Structure Of ZnO Nanorod Arrays Research Articles

In-situ stretching strain-driven high piezoelectricity and enhanced electromechanical energy-harvesting performance of a ZnO nanorod-array structure

Abstract Although strain engineering has been extensively recognized as a critical pathway in controlling the properties of inorganic materials, there have been very limited reports on the external strain-dependent modulation of piezoelectricity in flexible systems. Herein, we introduce a technical way of imposing extra stress during the deposition of the ZnO nanorods by using the stretching mode of a polymer substrate, specifically for the purpose of enhancing piezoelectricity and bending-driven energy harvesting performance. Depending on the level of stretching up to 4.87% strain, the induced stress of the nanorod structure was modulated after the substrate-releasing step. The 4.87%-stretching mode resulted in an effective piezoelectric coefficient of 33.3 p.m./V corresponding to an enhancement by ~270% compared to the unstrained case. The resultant piezoelectric energy harvester demonstrated ~3.43 V output voltage and ~226 nA output current for the 4.87%-strained sample, which means respective increments by ~90% and ~85% with the application of in-situ strain. The origin of the improvements is chased by estimating the changes in lattice constants and spontaneous polarization, which are dependent on the level of in-situ strain.

Synthesis of ZnO Nanorod Arrays by Chemical Solution and Microwave Method for Sensor Application

One-dimensional ZnO semiconductor nanomaterials have been attracting increasing attention due to their outstanding properties, which are different from bulk materials. ZnO has a direct band gap of 3.37 eV and large exciton binding energy hence its nanowires and nanorods have been regarded as one of the most promising materials for nanoscale electronic and optoelectronic devices such as ultraviolet laser diodes, optical detectors and gas sensor. ZnO nanowires and nanorods have been successfully synthesized by various techniques such as evaporation, sputtering and pyrolysis. In this paper we report the preparation of nanorod arrays of ZnO on ITO glass substrates which were pre-coated with ZnO nanoparticles by using low temperature chemical solution method and the result was compared with microwave hydrolysis process. The morphology and structure of ZnO nanorod arrays were investigated using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The ZnO nanorod arrays with a diameter of 40-70 nm were successfully synthesized. In microwave hydrolysis method, the diameter, density and surface roughness was found to depend on the microwave power. The microwave method is far superior in producing ZnO nanostructure growth.

Multilayer Hybrid Structure of ZnO Nanorod Arrays Imbedded in TiO2 Network as Photoanode

ABSTRACTWe developed a multilayer hybrid structure by imbedding ZnO nanorod arrays in TiO2 network for each layer, for the pourese of taking ZnO nanorods as the highway of electron transport. ZnO nanorods can be prepared by hydrothermal process, which is simple, low cost and easy control. The ZnO nanorod arrays were grown by reported hydrothermal method, then TiO2 network was constructed by spin-coating titanium precursor sol on ZnO nanorod arrays and calcining. The electrochemical impedance spectrum measurements were taken to study the electrical properties of this kind of hybrids, and the results indicated that the effective electron lifetime reaches a magnitude of microsecond which is similar to the pure ZnO nanorod arrays. It reveals to us that ZnO nanorods may dominate the electrical properties of this nano-hybrid structure.

Flexible organic/inorganic hybrid solar cells based on conjugated polymer and ZnO nanorod array

We report on the photovoltaic characteristics of organic/inorganic hybrid solar cells fabricated on ‘flexible’ transparent substrates. The solar cell device is composed of ZnO nanorod array and the bulk heterojunction structured organic layer which is the blend of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The ZnO nanorod array was grown on indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates via a low-temperature (85 °C) aqueous solution process. The blend solution consisting of conjugated polymer P3HT and fullerene PCBM was spin coated at a low spinning rate of 400 rpm on top of the ZnO nanorod array structure and then the photoactive layer was slow dried at room temperature in air to promote its infiltration into the nanorod network. As a top electrode, silver was sputtered on top of the photoactive layer. The flexible solar cell with the structure of PET/ITO/ZnO thin film/ZnO nanorods/P3HT:PCBM/Ag exhibited a photovoltaic performance with an open circuit voltage (VOC) of 0.52 V, a short circuit current density (JSC) of 9.82 mA cm−2, a fill factor (FF) of 35% and a power conversion efficiency (η) of 1.78%. All the measurements were performed under 100 mW cm−2 of illumination with an air mass 1.5 G filter. To the best of our knowledge, this is the first presentation of investigation into the fabrication and characterization of organic/inorganic hybrid solar cells based on bulk heterojunction structured conjugated polymer/fullerene photoactive layer and ZnO nanorod array constructed on flexible transparent substrates.

Thermal stability of sol–gel p-type Al–N codoped ZnO films and electric properties of nanostructured ZnO homojunctions fabricated by spin-coating them on ZnO nanorods

The thermal stability of sol–gel p-type Al–N codoped ZnO films was investigated by high-resolution X-ray photoelectron spectroscopy (XPS). XPS revealed the chemical bonding states and solubility of N-related complex defects in the ZnO films. The concentrations of NO and (NC)O varied with annealing temperature, which led to the change in conduction between p-type and n-type. Variable-temperature Hall-effect measurement showed that NO acted as a shallow acceptor, with its energy level locating at ∼114meV above the valance band maximum. Transmission electron microscopy confirmed the presence of undesired carbon clusters as a graphite state in the ZnO films. In order for Al–N codoped ZnO films to exhibit p-type conductivity, samples could only be annealed in a certain range of temperatures. A hybrid structure with nanostructured ZnO homojunctions was fabricated by spin-coating the p-type Al–N codoped ZnO film on an n-type ZnO nanorod array (ZNA). The hybrid nanostructure was demonstrated to possess rectification behavior characteristic of a p–n junction. The leakage current of the nanostructured ZnO homojunctions was smaller by a factor of 2 than that of the film-based ZnO homojunction at a reverse bias of 5V. The p-type ZnO film/n-type ZNA structure can be applied as a versatile p–n optoelectronic device.

A Three-Dimensional Transparent Electrode Structure With Al-Doped ZnO Nanorods

ZnO nanorod arrays on a transparent indium tin oxide/glass substrate were synthesized using a hydrothermal method. The tip diameters of the fabricated ZnO nanorods varied between 20 and 30 nm with lengths of 1 μm. Addition of Al3+ ions to the reaction solution produced Al-doped ZnO nanorods. The morphology and crystallinity of Al-doped ZnO nanorods were investigated by scanning electron microscopy and transmission electron microscopy. The crystal structure was analyzed by X-ray diffraction spectroscopy. Inductively coupled plasma atomic emission spectroscopy confirmed the level of Al doping. The electrical properties were obtained using I- V data from an entire structure of ZnO nanorod arrays.

纳米结构ZnO在TiO<sub>2</sub>薄膜上的电化学沉积及其表征

One-dimensional structure of ZnO nanorod arrays on nanocrystalline TiO 2 /ITO conductive glass substrates have been fabricated by cathodic reduction electrochemical deposition methods in the three-electrode system, with zinc nitrate aqueous solution as the electrolyte, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence (PL) spectra. The effects of film substrates, electrolyte concentration, deposition time, and methenamine (HMT) addition on ZnO deposition and its luminescent property were investigated in detail. The results show that, compared with on the ITO glass substrate, ZnO is much easily achieved by electrochemical deposition on the TiO 2 nanoparticle thin films. ZnO is hexagonally structured wurtzite with the c-axis preferred growth, and further forms nanorod arrays vertically on the substrates. It is favorable to the growth of ZnO to extend the deposition time, to increase the electrolyte concentration, and to add a certain amount of HMT in the system, consequently improving the crystallinity and orientation of ZnO arrays. It is demonstrated that the obtained ZnO arrays with high crystallinity and good orientation display strong band-edge UV (375 nm) and weak surface-state-related green (520 nm) emission peaks.

Electrochemical deposition of nano-structured ZnO on the nanocrystalline TiO2 film and its characterization

One-dimensional structure of ZnO nanorod arrays on nanocrystalline TiO2/ITO conductive glass substrates has been fabricated by cathodic reduction electrochemical deposition methods in the three-electrode system, with zinc nitrate aqueous solution as the electrolyte, and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence (PL) spectra. The effects of film substrates, electrolyte concentration, deposition time, and methenamine (HMT) addition on ZnO deposition and its luminescent property were investigated in detail. The results show that, compared with on the ITO glass substrate, ZnO is much easily achieved by electrochemical deposition on the TiO2 nanoparticle thin films. ZnO is hexagonally structured wurtzite with the c-axis preferred growth, and further forms nanorod arrays vertically on the substrates. It is favorable to the growth of ZnO to extend the deposition time, to increase the electrolyte concentration, and to add a certain amount of HMT in the system, consequently improving the crystallinity and orientation of ZnO arrays. It is demonstrated that the obtained ZnO arrays with high crystallinity and good orientation display strong band-edge UV (375 nm) and weak surface-state-related green (520 nm) emission peaks.

Low-temperature growth of ZnO nanorods on PET fabrics with two-step hydrothermal method

An effective low-temperature growth method to fabricate hexagonally oriented ZnO nanorod arrays onto PET fabrics is reported. The effect of substrate pre-treatment and C 6H 12N 4 concentration on the structure of ZnO nanorod arrays were investigated in details by X-ray diffraction (XRD), FE-SEM and ultraviolet protection factor (UPF). The results show that substrate pre-treatment, C 6H 12N 4 concentration indeed have great influence on the growth of ZnO nanorod arrays. It is indispensable to introduce a ZnO seed layer on the substrate and under growth condition of n(C 6H 12N 4): n[Zn(NO 3) 2] = 1:1, T = 90 °C, t = 3 h, the well-aligned ZnO nanorod arrays with 40–50 nm in diameter and 300–400 nm in length were achieved on the pre-treated PET fabrics. The ZnO nanorods grown on PET fabrics possessed an ultrahigh ultraviolet protection factor of 480.52 in this study, indicating an excellent protection against ultraviolet radiation in comparison with the untreated PET fabrics.

Defect study in ZnO related structures—A multi-spectroscopic approach

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/ n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.