Enormous enhancement of ZnO nanorod photoluminescence

ZnO nanorod arrays were grown on quartz slices in the aqueous solution of zinc acetate and hexamethylenetetramine at 90 °C. Then ZnO:Mg shells were epitaxially grown on the nanorods to form core/shell structures in the aqueous solution of zinc acetate, magnesium acetate and hexamethylenetetramine at the same temperature. Effects of the shells and UV laser beam irradiation on the crystal structure and photoluminescence properties of ZnO nanorods were studied. ZnO:Mg shells suppress the green emission and enhance the UV emission intensity of the nanorods by 38 times. Enhancement of the UV emission depends on the Mg content in the shells. Short time UV laser beam irradiation could improve ZnO nanorod emission efficiently. The UV emission intensity of ZnO nanorods is enhanced by 71 times by capping and subsequent UV laser beam irradiation.     

Rapid synthesis of novel flowerlike ZnO structures by thermolysis of zinc acetate

Novel flowerlike ZnO structures have been rapidly synthesized on (1 0 0)-Si substrates via thermolysis of zinc acetate in air ambient without any catalyst. The obtained ZnO products exhibit well-defined flowerlike morphologies consisting of multilayer petal crystals with tapering feature. High-resolution transmission electron microscope (HRTEM) and corresponding selected area electron diffraction pattern (SAED) reveal that these petal crystals are single crystal in nature and preferentially oriented in the c-axis direction. Room-temperature photoluminescence (PL) spectra show that all the samples exhibit prominent UV emissions around 376.8 nm and very weak visible emission peaks, which demonstrates that there are few deep-level defects in the single crystal petals of the flowerlike ZnO structures. The growth mechanism of the as-synthesized flowerlike ZnO structures was also discussed.     

Influence of pH value on the quality of sol-gel derived ZnO films

In sol-gel derived ZnO films the pH value of the sol plays an important role in controlling their properties. In this study, the influence of adding monoethanolamine to zinc acetate solution in methanol on structural, surface morphology and optical properties has been investigated. Addition of monoethanolamine to zinc acetate solution transforms the nature of the sol from acidic to alkaline by changing the pH value from 6.4 to 10.6. The investigations indicate that high quality ZnO films are obtained by using sol having monoethanolamine to zinc acetate ratio of 1:1 and pH value of 10.6.     

Spray pyrolysis deposition of ZnO thin films on FTO coated substrates from zinc acetate and zinc chloride precursor solution at different growth temperatures

ZnO thin films were fabricated using zinc chloride and zinc acetate precursors by the spray pyrolysis technique on FTO coated glass substrates. The ZnO films were grown in different deposition temperature ranges varying from 400 to 550 °C. Influences of substrate temperature and zinc precursors on crystal structure, morphology and optical property of the ZnO thin films were investigated. XRD patterns of the films deposited using chloride precursor indicate that (1 0 1) is dominant at low temperatures, while those deposited using acetate precursor show that (1 0 1) is dominant at high temperatures. SEM images show that deposition temperature and type of precursor have a strong effect on the surface morphology. Optical measurements show that ZnO films are obviously influenced by the substrate temperatures and different types of precursor solutions. It is observed that as temperature increases, transmittance decreases for ZnO films obtained using zinc chloride precursor, but the optical transmittance of ZnO films obtained using zinc acetate precursor increases as temperature increases.     

Properties of ZnO thin films grown on Si substrates by photo-assisted MOCVD

ZnO thin films were grown on (1 0 0) p-Si substrates by Photo-assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) using diethylzinc (DEZn) and O₂ as source materials and tungsten-halogen lamp as a light source. The effects of tungsten-halogen lamp irradiation on the surface morphology, structural and optical properties of the deposited ZnO films have been investigated by means of atomic force microscope (AFM), X-ray diffraction and photoluminescence (PL) spectra measurements. Compared with the samples without irradiation, the several characteristics of ZnO films with irradiation are improved, including an improvement in the crystallinity of c-axis orientation, an increase in the grain size and an improvement in optical quality of ZnO films. These results indicated that light irradiation played an important role in the growth of ZnO films by PA-MOCVD.     

Photosensitive sol-gel preparation and direct micro-patterning of c-oriented ZnO film

Using zinc acetate as the raw material, isopropanol as the solvent, and monoethanolamine as the stabilizer, photosensitive ZnO sol is prepared by chemical modification with the acetylacetone. Chelate rings of acetylacetone with zinc ions are formed in the ZnO sol and its corresponding gel films. Irradiation of the gel film by a UV lamp in air leads to the decomposition of the chelate ring. Using the photosensitivity of the gel films, ZnO gel patterns can be obtained by selective irradiation followed by leaching in organic solvents. After the patterned ZnO gel film is preheated at 500 °C, and fired at 600 °C, c-oriented ZnO patterned films are obtained.     

Growth mechanism and optical property of ZnO nanoparticles synthesized by sonochemical method

ZnO nanoparticles have been synthesized by ultrasonic irradiation of an aqueous-alcoholic/aqueous-alcoholic-ethylenediamine (EDA) solutions of zinc nitrate and sodium hydroxide. ZnO nanoparticles possess hexagonal wurtzite structures and they exhibit special photoluminescence properties with a red-shift of 22 nm in UV emission band. It is found that the ultrasonic irradiation time and the solvents both influence the growth mechanism and optical properties of ZnO nanoparticles. The possible growth mechanism of ZnO nanoparticles formation by sonochemical method has been tried to discuss.     

In situ formation deposited ZnO nanoparticles on silk fabrics under ultrasound irradiation

Deposition of zinc(II) oxide (ZnO) nanoparticles on the surface of silk fabrics was prepared by sequential dipping steps in alternating bath of potassium hydroxide and zinc nitrate under ultrasound irradiation. This coating involves in situ generation and deposition of ZnO in a one step. The effects of ultrasound irradiation, concentration and sequential dipping steps on growth of the ZnO nanoparticles have been studied. Results show a decrease in the particles size as increasing power of ultrasound irradiation. Also, increasing of the concentration and sequential dipping steps increase particle size. The physicochemical properties of the nanoparticles were determined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersive X-ray (WDX).     

Influence of solution parameters for the fast growth of ZnO nanostructures by laser-induced chemical liquid deposition

ZnO nanorods, nanoneedles, nanoparticles, and nanoballs were synthesized on fused quartz substrates upon irradiation of a droplet of methanolic zinc acetate dihydrate solution by an infrared (IR) continuous wave CO₂ laser for a few seconds. The addition of monoethanolamine and water to the solution improved the alignment of the nanorods and had a significant effect on the volume and morphology of the deposits. An increase of the zinc acetate concentration was found to lead to an increase of the thickness and area covered by the initial ZnO seed layer on which the nanostructures grew. By investigating the crystal structure of the deposits using X-ray and electron diffraction, we were able to show that the nanorods grow along the c axis with a high crystalline quality. Raman and photoluminescence spectroscopy confirmed the high quality of the grown ZnO nanostructures. As a matter of fact, their photoluminescence spectra are dominated by an intense UV emission around 390 nm.     

A Simple Hydrothermal Method for the Growth of ZnO Crystals

ZnO microstructures have been grown from zinc chloride (ZnCl₂) and ammonia solution at 100 °C for 1 – 24 hours. X‐ray diffraction, scanning electron microscope and field‐emission scanning microscope were utilized to investigate the structural properties and morphology of the ZnO crystals. Structural investigations show that phase‐pure hexagonal structure ZnO has been successfully synthesized, and the hexagonal structure ZnO can be achieved in solutions with an appropriate range of concentrations. Under our experimental conditions, several different morphologies of ZnO structures were obtained, including flower‐like and bar flower‐like. The relationship between the morphology and experimental conditions are discussed.     

Sonochemically assisted synthesis and application of hollow spheres, hollow prism, and coralline-like ZnO nanophotocatalyst

Nanosheet-based microspheres of ZnO with hierarchical structures, hollow prism, and coralline-like ZnO nanostructures were successfully prepared by ultrasonic irradiation in acidic ionic liquids (AILs). The hollow spherical is made up of many thin petals, the thickness of which is only about 90 nm. In the presence of AIL2, the one prepared at a frequency of 40 kHz is a mixture of nanofibers with diameters ranging from less than 30 nm to about 100 nm. ZnO nanostructure (with AIL1) reveals lozenge-shape hollow prism structures. The products were hollow prism structure covered with some nanometric-size nanoparticles. The average size of the nanoparticles is in the range of 40?C80 nm. It is found that the ultrasonic irradiation time, ultrasonic frequency, and the AILs influence the growth mechanism and optical properties of ZnO nanostructures. Producing Zno nanostructures by different traditional methods (e.g., hydrothermal method) requires basic media. These methods are not economical and environmentally friendly in many industrial processes. In so doing, a critical problem has been the point that, normally, a high concentration of base causes reactor metal corrosion. This is a simple and low-cost method, which can be expected to be applied in industry in the future. Also, importantly, the structures synthesized in this experiment can indicate a new way to construct nanodevices by self-organization in one step.     

Strong temperature and substrate effect on ZnO nanorod flower structures in modified chemical vapor condensation growth

We have reported low temperature growth (300 °C) of ZnO nanorod flower structures by depositing zinc acetate vapor on Ge (100) substrate in the form of a jet using chemical vapor condensation technique. The flowers were comprised of hierarchical arrangement of highly crystalline ZnO nanorods oriented isotropically around a common nucleus. The temperature window for stability of these structures was found to be very narrow and the formation of the flowers was highly depended on the type of the substrates used. The flower morphology changed to a different hemispherical shape when the growth temperature was increased by only 50 °C while decreasing the growth temperature of the same degrees resulted in an amorphous deposition of ZnO. The temperature and substrate effect has been explained on the basis of adatom kinetics during growth. X-ray diffraction and TEM study revealed wurtzite ZnO nanorods with lattice constants a and c of 3.2 and 5.19 Å, respectively. The flower structures showed strong room temperature photoluminescence having pure excitonic transition at around 3.298 eV.     

Nanocomposite materials based on poly(vinyl chloride) and bovine serum albumin modified ZnO through ultrasonic irradiation as a green technique: Optical,thermal, mechanical and morphological properties

In this project, physicochemical properties of poly(vinyl chloride) (PVC) reinforced by ZnO nanoparticles (NPs) were studied. Firstly, ZnO NPs were modified with bovine serum albumin (BSA) as an organo-modifier and biocompatible substance through ultrasound irradiation as environmental friendly, low cost and rapid means. Nanocomposite (NC) films were prepared by loadings of various ratios of ZnO/BSA NPs (3, 6 and 9 wt%) inside the PVC. Structural morphology and physical properties of the ZnO-BSA NPs and NC films were investigated via Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), transmission electron microscopy and field emission scanning electron microscopy. According to the obtained information from the TGA, an increase in the thermal stability can be clearly observed. Also the results of contact angle analysis indicated with increasing percent of ZnO/BSA NPs into PVC the hydrophilic behaviors of NCs were increased.     

Effect of doping on structural,optical and electrical properties of nanostructure ZnO films deposited onto a-Si:H/Si heterojunction

We investigated the structural; optical and electrical properties of ZnO thin films as the n-type semiconductor for silicon a-Si:H/Si heterojunction photodiodes. The ZnO film forms the front contact of the super-strata solar cell and has to exhibit good electrical (high conductivity) and optical (high transmittance) properties. In this paper we focused our attention on the influence of doping on device performance. The results show that the X-ray diffraction (XRD) spectra revealed a preferred orientation of the crystallites along c-axis. SEM images show that all films display a granular, polycrystalline morphology and the ZnO:Al exhibits a better grain uniformity. The transmittance of the doped films was found to be higher when compared to undoped ZnO. A low resistivity of the order of 2.8 × 10⁻⁴ Ω cm is obtained for ZnO:Al using 0.4 M concentration of zinc acetate. The photoluminescence (PL) spectra exhibit a blue band with two peaks centered at 442 nm (2.80 eV) and 490 nm (2.53 eV). It is noted that after doping the ZnO films a shift of the band by 22 nm (0.15 eV) is recorded and a high luminescence occurs when using Al as a dopant. Dark I–V curves of ZnO/a-Si:H/Si structure showed large difference, which means there is a kind of barrier to current flow between ZnO and a-Si:H layer. Doping films was applied and the turn-on voltages are around 0.6 V. Under reverse bias, the current of the ZnO/a-Si:H/Si heterojunction is larger than that of ZnO:Al/a-Si:H/Si. The improvement with ZnO:Al is attributed to a higher number of generated carriers in the nanostructure (due to the higher transmittance and a higher luminescence) that increases the probability of collisions.     

Synthesis and characterization of ZnO nanoparticles using polyethylene glycol (PEG)

ZnO nanoparticles and ZnO encapsulated with polyethylene glycol (PEG) was synthesized using zinc acetate as a precursor at low temperature and characterized by different techniques. The influence of the types of solvent, synthesis parameters, and PEG encapsulation on the crystallization, the surface morphology, and the luminescent properties of ZnO nanoparticles prepared by the sol–gel process were investigated. The influence of different addition molar masses of the PEG during the synthesis on the ZnO emission peaks was systematically monitored. The crystallinity, the surface morphology, and the photoluminescence (PL) properties of ZnO depended highly on the synthesis process and PEG encapsulation. X-ray diffraction (XRD) spectra of ZnO nanoparticles show that all the peaks corresponding to the various planes of wurtzite ZnO indicate the formation of a single phase. The absorption edges of these ZnO nanoparticles are shifted by additions of the PEG polymer. The photoluminescence (PL) characterization of the ZnO nanostructures exhibited a broad emission in the visible range with maximum peak at 450 and/or 560 nm.     

Structural and optical properties of Mn-doped ZnO nanocrystalline thin films with the different dopant concentrations

The transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn_1−xMn_xO) have been deposited on glass substrates via the sol–gel technique using zinc acetate dehydrate and manganese chloride as precursor. The as-deposited films with the different manganese compositions in the range of 2.5–20 at% were pre-heated at 100 °C for 1 h and 200 °C for 2 h, respectively, and then crystallized in air at 560 °C for 2 h. The structural properties and morphologies of the undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/Vis spectroscopy. The analyzed results indicates that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn related phases. Room temperature photoluminescence is observed for the ZnO and Mn-doped ZnO thin films.     

Effect of zinc sources on the morphology of ZnO nanostructures and their photoluminescence properties

The morphology and photoluminescence properties of ZnO nanostructures synthesized from deferent zinc sources by a vapor deposition process were investigated. The zinc sources involved pure zinc, ZnO, and ZnCO₃ powders, respectively. It was found that the zinc sources have a strong effect on the morphology of the ZnO nanostructures. For the pure zinc and ZnO sources, uniform ZnO nanowires and tetrapods are obtained, respectively. However, in the case of the ZnCO₃ source, the products are nanowire–tetrapod combined nanostructures, in which ZnO nanowires grow from the ends of tetrapod arms. The morphology differences of these products may be mainly concerned with the yield and constituents of the corresponding zinc vapor. Photoluminescence measurements show that the nanowires have a relatively stronger near-band UV emission than the other products. The strongest green-light emission from the tetrapods implies that more defects exist in the tetrapods. An evident peak at 430 nm is found in the spectrum of the nanowire–tetrapod combined nanostructures, which may be caused by oxygen-depletion interface traps. PACS 73.61.Tm; 81.10.Bk; 78.55.Et     

Zinc oxide nano-particles--sonochemical synthesis, characterization and application for photo-remediation of heavy metal

Zinc oxide nanoparticles have been synthesized sonochemically from zinc acetate solution in aqueous methanol, ethanol and iso-propanol containing about 5 volume% of alcohol. Characterization with FESEM, XRD, AFM and BET surface area shows that the synthesized particles differ in shape and size. ZnO synthesized using isopropanol was observed to be the most crystalline one. The synthesized nanoparticles were used for the photocatalytic reduction of hexavalent chromium in aqueous medium under solar radiation. It was observed that the initial reduction rates varied with the difference in morphology of ZnO crystallites.     

Hydrophobic Functionalization of ZnO Nanosheets by In Situ Center‐Substituted Synthesis for Selective Photocatalysis under Visible Irradiation

The selective degradation of specific substances in mixed contaminants is quite challenging. And a general approach for sensitized oxide semiconductor relies on dip‐coating method with sensitizer. Here, hydrophilic 2D, nest‐like architecture ZnO (ZnO NA) was hydrophobicly functioned by monomolecular–layer tetraphenylporphyrin zinc (ZnTPP), where ZnTPP was synthesized by means of an in situ center‐substituted (ISCS) process., i.e., the hydrogen atoms in the core of metal‐free tetraphenylporphyrin (H₂TPP) are substituted by the unsaturated zinc ions in ZnO NAs. ZnTPP/ZnO NA was exhibited with significant hydrophobicity, benefitting to absorb hydrophobic phenol (PL). Further, it is realized to selectively photodegradate PL in the mixture by ZnTPP/ZnO NAs under visible irradiation. Note that the rate of degradation to hydrophobic PL by ZnTPP/ZnO NA is 9.17 times of that for ZnO NA within 150 min; on the contrary, the degradation rate of hydrophilic rhodamine B (RhB) by ZnTPP/ZnO is reduced by 40%. Radiative lifetime of photogenerated charges is obviously increased by ZnTPP/ZnO NA compared with that of ZnTPP, indicating the effective charge separation for ZnTPP/ZnO NAs. In addition, ZnTPP/ZnO NA produced more superoxide radicals (·O₂^?) in comparison to ZnO NA. With surface functionalization, the feasibility of selective photocatalysis under visible irradiation is demonstrated.     

Nanostructure and optical properties of M doped ZnO (M=Ni, Mn) thin films prepared by sol-gel process

The transparent thin films of undoped, Mn-doped, and Ni-doped zinc oxide (ZnO) have been deposited on glass substrates via sol-gel technique using zinc acetate dehydrate, nickel chloride, and manganese chloride as precursors. The structural properties and morphologies of the deposited undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/vis spectroscopy. The analyzed results indicate that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn or Ni related phases. The band gap energy was estimated by Tauc's method and found to be 3.28, 3.26, and 3.34 eV for ZnO, Ni-doped ZnO, and Mn-doped ZnO thin films at room temperature, respectively. Room temperature photoluminescence is observed for the ZnO, Ni-doped ZnO, and Mn-doped ZnO thin films.