Self-assembly of ZnO nanosheets into nanoflowers at room temperature

A singularity flower-like ZnO nanostructure was prepared on a large scale through a very simple solution method at room temperature and under ambient pressure in a very short time. The flower-like ZnO nanostructures were self-assembled by thin and uniform nanosheets, with a thickness of around 5 nm. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology. The possible growth mechanism was discussed based on the reaction process. The blue shift in the UV-vis spectra of the ZnO nanostructures was also observed.     

Growth and characterizations of ZnO nanorod/film structures on copper coated Si substrates

ZnO deposits were obtained on electroless copper coated Si substrates using a conventional RF magnetron sputter deposition technique at room temperature. The deposition pressure was varied from 6.67 Pa to 0.667 Pa. The RF powers were from 100 to 200 W and the electrode distance was fixed at 5 cm. The ZnO deposition time was varied from 1 to 30 min. The deposits consist of ZnO nanorods and a ZnO film, with the roots of the nanorods embedded in the film. The growth of the nanorods far exceeds the growth of the film in the beginning of the deposition process. The nanorod lengthening rate then slows down and becomes lower than the film growth rate. Effects of sputter deposition parameters on the growth of ZnO nanorods/film structures were also investigated.     

A study on rapid growth and piezoelectric effect of ZnO nanowires array

This work presents a rapid and simple synthesis procedure for ZnO nanowires (NWs) array by using the vapor–solid (VS) method. Experimental results indicate that the length and diameter of the grown ZnO NWs are associated with the temperature effect, while the growth density of NWs is strongly related to gas flux during the VS process. Additionally, the synthesized ZnO NWs possess specific crystalline qualities, making them highly promising for piezoelectric device applications. Therefore a piezoelectric type nanogenerator based on the ZnO NWs is also designed in this work, with a high output of piezoelectric current of 0.6 μA cm⁻² obtained as well. Our results further demonstrate the feasibility of applying piezoelectric energy via the rapidly grown ZnO NWs array.     

Effect of doping on properties of Zno:Cu and Zno:Ag thin films

ZnO:Cu and ZnS thin films were grown by metal-organic chemical vapour deposition (MOCVD) under atmospheric pressure onto glass substrates. The ZnO:Ag films were fabricated from ZnS films by non-vacuum method that consists of simultaneous oxidation and Ag-doping by the close spaced evaporation (CSE) of silver at the temperature of 500–600 °C. Photo-assisted rapid thermal annealing (PARTA) at ambient air during 10–30 s at the temperature of 700–800 °C was used for the ZnO:Cu films. The samples were studied by X-ray diffraction technique (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The grain size of ZnO:Cu films increased with an increase of Cu concentration. PL spectra of as-deposited ZnO:Cu films depended on Cu concentration and contained the bands typical for the copper. After PARTA at high temperature the emission maximum shifted towards the short-wave region. During the fabrication of ZnO:Ag films the grain growth process was strongly affected by the Ag loading level. The grain size increased with an increase of Ag concentration and ZnO:Ag films with surface roughness of 8 nm were obtained. Observed 385 nm PL peak for these samples can be attributed to the exciton–exciton emission that proves the high quality of the obtained ZnO:Ag films.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Preparation of polymorphic ZnO with strong orange luminescence

Polymorphic ZnO has been prepared by a solution method at low temperature (40–90 °C) and the product has been characterized by transmission electron microscopy, UV–vis absorption, and photoluminescence spectroscopy. It is found that the morphology and microstructure of ZnO can be tuned by varying the growth temperature and crystallization condition. The as-synthesized product exhibits narrowed band gap and strong orange luminescence at 620 nm, which may arise from the interstitial oxygen ion defect introduced into ZnO in the solution growth process.     

Deposition of zinc oxide thin films by an atmospheric pressure plasma jet

The ZnO thin film deposition process by using an atmospheric pressure (AP) plasma jet is studied. In this process, nebulized ZnCl₂ solution is sprayed into the downstream of the nitrogen plasma jet to perform thin film deposition. X-ray diffraction analysis confirms that this AP jet has the capability to convert ZnCl₂ solution to well-crystallized ZnO thin films with a hexagonal wurtzite structure in a short time. This film exhibits a smooth and mirror-like appearance visually. Scanning electron microscopy and atomic force microscopy show that the deposited film is dense and continuous with a root mean square surface roughness of 8.6 nm. A 1.29 nm/s deposition rate is obtained using this process. Given the fast deposition rate, we believe that both the temperature and the reactivity of the plasma play important roles. A ZnO film on a larger substrate is fabricated, which suggests the process capability in large area and continuous processing applications.     

The effect of arsenic thermal diffusion on the morphology and photoluminescence properties of sub-micron ZnO rods

As-doped sub-micron ZnO rods were realized by a simple thermal diffusion process using a GaAs wafer as an arsenic resource. The surface of the sub-micron ZnO rods became rough and the morphology of As-doped sub-micron ZnO rods changed markedly with increasing diffusion temperature. From the results of energy-dispersive X-ray spectroscopy, X-ray diffraction and photoluminescence, arsenic elements were confirmed to be introduced into the sub-micron ZnO rods. The acceptor ionization energy was deduced to be about 110 meV based on the temperature-dependent PL spectra.     

Electrical and optical properties of ZnO:Al thin films grown by magnetron sputtering

The properties of transparent conductive ZnO:Al thin films grown by R.F. magnetron sputtering method are investigated. The working pressure (argon gas) is changed from 2.5 to 40.0 mTorr to study its influence on the characteristics of ZnO:Al thin films. The ZnO:Al thin films have better texture due to the increase in the surface mobility, which resulted from the increase in the mean free path of sputtering gas under lower working pressure. The microstructure of ZnO:Al films is found to be affected obviously by changing the working pressure. It is shown that the grain size of ZnO:Al thin films decreases with the increase of working pressure. The X-ray diffraction patterns indicate that the poor crystallized structure of ZnO:Al films is obtained at higher working pressure. Except 40 mTorr, the highly (002)-oriented ZnO:Al thin films can be found at the measured range of working pressure. Moreover, the growth rate of the films decreases from 1.5 to 0.5 nm/min as the working pressure increases from 2.5 to 40.0 mTorr. The results of optical transmittance measurement of ZnO:Al thin films reveal a high transmittance (>80%) in visible region and exhibit a sharp absorption edge at wavelength about 350 nm.     

Growth of ZnO nanostructure on Cu0.62Zn0.38 brass foils by thermal oxidation

Cu_0.62Zn_0.38 brass foil was heated at temperatures of 400–700 °C in flowing N₂–5%O₂ at a pressure of 1 atm. for 1–24 h. The oxidized specimens were characterized with a scanning electron microscope, an X-ray diffractometer and a transmission electron microscope. The results show that hexagon ZnO nanowires and nanowalls grew on convoluted oxide scales when brass foils were oxidized at 500 and 600 °C. Thermodynamics of forming ZnO is analyzed based on oxidation theory of an alloy. Pilling–Bedworth ratio of Cu–Zn alloy is calculated based on the volume differences between the formed oxide and the consumed metal. The growth stresses caused by Pilling–Bedworth ratio of the alloy and stress relief of oxide scale at different oxidation temperature are analyzed. The mechanism of forming nanostructural ZnO on the convoluted oxide scales is explained by the change in the growth stresses and stress relief of oxide scale during thermal oxidation.     

Thickness dependent growth of needle-like and flower-like ZnO nanostructures

Needle-like nanorods and micron-scale flower-like structures of ZnO were synthesized by thermal evaporation of metallic zinc films with different thicknesses, followed by thermal annealing. Needle-like nanorods of ZnO were found through out the sample surface after annealing of the 1.3 μm thick Zn film. Three-dimensional crystalline nanorod-based flower-like structures of ZnO were also observed after annealing of the relatively thick (3.3 μm) Zn film. Thermal annealing of the Zn films was done at 800 °C in air for different time durations (30, 45, and 90 min). The flower size and number increase with increase in film thickness for the same annealing temperature and time. The X-ray diffraction results show that both the needle-like nanorods and flower-like structures are hexagonal wurtzite structure of ZnO. The room temperature PL spectrum shows a strong defect related violet emission peak centered at 441 nm for both the structures. The possible growth process based on root growth technique is proposed.     

Optical and electrical properties of ZnO nanoparticle thin films deposited on quartz by sparking process

ZnO nanoparticle thin films were deposited on quartz substrates by a novel sparking deposition which is a simple and cost-effective technique. The sparking off two zinc tips above the substrate was done repeatedly 50-200 times through a high voltage of 10 kV in air at atmospheric pressure. The film deposition rate by sparking process was approximately 1.0 nm/spark. The ZnO thin films were characterized by X-ray diffraction, Raman spectroscopy, UV-vis spectrophotometry, and ionoluminescence at room temperature. The two broad emission peaks centered at 483 nm (green emission) and 650 nm (orange-red emission) were varied after two-step annealing treatments at 400-800 °C. Moreover, the electrical resistivity of the films was likely to be proportional to the peak intensity of the orange-red emission.     

Photoluminescence of ZnO nanoparticles prepared by a low-temperature colloidal chemistry method

ZnO nanoparticles have been synthesized by a low-temperature colloidal chemistry method using ethylene glycol as the reaction medium. Crystalline ZnO nanoparticles were formed at a temperature as low as 150 °C. The crystallite size of the ZnO nanoparticles ranged from 8 to 20 nm. The synthesized ZnO nanoparticles exhibited size-dependent photoluminescence. Photoluminescence of the ZnO nanoparticles depended largely on the post-annealing temperature. Both DL and UV emissions were suppressed at a lower post-annealing temperature of 300 °C; however they were recovered at a higher annealing temperature of 900 °C.     

ZnO纳米微粒的超临界制备实验研究

文章利用超临界水解过程成功制备了平均粒径为78nm的ZnO纳米微粒。将制备的微粒样品,用X射线衍射仪、扫描电镜和激光粒度分析仪进行表征,产物为纯度较高的ZnO微粒,微粒粒径较小、分散性较好、且粒度分布集中。试验同时考察了操作压力、操作温度、系统总流量和支路流量比等各过程参数对微粒粒径的影响,实验结果表明,随操作压力、操作温度的升高,制备的微粒粒径有明显的增大趋势;随系统总流量的提高,微粒的粒径减小;随支路流量比的增加,微粒的粒径略有下降,但变化不大。     

Effect of the oxygen pressure on the photoluminescence properties of ZnO thin films by PLD

ZnO thin films on Si(111) substrate were deposited by laser ablation of Zn target in oxygen reactive atmosphere; Nd-YAG laser with wavelength of 1064 nm was used as laser source. The experiments were performed at laser energy density of 31 J/cm², substrate temperature of 400 °C and various oxygen pressures (5–65 Pa). X-ray diffraction was applied to characterize the structure of the deposited ZnO films and the optical properties of the ZnO thin films were characterized by photoluminescence with an Ar ion laser as a light source using an excitation wavelength of 325 nm. The influence of the oxygen pressure on the structural and optical properties of ZnO thin films was investigated. It was found that ZnO film with random growth grains can be obtained under the condition of oxygen pressure 5–65 Pa. It will be clearly shown that the grain size and the formation of intrinsic defects depend on the oxygen partial pressure and that high optical quality of the ZnO films is obtained under low oxygen pressure (5 Pa, 11 Pa) conditions.     

The formation and UV-blocking property of needle-shaped ZnO nanorod on cotton fabric

ZnO nanoparticles were in-situ grown on SiO₂ coated cotton fabric through hydrothermal method. A following hot water treatment at 100 °C or higher could transform the morphology of the ZnO nanoparticles on the surface of cotton fabric from sphere and rod to much smaller diameter needle shape through a recrystallization process. After water treatment at 100 °C or higher, the cotton fabric was covered with approximately 24 nm diameter needle-shaped ZnO nanorod and had an excellent UV-blocking property with UV protection factor value over 50. The effects of temperature and time of hot water treatment on the size and crystalline perfection of ZnO nanorod and the UV-blocking property were also studied.     

Nanocrystalline ZnO thin film for photocatalytic purification of water

ZnO thin film was prepared via evaporation of Zn metal on a glass sheet following by calcination (oxidation) process. The influences of calcination parameters such as temperature and time on the surface morphology and phase structure of ZnO films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The analysis of XRD patterns indicated that the growth of ZnO nano-structure was controlled by calcination time and temperature. Optimum ZnO nano-fibers can be formed uniformly after 2 h of oxidation at 550 °C. Nanostructured ZnO catalyst exhibited a significantly greater superiority for the photodegradation of 2,4,6-Trichlorophenol (TCP) as a model pollutant in water over photolysis via irradiation with UV of 254 nm wavelength. The role of ZnO catalyst is discussed and the chemical composition of degradation products and intermediates are identified.     

High-temperature-dependent optical properties of ZnO film on sapphire substrate

In order to fabricate fiber-optic temperature sensors based on ZnO film, it is important to study the temperature-dependent optical properties of this material. In this work, we deposited ZnO films on c-plane (0001) sapphire substrate at 250 °C. Atomic force microscope and X-ray diffraction measurements show the smooth surface and high orientation along [0001] of ZnO film, respectively. The high-temperature-dependent optical properties of ZnO film were measured by ultraviolet-visible transmission with temperatures ranging from room-temperature to 300 °C and analyzed by theoretically fitting the optical absorption edge curve. It is observed that the band gap energy red shifts nonlinearly from 3.345 to 3.153 eV with increasing temperature. The sharp absorption edge of ZnO films after annealing at 300 °C is almost consistent with that of the as-deposited sample, indicating an excellent thermal stability and the potential application in fiber-optic temperature sensors.     

Synthesis and microstructure of vertically aligned ZnO nanowires grown by high-pressure-assisted pulsed-laser deposition

The microstructure and growth behavior for vertically aligned Zinc oxide (ZnO) nanowires, synthesized on a ZnO thin film template by pulsed-laser deposition (PLD), is reported. The nanowire growth proceeds without any metal catalyst for nucleation, although an epitaxial ZnO thin film template is necessary in order to achieve uniform alignment. Nanowire growth at argon or oxygen background pressures of 500-mTorr results in nanowire diameters as small as 50–90 nm, with diameters largely determined by growth pressure and temperature. Room temperature photoluminescence show both near-band-edge and deep-level emission. The deep-level emission is believed caused by oxygen vancancies formed during growth.     

Growth specificity of vertical ZnO nanorods on patterned seeded substrates through integrated chemical process

A simple and cost effective method has been employed for the random growth and oriented ZnO nanorod arrays over as-prepared and patterned seeded glass substrates by low temperature two step growth process and growth specificity by direct laser writing (DLW) process. Scanning electron microscopy (SEM) images and X-ray diffraction analysis confirm the growth of vertical ZnO nanorods with perfect (0 0 2) orientation along c-axis which is in conjunction with optimizing the parameters at different reaction times and temperatures. Transmission electron microscopy (TEM) images show the formation of vertical ZnO nanorods with diameter and length of ∼120 nm and ∼400 nm respectively. Photoluminescence (PL) spectroscopic studies show a narrow emission at ∼385 nm and a broad visible emission from 450 to 600 nm. Further, site-selective ZnO nanorod growth is demonstrated for its high degree of control over size, orientation, uniformity, and periodicity on a positive photoresist ZnO seed layer by simple geometrical (line, circle and ring) patterns of 10 μm and 5 μm dimensions. The demonstrated control over size, orientation and periodicity of ZnO nanorods process opens up an opportunity to develop multifunctional properties which promises their potential applications in sensor, piezoelectric, and optoelectronic devices.