Electroless deposition of Cu dendrites decorated with ZnO rods

In this paper, copper dendrites decorated with ZnO rods have been electrolessly deposited on brass substrate by a simple galvanic replacement method. SEM images show that these copper dendrites possess a pronounced trunk and highly ordered branches distributed on both sides of the trunk. Meanwhile, both the trunk and branches are decorated with ZnO rods. The diffusion‐limited aggregation (DLA) model has been used to explain the fractal growth of Cu dendritic structures. This method provides a facile route to the synthesis of copper dendrites with ZnO, which can be extended to the preparation of other forms three‐dimensional (3‐D) metal structures or metal/ZnO composites by modifying electrolyte parameters such as composition, concentration, pH and temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure‐controlled growth of ZnO nanonails by thermal evaporation technique

Wurtzite ZnO nanonail structures have been grown on sapphire substrate by simple thermal evaporation of Zn powder in oxygen ambient. Growth parameters such as growth temperature and oxygen gas flow have been examined for the growth of nanonail structure. It is found that the nanonail structures repeatedly grow under a certain relation between the growth temperature and the oxygen flow. Also, at higher growth temperature, the nanonails grow in the form of branched‐structures. The grown ZnO nanonails have hexagonally well‐faceted cap and grow mostly perpendicular to the sapphire substrate. Excellent luminescence properties of a strong UV emission peak with negligible green band have been obtained at room temperature. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controlled synthesis of various morphologies of nanostructured zinc oxide: flower,nanoplate, and urchin

Nanoplates, flower‐like nanostructure of ZnO were successfully synthesized by employing ZnSO₄·7H₂O, NaOH as the starting materials at 120°C under hydrothermal condition. Keeping the same parameters, ZnO urchin shape was obtained by addition of vitamin C at 190°C. Characterizations were carried out by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) at room temperature. Selected area electron diffraction (SAED) pattern confirms that the product is single crystalline nature. The possible formation mechanisms for synthesized ZnO nanosturcture with various morphologies have also been proposed. PL spectrum from the ZnO flower‐like structures reveals weak UV emission and strong green emission. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of radial‐like ZnO structure by hydrothermal method with ZnSO4·7H2O and Zn(CH3COO)2·2H2O as zinc sources

Radial‐like ZnO structures were prepared using zinc sulfate (ZnSO₄·7H₂O) and zinc acetate [Zn(CH₃COO)₂·2H₂O] as zinc sources by a facile template‐free hydrothermal method in this paper. Structural and optical properties of radial‐like ZnO structures are characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV‐vis spectrophotometer and photoluminescence measurement (PL). It has been found that the distinct surface morphologies of radial‐like ZnO structures grown by different zinc sources. Slim radial‐like ZnO with a hexagonal wurtzite structure is grown by using ZnSO₄·7H₂O as zinc sources, whereas coarse radial‐like ZnO with zincite structure is achieved by zinc acetate. The UV‐vis absorption spectra of them both display an obvious and significant absorption in the ultraviolet region. The room temperature PL spectra of ZnO structures grown by two different zinc sources possess a common feature that consists of a strong ultraviolet (UV) peak and visible emission band.     

氧化锌单晶生长、载流子调控与应用研究进展

氧化锌(ZnO)是一种历史悠久的材料,由于其微观结构非中心对称,最初被预测可以应用于压电和非线性光学领域,又因为它在室温下具有宽的禁带和高的激子束缚能,是一类重要的第三代宽禁带半导体材料,在半导体领域受到了广泛关注.然而,在实际应用中,ZnO在上述各个领域都遇到了一些瓶颈问题:在压电领域,原本被认为是绝缘的ZnO出现了...     

衬底温度对磁控溅射法制备掺Ta氧化锌薄膜性能的影响

采用射频磁控溅射法,在不同的衬底温度下制备了钽(Ta)掺杂的氧化锌(ZnO)薄膜,采用X射线能谱(EDS)、X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见分光光度计和光致发光(PL)光谱研究了衬底温度对制备的Ta掺杂ZnO薄膜的组分、微观结构、形貌和光学特性的影响.EDS的检测结果表明,Ta元素成功掺入到了ZnO薄膜;XRD图谱表明,掺入的Ta杂质是替代式杂质,没有破坏ZnO的六方晶格结构,随着衬底温度的升高,(002)衍射峰的强度先增大后降低,在400℃时达到最大;SEM测试表明当衬底温度较高时(400℃和500℃),Ta掺杂ZnO薄膜的晶粒明显变大;紫外-可见透过光谱显示,在可见光范围,Ta掺杂ZnO薄膜的平均透光率均高于80;,衬底不加热时制备的Ta掺杂ZnO的透光率最高;制备的Ta掺杂ZnO薄膜的禁带宽度范围为3.34~3.37eV,衬底温度为500℃时制备的Ta掺杂ZnO薄膜的禁带宽度最小,为3.34eV.PL光谱表明衬底温度为500℃时制备的Ta掺杂ZnO薄膜中缺陷较多,这也是造成薄膜禁带宽度变小的原因.     

Facile synthesis of pencil‐like ZnO nanostructures at low temperature

Pencil‐like ZnO nanostructure was synthesized by directly oxidizing granular Zn films, which was thermal deposited in a nitrogen atmosphere from Zn powder in a horizontal tube furnace. The formation of the pencil‐like structure, including a hexagonal rod and a sharp tip with diameter about 60 nm, highly depend on the thickness of the initial zinc film and the temperature of the oxidizing process. ZnO nanorods were formed in a relatively low temperature, while thicker zinc film was apt to form a dense ZnO film with tubular structures. The different structured ZnO materials showed distinguishing optical properties which indicate the intrinsic defects forming in the different growth conditions. The pencil‐like ZnO structures exhibit a relatively strong green emission attributed to the high concentrations of oxygen vacancies and its taper tip has great prospects in field‐emission devices.     

蓝宝石衬底上磁控溅射法室温制备外延ZnO薄膜

在室温条件下,采用磁控溅射方法在蓝宝石(0001)衬底上制备了外延的ZnO薄膜.采用原子力显微镜(AFM)、X射线衍射仪(XRD)、可见-紫外分光光度计系统研究了ZnO薄膜微观结构和光学特性.AFM测量结果表明ZnO薄膜具有较为均匀的ZnO晶粒,表面平整,具有较小的均方根粗糙度(0.9 nm);X射线衍射结果表明制备的ZnO薄膜为具有六角纤锌矿结构的外延薄膜;光学透射谱显示样品在可见光范围内具有较高的透过性,并在370 nm附近出现一个较陡的吸收边,表明在室温下制备出了具有较高质量的ZnO薄膜.     

Crystallographic,optical and magnetic properties of Co‐doped ZnO thin films synthesized by sol gel route

ZnO thin films with various Co doping levels (0%, 1%, 3%, 5%, 8%, respectively) have been synthesized by sol gel spin coating method on glass substrates. XRD and XPS studies of the films reveal that cobalt ions are successfully doped into ZnO crystal lattice without changing the hexagonal wurtzite structure. The morphologies are studied by SEM and AFM and show wrinkle network structures with uniform size distribution. With Co doping concentration increasing, the wrinkle network width decreases gradually. The transmittance spectra indicate that Co doping can effectively reduce the optical bandgap of ZnO thin films. Photoluminescence show that all samples have ultraviolet, violet and green emission. When Co doping concentration increases up to 5%, the intensity of violet emission is greatly increased and a strong deep blue emission centered at 439 nm appears. The ferromagnetism of all samples was observed at room temperature. The emission mechanisms and ferromagnetism origination are discussed in detail. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation on growth defects in Pb(Zn1/3Nb2/3)O3‐PbTiO3 crystals

Relaxor ferroelectric crystal (1‐x)Pb(Zn_1/3Nb_2/3)O₃‐xPbTiO₃ (PZNT) with x=0.07 (PZNT93/7) has been grown by the vertical Bridgman method from the high temperature solution of PZNT‐PbO system. The growth defects, such as nucleation core, inclusions, boundaries and particles, were investigated by optical microscope and scanning electron microscope. Sub‐structures were found in the flux inclusions and the lack of ZnO component in PZNT crystals was attributed to the existence of ZnO particles in the inclusions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

以NH4Cl为矿化剂水热合成ZnO自组装微纳米结构

采用NH4Cl为矿化剂,以金属锌片为锌源,水热合成出多种不同形貌的ZnO微纳米结构.其中ZnO纳米棒及铅笔都沿[001]方向生长,结晶性很好.在水热条件下, ZnO纳米棒通常倾向于自组装成花状的结构.本文从鲍林电负性的角度揭示了形成这些微纳米结构的化学反应机理,分析了Cl 和NH+4在这些微纳米结构形成过程中所起的作用.研究结果表明:温度和填充度对ZnO纳米结构的结晶性和形貌也有重要的影响.当温度从150 ℃升至180 ℃时,ZnO纳米晶的结晶性明显更好.当填充度从60;增加到80;时,除了形成ZnO纳米棒花状自组装结构以外,在金属锌片表面还趋于生成大量的ZnO微球.     

Deep ultraviolet emission of ZnO films prepared by RF magnetron sputtering at changing substrate temperature

ZnO films with deep ultraviolet emission on (0 0 0 6) sapphire substrates were prepared by RF magnetron sputtering at periodically changing substrate temperature. It is found that the as-prepared ZnO films consist of the obvious multilayered structures from the SEM images of their cross-sections. Room temperature photoluminescence of ZnO films with multilayered structure shows two emissions centered at 332 and 388 nm with 260 nm excited wavelength. The strong deep ultraviolet emission at 332 nm is due to the O 2p dangling-bond state in the multilayered structure of ZnO films. Raman scattering spectrum of sample shows that such structured ZnO film possesses strong compressive stress.     

采用MOCVD方法在GaAs衬底上生长ZnO(002)和ZnO(100)薄膜

采用金属有机化学汽相沉积生长法（MOCVD）,在不同的衬底表面处理条件和生长温度下,在GaAs衬底上生长出了ZnO薄膜。随着化学腐蚀条件的不同,可生长出优先定位不同的ZnO（100）和ZnO（002）薄膜。该薄膜的晶体结构特性是由X光衍射谱仪（XRD）所获得的,而其光学特性是由光荧光谱仪（PL）来测的。与ZnO（002）相比,ZnO（100）薄膜具有更优越的晶体结构特性,并且在同样的生长温度下都具有相似的光学特性。对于腐蚀条件不同的GaAs衬底所进行的XPS分析结果表明,ZnO薄膜优先定位变化的主要原因在于腐蚀过程中形成的富As层。     

Morphology‐photocatalytic properties‐growth mechanism for ZnO nanostructures via microwave‐assisted hydrothermal synthesis

ZnO nanostructures with various morphologies including rod‐like, sheet‐like, needle‐like and flower‐like structures were successfully synthesized via a fast and facile microwave‐assisted hydrothermal process. Reaction temperature, reaction time and the addition of NaOH were adjusted to obtain ZnO with different morphologies. Scanning electron microscopy(SEM), transmission electron microscope(TEM), X‐ray diffraction (XRD) and ultraviolet spectrophotometer (UV) were used to observe the morphology, crystal structure, ultraviolet absorption and photocatalytic activity of the obtained ZnO. The results indicated that growth rate of ZnO nanostructure along [001] direction was more sensitive to temperature compared with those along [101] and [100] directions. The competition between anionic surfactant and OH⁻ played an important role in the formation of ZnO with various morphologies. Flower‐like ZnO had better ultraviolet absorption property and excellent photocatalytic activity than ZnO in the other morphologies. On the basis of the above results, a possible growth mechanism for the formation of ZnO nanostructures with different morphologies was described.     

Synthesis,characterization and photoluminescence of ZnO spindles by polyvinylpyrrolidone-assisted low-temperature wet-chemistry process

ZnO spindles were prepared by wet-chemistry process with surfactant polyvinylpyrrolidone at a low temperature of 35 °C. The morphologies and structures of the products were characterized by X-ray powder diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The addition of polyvinylpyrrolidone promoted the formation of ZnO crystal nuclei, and accelerated the growth rate of (0001) plane rich in Zn²⁺ ions. The as-obtained ZnO spindles were twin crystal wurtzite structures, with the size of 30 nm at the tips, 350–450 nm at the center, and 1–1.5 μm in length. The room-temperature photoluminescence results showed that surface effects played a major role in the luminescence of the ZnO spindles, which exhibited a broad violet–blue–green emission band related to deep level defects. We proposed a new growth mechanism, which might be useful for applications in synthesis of size- and shape-controlled ZnO crystals.     

One‐step synthesis of ZnO/MgO core‐sheath structures

A kind of ZnO/MgO core‐sheath structure has been prepared directly by the pyrolysis of a mixture of polyvinyl alcohol, magnesium acetate, and zinc chloride coating on glass fiber mats at 450 °C for 60 min. The growing process and effect of the anions on the morphology of ZnO/MgO structures have been preliminarily discussed. The results indicate that ZnCl₂ will transform to ZnO crystal through an intermediate of zinc hydroxide chloride. ZnO crystal act as the core of the micorod, and MgO lamellas act as the sheath. The concurrence of chloride and acetate anions in the precursor is necessary for the growth of ZnO/MgO core‐sheath structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Precursor-controlled synthesis of hierarchical ZnO nanostructures,using oligoaniline-coated Au nanoparticle seeds

Shape-selected synthesis of a large number of zinc oxide (ZnO) nano- and microstructures was achieved by the seed-mediated growth of oligoaniline-coated gold nanoparticle precursors. Distinctive ZnO structures such as nanoplates, nanospheres, microstars, microflowers, microthorns and micromultipods were synthesized by this method. Slightly different shapes were obtained in the absence of the seed solution. This is a fast, low temperature (60 °C) and biomimetic route to make a wide variety of structures. The structure and morphology of the nanostructures were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were utilized for the characterization of the nanostructures. A growth mechanism for these nanostructures was proposed based on these results. The concentrations of the reacting species were the main parameter causing the changes in the morphologies. The variation in morphologies of these structures is believed to be due to the ability of the seed solution as well as polyvinylpyrrolidone (PVP) to selectively suppress/depress the growth of certain planes, allowing growth to occur only in certain specific directions. Changes in the amount of growth nuclei with varying sodium hydroxide (NaOH) concentration is also seen to affect the morphology of these structures.     

Optical properties of ZnO nanotubes

Tubular ZnO nanostructures have been obtained via a hydrothermal method at low temperature (90 °C) without any catalysts or templates. The XRD measurement reveals that the tubes are single crystals with hexagonal wurtzite structure. SEM shows that the diameters of ZnO nanotubes ranged from 400 to 550 nm. The Raman and PL spectra indicate that oxygen vacancies or Zn interstitials are responsible for the green emission in the ZnO nanotubes. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

HREM investigations of intermediate ZnO and ZnO/Y–ZrO2 layers in Y–ZrO2 bicrystals and ZnO films grown on Y–ZrO2 bicrystal substrates

The structure of yttrium-stabilized ZrO₂ (YSZ) bicrystals with ZnO and ZnO/YSZ/ZnO/YSZ/ZnO intermediate layers, as well as ZnO films grown on YSZ bicrystal (1 1 0)/90° substrates, has been investigated by means of high-resolution electron microscopy (HREM) and microanalysis. All bicrystals were produced by the solid-phase intergrowth (SPI) method. The internal ZnO film in the bicrystal formed at the SPI temperature of 1400°C consisted of domains with two symmetrical orientations: , and , . A bicrystal with a ZnO/YSZ/ZnO/YSZ/ZnO internal film was formed at the temperature of 1200°C. There was no mixing of ZnO and YSZ films and no traces of any solid-phase reactions were observed. Grains in all internal ZnO films and ZnO films grown on the bicrystal substrates had numerous stacking faults. It was found that SPI does not influence the density and structure of these defects. Orientational relationships between YSZ and ZnO in all samples were determined. The ZnO films grown on (1 1 0)/90° bicrystal substrates inherited the grain boundary (GB) from the substrate. Its structure and geometry is determined by four variants of ZnO grain growth.