Al-doped ZnO Nanorods Research Articles

Investigation of structural, optical, surface, electrochemical and corrosion properties of ZnO and AZO nanorod arrays for dye absorption applications

In dye-sensitized solar cells (DSSC), photoanodes have special importance in the processes of dye support, photon absorption and electron transport. ZnO nanorod arrays are promising photoanode materials, but their properties need to be improved by innovative fabrication approaches to improve the performance of ZnO-based DSSCs. In this study, pure and Al-doped ZnO (AZO) nanorod arrays were grown by hydrothermal method onto ZnO seed layers produced by sol-gel spin coating. As far as we know, for the first time in the literature, HMTA-HMDA ligand mixture was used instead of HMTA in the preparation of hydrothermal precursor solutions. To investigate the potential use of ZnO and AZO nanostructured films as photoanodes in DSSCs; their surface, structural and optical properties were examined. Additionally, charge transfer kinetics, corrosion resistance and dye loading capacities were determined by advanced analyzes such as electrochemical impedance spectroscopy, potentiodynamic polarization and adsorption-desorption methods. The supporting HMDA ligand and Al impurity used in the preparation of hydrothermal precursor solutions led potential usages as photoanode of ZnO nanorod arrays to increase by improving their structural, optical, surface, and electrochemical properties, corrosion resistance and dye loading capacities.

Improvement of the structural, morphological, optical, and photoelectrochemical properties of Al-doped ZnO nanorods for use in biosensors and solar cells

Improvement of the structural, morphological, optical, and photoelectrochemical properties of Al-doped ZnO nanorods for use in biosensors and solar cells

PH Controlled Nanostructure and Optical Properties of ZnO and Al-Doped ZnO Nanorod Arrays Grown by Microwave-Assisted Hydrothermal Method.

The low-temperature microwave-assisted hydrothermal method was used to successfully grow pure and Al-doped ZnO (AZO) nanorod (NR) arrays on glass substrates. The combined effects of doping and pH on the structural properties, surface chemistry, and optical properties of all samples were investigated. Thermodynamic-based simulations of the growth solution were performed and a growth mechanism, that considers the effects of both the pH and Al-doping, is proposed, and discussed. Tuning the solution pH is key parameter to grow well-aligned, single crystal, highly packed, and high aspect ratio nanorod arrays. Moreover, the optical absorption in the visible range is enhanced by controlling the pH value. The PL spectra reveal a shift of the main radiative emission from the band-to-band into a transition involving deep defect levels of Zinc interstitial Zni. This shift is caused by an enhancement of the non-radiative components (phonon relaxation) at high pH values. The production of well-ordered ZnO and AZO nanorod arrays with visible-active absorption/emission centers would increase their potential use in various applications.

NO2 gas sensing properties of chemically grown Al doped ZnO nanorods

This report highlights nanocrystalline aluminium doped ZnO (Al doped ZnO: AZO) samples deposited on seeded glass substrates using cost-effective reflux method. The doping concentration of ‘Al’ ions varied from 1 to 3 vol percentage (vol%). The deposited AZO samples exhibit wurtzite hexagonal crystal structure and the surface morphological analysis study confirms the formation of nanorods for undoped ZnO and reduction in diameter with the formation of the fine tips for AZO samples. The photoluminescence (PL) study confirms oxygen vacancies and defects in the AZO samples. Moreover, the AZO samples exhibit excellent gas sensing performance towards NO2 gas at an operating temperature of 175 °C. The gas sensitivity of 5 ppm NO2 gas was 85% at 175 °C. This work is promising for the practical approach for the low detection limit at low operating temperature in the field of gas sensor technology.

High-Vacuum Annealed Al-Doped ZnO Nanorods for Fast-Switching Electrochromic Windows with High-Optical Contrast and Long-Term Stability

High-Vacuum Annealed Al-Doped ZnO Nanorods for Fast-Switching Electrochromic Windows with High-Optical Contrast and Long-Term Stability

Structural and Electrical Characterization of Pure and Al-Doped ZnO Nanorods.

Pure and Al-doped (3 at.%) ZnO nanorods were prepared by two-step synthesis. In the first step, ZnO thin films were deposited on silicon wafers by spin coating; then, ZnO nanorods (NR) and Al-doped ZnO NR were grown using a chemical bath method. The structural properties of zincite nanorods were determined by X-ray diffraction (XRD) and corroborated well with the morphologic properties obtained by field-emission gun scanning electron microscopy (FEG SEM) with energy-dispersive X-ray spectroscopy (EDS). Morphology results revealed a minute change in the nanorod geometry upon doping, which was also visible by Kelvin probe force microscopy (KPFM). KPFM also showed preliminary electrical properties. Detailed electrical characterization of pure and Al-doped ZnO NR was conducted by temperature-dependent current–voltage (I–V) measurements on Au/(Al)ZnO NR/n-Si junctions. It was shown that Al doping increases the conductivity of ZnO NR by an order of magnitude. The I–V characteristics of pure and Al-doped ZnO NR followed the ohmic regime for lower voltages, whereas, for the higher voltages, significant changes in electric conduction mechanisms were detected and ascribed to Al-doping. In conclusion, for future applications, one should consider the possible influence of the geometry change of (Al)ZnO NRs on their overall electric transport properties.

Aluminum Doped ZnO Nanorods for Enhanced Phenylhydrazine Chemical Sensor Applications

The fabrication and characterization of nanorod-shaped Al-doped ZnO nanostructures are described in this paper. The hexagonal wurtzite phase of ZnO was confirmed by XRD investigation, with efficient doping of Aluminum ions in the ZnO crystal. The length and diameter of the high density produced doped ZnO nanorods were shown to be heterogeneous using FESEM analysis. EDS, FTIR, and Raman spectroscopy examinations validated purity, composition, and vibrational characteristics. Even at very low analyte concentrations, the constructed Al-doped ZnO nanorods modified silver electrode (AgE) displayed exceptional electron mediating characteristics towards phenylhydrazine. The sensitivity, linear dynamic concentration range (LDR) and limit of detection (LOD) were found to be 64.77 μAmM−1cm−2, 0.313–2.5 mM, and 0.313 mM, respectively. As a result of the research described, Al-doped ZnO nanorods appear to be promising candidates for building efficient and repeatable electrochemical sensors in the future.

UV random laser in aluminum-doped ZnO nanorods

Vertically aligned Al-doped ZnO nanorods (AZO-NRs) were grown on glass substrate using a chemical bath deposition (CBD) method at various temperatures between 80°C and 130°C. The results showed the Al content in the AZO-NRs strongly depends on the growth temperature. The optimum doping level was attained at 110°C. The morphology was maintained in each sample, and the lasing properties were investigated against the Al-doped variation. The sample with a high doping level exhibited superior random lasing, with high intensity and spectral width of less than 0.08 nm. The same sample also had the lowest pumping threshold of 0.192 mW. More importantly, this study showed the possibility of utilizing doping as a tuning parameter for random lasing, whereby a 7.3 nm redshift in the lasing peak was observed with increasing doping concentration. This study also placed an emphasis on AZO-NRs as potential candidates for tunable random laser devices.

Efficient Light Trapping from Nanorod-Like Single-Textured Al-Doped ZnO Transparent Conducting Films

Nanorod-like single-textured Al-doped ZnO (AZO) transparent conducting films were prepared by the simple hydrothermal growth of AZO nanorods on AZO seed layers. The structures, morphologies, optoelectronic properties and light trapping abilities of the AZO films were investigated. The morphological changes of single-textured AZO films depending on growth temperature were shown. Above all, the relation between light trapping abilities and surface morphologies of the single-textured AZO films was studied in detail. The nanorod-like single-textured AZO films prepared at 100 °C exhibited low resistivity, high total transmittance and remarkable enhancement of haze value, which can be acted as transparent electrodes for improving the conversion efficiency of Si-based thin film solar cells.

Mechanism and Optimized Process Conditions of Forming One-Dimensional ZnO Nanorods with Al-Doping by Electrodeposition Method

Textured transparent conductive electrodes for thin-film solar cells have been considered as an effective route for enhancing sunlight harvest due to light trapping. Here, we report a self-assembling electrochemical approach for preparing Al-doped ZnO nanorod arrays (NRAs) as light-trapping electrodes from a mixed aqueous solution of zinc nitrate and aluminium nitrate. The mechanism and optimized process conditions of forming one-dimensional ZnO nanorods with Al-doping were systematically investigated. The results showed that Al atoms were successfully doped into ZnO crystal lattice, and the morphologies could be controlled by adjusting the Al3+/Zn2+ ratio in the precursors and deposition time. The Al-doped ZnO films grew into well-aligned hexagonal NRAs with c-axis perpendicular to the substrates and then transited into a mixture of nanosheets and nanorods with Al3+/Zn2+ ratio increasing. They exhibited good electrical conductivity with a sheet resistance of 68-167Ω/square and appropriate visible light transmittance of 61-82%. Taking into account of desired morphology and phase purity, as well as good electrical conductivity and optical transmittance, the optimal window of Al3+/Zn2+ ratio in the precursors was determined between 1 at% and 2 at% with applied potential of -1.5V, bath temperature of 80°C, and deposition time of about 30min. The electrodeposition method provides a facile and efficient route for obtaining large-area textured transparent electrodes at a low cost.

Rapid microwave-assisted fabrication of Al-doped zinc oxide nanorods on a glass substrate for photocatalytic degradation of phenol under visible light irradiation

A rapid microwave-assisted process was used to synthesize a quasi-aligned Al-doped ZnO nanorods on a glass substrate. X-ray diffraction and scanning electron microscopy were used to investigate the crystal structure and morphological properties while the optical properties of the prepared materials have been examined by UV–visible and photoluminescence spectroscopy. Two different Al concentrations, 1% and 5%, were used to dope ZnO nanorods. The prepared Al-doped ZnO samples were annealed at 350 °C–550 °C temperature range. 1% AZO sample annealed at 550 °C showed the highest visible light absorption. Synthesized NRs surface chemistry have been characterized using X-ray photoelectron spectroscopy. Samples morphology, NRs density and diameter significantly changed with Al doping. Results show that the crystal orientation and surface oxidation states are dependent on Al content. Overall, Al-doping of ZnO NRs enhanced the photocatalytic degradation of phenol, especially at 1% Al due to bandgap narrowing and enhancement of visible light absorption.

High efficient Al: ZnO based bifocus metalens in visible spectrum**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0403101).

The optical components of the visible light band are widely used in daily life and industrial development. However due to the serious loss of light and the high cost, the application is limited. The broadband gap metasurface will change this situation due to its low absorption and high efficiency. Herein, we simulate a size-adjustable metasurface of the Al doped ZnO (AZO) nanorod arrays based on finite difference time domain method (FDTD) which can realize the conversion of amplitude polarization and phase in the full visible band. The corresponding theoretical polarization conversion efficiency can reach as high as 91.48% (450 nm), 95.27% (530 nm), and 91.01% (65 nm). The modulation of focusing wavelength can be realized by directly adjusting the height of the AZO nanorod. The designed half-wave plate and metalens can be applied in the imaging power modulation halfwave conversion and enriching the spectroscopy.

Highly sensitive CO sensor based on Al-doped-ZnO nanorods-coated resonant microcantilevers

A highly sensitive (at the picogram order) Al-doped-ZnO nanorods (AZNRs)-coated resonant microcantilever (MC) for carbon monoxide (CO) gas sensing, operable at ambient temperature and under humid condition was synthesized. The ZnO nanorods were grown on the MC surface by using the hydrothermal method and doped by aluminum (Al). The sensitivities of un-doped and AZNRs for various CO gas concentrations were investigated by measuring the changes in the resonant frequencies and the Q-factor analysis of the vibrating MCs. The mechanisms of the remarkable enhancement of the sensitivity of the AZNRs-coated-microcantilever to CO were thoroughly investigated and discussed on the basis of energy gap between the highest occupied molecular orbital-lowest occupied molecular orbital of AZNRs and CO, active surface area of AZNRs, and the interaction of water vapor on AZNRs surface with CO.

Surfactant and catalyst free facile synthesis of Al-doped ZnO nanorods – An approach towards fabrication of single nanorod electrical devices

Classical models illustrate the genesis of bottom-up techniques for synthesis of pristine ZnO or Al-doped ZnO nanoparticles via surfactant aided or hydrothermal chemistry, to constitute the fundamental modules of nanotechnology and nanodevices. The present study demonstrates a facile as well as surfactant and catalyst free route for synthesis of morphology controlled Al-doped ZnO nanorods. Morphological evaluation (via FESEM and TEM characterization) clearly verifies the successful synthesis of ZnO and Al-doped ZnO nanorods. Moreover, crystallographic and FTIR studies ratified presence of multiple different planes as well as phases of ZnO and Al-doped ZnO nanostructures, eventually confirming the doping process. Further, the alteration in mode of electronic transition and surface charge of ZnO nanorods post doping with Al was witnessed from its UV–visible or photoluminescence spectra and zeta potential measurements, respectively. Electrical measurements were performed on prepared Al-doped ZnO nanorods which were fabricated as single nanorod devices. Owing to substitutional and interstitial doping, the electrical conductivity of the devices was drastically enhanced after doping. Excellent electrical attribute of the nanorods when fabricated into single nanorod device was indicative of its potential to be deployed as next generation nano-biosensors or piezo-electric devices.

Effect of Al Doping on Hydrothermal Growth and Physical Properties of Doped ZnO Nanoarrays for Optoelectronic Applications

Abstract Renewable energy production via solar energy is a promising solution to advent the globally mounting energy needs. Therefore, our work has been planned to develop, high efficient optoelectronic devices, which are cost effective and easily fabricated. Successfully, we developed Al doped ZnO nanorods (NRs) by two step process. Initially by using sol-gel technique we grow the seed layers and further we succeed ZnO nanorods by a simple hydrothermal process without using any toxic solvents. The obtained nanorods show remarkable electrical and optical properties characterized by I-V characteristics, UV- vis, Photoluminescence (PL) spectroscopy techniques. In addition, we have also investigated the surface morphological properties from FESEM which indicates that NRs are hexagonal in shape and the diameter of the rod varies from 232 nm to 297 nm as the Al concentration changes from 1% to 10% in ZnO. Band gap of Al doped ZnO NR decreases on increasing the concentration of doping from 3.23 to 2.73 eV. The PL spectrum shows emission peaks in the UV and visible region. From this we conclude that, these materials are good candidate for the optoelectronic applications. Thus, our approach will probably fetch and derive a noble route for the fabrication of new materials.

Tailoring the optical properties of Al-doped ZnO Nanorods by electrodeposition

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Monodisperse Al-Doped ZnO/Perovskite Nanocapsule.

We developed monodisperse ZnO nanocapsules and atmospheric N plasma was used to develop a ZnO-organic nanocomposite. To test the seal of the ZnO nanocapsule, the halide perovskite CH3NH3PbBr3 was used as the filler. Al atoms were doped into ZnO nanorods to increase the conductivity of ZnO nanorods. A green emission peak located at 535 nm was observed in the nanocapsules with a 410 nm excitation because of the free-exciton recombination of CH3NH3PbBr3. The Al-doped ZnO (AZO)/CH3NH3PbBr3 nanocapsules was further tested under using a three-electrode photoelectrochemistry cell. AZO/CH3NH3PbBr3 nanocapsule arrays yield an elevated photocurrent of approximately 0.2 mA/cm2 at 1 V versus Ag/AgCl under air mass 1.5 (AM 1.5), almost 1.5 times larger than that of the AZO nanorod arrays. The photo-current stability of AZO/CH3NH3PbBr3 nanocapsule arrays photoelectrode is better than that of AZO nanorod arrays under a repeated on/off light test. This confirmed that the AZO/CH3NH3PbBr3 nanocapsules had been successfully sealed and that the degradation of CH3NH3PbNBr3 was thus dramatically reduced. Our study yields a novel platform for nanoscale optical and optoelectronic devices or for delivery of highly toxic drugs.

Effect of Al Doping on the Structural, Electrical, Gas Sensing Properties of ZnO Nanorods Synthesized by Hydrothermal Growth

The effect of Al doping on the morphology and sensing properties of ZnO nanorods have been shown. Undoped and Al-doped well-aligned ZnO nanorods have been grown on sputtered ZnO/SiO2/Si (100) pre-grown seed layer substrate by the hydrothermal method. The molar ratio of dopant (aluminum nitrate) in the solution, [Al/Zn], was varied from 0.1% to 3%. The prepared ZnO nanorods showed preferred orientation [Formula: see text]0001[Formula: see text] and were well aligned vertically. We observed that for 0.5% Al doping the diameter and resistivity of the nanorods became the least, carrier concentration became large. Sensing behavior of the doped samples tested for H2 gas shows the sensitivity of [Formula: see text] at [Formula: see text]C and [Formula: see text] at [Formula: see text]C, respectively.

Al-ZnO/CdS Photoanode Modified with a Triple Functions Conformal TiO2 Film for Enhanced Photoelectrochemical Efficiency and Stability

ZnO/ CdS based nanorod arrays is an excellent class of photoanode materials with high photoelectric response. However, the poor photostability of CdS in aqueous solution seriously prevents its practical application. Although efforts have been made, it still challengeable to improve stability while maintaining initial photocurrent. Herein, a highly efficient photoanode system consisting of Al-doped ZnO nanorod arrays (NRs) served as effective electron-transfer layer and CdS as a light harvesting layer was designed. At last, TiO2 protective layer was deposited onto Al-ZnO/CdS photoanodes through atomic layer deposition (ALD) to enhance the photostability. The integrated Al-ZnO/CdS/TiO2 photoanode exhibits a photocurrent of 11.7 mA/cm2 at 1.23 V versus reversible hydrogen potential (RHE) and conversion efficiency of 5.9 % at 0.48 V versus RHE for 60 ALD TiO2 cycles. More importantly, the photostability of Al-ZnO/CdS/TiO2 photoanode was significantly prolonged comparing with the untreated Al-ZnO/CdS photoanode. The strengthen stability is benefited from the triple functions of ALD TiO2 layer, that is, isolating the direct contact between the photoanode with the surrounding liquid environment, passivating the surface state of the CdS, and capturing as well as storing the photogenerated hole.

Efficient enhancement of light trapping in the double-textured Al doped ZnO films with nanorod and crater structures

Double-textured Al doped ZnO (AZO) films with nanorod and crater structures were prepared by the simple hydrothermal growth of AZO nanorods on the single-textured AZO films with crater structures. The light trapping capabilities, morphological, structural and optoelectronic properties of double-textured AZO films prepared with different precursor concentrations were demonstrated systematically. Remarkable surface morphology evolution of the double-textured films depending on precursor concentration was observed. Especially, the relationship between surface morphologies and light trapping capabilities of the AZO films with nanorod and crater structures was discussed. The double-textured AZO films having nanorod and crater structures prepared with 0.01 M precursor concentration exhibited low sheet resistance, high visible total transmittance and haze value, which could be used as transparent front electrodes for enhancing the light trapping in solar cells.