Growth Of ZnO Nanostructures Research Articles

Droplet-Based Preparation of ZnO-nanostructure Array for Microfluidic Fluorescence Biodetection.

Nanostructure-enhanced biodetection is widely used for early diagnosis and treatment, which plays an essential role in improving the cure rates of cancer patients. ZnO nanostructure-based fluorescence immunoassay has been demonstrated to enable effective and sensitive detection of cancer biomarkers for their excellent biocompatibility, high electrical point, and unique fluorescence enhancement properties. Further optimization of such fluorescence detection technology is still in demand to meet the requirements of highly sensitive, multiplex detection, and user-friendly devices. Droplet microfluidics is a promising platform for high-throughput analysis of biological assays, and they have been intensively used in analytical chemistry and synthesis of nanoparticles. Here, we propose a simple droplet chip, where a static droplet array was successfully obtained for in situ growth of ZnO nanostructures with varied diameters by changing the entire growth time and replenishment interval. This device provides a novel and alternative approach for patterned growth of ZnO nanostructures and understanding the growth condition of ZnO nanostructures in static droplet, which offers some guidance toward the design of multiple fluorescence amplification platforms potentially for biosensing. As a demonstration, we used the patterned grown ZnO nanostructures for multiple detection of cancer biomarkers, achieving a low limit of detection as low as 138 fg/mL in the human α-fetoprotein assay and 218 fg/mL in the carcinoembryonic antigen assay with a large dynamic range of 8 orders. These results suggest that such multifunctional microfluidic devices may be useful tools for efficient fluorescence diagnostic assays.

Synthesis and growth mechanism of ZnO nanocandles using thermal evaporation and their efficient CO sensing performance

We report on the single step grown ZnO nanocandles without adding any catalyst for efficient CO gas sensing application. A simple, scalable, and cost-effective thermal evaporation technique was employed for the growth of ZnO nanostructures on alumina substrate at 600 °C. It was observed that oxygen ambient (variation in oxygen flow rates from 20 to 40 sccm) strongly influences the shape and size of the ZnO nanostructures (i.e., the formation of nanocandles or nanorods). The as grown ZnO nanostructures were characterized using various techniques such as X-ray diffraction, Field emission scanning electron microscopy, photoluminescence, and X-ray photoelectron spectroscopy. Further, a comprehensive analysis of the CO gas sensing performance of each sample was recorded under various conditions, and the corresponding mechanism was reported. We have achieved the maximum sensor response (SR%) ∼ 78.3% along with a response/recovery time ∼ 59.5 s/109.4 s towards 91 ppm of CO gas at 400 °C for the sample synthesized at 40 sccm oxygen gas flow rate (i.e., for nanocandles). While, a relatively lower SR ∼ 70.1% and ∼ 64.1% and higher response/recovery time of ∼ 77.8 s/118.6 s and ∼ 84.6 s/122.1 s were obtained for the samples synthesized at 30 sccm and 20 sccm, respectively (i.e., for nanorods). Moreover, the calculated detection limit for ZnO nanocandles was 110 ppb. The selectivity test shows that the ZnO nanocandles are highly responsive to CO gas and exhibits long term stability (tested over 360 days). Thus, ZnO nanocandles can be used for the fabrication of robust CO gas sensors.

The Interplay of Growth Mechanism and Properties of ZnO Nanostructures for Different Applications.

This review provides a background on the structure and properties of ZnO nanostructures. ZnO nanostructures are advantageous for many applications in sensing, photocatalysis, functional textiles, and cosmetic industries, which are described in this review. Previous work using UV Visible (UV-vis) spectroscopy and scanning electron microscopy (SEM) for ZnO nanorod growth analysis in-solution and on a substrate for determination of optical properties and morphology is discussed, as well as their results in determining the kinetics and growth mechanisms. From this literature review, it is understood that the synthesis process greatly affects nanostructures and properties; and hence, their applications. In addition, in this review, the mechanism of ZnO nanostructure growth is unveiled, and it is shown that by having greater control over their morphology and size through such mechanistic understanding, the above-mentioned applications can be affected. The contradictions and gaps in knowledge are summarized in order to highlight the variations in results, followed by suggestions for how to answer these gaps and future outlooks for ZnO nanostructure research.

Rose Petal Mimetic Surfaces with Antibacterial Properties Produced Using Nanoimprint Lithography.

In this study, we produced bioinspired micro/nanotopography on the surface of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films and demonstrated that these films display antibacterial properties. In the first step, structures that are found on the surface of a rose petal were copied on the surface of PVDF-HFP films. Following this, a hydrothermal method was used to grow ZnO nanostructures on top of this rose petal mimetic surface. The antibacterial behavior of the fabricated sample was demonstrated against Gram-positive Streptococcus agalactiae (S. agalactiae) and Gram-negative Escherichia coli (E. coli) as model bacteria. For comparison purposes, the antibacterial behavior of a neat PVDF-HFP film was also investigated against both bacterial species. The results show that the presence of rose petal mimetic structures on PVDF-HFP helped the material to display improved antibacterial performance against both S. agalactiae and E. coli compared to the antibacterial performance of neat PVDF-HFP. The antibacterial performance was further enhanced for samples that had both rose petal mimetic topography and ZnO nanostructures on the surface.

Morphology and orientation controlling of ZnO nanofibers via chemical bath deposition

Growth of high-quality ZnO nanomaterials along specific orientations has still been a hot issue nowadays. Here, ZnO nanofibers with various orientations have been demonstrated. Electrospinning ZnO fibers have been acted as seed templates for fabricating ZnO crystals with different orientations depended on the increased volume ratio of isopropanol (IPA). ZnO nanofibers have been characterized and the results have shown that ZnO crystals experience the growth transition from polar to nonpolar orientation owing to the enhanced steric hindrance originated from the increased IPA volume fraction in chemical bath deposition (CBD) solutions. In this work, an effective synthesized approach has been applied for growing ZnO nanostructures with specific orientations of the crystals.

Seedless and surfactant-free growth of flower-shaped ZnO nanostructures: Growth evolution mechanism

In this work, an innovative seedless and surfactant-free chemical bath deposition (CBD) method at low temperature was applied to obtain flower-shaped ZnO nanostructures (FZONSs) on glass and [Formula: see text]-type silicon substrates for the first time. Structural properties of these FZONSs were examined. The NSs were produced from zinc nitrate hexahydrate and hexamethylenetetramine, HMTA solution without any catalyst, template, or seed layer. An electric soldering iron pen was used to simultaneously heat the substrate and aqueous mixture of the constituents to grow the FZONSs. Field emission scanning electron microscopy images of the samples showed the presence of three-dimensional (3D) flower-shaped nanomorphology. Energy-dispersive X-ray spectroscopy detected the right trace elements in the FZONSs. X-ray diffraction analysis of the as-grown samples confirmed the existence of high purity nanocrystalline hexagonal phase of ZnO with preferred growth along (002) lattice planer orientation. The growth of ZnO nanorods into unified flower-like morphology was interpreted using a nucleation dissolution-mediated recrystallization mechanism. The fabricated FZONSs may provide potential in various applications including advanced catalysts, sensing devices, and solar cells.

Optimization of Pulsed Laser Ablation and Radio-Frequency Sputtering Tandem System for Synthesis of 2D/3D Al2O3-ZnO Nanostructures: A Hybrid Approach to Synthesis of Nanostructures for Gas Sensing Applications.

In this paper, a unique hybrid approach to design and synthesize 2D/3D Al2O3-ZnO nanostructures by simultaneous deposition is presented. Pulsed laser deposition (PLD) and RF magnetron sputtering (RFMS) methods are redeveloped into a single tandem system to create a mixed-species plasma to grow ZnO nanostructures for gas sensing applications. In this set-up, the parameters of PLD have been optimized and explored with RFMS parameters to design 2D/3D Al2O3-ZnO nanostructures, including nanoneedles/nanospikes, nanowalls, and nanorods, among others. The RF power of magnetron system with Al2O3 target is explored from 10 to 50 W, while the ZnO-loaded PLD's laser fluence and background gases are optimized to simultaneously grow ZnO and Al2O3-ZnO nanostructures. The nanostructures are either grown via 2-step template approach, or by direct growth on Si (111) and MgO<0001> substrates. In this approach, a thin ZnO template/film was initially grown on the substrate by PLD at ~300 °C under ~10 milliTorr (1.3 Pa) O2 background pressure, followed by growth of either ZnO or Al2O3-ZnO, using PLD and RFMS simultaneously under 0.1-0.5 Torr (13-67 Pa), and Ar or Ar/O2 background in the substrate temperate range of 550-700 °C. Growth mechanisms are then proposed to explain the formation of Al2O3-ZnO nanostructures. The optimized parameters from PLD-RFMS are then used to grow nanostructures on Au-patterned Al2O3-based gas sensor to test its response to CO gas from 200 to 400 °C, and a good response is observed at ~350 °C. The grown ZnO and Al2O3-ZnO nanostructures are quite exceptional and remarkable and have potential applications in optoelectronics, such in bio/gas sensors.

Laser-Induced Au Catalyst Generation for Tailored ZnO Nanostructure Growth.

ZnO nanostructures, semiconductors with attractive optical properties, are typically grown by thermal chemical vapor deposition for optimal growth control. Their growth is well investigated, but commonly results in the entire substrate being covered with identical ZnO nanostructures. At best a limited, binary growth control is achieved with masks or lithographic processes. We demonstrate nanosecond laser-induced Au catalyst generation on Si(100) wafers, resulting in controlled ZnO nanostructure growth. Scanning electron and atomic force microscopy measurements reveal the laser pulse's influence on the substrate's and catalyst's properties, e.g., nanoparticle size and distribution. The laser-induced formation of a thin SiO2-layer on the catalysts plays a key role in the subsequent ZnO growth mechanism. By tuning the irradiation parameters, the width, density, and morphology of ZnO nanostructures, i.e., nanorods, nanowires, and nanobelts, were controlled. Our method allows for maskless ZnO nanostructure designs locally controlled on Si-wafers.

In English

Zinc oxide nanostructures (NS) were grown on thin discontinuous films of noble metals of silver and gold in order to study their structure, optical properties as well as photocatalytic and antiviral activity. The paper presents the results of X-ray diffraction study, scanning electron microscopy study, photoluminescence and Raman measurements. X-ray diffraction experiments demonstrate similar patterns for all grown ZnO nanostructures. The SEM images of ZnO NS grown on Ag/Si and Au/Si wafers demonstrate more dense surface microstructure compared to ZnO NS grown on bare Si wafers. The most intensive ultraviolet and deep level emissions are observed for ZnO NS grown on Ag/Si wafers. Increase in thicknesses of Ag island film from 5 nm to 10 nm gives significant increase in intensity of ultraviolet and deep level emissions. Photocatalysis of grown ZnO nanostructures was studied by methyl orange dye degradation. Superior photocatalytic results are demonstrated by ZnO nanostructures grown on Ag/Si wafers, for which constants of dye degradation were twice higher than for ZnO nanostructures grown on Si and Au/Si substrates. The photocatalytic results correlates with photoluminescence spectra: more intensive photoluminescence in ultraviolet and visible ranges of optical spectrum leads to better photocatalytic performance. The cytotoxic effect of ZnO nanostructures was studied without photoactivation by the help of cell cultures MDCK and Hep-2 while the virucidal effect of ZnO nanostructures was studied by the help of Influenza A virus (H1N1) (strain FM / 1/47) and human adenovirus serotype 2 (HAdV2). ZnO nanostructures in a 1:10 dilution were not toxic to Hep-2 and MDCK cells. Most of the tested ZnO nanostructures exhibited no virucidal activity against human adenovirus serotype 2 (HAdV2) and influenza A virus (H1N1) (strain FM / 1/47) in the absence of photoexcitation.

Hydrothermal growth of ZnO nanostructures with dopants Co2+, Ni2+ and Cu2+ - Structural and luminous characteristics

Transition metal doped ZnO: (Co/Ni/Cu) nanostructures grown using hydrothermal technique at an optimized growth temperature of 200 °C and a growth time of 3 hours exhibit violet photoluminescence emission. The scanning electron micrographs recorded from the as synthesized samples (ZnO:Co, ZnO:Ni and ZnO:Cu) display nanorods, nanosheet and nanoflower morphology depending upon the dopant/doping percentage. The X-ray diffraction and Raman analysis confirm that hexagonal wurtzite structure of ZnO is retained even after nominal doping of Co, Ni and Cu ions. Optical properties of hydrothermally grown ZnO crystals were analysed with respect to doping concentration (3, 4 and 5 wt%) of Co, Ni and Cu. The optical band gap of ZnO:Co decreases with increasing doping concentration, where as in the case of ZnO:Ni and ZnO:Cu, the band gap increases with increasing the doping concetration. Intense violet deep level emission was observed from ZnO:Co, ZnO:Ni and ZnO:Cu samples at room temperature and the intensity of violet luminescence decreased with increasing the doping concentration of Co2+, Ni2+ and Cu2+ ions into ZnO.

The Effect of Ag-Doping on the Cytotoxicity of ZnO Nanostructures Grown on Ag/Si Substrates by APMOCVD

The search and development of new nanostructures and nanomaterials are very important for the progress of nanotechnology and modern microbiology. Due to the unique properties of silver and zinc oxide, these nanoparticles are the optimal basis for creating nanostructures with potential antiviral activity. An important issue in these studies is the establishment of cytotoxicity of these nanoparticles and their composites. Aim. To define the influence of substrate temperature and Ag concentration in ZnO lattice on the microstructure and cytotoxicity of zinc oxide nanostructures. Methods. Pure and Ag-doped ZnO nanostructures were grown on Ag/Si substrates by atmospheric pressure metalorganic chemical vapor deposition method using a mixture of zinc acetylacetonate and silver acetylacetonate powders as a precursor. Argentum thin films were deposited on Si substrates by a thermal evaporation method. MTT-assay was used for the analysis of MDBK and MDCK cell viability in the definition of zinc oxide nanostructure cytotoxicity. Results. Ag-doped zinc oxide nanostructures were grown and characterized by X-ray diff raction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. It was found that Si substrate and pure zinc oxide do not inhibit the cell viability of both epithelial cultures whereas Ag-doped ZnO nanostructures inhibit the cell viability because of all-time exposure in a sample without dilution. The cytotoxic effect was not observed at higher dilutions for Ag-doped zinc oxide nanostructures. Conclusions. The investigation of the effect of Ag-doping on the morphology and cytotoxicity of zinc oxide nanostructures is very important for implementing zinc oxide nanostructures into the current optoelectronics and photocatalysis.

Structure, Optical and Photocatalytic Properties of ZnO Nanostructures Grown on Ag-Coated Si Substrates

Structure, Optical and Photocatalytic Properties of ZnO Nanostructures Grown on Ag-Coated Si Substrates

Vacancy driven surface disorder catalyzes anisotropic evaporation of ZnO (0001) polar surface

The evaporation and crystal growth rates of ZnO are highly anisotropic and are fastest on the Zn-terminated ZnO (0001) polar surface. Herein, we study this behavior by direct atomic-scale observations and simulations of the dynamic processes of the ZnO (0001) polar surface during evaporation. The evaporation of the (0001) polar surface is accelerated dramatically at around 300 °C with the spontaneous formation of a few nanometer-thick quasi-liquid layer. This structurally disordered and chemically Zn-deficient quasi-liquid is derived from the formation and inward diffusion of Zn vacancies that stabilize the (0001) polar surface. The quasi-liquid controls the dissociative evaporation of ZnO with establishing steady state reactions with Zn and O2 vapors and the underlying ZnO crystal; while the quasi-liquid catalyzes the disordering of ZnO lattice by injecting Zn vacancies, it facilitates the desorption of O2 molecules. This study reveals that the polarity-driven surface disorder is the key structural feature driving the fast anisotropic evaporation and crystal growth of ZnO nanostructures along the [0001] direction.

Morphological and optical characterizations of different ZnO nanostructures grown by mist-CVD

In this study, the effects of growth temperatures, post-growth treatment, and substrate cleaning recipes on structural, morphological, luminescence, and growth kinetics of ZnO nanostructures grown by mist Chemical Vapor Deposition method (mist-CVD) on SiO2/Si substrates are investigated. The grown ZnO nanostructures have polycrystalline wurtzite (wz) hexagonal crystal structure according to X-ray Diffraction (XRD) measurements. However, the lower growth temperature is found to lead to the formation of ZnO nanostructures oriented in the [0002] direction. From Atomic Force Microscope (AFM) measurements, it is seen that the Root Mean Square (RMS) values decrease with decreasing growth temperature. In addition, it is shown that the surface covering is tightly dependent on decreasing growth temperature of the ZnO nanostructures. The hexagonal and triangular pyramid-like ZnO nanostructures are grown on the surface according to the Scanning Electron Microscope (SEM) measurements. The wurtzite type of crystallization is also demonstrated by confocal Raman measurements. The characteristic vibration modes related to Zn and O motion in the lattice are found to be ∼435 cm−1 and ∼100 cm−1, respectively. The luminescence properties are studied by low-temperature (10 K) Photoluminescence (PL) measurements. The spectra are dominated by the transition related to the donor-bound exciton (DBE) with a peak position typically observed at ∼369 nm (3.362 eV) in hexagonal ZnO structures. Defect-related transitions are observed to be strongly correlated with growth temperature and post-growth treatment.

Sol–gel/hydrothermal synthesis of well-aligned ZnO nanorods

The nucleation and growth of ZnO nanorods by hydrothermal method onto seed layer deposited onto an ITO/PET substrate. Concentrations of 10 and 15mM were used for the synthesis of the seed layer solution, as well as 10 and 15mM for the hydrothermal treatment, it is noted that the entire process was carried out at low temperature (<100°C). The synthesis of ZnO nanorods was carried out in two stages: (i) A nucleation process, using the sol–gel method to obtain a seed layer; and (ii) a growth process, using the hydrothermal process to promote the perpendicular growth of ZnO nanostructures. The X-ray diffraction (XRD) ZnO results revealed a preferential orientation along the (002) axis, with a wurtzite hexagonal structure. The crystallite size (27nm) and Gibbs free energy of the films were calculated, which exhibited a minimum diameter for the nucleation of ZnO nanorods (22 and 30nm of the core diameter). The thickness layer is between 200 and 500nm. These results indicate that ZnO nanorods with an average diameter between 50 and 195nm are obtained, oriented perpendicularly to the ITO/PET substrate, synthesized by a low temperature process. Their potential applications are in power generators and sensors.

Growth of Al-doped ZnO nanostructures in low pressure background gas by pulsed laser deposition

In this work, the deposition of nanostructures by room temperature pulsed laser deposition (PLD) in low pressure (2.6 Pa) O2, N2, He, and Ar at different substrate positions are studied. The substrates are placed at the normal on-axis/center position; and off-axis i.e. 4.5 cm above and below the center position. Optical emission spectra and ion velocity are measured by using spectrometer and ion probe. The overall intensity of optical emission is in the order of Ar > O2/N2 > He while the ion velocity is in the reverse order. The inverse relation of optical emission and ion velocity suggest that collisions of the ablated specie possibly result in strong emission and impede the ion velocity at the same time. Amorphous films are obtained for the substrates placed at on-axis/center in all the background gases and at the bottom position for O2. However, crystalline ZnO and Zn nanostructures are deposited at the bottom position in N2, He, and Ar. Larger structures are deposited in Ar and the presence of nanorods are detected by TEM. The results further suggest that in N2, He or Ar, the ablated plasma plume is spatially and thermally confined; governed by the properties of the gas. Nucleation of nanostructures occurred in the plasma plume even at low background pressure and deposited on the substrates that are placed at the bottom position. Between the two inert gases, Ar with higher atomic mass and lower thermal conductivity results in high collisions and thermal confinement that leads to some large structure as compared to those obtained in He. In addition, in the presence of N2, He or Ar, Zn crystallites are also detected, which can act as catalyst for nanostructure formation.

A novel semi-dry method for rapidly synthesis ZnO nanorods on SiO2@PTFE nanofiber membrane for efficient air cleaning

Particulate matter including dust and airborne microorganisms has severe effect on indoor air quality and thus be injurious to human health. In this research, inspired by corals, a tentacle-like ZnO nanorods (NRs) decorated SiO 2 @PTFE nanofibers was prepared by a novel semi-dry method combining rapid dipping and solid-phase drying process. The controllable growth of ZnO nanostructures can be achieved by adjusting the numbers of dipping cycles. It may be the most simple and effective way to prepare sufficiently crystallized ZnO nanostructures at relatively facile conditions without high temperature calcination and any pressure vessels. The obtained ZnO NRs-SiO 2 @PTFE nanofiber membrane (NFM) with a hierarchical fibrous structure possesses uniform pore structure (average pore size 0.92 μm), high gas permeance (626.4 m 3 ∙m −2 ∙h −1 ∙kPa −1 ), and a superior filtration property (99.997% for 0.3 μm particulates). Moreover, the active ZnO with enhanced specific surface also exhibits good antibacterial property with sterilization rate of 99.67% and 99.93% for E. coli and B. subtilis , respectively. The ZnO growth mechanism and air cleaning principle including dust filtration and bacteria sterilization were analyzed by the corresponding experiments. This work provides a new insight into the dual-function air cleaning membrane preparation via a mild and simple reaction conditions, energy efficient and environment friendly strategy. • A facile semi-dry method for preparing ZnO NRs decorated SiO 2 @PTFE NFMs. • The corals tentacle-like ZnO NRs help to capture and deactivate microorganisms. • The membrane exhibits excellent filtration property with low pressure drop. • The method is energy saving and environment friendly for scale up application.

Growth and Gd doping of ZnO nanostructures with enhanced structural, optical properties and photocatalytic applications

In this study, pure and Gadolinium doped ZnO (Gd-ZnO) nanoparticles have been synthesized by wet chemical method and the effect of Gadolinium incorporation on the structure and optical activity of ZnO was examined. The average size of the undoped ZnO and Gd-ZnO (0.002 M and 0.003 M) nanoparticles was found to be 48 nm, 44 nm and 42 nm respectively which shows the lattice compression of ZnO after Gd doping. TEM study shows the hexagonal nanocrystallites of Gd-ZnO with size around 45 nm is formed. FTIR study shows the metal-oxygen band below 600 cm−1 and absorbance study gives the information about the narrowing of band gap of ZnO after Gd doping. The photocatalytic degradation efficiency of Gd-ZnO (92 %) has been found to be better as compared to undoped ZnO (89 %) in degrading methyl blue (MB). The photodegradation of MB is found to follow first order kinetics.

DES-mediated synthesis of ZnO nanostructures with exposed {0001} facets: photoluminescence and photocatalytic properties

Optimizing the facet growth of ZnO nanostructures using green solvents via a controlled route.

Fabrication of Graphene/Zinc Oxide Nano-Heterostructure for Hydrogen Sensing.

In this study, hydrogen (H2) and methane (CH4) were used as reactive gases, and chemical vapor deposition (CVD) was used to grow single-layer graphene on a copper foil substrate. The single-layer graphene obtained was transferred to a single-crystal silicon substrate by PMMA transfer technology for the subsequent growth of nano zinc oxide. The characteristics of CVD-deposited graphene were analyzed by a Raman spectrometer, an optical microscope, a four-point probe, and an ultraviolet/visible spectrometer. The sol–gel method was applied to prepare the zinc oxide seed layer film with the spin-coating method, with methanol, zinc acetate, and sodium hydroxide as the precursors for growing ZnO nanostructures. On top of the ZnO seed layer, a one-dimensional zinc oxide nanostructure was grown by a hydrothermal method at 95 °C, using a zinc nitrate and hexamethylenetetramine mixture solution. The characteristics of the nano zinc oxide were analyzed by scanning electron microscope(SEM),x-ray diffractometer(XRD), and Raman spectrometer. The obtained graphene/zinc oxide nano-heterostructure sensor has a sensitivity of 1.06 at a sensing temperature of 205 °C and a concentration of hydrogen as low as 5 ppm, with excellent sensing repeatability. The main reason for this is that the zinc oxide nanostructure has a large specific surface area, and many oxygen vacancy defects exist on its surface. In addition, the P–N heterojunction formed between the n-type zinc oxide and the p-type graphene also contributes to hydrogen sensing.