Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.     

Structural and optical properties of ZnO nanorods grown on MgxZn1−xO buffer layers

ZnO nanorod arrays were synthesized by chemical-liquid deposition techniques on Mg_xZn_1−xO (x = 0, 0.07 and 0.15) buffer layers. It is found that varying the Mg concentration could control the diameter, vertical alignment, crystallization, and density of the ZnO nanorods. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) data show the ZnO nanorods prefer to grow in the (0 0 2) c-axis direction better with a larger Mg concentration. The photoluminescence (PL) spectra of ZnO nanorods exhibit that the ultraviolet (UV) emission becomes stronger and the defect emission becomes weaker by increasing the Mg concentration in Mg_xZn_1−xO buffer layers.     

Controlled synthesis of oriented ZnO nanorod arrays by seed-layer-free electrochemical deposition

Oriented ZnO nanorod arrays were successfully prepared on transparent conductive substrates by seed-layer-free electrochemical deposition in solution of Zn(NO₃)₂ at a low temperature of 70 °C without using any catalysts, additives, and additional seed crystals. The effects of the Zn(NO₃)₂ concentration, deposition time and applied current on the localized nanorod arrays are investigated. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structures and the morphologies of ZnO nanorod arrays. The heights and diameters of ZnO nanorods can be tuned by controlling the electrodeposition parameters.     

Effect of synthesis conditions on microstructures and photoluminescence properties of Ga doped ZnO nanorod arrays

Ga doped ZnO nanorod arrays were prepared on silicon substrates in a mixture solution of zinc nitrate hexahydrate, methenamine, and gallium nitrate hydrate. Effect of synthesis conditions on crystal structures, morphologies, surface compositions, and optical properties was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence techniques (PL). Experimental results reveal that Ga doping amount can reach 1.67 at% with the increase of gallium nitrate concentration. Ga doping greatly affects the morphologies of ZnO nanorod arrays. The photoluminescence spectra show a sharp UV emission and a broad visible emission. With Ga doping, UV emission has an apparent broadening effect and its peak shifts from 3.27 eV to 3.31 eV. The intensity ratio of UV emission to visible emission demonstrates that appropriate Ga doping amount is beneficial for the improvement of ZnO crystalline quality.     

两步法制备空间取向高度一致的ZnO纳米棒阵列

采用两步法,即先用磁控溅射在Si(100)表面生长一层ZnO籽晶层、再利用液相法制备空间取向高度一致的ZnO纳米棒阵列.用扫描电子显微镜、X射线衍射、高分辨透射电子显微镜和选区电子衍射对样品形貌和结构特征进行了表征.结果表明,ZnO纳米棒具有垂直于衬底沿c轴择优生长和空间取向高度一致的特性和比较大的长径比,X射线衍射的(XRD)(0002)峰半高宽只有0.06°,选区电子衍射也显示了优异的单晶特性.光致发光谱表明ZnO纳米棒具有非常强的紫外本征发光和非常弱的杂质或缺陷发光特性. 关键词： ZnO纳米棒阵列 ZnO籽晶层 两步法 液相生长     

水热法制备Co掺杂ZnO纳米棒及其光学性能

采用水热法在石英衬底上以Zn(CH3COO)2.2H2O和Co(NO3)2.6H2O水溶液为源溶液,以C6H12N4(HMT)溶液作为催化剂,在较低温度下制备了Co掺杂的ZnO纳米棒。采用X射线衍射(XRD)和扫描电子显微镜(SEM)对所生长ZnO纳米棒的晶体结构和表面形貌进行了表征,考察了Co掺杂对ZnO纳米棒微观结构和对发光性能影响的机制。结果表明:Co掺杂的ZnO纳米棒呈六方纤锌矿结构,具有沿(002)面择优生长特性,Co掺杂使ZnO纳米棒的直径变细;同时室温光致发光(PL)谱检测显示Co掺杂ZnO纳米棒具有很强的近带边紫外发光峰,而与深能级相关的缺陷发光峰则很弱。本研究采用水热法在石英衬底上于较低温度下生长出了具有较高光学质量的Co掺杂ZnO纳米棒。     

Growth of ZnO nanorods by aqueous solution method with electrodeposited ZnO seed layers

ZnO nanorod arrays on ZnO-coated seed layers were fabricated by aqueous solution method using zinc nitrate and hexamethylenetetramine at low temperature. The seed layers were coated on ITO substrates by electrochemical deposition technique, and their textures were dominated by controlling the deposition parameters, such as deposition potential and electrolyte concentration. The effects of the electrodeposited seed layers and the growing parameters on the structures and properties of ZnO nanorod arrays were primarily discussed. The orientation and morphology of both the seed layer and successive nanorods were analyzed by using X-ray diffraction (XRD), SEM and TEM. The results show that the seed layer deposited at −700 mV has evenly distributed crystallites and (0 0 2) preferred orientation; the density of resultant nanorods is high and ZnO nanorods stand completely perpendicular onto substrates. Meanwhile, the size of nanorods quite also depends on the growth solution, and the higher concentration of growth solution primary leads to a large diameter of the ZnO nanorods.     

A template-free sol-gel technique for controlled growth of ZnO nanorod arrays

The growth of ZnO nanorod arrays via a template-free sol-gel process was investigated. The nanorod is single-crystalline wurtzite structure with [0 0 0 1] growth direction determined by the transmission electron microscope. The aligned ZnO arrays were obtained directly on the glass substrates by adjusting the temperatures and the withdrawal speeds, without seed-layer or template assistant. A thicker oriented ZnO nanorod arrays was obtained at proper experimental conditions by adding dip-coating layers. Room temperature photoluminescence spectrum exhibits an intensive UV emission with a weak broad green emission as well as a blue double-peak emission located at 451 and 468 nm, respectively. Further investigation results show that the difference in the alignment of nanorods ascribes to the different orientations of the nanoparticles-packed film formed prior to nanorods on the substrate. Well ordered ZnO nanorods are formed from this film with good c-axis orientation. Our study is expected to pave a way for direct growth of oriented nanorods by low-cost solution approaches.     

Controllable vertical growth onto anatase TiO2 nanoparticle films of ZnO nanorod arrays and their photoluminescence and superhydrophilic characteristics

Well-aligned ZnO nanorod arrays have been successfully fabricated directly on anatase TiO₂ nanoparticle films via low-temperature hydrothermal processes. The effects of the reactive time, temperature and reactant concentration on the growth of the as-prepared ZnO crystals are investigated in detail, and the possible mechanisms of crystal ZnO nanorod growth are also suggested. The results show that the low reactant concentration is in favor of the increase in the aspect ratio of crystal ZnO nanorods with weak orientation, while the long reactive time and high reactant concentration are useful to prepare well-aligned crystal ZnO nanorod arrays. Interestingly, the typically constructed composite films exhibit superhydrophilic characteristic without UV irradiation. Moreover, a strong near-ultraviolet PL band centering at about 385 nm and a weak green PL band centering at about 525 nm can appear at the room temperature.     

Aligned ZnO nanorod arrays fabricated on Si substrate by solution deposition

Aligned ZnO nanorod arrays were fabricated by chemical solution deposition based on Si substrate which was spin coated with ZnO colloid as nucleation seeds. Their microstructures were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The results indicated that ZnO nanorods nucleated and grew vertically on Si substrates along the [0 0 1] direction with single-crystalline structure. The diameter of ZnO nanorods was greatly affected by the grain size of ZnO seeds. Room-temperature photoluminescence of nanorods has a strong emission band at about 384 nm.     

Growth and investigation of antifungal properties of ZnO nanorod arrays on the glass

In this study, we have investigated the antifungal activity of ZnO nanorods prepared by the chemical solution method against Candida albicans. In the study, Zinc oxide nanorods have been deposited on glass substrates using the chemical solution method. The as-grown samples are characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray diffraction (XRD) showed zinc oxide nanorods grown in (0 0 2) orientation. The antifungal results indicated that ZnO nanorod arrays exhibit stable properties after two months and play an important role in the growth inhibitory of Candida albicans.     

Modulation of field emission properties of vertically aligned ZnO nanorods with aspect ratio and number density

Vertically aligned ZnO nanorod arrays with different aspect ratios were synthesized by hybrid wet chemical route. Modulation of the field emission properties (FE) with aspect ratio of ZnO nanorods was examined. With the increase in the aspect ratio, the emission current density increases from 0.02 to 8 μA/cm² at 7.0 V/μm. Turn-on voltage was seen to decrease from 9.6 to 7 V/μm at a current density of 10 μA/cm² with the increase in aspect ratio in the ZnO films. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure of the ZnO nanostructure obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) was discussed. Quality of the ZnO nanorods was also examined by using Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). It was found that the observed enhancements of FE characteristics could mainly be attributed to the increase in aspect ratio and associated number density of ZnO nanorods.     

Field electron emission improvement of ZnO nanorod arrays after Ar plasma treatment

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved after radio-frequency (rf) Ar plasma treatment. With Ar plasma treatment for 30 min, flat tops of the as-grown ZnO nanorods have been etched into sharp tips without damaging ZnO nanorod geometrical morphologies and crystallinity. After the Ar ion bombardment, the emission current density increases from 2 to 20 μA cm⁻² at 9.0 V μm⁻¹ with a decrease in turn-on voltage from 7.1 to 4.8 V μm⁻¹ at a current density of 1 μA cm⁻², which demonstrates that the field emission of the as-grown ZnO nanorods has been efficiently enhanced. The scanning electron microscopy (SEM) results, in conjunction with the results of transmission electron microscopy (TEM), Raman spectroscopy and photoluminescence observation, are used to investigate the mechanisms of the field emission enhancement. It is believed that the enhancements can be mainly attributed to the sharpening of rod tops, and the decrease of electrostatic screening effect.     

纳米ZnO生长及性质分析

利用低压金属有机化学气相沉积(LP-MOCVD)技术,在表面含有ZnO颗粒作为催化剂的Si(111)衬底上制备了ZnO纳米柱阵列。采用X射线衍射(XRD)、喇曼光谱(Raman)、扫描电子显微镜(SEM)、光致发光(PL)谱分析了样品的晶体结构质量、表面性质和光学性质。结果表明,生长出来的纳米ZnO具有较好的c轴择优取向性。发现氧分压对ZnO纳米柱的生长有重要影响:当氧分压较低时,生长基于VLS机制;当氧分压较高时,生长基于VS机制;通过对N2O流量的控制可实现对ZnO纳米材料的可控生长。     

硝酸铟诱导的电沉积氧化锌纳米柱光学性质裁剪

为在新型太阳能电池等光电器件中应用ZnO纳米结构,需要对ZnO纳米结构阵列的几何形貌及光电物理性质进行裁剪与操控。采用电化学沉积路线制备ZnO纳米柱阵列,In(NO3)3与NH4NO3两种盐类被溶入在传统Zn(NO3)2主电解液中。对ZnO纳米柱阵列进行扫描电子显微镜、透射反射光谱、光致发光光谱测试,分析其形貌与光电物理性质。随着引入的In(NO3)3浓度的增加,ZnO纳米柱阵列的平均直径随之由57 nm减小至30 nm。同时ZnO纳米柱的阵列密度也可降低,进而增大纳米柱间距至41 nm。由于新的盐类的引入,ZnO纳米柱的光学带隙由3.46 eV蓝移至3.55 eV。随着电解液中In(NO3)3的增加,ZnO纳米柱的斯托克斯位移由198 meV减小至154 meV,ZnO纳米柱中的非辐射复合可以得到一定程度的抑制。通过在主电解液中引入In(NO3)3与NH4NO3两种盐类,可对ZnO纳米柱的直径、密度、间距、透射反射率、光学带隙、近带边发射与非辐射复合进行操控与裁剪。     

ZnO thin film with nanorod arrays applied to fluid sensor

A ZnO guiding layer with nanorod arrays grown on a 90°-rotated ST-cut (42°45) quartz substrate was used to fabricate a Love wave fluid sensor. ZnO nanorod arrays synthesized on the guiding layer enhance the sensitivity of the flow rate. ZnO thin films were deposited by radio frequency magnetron sputtering and ZnO nanorod arrays were then synthesized on the thin films via the hydrothermal method. The crystalline structure and surface morphology of ZnO thin films and nanorod arrays were examined by X-ray diffraction and scanning electron microscopy. The effects of the thickness of ZnO thin film and the surface morphology of ZnO nanorod arrays on the sensitivity of flow rate were investigated. A linear response between flow rate and the return loss of the sensor with one-port resonator type can be obtained by adjusting the thickness of ZnO thin film and the length of nanorod arrays.     

Effects of thermal annealing temperature and duration on hydrothermally grown ZnO nanorod arrays

In this study, the effects of thermal annealing temperature and duration on ZnO nanorod arrays fabricated by hydrothermal method were investigated. The annealed ZnO/Si(1 1 1) substrate was used for ZnO nanorod array growth. The effects of annealing treatment on the structural and optical properties were investigated by scanning electron microscopy, X-ray diffraction, and room-temperature photoluminescence measurements. With the annealing temperature of 750 °C and the annealing duration of 10 min, both the structural and optical properties of the ZnO nanorod arrays improved significantly, as indicated in the X-ray diffraction and photoluminescence measurement.     

ZnO薄膜的性质对水热生长ZnO纳米线阵列的影响

用水热法在ZnO薄膜上制备了直径、密度及取向可控的ZnO纳米线阵列。ZnO薄膜是通过原子层沉积(ALD)方法制备并在不同温度下退火处理得到的,退火温度对ZnO薄膜的晶粒尺寸、结晶质量和缺陷性质有很大的影响。而ZnO薄膜的性质对随后生长的ZnO纳米线的直径、密度及取向能起到调节控制的作用。通过扫描电子显微镜(SEM)、X射线衍射(XRD)仪和光致发光(PL)测试对ZnO薄膜和ZnO纳米线进行了表征。最后得到的垂直取向的ZnO纳米线阵列适合在发光二极管和太阳能电池等领域使用。     

Synthesis and characterization of Cu2ZnSnSe4 nanotube arrays on fluorine-doped tin oxide glass substrates

Highly ordered arrays of Cu₂ZnSnSe₄ nanotubes have been successfully synthesized on fluorine-doped tin oxide glass substrate using ZnO nanorod arrays as sacrificial templates. The structure, morphology and optical properties of the Cu₂ZnSnSe₄ arrays were characterized by X-ray diffraction, Raman spectrometry, field-emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray, and UV–Vis absorption spectroscopy. The diameter and length of the Cu₂ZnSnSe₄ nanotubes can be adjusted by tuning the diameter and length of the ZnO nanorods. In addition, the effect of the length on the performance of the photoelectrochemical cells was also investigated.     

The structural and optical properties of ZnO nanorod arrays

High quality vertical-aligned ZnO nanorod arrays were synthesized by a simple vapor transport process on Si (111) substrate at a low temperature of 520 °C. Field-emission scanning electron microscopy (FESEM) showed the nanorods have a uniform length of about 1 μm with diameters of 40-120 nm. X-ray diffraction (XRD) analysis confirmed that the nanorods are c-axis orientated. Selected area electron diffraction (SAED) analysis demonstrated the individual nanorod is single crystal. Photoluminescence (PL) measurements were adopted to analyze the optical properties of the nanorods both a strong UV emission and a weak deep-level emission were observed. The optical properties of the samples were also tested after annealing in oxygen atmosphere under different temperatures, deep-level related emission was found disappeared at 600 °C. The dependence of the optical properties on the annealing temperatures was also discussed.