Zinc Oxide Microrods Research Articles

Random Laser Emission from Fiber coated ZnO

Random lasing from a solid-state gain medium prepared on photonic crystal fibre (PCF) is observed for the first time. Vertically aligned ZnO microrods were prepared on PCF using a simple technique of chemical bath deposition (CBD). A low lasing threshold of 12.2 mJ/cm2 was observed in sample with longer zinc oxide (ZnO) rod length. The variation in morphology and population density did not affect the lasing threshold significantly. Further investigation of the effect of fiber length revealed that a shorter fiber had a lower threshold and showed quenching of the spontaneous emission revealing better lasing output. Simulations based on the morphology of the gain medium revealed light confinement in the structure, validating the origin of the lasing emission. Overall, this study shows the potential of utilising optical fiber as random lasers with a sustainable solid state gain medium.

Supersonically Sprayed Flexible ZnO/PVDF Composite Films with Enhanced Piezoelectricity for Energy Harvesting and Storage

A flexible piezoelectric nanogenerator (PENG) was developed to convert ambient mechanical energy into electrical energy. Highly crystalline template-free zinc oxide (ZnO) microrods were prepared using a wet chemical method at a low temperature. As-synthesized ZnO microrods were blended with polyvinylidene fluoride (PVDF) to prepare a piezoelectric composite film using the supersonic spraying method. A PENG electrode comprising ZnO microrods (0.5 g) produced 15.2 V under a tapping force of 20 N at 5 Hz. In addition, an output current of 32 μA was produced with a maximum power density of 12.5 μW cm–2. The output voltage considering various body movements was investigated to demonstrate the flexibility and durability of the proposed PENG. Furthermore, the supercapacitive properties of ZnO/reduced graphene oxide were studied.

Peculiarities of erbium incorporation into ZnO microrods at high doping level leading to upconversion and the morphology change. Influence on excitonic as well as shallow donor states

Heavily Er-doped zinc oxide (ZnO) microrods with nominal compositions, ZnO:Er(2, 10, 30%), were prepared by the hydrothermal growth method. The crystallographic phases present in the as grown and annealed materialswere determined. The presence of the hexagonal Wurtzite ZnO phase in the form of the hexagonal shape nanoplatelets and microrods was confirmed. Moreover, the Er2O3phase in the form of nanosheets has been revealed as well. Erbium is partly incorporated into the ZnO hosts. It was thinning upon erbium doping level contributing to erbium oxide. This effect was even more pronounced upon annealing in air. Moreover, the influence of erbium doping and annealing on paramagnetic shallow donor centers has been studied. There were two types of these centers, both affected by the erbium presence. The increase of the neutral zinc vacancies amount upon erbium doping has been proven. Annealing in air moderated the charge distribution between them. Moreover, upconversion processes between the two erbium ions were observed and explained. The surface distribution of excitonic emission centers was studied. The larger the erbium content the weaker the exciton luminescence. The smaller the ZnO microrods the stronger the exciton emission.

Template-free microwave-assisted growth of 3D hexagonal ZnO rods

Here, a rapid synthesis method for growing template-free three-dimensional hexagonal zinc oxide (ZnO) micro-rods (HZMR) using a pulsed-microwave (p-MW) irradiation technique is reported. The effects of microwave exposure time and power are shown to tune the morphology of hexagonal rods from solid to blind hole to hollow rods. X-ray diffraction (XRD) confirmed the growth of pure ZnO phase. Morphological investigations by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM), optical properties by micro-Raman, Diffuse Reflectance Spectroscopy (DRS), Attenuated Total Reflectance (ATR) and Photoluminescence (PL) spectroscopy techniques were carried out. The PL studies reveal a dominant red emission along with characteristic blue and green emissions. The resulting structures have the scope of being applied as miniature sensors or in lasing applications. The blind-holed structures can be used as miniature crucibles/pots in reactions. This template-free growth of hexagonal rods is a very simple and economical technique that can result in solid, hollow or one-end blind hexagonal rods. The paper discusses the growth mechanism of these unique hierarchical HZMR.

Synthesis of Rod-Shaped ZnO/Polysiloxane Micromotors with Patch-Dependent Motion Modes.

Inorganic particles with photocatalytic properties are excellent candidates for the fabrication of micromotors. To achieve self-propulsion, the geometric and chemical symmetries of inorganic particles should be broken. However, the synthesis of micromotors with different geometric and chemical symmetries remains challenging. In this paper, a simple synthesis method is proposed to prepare rod-shaped micromotors with different patches, leading to distinct geometric and chemical symmetries. The micromotors are composed of zinc oxide (ZnO) microrods partially patched with polysiloxanes at different positions. The patches of the micromotors can be roughly regulated by varying the amount of siloxanes used in the synthesis. These micromotors are propelled in H2O2 solution by an ionic self-diffusiophoresis mechanism, which exhibits two motion modes, including linear motion and circular motion, due to different patch positions. Moreover, the degradation of organic dyes by the micromotors depending on the patches is demonstrated.

Effect of Cu\(^{2+}\) Dopant on the Formation of Zinc Oxide Microrod Fabricated by a Hydrothermal Method

Reconstruction and stabilization of polar oxide surfaces, such as ZnO, contribute a significant role in photocatalysis, chemical sensing, and optoelectronic applications, however their physical chemistry insight is still a puzzle in the surface science. In this work, the polar surface instability induced the morphological evolution of hydrothermally synthesized micro-rod ZnO doped with various contents of Cu2+ ion (1-10 at.%) was investigated. The transformation of micro-rod morphology from the high aspect ratio flower-like shape of the pure ZnO to the hexagonal prism-like shape of the doped ZnO was characterized by X-ray diffractometry, scanning electron microscopy and micro Raman spectroscopy. The chemically active Zn-terminated polar surface in doped samples was less positive charge density which was the main reason to cancel the electrostatic instability for the dominant growing direction. Furthermore, the schematic models of the electron transferring from the conduction band region to the electron trap centre of Cu2+, and the Zn-terminated polar surface reconstruction were proposed for the morphological evolution mechanism.

Picosecond UV emissions of hydrothermal grown Fe3+-doped ZnO microrods

We report the successful iron (III), Fe3+ doping of hydrothermal-grown zinc oxide (ZnO) microrods. The Fe3+-doped ZnO microrods were synthesized at 90 °C using zinc acetate dihydrate, hexamethylenetetramine, and iron (III) chloride aqueous solutions. Compared to the undoped microrods, the Fe3+-doped microrods exhibit more intense, sharper 564-nm (visible) emissions and shorter 388-nm (ultraviolet) emission lifetimes attributed to the successful incorporation of Fe3+ in a 6-coordinated geometry. Fe3+ is incorporated as an interstitial or part of a defect complex that effectively modified the defect structure while preserving the hexagonal wurtzite lattice. These results reveal the possibility of intentional transition metal doping of hydrothermal-grown ZnO micro/nanostructures with faster emission lifetimes for possible scintillator applications.

Surface photovoltage response of zinc oxide microrods on prismatic planes: effect of UV, temperature and oxygen ambience

In this study, we report the time evaluation of work function measurements on ZnO microrods in Kelvin probe method under photoexcitation, called Surface Photovoltage (SPV). The SPV measurements are one of the most important techniques for characterizing both surface and bulk of the semiconductors. The ZnO microrods synthesized by hydrothermal method are highly crystalline with typical length of 50–100 µm and hexagonal cross section of about 2 µm. Upon drop-casting, most of the rods lie flat on the surface making the basal (002) plane vertical and the prismatic (101) and (100) plane on top. Thus, the SPV measurements are performed on these prismatic planes which are non-polar in nature. The SPV response of microrods has been studied for UV laser of photon energy 3.45 eV which is higher than that of the observed bandgap of 3.3 eV of ZnO microrods. The response is studied in varying oxygen ambience and temperatures. The average work function of the material at room temperature (25 °C) and ambient atmosphere is found to be 4.52 ± 0.3 eV. The work function was found to decrease with increasing temperature and upon photoexcitation. The photovoltage recovery time depicts that the presence of oxygen in atmosphere greatly accelerates the photocurrent recovery through trapping of photo-generated charge carriers by the surface states. The minority carrier diffusion length thus estimated from variable energy photoexcitation is found to be 160 nm.

The growth mechanism of zinc oxide micro-rods via vapor-phase method

Two different ZnO micro-structures were deposited by a Chemical Vapour Deposited method in a small quartz tube. The micro-rods and micro-wires were found on the edge of the tube respectivly. The morphology and structural properties were texted by scanning electronic microscopy technique and X-ray diffraction. The results shows that the micro-rods have typical hexagonal wurtzite structure without any defect and the micro-wires have two types, the single ZnO crystal and the double-like one. The X-ray diffraction gives some information through the intense 002 peak which means the samples have a great wurtzite structure and grown up along the c-axis. The mechanism of the two samples also discussed, it is in relation to the substrate temperature and the concentration of the mixed gas.

Facile growth of high transmittance ZnO micro-rod clusters on indium tin oxide by a wet-chemical synthesis method

A simple wet-chemical synthesis method was developed to fabricate Zinc oxide micro-rod clusters. The synthesis process involved the rapid dilution of a zinc-bearing alkaline solution at 150°C in a convection oven on indium tin oxide (ITO) substrates. The synthesis was carried out by immersing an unseeded ITO substrate in a mixture of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and hexamethylenetetramine ((CH2)6N4) aqueous solution. The obtained sample was annealed at 400°C for 2 h. The structural, morphological and optical properties of the synthesized ZnO microstructures were investigated by X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy, respectively. The ZnO rod clusters are hexagonal phase of the wurtzite structure. The crystal grain sizes of the films were found to be 72.6, 84.3 and 66.3 nm for the (100), (002) and (101) crystal planes, respectively. The optical bandgap of the ZnO was determined to be 3.147 eV.

Controllable Heterogeneous Nucleation for Patterning High-Quality Vertical and Horizontal ZnO Microstructures toward Photodetectors.

High-quality crystalline micro- and nanostructures based on inorganic semiconductors including zinc oxide (ZnO) have attracted considerable interest in electronic and optoelectronic applications due to their outstanding properties. ZnO micro- and nanocrystals can be fabricated by the moderate and high throughput hydrothermal synthesis. Yet it is restricted by patterning large-area ZnO crystals with high-quality and programmable geometries through the hydrothermal process for the optoelectronic integration. Here, a capillary-bridge manipulation approach is demonstrated to control the dewetting process of ZnO precursor solution for patterning precursor arrays. Based on precursor arrays, vertically aligned high-quality ZnO microrod arrays with homogeneous morphology and pure crystallographic orientation are fabricated via a hydrothermal epitaxial method. Statistical results and crystallization theories guide the experimental optimization and discussion of the crystallization mechanism, dominated by the competition between homogeneous nucleation and heterogeneous nucleation. High-quality ZnO microbelt arrays are achieved through a surfactant-mediated hydrothermal method after ZnO microrod arrays are transferred to a polydimethylsiloxane substrate. Photodetectors based on ZnO microbelts exhibit a high responsivity of 2.3 × 104 A W-1 , a light on-off ratio exceeding 105 , and stable recyclability. It is anticipated that this work provides new insights into patterning inorganic high-quality micro- and nanostructures for multi-functional integrated devices.

Effect of the Morphology of an Ensemble of ZnO Microrods on the Optical and Luminescence Properties

The effect of morphology on the optical and X-ray luminescence properties of an ensemble of zinc oxide microrods on single-crystal sapphire substrates has been studied. It has been shown that the intensity of X-ray luminescence depends on the volume of the ZnO single-crystal phase and the corresponding effective density of the absorbing medium. It has been found that the total transmission spectra of the samples have a complex structure. The transmittance primarily depends on the conditions of synthesis and nucleation, on the morphology of ZnO microrods, and on the degree of their misorientation in an ensemble. An array of ZnO microrods characterized by the rapid component of the X-ray luminescence kinetics in the range of 0–5 ns with a descending time of about 0.7 ns (taking into account the pump pulse) has been obtained.

The Potential of Pandanus Amaryllifolius Leaves Extract in Fabrication of Dense and Uniform ZnO Microrods.

Zinc oxide (ZnO) micro and nanorods were successfully prepared using Pandanus amaryllifolius and hexamethylenetetramine (HMTA) separately as stabilizers using the solution immersion method. Two types of ZnO seed layer were prepared using the same pre-cursor with the different stabilizers. The fabricated ZnO microrods exhibit absorption at ~375 nm as revealed from the UV–Visible absorption spectrum, and this is comparable with ZnO nanorods synthesized using HMTA. X-ray diffraction (XRD) measurement displayed a sharp peak corresponding to the hexagonal wurtzite structure of ZnO microrods. Field emission scanning electron microscopy (FESEM) of ZnO microrods showed average diameter at approximately 500 nm compared to 70 nm of those synthesized from HMTA. A new finding is the ability of Pandanus amaryllifolius as a green stabilizer to grow a dense ZnO microrod structure with high crystallinity. Results reveal that both samples from different stabilizers during the preparation of the ZnO seed layer greatly improved the morphological and structural properties and optical absorption of ZnO. The main outcomes from this study will benefit optoelectronic application, such as in ultraviolet (UV) sensors.

Study of acidosis, neutral and alkalosis media effects on the behaviour of activated carbon threads decorated by zinc oxide using extended gate FET for glucose sensor application

In recent times, semiconductor-carbon composite microstructure offers new prospects in bio-chemical sensor research. In this study, hexagonally structured zinc oxide micro rods (ZnOMRs) were synthesized on activated carbon threads (ACTs) using the chemical bath in the absence of a ZnO seed layer. The ZnOMRs/ACTs based extended gate field effect transistor (EGFET) was characterized as a bio-chemical sensor for pH and glucose in acidosis, neutral and alkalosis media. The ZnOMRs/ACTs based EGFET sensor exhibited glucose sensitivities in terms of reference voltage (VRef) of (20.71, 18.21, and 16.72) mV/mM and drain source current (IDS) of (29.00, 25.60, and 23.62) μA/mM for pH values of 7.2, 7.4, and 7.6, respectively, at room temperature. Thus, the glucose sensitivity of the ZnOMRs/ACTs based EGFET increased with decrease in pH, due to the increased participation of hydrogen ions in the electrochemical exchange reaction between the solution and ZnOMRs/ACTs electrode. Based on the high sensitivity, ZnOMRs/ACTs composite could be a favourable micromaterial for bio-chemical sensor applications.

Mimicking Saharan silver ant’s hair: A bionic solar heat shielding architextile with hexagonal ZnO microrods coating

Inspired by the amazing capability of Saharan silver ants (SSant) to keep cool under extremely hot conditions, we develop a new functional architextile product by mimicking its microrod shaped hair to obtain an effective solar heat shielding function. To be specific, unique hexagonal zinc oxide (ZnO) microrods (MRs) were rationally synthesized and further coated on polyester fabric with polydimethylsiloxane (PDMS) to achieve a bionic solar heat shielding architextile product. The surface temperature of the as-prepared fabric can be lowered by 10 °C compared to the control sample under the irradiation of a solar simulator of AM 1.5 G condition for 1 h. The test results show that the as-synthesized coating material can reflect nearly 90% of the solar irradiance and thus leads to an efficient reduction in temperature. Additionally, the thermal conductivity and transmittance of fabric are also significantly enhanced after the coating process. In summary, the proposed bionic coating materials possess similar thermal shielding functions of SSant hairs and can have a potential application in developing solar heat shielding architextile.

Multi-length scale wear damage mechanisms of ultra-high molecular weight polyethylene nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE) is reinforced with 1–3 wt % sliver (Ag) nanoparticles and zinc oxide (ZnO) micro-rods, and tensile strength as well as wear resistance of the samples is evaluated. Tensile strength was observed to increase with Ag and ZnO reinforcement up to 18% for 1 wt % ZnO and 1 wt % Ag, but in case of 3 wt % ZnO and 3 wt % Ag + 3 wt % ZnO, it decreases marginally by 4% when compared with neat polymer. The sliding wear rate for 1 wt % Ag + 1 wt % ZnO and 3 wt % Ag + 3 wt % ZnO decreases from 9.54 × 10−5 mm3 (neat polymer) to 7.49 × 10−5 mm3 and 5.65 × 10−5mm3, respectively, showing the synergistic effect of Ag and ZnO reinforcement. In scratch testing, minimum damage is obtained in 1 wt % ZnO reinforced polymer. On one hand, where micro-scratch damage is resisted by harder ZnO, whereas on the other hand, pin on disc wear (repeated surface damage) is protected by softer Ag tribolayer. The improved tensile strength (up to 9.7%) and wear resistance with synergistic addition of Ag and ZnO (both 1 wt %) opens a window in the development of bearing surface biomaterials providing improved longevity and durability, thus, may reduce the chances of revision surgery.

A novel template-free wet chemical synthesis method for economical production of zinc oxide microrods under atmospheric pressure

This work reports a template-free wet chemical synthesis method for economical production of zinc oxide (ZnO) microrods by using an inexpensive polypropylene beaker as a reactor under atmospheric pressure. The morphology and crystal structure of the as-prepared ZnO microrods were investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Raman scattering. Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), Ultraviolet–visible (UV/Vis) spectroscopy and methylene blue photocatalytic degradation test were also conducted to study their physical and chemical properties. The results show that the as-prepared ZnO microrods have a hexagonal crystal structure. Under the optimal synthesis condition, they have a diameter of 0.8–2.6 μm and a length of 10–40 μm. Compared with commercial ZnO powders, the as-prepared ZnO microrods have a higher whiteness. Meanwhile, the as-prepared ZnO microrods have very low photocatalytic activity, indicating that they have good photostability and are unlikely to cause the photodegradation of polymers such as binders. As a result, they will be an excellent and economical white pigment with great potential in coating applications.

Effect of metal/metal oxide coupling on the photoluminescence properties of ZnO microrods

Despite its unique properties, zinc oxide (ZnO) particles have limited usage in optoelectronic devices and biochemical sensors due to its relatively poor ultraviolet (UV) emission. In this research, the localized surface plasmon resonance (LSPR) effect of metal nanoparticles such as silver (Ag), aluminium (Al), copper (Cu) and iron (Fe) that were coupled with ZnO microrods was studied. The metal coupled ZnO microrods were synthesized by solution impregnated method. The metal nanoparticles were clearly observed deposited onto the surface of ZnO microrods using transmission electron microscope (TEM) and energy dispersive X-ray (EDX) mapping. The room temperature photoluminescence (RTPL) analysis of ZnO microrods coupled with Al, Ag, Fe showed remarkable improvement of UV emission and quenching of defect related emission. The intensity ratio (Iuv/Ivis) of ZnO microrods was 1.6 but was enhanced to 26.1, 4.4, and 4.0 by coupling of Al, Ag and Fe, respectively. However, when Cu was embedded onto ZnO microrods, the Iuv/Ivis of ZnO microrods was suppressed to 0.1. The photoluminescent mechanism of Al, Ag and Fe–ZnO particles was attributed to LSPR effect. In contrary, deposition of Cu onto ZnO microrods induced energy level in bandgap of ZnO, producing the visible light emission.

UV Luminescence and Lasing in Ensembles of Zinc-Oxide Microcrystals with Copper

Microrod arrays of zinc oxide with copper have been grown by chemical vapor deposition on single-crystal sapphire substrates preliminarily covered with a nanoscale copper layer. The presence of copper (about 0.3%) in zinc-oxide microrods has been experimentally shown to increase the photoluminescence intensity of the ZnO microcrystal arrays, reduce the lasing threshold, and lead to a small (by ~2.5 nm) blue shift of the radiation intensity peak of the ZnO microcrystals. It is shown that the laser-radiation character depends on the morphology of the ZnO microrod arrays.

Emission spectra of hexagonal zinc oxide microrods due to resonant modes

Experimental observation and theoretical analysis of the whispering gallery mode (WGM) related emission spectra of ZnO microrods with a hexagonal cross-section are reported. ZnO microrods of various sizes are fabricated, and their individual geometric information (including the inner radius, edge profile modification, and tilt angle) are characterized via scanning electron microscopy (SEM). The photoluminescence spectra in the visible range (with energies between 1.77 and 2.76 eV) are compared with theoretical simulation based on Green function calculation within a nearly complete set of basis functions. WGM resonance peaks for TE and TM modes of five different sizes of microrods are analyzed. By using the SEM determined geometry with a slight adjustment, we obtain realistic simulation of the line shapes of the emission spectra, which agree well with experimental observation. To gain better understanding of the WGM resonance modes, we also calculate the WGM resonance profile of ZnO microrods with the cylindrical cross-section for both TE and TM modes for comparison.