Grown Zinc Oxide Nanostructures Research Articles

The Influence of Varying Ar/O2 Gas Ratio with Catalyst-Free Growth by Homemade Thermal Evaporation Technique

A nanostructured zinc oxide (ZnO) with different percentages of argon and oxygen gas flow rate was deposited on a silicon wafer by a simple hot tube thermal evaporation technique. The effect of different percentages of gas flow rate on the crystal structure, surface morphology and optical properties were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and RAMAN spectroscopy, respectively. The changes of morphologies from FESEM were significant where the grown ZnO nanostructures show three different shapes which are nanotripods, nanoclusters and nanorods at 5%, 10% and 25% of oxygen gas, respectively. EDX results revealed that Zn and O elements have a major percentage in the sample indicating a composition has high purity of ZnO. XRD patterns displayed the most intense diffraction peak of ZnO at (101), which exhibited a single crystalline hexagonal structure with preferred growth orientation in the c-axis. RAMAN scattering study found that synthesized ZnO shows the high intensity of E2 mode and low intensity of E1 mode attributed to all the samples having good crystal quality containing fewer structural defects. In conclusion, the E15 sample with a 25% oxygen gas flow rate was selected as an optimum result for synthesizing a homogenous surface and high crystallinity of ZnO by using a hot tube thermal evaporation process. This work can enhance the development of ZnO production in various applications.

Deep-Level Emission Tailoring in ZnO Nanostructures Grown via Hydrothermal Synthesis

Zinc oxide (ZnO) nanostructures are widely used in various fields of science and technology due to their properties and ease of fabrication. To achieve the desired characteristics for subsequent device application, it is necessary to develop growth methods allowing for control over the nanostructures' morphology and crystallinity governing their optical and electronic properties. In this work, we grow ZnO nanostructures via hydrothermal synthesis using surfactants that significantly affect the growth kinetics. Nanostructures with geometry from nanowires to hexapods are obtained and studied with photoluminescence (PL) spectroscopy. Analysis of the photoluminescence spectra demonstrates pronounced exciton on a neutral donor UV emission in all of the samples. Changing the growth medium chemical composition affects the emission characteristics sufficiently. Apart the UV emission, nanostructures synthesized without the surfactants demonstrate deep-level emission in the visible range with a peak near 620 nm. Structures synthesized with the use of sodium citrate exhibit emission peak near 520 nm, and those with polyethylenimine do not exhibit the deep-level emission. Thus, we demonstrate the correlation between the hydrothermal growth conditions and the obtained ZnO nanostructures' optical properties, opening up new possibilities for their precise control and application in nanophotonics, UV-Vis and white light sources.

Hydrothermally Grown ZnO Nanostructures for Water Purification via Photocatalysis

Semiconductor-based photocatalysis is a well-known and efficient process for achieving water depollution with very limited rejects in the environment. Zinc oxide (ZnO), as a wide-bandgap metallic oxide, is an excellent photocatalyst, able to mineralize a large scale of organic pollutants in water, under UV irradiation, that can be enlarged to visible range by doping nontoxic elements such as Ag and Fe. With high surface/volume ratio, the ZnO nanostructures have been shown to be prominent photocatalyst candidates with enhanced photocatalytic efficiency, owing to their being low-cost, non-toxic, and able to be produced with easy and controllable synthesis. Thus, ZnO nanostructures-based photocatalysis can be considered as an eco-friendly and sustainable process. This paper presents the photocatalytic activity of ZnO nanostructures (NSs) grown on different substrates. The photocatalysis has been carried out both under classic mode and microfluidic mode. All tests show the notable photocatalytic efficiency of ZnO NSs with remarkable results obtained from a ZnO-NSs-integrated microfluidic reactor, which exhibited an important enhancement of photocatalytic activity by drastically reducing the photodegradation time. UV-visible spectrometry and high-performance liquid chromatography, coupled with mass spectrometry (HPLC-MS), are simultaneously used to follow real-time information, revealing both the photodegradation efficiency and the degradation mechanism of the organic dye methylene blue.

Fabrication of vibration sensors using precursor molar concentration varied ZnO nanostructures grown by refresh hydrothermal method

PurposeVarious approaches have been made to alter the vibration sensing properties of zinc oxide (ZnO) films to achieve high sensitivity. This paper aims to report the experimental study of the fabrication of precursor molar ratio concentration varied ZnO nanostructures grown on rigid substrates using the refresh hydrothermal method. The effect of these fabricated ZnO nanostructures-based vibration sensors was experimentally investigated using a vibration sensing setup.Design/methodology/approachZnO nanostructures have been grown using low temperature assisted refresh hydrothermal method with different precursor molar concentrations 0.025 M (R1), 0.075 M (R2) and 0.125 M (R3). Poly 3,4-ethylenedioxythiophene polystyrene sulfonate, a p-type material is spun coated on the grown ZnO nanostructures. Structural analysis reveals the increased intensity of the (002) plane and better c-axis orientation of the R2 and R3 sample comparatively. Morphological examination shows the changes in the grown nanostructures upon increasing the precursor molar concentration. The optical band gap value decreases from 3.11 eV to 3.08 eV as the precursor molar concentration is increased. Photoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was obtained from Nyquist analysis for R2 compared with the other two fabricated samples. Vibration testing experimentation showed an improved output voltage of the R2 sample (2.61 V at 9 Hz resonant frequency and 2.90 V for 1 g acceleration) comparatively. This also gave an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.FindingsPhotoconductivity study confirms the formation of a p-n junction with less turn-on voltage for all the fabricated devices. A less internal resistance of 0.37 kΩ was calculated from the Nyquist plot. Vibration testing experimentation proves an increased sensitivity of 4.68 V/g confirming its better performance when compared to the other fabricated two samples.Originality/valueVibration testing experimentation proves an increased sensitivity of 4.68 V/g for R2 confirming its better performance when compared to the other fabricated two samples.

Effective photocatalytic dye degradation using low temperature grown zinc oxide nanostructures

The present work reports on the synthesis of highly dense zinc oxide (ZnO) nanochips via the hydrothermal process and checks their photocatalytic activity on the way to the degradation of crystal violet (Cv) dye. The synthesized materials possessed the chips like morphology having the average thickness of 20 nm with typical wurtzite hexagonal structure. The structure and composition of synthesized materials were analyzed by UV/VIS, EDX, XPS, and Raman spectroscopy. The synthesized ZnO-nanochips were used as photocatalyst in photodegradation process of Cv-dye under illumination of light and presented a rapid degradation of Cv-dye.

Modulation of secondary phases in hydrothermally grown zinc oxide nanostructures by varying the Cu dopant concentration for enhanced thermo power

In this study, we have successfully controlled the number of secondary phases in Zinc Oxide (ZnO) nano-structures by changing the concentration of Copper (Cu) atoms. Zinc Copper Oxide (Zn1-xCuxO) nanostructures with x = 0.1, 0.2, 0.3, 0.4 and 0.5 were grown by hydrothermal technique. The increased number of secondary phases with Cu concentration were resulted in the enhancement of Seebeck coefficient (72–124 μV/°C) and power factor (2.3 × 10−4 Wm−1K−2). The secondary phases are served as barrier therefore, filtered the low energy carriers at the interface of two secondary phases which resulted in the enhancement of Seebeck coefficient and electrical conductivity simultaneously. The emergence of secondary phases with Cu concentration was confirmed with the help supplementary measurements. X-Ray Diffraction (XRD) data is confirmed the formation of the wurtzite structure of ZnO along with the presence of Copper Oxide (CuO) based secondary phases. Furthermore, the intensity of secondary phases related XRD peaks were found to be increased with the increase of Cu concentration. Raman spectroscopy data was suggested that the intensity of E2 high mode was decreased due to the development of a number of secondary phases with Cu concentration. Scanning electron microscope images are shown the formation of hexagonal shaped nano structures. Fourier Transform Infrared Spectroscopy (FTIR) data was used to further confirm the presence of secondary phases in the grown Zinc Copper Oxide (ZCO) samples at higher concentration of Cu atoms.

Nondestructive growing nano-ZnO on aramid fibers to improve UV resistance and enhance interfacial strength in composites

It is a great challenge in various applications to improve the resistances of aramid fibers (AFs) to harsh environments and enhance the interfacial bonding strength in composites along with maintaining the excellent mechanical properties. Herein, a simple nondestructive method was developed to prepare modified AF with zinc oxide (ZnO) micro-nano structures. Assisted by the adhesion and secondary functionalization of poly L-3,4-dihydroxyphenylalanine (PDOPA), ZnO nanoparticles (NPs) were successfully “seeded” onto the AF surface, and subsequently ZnO nanowires (NWs) were grown on the seed layer. As a result, the surface modification did not cause the significant changes of the tensile strength, and the surface roughness and UV resistance of the modified fibers were significantly improved. After 168 h of UV exposure, the retention of the tensile strength for the modified fiber was as high as 97.2%. Comparing with the pristine AF-reinforced composite, the interfacial shear strengths of AF-PDOPA-ZnO NP/epoxy resin and AF-PDOPA-ZnO NW/epoxy resin composites increased by 31.8% and 37.8%, respectively. Therefore, this effectively nondestructive modification method to grow ZnO nanostructures on a polymer substrate exhibits an extensive application prospect for organic fibers and their composites.

Growth of ZnO nanorods on different substrates using hydrothermal method

Zinc oxide (ZnO) nanorods have been grown on different substrates, i.e. gold film-coated BK-7 glass (Au-film/BK7), microscope glass slide (MGS), silicon oxide film-coated silicon (SiO2-film/Si), to investigate the effects of different substrates on its material properties. The growth process was started by dipping substrates in zinc acetate solution to fabricate a seed layer, followed by growing the ZnO nanorods in zinc nitrate tetrahydrate solution based on hydrothermal method at 95 °C for 6 hour. In this process, seed layer and ZnO nanorods were annealed at 350 °C for 2 hours. The characterization results using X-ray diffraction and field effect scanning electron microscope showed that ZnO nanorods were successfully grown homogenously and mostly in vertical direction with hexagonal wurtzite structure. The diameter size of ZnO nanorods was significantly influenced by the type of material substrate. ZnO nanorods on Au-film/BK-7 glass have the smallest diameter size of (239±51) nm, while the average diameter size of ZnO nanorods on MGS is of (269±53) nm and ZnO nanorods on SiO2-film/Si have the largest diameter size of (354±80) nm. The effect of substrates on different size of ZnO nanorods may be regarded to the intrinsic thermal conductivity of substrate material. Hence, the synthesis and growth parameters for the different substrates differ from each other and need to be optimized in order to grow ZnO nanostructures

Surface Passivated Zinc Oxide (ZnO) Nanorods by Atomic Layer Deposition of Ultrathin ZnO Layers for Energy Device Applications

Chemically stoichiometric and electrically low-resistive high-quality zinc oxide (ZnO) nanostructures have been developed by surface passivation with atomic layer deposited ZnO layers. The impacts of homogeneous ZnO layer growth and its thickness on the physical properties ZnO nanorods were investigated. Vertically aligned ZnO nanorod structures were synthesized by two-step process, and the surface passivation was performed by atomic layer deposition ZnO at low temperatures. Surface passivated ZnO nanorods exhibit excellent improvement in crystallinity, chemical stoichiometry, optical, and electrical properties. Further, the surface passivated structures show significant enhancement in water-oxidation performance (nearly 3 orders of magnitude, i.e., μA → mA) with greatly reduced overpotentials. These investigations emphasize that surface passivation of hydrothermally grown ZnO nanostructures with the homogeneous materials can significantly enhance the structural and optical quality along with their device...

Dimensional tailoring of hydrothermally grown zinc oxide nanostructures in a continuous flow micro reactor.

Dynamic deposition of ZnO nanostructures with varying morphologies (nanorods, nanocones, nanopencils, nanosheets, etc.), diameters, lengths and aerial densities on ITO-PET substrates has been achieved using a continuous flow microreactor in which we maintained a homeostatic zinc concentration and varied the other reactants' concentrations.

Influence of pH on hydrothermally derived ZnO nanostructures

Zinc oxide (ZnO) nanostructures with numerous morphology was prepared by using hydrothermal method. The effect of pH on structural, optical and photocatalytic activity of ZnO was investigated systematically. The prepared ZnO samples were characterized by various characterization techniques. The X-ray diffraction study revealed that the crystalline hexagonal phase of ZnO nanostructures was observed. Scanning electron microscopic observations revealed that the variation of pH significantly alters the morphology of the grown ZnO nanostructures. The UV–vis spectrum shows an optical bandgap was not significantly influenced by pH of reactant solution. Photoluminescence studies at room temperature for different pH values revealed a weak band edge emission altogether with strong defect-related visible emission peaks. Photocatalytic activity of methylene blue (MB) under visible light illumination was studied. Maximum degradation of 99% was observed in 100 min for ZnO nanostructure prepared at pH 11.

(Invited) Tailoring Zinc Oxide Nanorod-Arrays for Photo-(electro)Chemical Applications

As one of the most studied metal-oxides Zinc Oxide (ZnO) already found its way into many industrial applications. Nevertheless enormous research interest is drawn to this earth-abundant, environmentally-friendly material as it offers interesting material properties such as a high exciton binding energy, a direct bandgap and comparably high charge carrier mobility.1 Furthermore the ability to grow ZnO nanostructures using a wide range of deposition techniques offers new perspectives for the material to be used in opto-electronics.2 Low-temperature solution based methods are of particular interest as possible routes to the low-cost growth of high surface-area nanostructures for the integration of ZnO into novel energy production and storage devices.3 The steadily growing research areas of solar water splitting and photo-catalysis are prominent examples of areas where interest in ZnO-based materials and devices may be found.4-6 For these applications the semiconductor/electrolyte interface plays a crucial role. It is of the highest importance to carefully engineer the materials properties in order ensure effective charge carrier transport across the interface. In turn it must be the goal of materials research to tailor the ZnO towards these target applications, where possible addressing the key issues of short timescale charge carrier recombination over intrinsic defects, low-visible light absorption and photo-corrosion. This paper describes strategies for the minimisation of the undesirable influences associated with these issues for ZnO nanorod-arrays grown from solution. Firstly it is demonstrated that careful defect-engineering can be used to increase the probability to run photo-(electro)chemical reactions. Here, the specific focus is directed towards orange-luminescent defect-centres. Linear sweep voltammetry in neutral electrolyte solution reveals that ZnO nanorod-arrays exhibiting strong orange emission show a defect-promoted increase in photo-current of ca. 200 % under simulated sunlight as compared to as-grown nanorod-arrays. As the large bandgap energy of ZnO, some 3.3 eV (< 380 nm), considerably limits the absorption of sunlight a doping strategy is applied in order to shift the materials absorption into the visible region. It is demonstrated that this may be achieved by the incorporation of significant amounts of cobalt into the ZnO host lattice using a newly developed low-temperature solution-based growth method. It is shown that the visible-light absorption of the resulting material, which consists of ZnO:Co nanorod-arrays directly deposited onto seed-layer coated glass substrates, extends up to 700 nm by controlling the cobalt concentration in the growth solution. Lastly, we address the issue of photocorrosion of ZnO-based photo-electrodes. Previously various attempts have been made to enhance the material`s chemical stability. Over-coating of ZnO with thin layers of e.g. C3N4 or TiO2 using different deposition techniques are among the most applied strategies.7-9 In order to produce effective and stable chemical barriers pin-hole free layers are essential. atomic layer deposition (ALD) offers the advantage of controlled and nominally pin-hole free deposition of ultrathin barrier layers even onto 3D-geometries, thus, making it potentially a powerful technique for the chemical stabilisation of ZnO nanostructures for photo-(electro)chemical applications. In this study the ZnO nanorod-arrays are over-coated with ultrathin ALD TiO2 layers. It is presented that TiO2 shells are able to chemically protect the ZnO core in acidic media. However, it was found that for some samples the TiO2 barriers are not complete – especially at the rod tips - leading to a considerably lower etch rate as compared to uncoated nanorod-arrays. Photo-electrochemically the core-shell structures show a photo-current stabilisation for several hours. Nevertheless the initial photo-current is lower when compared to uncoated nanorod-arrays indicating a higher charge transfer resistance for the ZnO-TiO2/electrolyte interface. Acknowledgements: This work was funded by Science Foundation Ireland, US: Ireland Grant RENEW- Research into Emerging Nanostructured Electrodes for the Splitting of Water, number 13/US/I2543. 1. H. Morkoç and Ü. Özgür, in Zinc Oxide - Fundamentals, Materials and Device Technology, Wiley-VCH Verlag GmbH & Co. KGaA, 2009, pp. 131-244. 2. A. B. Djurišić et al., Progress in Quantum Electronics, 2010, 34, 191-259. 3. P. S. Xu et al., Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003, 199, 286-290. 4. Y. Lu et al., Nano Research, 2011, 4, 1144-1152. 5. Y. Mao et al., Nano Energy, 2014, 6, 10-18. 6. L. Cai et al., International Journal of Hydrogen Energy, 2015, 40, 1394-1401. 7. R. T. Sapkal et al., Journal of photochemistry and photobiology. B, Biology, 2012, 110, 15-21. 8. Y. Wang et al., Energy & Environmental Science, 2011, 4, 2922. 9. M. Liu et al., The Journal of Physical Chemistry C, 2013, 117, 13396-13402.

Improving the mechanical properties of p‐aramid fabrics and composites by developing ZnO nanostructures

Zinc oxide (ZnO) nanostructures have been grown on p‐aramid (Kevlar) fabric to improve interfacial properties of reinforced composites. Whiskerization technique was adopted to develop ZnO nanostructures, like an array of whiskers, on the surface of Kevlar fabric. Hydrothermal process was used which involves three steps i.e. functionalization, seed layer formation and growth of nanorods. Hexamethylenetetramine and zinc nitrate were used to grow ZnO nanostructures. It was found that pressure controlled autoclave was the best method for generation of nanostructures. It was also observed that the material (fabric) to solution ratio (M:S) significantly affected the morphology and density of developed nanostructures. Incorporation of ZnO nanostructures on Kevlar fabric improved the tensile and impact properties of Kevlar fabric and its composites. The deposition of nanostructures improved the interfacial properties by causing fibers to interlock with matrix thus allowing the formation of a graded interface between the two phases. POLYM. COMPOS., 39:3300–3306, 2018. © 2017 Society of Plastics Engineers

Electrochemical nanostructured ZnO biosensor for ultrasensitive detection of cardiac troponin-T.

Vertically oriented zinc oxide nanostructures based disposable diagnostic biosensor for detecting and quantifying levels of cardiac troponin-T from human serum has been developed. The biosensors were designed by integrating hydrothermally grown zinc oxide nanostructures on glass and printed circuit board platforms, resulting in the generation of high-density nanostructure arrays with nanotextured zinc oxide based electrodes. The size, density and surface terminations of the nanostructures were leveraged toward achieving surface confinement of the target cTnT molecules on to the nanostructures. A combination of AC and DC spectroscopy was used to characterize the biosensor response to cTnT. LOD of 0.1 pg/ml in human serum was achieved.

Effect of Addition of KI on the Hydrothermal Growth of ZnO Nanostructures Towards Hybrid Optoelectronic Device Applications.

We report the structural and optoelectronic properties of Zinc oxide (ZnO) nanostructures prepared by hydrothermal method. The morphological, structural and optical properties of the grown ZnO nanostructures were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectroscopy (PL) respectively. Upon addition of relatively small amount of KI during the in-situ hydrothermal growth the nanorods were formed, further increasing the concentration led to increased diameter of these nanorods and finally at relatively higher concentration of KI, ZnO nanosheets were formed. Later these structures were used to fabricate bi-layer ZnO/P3HT based hybrid photodiode. Subsequent hybrid photodiode measurement with ZnO nanorods and ZnO nanosheets indicated that the nanosheets exhibited improved photodiode response. Compared to the ZnO nanorod/P3HT devices, the optimized photodiode with the dense ZnO nanosheets/P3HT have shown significant increase in the rectification ratio and the photosenstivity from 3.21 to 1420 and from 5.85 to 1330 respectively. The enhanced photodiode response of bi-layered devices consisting of ZnO nanosheets indicated that optimizing the shape and size of ZnO nanostructures had a significant influence on the overall photocurrent and the observed results have been explained on the basis of reduction in the defect density with pronounced absorption in the UV region, thus leading to improved transmission of light in the visible range through these layers.

Growth of Nanostructured ZnO Nanosheet on ITO/PET Substrate Prepared via Sol Gel Spin Coating and Hot Water Treatment

Zinc Oxide (ZnO) is well known for its wide band gap semiconductor with large excitation energy that serves various application. These unique characteristics had gained much research attention on ZnO nanostructure synthesis and physical properties. In this study, ZnO thin films were deposited on ITO/PET substrate by a spin coating sol-gel process. The starting solution were prepare by dissolved zinc acetate dehydrate (ZnAc) and diethanolamine (DEA) in water (H2O) and 2-propanol (2-PrOH). Acid Citric (C6H8O7) from 0.2 to 1.0 M were dropped into 100 ml sol-gel solution to study effect of sol-gel environment condition. ZnO thin films were obtained after pre-heating the spin coated thin films at 100 °C for 5 minutes after each coating. The coated substrates were undergone for Hot Water Treatment (HWT) process at 90 °C for 6 hours to grow ZnO nanostructures. The effects of sol-gel environment condition by drop different concentrations of C6H8O7 into the solution were studied. Nanoflakes ZnO were obtained after hot water and hydrothermal treated at 90 °C for 6 hours with 0.2 till 1.0 concentration of C6H8O7 dropped directly in the sol-gel solution. On the basis of the changes in morphology and microstructure induced by hot water treatment, it is concluded that the nanosheets were highly transparent with the visible range (350 – 800 nm) with 70%-90% of Transmittance spectra. Growth of ZnO nanosheet influenced by increment of C6H8O7 mol concentration also with value of roughness RMS.

Effect of ZnO Seed Layer with Various Concentrations of Precursor on the Growth of ZnO Nanostructures

In this work, Zinc oxide (ZnO) thin films were deposited on silicon and glass substrates using spin-coating method with different concentrations of precursor (zinc acetate dihydrate) and stabilizer (monoethanolamine). The concentrations of zinc acetate dihydrate and monoethanolamine in isopropanol were varied from 6 mM to 500 mM. Subsequently, the substrate with ZnO thin film as a seed layer was used to grow ZnO nanostructures by hydrothermal process with the same concentration of precursor (zinc nitrate hexahydrate), temperature, and time for each growth. The samples were characterized by field-emission scanning electron microscopy (FESEM), X-rays diffractometer (XRD), and UV-visible spectrophotometer (UV-vis) to study morphology, crystallographic structure, and optical property, respectively. The results showed that particle size, crystallinity, and transmittance of seed layers were changed with increasing concentrations of spin-coated precursor. Furthermore, the nanostructures were found that higher precursor concentration of seed layers affected the formation of ZnO nanorods to be nanosheets.

Studies on Effect of Zinc Oxide (ZnO) Nanostructures Morphology by Modification of Sol-Gel Solution

Zinc Oxide (ZnO) known as wide band gap semiconductor with large excitation energy 60 meV, noncentral symmetry, piezoelectric and biocompatible for biomedical application are the unique characteristic that attract many researcher’s attention on ZnO nanostructure synthesis and physical properties. ZnO thin films were deposited on Si Glass substrate by a sol-gel process. The starting solution were prepare by dissolved zinc acetate dehydrate (ZnAc) and diethanolamine (DEA) in water (H2O) and 2-propanol (2-PrOH). 0 to 60 drops of NaOH were dropped into 100 ml sol-gel solution to study effect of sol-gel modification. ZnO thin films were obtained after preheating the spin coated thin films at 100 °C for 10 minutes after each coating. The coated substrates were undergone for Hot Water Treatment (HWT) process at 90 °C for 6 hours to grow ZnO nanostructures. The effects of sol-gel modification by drop of NaOH into the solution were studied. ZnO nanorods and nanoflakes were obtained after hot water treated at 90 °C for 6 hours with different amount of NaOH dropped directly in the sol-gel solution. On the basis of the changes in morphology and microstructure induced by hot water treatment, it is concluded that the amount of NaOH dropped into sol-gel effected morphology of ZnO growth.

Effect of Metal Catalysts Type and Annealing Time on the Growth of Zinc Oxide Nanostructures by Thermal Vapor Deposition Method

This paper reports the results of zinc oxide (ZnO) nanostructure growth on different types of metal catalysts, namely gold and platinum, and also the effect of annealing time of the metal catalysts prior to the deposition of ZnO nanostructures. The metal catalysts layers with 15 nm thickness were deposited on glass substrates by sputter coater and then annealed in air ambient for 15 and 30 min at 500 °C. ZnO nanostructure was then deposited on the metal catalysts by thermal chemical vapour deposition (TCVD) method. We found that the Au catalyst morphologies varied with the annealing time, and the growth morphology of the ZnO followed the morphology of the Au catalyst. The morphology of the metal catalysts and ZnO nanostructures were characterized using field emission scanning electron microscopy (FESEM). The grown ZnO nanostructures were tested for their ability for extended gate field effect transistor (EGFET) sensor application. The samples were attached to the gate of an NFET and were dipped in acid and alkali buffer solutions while the gate voltage was measured. We found that the extended gate gave different voltage in buffer solutions with different pH which indicated that the samples can act as the extended gate of an EGFET sensor.

Structural, optical and ferroelectric behavior of hydrothermally grown ZnO nanostructures

In the present study, zinc oxide (ZnO) nanostructures have been synthesized at 100°C for different aging periods, 1, 24, 48 and 96h by hydrothermal method. Structural, optical and ferroelectric properties were investigated using X-ray diffractometer, field emission scanning electron microscope, Transmission electron microscope, photoluminescence, UV–visible, Raman spectroscopy and P–E loop tracer. The X-ray diffractometer pattern indicates the pure phase formation of ZnO without any impurity for the samples synthesized from 1 to 96h aging periods, respectively. Field emission scanning electron microscope and transmission electron microscope analysis also shows that the average diameter and length of these nanorods increases with increasing the aging periods. Moreover Raman and Photoluminescence spectrum also confirm the wurtzite phase formation of ZnO. The optical band gaps calculated through UV–visible spectroscopy are found to decrease from 3.81 to 3.45eV with increase in aging periods, 1–96h, respectively. Further, improved ferroelectric behavior has been observed for 48 and 96h aged samples.