Preparation, characterization and room temperature photoluminescence properties of a zinc oxide nanosheet network grown on glass substrate by a facile chemical route

An ultralong and ultrathin zinc oxide nanosheet network grown on glass substrate is prepared using an organic CTAB (cetyltrimethylammonium bromide, CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻) and the simple chemical materials (Zn(AC)₂·2H₂O and NaOH) by hydrothermal method. The morphology and microstructure of ZnO nanosheet network have been characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–vis spectroscopy. The results revealed that the product grown on glass substrate was the ultralong and ultrathin zinc oxide nanosheet network and the crystalline hexagonal wurtzite ZnO crystal structure. The zinc oxide nanosheet network exhibits room temperature photoluminescence (RTPL) characteristics and three blue emissions located at 452, 459, and 469 nm, and a green emission located at about 494 nm were observed.     

UV photodetector behavior of 2D ZnO plates prepared by electrochemical deposition

Zinc oxide (ZnO) with 2D hexagonal structure was successfully prepared using electrochemical deposition (ECD) method on a quartz substrate pre-coated with indium-doped ZnO layer. The X-ray diffraction of the prepared sample confirmed that the hexagonal structure had a dominant c-axis orientation. The scanning electron microscopy revealed the 2D hexagonal structure of the prepared ZnO.     

Growth of hierarchical based ZnO micro/nanostructured films and their tunable wettability behavior

Hierarchical zinc oxide (ZnO) micro/nanostructured thin films were grown onto as-prepared and different annealed ZnO seed layer films by a simple two step chemical process. A cost effective successive ionic layer adsorption and reaction (SILAR) method was employed to grow the seed layer films at optimal temperature (80 °C) and secondly, different hierarchical based ZnO structured thin films were deposited over the seed layered films by chemical bath deposition (CBD). The influence of seed layer on the structural, surface morphological, optical and wettability behavior of the ZnO thin films were systematically investigated. The XRD analysis confirms the high crystalline nature of both the seed layer and corresponding ZnO micro/nanostructured films with a perfect hexagonal structure oriented along (0 0 2) direction. The surface morphology revels a complex and orientated hierarchical based ZnO structured films with diverse shapes from plates to hexagonal rod-like crystal to tube-like structure and even much more complex needle-like shapes during secondary nucleation, by changing the seed layer conditions. The water contact angle (WCA) measurements on hierarchical ZnO structured films are completely examined to study its surface wettability behavior for its suitability in future self-cleaning application. Photoluminescence (PL) spectra of the ZnO structured film exhibit UV and visible emissions in the range of 420-500 nm. The present approach demonstrates its potential for low-temperature, large-scale, controlled synthesis of crystalline hierarchical ZnO nanostructures films.     

CdS quantum dot-sensitized ZnO nanorod-based photoelectrochemical solar cells

ZnO nanorods have been grown using ZnO seed layer onto ITO-coated glass substrates. CdS quantum dots have been deposited onto ZnO nanorods using simple precursors by chemical method and the assembly of CdS quantum dots with ZnO nanorod has been used as photo-electrode in quantum dot-sensitized solar cells. X-ray diffraction results show that ZnO seed layer, ZnO nanorods, and CdS quantum dot-sensitized ZnO nanorods exhibit hexagonal structure. The particle size of CdS nanoparticle is 5 nm. The surface morphology studied using scanning electron microscope shows that the top surface of the vertically aligned ZnO nanorods is fully covered by CdS quantum dots. The ZnO nanorods have diameter ranging from 100 to 200 nm. The absorption spectra reveal that the absorption edge of CdS quantum dot-sensitized ZnO nanorods shift toward longer wavelength side when compared to the absorption edge of ZnO. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 0.69% and is the best efficiency reported so far for this type of solar cells.     

Direct assembly of ZnO nanostructures on glass substrates by chemical bath deposition through precipitation method

In this work, spindle/flower-like zinc oxide (ZnO) nanostructured arrays have been directly grown on glass substrates using triethanolamine (TEA) as a complexing agent by chemical bath deposition (CBD). Control over the morphology of ZnO nanocrystallites was achieved by varying the concentration of the complexing agent in the bath solution. ZnO crystallites exhibited a hexagonal wurtzite structure with preferential orientation along the c-axis. The morphology of the ZnO crystallites with star or needle-like spindles was altered to flower like nanostructures by adjusting the complexing agent concentration. Compared to as-deposited films, films sintered at 300 ^°C exhibited a sharp UV emission due to a decrease in the defect density. A possible growth mechanism for obtaining ZnO nanoflower arrays without a seed layer on glass substrates has been discussed.     

Morphology and photoluminescence study of electrodeposited ZnO films

ZnO films on ITO substrates and Au coated ITO substrates were fabricated by using electrodeposition technique. We carried out the experiments by adjusting the concentration of solution, potential, substrate, and temperature. The effect of temperature on the growth of the film has been examined. SEM images have shown that there are several kinds of grown competitions for the deposition of ZnO films, but three kinds of them are dominant. One is the discrete hexagonal column structure, the other is the pentagonal structure, and the third one is of well-oriented hexagonal columns with well-aligned structure. The explanation on the grown competition is discussed. ZnO hexagonal column structures with well-aligned and well-perpendicular to the surface were successfully obtained on Au/ITO substrate in aqueous solvent of electrolyte. Clearly the main columns in the film were obtained by increasing the temperature. Its photoluminescence (PL) study at low temperature exhibited the optical properties as wurtzite ZnO and indicated the existence of macrocrystalline ZnO. A better quality of ZnO columnar structures after annealing was demonstrated from PL analysis and discussion on the existence of 370 nm, 384 nm and 639 nm in the emission bands before and after annealing.     

The influence of using different substrates on the structural and optical characteristics of ZnO thin films

ZnO thin films with thikness d = 100 nm were deposited onto different substrates such as glass, kapton, and silicon by radio frequency magnetron sputtering. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure.The ZnO layer deposited on kapton substrate shows a stronger orientation of the crystallites with (0 0 2) plane parallel to the substrate surface, as compared with the other two samples of ZnO deposited on glass and silicon, respectively.All three layers have nanometer-scale values for roughness, namely 1.7 nm for ZnO/glass, 2.4 nm for ZnO/silicon, and 6.8 nm for ZnO/kapton. The higher value for the ZnO layer deposited on kapton substrate makes this sample suitable for solar cells applications. Transmission spectra of these thin films are strongly influenced by deposition conditions. With our deposition conditions the transparent conducting ZnO layer has a good transmission (78-88%) in VIS and NIR domains. The values of the energy gap calculated from the absorption spectra are 3.23 eV for ZnO sample deposited onto glass substrate and 3.30 eV for the ZnO sample deposited onto kapton polymer foil substrate. The influence of deposition arrangement and oxidation conditions on the structural, morphological, and optical properties of the ZnO films is discussed in the present paper.     

Ag掺杂氧化锌纳米材料的制备及高压相变拉曼光谱研究

宽禁带直接带隙半导体材料氧化锌（ZnO）,具有优异的光电性能、机械性能和化学特性。ZnO材料的结构对其性能影响较大,元素掺杂可改变ZnO晶体结构和带隙宽度,是提升ZnO材料性能的有效手段,当前常用Ag掺杂ZnO即为提高光催化反应效率。高压独立于温度、成分,是调控材料结构组织性能的重要手段,是产生新材料、发现新调控原理的重要因素。该研究通过对比纯ZnO晶体和Ag掺杂ZnO晶体的高压相变行为,揭示了元素掺杂对ZnO纳米晶体材料结构性能的影响。研究首先采用水热法辅助制备纯ZnO纳米微球和Ag掺杂ZnO纳米微球（1∶150Ag/ZnO）,表征结果显示水热法合成的纯ZnO和1∶150Ag/ZnO均为六角纤锌矿晶体结构,形貌均为几十纳米尺寸小颗粒堆积形成的微球,ZnO晶格常数随着Ag离子掺杂而变大,Ag掺杂导致ZnO晶格膨胀。随后应用金刚石压腔结合原位拉曼光谱技术测定了纯ZnO和Ag掺杂ZnO的高压结构相变行为。相比于纯ZnO拉曼峰,Ag掺杂ZnO的E₂（high）振动模式439 cm-1拉曼峰峰宽变窄,并呈现向低频方向移动的趋势,与无定形ZnO谱峰相近,表明Ag+取代Zn2+影响了Zn-O键,同时也影响了ZnO晶格结构的长程有序性。随体系压力增大,表征六角纤锌矿结构ZnO的拉曼特征峰439 cm-1出现瞬间弱化和宽化。压力增大至9.0 GPa时,纤锌矿结构ZnO拉曼特征峰439 cm-1消失,585 cm-1处出现新峰,ZnO晶体发生由六角纤锌矿向岩盐矿的结构转变。压力继续增大至11.5 GPa,新的拉曼峰显著增强,峰形变窄,同时向高波数方向移动,相变完成,岩盐矿结构ZnO性能稳定。1∶150 Ag/ZnO从六角纤锌矿结构到立方岩盐结构的相变压力为7.2 GPa,低于纯ZnO。相变压力降低表明晶体结构稳定性下降,可能的原因在于掺杂Ag导致ZnO晶格膨胀,晶体结构松弛,两相相对体积变化增加,从而导致相变势垒降低,使样品在较低压力下发生相变。纳米材料的高压研究揭示了元素掺杂对材料结构稳定性的影响,是纳米材料调控原理的潜在研究手段。     

电泳法制备ZnO/YBCO异质结及电学性质研究

采用电泳方法及高温煅烧工艺制备ZnO/YBCO异质结,XRD图谱显示ZnO具有c轴方向的择优取向。在SEM的截面图中可观察到ZnO与YBCO结合致密,放大500倍的表面形貌图呈现织构(textured)的微结构特征,放大5000倍的表面形貌图中可观察微米量级的六方晶粒。通过对ZnO/YBCO异质结的电学性质进行测试,结果显示整流特性。     

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.     

Growth mechanism studies of ZnO nanowire arrays via hydrothermal method

Well-controlled ZnO nanowire arrays have been synthesized using the hydrothermal method, a low temperature and low cost synthesis method. The process consists of two steps: the ZnO buffer layer deposition on the substrate by spin-coating and the growth of the ZnO nanowire array on the seed layer. We demonstrated that the microstructure and the morphology of the ZnO nanowire arrays can be significantly influenced by the main parameters of the hydrothermal method, such as pH value of the aqueous solution, growth time, and solution temperature during the ZnO nanowire growth. Scanning electron microscopy observations showed that the well oriented and homogeneous ZnO nanowire arrays can be obtained with the optimized synthesis parameters. Both x-ray diffraction spectra and high-resolution transmission electron microscopy (HRTEM) observations revealed a preferred orientation of ZnO nanowires toward the c-axis of the hexagonal Wurtzite structure, and HRTEM images also showed an excellent monocrystallinity of the as-grown ZnO nanowires. For a deposition temperature of 90 °C, two growth stages have been identified during the growth process with the rates of 10 and 3 nm/min, respectively, at the beginning and the end of the nanowire growth. The ZnO nanowires obtained with the optimized growth parameters owning a high aspect ratio about 20. We noticed that the starting temperature of seed layer can seriously influence the nanowire growth morphology; two possible growth mechanisms have been proposed for the seed layer dipped in the solution at room temperature and at a high temperature, respectively.     

Synthesis of ZnO nanostructures with controlled morphology and size in ionic liquids

Nanostructured ZnO has been synthesized by a hydrothermal route, using different ionic liquids (ILs) as the morphology templates. The morphology of ZnO changes from rod-like to star-like and flower-like in different ILs. A 3D nano/micro structure ZnO with unique flower-like morphology has been synthesized via the assembly of dicationic IL and [Zn(OH)₄]²⁻. The flower-like pattern was obtained in the presence of IL 1. The flower-like ZnO structure has a hexagonal prism, with a hexagonal pyramid on the tip, and diameter of ~444 nm. While the ZnO prepared in IL 2, shows uniform rod-like shape with a diameter of 91 nm, star-like morphology consisting of nanorods with diameter of ~109 nm was formed in IL 3. The XRD, SEM, and PL spectra have been employed for characterization of the synthesized ZnO nano structures.     

Fabrication and electrical characterization of ZnO rod arrays/CuSCN heterojunctions

ZnO rod arrays/CuSCN heterojunctions are fabricated by depositing ZnO rod arrays films using two-step chemical bath deposition (CBD) and CuSCN thin films using successive ionic layer adsorption and reaction (SILAR) on ITO substrate successively. The structures and morphologies of ZnO films and CuSCN films, analyzed by X-ray diffraction (XRD) spectroscopy and metallurgical microscope, show that ZnO films are hexagonal wurtzite structure and consisted of vertical polycrystalline rods with diameter of 1 μm, CuSCN films are β-phase structure and consisted of elongated grains with length of 3 μm. Current–voltage (I–V) measurements of ZnO/CuSCN heterojunctions show good diode characteristics with rectification ratio about 48.3 at 3 V. The forward conduction is, respectively, determined by carrier recombination in the space charge region, defect-assisted tunneling and exponential distribution trap-assisted space charge limited current mechanism with the increase of forward voltage. Also, a band diagram of ZnO/CuSCN heterojunctions has been proposed to explain the transport mechanism.     

温度对ZnO/Al2O3(0001)界面的吸附、扩散及生长初期模式的影响

构建了一个ZnO沉积在α-Al₂O₃(0001)表面生长初期的模型，采用基于密度泛函理论的平面波超软赝势法进行了动力学模拟.发现在400，600和800℃的条件下界面原子有不同的扩散能力，因此温度对ZnO/α-Al₂O₃(0001)表面界面结构以及ZnO薄膜生长初期模式有决定性的影响.在整个ZnO吸附生长过程中，O原子的扩散系数大于Zn原子的扩散系数，O原子的层间扩散对薄膜的均匀生长起着重要作用.进一步从理论计算上证实了ZnO在蓝宝石(0001)上两种生长模式的存在，400℃左右生长模式主要是Zn螺旋扭曲生长，具有Zn六角平面对称特征，且有利于Zn原子位于最外表面.600℃左右呈现为比较规则的层状生长，且有利于O原子位于最外表面.模拟观察到在ZnO薄膜临近Al₂O₃基片表面处，Zn的空位缺陷明显多于O的空位缺陷. 关键词： 扩散 薄膜生长 2O₃(0001)')" href="#">α-Al₂O₃(0001) ZnO     

Effect of ZnO sacrificial layer thickness on the structure and optical properties of GaN nanoparticles prepared by RF magnetron sputtering

GaN nanoparticles were prepared on sapphire (0001) substrates with ZnO sacrificial layers by self assembly of Ga₂O₃ films in their reaction with NH₃. ZnO sacrificial layers with different thicknesses and Ga₂O₃ films were deposited on sapphire substrates in turn by a radio frequency (RF) magnetron sputtering system. Nitridation of the Ga₂O₃ films was then carried out in a quartz tube furnace. The effect of ZnO sacrificial layer thickness on the structure and optical properties of nanoparticles prepared by RF magnetron sputtering were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL). GaN nanoparticles with ZnO sacrificial layers of different thicknesses possess hexagonal wurtzite crystal structure and have a preferred orientation with c axis perpendicular to the sapphire substrates. XRD, SEM, and AFM results reveal that the better-crystallinity, uniform, and well-dispersed GaN nanoparticles (～30 nm) without agglomeration were obtained with a ZnO sacrificial layer 300-nm thick. The PL result reveals that the optical properties of the GaN nanoparticles are improved with a ZnO sacrificial layer 300-nm thick. Therefore, we suggest that a ZnO sacrificial layer 300-nm thick is the most suitable condition for obtaining better-quality GaN nanoparticles with good luminescence performance. Moreover, the mechanism of the formation of GaN nanoparticles with ZnO sacrificial layers is also discussed.     

Characterisation of ZnO nanorod arrays grown by a low temperature hydrothermal method

In this paper, growth steps of well defined ZnO nanorod arrays deposited on seeded substrates were investigated. To obtain ZnO seed layer on glass substrates, a successive ionic layer adsorption and reaction (SILAR) method was used and then ZnO nanorods were grown on seed layer using a chemical bath deposition (CBD) method. The effects of seed layer and deposition time on morphology, crystallographic structure (e.g. grain size, microstrain and dislocation density) and electrical characteristics of ZnO nanorods were studied. From the SEM micrographs, it could be seen that the ZnO nanorods densely covered the substrate and were nearly perpendicular to the substrate surface. The XRD patterns showed that the ZnO nanorod arrays had a hexagonal wurtzite structure with a preferred orientation along the (002) plane. An increase in deposition time resulted in an increase in the intensity of the preferred orientation and grain size, but a decrease in microstrain and dislocation density. Electrical activation energies of the structures were calculated as 0.15–0.85?eV from current–temperature characteristics. It was concluded that the morphologies of the structures obtained in this study via a simple and fast solution method can provide high surface areas which are important in area-dependent applications, such as solar cells, hydrogen conversion devices, sensors, etc.     

Aqueous chemical growth of free standing vertical ZnO nanoprisms,nanorods and nanodiskettes with improved texture co-efficient and tunable size uniformity

Tuning the morphology, size and aspect ratio of free standing ZnO nanostructured arrays by a simple hydrothermal method is reported. Pre-coated ZnO seed layers of two different thicknesses (≈350 nm or 550 nm) were used as substrates to grow ZnO nanostructures for the study. Various parameters such as chemical ambience, pH of the solution, strength of the Zn²⁺ atoms and thickness of seed bed are varied to analyze their effects on the resultant ZnO nanostructures. Vertically oriented hexagonal nanorods, multi-angular nanorods, hexagonal diskette and popcorn-like nanostructures are obtained by altering the experimental parameters. All the produced nanostructures were analysed by X-ray powder diffraction analysis and found to be grown in the (002) orientation of wurtzite ZnO. The texture co-efficient of ZnO layer was improved by combining a thick seed layer with higher cationic strength. Surface morphological studies reveal various nanostructures such as nanorods, diskettes and popcorn-like structures based on various preparation conditions. The optical property of the closest packed nanorods array was recorded by UV-VIS spectrometry, and the band gap value simulated from the results reflect the near characteristic band gap of ZnO. The surface roughness profile taken from the Atomic Force Microscopy reveals a roughness of less than 320 nm.     

High-quality ZnO nanorods grown on graphite substrates by chemical solution method

ZnO nanorods (NRs) were grown perpendicularly on graphite substrates using low-temperature wet chemical bath deposition (CBD) with sputtered ZnO film as seed layer. The individual ZnO NRs exhibit single-crystalline feature with well defined hexagonal prism shape and smooth side facets. The high optical qualities of ZnO NRs on graphite substrates were demonstrated by the dominant near-band edge emission and nearly undetectable deep level emissions in room-temperature photoluminescence spectra. The extremely low average reflectance of 0.45 % was obtained for the ZnO NRs/graphite structure in the spectra range from 200 to 1100 nm, indicating that the reported ZnO NRs/graphite structures have significant opportunity for potential application in high-performance photovoltaic devices. Considering the excellent material characteristics of ZnO NRs and the versatile and fascinating features of graphite substrates, the achievements make it possible for the development of high-performance ZnO-based nano-devices even in transferable, flexible, or stretchable forms.     

Synthesis and characterization of ZnO columns grown on MgO-coated silicon substrates by carbon-thermal evaporation

Zinc oxide columns have been grown on an MgO-coated silicon (111) substrate by the carbon-thermal evaporation method at 1050 °C. The MgO layer obtained from the substrate pre-dripped in Mg(NO₃)₂ solution by the use of a dropper can solve the troublesome lattice mismatch problem in the heteroepitaxy and promote the growth of ZnO columns effectively. The as-prepared ZnO structures were characterized by using X-ray diffraction (XRD), field-emission transmission electron microscope (FETEM), selection area electron diffraction (SAED), and photoluminescence (PL) spectrum. The results show that the columns are highly crystalline with the wurtzite hexagonal structure, and grow along the [0001] in the c-axis direction. Photoluminescence (PL) spectra of the as-synthesized microstructures exhibit broad green emission peaks at ∼514 nm. In addition, the growth mechanism of the two ZnO structures is discussed based on the analysis briefly based on the time-dependent experiment.     

Ultraviolet-assisted synthesis of hourglass-like ZnO microstructure through an ultrasonic and microwave combined technology

Well-defined hexagonal hourglass-like ZnO microstructures have been synthesized by using simultaneous ultrasound and microwave irradiation methods with the assistance of ultraviolet as well as double sonication (at 25 and 40 kHz). The structure and morphology of as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectrum. The results show the synergistic effect of ultrasound and microwave on the formation of ZnO microstructures. Meanwhile, the possible growth mechanism was proposed to elucidate the formation of hexagonal hourglass-like ZnO microstructures.