Optical Properties Of Zinc Oxide Nanorods Research Articles

ZnO Multilayer Thin Films as The Seed Layer for ZnO Nanorods: Morphology, Structural and Optical properties

The effect of zinc oxide (ZnO) multilayer thin film thicknesses, deposited via the sol-gel spin coating technique, on the morphology, structural and optical properties of ZnO nanorods (ZNR) grown on the ZnO thin films were explored in this investigation. The ZNR was grown using the chemical bath deposition method on the ZnO thin film seed layer (SL). We found that ZnO thin film SL morphology changes according to the number of layers based on the results. Eventually, these changes also influence the structures of ZNR. ZNR structures improved when the thickness of the seed layer increased. Besides the surface roughness, better crystalline quality films were obtained when more layers were deposited. This crystalline quality then influenced the optical characteristics of both ZnO and ZNR thin films. The optical properties from UV-Vis showed transmittance in the visible region, showing that the ZnO films produced were suitable to be applied to solar cells. ZNR-based solar cells have become one of the promising materials to be studied further due to the environment-friendly, low-cost, and well-abundant material for solar cell applications.

Optimization and characterization of SILAR synthesized ZnO nanorods for UV photodetector sensor

In the current research, zinc oxide (ZnO) nanorods (NRs) have been grown upon glass-slide substrates by employing the effective chemical bath deposition (CBD) method at low-temperature. ZnO seed-layer has been coated over the whole substrates by using very simplicity successive ionic-layer adsorption and reaction (SILAR) approach. The impact of the four different SILAR process cycle for ZnO seed-layer deposition on the characteristic of ZnO NRs have been investigated. The surface morphological, structural, optical properties of the produced ZnO NRs have been studied using several techniques for different SILAR process cycles. Also, the high-quality UV photodetector (PDs) based on ZnO NRs at different SILAR process cycles have been successfully fabricated by applying bias voltage in range of (-5 V to 5 V). The results indicated that the variation of SILAR process cycles have the large and significant impact on the morphological, structural, and optical properties of ZnO NRs. The average size and length of fabricated ZnO NRs were increased with increases the SILAR cycles in the range of 32−98 nm and 291−1210 nm, respectively. The large aspect ratio was noted for ZnO NRs formed at 15 SILAR cycles about 14.93. The growth rate and crystal size of ZnO NRs were increases with increases the SILAR cycles in the range of 1.161–6.722 nm/min and 28.9–94.24 nm/min, respectively. All the samples display a dominant peak at wavenumber of 436.5 cm−1 which is attributed to the E2 active mode and characteristic of the hexagonal phase of ZnO NRs. The energy gap of ZnO NRs was decreased from 3.25 eV to 3.23 eV as the SILAR cycles increases from 5 cycles to 20 cycles. The overall ultraviolet (UV) emission peak centered at 380 nm is found to correlate to near-band emissions (NBE). The ZnO NRs based UV-detector displays repeatable characteristics with a peak photoresponse of 116.6 μA. The UV-sensor based ZnO NRs grown at 15 SILAR process cycles at 5 V bias voltage shows optimal performance responsivity, high photosensitivity, low dark current, quick rise and recovery times were 0.5477 A/W, 3573.57 %, 3.1743 μA, 1.04259 s, and 0.3046 s, respectively.

The effect of different substrate-inclined angles on the characteristic properties of ZnO nanorods for UV photodetectors applications

The effect of six different substrate-inclined angle with the vessel on the characteristics properties of the Zinc Oxide (ZnO) nanorods was explored and reported. The vertically well-aligned ZnO Nanorods (NRs) were synthesized on glass substrates by using the low-cost chemical bath deposition (CBD) method at 90 °C. The RF magnetron sputtering has been employed to deposit the ZnO nanoseed layer on glass substrates and electrodes for UV photodetectors (PDs) devices. The morphological, structural, and optical properties of the synthesized ZnO NRs have been investigated using various characterization techniques for different substrate- inclined angles. Also, the high-quality UV photodetector-based ZnO NRs have been fabricated for the optimum substrate-inclined angle of 70° with the vessel by applying a different bias voltage. The results found that variation of substrate-inclined angles have the remarkable and significant effect on the shape, size, length, alignment, density distribution, structure, lattice parameters, crystalline size, energy band gap (Eg), and optical properties of ZnO NRs. The average diameters and length of grown ZnO NRs were in the range of (58–249) nm and (303–2518) nm, respectively. The high aspect ratio, length, and growth rate were observed for ZnO nanorods grown at 70° substrate-inclined angle. The preferred orientation of ZnO NRs was along (002) hexagonal wurtzite plane and the intensity of (002) diffraction peak for ZnO NRs was increased with increasing substrate-inclined angles. The average crystalline size was in range of (46.7–58.8) nm. The average transmittance of ZnO NRs showed a reduction in the range of (44.5–3.3)% as the substrate angle increased. The optical studies show that the synthesized ZnO NRs have the direct Eg in the range of (3.16–3.254) eV. The fabricated UV PD-based ZnO NRs showed high performance and quality. The different bias voltage study shows that the ZnO nanorod UV PD has higher stability and repeatability at 5 V bias voltage. The PDs device exhibited the responsivity value of 3.49903 A/W to 390 nm light wavelength at 5 V, which is higher than those reported for UV PDs-based ZnO NRs. At 5 V bias voltages, the fabricated UV PDs showed a faster response and recovery times of 0.3402 S and 0.1639 S, respectively.

Influence of concentration on the geometry of ZnO nanostructures prepared by chemical bath deposition

Zinc Oxide (ZnO) nanostructures such as nanorods (NRs), nanowalls (NWs) and nanoflakes (NFs) were successfully grown on a glass substrate via chemical bath deposition (CBD) method by varying solutions concentration (0.01 M, 0.05 M, 0.10 M, 0.15 M, 0.20 M and 0.25 M). Effect of CBD concentration on the growth and morphology of ZnO nanostructures are dignified. The structural and optical properties of ZnO NRs, NWs, and NFs were investigated by Field Emission Scanning Electron Microscope (FESEM), energy-dispersive X-ray (EDX), X-Ray Diffraction (XRD), and UV-Visible (UV-Vis) analyses. Results reveal that as the CBD concentration increases, FESEM images showed differ top-down morphology of ZnO nanostructures from NRs, NWs to NFs. Likewise, the alignment of ZnO cross-section evolved from randomly oriented to vertically oriented. As revealed by EDX, the stoichiometric ratio of Zn:O were mostly towards 1:1. From XRD analyses, the preferred structure was wurtzite hexagonal with c-axis orientation along (002) plane. The UV-Vis analysis exposed the optical band gap energy closes to the standard energy gap value of ZnO at 3.37 eV. Thus, this work introduces a variable geometry of ZnO nanostructures (NRs, NWs, and NFs) grown on glass with high structural and optical quality as standard ZnO. The fabricated materials are potential candidates for investigating random lasing in ZnO from different structural geometry.

ZnO Nanorods Prepared by Ultrasonic Spray Pyrolysis: Effect of Deposition Time on the Structural Morphological and Optical Properties

Zinc oxide Nanorods (ZnO-NRs) were deposited onto glass substrates using zinc chloride by Ultrasonic Spray Pyrolysis (USP) method. The films were prepared in different deposition time at optimum deposition parameters. The effect of deposition time on the structural, morphological and optical properties of ZnO-NRs was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectrometry (UV-Vis). XRD and SEM measurements indicated that all films show a hexagonal wurtzite Nano rods (NRs) structure growing preferentially along c-axis perpendicular to the surface of the substrate. Optical transmission spectra showed high transmittance of 80-85% in the visible range for all thin films, and increase of optical band gap from 3.24 to 3.265 eV with deposition time. The high quality c-axis orientated ZnO thin films with minimum strain and tuneable optical properties could be used as a transparent conducting oxide (TCO) for optoelectronic applications.

Morphology evolution and luminescence enhancement in hydrothermally synthesized Ag doped ZnO nanorods

Influence of silver doping has been investigated on structural, morphological and optical properties of zinc oxide (ZnO) nanorods. Ag-doped ZnO nanorods have been synthesized using hydrothermal method. X-ray powder diffraction results indicate that ZnO doped with Ag retains wurtzite structure and crystallite size is increased as estimated by Debye-Scherrer method. Scanning electron microscopy reveals nanorod-shaped structures of the samples. Incorporation of Ag has led to a marked morphological evolution with increased length and diameter of nanorods. UV–visible absorption spectra do not show any appreciable change in absorbance edge and the band gap of ZnO remains almost constant with Ag doping. Photoluminescence (PL) spectroscopy shows that the intensity of near band edge emission at 390 nm can be enhanced by Ag doping. Excellent enhancement of luminescence properties in the visible range is also observed in Ag-doped ZnO nanorods. CIE chromaticity diagram reveals the enhancement toward white zone. The origin of enhancement of PL emission is attributed to increase in number density of charge carriers and excitons. Present results demonstrate a profound effect of Ag doping on structural and optical properties of ZnO nanorods which may have good prospects in scientific and industrial applications.

Influence of Al, Ta Doped ZnO Seed Layer on the Structure, Morphology and Optical Properties of ZnO Nanorods

Background:Zinc oxide (ZnO) is one of the most attractive II-VI semiconductor oxide material, because of its direct wide band gap (3.37 eV) and large binding energy (60 meV). Zinc oxide (ZnO) is a promising semiconductor due to its optimised optical properties. Among semiconductor nanostructures, the vertically aligned one-dimensional ZnO nanorods are very important for nano device application.Methods:Vertically aligned ZnO nanorod arrays were grown on ZnO, aluminum doped ZnO (ZnO:Al), tantalum doped ZnO (ZnO:Ta) and aluminum and tantalum co-doped ZnO (ZnO:Al,Ta) seed layer by hydrothermal method.Results:The X-Ray Diffraction (XRD) investigation indicated the presence of hexagonal phase for the both seed layers and nanorods. The Scanning Electron Microscope (SEM) images of ZnO and doped ZnO seed layer thin-films show spherical shaped nanograins organized into wave like morphology. The optical absorption spectra revealed shift in absorption edge towards the shorter wavelength (blue shifted) for ZnO nanorods grown on ZnO:Al, ZnO:Ta and ZnO:Al,Ta seed layer compared to ZnO nanorods grown on ZnO seed layer.Conclusion:The increase in band gap value for the ZnO nanorods grown on doped ZnO seed layers due to the decrease in crystallite size and lattice constant as evidenced from XRD analysis. The unique property of Al, Ta doped ZnO can be used to fabricate nano-optoelectronic devices and photovoltaic devices, due to their improved optical properties.

Evaluation of anticorrosive behaviour of ZnO nanotetra-pods on a AZ91-grade Mg alloy

Highly cross-linked zinc oxide (ZnO) with the nanorod morphology of tetra-pods was successfully prepared using a microwave irradiation (MWI) technique. In comparison with the available conventional techniques, the MWI technique has the advantage of producing different morphological structures with high purity and in a shorter reaction time. These tetra-pods consist of a ZnO core in the zinc blende from which four ZnO arms emerge in the wurtzite structure. In this investigation, the effects of irradiation times and the growth mechanism of ZnO nanotetra-pods were discussed. The structural, morphological and optical properties of ZnO nanorods were investigated by field emission scanning electron microscopy, X-ray diffraction, an ultra violet visible spectrometry and energy-dispersive spectroscopy. The electrochemical corrosion behaviours of an AZ91-grade Mg alloy and a ZnO/PN nanotetra-pod-coated Mg alloy were investigated. The Tafel plot revealed that the corrosion of Mg drastically decreased on coating with a thin layer of ZnO nanotetra-pods and PN (Mg/PN/ZnO) compared to Mg in a KOH electrolyte.

Optical properties of ZnO nanorods derived from chemical bath deposition process with different seeds solution concentration

Owing to their high surface to volume ratio and fast electron transfer, zinc oxide (ZnO) nanorods have been well-known as potential nanostructured material for various applications including sensors, dye sensitized solar cells, optoelectronic, transparent heater and biomedical devices. Among other synthesizing techniques for obtaining ZnO nanorods, chemical bath deposition (CBD) has been thought as a simple and low-cost method. However, there are several processing parameters that need to be investigated for the above-mentioned applications where the highly optical transparency of thin film ZnO nanorods grown on glass substrates is one of important targets to be achieved. In this work, ZnO nanorods were synthesized through CBD process at low temperature (0°C) by using seed solution prepared by dissolving 1: 1 equimolar zinc nitrate tetrahydrate and hexamethylene tetraamine. For investigation purposes, three different concentration of seed solutions i.e. 0.005, 0.025 and 0.05 M were used. Thin films containing ZnO nanoseeds were formed by spin coating the precursors on the glass substrates, followed with annealing at 2000C for 5 minutes. Finally, the ZnO nanorods were further grown at 90ºC for 3 hours in the beaker glass using the same solution. Xray diffraction (XRD) analysis showed that all ZnO nanorods demonstrated a strong (002) peak belong to wurtzite phase. It was found that the estimated crystallite size and band gap energy (Eg) for ZnO nanorods derived from the seed solutions of 0.005, 0.025 and 0.05 M were 21.42, 137.11, 171.39 nm, and 3.60, 3.20, 3.18 eV, respectively. However, the optical transparency was adversely lowered from about 75 to 40 % as a result of increased coverage of ZnO nanorods on the glass substrate. For transparent heater application where, a desired combination of high optical transparency and suitable electronic properties is needed, the current results were considered to be promising.

Structural and optical properties of ZnO nanorods prepared by spray pyrolysis method

Zinc oxide (ZnO) nanorods (NRs) are encouraging constituents in a wide range of nanoscale apparatus for future applications in biochemical sensing, optical devices and solar cells. ZnO-NRs were prepared by the ultrasonic spray pyrolysis deposition (USP) method on glass substrate at 400 °C. The effect of seed layer morphologies on the structural, morphological, electrical and optical properties of ZnO-NRs was examined using X-ray diffraction (XRD), field emission electron microscopy (FE-SEM) and UV–Vis spectrometry (UV–Vis). The XRD patterns were indexed as a wurtzite structure. The FE-SEM images showed that the growth of ZnO-NRs was influenced by the crystallinity and physical properties of the underlying seed layer morphologies. Electrical conductivity measurements of the ZnO samples were carried out via the four probe dc system. The conductivity increases with applied temperature. The optical spectra of the ZnO samples were measured in the UV–Vis range and the band gap (Eg) was found to be approximately 3.25 eV for the ZnO-NRs samples.

Effects of precursor concentrations on the optical and morphological properties of ZnO nanorods on glass substrate for UV photodetector

In this study, zinc oxide (ZnO) nanorod arrays with various precursor concentrations (0.05, 0.10 and 0.15 M) were synthesized using a simple hydrothermal reaction on ZnO seeds/glass substrate and tested for UV-photodetector. The structural and optical properties of the ZnO nanorods have been investigated. The results demonstrate that morphology and crystallinity of ZnO nanorods influenced by the concentration of the precursor and had a high impact on the UV-photosensing. As the precursor concentration increased by 0.1 M, the density and the surface-to-volume ratio of ZnO nanorods decreased by 49 nanorods per μm2 and 22.9 respectively. At the lowest concentration of 0.05 M, the ZnO nanorods grew with high density of 85 nanorod per μm2 and high surface-to-volume ratio of 28.5. Moreover, a strong ultraviolet (UV) emission peak (λ = 375 nm) was observed with a low deep-level emission peak (λ = 580 nm), which indicated high optical property and crystallinity of the nanorods. The synthesized ZnO nanorods exhibited different sensing characteristics that correlated with the morphological and structure of ZnO nanorods formed at different concentrations. The sample grew with concentration of 0.05 M showed the highest photocurrent of 1.949 × 10−4 A and current gain of 562.1 under low power intensity UV illumination at λ = 375 nm with 5 V bias.

The effect of Cu dopant on morphological, structural and optical properties of ZnO nanorods grown on indium tin oxide substrate

Zinc oxide (ZnO) is a promising semiconductor due to its tunable optical properties. Among semiconductor nanostructures, one-dimensional structure such as ZnO nanorods becomes the main focus due to their wide potential application. Cu doped ZnO has attracted much attention recently because of its interesting properties, such as room temperature ferromagnetism, multiferroics properties and green emission. In this work, we deposited ZnO nanoseeds on indium tin oxide coated glass substrates and then ZnO nanorods were grown and doped with three different Cu concentrations (1, 4 and 7 at. %) by hydrothermal method. The scanning electron microscope showed that ZnO nanorod were grown with a hexagonal shape with diverse growth orientation. The X-ray diffraction analysis reveals that the addition of Cu doping tends to decrease the crystallite size and the lattice parameter. Generally, Cu doping reduces the absorbance at ultraviolet wavelength region except on the ZnO nanorods with 4% Cu. The addition of Cu also increases the bandgap energy and decreases the luminescence intensity in UV and visible regions, that is a sign that number of radiative transitions and the natural defects have been reduced.

Synthesis and Enhanced Photocatalytic Activity of Ce-Doped Zinc Oxide Nanorods by Hydrothermal Method

Zinc oxide (ZnO) is a n-type semiconductor material which has a wide direct band gap energy of ∼ 3.3 eV, and other interesting optical properties, hence it’s potentially applied to various fields such as electronics, optoelectronics, sensors, photonic devices, and also photocatalyst. Dopant in ZnO nanostructures is an effective way to improve ZnO’s structural properties in various applications. In this study, undoped and Ce doped ZnO nanorods were synthesized on ITO coated glass substrates by ultrasonic spray pyrolysis for seeding deposition and hydrothermal methods at a temperature of 95 0C for 2 hours for growth. X-ray diffraction, field emission scanning electron microscopy (FESEM), UV-VIS and Photoluminescence spectroscopy were used to characterize the crystal structure, surface morphology and optical properties of ZnO nanorods and the photocatalytic activity test for methylene blue degradation. The experimental results showed that 3% Cerium dopant has produced hexagonal morphology ZnO nanorod growing more uniform on (002) crystal planes, increased the intensity of ultraviolet absorbance thereby increase the degradation speed of methylene blue.

Self-assembled, aligned ZnO nanorod buffer layers for high-current-density, inverted organic photovoltaics.

Two different soft-chemical, self-assembly-based solution approaches are employed to grow zinc oxide (ZnO) nanorods with controlled texture. The methods used involve seeding and growth on a substrate. Nanorods with various aspect ratios (1-5) and diameters (15-65 nm) are grown. Obtaining highly oriented rods is determined by the way the substrate is mounted within the chemical bath. Furthermore, a preheat and centrifugation step is essential for the optimization of the growth solution. In the best samples, we obtain ZnO nanorods that are almost entirely oriented in the (002) direction; this is desirable since electron mobility of ZnO is highest along this crystallographic axis. When used as the buffer layer of inverted organic photovoltaics (I-OPVs), these one-dimensional (1D) nanostructures offer: (a) direct paths for charge transport and (b) high interfacial area for electron collection. The morphological, structural, and optical properties of ZnO nanorods are studied using scanning electron microscopy, X-ray diffraction, and ultraviolet-visible light (UV-vis) absorption spectroscopy. Furthermore, the surface chemical features of ZnO films are studied using X-ray photoelectron spectroscopy and contact angle measurements. Using as-grown ZnO, inverted OPVs are fabricated and characterized. For improving device performance, the ZnO nanorods are subjected to UV-ozone irradiation. UV-ozone treated ZnO nanorods show: (i) improvement in optical transmission, (ii) increased wetting of active organic components, and (iii) increased concentration of Zn-O surface bonds. These observations correlate well with improved device performance. The devices fabricated using these optimized buffer layers have an efficiency of ∼3.2% and a fill factor of 0.50; this is comparable to the best I-OPVs reported that use a P3HT-PCBM active layer.

Structural and optical properties of Cu-, Ag, and Al-doped zinc oxide nanorods

We investigated structural and optical properties of Cu-, Ag-, and Al-doped zinc oxide (ZnO) nanorods grown on ZnO seed layers. Cu-doped ZnO (ZnO:Cu) nanorods showed increased length and improved crystallinity, compared to undoped ZnO nanorods, where the average transmittance in the visible region is lower than that of ZnO nanorods. Meanwhile, the Ag incorporation led to quite opposite behaviors: decreased length and crystallinity of nanorods. It was also found that Ag-doped ZnO (ZnO:Ag) nanorods exhibited high transparency. The incorporation of Al dopant led to a marked morphological variation, with randomly oriented microrods grown on the surface of the ZnO seed layer, instead of nanorods. Al-doped ZnO (ZnO:Al) microrods exhibited excellent transparency over the visible region. The present results thus show that incorporation of Cu, Ag, and Al dopants has a critical effect on structural and optical properties of ZnO nanorods.

Fast synthesis, morphology transformation, structural and optical properties of ZnO nanorods grown by seed-free hydrothermal method

A fast and low cost seed-free hydrothermal synthesis method to synthesize zinc oxide (ZnO) nanorods with controllable morphology, size and structure has been developed. Ammonia is used to react with water to tailor the ammonium hydroxide concentration, which provides a continuous source of OH− for hydrolysis and precipitation of the final products. Hence, allowing ZnO nanorods to growth on large areas of metal (Au and Ag coated glass), p-type Si and organic flexible (PEDOT: PSS) substrates. Increasing the growth time, the morphology transforms from pencil-like to hexagonal shape rod-like morphology. Within one hour the length of the ZnO nanorods has reached almost 1 µm. The optical characteristics has shown that the grown ZnO nanorods are dominated by two emission peaks, one is in the UV range centered at 381 nm and other one with relatively high intensity appears in the visible range and centered at 630 nm. While the growth duration was increased from 2 h to 6 h, the optical band gap was observed to increase from 2.8 eV to 3.24 eV, respectively. This fast and low cost method is suitable for LEDs, UV-photodetector, sensing, photocatalytic, multifunctional devices and other optoelectronic devices, which can be fabricated on any substrates, including flexible and foldable substrates.

Processing temperature dependent morphological and optical properties of ZnO nanorods

Zinc Oxide (ZnO) nanorods were synthesized by thermal decomposition of zinc acetate dihydrate at various processing temperatures. The morphology of samples, examined using transmission electron microscopy and field emission scanning electron microscopy, revealed large variations in length and diameter of nanorods. As temperature was increased from 300°C to 450°C, ZnO nanocrystal morphology changed from wire-like to rod-like. This morphology change is a result of competition between nucleation and growth rate in the vapor–solid growth mechanism of nanorods. Photoluminescence spectrum of the nanorods showed both band edge emission as well as native defect related visible emission. Relative intensity of UV and visible emission indicated crystal quality of the nanorods, the ratio increased upto 400°C and deteriorated at higher processing temperature. It is argued that process induced defects dominate at processing temperatures ≤400°C, whereas equilibrium concentration of native defects is high at temperatures >400°C.

Self-assembled monolayer assisted fabrication of zinc oxide nanorods

In this study, self-assembled monolayers (SAMs) with different tail groups were employed to control the surface property of zinc oxide (ZnO) coated indium tin oxide substrates for the fabrication of ZnO nanorods. By modulating the tail group of the SAM molecule and the growth time of SAM, the thickness, diameter, morphology, and optical properties of ZnO nanorods can be controlled effectively. X-ray diffraction patterns confirmed that high quality crystals with preferential orientation along the (002) plane of the ZnO nanorods can be fabricated by utilizing proper SAM with the growth temperature of 60 °C and the growth time of 7 h. Such ZnO nanorods were reported as potential candidates for hybrid polymer solar cells.

A study on morphology control and optical properties of ZnO nanorods synthesized by microwave heating

In this study, we present morphology control investigations on zinc oxide (ZnO) nanorods synthesized by microwave heating of a mixture of zinc nitrate hexahydrate and hexamethylenetetramine (HMTA) precursors in deionized water (DI water). To study the morphology and structural variations of the obtained ZnO nanorods in different molar ratio of zinc nitrate hexahydrate to HMTA, X-ray diffraction (XRD), scanning electron microscopy (SEM) images, Raman scattering, and photoluminescence (PL) spectroscopy were measured. XRD and SEM images are utilized to examine the crystalline quality as well as the morphological properties of the ZnO nanorods. It is found that morphology control can be achieved by simply adjusting the reactant concentrations and the molar ratio of zinc nitrate hexahydrate to HMTA. Raman scattering and PL spectroscopy measurements were demonstrated to study the size- and shape-dependent optical response of the ZnO nanorods. The Raman scattering result shows that the intensity of LO mode at around 576 cm −1 decreases with the increase in the molar ratio of zinc nitrate hexahydrate to HMTA, indicating the reduction of defect concentrations in the synthesized ZnO nanorods. Room temperature PL spectrum of the synthesized ZnO nanorods reveals an ultraviolet (UV) emission peak and a broad visible emission. An enhancement of UV emission appears in the PL spectra as the molar ratio of zinc nitrate hexahydrate to HMTA increases, indicating that the defect concentration of the synthesized ZnO nanorods can be reduced by increasing the molar ratio.

Effects of growth duration on the structural and optical properties of ZnO nanorods grown on seed-layer ZnO/polyethylene terephthalate substrates

Well-aligned single crystalline zinc oxide (ZnO) nanorods were successfully grown, by hydrothermal synthesis at a low temperature, on flexible polyethylene terephthalate (PET) substrates with a seed layer. Photoluminescence (PL), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) measurements were used to analyze the optical and structural properties of ZnO nanorods grown for various durations from 0.5 h to 10 h. Regular and well-aligned ZnO nanorods with diameters ranging from 62 nm to 127 nm and lengths from 0.3 μm to 1.65 μm were formed after almost 5 h of growth. The growth rate of ZnO grown on PET substrates is lower than that grown on Si (1 0 0) substrates. Enlarged TEM images show that the tips of the ZnO nanorods grown for 6 h have a round shape, whereas the tips grown for 10 h are sharpened. The crystal properties of ZnO nanorods can be tuned by using the growth duration as a growth condition. The XRD and PL results indicate that the structural and optical properties of the ZnO nanorods are most improved after 5 h and 6 h of growth, respectively.