Dimensional ZnO Nanostructures Research Articles

Solvent assisted evolution and growth mechanism of zero to three dimensional ZnO nanostructures for dye sensitized solar cell applications

We report the structural engineering of ZnO nanostructures by a consistent solution method using distinct solvents such as ethylene glycol, 1-butanol, acetic acid and water. The growth kinetics are found to depend strongly on the physicochemical properties of the solvent and zeta potential of the colloidal solution. Furthermore, the resulting nanostructures as a photoanode material, displayed a prominent structure dependent property in determining the efficiency of dye-sensitized solar cells (DSSCs). The fabricated solar cell with ZnO nanostructures based photoanode exhibited improved conversion efficiency. Moreover, the nanoflower based DSSCs showed a higher conversion efficiency of 4.1% compared to the other structures. The excellent performance of ZnO nanoflower is attributed to its better light-harvesting ability and increased resistance to charge-recombination. Therefore ZnO nanostructures can be a promising alternative for TiO2 in DSSCs. These findings provide new insight into the simple, low cost and consistent synthetic strategies for ZnO nanostructures and its outstanding performance as a photoanode material in DSSCs.

Boosting of Power Conversion Efficiency of 2D ZnO Nanostructures-Based DSSC by the Lorentz Force with Chitosan Polymer Electrolyte

Power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) fabricated from titanium tetra-isopropoxide (TTIP) treated Li doped two dimensional (2D) ZnO nanostructures based photoelectrode with chitosan polymer electrolyte is reported here. The defect induced room temperature ferromagnetism (RTFM) is observed and has been established from the bound magnetic polaron mechanism (BMP) for an optimum concentration of Li doped ZnO (ZnO:Li) nanostructures. Also, the incorporation of Li in the 2D ZnO nanostructure (2DZL) reduces the charge transfer resistance and hence an enhanced PCE of 5.58% (which is about two and half times superior to that of pristine ZnO). As the fabricated 2DZL exhibits RTFM, a field of 200 Oe when applied to this DSSC showed an improved PCE of 5.83%. The mechanism of such an enhancement is explained from the effect of Lorentz force and the results are discussed.

Highly Textured Seed Layers for the Growth of Vertically Oriented ZnO Nanorods

One dimensional ZnO nanostructures prepared by favorable and simple solution growth methods are at the forefront of this research. Vertically oriented ZnO nanorods with uniform physical properties require high-quality seed layers with a narrow size distribution of the crystallites, strong c-axis orientation, and low surface roughness and porosity. It has been shown that high quality seed layers can be prepared by the sol–gel process. The sol–gel process involves three essential steps: preparation of the sol, its deposition by dip coating, and thermal treatment comprising preheating and annealing. We put emphasis on the investigation of the heat treatment on the properties of the seed layers and on the vertical alignment of the nanorods. It was demonstrated that for the vertical alignment of the nanorods, the preheating step is crucial and that the temperatures reported in the literature have been too low. With higher preheating temperatures, conditions for the vertical alignment of the nanorods were achieved in both investigated annealing atmospheres in air and in argon.

Growing one-dimensional ZnO nanostructures

Using zinc foils as the only starting material, we synthesized one-dimensional ZnO nanostructures (nanorods, nanoneedles and nanowires) in air by zinc vapor condensation method at 500oC.The morphology, structure and photoluminescence of the synthesized one-dimensional ZnO nanostructures were investigated with scanning electron microscopy, X-ray diffractometry, transmission electron microscopy and spectrophotoscopy. It is found that the size, shape and photo luminescent properties of the one-dimensional ZnO nanostructures depend on the growth time of ZnO in the furnace. Mechanisms on the growth of the nanostructures were discussed, and controllable morphology and photoluminescence of the ZnO nanostructures were achieved by varying the growth time of ZnO in the furnace. It provides a simple, energy-saving and environment benign route to synthesize one dimensional ZnO nanostructures with controllable morphology and emission properties.

Seed layer effect on different properties and UV detection capability of hydrothermally grown ZnO nanorods over SiO2/p-Si substrate

Hydrothermally grown one dimensional ZnO nanostructures are among the most widely used semiconductor materials to build high-efficiency electronic devices for various applications. Few researchers have addressed the growth mechanism and effect of ZnO seed layer on different properties of ZnO nanorods grown by hydrothermal method, instead, no one has synthesized ZnO nanorod over SiO2/p-Si substrate. The aim of this study is to study the effect of ZnO seed layer and the growth mechanism of ZnO nanorods over SiO2/p-Si substrate. To achieve the goal, we have synthesized ZnO nanorods over different thickness ZnO seed layers by using the hydrothermal method on SiO2/p-Si substrate. The effects of c-plane area ratio were identified for the growth rate of c-plane, reaction rate constant and stagnant layer thickness also calculated by using a modified rate growth equation. We have identified maximum seed layer thickness for the growth of vertical ZnO nanorod. A step dislocation in the ZnO nanorods grown on 150and200nm thick seed layers was observed, the magnitude of Burges vector was calculated for this disorder. The seed layer and ZnO nanorods were characterized by AFM, XPS, UV-visible, XRD (X-ray diffraction, and SEM(scanning electron microscope). To justify the application of the grown ZnO nanorods Ti/Au was deposited over ZnO nanorods grown over all seed layers for the fabrication of photoconductor type UV detector.

Morphology engineering of ZnO nanostructures for high performance supercapacitors: enhanced electrochemistry of ZnO nanocones compared to ZnO nanowires

In this work, the morphology of ZnO nanostructures is engineered to demonstrate enhanced supercapacitor characteristics of ZnO nanocones (NCs) compared to ZnO nanowires (NWs). ZnO NCs are obtained by chemically etching ZnO NWs. Electrochemical characteristics of ZnO NCs and NWs are extensively investigated to demonstrate morphology dependent capacitive performance of one dimensional ZnO nanostructures. Cyclic voltammetry measurements on these two kinds of electrodes in a three-electrode cell confirms that ZnO NCs exhibit a high specific capacitance of 378.5 F g−1 at a scan rate of 20 mV s−1, which is almost twice that of ZnO NWs (191.5 F g−1). The charge–discharge and electrochemical impedance spectroscopy measurements also clearly result in enhanced capacitive performance of NCs as evidenced by higher specific capacitances and lower internal resistance. Asymmetric supercapacitors are fabricated using activated carbon (AC) as the negative electrode and ZnO NWs and NCs as positive electrodes. The ZnO NC⫽AC can deliver a maximum specific capacitance of 126 F g−1 at a current density of 1.33 A g−1 with an energy density of 25.2 W h kg−1 at the power density of 896.44 W kg−1. In contrast, ZnO NW⫽AC displays 63% of the capacitance obtained from the ZnO NC⫽AC supercapacitor. The enhanced performance of NCs is attributed to the higher surface area of ZnO nanostructures after the morphology is altered from NWs to NCs.

Identification and origin of visible transitions in one dimensional (1D) ZnO nanostructures: Excitation wavelength and morphology dependence study

In this present work, one dimensional (1D) ZnO nanostructures were synthesized by mechanical assisted thermal decomposition process. The samples were characterized by transmission electron microscopy (TEM) for morphology, high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) for structural characterization. Photoluminescence (PL) and Photoluminescence spectra evolution was studied as a function of (i) excitation wavelength (λEx: 310–370nm) and (ii) morphology (nanoneedles and nanorods). PL spectra were observed to be highly asymmetric with strong dependence on excitation wavelength (λEx). PL spectra categorized into two types as a function of excitation wavelength (λEx): I. λEx≤345nm and II. λEx≥350nm.The PL spectra were deconvoluted into multiple Gaussian components for each excitation wavelength. The position of each component is a signature of its origin and corresponds to specific visible transition. The transition involving origin from conduction band (CB) are absent for excitation wavelength λEx≥350nm. The tunable photoresponse is achieved in 1D ZnO nanostructures by varying (i) excitation wavelength and (ii) morphology: nanoneedles to nanorods. PL intensity increases as aspect ratio decrease from nanoneedles to nanorods morphology. This is attributed to non-radiative quenching by near surface defects.

Synthesis High Sensivity ZnO Cholesterol Biosensor with One Dimensional Nanostructures

Chelosterol ZnO biosensors were synthesized by hydrothermal method with predeposited ALD-ZnO seed layers. The ZnO nanostructures were examined by SEM, XRD, AFM, respectively. The XRD is used to analyze the crystal structures of ZnO seed layers that were grown by ALD process, then using SEM and AFM to analysis the surface morphologies of them. Growing of one dimensional ZnO nanostructures on seed layer of 10nm thickness, reveals high sensitivity of 3.15 uA (mg/dl)-1cm-2(121.96 uAmM-1cm-2) and low Km value of 29mM in 25-100mg/dl cholesterol concentration range. The response time could be as low as 10seconds. In the study, it is found that increasing the aspect ratio of ZnO one dimensional nanostructure also increases the sensitivity and expends the linear measureable range of detecting cholesterol in solution. The thickness of seed layer has a significant influence on sensitivity for one dimensional nano ZnO cholesterol biosensor.

Solvothermal Synthesis of One Dimensional ZnO Nanostructures and its Photocatalytic Applications

Here in, we have synthesized ZnO nanostructures using solvothermal reaction method at 200°C for 48h. The synthesized product was systematically characterized with various spectroscopic techniques. XRD analysis revealed the formation of crystalline hexagonal ZnO structure. ZnO indicate the UV-Visible absorbance peak at 379nm and photoluminescence spectra exhibited two peaks one at 391nm attributed to band edge emission and second at 500nm corresponds to certain defects. FE-SEM analysis showed formation of hexagonal shaped rod like morphology. Photocatalytic activity of the prepared ZnO nanostructures was evaluated using methylene blue degradation. The observed rate constant for photocatalytic MB degradation was (Kaap) 6.93 x 10-2 min-1.

Superhydrophobic polymethylsilsesquioxane pinned one dimensional ZnO nanostructures for water remediation through photo-catalysis

In this work we have developed ultra-dense high aspect ratio ZnO nano-forest like structures and explored their potential as photo-catalysts.

Hydrothermal Synthesis and Acetylene Sensing Properties of Variety Low Dimensional Zinc Oxide Nanostructures

Various morphologies of low dimensional ZnO nanostructures, including spheres, rods, sheets, and wires, were successfully synthesized using a simple and facile hydrothermal method assisted with different surfactants. Zinc acetate dihydrate was chosen as the precursors of ZnO nanostructures. We found that polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), glycine, and ethylene glycol (EG) play critical roles in the morphologies and microstructures of the synthesized nanostructures, and a series of possible growth processes were discussed in detail. Gas sensors were fabricated using screen-printing technology, and their sensing properties towards acetylene gas (C2H2), one of the most important arc discharge characteristic gases dissolved in oil-filled power equipments, were systematically measured. The ZnO nanowires based sensor exhibits excellent C2H2 sensing behaviors than those of ZnO nanosheets, nanorods, and nanospheres, indicating a feasible way to develop high-performance C2H2 gas sensor for practical application.

Effect of architectures assembled by one dimensional ZnO nanostructures on performance of CdS quantum dot-sensitized solar cells

Effect of ZnO architectures on photoelectric conversion efficiency of CdS quantum dot-sensitized ZnO solar cells is investigated. Four kinds of architecture assembled by one dimensional ZnO nanostructures, including ZnO nanorod arrays, nanotube arrays, forest, and pyramid arrays formed by thin nanowires, are designed and fabricated as photoanodes. Light-to-electricity conversion efficiency of these cells is 1.60% for the pyramid arrays, 1.34% for the forest, 1.08% for the nanotube arrays and 0.50% for the nanorod arrays, respectively, indicating that the architecture strongly affects the photoelectric conversion efficiency. Absorption spectra, dark current curves and photoelectron decay are measured to analyze the causes of differences. We find that light absorption and photoelectron transmission from ZnO nanostructures to FTO substrate are important factors for the cells. As the ZnO pyramid arrays formed by thin nanowires have anti-reflection character, high specific area for deposition of CdS sensitizer and fast photoelectron transmission channels to FTO substrate, higher photoelectric conversion efficiency is achieved. This investigation is important to the improvement on conversion efficiency for quantum dot-sensitized solar cells.

Hydrothermal growth and characterizations of dandelion-like ZnO nanostructures

Three dimensional (3D) ZnO nanostructures have been synthesized by using a facile low-cost hydrothermal method under mild conditions. Aqueous alkaline ammonia solution of Zn(CH3COO)2 is used to grow 3D ZnO nanostructures. The X-ray diffraction (XRD) study reveals the well crystallized hexagonal structure of ZnO. SEM observations depict that the ZnO product grows in the form of nanorods united together to form 3D dandelion-like nanostructures. The elemental analysis using EDAX technique confirms the stoichiometry of the ZnO nanorods. The product exhibits special optical properties with red-shifts in optical absorption peak (376 nm) as compared with those of conventional ZnO nanorods. PL spectra show emission peak (396 nm) at the near band-edge and peak (464 nm) originated from defects states that are produced during the hydrothermal growth. TEM and SAED results reveal single crystalline structure of the synthesized product. The reaction and growth mechanisms on the morphological evolution of the ZnO nanostructures are discussed. The morphology of ZnO product is investigated by varying the reaction time, temperature, and type of complexing reagent.

Investigations on the growth and optical properties of one dimensional ZnO nanostructures grown by radio frequency magnetron sputter deposition

We report the fabrication of one dimensional ZnO nanostructures under various argon sputtering pressures by radio frequency magnetron sputter deposition technique. The transition of the nanostructures from vertical to inclined is monotonously increased with the argon sputtering pressure owing to the decrease in migration length of the adatoms by the increased number of collisions. The blue shift, intensity quenching and peak broadening of A1(LO) phonon mode in the Raman spectra indicates the increase of free carrier concentration with the argon sputtering pressure due to the enhancement of point defects such as zinc and oxygen vacancies. The dominant neutral donor to bound exciton emission with narrow full width at half maximum implies the high optical quality of the nanostructures irrespective of argon sputtering pressure. The characteristic of visible emission at 3.01 and 2.28eV provides a strong evidence for the existence of zinc and oxygen vacancies in ZnO nanostructures.

The effect of annealing time and temperature on morphology and optical properties of ZnO nanostructures grown by a self-assembly method

Synthesis of ZnO nanostructures was achieved on glass substrate by the resistive evaporation of metallic zinc granules followed by dry oxidation process at 350, 450 and 550 °C. Characterization of the products with FESEM and TEM revealed that the structures obtained at 450 °C are mostly nanorods with diameters between 40 and 105 nm and lengths from 1 to 5 μm. One dimensional ZnO nanostructures such as ultra thin nanobelts, nanowires and nanorods were successfully synthesized at 550 °C, with lengths up to several micrometers. XRD patterns indicated that the structures are crystalline and that ZnO nanostructures grown at 550 °C are fully oxidized and are crystalline with wurtzite hexagonal structure. PL measurements were carried out at room temperature and they revealed that there are three band emissions; one sharp strong peak in the UV region and two weaker peaks in the visible region. A strong UV emission was observed in the spectra of the ZnO nanorods and nanowires which confirms the good optical properties of products. The PL spectra also exhibited a considerable shift toward the shorter wavelength in the UV region. It is clear that after the second annealing step photoluminescence of the 1D nanostructures, fabricated at 550 °C, have improved, especially in the UV region.

WITHDRAWN: Magnetic properties of one dimensional Sm-doped ZnO nanostructures fabricated by hydrothermal method

WITHDRAWN: Magnetic properties of one dimensional Sm-doped ZnO nanostructures fabricated by hydrothermal method

Synthesis of ZnO Nanostructures for Low Temperature CO and UV Sensing

In this paper, synthesis and results of the low temperature sensing of carbon monoxide (CO) gas and room temperature UV sensors using one dimensional (1-D) ZnO nanostructures are presented. Comb-like structures, belts and rods, and needle-shaped nanobelts were synthesized by varying synthesis temperature using a vapor transport method. Needle-like ZnO nanobelts are unique as, according to our knowledge, there is no evidence of such morphology in previous literature. The structural, morphological and optical characterization was carried out using X-ray diffraction, scanning electron microscopy and diffused reflectance spectroscopy techniques. It was observed that the sensing response of comb-like structures for UV light was greater as compared to the other grown structures. Comb-like structure based gas sensors successfully detect CO at 75 °C while other structures did not show any response.

Enhancement in field emission characteristics of multifunctional ZnO/C hybrid nanostructures

Multifunctional hybrid nanostructures have recently drawn immense attention due to their interesting physical and chemical properties and also due to their potential for applications in novel electronic devices. Herein, we report the luminescence and enhancement of field emission (FE) properties of multifunctional ZnO/C hybrid nanostructures prepared by the decomposition of zinc acetate and dextrose inside the nanopores of anodic aluminium oxide templates, which are fabricated by controlled electrochemical anodization of pure aluminium. Microscopic investigations show that the average pore diameter of the as prepared templates is ∼50 nm and ZnO/C hybrid nanostructures are formed around the inner pore walls. The template, containing the ZnO/C hybrids, exhibits visible light emission in blue wavelength region along with luminescence in the ultra-violet region. Investigations on the field emission property of the hybrid ZnO/C nanostructures reveals, that they are better and more efficient field emission material compared to one dimensional ZnO nanostructures.

Morphology-controllable ZnOnanotubes and nanowires: synthesis, growth mechanism and hydrophobic property

Controlled growth of nanostructures has long been regarded as one of the biggest obstacles to their commercial applications. Herein we demonstrate the feasibility of controlling growth of ZnO nanotubes and nanowires by floating substrates on the surfaces of reacting solutions with different concentrations, a key factor for differential growth. These slim ZnO nanotubes with outer diameters of 26.6 ± 12.2 nm and inner diameters of 8.3 ± 6.2 nm (confidence level of 95%) are a recently discovered new class of nanostructures whose growth is driven by screw dislocations (S. A. Morin et al., Science2010, 328, 476–480). Concentrations of precursors below 0.5 mmol L−1 adequately allow the slow relocation of solute clusters and spontaneous formation of the single crystal tube while the concentrations above 15 mmol L−1 induce high-speed deposition of newly forming solute clusters and fast growth of nanowires; therefore the concentration plays a crucial role in determining the morphology of one dimensional (1D) ZnO nanostructures. Furthermore, the ZnO nanotube surface, which apparently displays smaller dimension and lower density of nanostructures, exhibits improved hydrophobic property compared to the ZnO nanowire surface. The large scale controlled growth of arrays with different 1D ZnO nanostructures should be essential for fabricating novel devices and exploring advanced applications.

Three dimensional ZnO nanostructures realized through a polymer mediated aqueous chemical route: candidate for transparent flexible electronics

A brand new three dimensional zinc oxide nanosheet array was developed through manipulating its crystal growth habits with the anionic polymer, polysodium 4-styrene sulfonate (PSS). Along with being low cost, the process separates itself from other nanosheet array production protocols not only in its unique hierarchical assembly but as it is also devoid of any post-growth high temperature pyrolysis thus offering the opportunity to integrate devices over temperature sensitive substrates. Efficient electron emissions with low operating fields (turn-on field 3.5 V μm−1) are registered from the transparent field emitter based on three dimensional nanosheet assemblies on polymeric substrates and it can preserve its high performance even in a bended state. UV photodetectors based on the same material exhibit photocurrent gains as high as 1.95 × 105 which is 42 times higher when compared to nanowires and this is attributable to the much higher surface area; even after 100 consecutive bending cycles the detector performance degradation is negligible. This study will motivate the development of new morphologies in chemical synthesis routes employing polymers as growth modifiers.