Effect of processing on structural features of anodic aluminum oxides

Morphological features of the anodic aluminum oxide (AAO) templates fabricated by electrochemical oxidation under different processing conditions were investigated. The selection of the polishing parameters does not appear to be critical as long as the aluminum substrate is polished adequately prior to the anodization process. AAO layers with a highly ordered pore distribution are obtained after anodizing in 0.6 M oxalic acid at 20 °C under 40 V for 5 minutes suggesting that the desired pore features are attained once an oxide layer develops on the surface. While the pore features are not affected much, the thickness of the AAO template increases with increasing anodization treatment time. Pore features are better and the AAO growth rate is higher at 20 °C than at 5 °C; higher under 45 V than under 40 V; higher with 0.6 M than with 0.3 M oxalic acid.     

Fabrication of Anodic Aluminum Oxide Templates with Small Interpore Distances

The influence of the electropolishing and anodization voltage on surface morphology has been carefully studied for fabrication of ordered anodic aluminum oxide （AAO） templates. In accordance with that in the anodization experiment, the size of small patterns on the foil surface formed from the electropolishing treatment increases with voltage. Using a combined method of small-voltage eleetropolishing and anodization, we have fabricated well ordered templates with much smaller interpore distances compared with that under normal-voltage fabrication conditions. The Ni nanowire arrays with two small diameters are eleetrodeposited through the above templates, exhibiting different magnetic properties. This also helps us to clarify the inner structure of this kind of templates.     

Fabrication and structural properties of LaFeO3 nanowires by an ethanol–ammonia-based sol–gel template route

Highly ordered LaFeO₃ nanowire arrays of composite oxides were synthesized within porous anodic aluminum oxide (AAO) templates by an ethanol–ammonia-based sol–gel route. The results of scanning electron microscopy and transmission electron microscopy revealed that the obtained LaFeO₃ nanowires had a uniform length and diameter, which were determined by the thickness and the pore diameter of the applied AAO template. Energy-dispersive X-ray spectroscopy demonstrated that the stoichiometric LaFeO₃ was formed. Furthermore, the results of X-ray diffraction and selected-area electron diffraction indicated that the LaFeO₃ nanowires had a perovskite-type crystalline structure. It is expected that the novel and effective technique presented in this article would also be appropriate for the preparation of nanowires of other mono-component or multi-component oxides. PACS 61.66.Fn; 61.46.+w; 81.20.Fw     

Synthesis of ordered ZnO nanowire arrays from aqueous solution using AAO template

In this paper we report a simple method that enables the easy fabrication of ordered ZnO nanowire arrays using Anodic Aluminium Oxide (AAO) template. We have used a vacuum injection technique to fill solution into the pores of an AAO template. The AAO template has been fabricated by a two-step anodization process using 0.3 M oxalic acid (H₂C₂O₄) solution under a constant voltage of 40 V. The AAO template formed through this process has been detached from Al substrate via an anodic voltage pulse using perchloric acid (HClO₄) solution (70%). The nanowires of ZnO have been synthesized by injecting the saturated Zn(NO₃)₂ solution into the pores of the detached AAO template using a vacuum pump. The ZnO nanowires synthesized by this technique have been found dense & continuous with uniform diameter throughout the length of the wire. The structural characteristics of AAO template and ZnO nanowires have been studied by Field Emission Scanning Electron Microscope (FESEM), Atomic force microscope (AFM) and Transmission Electron Microscope (TEM).     

The fabrication of Ag nanoflake arrays via self-assembly on the surface of an anodic aluminum oxide template

Vertical-aligned Ag nanoflake arrays are fabricated on the surface of an anodic aluminum oxide (AAO) template under a hydrothermal condition for the first time. The porous surface of AAO templates and the precursor solution may play key roles in the process of fabricating Ag nanoflakes. The rim of pores can provide many active sites for nucleation and growth, and then nanoflake arrays gradually form through self-assembly of Ag on the surface of AAO membranes. The product is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and a growth mechanism of nanoflake is deduced. This work demonstrates that it is possible to make ordered nanoarrays without dissolving templates using the hydrothermal method, and this interesting Ag nanoflake arrays may provide a wider range of nanoscale applications.     

高质量多孔氧化铝模板的制备

在草酸电解液中研究了阳极氧化法制备多孔氧化铝模板(AAO模板)。采用场发射扫描电子显微镜对多孔模板的形貌进行表征,结果表明:模板孔的分布均匀有序,孔径在40~70 nm;电解液浓度、氧化电压、氧化温度和氧化时间都会影响模板的形态;不经过高温退火及抛光也可以制得规则排布的多孔AAO模板。X射线衍射分析表明:氧化铝膜的主要成分为非晶态Al2O3。     

Roughness evolution of highly ordered nanoporous anodic aluminum oxide films

In this paper, we report on the surface roughness evolution of highly ordered anodic aluminum oxide (AAO) films based on an atomic force microscopy (AFM) study. Root mean square of the surface roughness was measured on AFM images taken from highly ordered AAO films produced by two-step anodization under different conditions including electrolyte type, anodization voltage, and anodization time. Surface roughness of highly ordered AAO films increases step by step through the two-step anodizing process including electropolishing, first-step anodization, dissolution, and second-step anodization. However, increase of the surface roughness is proportional to the anodization voltage and time. The surface roughness of AAO films changes as a function of length scale until it finally approaches a maximum termed the saturation roughness. The variation of roughness of the growth of AAO could be scaled with an anomalous dynamic behavior as it saturates over a critical length scale while the saturation roughness is dependent on the anodizing time and voltage.     

Silver nanorods used to promote SERS as a quantitative analytical tool

We have fabricated silver nanorod arrays by electrodepositing the nanorods evenly in the shallow pores of porous anodic aluminum oxide (AAO) templates. The diameter and length were 28 and 44 nm, respectively. The maxima of the transverse and longitudinal modes of the surface plasmon were near 417 and 511 nm, respectively. A good surface‐enhanced Raman scattering (SERS) spectrum was observed by excitation with the 514.5‐nm laser line. The SERS intensity increased almost linearly upon malachite green isothiocyanate adsorption on the tips of the silver nanorods as the concentration of the mother solutions increased. Our results show that silver nanorods fabricated on AAO templates could be used as an SERS substrate for quantitative analyses. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrodeposition and magnetic properties of Ni nanowire arrays on anodic aluminum oxide/Ti/Si substrate

Ni nanowire arrays with different diameters have now been extended to directly fabricate in porous anodic alumina oxide (AAO) templates on Ti/Si substrate by direct current (DC) electrodeposition. An aluminum film is firstly sputter-deposited on a silicon substrate coated with a 300 nm Ti film. AAO/Ti/Si substrate is synthesized by a two-step electrochemical anodization of the aluminum film on the Ti/Si substrate and then used as template to grow Ni nanowire arrays with different diameters. The coercivity and the squareness in parallel direction of Ni nanowires with about 10 nm diameters are 664 Oe and 0.90, respectively. The Ni nanowire arrays fabricated on AAO/Ti/Si substrates should lead to practical applications in ultrahigh-density magnetic storage devices because of the excellent properties.     

Influence of defects on the ordering degree of nanopores made from anodic aluminum oxide

Anodic aluminum oxide (AAO) templates with highly ordered nanoporous structure were fabricated by means of the electrochemical anodization under the constant anodic voltage and electrolyte temperature. The dependence of the ordering degree of nanopores on the point defects, dislocation configuration and grain boundary of aluminum is qualitatively analyzed. Experiment results show that the size of the ordered region of nanopores depends strongly on the point defects, dislocation cell configuration.     

Simple fabrication of hexagonally well-ordered AAO template on silicon substrate in two dimensions

In this study, thin anodic aluminum oxide (AAO) templates both on silicon substrates (AAO template/SiO₂/Si) and Ti-coated silicon substrates (AAO template/Ti/SiO₂/Si) were developed for design of magnetic, electronic and optoelectronic devices, chemical sensors and chip-scale lithium-ion rechargeable microbatteries. Two types of AAO template were prepared by using a two-step anodization procedure. The templates were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The obtained thin AAO templates were approximately 50 nm in diameter and 700 nm in length with 80-nm interpore distances in a relatively large area of 6 cm². A barrier layer of the AAO templates was removed by a cathodic polarization method in KCl solution for several seconds. The current–time transient during removing the alumina barrier layer of the thin AAO template and the mechanism of electrochemical dissolution of the barrier layer are given in detail.     

强辐射源用铜纳米线阵列靶的结构与性能

 采用多孔阳极氧化铝（AAO）模板脉冲电沉积法制备了强辐射源用铜纳米线阵列靶,并用扫描电子显微镜（SEM）、能谱（EDS）和X射线衍射（XRD）对其进行了结构表征。结果表明：去除AAO模板后铜纳米线平均直径比去除AAO模板前的平均孔径大32%,长度缩短5%。对电沉积2 000 s的样品进行铜纳米线长度分布表征,结果显示:距离模板圆心越远,铜纳米线越长。与超短脉冲激光相互作用实验结果表明:纳米线平均长度在18~50 μm范围内,铜Kα光子产额先随纳米线长度增加而增加,当长度大于33 μm时,铜Kα光子产额开始下降。     

新型氧化铝模板自组装制备非晶碳纳米点阵列膜及其场发射性能研究

通过对阳极氧化铝(AAO)模板进行特殊扩孔处理,消除了AAO模板中带电阴离子对沉积碳离子的不良影响,利用磁过滤阴极弧等离子体沉积技术成功制备了非晶碳纳米尖点阵列膜.场发射扫描电镜(FESEM)分析表明,经过氧化和扩孔多步处理制备的AAO模板具有特殊的开口结构,制备的非晶碳纳米尖点阵列完整地复制了AAO模板的孔道阵列结构,纳米点排列整齐有序,直径约100nm,密度达1010cm-2,样品的场发射测试显示,非晶碳纳米点阵列具有良好的电子发射性能,发射电流为10mA/cm-2时的阈值电场为3.7V/μm.     

Large‐area Ag nanorod array substrates for SERS: AAO template‐assisted fabrication,functionalization, and application in detection PCBs

Highly ordered arrays of thiolated β‐cyclodextrin (HS‐β‐CD) functionalized Ag‐nanorods (Ag‐NRs) with plasmonic antennae enhancement of electrical field have been achieved for encapsulation and rapid detection of polychlorinated biphenyls (PCBs). The large‐area ordered arrays of rigid Ag‐NRs supported on copper base were fabricated via porous anodic aluminum oxide (AAO) template‐assisted electrochemical deposition. The inter‐nanorod gaps between the neighboring Ag‐NRs were tuned to sub‐10 nm by thinning the pore‐wall thickness of the AAO template using diluted H₃PO₄. The nearly perfect large‐area ordered arrays of Ag‐NRs supported on copper base render these systems excellent in surface‐enhanced Raman scattering (SERS) performance with uniform electric field enhancement, as testified by the SERS spectra and Raman mappings of rhodamine 6 G. Furthermore, the Ag‐NRs were functionalized with HS‐β‐CD molecules so as to capture the apolar PCB molecules in the hydrophobic cavity of the CD. Compared to the ordinary undecorated SERS substrates, the HS‐β‐CD modified Ag‐NR arrays exhibit better capture ability and higher sensitivity in rapid detection of PCBs. Copyright © 2012 John Wiley & Sons, Ltd.     

Controllable synthesis of Ag nanorods using a porous anodic aluminum oxide template

This paper describes a new approach to the synthesis of Ag nanorods. A solvothermal method was used to make Ag nanoparticles inside anodic aluminum oxide (AAO) templates. The nanoparticles were then annealed at 300 °C to produce Ag nanorods. The size of AAO templates, which is focused on in this study, would determine the diameter of Ag nanorods. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this study, a nanorod growth mechanism is deduced, and understanding of the growth of nanorods inside AAO templates is furthered. This work demonstrates that it is possible to make crystalline nanorods that the size can be varied.     

钛酸锶钡纳米管的制备及其红外吸收性能研究

首次采用溶胶凝胶法结合通孔阳极氧化铝模板, 成功制备出了钛酸锶钡纳米管. 该制备工艺简单、易实现而且成本低. 首先制备通孔阳极氧化铝模板和钛酸锶钡溶胶, 然后通过浸渍加上匀胶的方法将钛酸锶钡溶胶引入到通孔阳极氧化铝模板的纳米孔洞中, 最后在650℃下煅烧1 h形成钛酸锶钡纳米管. X射线衍射(XRD)证明, 制得的钛酸锶钡纳米管为立方钙钛矿相, 主要沿(110)晶向生长. 扫描电子显微镜(SEM)显示, 钛酸锶钡纳米管外径、内径和管长分别为75 nm, 50 nm, 16 μm. 傅里叶变换显微红外光谱仪(FTIR)测试结果表明在波数为1350-1650 cm^-1红外波段, 阳极氧化铝/钛酸锶钡纳米管复合结构较钛酸锶钡薄膜有两处明显的吸收峰, 吸收峰位于1470和1550 cm^-1处, 与通孔阳极氧化铝模板相比其吸收峰强度高出一倍, 最后分析了出现这一现象的可能原因.     

Novel structure formation at the bottom surface of porous anodic alumina fabricated by single step anodization process

A simple approach for the growth of long-range highly ordered nanoporous anodic alumina film in H₂SO₄ electrolyte through a single step anodization without any additional pre-anodizing procedure is reported. Free-standing porous anodic alumina film of 180 μm thickness with through hole morphology was obtained. A simple and single step process was used for the detachment of alumina from aluminum substrate. The effect of anodizing conditions, such as anodizing voltage and time on the pore diameter and pore ordering is discussed. The metal/oxide and oxide/electrolyte interfaces were examined by high resolution scanning transmission electron microscope. The arrangement of pores on metal/oxide interface was well ordered with smaller diameters than that of the oxide/electrolyte interface. The inter-pore distance was larger in metal/oxide interface as compared to the oxide/electrolyte interface. The size of the ordered domain was found to depend strongly upon anodizing voltage and time.     

Direct imprinting of ordered and dense TiO2 nanopore arrays by using a soft template for photovoltaic applications

Highly ordered and dense TiO₂ nanopore arrays are directly nanoimprinted on a transparent conductive glass substrate by using a polymethylmethacrylate/polydimethylsiloxane (PMMA/PDMS) composite soft template, which is replicated from an anodic aluminum oxide (AAO) replica mold. Results indicate that heat infiltration under vacuum conditions can ensure complete filling of PMMA into the AAO pores, and that free-standing PMMA nanorods with an aspect ratio more than 5 can be obtained by adjusting the AAO pore depth based on a freeze-drying technique. TiO₂ nanopore arrays with different diameters from 30 to 300 nm and inter-pore distances between 70 and 450 nm can be easily fabricated by using the corresponding templates with different sizes. Preliminary solar cells are also assembled with a heterojunction of conjugated polymer/TiO₂ nanopore arrays. Results indicate that the construction of poly-(3-hexylthiophene) (P3HT)/TiO₂ nanopore arrays can be more helpful in quenching the PL emission of P3HT than that of P3HT/flat TiO₂ film, and a maximum efficiency of about 0.32% can be obtained for a photovoltaic device with a TiO₂/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)/P3HT structure.     

Synthesis of highly ordered LiMnO<Subscript>2</Subscript> nanowire arrays (by AAO template) and their structural properties

LiMnO₂ nanowire arrays were prepared using a porous anodic aluminum oxide (AAO) template from a sol–gel solution containing Li(OAc) and Mn(OAc)₂. Electron-microscope results showed that a uniform length and diameter of LiMnO₂ nanowires were obtained, and the length and diameter of the LiMnO₂ nanowires are dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrate that LiMnO₂ nanowires are a layered structure of LiMnO₂ crystal. X-ray photoelectron spectroscopy analysis indicates that a material closely resembling stoichiometric layered LiMnO₂ has been obtained. Received: 2 September 2001 / Accepted: 6 January 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-931/891-2582, E-mail: lihl@lzu.edu.cn     

Study on Fluorescence Characteristic of Quercetin–Nanoporous Anodic Aluminum Oxide Composites

Nanoporous Anodic Aluminum Oxide (AAO), its average diameters of porous were 50 nm, was obtained by two-step electrochemical anodization aluminum process. Highly ordered luminescence arrays formed by filling AAO nanopores with quercetin molecules has been studied by fluorescent spectroscopy in this work. AAO showed stronger adsorption capability of quercetin than Al³⁺-quercetin complex. The mechanism may be physical and chemical adsorption all together. Meanwhile, red shift of the maximum fluorescence peak of quercetin in AAO was observed. The molecular assemblies in the nanopore array are highly ordered and the fluorescence polarization dependence indicates a preferred molecular orientation along the pore axis. This maybe explains the mechanism of molecular luminescence depending on its environment.