanisms for such improved responses to UV and H2 were discussed. The developed nanomaterial is of great scientific interest for further studies as promising candidates for fabricating multifunctional nano-sensors, LEDs and photodetectors by bottom-up and hybrid nanotechnologies.