ZnO Nanorod Arrays Research Articles

Ultrasensitive SERS Analysis of Liquid and Gaseous Putrescine and Cadaverine by a 3D-Rosettelike Nanostructure-Decorated Flexible Porous Substrate.

Putrescine and cadaverine are toxic biogenic amines in spoiled food, which poses a serious threat to food security. In this work, we reported a highly sensitive three-dimensional (3D)-rosettelike surface-enhanced Raman spectroscopy (SERS) substrate functionalized with a p-mercaptobenzoic acid (p-MBA) monolayer to detect liquid and gaseous putrescine and cadaverine in pork samples. The SERS substrate was made by a combination of the merit of the 3D morphology of ZnO nanorod arrays on a flexible porous poly(vinylidene fluoride) (PVDF) membrane and the in situ chemical growth of Au nanoparticle seeds on Au film-coated ZnO nanorods, which produced a 3D-rosettelike BigAuNP/Au/ZnO/P heterostructure with abundant SERS-active hot spots that significantly enhanced the localized surface plasmonic resonance (LSPR) effect and charge-transfer (CT) effect of Raman enhancement. This SERS substrate showed high sensitivity, reproducibility, stability, and uniformity. With the p-MBA molecular monolayer as the sensing interface, our SERS substrate realized the highly sensitive and quantitative detection of liquid putrescine and cadaverine within 10 min, with a limit of detection (LOD) of 3.2 × 10-16 and 1.6 × 10-13 M, respectively. Additionally, the sensor showed efficient SERS responses to gaseous amine molecules at low concentrations (putrescine: 1.26 × 10-9 M, cadaverine: 2.5 × 10-9 M). Further, the sensor was successfully applied to determine the total content of putrescine and cadaverine. Moreover, the practicability of this SERS sensor was verified by the measurement of liquid and gaseous amines in pork samples, and it showed great potential applications for sensitive detection of food spoilage.

The Fowler–Nordheim plot behaviour from virtual field emitters arrays of zinc oxide nanorods mixed with carbon nanotubes

ABSTRACT The Fowler–Nordheim plot behaviour is investigated for large area field emitters arrays composed of mixtures of ZnO nanorods and single-wall carbon nanotubes (CNTs). The field emission current–voltage characteristics are calculated using the Murphy-Good equation based on the Fowler–Nordheim model. The influencing factors taken into consideration are the radii of the ZnO rods, the heights of the CNTs, the variation of the onset voltage of the saturation of the ZnO conduction band (CB) emission current and the degradation of the CNTs at high applied voltages. The results show that the FN plots of the mixed arrays exhibit nonlinear behaviour near the high-field region which could be related to the FN plot behaviour of the constituting emitters arrays. The distribution of the emitters geometrical parameters and the onset of saturation of the ZnO CB current are found to affect the FN plot behaviour of the pure ZnO, CNTs arrays as well as mixed arrays. The comparisons between the FN plots from the present work and those measured experimentally are found useful to shed light on the field emission mechanism. This may in turn aid the development of complex field emission arrays for future technological applications. The work also shows the possibility to apply the standard FN model to complex large area field emitters arrays.

Controllable synthesis of nickel doped hierarchical zinc MOF with tunable morphologies for enhanced supercapability

Metal-organic frameworks (MOFs) are attracting tremendous research interest because of their rich redox sites and high specific area which are beneficial for the energy storage applications. Nevertheless, the poor conductivity, low mechanical strength and unsatisfactory capacity severely hinder their wide application. Hence, it is of practical significance to design highly efficient and facile strategy to solve these issues. Herein, vertically oriented ZnO nanorod arrays are applied as precursor to synthesize laminated scale-like and highly-oriented Ni/Zn-MOF/ZnO nanocomposite. Owing to the desirable conductivity resulting from the doping nickel ions and the interaction between ZnO and its relative MOF, the fabricated 0.3Ni/Zn-MOF/ZnO@CC electrode exhibits an electrochemical capacitance of 1693 mF cm−2 at 1 mA cm−2. Moreover, the electrochemical capacitance retention of 80.7 % after 2500 cycling numbers is obtained under the constant current density of 10 mA cm−2 and the low internal resistance Rs of 0.89 Ω is observed. For practical application, the as-synthesized laminated scale-like Ni/Zn-MOF/ZnO@CC nanocomposite is served as positive electrode to fabricate solid-state asymmetric supercapacitor device. Moreover, a 2.5 V indicator could be powered for 8 min when the prepared supercapacitor units are connected. This work demonstrates the promising potential of the synthesized scale-like Ni/Zn-MOF composites for electrochemical energy storage applications.

Optimization of UVB photodiode based on ZnO nanorod arrays grown via the hydrothermal process

In this work, n-Type ZnO nanorods (NRs) were grown on a p-type Si (100) substrate using the hydrothermal technique. These p-n heterojunctions were made to fabricate ZnO-based ultraviolet (UV) photodiodes (PDs). To study the effect of solution volume -in the hydrothermal process-on the structural properties of the ZnO NRs arrays, three samples were prepared with different conditions. SEM characterization shows the well-aligned ZnO NRs arrays grown on all three substrates. X-ray diffraction characterization indicates the crystalline structure of all samples with a preferred orientation of c-plane (002). XRD results show the ZnO grain size enlargement concerning solution volume. To analyze the electric characterization of the samples, the current-voltage (I–V) analysis was performed under dark and illuminated conditions. The I–V measurement indicates that the increase of growth solution volume is leading to increasing in the responsivity of ZnO-based PDs. Additionally, the PL and UV–Vis characterizations exhibit that the optical properties of samples were also affected and therefore could be controlled and optimized by growth conditions.

Ultraviolet light sensing property in ZnO nanorod arrays doped by various elements

Here we have synthesized undoped and doped (Co, Cu, N) ZnO nanorods (NRs) using the chemical bath deposition (CBD) method and compared their ultraviolet (UV) light sensitivity in metal-semiconductor-metal (MSM) configuration. The layers were characterized by FESEM, EDX, XRD, UV–Vis., PL spectra, Seebeck effect, also I–V and I-t in the dark and under 365 nm illumination. We found: (1) that the addition of these dopants, even N-dopant, led to n-type conductivity with different activation energies of 66, 36, and 11 meV for Co, Cu, and N dopants, respectively; (2) that compared to undoped conditions, the doped NRs are longer and narrower, furthermore, they have better crystallinity and higher UV absorbance; (3), based on a comparative study, ZnO:Co NRs have the highest photoresponse ratio (IL/ID) of 833.

Piezocatalytic and doping effects synergistically enhance the oxygen evolution in Sb-doped zinc oxide nanorod arrays as a photoanode for photoelectrochemical water splitting

Piezocatalytic and doping effects synergistically enhance the oxygen evolution in Sb-doped zinc oxide nanorod arrays as a photoanode for photoelectrochemical water splitting

In-situ deposition of POMA/ZnO nanorods array film by vapor phase polymerization for detection of trace ammonia in human exhaled breath at room temperature

The o-methoxyaniline (OMA) monomer was polymerized in-situ by vapor phase polymerization to form uniform and dense poly-o-methoxyaniline (POMA) film on the surface of ZnO nanorods array film which was pre-prepared by hydrothermal method. The as-prepared POMA/ZnO composite shows the best response at 40 min of vapor phase polymerization time. The response to 100 ppm ammonia at 25 °C is 8.88. The recovery time of 136 s has a certain advantage in the reported room temperature ammonia sensors. The lowest detectable concentration is as low as 0.01 ppm. The fast recovery time and low detection limit make the sensor have broad application prospects. In order to explore the response mechanism of POMA/ZnO composite to ammonia gas, the work function of POMA and ZnO and corresponding band gap energies were tested respectively. And the effect of the formation of p-n heterostructure on gas response was further explored. The actual application test results reflect that the sensor can effectively identify NH3 in the mixed gas during the production, storage and transportation of NH3. This can provide real-time early warning of NH3 leakage. Especially, the sensor can detect trace amount of NH3 in the human body's exhaled breath which is expected to realize the preliminary screening of patients with kidney disease through the detection of exhaled breath in the medical field.

Piezo-phototronic effect boosted catalysis in plasmonic bimetallic ZnO heterostructure with guided fermi level alignment

High photo-induced carriers (PCs) recombination rate, low PC mobility, and limited solar energy utilization rate are the three main roadblocks that severely limit the photocatalytic activity of semiconductors. In this work, we designed a plasmonic bimetallic ZnO nanorod array (Au/ZnO/Pt) with Au nanoparticles (NPs) located on top of ZnO nanorods and Pt NPs evenly distributed on the ZnO nanorods for improving catalysis through the piezo-phototronic effect. With the rational design of guided Fermi level alignment, the photoinduced hot electrons of Au NPs with localized surface plasmon resonance effect can transfer to Pt NPs through ZnO to promote the separation and migration of PC. More importantly, under the stimulation of ultrasound, ZnO with piezo-phototronic effect generates an interfacial piezo-potential, thereby further promoting the separation and transport of carriers in compliance with the direction of piezo-potential to promote the surface redox reaction. Under the synergy of piezo-phototronic effect and localized surface plasmon resonance effect, the Au/ZnO/Pt realized 97.5% dye degradation in 60 min, which was 1.2, 1.36, and 1.79 folds of that with Au/ZnO/Au, Pt/ZnO/Pt, and ZnO, respectively. The unique plasmonic bimetallic heterostructure with piezo-phototronic effect and guided Fermi level alignment can guide the directional migration of carriers and provides useful instruction for the design of high-efficiency catalysts.

In situ growth of ZnO nanorods array film on the surface of ITO for low temperature detection of NOx gas

Nitrogen oxides are one of the most harmful gases and highly toxic to human health if inhaled at moderate atmospheric concentrations or above (10–20 mmHg). Sensing NOx is one of the most challenging tasks at low temperature levels and room temperature. The ZnO nanostructures were successfully synthesized by hydrothermal method. The wettability and gas sensitivity of the ZnO nanorods array film were studied. The results show that the ZnO nanorods array film is hydrophobic by adding KCl. In addition, the ZnO nanorods array film shows a positive response to NOx. The gas sensing performance shows that the sensor response based on ZnO nanorods array film has a linear relationship with the concentration of NOx in the range of 0.1–3 ppm. It has good reproducibility and selectivity. The maximum sensitivity to NOx was obtained at an operating temperature of 120 °C. The response of the sensor is 25 when the concentration of NOx is 3 ppm.

Enhancement in absorption spectrum by ITO coated, down converting glass as a photoanode substrate for efficient PbS/CdS quantum dots sensitized ZnO nano-rods array solar cell

An efficient, simple and cost effective architecture of PbS/CdS quantum dots sensitized ZnO nano rods array solar cell has been proposed. A normal glass substrate in photoanode has been replaced by down converting glass to broad the absorption spectrum of solar cell. Three PbS/CdS quantum dots sensitized ZnO nano rods array solar cells with ITO coated down converting glass as a substrate have been fabricated by changing 10, 15 and 20 SILAR cycles for PbS/CdS quantum dots sensitization. SEM analysis confirmed the formation of ZnO nano rods. Grown nano rods were not closely packed which provided PbS/CdS quantum dots proper surface area to get attached. Optical properties analyzed by UV–Visible spectroscopy revealed the optical absorption in UV range which eventually was converted in visible spectra by down converting glass also the ZnO nano rod arrays increased the possibility of light scattering hence improved light absorption. The purposed architecture of solar cell hence played important role to achieve high power conversion efficiency of 8.6%.

Bioinspired Self-Powered Piezoresistive Sensors for Simultaneous Monitoring of Human Health and Outdoor UV Light Intensity.

The exact fabrication of precise three-dimensional structures for piezoresistive sensors necessitates superior manufacturing methods or tooling, which are accompanied by time-consuming processes and the potential for environmental harm. Herein, we demonstrated a method for in situ synthesis of zinc oxide nanorod (ZnO NR) arrays on graphene-treated cotton and paper substrates and constructed highly sensitive, flexible, wearable, and chemically stable strain sensors. Based on the structure of pine trees and needles in nature, the hybrid sensing layer consisted of graphene-attached cotton or paper fibers and ZnO NRs, and the results showed a high sensitivity of 0.389, 0.095, and 0.029 kPa-1 and an ultra-wide linear range of 0-100 kPa of this sensor under optimal conditions. Our study found that water absorption and swelling of graphene fibers and the associated reduction of pore size and growth of zinc oxide were detrimental to pressure sensor performance. A random line model was developed to examine the effects of different hydrothermal times on sensor performance. Meanwhile, pulse detection, respiration detection, speech recognition, and motion detection, including finger movements, walking, and throat movements, were used to show their practical application in human health activity monitoring. In addition, monolithically grown ZnO NRs on graphene cotton sheets had been integrated into a flexible sensing platform for outdoor UV photo-indication, which is, to our knowledge, the first successful case of an integrated UV photo-detector and motion sensor. Due to its excellent strain detection and UV detection abilities, these strategies are a step forward in developing wearable sensors that are cost-controllable and high-performance.

High-quality CdS quantum dots sensitized ZnO nanotube array films for superior photoelectrochemical performance

The surface characteristics of ZnO were synthetically optimized by a self-designed simultaneous etching and W-doping hydrothermal method utilizing as-prepared ZnO nanorod (NR) array films as the template. Benefiting from the etching and regrowth process and the different structural stabilities of the various faces of ZnO NRs, the uniquely etched and W-doped ZnO (EWZ) nanotube (NT) array films with larger surface area, more active sites and better energy band structure were used to improve the photoelectrochemical (PEC) performance and the loading quality of CdS quantum dots (QDs). On the basis of their better surface characteristics, the CdS QDs were uniformly loaded on EWZ NT array film with a good coverage ratio and interface connection; this effectively improved the light-harvesting ability, charge transportation and separation as well as charge injection efficiency during the PEC reaction. Therefore, all the CdS QD-sensitized EWZ NT array films exhibited significantly enhanced PEC performance. The CdS/EWZ-7 composite films exhibited the optimal photocurrent density with a value of 12 mA⋅cm−2, 2.5 times higher than that of conventional CdS/ZnO-7 composite films under the same sensitization times with CdS QDs. The corresponding etching and optimizing mechanisms were also discussed.

Morphology and Field Emission of ZnO Nanomaterials at Different Positions

By simply adjusting the temperature and the number of materials, rod-like ZnO with different morphology, such as ZnO nanoneedles, were synthesized by a flexible thermal evaporation method. The ZnO nanorod array has the lowest turn-on field, the highest current density, and the highest emission efficiency due to its good contact with the substrate and relatively weak field shielding effect. Experiments show that the morphology and orientation of one-dimensional ZnO nanomaterials have a great influence on its conduction field and emission current density, and the nanoarrays also contribute to electron emission. The research results have a certain reference value for the application of ZnO nanorod arrays as cathode materials for field emission devices.

Highly Sensitive Detection of T-2 Toxin Using Photo Induced Zero-Gating Voltage Organic Electrochemical Transistor Aptasensor Based on Zno Nanorod Arrays

Highly Sensitive Detection of T-2 Toxin Using Photo Induced Zero-Gating Voltage Organic Electrochemical Transistor Aptasensor Based on Zno Nanorod Arrays

Dual functionality of surface plasmon resonance and barrier layer on the photosensing and optical nonlinearity of ZnO nanorod arrays.

The dual functionality of plasmonic light harvesting and barrier spacing between Au nanoparticles (NPs) and ZnO nanorod arrays (NRsA) are spotlighted to investigate their impact on the photoconversion and optical nonlinearity in the present study. The passivating Al2O3 barrier layer permits high-energy hot electron tunneling and injection from Au to the ZnO NRsA. The structural, vibrational, morphological/elemental, and optical properties of ZnO NRsA/a-Al2O3/Au were characterized by X-ray diffraction (XRD), Raman scattering, field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDX), and ultraviolet-visible-near IR (UV-Vis-near IR) absorption, respectively. The optoelectronic and nonlinear optical properties were analyzed by current-voltage measurement and z-scan tests under red laser (655 nm) irradiation, respectively. To highlight the effect of surface plasmon charge transport-based photosensing and photo-harvesting, the irradiated light source is selected to have a photon energy lower than the ZnO bandgap energy and detuning from LSPR. The transfer of photo-induced hot electrons from the Au NPs localized surface plasmon resonance (LSPR) to the ZnO NRsA translates into photocurrent generation in photosensing performance. The reverse saturable absorption process is changed to saturable absorption after intercalating the Al2O3 spacing layer into the ZnO NRsA/Au interface. The typical values of the nonlinear refraction index and absorption coefficient are calculated as n2 = +2.38 × 10-5 cm2 W-1 and β = -0.17 cm W-1 for the sandwiched ZnO NRsA/Al2O3/Au heterostructure, respectively. The sandwiched ZnO NRsA/amorphous Al2O3/Au heterostructure exhibits strong nonresonant optical nonlinearity, which has an excellent figure of merit for optical switching.

Effects of Schottky Contact and Ohmic Contact on the Emission Properties of Metal-Covered Zno Nanorod Arrays

Effects of Schottky Contact and Ohmic Contact on the Emission Properties of Metal-Covered Zno Nanorod Arrays

An efficient dual functional Raman and Fluorescence detection platform achieved by controlling the electromagnetic enhanced field in three-dimensional Ag/ZnO composited arrays

Integrating SERS and MEF into a single platform is a challenge. Here, we design a three-dimensional electromagnetic field via decorating Ag nanoparticles onto ZnO nanorod arrays to realize dual-function detection by SERS and MEF simultaneously.

Hydrophilic polypyrrole and g-C3N4 co-decorated ZnO nanorod arrays for stable and efficient photoelectrochemical water splitting.

It is of practical significance to manufacture high-performance and durable semiconductor heterojunctions for photoelectrochemical (PEC) water splitting. Herein, hydrophilic polypyrrole and graphitic carbon nitride (g-C3N4) co-decorated ZnO nanorod arrays were synthesized as a photoanode by facile spin-coating and plasma-treatment methods. On the one hand, g-C3N4 nanosheets are modified on ZnO nanorod arrays to broaden the light-absorption range and suppress the recombination of photogenerated charges. On the other hand, the polypyrrole coating layer inhibits the dissolution and corrosion of ZnO nanorods and constructs a p-n heterojunction with ZnO to further promote the separation and transfer of photogenerated charge carriers. Furthermore, its hydrophilic surface provides a vast electrochemically active surface area for efficient charge/mass transfer. As a result, the as-prepared photoanode exhibits an enhanced PEC performance with a distinctly increased photocurrent and remarkably ameliorated stability in contrast to the ZnO photoanode. This research would provide an innovative perspective on the design of organic/inorganic semiconductor heterojunctions with excellent performance and stability for PEC water-splitting systems.

ALD oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO arrays for high-performance self-powered solar-blind photodetectors.

The exploration of efficient self-powered solar-blind photodetectors is essential for applications in future sustainable optoelectronic systems. Herein, we demonstrate a photoelectrochemical (PEC)-type heterojunction-driven solar-blind detector constructed by atomic layer deposition (ALD) of oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO nanorod arrays (3D VO-Ga2O3/ZnO). The as-fabricated device achieves excellent solar-blind photodetection performance in terms of a high photoresponsivity of 7.97 mA W-1 at 0 V bias, an ultrahigh light to dark ratio of 6.93 × 104 under 266 nm light illumination as well as fast response and recovery times. The excellent performance originates from abundant oxygen vacancies in a-Ga2O3 as donors, high specific surface area and good interface contact enabled by the 3D ordered nanostructure, and high carrier separation rates benefited from the Ga2O3/ZnO heterojunction. Our research offers a feasible and cost-effective approach towards the realization of a high-performance self-powered photodetection system for various applications.

Novel homo-epitaxial approaches in solvothermal synthesis for preparing surface tethered uni-directionally oriented zinc oxide micro and nano structured arrays

Surface aligned, uni-directionally grown, hexagonal nanorod bundles and microrod pillared arrays of zinc oxide (ZnO), were synthesized through a simple, homo-epitaxial growth approach. A uniform layer of ZnO seed was initially prepared on cleaned glass substrates by dip coating and calcination. Uni-directionally oriented ZnO micro– nano structures were subsequently developed on the seeded glass substrates through solvothermal methods, by employing equi-molar solutions of zinc nitrate and hexamethylenetetramine. The reaction parameters that control the surface morphologies and crystal orientations were explored. A solution exchange process was also carried out to prepare perpendicularly aligned ZnO nanorod arrays. The structural and functional features of the resultant samples were studied and discussed with the help of X-ray diffractometry, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectrophotometry. A plausible structure dependent growth mechanism of the morphologically varied ZnO was also proposed.