Aligned ZnO Nanorods Research Articles

Rectifying Behaviour and Photocatalytic Activity in ZnO Nanorods Array/Ag/CuSe Heterostructure

Ag incorporated vertically aligned ZnO nanorods array/CuSe thin film (ZnO NRs/CuSe TF) have been fabricated via a solution route, thermal evaporation and magnetron sputtering process. Ternary ZnO nanorods/Ag/CuSe heterostructure was studied by X-ray diffractometry, field emission-scanning electron microscopy/energy dispersive X ray spectroscopy, current–voltage measurement and a UV–Vis–near IR spectrophotometer. The photocatalytic performance was estimated by the degradation of Rhodamine B solution under UV–Vis light irradiation. The photocatalytic efficiency of the ZnO NRs/Ag/CuSe heterostructure is higher than that of ZnO NRs/Ag and ZnO NRs/CuSe counterparts due to the robust effects of the three functional components coupling. The localized surface plasmon resonance and two Schottky junctions (e.g. Ag/ZnO and Ag/CuSe) motivates photogenerated electron–hole separation and transfer. This work presents an artificial manipulated system to enhance light harvesting, efficient charge separation and transfer, and low recombination rate in solar energy conversion.

Enhanced room temperature gas sensing properties of low temperature solution processed ZnO/CuO heterojunction

The development of room temperature gas sensors having response towards a specific gas is attracting researchers nowadays in the field. In the present work, room temperature (29 °C) ethanol sensor based on vertically aligned ZnO nanorods decorated with CuO nanoparticles was successfully fabricated by simple cost effective solution processing. The heterojunction sensor exhibits better sensor parameters compared to pristine ZnO. The response of the heterojunction sensor to 50 ppm ethanol is, at least, 2-fold higher than the response of the ZnO bare sensor. Also the response and recovery time of ZnO/CuO sensor to 50 ppm ethanol are of 9 and 420 s whereas the values are 16 and 510 s respectively for ZnO sensor. The vertical alignment of ZnO nanorods as well as its surface modification by CuO nanoparticles increased the effective surface area of the device and the formation of p-CuO/n-ZnO junction at the interface are the reasons for the improved performance at room temperature. In addition to ethanol, the fabricated device has the capability to detect the presence of reducing gases like hydrogen sulfide and ammonia at room temperature.

Effect of ZnO Seed Layer on the Growth of ZnO Nanorods on Silicon Substrate

Abstract Highly vertically aligned ZnO nanorods (NRs) are preferred for the fabrication of devices such as solar cells, integrated circuits and light emitting diodes. However, ZnO NRs are randomly grown on silicon (Si) (100) substrate attributed to a large lattice mismatch (∼40 %) between Si and ZnO. The alignment of ZnO NRs could be improved by pre-deposition of a highly (002) oriented ZnO seed layer on the of surface Si substrate. In this work, ZnO seed layer was pre-deposited onto the Si substract by spin coating and followed by annealing. Parameters such as rotation speed, number cycles of spin coating and annealing temperatures were systematically studied. The results showed that 1000 rpm spin coating rate with the 11 spin cycles produced the most uniform coverage of ZnO NRs on Si with annealing temperature of 350°C. Micrographs of the samples show that the ZnO NRs are well-aligned with average diameters of ∼ 23 nm. In addition, the XRD analysis indicated highly aligned ZnO NRs were grown in [0001], i.e. perpendicular to (002) of the ZnO seed layer.

Enhanced green luminescence from ZnO nanorods

Preferentially c-axis oriented ZnO nanorods were grown on a ZnO seed layer spin coated on a crystalline silicon substrate. A low-temperature aqueous chemical growth method using the chemical bath deposition technique was used to grow the ZnO nanorods. The samples were annealed at 700 °C in a reducing atmosphere (H2/Ar) with a relative ratio of 5%:95% for different times (20, 30, and 50 min). X-ray diffraction analysis revealed that the crystallite sizes increased with an increasing annealing time up to 30 min and then decreased for longer annealing time. Scanning electron microscope images showed a successful growth of the vertically aligned ZnO nanorods which were approximately 500 nm in length and 50 nm in diameter. The diameter of the nanorods increased with an increasing annealing time up to 30 min and then decreased when the annealing time was increased further. Photoluminescence (PL) measurements confirmed that the unannealed sample exhibited two distinct emissions, namely, the band to band emission around 378 nm and a broad orange emission centered at 600 nm which was due to the oxygen related defects. The annealed samples exhibited only a broad green emission centered at 500 nm and their intensities increased with annealing time. The highest intensity was recorded for the sample annealed for 30 min and the intensity decreased for further annealing time. The deconvoluted PL peak of the green emission indicated that three different kinds of defects were responsible for the emission at 500 nm. The decay measurements indicated that the green emission (500 nm) had an average lifetime of 11.58 μs. The quantum yield of the sample annealed for 30 min was measured using an integrating sphere at a wavelength of 325 nm, and it was found to be 43%. These ZnO nanorods can be very useful in optoelectronic applications, such as green light emitting diodes and field emission displays.

Enhanced ultraviolet emission from self-assembled ZnO nanorods grown on graphene

We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-assembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO, which is modulated by surface corrugation of graphene and followed by its transformation into the propagating photon.

Synthesis and characterization of aligned ZnO nanorods for visible light photocatalysis

Aligned ZnO nanorods (NRs) were synthesized by a simple and inexpensive hydrothermal method. Morphological, structural, photoabsorbance and photoluminescence studies have been carried out using field emission scanning electron microscopy (FE-SEM), grazing incidence X-ray diffraction (GIXRD), Raman, UV–visible and Photoluminescence spectroscopy. Results show that crystallinity and alignment of ZnO NRs lead to good photocatalytic activity in the presence of visible light. The Photoluminescence spectra revealed a decrease in the UV emission, suggesting a reduced recombination of the photo generated carriers. The visible region emission is due to the surface oxygen vacancies. Increase of charge separation rate observed from emission spectra and the vacancy related sub-bands in the absorbance spectra are together responsible for the enhanced visible light photocatalytic activity of ZnO NRs. Vertically aligned 1-D morphology of ZnO NRs and the presence of oxygen vacancy states assist in the visible light photocatalytic degradation of Methylene Blue dye.

The sonochemical synthesis of vertically aligned ZnO nanorods and their UV photodetection properties: Effect of ZnO buffer layer

Vertically aligned Zinc oxide nanorods (ZnO NRs) were successfully synthesized in this study using the sonochemical method to improve the intrinsic properties of UV photodetector (PD). Three different thin films: Ti/Zn, Ti/ZnO, and Ti/ZnO/Zn, with the thicknesses of 10 nm/55 nm, 10 nm/85 nm, and 10 nm/85 nm/55 nm respectively, were deposited on glass substrates using the RF-sputtering technique. The synthesized ZnO NRs were investigated using XRD, FESEM and Raman spectroscopy to determine the effect of Zn and ZnO as seed layers, and ZnO as a buffer layer on the surface morphology, crystal structure, optical properties of ZnO NRs. The ZnO NRs grown on Zn/Ti, ZnO/Ti, and Zn/ZnO/Ti are characterized by hexagonal crystal structure with preferential growth in the c-axis direction. The ZnO NRs grown on Zn/ZnO/Ti displayed the highest density, uniform size distribution, vertically aligned rods and aspect ratio. The UV device fabricated from the ZnO NRs grown on Zn /ZnO/Ti also showed the highest photocurrent (360 µA) and responsivity of (878 mA/W). ZnO NRs grown on Zn/ZnO/Ti were also observed to be highly stable and exhibited a relatively rapid response and recovery times for different time intervals when exposed to the UV light of 365 nm wavelength. Thus, the inclusion of the ZnO as a buffer layer (Zn as a seed layer/ZnO as buffer layer/Ti as a buffer layer) improve the properties of the ZnO NRs. In addition, the current gain of ZnO NRs grown on Zn (55 nm)/ZnO (85 nm)/Ti (10 nm) – based ultraviolet (UV) photodetector (PD) is about two times higher than that of conventional Zn (55 nm)/ZnO (85 nm)/Ti (10 nm) thin-films UV PD, which is due to the higher surface-to-volume ratio of ZnO nanorods (NRs) compared with their thin films. This study confirms the possibility of sonochemically fabricating vertically aligned ZnO nanorods as well as its applicability as a viable UV photodetector.

Effect of Ethane-1,2-Diamine on Growth of ZnO Nanorods and Cyclohexane Sensing by Current-Voltage Characteristics Investigations

The growth of vertically aligned ZnO Nanorods arrays using Zinc Nitrate hexahydrate and Hexamethylene Tetramine (HMTA), by Chemical Bath Deposition on Silicon Wafer was investigated. The growth is conducted under influence of Ethane-1,2-diamine, the amine based enhancer was evaluated based on three different ratios (1:0.5, 1:1, 1:1.5) of enhancer to the precursor (Zinc Nitrate and HMTA). The effect different ratios of enhancers on morphology aspect ratio and crystallinity of the as grown Nanorods were studied under Scanning electron microscope (SEM) and X-ray powder diffraction (XRD). Electrical Properties such as current–voltage characteristics were investigated, its correlation to the morphology and aspect ratio of the Nanorods in the presence of 100μL-500μL of Aromatic Compound Cyclohexane and at different applied voltages.

STUDY OF NANOSTRUCTURES OF ZINC OXIDE SYNTHESIZED BY LOW-TEMPERATURE HYDROTHERMAL METHOD

Room temperature photoluminescence (PL) properties of vertically aligned and spindle-shaped, randomly oriented ZnO nanorods synthesized by using a low temperature hydrothermal method are studied. In air, the vertically aligned ZnO nanorods oriented mainly parallel to the luminescencerecording axis exhibited only one, very strong UV emission peak at 382 nm. This band is assigned to emission of free excitons. A new violet PL band near 400 nm arises with increasing angle between the nanorod growth direction and the luminescence-recording axis. The violet band also appears under UV illumination in vacuum and vanishes after exposure to air. The randomly oriented ZnO nanorods along with free exciton related PL band reveal a broad yellow-orange emission band around 590 nm. The violet band is attributed to Zn vacancy related defects or their complexes, while the yellow-orange emission band is ascribed to oxygen interstitial related defects.

Transparent Thin-Film Transistors Based on c-Axis Oriented, Vertically Aligned ZnO Nanorod Arrays via Solution Processing

A bottom-gate, top-contact transparent thin film transistor (TFT) based on c-axis oriented, vertically aligned ZnO nanorod arrays was fabricated on glass substrates via solution processing, in which ZnO nanorod arrays were synthesized on ZnO seed layers through a simple hydrothermal route. This TFT used SiO2 and indium tin oxide as the gate insulator and gate electrode, respectively. The source and drain electrodes were formed by radio frequency sputtered Au through a shadow mask. This ZnO TFT exhibited n-channel enhancement behavior with a field effective mobility of 3.86 cm2 V−1 s−1, a current on-to-off ratio of 65.5 and a threshold voltage of 1 V. Moreover, the ZnO TFT has a high transmittance of 80% in the visible spectrum. Our results demonstrate that hydrothermally grown, vertically aligned ZnO nanorod arrays are very promising for the fabrication of cost effective and high performance transparent thin-film transistors.

UV-laser-induced orientation of ZnO seed layer crystals for the growth of ZnO nanorods

We found that UV laser irradiation on a ZnO seed layer induced the crystal orientation at the surface, consequently leading to the growth of densely aligned ZnO nanorods on such a laser-irradiated layer. A single nanosecond pulse with a wavelength of 266 nm was irradiated to a ZnO seed layer on a glass substrate, and then, ZnO nanorods were synthesized on a laser-treated layer by a hydrothermal method. Electron microscopic observations revealed the growth of highly oriented ZnO nanorods on a laser-irradiated seed layer as well as the orientation of seed layer crystals to [0001].

Hybrid ZnO Nanorod Grafted Carbon Fiber Reinforced Polymer Composites; Randomly versus Radially Aligned Long ZnO Nanorods Growth.

Integrating nano-sized reinforcing materials into carbon fiber polymer composites (CFRPs) could enhance several aspects of their mechanical performance; e.g., interfacial strength, delamination resistance and vibrations attenuation. In this study, ZnO nanorods were grown on the surface of carbon fibers to create hybrid reinforcements. The hydrothermal synthesis of ZnO nanorods was tuned such that relatively long (>2.0 μm) nanorods can be grown. This synthesis technique requires pre-deposition of a thin seeding layer of ZnO particulates on the carbon fibers to initiate the ZnO nanorods growth. Depending on the method by which the seeding layer is deposited, the grown ZnO nanorods could display different morphologies. In this study, two different techniques were utilized to pre-deposit the ZnO seeding layer on the carbon fibers; ZnO nanoparticles/solution mixture airbrush spraying, and magnetron sputtering. The carbon fibers pre-coated with the airbrush spraying method yielded forests of randomly oriented ZnO nanorods, while the fibers pre-coated via the sputtering technique exhibited radially aligned ZnO nanorods forests. Hybrid CFRPs were fabricated based on the aforementioned carbon fiber fabrics and tested via 3-point bending dynamic mechanical analysis (DMA) and quasi-static tension tests. The loss tangent of the CFRPs, which delineates the damping capability, increased by 28% and 19% via radially and randomly grown ZnO nanorods, respectively. The in-plane tensile strength of the hybrid CFRPs were improved by 18% for the composites based on randomly oriented ZnO nanorods over the carbon fibers. The fractographs of the tension samples were also captured to reveal the role of the long ZnO nanorods in the in-plane performance of the hybrid CFRPs.

Ethanol-sensitive nearly aligned ZnO nanorod thin films covered by graphene quantum dots

Graphene quantum dots (GQDs) were simply synthesized by pyrolysis of citric acid, and zinc oxide nanorods (ZnO NRs) were grown on pre-seeded glass substrates by a solvothermal method. Finally, the GQDs were dropped on the ZnO NR thin film. It was found that the incorporation of GQDs eliminated the photoluminescence (PL) intensity of the ZnO NR thin film, suggesting that electrons of ZnO can be readily transferred to GQDs, contributing to the passing current. Finally, the ethanol sensing analysis was performed, showing that the incorporation of GQDs enhanced the sensitivity of ZnO NR thin film to ethanol gas, and the mechanism behind the enhancement was discussed.

PPV derivative/ZnO nanorods heterojunction: Fabrication, Characterization and Near-UV light sensor development

Poly(1,4-phenylenevinylene) derivative (PPV-C6) based solution was spin-coated onto hydrothermally grown and vertically aligned ZnO nanorods (ZnO NRs).The morphological and the optical properties of the PPV-C6/ZnO NRs hybrid heterojunction have been studied and shown a penetration of PPV-C6into the interspaces between the ZnO NRs with enhanced excitonic dissociation. The current–voltage characteristics in dark and under 395 nm LED illumination have been analyzed. A short-circuit current Jsc of 4691.42 μA/cm2, an open-circuit voltage Voc of 0.46 V giving rise to a responsivity of about 29.32 mA/W have been obtained for the illuminated graphite/PPV-C6/ZnO NRs/Si/EGa-In structure based near UV light sensor showing an enhanced responsivity by a factor of about 200 compared with bare ZnO NRs based one. We have succeeded in the development of low cost near-UV light sensors by simple low temperature hydrothermal method using eco-friendly, low cost and easily fabricated electrodes.

Effect of Temperature and Growth Time on Vertically Aligned ZnO Nanorods by Simplified Hydrothermal Technique for Photoelectrochemical Cells.

Despite its large band gap, ZnO has wide applicability in many fields ranging from gas sensors to solar cells. ZnO was chosen over other materials because of its large exciton binding energy (60 meV) and its stability to high-energy radiation. In this study, ZnO nanorods were deposited on ITO glass via a simple dip coating followed by a hydrothermal growth. The morphological, structural and compositional characteristics of the prepared films were analyzed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). Photoelectrochemical conversion efficiencies were evaluated via photocurrent measurements under calibrated halogen lamp illumination. Thin film prepared at 120 °C for 4 h of hydrothermal treatment possessed a hexagonal wurtzite structure with the crystallite size of 19.2 nm. The average diameter of the ZnO nanorods was 37.7 nm and the thickness was found to be 2680.2 nm. According to FESEM images, as the hydrothermal growth temperature increases, the nanorod diameter become smaller. Moreover, the thickness of the nanorods increase with the growth time. Therefore, the sample prepared at 120 °C for 4 h displayed an impressive photoresponse by achieving high current density of 0.1944 mA/cm2.

Fast and convenient growth of vertically aligned ZnO nanorods via microwave plasma-assisted thermal evaporation

A new approach to grow vertically aligned ZnO nanorods on glass substrates under ambient pressure was developed using microwave plasma-assisted thermal evaporation (MPATE). The results revealed that ZnO nanorods grew preferentially along their (002) plane on glass substrates without using catalysts/seed layers. Interestingly, the ZnO nanorods were completely formed within 7 min, which was much faster than other methods. The optical band gap of ZnO nanorods was 3.22 eV, indicating the photoresponse at UV region (<400 nm). Moreover, room-temperature photoluminescence of the ZnO nanorods, excited by 325 nm light, showed a dominance of green-light emission and a small UV emission.

Fabrication and Characterization of Vertically Aligned ZnO Nanorod Arrays via Inverted Monolayer Colloidal Crystals Mask

The periodically ordered ZnO nanorod (NR) arrays have been successfully synthesized via a hydrothermal approach on the silicon substrates by templating of the TiO2 ring deriving from the polystyrene (PS) nanosphere monolayer colloidal crystals (MCC). With the inverted MCC mask, sol–gel-derived ZnO seeds could serve as the periodic nucleation positions for the site-specific growth of ZnO NRs. The large-scale patterned arrays of single ZnO NR with good side-orientation can be readily produced. According to the experimental results, the as-integrated ZnO NR arrays showed an excellent crystal quality and optical property, very suitable for optoelectronic applications such as stimulated emitters and ZnO photonic crystal devices.

Effective shell wall thickness of vertically aligned ZnO-ZnS core-shell nanorod arrays on visible photocatalytic and photo sensing properties

Development of hierarchical core-shell semiconductor heterostructures ensue significant advancement in catalytic functional structures with improvised optical functionalities. Shell wall controlled vertically aligned ZnO-ZnS core-shell nanorod (NR) heterostructures were grown on transparent conductive substrates along the c-axis by sulfidation of aligned ZnO nanorod arrays for visible photocatalytic properties. The effects of the sulfidation time on the morphology, crystalline properties, optical property, photocurrent response, and photocatalytic activity of the catalyst arrays were studied under UV and visible light irradiation. The shell wall thickness of these heterostructures influenced in great extent the effective photo responsive charge separation and improved carrier mobility. ZnO-ZnS core-shell heterostructure having the shell wall thickness of 20 nm has exhibited more efficient visible photocatalytic behavior due to effective separation of carriers and improved visible absorption. On further increasing the wall thickness the catalytic efficiency was reduced due to the poor carrier (hole) mobility in the polycrystalline shell grains which induced the higher recombination rate. Stability and reusability of ZnO-ZnS core-shell nanostructures reveals that the ZnS acted as a protective layer over the ZnO NR arrays. In appraisal with ZnO NR arrays, the control over the shell wall thickness of ZnO-ZnS core-shell NR array attributed to the excellent visible photocatalytic activity and improvised absorption of light in visible region at ZnO-ZnS interface and effective separation of photogenerated electron-hole pairs at ZnO-ZnS heterojunctions.

Growth of aligned ZnO nanorods on carbon fabric and its composite for superior mechanical and tribological performance

A novel idea was implemented to grow aligned ZnO nanorods on carbon fabric by directly chemical bonding to form a multi-scale reinforcing resin composite. The aligned ZnO nanorods/carbon fabric were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectra and X-ray photoelectron spectroscopy, indicating an existence of chemical bonding (COZn) between ZnO nanorods and carbon fiber. The tensile and inter-laminar shear strength (ILSS) of ZnO nanorods/carbon fabric/resin composite (C1) were 182.4 and 147.1 MPa, which increased by 27% and 134% compared with bare carbon fabric/resin composite (C0), respectively. And the sample C1 possessed lower compressibility and higher recovery. As a result, the sample C1 obtained the high and stable friction coefficient. The wear rate of sample C1 decreased by about 38% compared with that of sample C0. The analysis of the worn surface by SEM and EDS showed that the ZnO nanorods were polished gradually and then fractured without peeling off as a whole from carbon fiber leading to excellent tribological performance. The development of an aligned interphase offering good interfacial bonding between carbon fabric and resin matrix will provide a means to produce multi-scale reinforcing resin composite with outstanding tribological performance.

Swift heavy ion induced effects on structural, optical and photo-catalytic properties of Ag irradiated vertically aligned ZnO nanorod arrays

Development of 1D array platforms for environmental remediation is of vitality in the current scenario where water bodies are overborne by organic pollutants. ZnO nanorod arrays (ZNRA) were synthesized using solution growth method and were irradiated by 120 MeV Ag ions at various ion fluences of 1E11, 5E11, 1E12 and 5E12 ions/cm2. The structural, morphological and optical properties were studied using X-ray diffraction (XRD), Field Emission Scanning Microscopy (FESEM), UV and Photoluminescence spectroscopy respectively. While the FESEM analysis shows that the length of ZNR is in the range of ∼4 μm and with a diameter ranging from 100 nm to 350 nm, the XRD results confirmed the formation of wurtzite hexagonal structure (0 0 2) of ZnO. The XRD peak broadened with the increase of Ag ion fluences from 1E11 to 5E12 ions/cm2. The UV absorption spectra show a red shift of the band edge absorption with increase in ion fluences and bandgap decreases from 3.24 eV to 2.94 eV. The photocatalytic activities of Ag irradiated ZNRA were evaluated through the degradation of methylene blue under the visible region of light irradiation. The degradation efficiencies for pristine and 5E12 ions/cm2 Ag irradiated ZNRA were 54.24% and 87.98% respectively for methylene blue after 120 min. These photocatalytic results show that the degradation efficiency increases with the Ag ion irradiations. The possible mechanism behind this enhancement due to the Ag ion irradiation is also discussed.