Aluminum-doped Zinc Oxide Nanorods Research Articles

Synthesis of Au or Ag/Cu2O/ aluminum doped zinc oxide nanorods hybrid electrode for high sensitive non-enzymatic glucose sensor: Mechanism investigation of formation and surface plasmon resonance

The proposal of the research mainly employs the surface plasmon resonance of gold (Au) and silver (Ag) nanoparticles (NPs) to stabilized induction current of hybrid cuprous oxide (Cu2O)/aluminum doped zinc oxide nano-rods (AZO NRs) for non-enzymatic glucose sensor. This research investigation concerns the mechanism of formation and surface plasmon resonance. There were mainly three synthesis processes for the hybrid electrode. The first involved the hydrothermal growth of AZO NRs, and the seed layer of AZO was sputtered with different thickness from 35 to 105 nm. The second concerned the deposition of Cu2O on AZO NRs by the method of electrochemical deposition, and the Cu2O films were prepared with different pH value from 3 to 10. The third was concerned with Au and Ag NPs, and they were formed with the hydrothermal method and the seed reduction method, respectively. These NPs were dripped uniformly on the surface of Cu2O/AZO NRs through Nafion dispersants. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA) were used to verify these formation performances for the Au or Ag NPs/Cu2O/AZO NRs hybrid electrodes. The results showed that the linear range changed from 70.5 to 37.5 and 54.5 mg/dL, and linear regression coefficients (R2) also increased from 0.982 to 0.9965 and 0.997, respectively for Au and Ag NPs modified Cu2O/AZO NRs electrodes.

Aluminum-doped zinc oxide nanorods and methyl alcohol gas sensor application

In this paper, we mainly discuss about Al-doped zinc oxide (ZnO) nanorods (NRs) grown by hydrothermal method with low temperature. Glass substrate was grown 100 nm ZnO seed layer by RF magnetron Sputter. Add zinc nitrate hexahydrate [Zn(NO3)2·6H2O] and hexamethylenetetramine (HMT, C6H12N4), and add aluminum nitrate [Al(NO3)3·9H2O] for changing conductive properties of ZnO NRs to reach the purpose of doped. Then we used field electron emission scanning electron microscope observing the surface morphology; energy dispersive spectrometer analyze element content; X-ray diffractometer; photoluminescence analyze optical properties; transmission electron microscopy view the internal type and structure of the material. Finally observing the Al-doped ZnO NRs and pure ZnO NRs sensor under methyl alcohol surroundings. The results the Al-doped ZnO NRs sensor were found to be more sensitive than the pure ZnO NRs sensor under methyl alcohol surroundings.

Concentration effect of aluminum nitrate on the Crystalline−Amorphous transition between Al-doped ZnO nanorods and nanostructures prepared by electrochemical deposition

In this study, an electrochemical deposition was conducted to prepare Al:ZnO. Products in three distinct phases were obtained depending on the [Al3+] added in the bath of 2.0 mM zinc nitrate. For convenient description, [Al3+] (total range 0–1000 μM) was termed as dilute (i.e., [Al3+] < 60 μM), medium (i.e. 60 μM < [Al3+] < 100 μM), and concentrated (i.e., [Al3+] > 250 μM). Field-emission scanning electron microscopy revealed that a compact phase of nanorods was deposited in the dilute [Al3+], a mixed phase consisting of nanorods and nanosheets was deposited in the medium [Al3+], and a loose phase of cloudy floc was produced in the concentrated [Al3+]. By analyzing the reaction products with grazing incidence X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, we distinguished the crystal film of aluminum-doped zinc oxide nanorods from the amorphous hydroxides. Mott-Schottky measurements revealed that the specimen of nanorods doped with 2.84 at.% Al displays the highest carrier concentration (3.83 × 1018 cm−3) and demonstrates the highest electric conductivity among the specimens in a compact phase of nanorods. Photovoltaic tests showed that these films have fill factor and solar cell power conversion efficiency of 70.6 and 2.15%, respectively. By means of cathodic polarization and analysis of basic chemistry in aqueous solution, we propose a comprehensive mechanism to illustrate the type of products depending on [Al3+].

Hybrid Organic–Inorganic Solar Cells with Electrodeposited Al-Doped Zinc Oxide

Hybrid solar cells were fabricated using aluminum-doped zinc oxide (AZO) grown by electrochemical deposition from chloride electrolyte solutions with Al/Zn molar ratios of 0.5, 2.5, and 5.0%. The substrates were AZO- and ZnO-seeded ITO. Ordered nanorod structures with high optical transmittance were grown at 0.5% Al/Zn ratio while interconnected micron-sized flakes were grown at 2.5% and 5.0%. The estimated band gap energies increase for higher Al dopant content, showing Burstein-Moss effect. EDX analysis detected high aluminum content in the 5.0% samples suggesting that insulating aluminum oxide phases were formed thus causing reduced solar cell efficiencies. The highest power conversion efficiency of 1.71%, from the 0.5% sample grown on ZnO-seeded ITO, can be attributed to the presence of AZO nanorods which provide a large interfacial area and effective charge transport.

Fabrication of Intrinsic Zinc Oxide-Coated, Aluminium-Doped Zinc Oxide Nanorod Array-Based Ultraviolet Photoconductive Sensors

Fabrication and performance of metal-semiconductor-metal (MSM)–type intrinsic zinc oxide-coated, aluminium-doped ZnO nanorod array-based ultraviolet photoconductive sensors were reported and discussed. The Al-doped ZnO nanorod arrays were prepared using sonicated sol-gel immersion method. The coating process of intrinsic ZnO onto Al-doped ZnO nanorod arrays was performed using radio-frequency (RF) magnetron sputtering at different deposition times varying from 0 to 10 min. We observed that responsivity of the sensors decreased with increasing intrinsic ZnO deposition time, decreasing from 4.81 A/W without coating to 1.37 A/W after 10 min of coating. Interestingly, the sensitivity of the sensors improved with intrinsic ZnO coating, having a maximum value of 19.0 after 1 min coating.

Structural Properties of Stannic Oxide Coated Aluminium-Doped Zinc Oxide Nanorods

Aluminium (Al) - doped zinc oxide (ZnO) nanorods was deposited using sol-gel immersion method. To study the effect of stannic oxide coating (SnO2) on the structural properties of the ZnO nanorods, SnO2with different layers were deposited on the top of ZnO nanorods, from 1 to 5 layers. The structural properties of the samples have been characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy and x-ray diffraction (XRD). The analyses showed that by increasing the deposited layer, the surface roughness of the samples reduced and also reduced the porosity of the surface.

Effect of Polyethylene Glycol Concentration on the Formation of Aluminium-Doped Zinc Oxide Nanorods

Aluminium (Al) - doped zinc oxide (ZnO) nanorods with different weight percent (wt%) of polyethylene glycol (PEG) has been deposited on glass substrate. The concentrations of PEG have been varied from 0 wt %, 15 wt % and 30 wt %. The percentage weight of the PEG is the ratio between PEG mass to the hexamethyltetramine (HMT) and zinc nitrate hexahydrate (Zn (NO3).6H2O) mass. The structural properties of the samples have been characterized using field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) and electrical properties has been characterized using current voltage (I-V) measurement. The analyses showed that PEG addition have reduced the crystallinity and conductivity of the samples.

Ultraviolet sensing properties of polyvinyl alcohol-coated aluminium-doped zinc oxide nanorods

Undoped and aluminium (Al)-doped zinc oxide (ZnO) nanorods have been synthesized by electrochemical route. The synthesized materials have been characterized by X-ray diffraction, UV–visible spectrometer and scanning electron microscope. The Al-doped ZnO nanorods have been coated with polyvinyl alcohol. Current–voltage characteristics have been investigated in dark and under UV-light illumination. Aluminium doping in ZnO increase its electrical conductivity and further polyvinyl alcohol coating on Al-doped ZnO increase UV sensitivity of the material. Response and recovery time of Al-doped ZnO and PVA-coated Al-doped ZnO nanorods have been recorded. PVA-coated Al-doped ZnO nanorods shows very fast response and recovery time of 10 s in comparison to uncoated ZnO (20 min) nanorods.

Fabrication of an ultraviolet photoconductive sensor using novel nanostructured, nanohole-enhanced, aligned aluminium-doped zinc oxide nanorod arrays at low immersion times

Novel nanostructured thin-film arrays of nanohole-enhanced aligned aluminium (Al)-doped zinc oxide (ZnO) nanorods were prepared using sonicated sol–gel and immersion methods for metal–semiconductor–metal (MSM)-type ultraviolet (UV) photoconductive sensor applications. These nanorod arrays were grown on a glass substrate coated with ZnO nanoparticle thin film as a seed layer at immersion times ranging from 10 to 120min. Notably, the nanoholes appeared on the nanorods after the annealing process due to the evaporation of water and impurities. The photocurrent properties for the Al-doped ZnO nanorod arrays were significantly improved, increasing by more than five-fold compared to the seed layer when the sensor was illuminated with 365nm UV light at a density of 750μA/cm2. Interestingly, the highest responsivity using the Al-doped ZnO nanorod arrays was 1350.84A/W with an improved photocurrent-to-dark current ratio of 22.7, achieved for the samples prepared with a 50min immersion time and a gap between metal contacts of 0.07mm. Our results show that high-performance UV photoconductive sensors can be achieved using a novel structure of nanohole-enhanced aligned Al-doped ZnO nanorod arrays prepared at low immersion times which reduces fabrication time and cost.

Gold‐Catalyzed Growth of Aluminium‐Doped Zinc Oxide Nanorods by Sputtering Method

Aluminium‐doped zinc oxide (AZO) nanorods thin films were grown by RF magnetron sputtering on gold (Au) metal catalyst. The Au catalyst layers with 5, 10, and 15 nm thickness were deposited on glass substrates by sputtering method followed by annealing for 15 min at 500°C to form Au nanostructures on the glass substrate. The AZO thin films were then deposited on the Au catalyst at different deposition temperature varying from 200 to 500°C. Postdeposition annealing processes of the Au catalyst resulted in different morphologies of the Au catalyst layers depending on their thicknesses. This in turn gave different AZO morphologies which suggest that the Au catalyst layer thickness and the deposition temperature contribute to the growth mechanism of the AZO nanostructures. AZO nanorods thin films having hexagonal wurtzite structure with individual nanorods on the film surface were obtained from the samples deposited on 5 and 10 nm thick Au catalyst with the deposition temperature of 300°C.

Investigation of Stress and Electrical Properties of Air-Annealed and Oxygen-Annealed Aluminium-Doped Zinc Oxide Nanorod Arrays

In this research, we prepared aluminium (Al)-doped ZnO nanorod arrays on the glass substrate using sonicated sol-gel method. These nanorod arrays were annealed at 500 °C in air and oxygen environment using thermal furnace. Field emission scanning electron microscopy (FESEM) image reveals that nanorod arrays were deposited vertically aligned on the substrate. The stress characteristics of air-annealed and oxygen-annealed Al-doped ZnO nanorod arrays were investigated using Raman spectroscopy and X-ray diffraction (XRD) measurement. The electrical properties of the samples were investigated using two-probe current-voltage (I-V) measurement system. The results show that annealing atmospheres greatly influenced the stress and electrical properties of the nanorod arrays.

CdS nanoparticles sensitization of Al-doped ZnO nanorod array thin film with hydrogen treatment as an ITO/FTO-free photoanode for solar water splitting

Aluminum-doped zinc oxide (AZO) nanorod array thin film with hydrogen treatment possesses the functions of transparent conducting oxide thin film and 1-D nanostructured semiconductor simultaneously. To enhance the absorption in the visible light region, it is sensitized by cadmium sulfide (CdS) nanoparticles which efficiently increase the absorption around 460 nm. The CdS nanoparticles-sensitized AZO nanorod array thin film with hydrogen treatment exhibits significantly improved photoelectrochemical property. After further heat treatment, a maximum short current density of 5.03 mA cm−2 is obtained under illumination. They not only are much higher than those without CdS nanoparticles sensitization and those without Al-doping and/or hydrogen treatment, but also comparable and even slightly superior to some earlier works for the CdS-sensitized zinc oxide nanorod array thin films with indium tin oxide (ITO) or fluorine-doped tin oxide (FTO) as substrates. This demonstrated successfully that the AZO nanorod array thin film with hydrogen treatment is quite suitable as an ITO/FTO-free photoanode and has great potentials in solar water splitting after sensitization by quantum dots capable of visible light absorption.

Ultraviolet sensing mechanism and characteristics of environmentally friendly aligned aluminium doped zinc oxide nanorod arrays prepared using low cost solution growth method

Ultraviolet (UV) photoconductive sensors have been fabricated on glass substrates using aligned aluminium (Al) doped zinc oxide (ZnO) nanorod arrays at different annealing temperatures. The Al doped ZnO nanorod arrays were prepared using a novel technique of sonicated sol–gel immersion utilising Al doped ZnO nanoparticle thin film as seeded catalyst. In this study, the authors were able to increase the crystallinity of the Al doped ZnO nanorod arrays while maintaining the morphology of the Al doped ZnO nanorod after annealing process in ambient. The surface defects of the nanorod were significantly suppressed at high temperature up to 500°C, as can be observed in the photoluminescence spectra. It has been demonstrated that the photoresponse of the UV sensor under 365 nm UV illumination showed significant improvement after the annealing process due to the high crystallisation degree of the ZnO nanostructures. The influences of surface defects on the photoresponse properties of the fabricated UV photoconductive sensor are discussed.

Fabrication of ultraviolet photoconductive sensor using a novel aluminium-doped zinc oxide nanorod–nanoflake network thin film prepared via ultrasonic-assisted sol–gel and immersion methods

Unique and novel thin films with aluminium (Al)-doped zinc oxide (ZnO) nanostructures consisting of nanorod–nanoflake networks were prepared for metal–semiconductor–metal (MSM)-type ultraviolet (UV) photoconductive sensor applications. These nanostructures were grown on a glass substrate coated with a seed layer using a combination of ultrasonic-assisted sol–gel and immersion methods. The synthesised ZnO nanorods had diameters varying from 10 to 40 nm. Very thin nanoflake structures were grown vertically and horizontally on top of the nanorod array. The thin film had good ZnO crystallinity with a root mean square roughness of approximately 13.59 nm. The photocurrent properties for the Al-doped ZnO nanorod–nanoflake thin films were more than 1.5 times greater than those of the seed layer when the sensor was illuminated with 365 nm UV light at a density of 5 mA/cm 2. The responsivity of the device was found to be dependent on the bias voltage. We found that similar photocurrent curves were produced over eight cycles, which indicated that the UV sensing capability of the fabricated sensor was highly reproducible. Our results provide a new approach for utilising the novel structure of Al-doped ZnO thin films with a nanorod–nanoflake network for UV sensor applications. To the best of our knowledge, UV photoconductive sensors using Al-doped ZnO thin films with a nanorod–nanoflake network have not yet been reported.

Controllable Growth of Vertically Aligned Aluminum-Doped Zinc Oxide Nanorod Arrays by Sonicated Sol–Gel Immersion Method depending on Precursor Solution Volumes

Aluminium (Al)-doped zinc-oxide (ZnO) nanorod arrays have been successfully prepared using a novel and low-temperature sonicated sol–gel immersion method. The photoluminescence (PL) spectrum reveals the appearance of two emission peaks from the nanorod that are centred at 381 and 590 nm. The nanorod has a hexagonal structure with a flat-end facet, as observed using field-emission electron microscopy (FESEM). Interestingly, all samples have similar surface morphologies and diameter sizes of 40 to 150 nm after immersion in different precursor-solution volumes. The thickness-measurement results show that the thicknesses of the samples increase after immersion in higher precursor-solution volumes. We show for the first time that the growth of nanorod arrays along the c-axis can be controlled using different precursor volumes, and its growth mechanism is discussed. X-ray diffraction (XRD) spectra indicate that the prepared nanorods are ZnO with a hexagonal wurtzite structure that grows preferentially along the c-axis.

Controllable Growth of Vertically Aligned Aluminum-Doped Zinc Oxide Nanorod Arrays by Sonicated Sol–Gel Immersion Method depending on Precursor Solution Volumes

Controllable Growth of Vertically Aligned Aluminum-Doped Zinc Oxide Nanorod Arrays by Sonicated Sol–Gel Immersion Method depending on Precursor Solution Volumes

Performance of an Ultraviolet Photoconductive Sensor Using Well-Aligned Aluminium-Doped Zinc-Oxide Nanorod Arrays Annealed in an Air and Oxygen Environment

Ultraviolet (UV) photoconductive sensors were fabricated using an aluminium (Al)-doped zinc-oxide (ZnO) nanorod array with a diameter between 40 and 150 nm and thickness of approximately 1.1 µm. The nanorod arrays were prepared using a sonicated sol–gel immersion and annealed at 500 °C under different ambient conditions of air and oxygen. The annealing process induced the formation of nanoholes on the nanorod surfaces, which increased the nanorod surface area. The nanoholes existed in larger quantities on the nanorod surfaces annealed in air compared with the nanorods annealed in an oxygen environment. This condition reduced the rise and decay time constants of the air-annealed UV sensor. However, the sample annealed in an oxygen ambient shows the highest responsivity of 1.55 A/W for UV light (365 nm, 5 mW/cm2) under a 10 V bias mainly due to defect reduction and improvement in stoichiometric properties. To the best of our knowledge, a UV photoconductive sensor using this ZnO nanostructure has not yet been reported.

Performance of an Ultraviolet Photoconductive Sensor Using Well-Aligned Aluminium-Doped Zinc-Oxide Nanorod Arrays Annealed in an Air and Oxygen Environment

Ultraviolet (UV) photoconductive sensors were fabricated using an aluminium (Al)-doped zinc-oxide (ZnO) nanorod array with a diameter between 40 and 150 nm and thickness of approximately 1.1 µm. The nanorod arrays were prepared using a sonicated sol–gel immersion and annealed at 500 °C under different ambient conditions of air and oxygen. The annealing process induced the formation of nanoholes on the nanorod surfaces, which increased the nanorod surface area. The nanoholes existed in larger quantities on the nanorod surfaces annealed in air compared with the nanorods annealed in an oxygen environment. This condition reduced the rise and decay time constants of the air-annealed UV sensor. However, the sample annealed in an oxygen ambient shows the highest responsivity of 1.55 A/W for UV light (365 nm, 5 mW/cm2) under a 10 V bias mainly due to defect reduction and improvement in stoichiometric properties. To the best of our knowledge, a UV photoconductive sensor using this ZnO nanostructure has not yet been reported.

Growth of Al-doped ZnO nanorod arrays on the substrate at low temperature

Aluminum-doped zinc oxide nanorod arrays are deposited on glass by a solution method at low temperature (80 °C). The as-grown samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectroscopy and Raman spectroscopy. We observe that Raman spectroscopy of aluminum-doped zinc oxide nanorods is different from undoped zinc oxide nanorods. The intensity of Raman peak at 437 cm −1 decreases for aluminum-doped zinc oxide nanorods sample while a peak at 750 cm −1 appears. X-ray diffraction (XRD) shows aluminum-doped zinc oxide nanorods grown in (0 0 2) orientation.