Aqueous Chemical Growth Process Research Articles

Enhanced luminescence property of 1 D nanorods realised by aqueous chemical growth on indium doped zinc oxide thin films

The current piece of research aims at the depiction of the adaptability of the 1 D nanorods on Zinc Oxide (ZnO) for Light Emitting Diode applications. Undoped and Indium doped ZnO films are deposited on glass substrates by Spray Pyrolysis at 425 °C. The indium doping level is varied from 1 to 4 at. % and the variation of structural, morphological and opto - electronic properties with indium doping are studied. The films with 2.5 at. % of indium doping showed better transmittance (~90%) and low electrical resistivity (1.77 × 10−2 Ωcm). 1 D nanorods have been deposited on In:ZnO thin films with better luminescence properties by Aqueous Chemical Growth (ACG) technique at various time durations. It is found that the morphology of the seed layer is the major factor determining the alignment of the nanorods. The In:ZnO 1 D nanorods deposited at 10 hours of ACG process is seen to have better electrical conductivity due to the effective networking of the nanorods. The X-Ray Diffraction analysis and X-Ray Photoelectron Spectroscopy analysis confirms the effective indium incorporation in the nanorods. The photoluminescence emission is found to depend strongly on the duration of ACG process and various defects are assigned for the emission in the visible region.

High-speed photoresponse properties of ultraviolet (UV) photodiodes using vertically aligned Al:ZnO nanowires

Ultraviolet (UV) photodiodes with fast photoresponse properties were fabricated using vertically aligned aluminum doped ZnO nanowires. Stable p-type ZnO have been achieved by doping equimolar concentration of P-N (0.75 at.%) simultaneously in ZnO. The vertically aligned and electrically conducting n-type Al (3 at.%) doped ZnO nanowires were grown by a simple aqueous chemical growth process. The structural, morphological, optical, and electrical properties were investigated. For the fabrication of UV photodiodes, the optimum p-type ZnO layers and n-type ZnO nanowires were stacked upon ITO substrate. A 250 nm thin NiO was deposited as an electron blocking layer (EBL) in between the ZnO p–n junctions. The current density–voltage (J–V) characteristic of the fabricated UV photodiode was measured under dark and UV illumination conditions. Under a reverse bias of 3 V, the device exhibits a high photoresponsivity (R) value of 15.07 (A/W) upon illumination of UV light (λ = 365 nm). The fabricated photodiode exhibits a fast photoresponse switching characteristics with a response and recovery time calculated as 61 ± 11 and 455 ± 41 ms, respectively. The role of vertically aligned nanowires in the formation of oxygen interstitial (Oi) defects and its impact on improving the UV photoresponse properties were investigated.

Growth and characterization of near white light emitting Al-Ga:ZnO nanowires

Aluminum and gallium dual doped ZnO (AGZO) thin film seed layers are deposited by doping equal concentration of Al and Ga ranging from 0.5–1.0 at% with a step of 0.1 at%. Structural analysis reveals hexagonal wurtzite structure of the AGZO films with a preferential orientation along (002) plane. Morphological analysis shows uniform distribution of crystallites. An average of 80% optical transmittance is observed for AGZO seed layers. The optimum doping concentration is found to be 0.8:0.8 at% of Al:Ga, which exhibits higher electron carrier concentration of 5.83 × 1020 cm−3 and lowest resistivity value of 1.72 × 10−2 Ω cm. The as-deposited conducting AGZO seed layers are eventually treated with an aqueous chemical growth (ACG) process with varying time duration, such as 5, 10 and 15 h in order to obtain one dimensional nanostructures. Morphological analysis shows that the as-grown nanowires are vertically aligned with higher growth density. Enhanced near white light emission has been observed for the as-grown AGZO nanowires with an increase in ACG process duration.

Novel one-dimensional ZnO nanorods synthesized through a two-step post-treatment for efficiency enhancement of dye-sensitized solar cells

Novel 1D irregular ZnO nanorods (ZNR) with a rough surface and a partially hollow structure (IZRH) was synthesized through an aqueous chemical growth process, followed by a two-step post-treatment. ZNR was first treated using an innovative hydrothermal method, followed by freezing at subzero temperatures to form IZRH. The as-prepared IZRH was compounded with hierarchical ZnO nanoparticles (ZNP) synthesized through low-temperature solid-phase method. The mixture of IZRH and ZNP was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy; it was used as photoanode in dye-sensitized solar cells (DSSCs). The photovoltaic performance of DSSCs was investigated. Result shows that after freezing post-treatment, IZRH can significantly enhance the conversion efficiency of DSSCs. The maximum power conversion efficiency reaches 7.08%, which is 33% and 45% higher than those of only hydrothermal post-treatment and without post-treatment, respectively.

Facile fabrication of ZnO nanorods/ZnO nanosheet–spheres hybrid photoanode for dye-sensitized solar cells

Zinc oxide ( ZnO ) nanorods (ZNRs) and hierarchical ZnO nanosheet–spheres (ZNSs) were prepared through a simple aqueous chemical growth process and a low-temperature solid-phase method, respectively. The prepared ZNRs and ZNSs were mixed to obtain a composite structure by using a circumference oscillator. After structure and morphology characterizations via X-ray diffraction and scanning electron microscopy, the mixture of ZNRs and ZNSs was used as a photoanode in dye-sensitized solar cells (DSSCs). Photovoltaic performance and optimal mixture ratio were investigated. The results indicated that the photovoltaic properties of DSSCs depended on the microstructures, morphologies and mixture ratios of the electrodes. In addition, the mixture of ZNRs and ZNSs (molar ratio of 1:12) yielded an overall light conversion efficiency of 6.02%, with a fill factor of 65.0%, a short-circuit current of 13.49 mA/cm2, and an open-circuit voltage of 0.69 V. These values are higher than those of pure ZNRs or pure ZNSs.

Investigation on P-N dual acceptor doped p-type ZnO thin films and subsequent growth of pencil-like nanowires

Phosphorous and nitrogen dual acceptor doped p-type ZnO (PNZO) have been deposited by spray pyrolysis method on glass substrates. An equimolar doping concentration of P and N were varied from 0.25–1.25 at% with a step of 0.25 at%. Preferred orientation along (002) planes with hexagonal wurzite structure was observed from structural analysis. Morphological analysis reveals uniform distributions of grains. Electrical studies showed dual acceptor doping of P and N in ZnO results in p-type behavior. The optimum doping concentration of P and N was found to be 0.75 at% which exhibited hole concentration of 4.48 × 1018 cm−3 and low resistivity value of 9.6 Ω.cm. Photoluminescence (PL) studies revealed that, as-deposited films exhibit strong UV emission at 383 nm of the spectrum. The surface morphology of the optimum PNZO (0.75 at%) samples were further modified in the form of vertically aligned pencil-like nanowires by modified aqueous chemical growth (ACG) process. During ACG process, more acceptor related defects such as oxygen interstitials (Oi) were formed in the PNZO nanopencils. These acceptor defects induce enhanced emission in the visible region (400 nm to 700 nm) and also promote stable p-type characteristics.

Low temperature growth of ZnO nanowire arrays with enhanced high performance photocatalytic activity and reusability

Aligned ZnO nanowire arrays have been grown on the silicon substrates with ZnO seed layer by an aqueous chemical growth process at low reaction temperature. The volumes of ammonium hydroxide solution are not only controlled by the dimension and density of ZnO nanowires, but are also influenced by their optical emission property. The ZnO nanowire arrays exhibit very strong and broad green emission from defect in the cathodoluminescence spectrum. In addition, the ZnO nanowires grown on the silicon substrates can serve as effective and convenient recyclable photocatalysts. Only a very slight decrease in the photodecomposition rate was observed after ten cycles of the photocatalysis experiment.

Enhanced visible emission from vertically aligned ZnO nanostructures by aqueous chemical growth process

ZnO nanostructures consisting of nanowires and nanorods have been grown by aqueous chemical growth (ACG) process on the ZnO seed layers. ACG process has been carried out for 5h and 15h to obtain the one dimensional nanostructures. This ZnO nanostructure comprises mixture of vertically aligned nanorods and nanowires. Structural analysis reveals that the crystal orientation is along (002) plane exhibiting a hexagonal wurtzite structure. The crystallinity of ZnO nanostructures increases after aqueous chemical treatment with respect to the growth duration. Optical studies revealed that when the duration of aqueous chemical treatment is increased, the transmittance of the films decreases considerably. The as-deposited ZnO seed layers exhibit electron carrier concentration of 4.69×1014cm−3 and the value increases to 9.44×1015cm−3 after 5h and 1.53×1016cm−3 after 15h of aqueous chemical treatment. It has been observed that ZnO nanostructures exhibit enhanced luminescence properties in visible region which covers the entire visible region of the spectrum.

Epitaxial growth of vertically aligned highly conducting ZnO nanowires by modified aqueous chemical growth process

We report the fabrication of one dimensional conducting Al doped ZnO nanowires by spray pyrolysis and subsequent aqueous chemical growth (ACG) process. Al doped ZnO (AZO) thin film seed layers have been prepared with the Al concentration varying from 1 to 5at% by spray pyrolysis technique. The structural analysis shows that the as grown films have hexagonal wurtzite crystal structure with a preferential orientation of (002). The AZO seed layers have an average optical transmittance of 80%. It is observed that 3at% is the optimum value of Al doping concentration in ZnO, showing lowest electrical resistivity of 3.51×10−2Ωcm with a carrier concentration of 1.52×1019cm−3 and exhibiting n-type behavior. This optimum AZO (3at%) films are used as a seed layers for the growth of vertically aligned one dimensional highly conducting ZnO nanowires by a modified aqueous chemical growth (ACG) process. The optical transmittance is found to decrease to the order 50% after the AZO nanowires grown upon AZO (3at%) films. As grown ZnO nanowires exhibit an increased carrier concentration of 2.87×1020cm−3 and a lower resistivity of 3.00×10−2Ωcm in comparison to AZO 3at% seed layers. Photoluminescence studies reveal that AZO seed layers and nanowires exhibit strong UV emission at 378nm. Moreover, AZO nanowires show enhanced luminescent properties in the visible region ranging from 400 to 700nm.

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.

Low Temperature Synthesis of Nanocrystallized Titanium Oxides with Layered or Tridimensional Frameworks, from [Ti8O12(H2O)24]Cl8·HCl·7H2O Hydrolysis

A low-temperature aqueous chemical growth process was developed to produce nanometric titanium oxide with controlled size and structural variety. Gentle hydrolysis of a commercial TiOCl2 solution, in a controlled relative humidity, leads to the formation of single crystals of [Ti8O12(H2O)24]Cl8·HCl·7H2O. Under autogenous pressure at 120 °C, the hydrolysis of the latter by tetramethylammonium hydroxide (noted TMAOH) is mainly governed by the R = Ti/TMAOH molar ratio and thus by the pH value. Two values are particularly important: R = 8/9 and 8/17. The former corresponds to the balance of the Cl− ions of the titanium oxychloride hydrate by TMA+ cations and the latter to the stoichiometric ratio for the formation of a layered oxo-hydroxide (TMA)2Ti2O4−x(CO3)x(OH)2·nH2O, x = 0.7, which is obtained under basic conditions. Above R = 8/9, that is, in an acidic medium, the solvothermal treatment at 120 °C directly leads to the crystallization of anatase and then rutile when the pH decreases. For intermediate R values, the amorphous dried solid is required to be rinsed and dried at 110 °C to lead to the crystallization of nanometric titania, either anatase or brookite. TEM studies show that titania nanoparticles exhibit superstructures involving a doubling of the cell parameters that could originate from the adsorption of carbonate, hydrogen carbonate, or hydroxyl groups on the nanocrystallite surface. During evaporation of the solvent, these crystallites can self-assemble to form micrometric platelets.

Optical properties of ZnO nanorods realised by aqueous chemical growth

Abstract Photoluminescence investigations of ZnO nanorods realised by an advanced two-step aqueous chemical growth process have been carried out revealing well-resolved near-band-edge emission accompanied by phonon replicas. The optical properties of nanorods with different lengths and diameters are quite similar indicating a good control of the growth process without influencing the optical properties even on plastic substrate. The near-band-edge emission has a very broad line-width of ∼ 10 meV. Annealing in Ar atmosphere reduces the deep-level emission with a corresponding increase of the near-band-edge emission.

Selective growth of ZnO nanorods in aqueous solution

ZnO nanorod arrays find applications in solar energy conversion, light emission and other promising areas. One approach to generate ZnO nanorods is the cost efficient aqueous chemical growth (ACG). Usually the ACG process is based on a nucleation step followed by growth of ZnO nanorods in aqueous solution at temperatures below 95 ∘C. We report on the fabrication of homogeneous, large scale arrays of nanorods on various substrate materials (Si, glass, polymer) by ACG. PL-measurements show surprisingly good optical quality although the rods were grown at low temperature. Even though we have developed patterning of these arrays with photolithographic techniques, a bottom up approach for lateral patterning is important concerning further applications especially for mass-production. The substrates with patterned metal layers were employed to realize selective growth of nanorods. The experiments were carried out on Ti-, Ag- and Pt-patterned substrates. Selective growth on metal structured glass substrates was developed and is described.