Vertically-aligned ZnO Nanorods Research Articles

Surface-engineered vertically-aligned ZnO nanorod for sensitive non-enzymatic electrochemical monitoring of cholesterol

Developing highly sensitive and selective non-enzymatic electrochemical biosensors for disease biomarker detection has become challenging in healthcare applications. However, advances in material science are opening new avenues for creating more dependable biosensing technologies. In this context, the present work introduces a novel approach by engineering a hybrid structure of zinc oxide nanorod (ZnO NR) modified with iron oxide nanoparticle (Fe2O3 NP) on an FTO electrode. This Fe2O3 NP-ZnO NR hybrid material functions as a nanozyme, facilitating the catalysis of cholesterol and enabling the direct transfer of electrons to the fluorine-doped tin oxide (FTO) electrode, limiting the need for costly and traditional enzymes in the detection process. This innovative non-enzymatic cholesterol biosensor showcases remarkable sensitivity, registering at 642.8 μA/mMcm2 within a linear response range of up to 9.0 mM. It also exhibits a low detection limit (LOD) of ∼12.4 μM, ensuring its capability to detect minimal concentrations of cholesterol accurately. Moreover, the developed biosensor displays exceptional selectivity by effectively distinguishing cholesterol molecules from other interfering biological species, while exhibiting outstanding stability and reproducibility. Our findings indicate that the Fe2O3 NP-ZnO NR hybrid nanostructure on the FTO electrode holds promise for enhancing biosensor stability. Furthermore, the present device fabrication platform offers versatility, as it can be adapted with various enzymes or modified with different metal oxides, potentially broadening its applicability in a wide range of biomarkers detection.

Effects of Reaction Parameters on the Geometry and Crystallinity of Hydrothermally Synthesized ZnO Nanorods for Bio-Fouling Applications

In this present work, we have successfully synthesized vertical aligned ZnO nanorod arrays (ZnO NRs) on conductive stainless-steel substrate. These ZnO NRs were obtained by using a low temperature, low cost, and eco-friendly hydrothermal approach. The effect of the sol-gel deposited ZnO seed layer on the vertical alignment ZnO NRs has been thoroughly studied. Characterizations of the seed layer and the as-obtained nanorods were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), and water contact angles (WCA) measurement. SEM analysis shows that these nanorods were grown with a high uniformity and density over the entire substrate. TEM and XRD studies confirmed the hexagonal wurtzite structure of ZnO nanorods. Finally, field immersion tests using the optimized samples were conducted in a coastal sea environment to study biofouling settlement. To the best of our knowledge, there are few articles that investigate the influence of the seed layer deposited on stainless steel on the formation of vertically aligned nanorods for antifouling applications. The novelty of this work is manifested by optimizing the ZnO seed layer to obtain either thick or fine ZnO nanorods (NRs). Moreover, another novelty of this study is the use of the hydrothermal deposition of ZnO NRs on stainless steel for biofouling to replace paints in marine applications.

Preparation of CZTS thin films for the fabrication of ZnO nanorods based superstrate solar cells

Intensive studies have recently been performed to produce low-cost, environmentally friendly and high-efficiency cells. Some of these studies are associated with the incorporation of one-dimensional nanostructures into thin film based solar cell architecture. The aim of this work was therefore to build one of these structures by incorporating ZnO nanorod into the conventional Cu2ZnSnS4 (CZTS) thin film system. To achieve this, conformally CdS-coated vertically-aligned ZnO nanorods (NRs) were first successfully synthesized on ITO-coated substrates by using the hydrothermal technique. ZnO NRs were then decorated with 600 nm thick CZTS thin layer by a one-step thermal evaporation route to produce a SLG/ITO/ZnO-NR/CdS/CZTS/Ag superstrate solar cell architecture. The findings revealed the formation of Cu-poor mono-phase kesterite CZTS thin film with an optical band gap of 1.45 eV. The performance of the fabricated solar cell was measured both in the dark and under irradiation of (AM) 1.5 G at room temperature. The superstrate solar cell had a short-circuit current density of ~20.80 mA/cm2, an open-circuit voltage of ~0.46 V, a fill factor of ~29.5%, providing ~2.82% of the energy conversion efficiency.

Controllable synthesis of ZnO nanorods at different temperatures for enhancement of dye-sensitized solar cell performance

Vertically-aligned ZnO nanorods were grown on fluorine-doped tin oxide (FTO) substrates at different bath temperatures. This method has been effectively applied to fabricate efficient nanorod based photo-anodes for dye-sensitized solar cells (DSSCs). Photovoltaic performance of the cell was found to be enhanced on the bath temperature used to synthesize nanorods. Crystallinity and morphology of the prepared ZnO nanorod has been studied using X-ray diffraction pattern (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectrometer (EDS), Transmission Electron Microscopy (TEM), UV–Visible spectroscopy and Current–Voltage (J–V) measurements. The effect of bath temperature on the photovoltaic performance was investigated under one-sun illumination. The photo-energy conversion efficiency (PCEs) shows that DSSCs prepared at lower bath temperature shows better performance than those prepared at higher bath temperature.

Flexible Microsensor Made of Boron-Doped Graphene Quantum Dots/ZnO Nanorod for Voltammetric Sensing of Hydroquinone

The micro size and mechanical properties of carbon fiber make it an ideal electrode material, but the low surface area of carbon fiber promotes a poor electrochemical response. The combination of graphene quantum dots and metal oxide may modulate their chemical and electrochemical properties, resulting in synergistic signal amplification effect. In this study, a new robust nano-hybrid microelectrode was designed by modifying carbon fiber with boron-doped graphene quantum dots/ZnO nanorod for the electrocatalytic analysis of hydroquinone (HQ). Remarkably, high specific surface area of vertically-aligned ZnO nanorod promoted loading of high-density boron-doped graphene quantum dots. Electrochemical results showed that these modifications promoted a larger active surface area and electron transfer of the carbon fiber microelectrode, as well as enhancement of the electrocatalytic activity toward HQ. Under optimal conditions, the linear response range of the proposed microelectrode to HQ was 0.1 to 100 μM, and the limit of detection was 0.03 μM. The proposed microelectrodes show good repeatability, reproducibility and electrode stability. Furthermore, the proposed microelectrode was successfully applied to environmental water samples analysis of HQ, providing a new method for the efficient detection of HQ.

Highly enhanced ultraviolet to visible room temperature photoluminescence emission ratio in Al implanted ZnO nanorods

We present here a comprehensive study on the effect of Al ion implantation on the room temperature (RT) photoluminescence (PL) emission properties of aqueous chemically grown vertically-aligned ZnO nanorods (NRs) implanted with 100 keV Al ions of various doses varying from 1 × 1013 ions/cm2 to 1 × 1016 ions/cm2 followed by annealing at 450 °C in an inert ambient. As compared to the pristine sample, an unprecedented enhancement (1.4 times) in the ratio of the intensities of the near band edge, INBE (ultraviolet) to the defect level, IDL (visible) emissions has been observed for the ZnO NRs implanted with a 5 × 1013 ions/cm2 dose of Al ions. Though the ratio INBE/IDL is decreased with an increase in the Al dose beyond 5 × 1013 ions/cm2, it is still higher than the pristine sample up to a Al dose of 1 × 1015 ions/cm2. Finally, a 0.87 times drop in the ratio is observed for the highest dose (1 × 1016 ions/cm2) Al implanted sample. Detailed analyses of the RT PL results show that excitons bound to neutral Al donor for lower and non-radiative surface defects related recombination centers for higher doses are responsible respectively for highly enhanced and reduced PL emissions in Al implanted ZnO NRs.

UV enhanced white-light response based on p-Si/n-ZnO nanorod heterojunction photosensor

Two-regime photosensor has been fabricated from p-n junction between p-Si and n-ZnO nanorods. The junction is obtained by simply grown vertically-aligned ZnO nanorods on silicon substrate via hydrothermal method. As expected, the device response to visible and UV spectrum due to the band gap of silicon and ZnO, respectively. However, it is found that photoresponse to visible light can be enhanced under UV activation. Detailed mechanism behind the phenomena is proposed along with the photoluminescence results of defect states in ZnO nanorods. The trapped electrons from UV stimulation could be excited to conduction band by white light and contributed to the increase of the photocurrent of the device under white-light irradiation. This low-temperature solution growth ZnO nanorod-based UV–vis photosensor also presents reproducible results and fast recovery time.

Charge transport on vertically aligned ZnO nanorods with different aspect ratios

Zinc Oxide is a semiconductor widely used in sensitized solar cells as an electron transport layer. Among the different nanostructures obtainable for this material, the vertically-aligned ZnO nanorods are of great interest for the design of photoanodes; mainly due to the directionality of charge transport. Vertically-aligned ZnO nanorods of different aspect ratios were prepared via hydrothermal synthesis. UV–Vis absorption was used to determine the dependence of the optical band gap energy on the nanorod diameter according to the Burstein-Moss shift theory due to the presence of surface states. Information about the electronic properties of the different nanorods was obtained by spectroelectrochemical measurements used to monitor the absorbance decrease and Egap shift at different potentials. Time of flight photocurrent transients indicated a dependence on charge transport time with ZnO nanorod length. All evidences point to a large distribution of trap states located in the semiconductor band gap.

Zero bias UV detection and precursor effect on properties of ZnO nanorods grown by hydrothermal method on SiO2/p-Si substrate

Here we present the effect of the precursor chemistry on the properties of ZnO nanorods prepared by using the hydrothermal method. The nanorods were grown over RF-sputtered 50 nm ZnO seed layers on integrated circuits compatible highly lattice mismatched SiO2/p-Si substrates. Two zinc sources namely zinc acetate and zinc nitrate were dissolved in solvent (a solution of deionized water and hexamethylenetetramine) in parallel to grow the highly conducting, vertically-aligned ZnO nanorods. Surface morphology and crystal structure of NRs were investigated using scanning electron microscope and X-ray diffraction. Nanorods synthesized in zinc acetate precursor's solution were highly crystalline and sparsely packed with well defined hexagonal top surface compared to nanorods grown in zinc nitrate precursors. Elemental composition of nanorods was studied using X-ray photoelectron spectroscopy. The oxygen and zinc observed in all the nanorods, zinc acetate synthesized nanorods show high atomic percentage of these two elements. To test the electrical and photo detection properties of the ZnO nanorods a metal semiconductor metal (MSM) structure was fabricated by depositing Ti/Au ohmic contacts over the nanorods. The MSM structure fabricated over the nanorods synthesized by using zinc nitrate precursor shows zero bias UV detection not reported up to present. The conducting properties of the nanorods were obtained from the current-voltage characteristics measurements of the MSM photosensor, and it is observed that the zinc acetate synthesized NRs were highly conducting. The UV detection capability of the MSM photosensor were tested by exposing UV light from light emitting diodes of same power and different wavelength. The ZnO NRs grown in zinc nitrate precursor shows high photosensitivity.

GROWTH TIME DEPENDENCE ON PHOTOELECTROCHEMICAL PROPERTY OF ZINC OXIDE NANORODS PREPARED BY HYDROTHERMAL SYNTHESIS

Here, the dependence of growth time on the growth behavior, morphology and photoelectrochemical (PEC) properties of ZnOnanorods (ZnO-NRs) as a photoanode are demonstrated. Vertical-aligned ZnO-NRs with [Formula: see text]-axis perpendicular to substrate were accomplished via seed-assisted hydrothermal technique at the growth time varying between 0.5 and 24[Formula: see text]h. Growth behaviors of ZnO-NRs can be described into three regimes, which consist of the nucleation stage, ZnO-NRs growth and saturation growth, respectively. ZnO nanoparticles (NPs) corresponding to the nucleation site occur at the growth time below 1[Formula: see text]h. Afterward, the growth regime of ZnO-NRs, which originated from the competition between the vertical and the lateral growth, is clearly observed, and leads to increase in length and diameter. The whole growth of ZnO-NRs is terminated after 16[Formula: see text]h, attributed to low amount of Zn[Formula: see text] and OH− supplied from growth solution. PEC measurement reveals the fast solar response and high photostability of ZnO-NRs. Additionally, the photoconversion efficiency ([Formula: see text] improves with the growth time of 4[Formula: see text]h and degrades for longer time due to the change of total surface area. The maximum [Formula: see text] of 0.13% at 0.63[Formula: see text][Formula: see text] is obtained for the growth time of 4[Formula: see text]h. Our results highlight that the growth time plays a crucial role in controlling growth behavior and the total surface area directly related with the PEC properties of ZnO-NRs.

Influence of growth temperature and duration on different properties of ultra-long ZnO nanorods grown by modified chemical bath deposition method

In this work, ultra-long ZnO nanorods (NRs) were grown on ZnO buffered Si substrates by using direct heat substrate-modified chemical bath deposition (DHS-MCBD) method. Initially, the growth temperature was varied in the range 140 °C to 250 °C while keeping the time fixed at 4h. In the second stage, the growth temperature was kept fixed at 220 °C and the time was changed from 4h to 8 h. The morphological, structural and optical properties of ZnO NRs at different growth temperatures were investigated by using field emission scanning electron microscope (FESEM), x-ray diffraction (XRD) and photoluminescence (PL) spectroscopy techniques. The surface morphology results revealed the formation of hexagonal-shaped, ultra-long and vertically-aligned ZnO NRs. The average length of the NRs was increased from 5.7 μm to 24.5 μm by increasing the growth temperature from 140 °C to 250 °C. The XRD results specified the formation of c-axis oriented diffraction peak corresponding to hexagonal ZnO NRs in all the samples. The intensity of this peak was increased by increasing the growth temperature up to 220 °C, however, on further increasing the temperature to 250 °C, the c-axis peak intensity was decreased. The PL analysis indicated higher UV to deep level emission intensity ratio (IUV/IDLE) of the NRs grown at 220 °C as compared to the others. Similarly, by changing the growth time from 4h to 8h, the length of ZnO NRs was also increased. The results obtained were correlated and the chemical reactions for ZnO NRs growth were discussed in this paper.

Electrophoretic deposition of single-source precursors as a general approach for the formation of hybrid nanorod array heterostructures

HypothesisSubjecting colloids to electric fields often results in (electrophoretic) deposition on conductive substrates. Dispersing a single-source precursor (SSP) of choice in an appropriate solvent, should allow its deposition on different substrates. The SSP-solvent interaction might play a role in the deposition (e.g., direction, rate, coverage). After thermal decomposition, the SSPs convert to the designed material, thus allowing formation of thin films or hybrid nanostructures. ExperimentsElectrophoretic deposition (EPD) was applied on two representative SSPs in different solvents. These SSPs were deposited onto substrates covered with vertically-aligned ZnO nanorod (NR) arrays. After thermal decomposition, hybrid nanostructures were obtained and their morphology and interfaces were characterized by electron microscopy, X-ray diffraction, UV–vis, and electrochemistry. FindingsTuning the organic dispersant-SSP interaction allows control over the final film morphology, which can result in coating and filling of NRs with metal-sulfides or metal-oxides after thermal decomposition of the SSP. These findings introduce a new facile method for a fast and large-scale uniform deposition of different (nanostructured) thin film semiconductors on a variety of substrates. We discuss the influence of the dispersant medium on the deposition of metallo-organic SSPs. As an example, the formed ZnO–CdS interface supports charge transfer upon illumination.

Passivating ZnO Surface States by C60 Pyrrolidine Tris-Acid for Hybrid Solar Cells Based on Poly(3-hexylthiophene)/ZnO Nanorod Arrays.

Construction of ordered electron acceptors is a feasible way to solve the issue of phase separation in polymer solar cells by using vertically-aligned ZnO nanorod arrays (NRAs). However, the inert charge transfer between conducting polymer and ZnO limits the performance enhancement of this type of hybrid solar cells. In this work, a fullerene derivative named C60 pyrrolidine tris-acid is used to modify the interface of ZnO/poly(3-hexylthiophene) (P3HT). Results indicate that the C60 modification passivates the surface defects of ZnO and improves its intrinsic fluorescence. The quenching efficiency of P3HT photoluminescence is enhanced upon C60 functionalization, suggesting a more efficient charge transfer occurs across the modified P3HT/ZnO interface. Furthermore, the fullerene modified hybrid solar cell based on P3HT/ZnO NRAs displays substantially-enhanced performance as compared to the unmodified one and the devices with other modifiers, which is contributed to retarded recombination and enhanced exciton separation as evidenced by electrochemical impedance spectra. Therefore, fullerene passivation is a promising method to ameliorate the connection between conjugated polymers and metal oxides, and is applicable in diverse areas, such as solar cells, transistors, and light-emitting dioxides.

Highly Efficient Non-Enzymatic Glucose Sensor Based on CuO Modified Vertically-Grown ZnO Nanorods on Electrode

There is a major challenge to attach nanostructures on to the electrode surface while retaining their engineered morphology, high surface area, physiochemical features for promising sensing applications. In this study, we have grown vertically-aligned ZnO nanorods (NRs) on fluorine doped tin oxide (FTO) electrodes and decorated with CuO to achieve high-performance non-enzymatic glucose sensor. This unique CuO-ZnO NRs hybrid provides large surface area and an easy substrate penetrable structure facilitating enhanced electrochemical features towards glucose oxidation. As a result, fabricated electrodes exhibit high sensitivity (2961.7 μA mM−1 cm−2), linear range up to 8.45 mM, low limit of detection (0.40 μM), and short response time (<2 s), along with excellent reproducibility, repeatability, stability, selectivity, and applicability for glucose detection in human serum samples. Circumventing, the outstanding performance originating from CuO modified ZnO NRs acts as an efficient electrocatalyst for glucose detection and as well, provides new prospects to biomolecules detecting device fabrication.

Highly stable hydrazine chemical sensor based on vertically-aligned ZnO nanorods grown on electrode

Herein, we report a binder-free, stable, and high-performance hydrazine chemical sensor based on vertically aligned zinc oxide nanorods (ZnO NRs), grown on silver (Ag) electrode via low-temperature solution route. The morphological characterizations showed that the NRs were grown vertically in high density and possess good crystallinity. The as-fabricated hydrazine chemical sensors showed an excellent sensitivity of 105.5 μAμM−1cm−2, a linear range up to 98.6μM, and low detection limit of 0.005μM. It also showed better long-term stability, good reproducibility and selectivity. Furthermore, the fabricated electrodes were evaluated for hydrazine detection in water samples. We found the approach of directly growing nanostructures as a key factor for enhanced sensing performance of our electrodes, which effectively transfers electron from ZnO NRs to conductive Ag electrode. Thus it holds future prospective applications as binder-free, cost-effective, and stable sensing devices fabrication.

Synthesis of zinc oxide nanorods from chemical bath deposition at different pH solutions and impact on their surface properties

Abstract The future of new generation superhydrophobic coatings supply depends on modern breakthroughs concerning the stability, low cost, simple synthesis process, sustainability and multi-functionality important for a futuristic application in field of science and technologies. Here we use a low-cost, and simple chemical bath deposition (CBD) to produce vertical-aligned ZnO nanorods with hydrophilic nature. Furthermore, hydrophilic surface has been converted into superhydrophobic surface by annealing at 460 °C in air for 1 h. It switches surface from Wenzel to Cassie-Baxter wettability states are corresponded to a transformation from non-polar into a polar nature occurs at top surface of ZnO nanorods. In addition, the effect of pH on their surface morphology, surface topography, surface roughness, ZnO nanorods growth nature, chemical composition, wettability and surface free energy is also systematically focused as an essential step to understanding functional surfaces with their futuristic applications.

Position controlled and seed/catalyst free growth of ZnO nanorod arrays on reduced graphene oxide nanosheets

A new type of seed/catalyst-free and selective-growth process is developed for in situ grown vertically-aligned ZnO nanorods on the reduced graphene oxide (rGO) nanosheets. The dense and single-crystalline ZnO nanorods have been successfully grow on rGO nanosheets with the position- and size-controlled. The effect of rGO layer on the ZnO nanorods and the growth mechanism were investigated. The position of ZnO nanorod arrays correlates well with the size and position of rGO nanosheets, which is determined by dangling bonds such as oxygen-containing groups on rGO surface. Meanwhile, ZnO nanorods could grow laterally to form a continuous arrays with a large coverage on rGO substrates, which is mainly due to the step edges in rGO boundaries. The diameter and density of ZnO nanorods were readily determined by the growth temperature, and the length was easily controlled by the growth time. The absorption and PL spectrums suggest that ZnO nanorods/rGO have a strong UV absorption ranging from 330 to 375 nm and no obvious UV PL emission at room temperature, which indicates that the ZnO nanorods/rGO nanohybrids could be an excellent candidate for application in UV photodetectors. This work represents the success in seed/catalyst-free fabrication of aligned ZnO nanorod arrays directly on rGO nanosheets and the process can be readily scaled up for industrial applications of optoelectronic devices.

Facile synthesis of ZnO/CuInS2 nanorod arrays for photocatalytic pollutants degradation

Vertically-aligned ZnO nanorod arrays on a fluorine-doped tin oxide glass substrate were homogeneously coated with visible light active CuInS2 quantum dots by using a controllable electrophoretic deposition strategy. Compared with the pure ZnO nanorod arrays, the formation of high-quality ZnO/CuInS2 heterojunction with well-matched band energy alignment expanded the light absorption from ultraviolet to visible region and facilitated efficient charge separation and transportation, thus yielding remarkable enhanced photoelectrochemical performance and photocatalytic activities for methyl orange and 4-chlorophenol degradation. The ZnO/CuInS2 film with the deposition duration of 80min showed the highest degradation rate and photocurrent density (0.95mA/cm2), which was almost 6.33 times higher than that of the pure ZnO nanorod arrays film. The CuInS2 QDs sensitized ZnO nanorod arrays film was proved to be a superior structure for photoelectrochemical and photocatalytic applications due to the optimized CuInS2 loading and well-maintained one-dimensional nanostructure.

Polarization-dependent DANES study on vertically-aligned ZnO nanorods

The local structural and local density of states of vertically-aligned ZnO nanorods are examined by using polarization-dependent diffraction anomalous near edge structure (DANES) measurements from c-oriented ZnO nanorods at the Zn K edge at the geometry of the incident x-ray electric field parallel and perpendicular to the x-ray momentum transfer direction. Orientation-dependent local structures determined by DANES are comparable with polarization- dependent EXAFS results. Unlike other techniques, polarization-dependent DANES can uniquely describe the orientation-dependent local structural properties and the local density of states of a selected element in selected-phased crystals of compounds or mixed-phased structures.

Patterned growth of zinc oxide nanorods using poly(vinyl alcohol)-N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal and zinc acetate mixture as a seed layer

This paper reports a new method for fabricating two-dimensional ZnO nanorod patterns. A water soluble mixture of poly(vinyl alcohol)-N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal (PVA-Sbq) and zinc acetate (ZnA) was used as a negative photoresist to produce the desired patterns using conventional photolithography. Hydrothermally-grown ZnO nanorods were grown selectively on the calcined PVA-Sbq/ZnA patterns. The appropriate concentration of PVA-Sbq and ZnA that can produce the desirable seed layer pattern was determined experimentally. Furthermore, the effects of the calcination time on the morphology and vertical alignment of ZnO nanorods were investigated. The vertically-aligned ZnO nanorods were generated by sufficient calcination of the patterned seed layer. On the other hand, the aspect ratio of ZnO nanorods decreased slightly with increasing calcination time. This new approach provides a simple and cost-effective method for fabricating ZnO nanorod patterns which can be beneficial in various solid-state devices and optoelectronic applications.