Low Temperature Aqueous Chemical Growth Research Articles

Hydrothermal Growth of Vertically Aligned ZnO Nanorods Using a Biocomposite Seed Layer of ZnO Nanoparticles.

Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO nanorods has been investigated. ZnO nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO nanorods can be grown with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role.

Low temperature aqueous chemical growth, structural, and optical properties of Mn-doped ZnO nanowires

Mn-doped ZnO nanowires were successfully synthesized by using the low temperature aqueous chemical growth (ACG) method. Field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy have been used to characterize the grown Zn1−xMnxO. The FESEM and the XRD measurements revealed that the grown of Mn-doped ZnO had wurtzite structure and the lattice parameters and the size of the crystal changed according to the change of concentration of the dopant. The chemical composition and charge states of the Mn ions doped in the ZnO nanowires was analyzed by the EDX and the XPS, respectively, indicated that the Mn ions is incorporated onto zinc sites in the ZnO nanowires. PL spectroscoCpy shows a strong ultraviolet (UV) emission peak at 378nm (3.27eV) from the Mn-doped ZnO nanowires, which is shifted 6nm to the lower wavelength compared to ZnO nanowires grown by the same ACG method. The unique feature of our samples were the simple low temperature growth method which provides no clustering and the as-synthesized Mn-doped ZnO nanowires have shown good crystal quality. This capability to fabricate Mn-doped ZnO nanowires is of potential to develop new spintronic, photonic and sensor devices fabrication on any substrates.

Indirect Determination of Mercury Ion by Inhibition of a Glucose Biosensor Based on ZnO Nanorods

A potentiometric glucose biosensor based on immobilization of glucose oxidase (GOD) on ZnO nanorods (ZnO-NRs) has been developed for the indirect determination of environmental mercury ions. The ZnO-NRs were grown on a gold coated glass substrate by using the low temperature aqueous chemical growth (ACG) approach. Glucose oxidase in conjunction with a chitosan membrane and a glutaraldehyde (GA) were immobilized on the surface of the ZnO-NRs using a simple physical adsorption method and then used as a potentiometric working electrode. The potential response of the biosensor between the working electrode and an Ag/AgCl reference electrode was measured in a 1mM phosphate buffer solution (PBS). The detection limit of the mercury ion sensor was found to be 0.5 nM. The experimental results provide two linear ranges of the inhibition from 0.5 × 10−6 mM to 0.5 × 10−4 mM, and from 0.5 × 10−4 mM to 20 mM of mercury ion for fixed 1 mM of glucose concentration in the solution. The linear range of the inhibition from 10−3 mM to 6 mM of mercury ion was also acquired for a fixed 10 mM of glucose concentration. The working electrode can be reactivated by more than 70% after inhibition by simply dipping the used electrode in a 10 mM PBS solution for 7 min. The electrodes retained their original enzyme activity by about 90% for more than three weeks. The response to mercury ions was highly sensitive, selective, stable, reproducible, and interference resistant, and exhibits a fast response time. The developed glucose biosensor has a great potential for detection of mercury with several advantages such as being inexpensive, requiring minimum hardware and being suitable for unskilled users.

Piezoelectric nanogenerator based on zinc oxide nanorods grown on textile cotton fabric

This investigation explores piezoelectricity generation from ZnO nanorods, which were grown on silver coated textile cotton fabrics using the low temperature aqueous chemical growth method. The morphology and crystal structure studies were carried out by x-ray diffraction, scanning electron microscopic and high resolution transmission electron microscopic techniques, respectively. ZnO nanorods were highly dense, well aligned, uniform in spatial distribution and exhibited good crystal quality. The generation of piezoelectricity from fabricated ZnO nanorods grown on textile cotton fabrics was measured using contact mode atomic force microscopy. The average output voltage generated from ZnO nanorods was measured to be around 9.5 mV. This investigation is an important achievement regarding the piezoelectricity generation on textile cotton fabric substrate. The fabrication of this device provides an alternative approach for a flexible substrate to develop devices for energy harvesting and optoelectronic technology on textiles.

The inorganic-organic hybrid junction with n-ZnO nanorods/p-polyfluorene structure grown with low-temperature aqueous chemical growth method

The inorganic-organic hybrid junction was synthesized on ITO glass substrate, which was consisted of an n-type ZnO nanorods (NRs) grown by low-temperature aqueous chemical growth method and a p-type polyfluorene (PF) organic film fabricated by spin-coating. The experimental results indicate that densely and uniformly distributed ZnO nanorods are successfully grown on the PF layer. The thickness of the PF layer plays a dominant role for the current-voltage (I–V) characteristic of the ZnO NRs/PF inorganic-organic hybrid junction device, and a p-n junction with obviously rectifying behavior is achieved with optimal PF layer thickness. The photoluminescence (PL) spectrum covering the broad visible range was obtained from the n-ZnO nanorods/p-polyfluorene (PF) structure, which was originated from the combination of the PF-related blue emission and the ZnO-related deep level emission.

Back Cover: Piezoelectric power generation from zinc oxide nanowires grown on paper substrate (Phys. Status Solidi RRL 2/2012)

Intense world-wide research efforts have been devoted to the search for materials which significantly enhance the capability for the piezoelectric effect. Paper substrate with so many advantages over conventional substrates can be one of the low-cost alternates for piezoelectric applications. It offers a potential solution for powering various nanodevices and nanosystems. ZnO has the highest effective piezoelectric coefficient among II–IV tetrahedrally coordinated wurtzite compound semiconductors. The lack of a center of symmetry, combined with a large electromechanical coupling, results in strong piezoelectric property. Due to the high piezoelectricity coefficient and electromechanical coupling ZnO has attracted substantial research, and various novel applications have been demonstrated. In this issue, Soomro et al. (pp. 80–82) report the piezoelectric effect and generation of piezo potential of vertically aligned ZnO nanowires grown by the simple low temperature aqueous chemical growth (ACG) method on paper substrate by using atomic force microscopy.

Selective zinc ion detection by functionalised ZnO nanorods with ionophore

In this paper, highly dense and well aligned single-crystal zinc oxide nanorods were grown along the c-axis on a gold coated glass substrate using a low temperature aqueous chemical growth approach. The prepared ZnO nanorods were functionalized with plastic membrane coatings containing specific ionophore (12-crown-4) which is highly selective to zinc ions (Zn+2). The electrochemical response of the sensor was found to be linear over a relatively wide logarithmic concentration range from 1 μM to 100 mM. The proposed sensor showed a good linearity with a high sensitivity of ∼35 mV/decade for sensing Zn+2 ions. A fast response time of less than 5 s with a good selectivity, repeatability, reproducibility, and negligible response to common interferents ions such as calcium (Ca2+), magnesium (Mg2+), or potassium (K+), and iron (Fe+3) and copper (Cu+2) was also demonstrated. Moreover, the proposed sensor showed good stoichiometric results for potentiometric titration.

ZnO Nanorods Based Enzymatic Biosensor for Selective Determination of Penicillin.

In this study, we have successfully demonstrated the fabrication of a biosensor based on well aligned single-crystal zinc oxide (ZnO) nanorods which were grown on gold coated glass substrate using a low temperature aqueous chemical growth (ACG) method. The ZnO nanorods were immobilized with penicillinase enzyme using the physical adsorption approach in combination with N-5-azido-2-nitrobenzoyloxysuccinimide (ANB-NOS) as cross linking molecules. The potentiometric response of the sensor configuration revealed good linearity over a large logarithmic concentration range from 100 µM to 100 mM. During the investigations, the proposed sensor showed a good stability with high sensitivity of ~121 mV/decade for sensing of penicillin. A quick electrochemical response of less than 5 s with a good selectivity, repeatability, reproducibility and a negligible response to common interferents such as Na1+, K1+, d-glucose, l-glucose, ascorbic acid, uric acid, urea, sucrose, lactose, glycine, penicilloic acid and cephalosporins, was observed.

GROWTH, PROPERTIES AND SENSOR APPLICATIONS OF LOW TEMPERATURE GROWN ZnO NANORODS

ZnO nanorods with the average diameter of about 60–300 nm have been grown by the low temperature aqueous chemical growth technique. The impact of growth time and reactant concentration on the morphology on ZnO structures was tested by scanning electron microscopy and photoluminescence spectroscopy. High optical quality of obtained ZnO nanorod films was evidenced by dominating free exciton transitions. The reduction of surface to volume ratio by increasing the diameter of ZnO nanorods resulted in a linear increase of excitonic luminescence intensity with respect to the defect related emission. Excellent photoluminescence properties and high surface area of ZnO nanorods can be used for the detection of organic contaminants dissolved in water. The quenching of both excitonic and defect luminescence was observed upon exposure of ZnO nanorod films to various organic contaminants.

Selective determination of urea using urease immobilized on ZnO nanowires

Well-aligned zinc oxide (ZnO) nanowire arrays were fabricated on gold-coated plastic substrates using a low-temperature aqueous chemical growth (ACG) method. The ZnO nanowire arrays with 50–130 nm diameters and ∼1 μm in lengths were used in an enzyme-based urea sensor through immobilization of the enzyme urease that was found to be sensitive to urea concentrations from 0.1 mM to 100 mM. Two linear sensitivity regions were observed when the electrochemical responses (EMF) of the sensors were plotted vs. the logarithmic concentration range of urea from 0.1 mM to 100 mM. The proposed sensor showed a sensitivity of 52.8 mV/decade for 0.1–40 mM urea and a fast response time less than 4 s was achieved with good selectivity, reproducibility and negligible response to common interferents such as ascorbic acid and uric acid, glucose, K + and Na + ions.

Study of the Distribution of Radiative Defects and Reabsorption of the UV in ZnO Nanorods-Organic Hybrid White Light Emitting Diodes (LEDs)

In this study, the low temperature aqueous chemical growth (ACG) method was employed to synthesized ZnO nanorods to process-organic hybrid white light emitting diodes (LEDs) on glass substrate. Electroluminescence spectra of the hybrid white LEDs demonstrate the combination of emission bands arising from radiative recombination of the organic and ZnO nanorods (NRs). Depth resolved luminescence was used for probing the nature and spatial distribution of radiative defects, especially to study the re-absorption of ultraviolet (UV) in this hybrid white LEDs structure. At room temperature the cathodoluminescence (CL) spectra intensity of the deep band emission (DBE) is increased with the increase of the electron beam penetration depth due to the increase of defect concentration at the ZnO NRs/Polyfluorene (PFO) interface and probably due to internal absorption of the UV. A strong dependency between the intensity ratio of the UV to the DBE bands and the spatial distribution of the radiative defects in ZnO NRs has been found. The comparison of the CL spectra from the PFO and the ZnO NRs demonstrate that PFO has a very weak violet-blue emission band, which confirms that most of the white emission components originate from the ZnO NRs.

Study of intrinsic white light emission and its components from ZnO-nanorods/p-polymer hybrid junctions grown on glass substrates

We report white-light luminescence from ZnO-organic hybrid light emitting diodes grown on glass substrate by low temperature aqueous chemical growth. The configuration used for the hybrid white light emitting diodes (HWLEDs) consists of two-layers of polymers (PEDOT:PSS/PFO) on glass with top ZnO nanorods. Electroluminescence spectra of the HWLEDs demonstrate the combination of emission bands arising from the radiative recombination in polymer and ZnO nanorods. In order to distinguish emission bands we used a Gaussian function to simulate the experimental data. The emitted white light was found to be the superposition of a blue line at 454 nm, a green emission at 540 nm, orange line at 617 nm, and finally a red emission at 680 nm. The transitions causing these emissions are identified and discussed in terms of the energy band diagram of the hybrid junction. Color coordinates measurement of the WLED reveals that the emitted light has a white impression with 70 color rendering index and correlated color temperature 5500 K. Comparison between ITO and aluminum top contacts and its influence on the emitted intensity is also discussed.

Growth, properties and sensor applications of low temperature grown ZnO nanorods

ZnO nanorods with the average diameter of about 60–300 nm have been grown by the low temperature aqueous chemical growth technique. The impact of growth time and reactant concentration on the morphology on ZnO structures was tested by scanning electron microscopy and photoluminescence spectroscopy. High optical quality of obtained ZnO nanorod films was evidenced by dominating free exciton transitions. The reduction of surface to volume ratio by increasing the diameter of ZnO nanorods resulted in a linear increase of excitonic luminescence intensity with respect to the defect related emission. Excellent photoluminescence properties and high surface area of ZnO nanorods can be used for the detection of organic contaminants dissolved in water. The quenching of both excitonic and defect luminescence was observed upon exposure of ZnO nanorod films to various organic contaminants.

Surface Modification of α-Fe2O3 Nanorod Array Photoanodes for Improved Light-Induced Water Splitting

ABSTRACTα-Fe2O3 nanorod arrays were fabricated by a low-temperature aqueous chemical growth (ACG) technique and followed by an annealing process. For the surface doping of α-Fe2O3 nanorods, β-FeOOH nanorods obtained via ACG were coated with a thin layer of Cr3+ precursor solution by spin coating, and then underwent the annealing treatment in air. Conducting polymer polypyrrole (PPy) decorated α-Fe2O3 nanorods were prepared by electrodeposition method using malic acid contained pyrrole aqueous solution. Primary results showed that the photocurrents of α-Fe2O3 nanorod array photoanodes were greatly enhanced by surface doping of Cr3+, as well as PPy decoration. This might be due to the retarded charge recombination and promoted surface reaction rate of photogenerated holes with water. Further investigation on surface modification of α-Fe2O3 nanorod array photoanodes is currently conducted in our group.

Functionalised zinc oxide nanotube arrays as electrochemical sensors for the selective determination of glucose

In the present study, highly oriented single-crystal zinc oxide nanotube (ZnO-NT) arrays were prepared by a trimming of ZnO nanorods along the c-axis on the gold-coated glass substrate having a diameter of 100–200 nm and a length of ∼1 µm using a low-temperature aqueous chemical growth process. The prepared (ZnO-NT) arrays were further used as electrochemical enzyme-based glucose sensors through immobilisation of glucose oxidase by the physical adsorption method in conjunction with a Nafion coating. The electrochemical response of the sensor was found to be linear over a relatively wide logarithmic concentration range from 0.5×10−6 to 12×10−3 M. The proposed sensor showed a high sensitivity of 69.12 mV/decade with R=0.9934 for sensing of glucose. A fast-response time less than 4 s with good selectivity, reproducibility and negligible response to common interferents such as ascorbic acid and uric acid prevailed.

Growth and Structure of ZnO Nanorods on a Sub-Micrometer Glass Pipette and Their Application as Intracellular Potentiometric Selective Ion Sensors.

This paper presents the growth and structure of ZnO nanorods on a sub-micrometer glass pipette and their application as an intracellular selective ion sensor. Highly oriented, vertical and aligned ZnO nanorods were grown on the tip of a borosilicate glass capillary (0.7 µm in diameter) by the low temperature aqueous chemical growth (ACG) technique. The relatively large surface-to-volume ratio of ZnO nanorods makes them attractive for electrochemical sensing. Transmission electron microscopy studies show that ZnO nanorods are single crystals and grow along the crystal’s c-axis. The ZnO nanorods were functionalized with a polymeric membrane for selective intracellular measurements of Na+. The membrane-coated ZnO nanorods exhibited a Na+-dependent electrochemical potential difference versus an Ag/AgCl reference micro-electrode within a wide concentration range from 0.5 mM to 100 mM. The fabrication of functionalized ZnO nanorods paves the way to sense a wide range of biochemical species at the intracellular level.

Fabrication and characterization of high-brightness light emitting diodes based on n-ZnO nanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN

Light emitting diodes (LEDs) based on n-ZnO nanorods (NRs)/p-4H-SiC and n-ZnO (NRs)/p-GaN were fabricated and characterized. For the two LEDs the ZnO NRs were grown using a low temperature (<100 °C) aqueous chemical growth (ACG) technique. Both LEDs showed very bright nearly white light electroluminescence (EL) emission. The observed luminescence was a result of the combination of three emission lines composed of violet-blue, green and orange-red peaks observed from the two LEDs. Room temperature photoluminescence (PL) was also measured and consistency with EL was observed. It was found that the green and violet-blue peaks are red-shifted while the orange peak is blue-shifted in the EL measurement. It was also found that due to the effect of the GaN substrate the violet-blue peak in the EL measurement is more red-shifted in n-ZnO (NRs)/p-GaN LEDs as compared to n-ZnO (NRs)/p-4H-SiC LEDs.

The effect of the post-growth annealing on the electroluminescence properties of [formula omitted]-ZnO nanorods/ [formula omitted]-GaN light emitting diodes

In this paper we investigated the effect of post-growth annealing treatment on the electroluminescence (EL) of n -ZnO nanorods/ p -GaN light emitting diodes. The ZnO nanorods were grown by the low temperature (<100 °C) aqueous chemical growth (ACG) technique. The as-grown ZnO nanorods were annealed in nitrogen, oxygen, argon, and air ambients at 600 °C for 30 min. The electroluminescence (EL) measurements showed that the deep level defects related emissions in ZnO were greatly affected by the annealing of the n -ZnO nanorods in different ambients. By comparing the EL spectra of ZnO nanorods annealed in different ambients it was found that nitrogen annealing ambient is very effective in shifting the emission peak from the green region to the red region. It was also concluded that the red emission in ZnO was attributed to oxygen vacancies ( V o ). The effect of the annealing ambient and the temperature dependence electroluminescence were discussed with relation to the intrinsic and extrinsic defects.

Zinc oxide nanorod-based heterostructures on solid and soft substrates for white-light-emitting diode applications

ZnO nanorods with excellent optical and electro-optical emission characteristics were grown using high- and low-temperature techniques on solid and soft substrate materials. The solid crystalline substrates included p-4H-SiC and p-GaN, while the soft amorphous substrates included p-type polymers deposited on glass and flexible plastic. Two different growth approaches were used to produce these samples. We used the vapor–liquid–solid (VLS) technique (high temperature) and aqueous chemical growth (ACG), which is a low-temperature technique. These ZnO nanorod samples were characterized by room temperature photoluminescence (PL) and processed to fabricate light-emitting diodes (LEDs). The LED characteristics were further investigated by I–V and electroluminescence (EL). As observed by PL measurements, all samples revealed a sharp narrow ultraviolet (UV) peak due to band-edge emission, indicating the good crystalline quality of the grown ZnO nanorods. The origin of the different peaks within the visible region was correlated to different deep level defects reported earlier for ZnO. All fabricated LEDs showed EL providing a wide band extended through the whole visible spectrum and hence produced clear white light observable to the naked eye. The emitted color quality investigation showed that superior color quality was manifested in a high color rendering index and stable color under current variation, indicating that these heterojunction and hybrid LEDs have potential for the development of future light sources. The ZnO nanorod-based LEDs grown by low-temperature ACG on glass and flexible plastic can, after further development, be candidates for future large-area white-light sources.

Dye-Sensitized Solar Cells on the Basis of ZnO Nanorods

We report on the fabrication of solid-state dye-sensitized solar cells with ZnO nanorods as n-type material and CuSCN as p-type material. The ZnO nanorods were grown on ITO-coated glass by using a low-temperature aqueous chemical growth approach employing di erent growth times. If the growth time is changed, the nanorod morphology can be varied in lentgh and diameter. CuSCN was deposited on the dye-coated ZnO nanorods from a solution in di-n-propyl sulphide, so that the nanorods are fully embedded in CuSCN. The ZnO/dye/CuSCN solar cells show photocurrents of 0.26 mA/cm2, an open circuit voltage of 0.34 V and an energy conversion e ciency of 0.1 %.