ZnO Sol Research Articles

Multifunctional zinc oxide nanostructures for a new generation of devices

ZnO is a natural n-type widespread semiconductor with wide direct bandgap of 3.37eV, large exciton bending energy (60meV) and high optical gain (300cm−1). One dimensional ZnO nanomaterials such as nanowires or nanorods have focused much attention due to their multifunctionality in optoelectronic devices, gas sensing, piezoelectricity and thin film transistors for transparent and flexible electronics. Solution-phase chemical synthesis of nanomaterials has several important advantages, as low temperatures, high versatility, low cost, simple equipments and handling.The paper presents the chemical bath deposition synthesis and characterization of ZnO 1D nanostructures grown on glass substrates seeded with gold layer, pre-prepared ZnO nanoparticles or sol–gel derived ZnO layer. The obtained ZnO nanowires/nanorods were structurally and morphologically characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and the growth mechanism is discussed. The seed layer significantly affects the surface distribution and orientation of the grown 1D nanostructures. The diameter of the nanowires is mainly controlled by the concentration and temperature of the growth solution. The effect of growth conditions on the surface chemical composition and surface states/defects of semiconducting 1D nanostructures was investigated using X-ray photoelectron spectroscopy. The optical and electrical properties are presented.

전기방사를 이용한 Al이 첨가된 ZnO 나노섬유의 제조 및 광학 특성평가

ZnO는 반도전성과 초전도성을 나타내며 광학적으로도 독특한 재료로 가스센서, 태양전지, 광학도파관 등 여러 방면에 널리 활용되고 있다. 본 논문에서는 이러한 ZnO에 Al을 첨가함에 따라 광학적 특성에 어떠한 영향을 미치는지 알아보기 위하여 ZnO에 Al 첨가량 변화에 따른 나노구조체를 제작하여 특성을 비교하였다. ZnO 용액은 PVP, ethanol, zinc acetate를 이용하여 Sol의 형태로 제작하였으며, Al첨가용액을 넣어 Al이 첨가된 ZnO Sol을 제작하였다. 제작된 Sol을 전기 방사법을 이용하여 나노구조체를 제조하였다. 제조된 섬유들을 각각 300, 500, <TEX>$700^{\circ}C$</TEX>로 열처리 한 후 나노 구조체를 XRD, XPS, SEM을 이용하여 분석하였다. 또한 TGA, DSC를 이용하여 온도변화에 따른 질량 및 열량의 변화를 측정하였다. UVvis를 이용하여 ZnO와 Al이 첨가된 ZnO의 흡광도를 측정 비교하였다. Zinc oxide has semi-conductivity and super conductivity characteristics. It can be used optically and is applied on many areas such as gas sensor, solar cell and optical waveguide. In this paper, to improve optical characteristics of ZnO, aluminum was added on zinc oxide. Zinc oxide and aluminum zinc oxide was fabricated as nano fiber form. ZnO solution was created by mixing poly vinyl pyrrolidone, ethyl alcohol, and zinc acetate. An Al doped ZnO was created by adding aluminum solution to ZnO sol. By applying these sols on electro spinning method, nano fibers were fabricated. These fibers are heat treated at 300, 500, and <TEX>$700^{\circ}C$</TEX> degrees and were analyzed with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to examine the nano structures. TGA and DSC measurement was also used to measure the change of mass and calorie upon temperature change. The absorbance of ZnO and Al-doped ZnO was carried out by UV-vis measurement.

Polymer assisted Ga doped ZnO nanodisk/nanorod structures prepared by a low temperature one-pot hydrothermal method

Ga-doped ZnO (GZO) nanodisks and hybrid nanodisk/nanorod structures have been synthesized by simple one-pot hydrothermal process. Ga–ZnO sol–gel solution of different concentrations (0.2M and 0.5M) was used to make Ga–ZnO film on AlN/Si substrate. The crystalline phase, morphology and chemical composition were characterized. The XRD and FE-SEM studies have confirmed that the GZO exist in the form of wurtzite structure with nanodisk and hybrid nanodisk/nanorod morphologies. FE-SEM images confirmed the formation of pure nanodisks of Ga–ZnO(0.5) at an optimum ZnO sol concentration (0.5M). Hybrid nanodisk/nanorod morphologies were observed with a 0.2M Ga–ZnO(0.2) sol concentration. Major Raman shift value of 437cm−1 was observed for both GZO nanodisks and undoped ZnO. The sensing behavior of GZO nanodisks and nanodisk/nanorod morphologies in the presence of UV light and hydrogen gas flow response has been studied.

An Au buffer layer for the growth of a ZnO sol–gel film on a Si substrate

In this work, we demonstrate the influence of an Au buffer layer on the structure and photoluminescence (PL) properties of ZnO sol–gel thin films on Si substrates. An Au layer was deposited on the silicon substrate by the evaporation deposition method from highly pure Au (99.99%) wires. Then, a ZnO film was prepared by the sol–gel method with spin-coating technology, followed by calcinations in air at 600 °C for 1 h. The structures and morphologies of the prepared films were characterized by x-ray diffraction, energy dispersive spectrum analysis, atomic force microscopy and PL. The results show that the prepared ZnO thin film with an Au buffer layer exhibits good crystallinity and surface morphology compared with that without an Au buffer layer. Interestingly, different from other previous reports on buffer layers with PL-enhanced properties, the ZnO thin film with Au buffer layer showed an obvious violet PL-quenched property.

Preparation of superhydrophobic surface with a novel sol–gel system

Sol–gel method is a simple and cheap way to prepare superhydrophobic coatings or films, however, most of the researches on sol–gel focus on silica or ZnO sol–gel. The present paper proposes a novel sol–gel which is made from hydrolysis and condensation of the by-product of polymethylhydrosiloxane (PMHS) reacting with γ-aminopropyltriethoxysilane (KH550). The mechanism of formation of the by-product and the sol–gel is discussed and the by-product is characterized by FT-IR. The mass ratio of KH550/PMHS of the sol–gel influences the water contact angle (WCA) and water sliding angle (WSA) of the film made of spraying the sol–gel to microscope glass. When the mass ratio of KH550/PMHS of the sol–gel reaches 0.25, WCA of the corresponding film is 157° and WSA of it is less than 1°. The mechanism of formation of the sol–gel is discussed, and the size of the sol–gel is characterized by polarization microscope as well. The morphology of the film made of the sol–gel is analyzed by means of scanning electron microscope (SEM). It was found that the diameter of the particle of the superhydrophobic film is about 40μm, nevertheless, from the larger magnification picture, the particle is found to be composed of micro-balls whose diameter is about 2μm, and the micro-ball is composed of nano-sphere whose diameter is less than 200nm.

Fabrication of surface-patterned ZnO thin films using sol–gel methods and nanoimprint lithography

Surface-patterned ZnO thin films were fabricated by direct imprinting on ZnO sol and subsequent annealing process. The polymer-based ZnO sols were deposited on various substrates for the nanoimprint lithography and converted to surface-patterned ZnO gel films during the thermal curing nanoimprint process. Finally, crystalline ZnO films were obtained by subsequent annealing of the patterned ZnO gel films. The optical characterization indicates that the surface patterning of ZnO thin films can lead to an enhanced transmittance. Large-scale ZnO thin films with different patterns can be fabricated by various easy-made ordered templates using this combination of sol-gel and nanoimprint lithography techniques.

Enhancement of light extraction efficiency of GaN-based light-emitting diode using ZnO sol–gel direct imprinting

ZnO nano-structures were formed on transparent conducting oxide layer of GaN LED device on non-patterned (non-PSS) and patterned sapphire substrates (PSS). Since ZnO nano-structures were formed by sol–gel direct imprinting process, plasma etching process, which may create the plasma induced damage, was not used. Due to the ZnO nano-structures, light extracted from active layer was coupled with ZnO nano-structures and thus total internal reflection at the ITO layer was suppressed. According to electroluminescence measurement, the emission intensities of GaN LED devices with ZnO nano-structures, on both non-PSS and PSS sapphire substrates were increased by 20.5% and 19.0%, respectively, compared to GaN LED devices without ZnO nano-structures, due to the suppression of total internal reflection. Moreover, it is confirmed that there is no decrease of light extraction on side direction due to light focusing to vertical axis by nanostructure. Electrical performance of GaN LED devices were not degraded by ZnO sol–gel direct imprinting process.

Preparation of Polyacrylate/ZnO Nanocomposite

In this study, ZnO sol was prepared by sol-gel method with zinc acetate, triethanolamine and sodium hydroxide as the main material. Then obtained ZnO sol was directly blended with polyacrylate latex to prepare polyacrylate/ZnO nanocomposite. The effects of ZnO sol contents on the mechanical properties and water absorption of polyacrylate/ZnO nanocomposite were investigated in details. The results showed tensile strength of polyacrylate/ZnO nanocomposite reduced, and water absorption of it increased with the increasing of ZnO sol. Transmission electron micrograph (TEM) analysis indicated ZnO sol dispersed uniformly and the size of it was about 20nm. Scanning electronic microscope (SEM) analysis showed ZnO sol and polyacrylate have good compatibility, however, ZnO sol would condensate and form short rods structure during the film forming process.

Titania-Assisted Dispersion of Carboxylated Single-Walled Carbon Nanotubes in a ZnO Sol for Transparent Conducting Hybrid Films

We report a facile chemical route for stabilizing a dispersion of carboxylated single-walled carbon nanotubes (SWCNTs) in a ZnO sol. The dispersion is stabilized via capping of the carboxyl groups on the SWCNT surface by a titania layer, which was confirmed by Fourier transform infrared spectroscopy and transmission electron microscopy. We also demonstrate that the conductivity of the films prepared from the SWCNT/TiO(x)/ZnO sol is dramatically enhanced by thermal treatment and that the thermal stability of the hybridized films with the ZnO sol is notably improved relative to that of a pristine SWCNT film. The structural and chemical changes of the fabricated films were characterized by Raman spectroscopy. As one application, it was presented that thermally treated SWCNT/TiO(x)/ZnO hybrid thin film sensors showed hydrogen sensing characteristics even at room temperature.

Nanostructured ZnO/Conjugated Polymer for p–n Heterojunctions

High-density vertically aligned ZnO nanotubes (NTs) were prepared by etching ZnO nanorods (NRs) in aqueous solution, which were grown from ZnO sol–gel-derived seeds coated on transparent conductive glass substrate. We investigated the preparation of nanostructured oxide/conjugated polymer hybrid solar cells, where the regioregular poly(3-hexylthiophene) was infiltrated into transparent ZnO nanorod or nanotube films. The hybrid can take advantage of the high electron mobility attainable in oxide semiconductors and can be fabricated using low temperature aqueous solution growth techniques. Additionally, the morphology of the hybrid can be controlled in a systematic way through growth of the nanostructured ZnO to obtain a large amount of surface area. Because of the increased specific surface area, the power efficiency of cells based on ZnO NTs enhances twice as that of ZnO NRs. In other words, the nanotubes can offer a highly ordered material architecture with efficient charge generation and collection of electron in hybrid solar cells. A relation between efficiency and surface area is demonstrated.

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.

Synthesis of TiO&lt;sub&gt;2&lt;/sub&gt;/Zno Core/Shell Type Nanocomposite via Sol-Gel Method

TiO2/ZnO Nanocomposite powders with different Zn/Ti ratios were synthesized via sol-gel method. The as prepared and calcined Titania nanopowders were added to the ZnO sols. Also the as prepared and calcined ZnO nanopowders were separately added to the TiO2 sols. However, in the latter case, the nanocomposite never formed due to the high acidity of the sols. After gelation, the powders were dried and calcined at 500°C for 1h. The phase composition, structure, morphology and optoelectrical properties of the powders were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-Vis photospectroscopy and photoluminescence spectroscopy (PL). The XRD patterns confirm the presence of TiO2 and ZnO crystalline phases in the TiO2 particles/ZnO sol samples. The FESEM micrographs show that TiO2/ZnO nanocomposites heat treated at 500°C were formed with average diameter of about 250nm with 50nm ZnO particles on clusters of 40nm TiO2 particles. It was found that the optoelectronic properties of the nanocomposites were improved according to the UV-Vis and photoluminescence spectroscopy.

Effect of preheating process on crystallization and optical properties of sol-gel derived ZnO semiconductor thin films

Highly transparent ZnO semiconductor thin films were deposited onto alkali-free glass substrates by a sol-gel spin coating process. This research investigated the effects of different preheating rates (4 or 10°C/min) on the various surface morphologies, crystallization characteristics, and optical properties of these thin films. The ZnO sol was synthesized by dissolving the zinc acetate dihydrate in isopropanol (IPA), and then adding monoethanolamine (MEA). These as-coated films were preheated at 300°C for 10 min and annealed in an air ambiance at 500°C for 1 h. Experimental results revealed that the as-prepared films had a hexagonal wurtzite structure, and that the heating rates of the preheating process obviously affected the surface morphologies, crystallization qualities, and transparency levels of the thin films. A ZnO thin film preheated at 10°C/min exhibited preferential orientation along the (002) plane, a flat surface, and also achieved a high transmittance value, 92.5%, for light with a wavelength of 550 nm.

Highly concentrated zinc oxide nanocrystals sol with strong blueemission

Abstract Highly concentrated ZnO sol was synthesized by an improved sol–gel method. Water was used as a modifier to control the sol–gel reaction and provide a way to increase the sol concentration. Concentration of ZnO in the prepared sol is higher than from other methods. Optical absorption and photoluminescence were used to investigate optical properties of the prepared sol. FTIR test was performed to study the influence of water on the compounds of as-prepared sol. The size and morphology of ZnO nanoparticles have been studied by HRTEM. The prepared colloidal ZnO nanocrystals have narrow size distribution (5–8 nm) and showed strong blue emission. The prepared sol has enough potential for optoelectronic applications.

Self-organization of ZnO wrinkles oriented by patterned PMMA templates

In this study, well-ordered ZnO wrinkles were fabricated by sol–gel derived ZnO films via heat treatment at 400 °C for 2 h with the assistance of polymethymethacrylate (PMMA) templates. PMMA templates with various patterns were employed to investigate the effects of template geometries on arrangements of the formed ZnO wrinkles. The influence of thickness on the transformation of the entire resulting structures of the spin-coated ZnO sol–gel films is discussed. With 2-dimensional arrangement of PMMA patterns, more than two orientations of wrinkled ZnO can be induced in one template. By controlling the arrangement of PMMA patterns and thickness of ZnO sol–gel films, specific circular, hexagonal, triangular and triangular-star complex structures were produced due to the constrained shrinkage force of the ZnO films applied toward the PMMA side walls during drying. By this technique, we can obtain 3-dimensional ZnO structures that conventional photolithography and nano-imprinting lithography are hard to achieve in few process steps.

LUMINESCENT PROPERTY OF ZNO GRANULAR FILMS WITH DIFFERENT PARTICLE SIZE

Zinc oxide has received extensive attention for its unique luminescence properties. In this paper, ZnO granular films were prepared on the Si wafer and quartz substrate by Layer-by-Layer electrostatic self-assembly method. The effect of sol concentration on particle size and photoluminescence properties was investigated. SEM images indicate that ZnO particle size increases with sol concentration improving. Absorption edge and photoluminescence peak have a red-shift with particle size increase. The emission peak shift is resulted from particle size effect and the change of oxygen vacancy concentration in surface. The luminescent property of granular film shows big difference with that of ZnO sol. This difference is related to the assembly state of ZnO nanoparticles.

Transparent semiconductor zinc oxide thin films deposited on glass substrates by sol–gel process

Transparent semiconductor ZnO thin films were spin-coated onto alkali-free glass substrates by a sol–gel process. The influence of ZnO sols synthesized via different solvents (2-ME, EtOH or IPA) on the surface morphologies, microstructures, optical properties and resistivities of the obtained films were investigated. The as-coated films were annealed in ambient air at 500 °C for 1 h. X-ray diffraction results showed all polycrystalline ZnO thin films to have preferred orientation along the (0 0 2) plane. The surface morphologies, optical transmittances and resistivity values of the sol–gel derived ZnO thin films depended on the solvent used. The ZnO thin films synthesized with IPA as the solvent exhibited the highest average transmittance 92.2%, an RMS roughness of 4.52 nm and a resistivity of 1.5 × 10 5 Ω cm.

Ferromagnetic Co-doped ZnO film and fine patterns prepared using photosensitive sol–gel method

Using zinc acetate and cobalt acetate as raw materials, isopropanol as solvent, and monoethanolamine as stabilizer, photosensitive Co-doped ZnO sol was prepared by chemical modification with benzoylacetone. Chelate rings of benzoylacetone with zinc ions are formed in the Co-doped ZnO sol and corresponding gel films. Irradiation of the gel film by a UV lamp in air leads to decomposition of the chelate ring. Selective irradiation followed by leaching and annealing gave rise to the formation of Co-doped ZnO fine patterns. The Co-doped ZnO film prepared using the photosensitive sol–gel method had a wurtzite structure and showed room-temperature ferromagnetic property.

Facile Synthesis, Characterization of ZnO Nanotubes and Nanoflowers in an Aqueous Solution

Two kinds of different ZnO nanostructures, nanotubes, and nanoflowers were synthesized using an aqueous solution approach. It was demonstrated that the addition of Al3+ and ZnO sol causes the different growth behavior of ZnO nanostructures, and leads to the formation of a nanotube array as well as self‐assembled nanoflowers, respectively. The effects of reaction parameters on the morphology of ZnO nanostructures were investigated. The present route reports the possibility for morphology control and assembly of ZnO nanostructures on arbitrary substrates at a low temperature on a large scale.

Effect of aging time of ZnO sol on the structural and optical properties of ZnO thin films prepared by sol–gel method

In this work, ZnO thin films were prepared by sol–gel method and the effect of aging time of ZnO sol on the structural and optical properties of the films was studied. The structural characteristics of the samples were analyzed by an atomic force microscope and an X-ray diffractometer. The optical properties were studied by a UV–vis spectrophotometer and a fluorophotometer. The results show that the ZnO thin film prepared by the as-synthesized ZnO sol had relatively poor crystalline quality, low optical transmittance in the visible range and relatively weak ultraviolet emission performance. After the as-synthesized ZnO sol was aged for 24 h, the degree of the preferred crystal orientation along the c-axis of the ZnO thin film prepared by this aged sol was improved. At the same time, this film had a very smooth surface with uniform grains and both its visible range transmittance and ultraviolet emission intensity were obviously increased. These results suggest that appropriate aging of ZnO sol is very important for the improvement of structural and optical quality of ZnO thin films derived from sol–gel method.