CVD法制备高质量ZnO纳米线及生长机理

以金做催化剂,采用化学气相沉积(CVD)方法在Si(100)衬底上生长了整齐紧密排列的ZnO纳米线.XRD图谱上只有ZnO的(002)衍射峰,说明ZnO纳米线沿[001]择优生长;扫描电子显微镜分析表明:ZnO纳米线整齐排列在Si(100)衬底上,直径在100nm左右,平均长度为4μm.研究发现ZnO纳米线的生长机理与传统的V-L-S机理有所不同:生长过程中,在Si(100)衬底上先生长了大约500nm厚的ZnO薄膜,而ZnO纳米线生长在薄膜之上.     

In2O3(ZnO)m超晶格纳米线的制备和性质

通过热蒸发ZnO和In粉末用化学气相沉积的方法合成了一维In2O3( ZnO)m超晶格纳米线,利用场发射扫描电子显微镜、透射电子显微镜对它们的结构和成分进行了表征.结果表明,In2O3 (ZnO)m超晶格纳米线是In-O层和In/Zn-O层沿着([1010])方向交替堆叠而成的.讨论了In2O3( ZnO)m超晶格纳米线形成的机制和光致发光特性.     

ZnO/GaN核/壳异质结纳米线能带结构和电荷分离的理论研究

采用密度泛函第一性原理的方法计算了 GaN纳米线、ZnO纳米线及其核/壳纳米线结构的能带结构,价带顶(VBM)和导带底(CBM)的电荷分布.计算表明本征GaN和ZnO纳米线材料VBM和CBM所对应电荷分布较为分散,且与直径关系不大,形成不了II型半导体电荷分离效应.GaN和ZnO组成的核/壳纳米线均保持本征GaN和ZnO纳米线的直接带隙性质.在ZnO包裹GaN的核壳纳米线结构中,不同比例的ZnO和GaN之间电荷转移均不明显, VBM和CBM电荷分布基本都是由壳层的ZnO的O原子占据,难于实现VBM和CBM电荷空间分离.在GaN包裹ZnO的核壳纳米线结构中,VBM电荷和CBM电荷分布分别主要由壳层的N原子占据和核层的O原子占据,同时ZnO和GaN之间的电荷转移量相对较大,容易形成较大的核壳内置电场,有利于促进空间电荷分离,并且随着ZnO的比例增加电荷转移量也相应增加,能有效的促进电荷分离有利于制备成 II型半导体.     

氧分压对化学气相沉积法合成ZnO纳米结构形貌的影响

本文利用化学气相沉积(CVD)法在镀有Au(10 nm)膜的单晶Si(100)上制备了ZnO薄膜,并研究了不同的氧分压对ZnO形貌的影响.借助扫描电镜(SEM)、X射线衍射仪(XRD)和透射电子显微镜(TEM)对样品的形貌、结晶质量和晶体生长取向进行了表征.结果表明:当O2分压较小的时候,O2只能与Zn团簇的某些界面发生反应并逐渐结晶生成层状的ZnO微米团簇.当 O2分压较大的时候,ZnO通过二次生长形成由微米柱阵列和表面无序纳米线构成的分层复合结构,并且表面纳米线的密度随着氧分压的增加而增加.高分辨透射电镜(HRTEM)和选取电子衍射(SAED)分析表明,单根纳米线是沿[001]方向生长的ZnO单晶.     

硅基AAO模板内电化学沉积ZnO纳米线及其光电性能研究

本文利用二次阳极氧化法在p型低阻〈100〉晶向的硅衬底上制备了AAO/Si,以硅基AAO为辅助模板,采用电化学沉积的方法以Zn(NO3).6H2O和HMT(C6H12N4)为原料,在80℃的水浴槽中制备了ZnO纳米线结构。采用SEM,XRD和拉曼光谱等手段对ZnO/AAO/Si复合结构进行表征。SEM图表明ZnO纳米线已成功组装到AAO/Si模板里,直径约45 nm,长度约为600 nm。XRD和拉曼光谱表明ZnO具有六角纤锌矿多晶结构。光致发光(PL)谱图表明ZnO/AAO/Si复合结构在565 nm附近有较宽黄绿发射峰,在395 nm附近有微弱的紫外发射峰。场发射测试结果表明,ZnO纳米线的场增强因子的β值为2490,场增强因子很高,具有广泛的应用前景。     

建筑环境下基于ZnO纳米线甲醛气体检测传感器的研究

为了检测建筑物室内甲醛,用ZnO纳米线作为监测甲醛的目标物.以氯化锌(ZnCl2)和柠檬酸钠(C6 H5 Na3 O7)为原料,使用水热法合成ZnO纳米线,利用X射线衍射仪(XRD)、扫描电镜(SEM)和X射线能谱仪(EDS)对制备出的ZnO纳米线的晶体结构和微观形貌进行表征.结构表征结果表明,所制备出的ZnO纳米线结晶良好、纯度较高,平均直径为(39±10)nm,其长度约为400 nm,且分散良好.将所制备的ZnO纳米线涂覆在陶瓷管上,组装成气敏元件并对其进行系统的气敏特性研究.气敏检测结果表明,基于ZnO纳米线的气体传感器对HCHO气体具有优异的气敏性能.该传感器在125℃时对50×10-6的HCHO气体获得最大灵敏度15.2,同时展现出了优良的稳定性、重现性以及选择性.     

光辐照对单根In掺杂ZnO纳米线电学性质的影响

通过化学气相沉积方法成功制备了高质量的In掺杂ZnO纳米线.选用325 nm的He-Cd激光器做为光源,进一步探究了单根In掺杂ZnO纳米线的光响应特性.结果表明:紫外光辐照可使金属电极与纳米线之间的有效肖特基接触势垒下降,使接触类型由肖特基接触转变到欧姆接触;撤去紫外光后,电极与纳米线之间的接触可以恢复到未光照时的肖特基接触.讨论了肖特基接触与欧姆接触之间转变的物理机制.     

Cu2O/ZnO异质结构纳米线阵列的光电化学性能

通过水热法和热还原法合成了Cu2O/ZnO异质结构纳米线阵列,研究了Cu2O/ZnO异质结构纳米线阵列的光电化学性能.与纯的ZnO纳米线阵列光阳极相比,这种Cu2O/ZnO异质结构光阳极在日光辐照时,展现出了更优异的光电化学性能.在1 V vs.Ag/AgCl偏压时,异质结构光阳极的光电流密度达到1.5 mA/cm2,是纯ZnO纳米线阵列的2倍多.这种光电化学性能的提高,一方面是由于Cu2O的加入,提高了光阳极对于可见光的吸收效率,增强了光生载流子的密度.另一方面,Cu2O和ZnO之间形成的空间电场加速了光生电子-空穴对的分离,从而提高了复合结构光阳极的光电化学性能.结果表明,用地球上储量丰富的元素合成的金属氧化物异质结,也可以实现利用太阳光分解水制备氢气.     

基于CVD自组装生长氧化锌半导体纳米结构的光电导紫外探测器研究

报道了一种基于自组装生长ZnO纳米结构的光电导型紫外探测器.首先,在石英衬底上制备银叉指电极,然后溅射ZnO纳米薄膜形成一种共面光电导型金属-半导体-金属(MSM)结构,再利用低压CVD生长方法进行ZnO纳米线的原位生长,从而在器件顶部形成了ZnO纳米线垂直阵列和其上交错排列ZnO纳米线所构成的双层ZnO纳米线结构.这种器件底部的ZnO薄膜既是MSM光电导器件的电荷传输层,也同时作为上层ZnO纳米结构自组装生长的籽晶层,顶部的ZnO纳米结构层作为紫外光敏感层,测试结果表明该器件具有光响应速度快、光响应电流大和良好的紫外响应可分辨特性.研究表明,相比于单根ZnO纳米线光电导紫外器件而言,基于ZnO纳米结构膜层的光电导紫外探测器能够大幅度提高可测光响应电流.     

ZnO纳米线的水热法生长

本文采用两步湿化学法在玻璃衬底上制备了ZnO纳米线。首先,利用Sol-gel方法在载玻片上制备含有ZnO纳米颗粒的薄膜作为“种子”衬底。然后,利用水热法在“种子”衬底上生长了高度取向的ZnO纳米线。并对“种子”衬底和随后生长的ZnO纳米线进行了X射线衍射(XRD)、扫描电子形貌图(SEM)和原子力显微镜(AFM)等分析。结果表明“种子”衬底为大范围内纳米颗粒均匀一致的ZnO薄膜。通过水热法制备的ZnO纳米线的直径在50～80nm,平均直径为60nm,长度大约为2μm。该ZnO纳米线除了具有很强的紫外发光(399nm)外,还在蓝光(469nm)和绿光(569nm)波段有较弱的光致发光现象。     

Synthesis of high aspect ratio ZnO nanowires with an inexpensive handcrafted electrochemical setup

In this work, high aspect ratio zinc oxide nanowires are synthesized using templated one-step electrodeposition technique. Electrodeposition of the nanowires is done using a handcrafted electronic system. Nuclear track-etched polycarbonate membrane is used as a template to form the high aspect ratio nanowires. The result of X-ray diffraction and scanning electron microscopy shows that nanowires with a good crystallinity and an aspect ratio of more than 30 can be achieved in a suitable condition. The height of electrodeposited nanowires reaches to about 11 μm. Based on the obtained results, high aspect ratio ZnO nanowires can be formed using inexpensive electrodeposition setup with an acceptable quality.     

Synthesis and photoluminescence properties of ZnO nanowire arrays

In this paper we report a chemical method named coordination reaction method to synthesize ZnO nanowire arreys. ZnO nanowires with the diameter about 80nm were successfully fabricated in the channels of the porous anodic alumina (PAA) template by the above coordination reaction method. The microstructures of ZnO/PAA assembly were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The results showed that the ZnO nanowires can be uniformly assembled into the nanochannels of PAA template. The growth mechanism of ZnO nanowires and the conditions of the coordination reaction are discussed. Photoluminescence (PL) measurement shows that the ZnO/PAA assembly system has a blue emission band caused by the various defects of ZnO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of ambient gases on the morphology and photoluminescence of ZnO nanostructures synthesized with nickel oxide catalyst

The morphology and luminescence properties of ZnO nanowires synthesized using NiO catalyst in a chemical vapor deposition system under different growth ambient have been studied. ZnO nanostructures were prepared in nitrogen, ammonia and hydrogen ambient and characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence. Growth in nitrogen ambient yields ZnO nanoneedles while growth with ammonia and hydrogen ambient ends up with ZnO nanowires. Presence of the Ni tip at the end in either morphology indicated the involvement of vapor–liquid–solid growth mechanism. Enhanced green emission in ZnO nanowires implies the presence of a high density of oxygen vacancies. Influence of the ambient gases on the morphology and optical properties of ZnO nanostructures is discussed.     

Self-sacrificed template method for the synthesis of ZnO-tubular nanostructures:reaction kinetics and pathways

Using Zn nanowires as a self-sacrificed template, hierarchical tubes constructed by zinc oxide (ZnO) nanoflakes and ZnO nanotubes have been successfully fabricated by two different thermal-oxidation modes. The products were characterized by the X-ray powder diffraction, transmission electron microscopy and field-emission scanning electron microscopy. The experimental results show that the formation processes of ZnO nanostructures are sensitive to the growth temperature, which is lower or higher the melting point of Zn (419 °C). ZnO nanoflake tubes and ZnO nanotubes can be controlled through the variation of the heat-treatment process of Zn nanowires and their growth pathway can be described by two types of growth mechanism, in terms of Kirkendall effect and the sublimation of the Zn cores, respectively. Our method provides an easy and convenient way to prepare metal oxides tubular nanostructures with different morphologies through self-sacrificed template method via adjusting the heat-treatment process.     

Structural and photoluminescence properties of GaN/ZnO core‐shell nanowires with their shells sputtered

We have reported the preparation of ZnO‐coated GaN nanowires and investigated changes in the structural and photoluminescence (PL) properties by the application of a thermal annealing process. For fabricating the core‐shell nanowires, Zn target was used to sputter ZnO shell onto GaN core nanowires. X‐ray diffraction (XRD) analysis indicated that the annealed core‐shell nanowires clearly exhibited the ZnO as well as GaN phase. The transmissoin electron microscopy (TEM) investigation suggested that annealing has induced the crystallization of ZnO shell layer. We have carried out Gaussian deconvolution analysis for the measured PL spectra, revealing that the core GaN nanowires exhibited broad emission which consist of red, yellow, blue, and ultraviolet peaks. ZnO‐sputtering induced new peaks in the green region. Thermal annealing reduced the relative intensity of the green emission. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication of Zn/ZnO nanocables through thermal oxidation of Zn nanowires grown by RF magnetron sputtering

Fabrication of Zn/ZnO nanocables by thermal oxidation of Zn nanowires grown by RF magnetron sputtering is reported. Single crystalline Zn nanowires could be grown by controlling supersaturation of source material through the adjustment of temperature and Zn RF power. X-ray diffraction and high-resolution transmission electron microscopy showed that surfaces of these Zn nanowires, grown along the [0 1 0] direction, gradually oxidized inward the Zn core to form coaxial Zn/ZnO nanocables in the subsequent oxidation at 200 °C. In the Zn/ZnO nanocable, epitaxial relations of [1 0 0]_Zn//[1 0 0]_ZnO, and (0 0 1)_Zn//(0 0 1)_ZnO existed at the interface between the Zn core and ZnO shell. A number of dislocations were also observed in the interface region of the Zn/ZnO nanocable, which are attributed to large differences in the lattice constants of Zn and ZnO. With further increasing the oxidation temperature over 400 °C, Zn nanowires were completely oxidized to form polycrystalline ZnO nanowires. The results in this study suggest that coaxial Zn/ZnO nanocable can be fabricated through controlled thermal oxidation of Zn nanowires, yielding various cross-sectional areal fractions of Zn core and ZnO shell.     

Structural,Raman, and photoluminescence properties of double‐shelled coaxial nanocables of In2O3 core with ZnO and AZO shells

We synthesized In₂O₃/ZnO/Al‐doped ZnO (AZO) core‐double shell nanowires, in which the inner shell (ZnO) and the outer shell (AZO) have been subsequently deposited on the core In₂O₃ nanowires. With their one‐dimensional morphology being preserved, the X‐ray diffraction (XRD), lattice‐resolved transmission electron microscopy (TEM) image, selected area electron diffraction, and Raman spectrum coincidentally revealed that the shell was comprised of hexagonal ZnO phase. In addition, TEM‐EDX investigation revealed the presence of Al elements in the shell region. The thermal annealing at 700 °C did not significantly change the nanowire morphology, however, the XRD spectrum indicated that the ZnO phase was crystallized by the annealing. PL spectrum of the 700 °C‐annealed In₂O₃/ZnO/AZO core‐double shell nanowires was comprised of three Gaussian bands at approximately 2.1 eV, 2.4 eV, and 3.0 eV, respectively. The integrated intensities of 2.1 eV‐, 2.4 eV‐, and 3.0 eV‐bands were decreased by the thermal annealing. This study will pave the road to the preparation and applicaition of double‐shelled nanowires. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Catalyst‐free thermally‐evaporated growth and optical properties of ZnO nanowires on Si,GaN and sapphire substrates

Vertically well‐aligned zinc oxide nanowires (NWs) with high density were successfully synthesized on Si, sapphire and GaN/sapphire substrates by thermal evaporation of zinc powders without catalysts or additives. The growth behavior of ZnO NWs was strongly dependent on the substrate materials. The effects of the substrate position on the structures and properties of ZnO NWs were primarily discussed. The morphology and crystallinity of the resultant NWs were studied by scanning electron microscope, transmission electronic microscope and X‐ray diffraction. The photoluminescence (PL) characteristics of the ZnO NWs on the different substrates were studied. The results showed that the as‐grown ZnO NWs exhibit a sharp and strong ultraviolet emission at 3.27 eV and a very weak green emission at around 2.48 eV, indicating that the a‐synthesized NWs have excellent PL properties with good crystalline quality and can be an ideal candidate for making luminescent devices. By comparison of PL spectra, we revealed that the green‐to‐UV emission intensity ratios were considerably dependent on the substrate materials, which was explained by the difference in the structural morphology of the produced nanowires.     

Effect of oxygen partial pressure on the growth of zinc micro and nanostructures

Zinc micro and nanostructures were synthesized in vacuum by condensing evaporated zinc on Si substrate at different gas pressures. The morphology of the grown Zn structures was found to be dependent on the oxygen partial pressure. Depending on oxygen partial pressure it varied from two-dimensional microdisks to one-dimensional nanowire. The morphology and structural properties of the grown micro and nanostructures were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Transmission electron microscopy (TEM) studies on the grown Zn nanowires have shown that they exhibit core/shell-like structures, where a thin ZnO layer forms the shell. A possible growth mechanism behind the formation of different micro and nanostructures has been proposed. In addition, we have synthesized ZnO nanocanal-like structures by annealing Zn nanowires in vacuum at 350 °C for 30 min.