Mn掺杂ZnO纳米棒阵列的制备及其磁学性质研究

在95 ℃条件下通过水热方法制备出垂直于ITO基底高密度均匀生长的Mn掺杂ZnO（ZnO：Mn）纳米棒阵列. 纳米棒的直径约为100纳米,长约1微米,且沿［001］方向生长. XRD和XPS结果证实了Mn以替位方式掺杂到纳米棒中,并且掺杂浓度与反应物中的Mn离子浓度似呈正比关系. 所制备的ZnO：Mn纳米棒在室温均有铁磁性,其饱和磁化强度随反应物中Mn离子浓度的提高,饱和磁化强度呈现出先增大,5at.%时达到最大值,0.11 emu/g,然后减小. 铁磁性来源于取代Zn离子的Mn离子之间的铁磁交换相互作用.     

Linear and nonlinear optical properties of ZnO nanorod arrays

Polarization-dependent linear absorption, second-harmonic generation （SHG） and 3rd-order nonlinearities of wellaligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0×10^4cm/GW at the wavelength -750nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.     

ZnO nanorod arrays fabrication via chemical bath deposition: Ligand concentration effect study

A new ligand, N,N,N′,N′-tetramethylethylenediamine, has been used to grow ZnO nanorods on silicon substrates via a two steps approach. A preliminary seeding on silicon substrates has been combined with chemical bath deposition using a Zinc acetate–N,N,N′,N′-tetramethylethylenediamine aqueous solution. The used diamino ligand has been selected as Zn²⁺ complexing agent and the related hydrolysis generates the reacting ions (Zn²⁺ and OH⁻) responsible for the ZnO growth. The seed layer has been annealed at low temperature (<200 °C) and the ZnO nanorods have been grown on this ZnO amorphous layer. There is experimental evidence that the ligand concentration (ranging from 5 to 50 mM) strongly affects the alignment of ZnO nanorods on the substrate, their lateral dimension and the related surface density. Length and diameter of ZnO nanorods increase upon increasing the ligand concentration, while the nanorod density decreases. Even more important, it has been demonstrated, as proof of concept, that chemical bath deposition can be usefully combined with colloidal lithography for selective ZnO nanorod deposition. Thus, by patterning the ZnO seeded substrate with polystyrene microsphere colloidal lithography, regular Si hole arrays, spatially defined by hexagonal ZnO nanorods, have been successfully obtained.     

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     

Growth and optical study of ZnO nanorods

ZnO nanorods were grown by a simple near room temperature, chemical solution method on ZnO-seeded silicon substrates. Study of the ZnO nanorods over different growth times by electron microscopy methods revealed that the resulting ZnO nanorods were single crystalline with a highly preferential growth perpendicular to the substrate and a very good c-axis alignment. The size of the nanorods increased with increasing growth time. The growth mechanism is briefly discussed. Post-annealing in oxygen slightly improved the surface roughness of the ZnO nanorods. Photoluminescence experiments at 1.6 K revealed a major emission peak of the nanorods at around 3.36 eV which is attributed to the band edge transition of ZnO, while defect-related emission is relatively weak.     

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.     

Light-induced antifungal activity of TiO2 nanoparticles/ZnO nanowires

Antifungal activity of TiO₂/ZnO nanostructures under visible light irradiation was investigated. A simple chemical method was used to synthesize ZnO nanowires. Zinc acetate dihydrate, Polyvinyl Pyrrolidone and deionized water were used as precursor, capping and solvent, respectively. TiO₂ nanoparticles were deposited on ZnO nanowires using an atmospheric pressure chemical vapor deposition system. X-ray diffraction pattern of TiO₂/ZnO nano-composite has represented the diffraction peaks relating to the crystal planes of the TiO₂ (anatase and rutile) and ZnO. TiO₂/ZnO nanostructure antifungal effect on Candida albicans biofilms was studied and compared with the activity of TiO₂ nanoparticles and ZnO nanowires. The high efficiency photocatalytic activity of TiO₂ nanoparticles leads to increased antifungal activity of ZnO nanowires. Scanning electron microscope was utilized to study the morphology of the as prepared nanostructures and the degradation of the yeast.     

Growth and electrical properties of ZnO nanorod arrays prepared by chemical spray pyrolysis

Chemical spray pyrolysis was applied to grow ZnO nanorod arrays from zinc chloride solutions with pH=2 and 5 on glass/ITO substrate at 480 and 550 °C. The obtained structures were characterized by their morphological, electrical and PL properties. According to SEM, deposition of acidic solutions retards coalescence of the growing crystals. The charge carrier density in ZnO nanorods was determined from the C-V characteristics of ZnO/Hg Schottky barrier. Carrier densities ∼10¹⁵ cm⁻³ and slightly above 10¹⁶ cm⁻³ were recorded for ZnO deposited at 550 and 480 °C, respectively. According to PL studies, intense UV-emission is characteristic of ZnO independent of growth temperature, the concentration of oxygen vacancy related defects is lower in ZnO nanorods deposited at 550 °C. Solution pH has no influence on carrier density and PL properties.     

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.     

Growth of b-axis oriented VO2 thin films on glass substrates using ZnO buffer layer

VO₂ thin films are grown on glass substrates by pulsed laser deposition using vanadium metal as a target. In this study, a ZnO thin film was used as a buffer layer for the growth of VO₂ thin films on glass substrates. X-ray diffraction studies showed that the VO₂ thin film had b-axis preferential orientation on a c-axis oriented ZnO buffer layer. The thickness of the ZnO buffer layer and the oxygen pressure during VO₂ deposition were optimized to grow highly b-axis oriented VO₂ thin films. The metal-insulator transition properties of the VO₂ film samples were investigated in terms of infrared reflectance and electrical resistance with varying temperatures.     

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.     

ZnO nanorod arrays with tunable size and field emission properties on an ITO substrate achieved by an electrodeposition method

In the present work,vertically aligned ZnO nanorod arrays with tunable size are successfully synthesized on nonseeded ITO glass substrates by a simple electrodeposition method.The effect of growth conditions on the phase,morphology,and orientation of the products are studied in detail by X-ray diffraction(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM).It is observed that the as-prepared nanostructures exhibit a preferred orientation along c axis,and the size and density of the ZnO nanorod can be controlled by changing the concentration of ZnCl2.Field emission properties of the as-synthesized samples with different diameters are also studied,and the results show that the nanorod arrays with a smaller diameter and appropriate rod density exhibit better emission properties.The ZnO nanorod arrays show a potential application in field emitters.     

Tunable and reversible surface wettability transition of vertically aligned ZnO nanorod arrays

Vertically aligned zinc oxide (ZnO) nanorods (NRs) with different surface morphology were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrate. To study the effect of surface morphology on wettability, the contact angle (CA) of water was measured. It was demonstrated that the CA of the deposited ZnO NRs varied between 104° and 135° depending upon the surface morphology. The ZnO NRs became super-hydrophilic after ultraviolet (UV) illumination. However, the NR arrays were reconverted to their previous hydrophobic state after low temperature annealing (50 °C) in open atmosphere. Structural effect and preferential adsorption of water molecules on the defective sites of UV illuminated surface was used to explain the transition mechanism. Under the alternations of heat treatment and UV illumination, a reversible transition between hydrophobicity and super-hydrophilicity were observed.     

Synthesis and properties of aligned ZnO microtube arrays

Two kinds of different aligned zinc oxide (ZnO) crystal microtube arrays were prepared on silicon (1 0 0) substrates by using of a simple thermal chemical reaction vapor transport deposition method. The synthesizing processes were done by using of heating the mixture of zinc oxide and graphite powders at 1150 °C in a quartz tube with one side opened to the air. The O₂ gas (99.9%) and air had been introduced as the assistant gases, respectively. Both the flow rates were 100 ml/min. And the temperature of the Si (1 0 0) substrate region was about 400 °C. There is no other metal catalyst on the Si wafers in the process. After growing for 30 min, one kind of synthesized sample is trumpet-shaped hexagonal microtube arrays assisted with O₂ gas and another produced sample is the uniform hexagonal microtubes only assisted with air. As the increasing of preparing time, their maximal lengths can range from several 10 μm to mm scale. The microstructure, room temperature photoluminescence properties and growth mechanism of both aligned microtube arrays were investigated and discussed.     

Post-annealing influence on electrical properties and photoluminescence of B-N codoping ZnO thin films

B-N codoped ZnO (ZnO:(B,N)) films were grown on quartz substrate by radio-frequency (rf) magnetron sputtering. The influence of post-annealing ambient on electrical and optical properties of ZnO:(B,N) films were investigated using Hall and Photoluminescence (PL) measurement, respectively. Electrical properties studies indicate that both post-annealing ZnO:(B,N) showed p-type conduction. However, compared with ZnO:(B,N) annealed in oxygen, the ZnO:(B,N) annealed in vacuum have low resistivity and high concentration. The PL spectra indicate that two new emission bands located at 3.303 and 3.208 eV originate from the recombination of A⁰X and FA related to N acceptor for the annealed p-ZnO:(B,N) in vacuum, but of A⁰X, FA related to Zn vacancy for the annealed p-ZnO:(B,N) in oxygen. The mechanism of influence of post-annealing on the electrical and optical properties of the ZnO:(B,N) film is discussed in this work.     

Well-aligned ZnO rod arrays grown on glass substrate from aqueous solution

Well-aligned ZnO rod arrays have been successfully synthesized on glass substrate from the aqueous solution of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ (HMT). Some critical issues such as seed layers, concentration and reaction time were investigated. The results show that ZnO seed layers were pre-requisite for the aligned growth of ZnO rod arrays. The length of rods is tunable in a range from 2 μm to 3 μm by varying the solution concentration and reaction time. X-ray diffraction results demonstrate that ZnO rods are wurtzite crystal structures preferentially orienting in the direction of the c-axis. Microstructure observation by scanning electron microscope confirms that ZnO rods grew up perpendicular to the substrate. Room-temperature photoluminescence (PL) spectrum of rod arrays shows a strong emission band at about 396 nm.     

Ultrafast laser assisted fabrication of ZnO nanorod arrays for photon detection applications

Orderly aligned ZnO nanorod arrays were grown by the ultrafast laser assisted ablation deposition method. These nanorod arrays were further used to make efficient p-n heterojunction photodetector arrays, which have the potential to have nanoscale spatial resolution for imaging, unique incident polarization discrimination capability, and much improved quantum efficiency as well as detection sensitivity. Both front- and back-illumination photodetection schemes were demonstrated by growing those ZnO nanorod arrays on p-type silicon and p-type Zn_0.9Mg_0.1O-coated Al₂O₃ (0 0 0 1) substrates, respectively. Typical diode rectification behavior and photosensitivity were observed in both designs through I-V and photocurrent measurements.     

Seed-assisted growth of epitaxial ZnO nanorod arrays with self-organized periodicity and directional alignment

In this article we report the seed-assisted growth of epitaxial ZnO nanorod (NR) arrays on (0 0 0 1) plane sapphire substrates at low temperatures in aqueous solutions. The self-organized periodic ZnO NR rows with a fairly constant separation were directly grown on bare sapphire surfaces, without the need for any complicated lithography or use of pre-patterned catalysts. The spatial ordering of the ZnO NRs was significantly influenced by the seed growth conditions and by the presence of a self-organized step structure on the annealed sapphire surface. In addition, the effect of the conditions employed to prepare the seeds, including growth parameters and post-growth annealing treatment, on the epitaxial relationship between the ZnO NRs and the sapphire substrate was systematically investigated by X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations. Post-growth annealing of the ZnO seeds changed the morphologies and crystallographic alignment of the generated ZnO nanostructures significantly, as a result of the formation of epitaxial spinel ZnAl₂O₄ interlayers, facilitated by zinc cation diffusion and solid state reactions at high temperature.     

Fabrication of an intelligent superhydrophobic surface based on ZnO nanorod arrays with switchable adhesion property

The superhydrophobic ZnO surface possessing water adhesive reversibility is fabricated by a facile method. The as-prepared surface is low adhesive; however, after being irradiated by UV light through a photomask, it becomes highly adhesive. A water droplet can suspend on the irradiated surface. Further annealing the irradiated surface, water droplets can roll on the surface again. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be realized simply by UV illumination and heat treatment alternately. The adhesion transition is attributed to the adsorption/desorption of surface hydroxyl groups and the organic chains rearrangement on the top surfaces of ZnO.