ZnO Nanorod Arrays Research Articles

The impact of green synthesized seed layer on ZnO nanorod arrays grown by chemical bath deposition

The impact of green synthesized seed layer on ZnO nanorod arrays grown by chemical bath deposition

An effective approach for hydrothermal synthesis of ZnO nanorod arrays activated under UV/Vis light: Different supporting ligands for hydrothermal precursor solutions

In this study, an effective approach is proposed for the controlled production of ZnO nanorod arrays that can be used in degradation of wastewater pollutants. Hydrothermal precursor solutions prepared using HMTA-different supporting ligands having different lengths and ends, which have not been tried before, allowed to control the type, size, and alignment of ZnO nanorods. Their physical properties were investigated by using X-ray diffraction patterns, Raman, FTIR and photoluminescence spectroscopies, UV/Vis Spectrophotometer, atomic force microscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. Photoactivity tests were performed using methylene blue under UV/visible light and the reusability of ZnO nanorod arrays with the best properties was checked. The approach of using different supporting ligands led to different effects on the physical and photocatalytic properties. ZnO nanorod arrays gained the ZnO films, which became photoactive with UV light, the ability to benefit from visible light as well. Especially ZnO-HMTA-HMDA nanorod arrays will shed light on researchers as an effective strategy for the development of new functional nanomaterials having high photodegradation efficiency and fast kinetic.

Fabrication and optimization of ZnO NR sensors in-situ grown on ITO substrates by a solution method

ZnO nanorod (NR) arrays in-situ grown on indium tin oxide (ITO) substrates by a solution method are investigated by optimizing the solution concentration and the thickness of ZnO seed layer. Using 5–1000 ppm ethanol as the target gas, the gas sensor prepared with as-grown ZnO NR arrays in 25 mM solution with ∼ 10-nm thick ZnO seed layer is found to have the best gas response at 250 °C and exhibit a pretty good stability. The morphology of ZnO NR arrays is found important for optimizing the gas sensing property and is predominated by coalescence, which varies with solution concentration and the thickness of ZnO seed layer, thus leading to a variation in the defect density and surface state of ZnO NRs and enabling the gas sensing property not to be determined only by the specific surface area of ZnO NRs. Different thick ZnO seed layers will convert into the low-resistance states within a few seconds to minutes after applying an electric voltage and thus the role of ZnO seed layers in determining the gas sensing performance is mainly to control the diameter distribution of ZnO NRs, in which the arrays with a relatively large difference in the diameter of ZnO NRs would exhibit good gas response.

Study of the Sensor Properties of Ordered ZnO Nanorod Arrays for the Detection of UV Radiation

Zinc oxide is one of the most promising materials used to create devices in the ultraviolet (UV) range. In this article, we study the sensor properties of ordered ZnO nanorod arrays grown by chemical vapor deposition. The possibility of their use as an indicator of UV radiation to control the dose of UV radiation, both from natural and artificial light sources, is assessed. The X-ray diffraction, Raman spectroscopy (RS), and cathodoluminescence (CL) data demonstrate the high quality of nanorods. Based on the ZnO nanorod array, a sensor prototype was fabricated based on the change in ZnO conductivity under the UV irradiation. A compari-son of the response of such a sensor with the readings of a UV radiometer showed a high correlation.

High-performance ultraviolet photodetector based on Sn-doped CuO@ZnO nanorod arrays composites

The Sn-doped CuO nanosheets were synthesized on the surface of ZnO nanorods arrays by a two-step method. The as-prepared samples were investigated by X-ray diffraction (XRD), electron microscopy techniques (SEM and EDS), X-ray photoelectron spectroscopy (XPS), UV–Vis spectroscopy, and evaluation of photoelectric performances. With the increase of [Sn4+]/[Cu2+] concentration ratio, the size and number of CuO nanosheets coated on the surface of ZnO nanorods become smaller, and the surface of ZnO nanorods become more and more rough. When the [Sn4+]/[Cu2+] concentration ratio is 2%, the dark current, photocurrent and photoelectric sensitivity of the prepared Sn-doped CuO@ZnO nanorod arrays composites photoelectric devices are 0.038 µA, 141.52 µA and 3724.2, respectively. In this sense, probing the Sn modified CuO@ZnO nanorod arrays composites can elucidate some useful keys for the development of high photoelectric properties.

Difunctional molecularly imprinted polymers and heterostructured CdS nanoparticle-sensitized ZnO nanorod arrays for antibody-free photoelectrochemical alpha-fetoprotein sensor

An antibody-free molecularly imprinted photoelectrochemical sensor was developed for alpha-fetoprotein (AFP) detection by means of difunctional polydopamine-based molecular imprinting polymers (PDA-MIP) on CdS nanoparticle-decorated ZnO nanorod arrays (CdS@ZnO NAs). Among them, the heterostructured CdS@ZnO NAs could accelerate the spatial separation of electron-hole pairs; while PDA-MIP not only provided abundant target recognition sites without expensive antibody, but also further increase the systemic photocurrent due to the enhanced light absorption capacity. After removing template molecules from PDA-MIP, the resulting imprinted cavities could be occupied by target AFP, leading to a decreased photocurrent. Moreover, the prepared sensor had a wide linearity in the range from 1 pg mL−1 to 1000 ng mL−1 with a low detection limit of 0.38 pg mL−1, as well as excellent selectivity and good stability. The application of AFP analysis in real human serum was also achieved, and the recoveries ranged from 99.2% to 105.2%.

Ultrasensitive self-powered photoelectrochemical sensing for enrofloxacin detection by coupling piezoelectric effect with nonmetallic surface plasmon resonance based on ZnO nanorod arrays/WO3-x

Exploring efficient strategy for high-efficiency photoelectric conversion is quite important to design sensitive self-powered photoelectrochemical (PEC) sensing platform. This work designed a high performance self-powered PEC sensing platform by the integration of piezoelectric effect with localized surface plasmon resonance (LSPR) effect based on ZnO-WO3-x heterostructures. Due to the fluid eddy induced piezoelectric effect by magnetic stirring, the piezoelectric semiconductor ZnO nanorod arrays (ZnO NRs) can facilitate the transfer of electrons and holes by generating piezoelectric potentials under external forces, thereby contributing to the performance of self-powered PEC platforms. Such working mechanism of the piezoelectric effect was studied by using the COMSOL software. Moreover, the introduction of defect engineered WO3 (WO3-x) can further broaden the light absorption and promote the charge transfer owing to the nonmetallic surface plasmon resonance effect. Remarkably, due to the synergizing piezoelectric and plasmonic effect, the photocurrent and maximum power output of ZnO-WO3-x heterostructures were enhanced by 3.3-fold and 5.5-fold than that of bare ZnO, respectively. After the immobilization of the enrofloxacin (ENR) aptamer, the self-powered sensor demonstrated an excellent linearity (1 × 10−14 M to 1 × 10−9 M) with a low detection limit of 1.8 × 10−15 M (S/N = 3). This work undoubtedly holds great promise to provide the innovative inspiration for the formation of high-performance self-powered sensing platform, which opens up a new horizon of potential in food safety and environmental monitoring.

Gas sensing property of ZnO NR arrays stabilized by high-temperature annealing and the mechanism of detecting reduce gases

Due to the high sensitivity and lithographic compatibility, gas sensors prepared with ZnO nanorod (NR) arrays in-situ grown on substrates receive much attention. In this work, ZnO NR arrays are grown on ITO glass by a solution method and the thermal stability is studied. It is found that the instability of as-grown sample can be associated with the metastable defects formed during the growth of ZnO NR arrays and the variation of surface states during the measurement. After high-temperature annealing, the thermal stability of ZnO NR arrays are improved, while the best working temperature is shifted to ∼350 °C. By studying the effects of annealing temperature on the thermal stability, the lowest annealing temperature is suggested to be 400 °C for stabilizing ZnO NR arrays. After annealing at 400 °C in air, the ZnO NR arrays exhibit sufficiently good reproducibility with the gas response of ∼45. Based on the dependences of electric currents on working temperature and O2 partial pressure, chemisorbed O− is suggested to play a predominant role in detecting reducing gases for the ZnO NR arrays and the best working temperature is probably in association with the conversion from irreversible to reversible chemisorption of O−.

Some Properties of Semiconductor-Ferroelectric Structures

This paper presents the properties of semiconductor-ferroelectric structures consisting of ZnO nanorods grown at low temperatures by the hydrothermal method on LiNbO3 and LiNbO3:Fe substrates. The resulting structures were analyzed by scanning electron microscope, photoluminescence, and spectrophotometry. SEM images and spectra, absorption spectra, and photoluminescence spectra in the ultraviolet and visible ranges are presented. The studies have shown the possibility of using, along with others, the hydrothermal method for synthesizing Zn(NO3)26H2O and C6H12N4 to obtain arrays of ZnO nanorods as a sensitive element of surfactant-based UV radiation sensors.

Enhanced Performance of CsPbIBr2 Perovskite Solar Cell by Modified Zinc Oxide Nanorods Array with [6,6]-Phenyl C61 Butyric Acid.

Although Metal oxide ZnO is widely used as electron transport layers in all-inorganic PSCs due to high electron mobility, high transmittance, and simple preparation processing, the surface defects of ZnO suppress the quality of perovskite film and inhibit the solar cells' performance. In this work, [6,6]-Phenyl C61 butyric acid (PCBA) modified zinc oxide nanorods (ZnO NRs) is employed as electron transport layer in perovskite solar cells. The resulting perovskite film coated on the zinc oxide nanorods has better crystallinity and uniformity, facilitating charge carrier transportation, reducing recombination losses, and ultimately improving the cells' performance. The perovskite solar cell with the device configuration of ITO/ZnO nanorods/PCBA/CsPbIBr2 /Spiro-OMeTAD/Au delivers a high short circuit current density of 11.83 mA cm-2 and power conversion efficiency of 12.05 %.

Developed interfacial charge transport in super-dimensional CuO branched ZnO nanorods array (CuO B ZnO NRsA)

Hierarchical CuO nanobranches have been synthesized through reactive etching of Cu thin film (50–200 nm in thickness) on hydrothermally processed ZnO nanorods array (ZnO NRsA), which in turn fabricated multi-interfacial CuO- ZnO heterostructure. The structural, morphological, elemental content and optical properties of CuO branched ZnO NRs array (CuO – B ZnO NRsA) heterostructures have been investigated by X-ray diffractometry (XRD), field emission- scanning electron microscope/ energy dispersive X-ray spectroscopy (FE-SEM /EDX) and UV–Vis- near IR optical absorption spectroscopy, respectively.Chemical etching modifies the surface morphology and manipulates one-dimensional hyperstructures. The CuO – B ZnO NRsA heterostructures improve/expand the optical absorption to visible region in comparison to the bare ZnO NRsA. The charge transferring in CuO – B ZnO NRsA hetero-interface has been engineered, by controlling the thickness of Cu thin film which tuned the electrical conductance and photocatalytic performance. The interfacial electric field can rapidly separate and drift the photoinduced charge carriers, which induces the highest photodegradation efficiency for the reduction of RhB. The electronic transport and the photocatalytic performance can be tuned by length of CuO branches.

Enhancement of electrochemical detection performance towards 2,4,6-trinitrotoluene by a bottom layer of ZnO nanorod arrays

The ZnO nanostructure layers have been widely investigated as electrodes for sensors due to their intrinsic advantages such as high active area and low cost. In this work, to enhance the detection properties of ZnO nanostructural electrodes, self-organized ZnO nanorod arrays were synthesized using the chemical bath deposition (CBD) method on FTO glasses and ZnO nanoparticles. The fabricated ZnO electrodes on the two different substrates were characterized by SEM, TEM, XRD, and XPS. Subsequently, the detection performance of ZnO nanorod electrodes was electrochemically measured in a 2,4,6-trinitrotoluene (2,4,6-TNT) solution by CV and EIS. The differences in current densities between the ZnO electrodes were determined by the width of the ZnO nanorods, resulting in a ∼45% higher detection efficiency with F-CBD (the ZnO nanorods on FTO) electrodes compared to S-CBD (the ZnO nanorods on ZnO nanoparticles) electrodes.

Influence of metal covering with a Schottky or ohmic contact on the emission properties of ZnO nanorod arrays

Influence of metal covering with a Schottky or ohmic contact on the emission properties of ZnO nanorod arrays

Enhanced Spectral Response of ZnO-Nanorod-Array-Based Ultraviolet Photodetectors by Alloying Non-Isovalent Cu-O with CuAlO2 P-Type Layer.

CuAlO2 was synthesized by a hydrothermal method, in which the Cu-O dimers were incorporated by simply altering the ratio of the reactants and the temperature. The incorporation process increases the grain size in CuAlO2, and modulates the work function and binding energies for CuAlO2 due to the partial substitution of Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying non-isovalent Cu-O with a CuAlO2 host. Based on the ZnO nanorod arrays (NRs) ultraviolet photodetector, CuAlO2/Cu-O fabricated by the low-cost drop-coating method was used as the p-type hole transport layer. The incorporation of the Cu-O clusters into CuAlO2 lattice to enhance the conductivity of CuAlO2 is an effective way for improving ZnO NRs/CuAlO2 device performance. The photodetectors exhibit significant diode behavior, with a rectification ratio approaching 30 at ±1 V, and a dark saturation current density 0.81 mA cm-2. The responsivity of the ZnO-NRs-based UV photodetector increases from 13.2 to 91.3 mA/W at 0 V bias, with an increase in the detectivity from 2.35 × 1010 to 1.71 × 1011 Jones. Furthermore, the ZnO NRs/[CuAlO2/Cu-O] photodetector exhibits a maximum responsivity of 5002 mA/W at 1.5 V bias under 375 nm UV illumination.

Nanopatterned rGO/ZnO:Al seed layer for vertical growth of single ZnO nanorods

In this work, we demonstrate a novel low-cost template-assisted route to synthesize vertical ZnO nanorod arrays on Si (100). The nanorods were grown on a patterned double seed layer comprised of reduced graphene oxide (rGO) and Al-doped ZnO nanoparticles. The seed layer was fabricated by spray-coating the substrate with graphene and then dip-coating it into a Al-doped ZnO sol–gel solution. The growth template was fabricated from a double-layer resist, spin-coated on top of the rGO/ZnO:Al seed layer, and patterned by colloidal lithography. The results show a successful chemical bath deposition of vertically aligned ZnO nanorods with controllable diameter and density in the nanoholes in the patterned resist mask. Our novel method can presumably be used to fabricate electronic devices on virtually any smooth substrate with a thermal budget of 1 min at 300 °C with the seed layer acting as a conductive strain-relieving back contact. The top contact can simply be made by depositing a suitable transparent conductive oxide or metal, depending on the specific application.

Formation of large-scale MoS2/Cu2O/ZnO heterostructure arrays by in situ photodeposition and application for ppb-level NO2 gas sensing

Photodeposition has been used extensively for nanomaterial growth on a substrate, but direct photodeposition of 2D transition metal dichalcogenides (TMDs) remains challenging. An alternative approach is to deposit 2D TMDs on a suitable nanomaterial template. In this work, large-scale MoS2/Cu2O/ZnO heterostructure arrays are formed by low-temperature in situ photodeposition and the nanocomposites are used for chemiresistive gas sensing at room temperature. Using 254 nm UV irradiation, Cu2O nanoclusters are photodeposited in solution on hydrothermally grown ZnO nanorod arrays and Cu2O/ZnO heterostructure arrays are first formed. MoS2 nanoparticles are subsequently photodeposited on Cu2O and MoS2/Cu2O/ZnO heterostructure arrays with good uniformity on a sub-millimeter scale are consequently produced. The ternary nanocomposite with a 45 min MoS2 photodeposition time shows the highest response of 890% toward 500 ppb NO2 under UV-activated sensing. An excellent linear sensitivity of 18.7 ppm–1 has been achieved and the estimated lowest detection limit is 1.3 ppb, exhibiting good potential for monitoring of environmental NO2 content. The outstanding performance is attributed to the combined chemical and electronic sensitization effects of the abundant heterojunctions in the nanocomposite. The present work reveals that facile in situ photodeposition is suitable for synthesis of large-scale MoS2/Cu2O/ZnO heterostructure arrays with remarkable gas sensing performance.

Fabrication of Vertically Aligned ZnO Nanorods Modified with Dense Silver Nanoparticles as Effective SERS Substrates

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted increasing attention due to its high spectral reproducibility and unique selectivity to target molecules. Here, a facile approach is proposed to prepare Ag nanoparticles modified ZnO nanorod arrays (Ag/ZnO NR arrays). Ag nanoparticles were densely decorated on the surface of ZnO nanorods through silver mirror reaction and subsequent seed-assisted electrodeposition. The prepared Ag/ZnO NR arrays can be used as a sensitive, uniform, and repeatable SERS substrate for the rapid detection of organic dye molecules and biomolecules with concentrations higher than the corresponding limits of detection (LODs). The LODs for rhodamine 6G (R6G), 4-aminothiophenol (PATP) and adenine are calculated to be 1.0 × 10−13 M, 1.6 × 10−12 M and 3 × 10−11 M, respectively. The enhancement factor (EF) of the SERS substrate is estimated to be as high as ~2.7 × 108 when detecting 10−10 M R6G. Particularly, the as-synthesized substrate exhibits high selectivity to multiple components. In addition, the fabricated Ag/ZnO NR arrays can be recycled due to their superior self-cleaning ability and can realize photocatalytic degradation of R6G in water within 1 h driven by UV light, showing that the three-dimensional recyclable SERS substrates have wide applications in environmental pollution monitoring and biomedical analysis.

UV-durable superhydrophobic ZnO/SiO2 nanorod arrays on an aluminum substrate using catalyst-free chemical vapor deposition and their corrosion performance

Dense ZnO nanorod arrays were obtained directly on Al substrate for the first time using catalyst-free chemical vapor deposition. The influence of temperature on the surface topography of ZnO nanostructures was analyzed. Then the ZnO nanorod arrays surface was coated with SiO2 films via pulsed laser deposition. After modifying with stearic acid, the Al/ZnO/SiO2 nanorod arrays showed superhydrophobic properties with a water contact angle of up to 157.9°. Notably, these Al/ZnO/SiO2 nanorod arrays exhibited UV resistance, and the water contact angle remained almost constant under UV light exposure for a long time. The electrochemical measurements showed that ZnO/SiO2 nanorod arrays had an excellent protective effect on metal Al. These results provided a basis for a feasible method for the corrosion protection of metals.

Self-powered dual-wavelength polarization-sensitive photodetectors based on ZnO/BiFeO3 heterojunction

The ferroelectric-photovoltaic (FE-PV) devices have received growing attention for the FE polarization-induced internal electric field to facilitate the separation and transport of the photogenerated electron-hole (e-h) pairs in the FE semiconductors. However, the low photocurrent output of the FE-PV devices is still a key challenge for the application and development of these devices. Here, ZnO/BiFeO3 (BFO) heterojunction photodetectors (PDs) are designed to utilize the built-in electric field at the heterojunction interface of ZnO nanoparticles (NPs)/BFO and the spontaneous FE polarization field of BFO to promote the separation and transport of the photogenerated carriers. ZnO nanorod arrays (NRs) grown on ZnO NPs provide a directional transport channel for the photogenerated electrons. ZnO/BFO heterojunction devices demonstrate a self-powered photoresponse in the ultraviolet (UV) and visible (vis) dual-wavelength. The devices show a responsivity of 1.32 mA/W, response time (τrise/τdecay) of 12.6/44.9 ms at 420 nm light illumination. In addition, the polarization imaging function of ZnO/BFO PDs is explored by extending the polarization photocurrent mapping values of a single PD unit to a complex array of optical information image processing utilizing the polarization-sensitive properties of BFO without external bias.

The Application of Combined Visible and Ultraviolet Irradiation to Improve the Functional Characteristics of Gas Sensors Based on ZnO/SnO2 and ZnO/Au Nanorods

Arrays of zinc oxide (ZnO) nanorods were synthesized over quartz substrates by the hydrothermal method. These nanorods were grown in a predominantly vertical orientation with lengths of 500–800 nm and an average cross-sectional size of 40–80 nm. Gold, with average sizes of 9 ± 1 nm and 4 ± 0.5 nm, and tin nanoclusters, with average sizes of 30 ± 5 nm and 15 ± 3 nm, were formed on top of the ZnO nanorods. Annealing was carried out at 300 °C for 2 h to form ZnO/SnO2 and ZnO/Au nanorods. The resulting nanorod-arrayed films were comprehensively studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). To fabricate resistive sensor elements, the films were supplied with V/Ni contact metallization on top of the nanorods. The gas sensor performance of the prepared films was evaluated at various temperatures in order to select 200 °C as the optimum one which enabled a selective detection of NO2. Adding UV-viz irradiation via a light-emitting diode, λ = 400 nm, allowed us to reduce the working temperature to 50 °C and to advance the detection limit of NO2 to 0.5 ppm. The minimum response time of the samples was 92 s, which is 9 times faster than in studies without exposure to UV-viz radiation.