Arrangement Of Nanopores Research Articles

Gradient and alternating diameter nanopore templates by focused ion beam guided anodization

Ordered arrays of anodic alumina nanopores with uniform pore diameters have been fabricated by self-organized anodization of aluminum. However, gradient or alternating diameter nanopore arrays with designed interpore distances have not been possible. In this study, focused ion beam lithography is used to fabricate hexagonally arranged concaves with different diameters in designed arrangements on aluminum surfaces. The patterns are then used to guide the further growth of alumina nanopores in the subsequent oxalic acid anodization. Gradient and alternating nanopore arrangements have been attained by FIB patterning guided oxalic acid anodization. The fundamental understanding of the process is discussed.

Through-hole membranes of nanoporous alumina formed by anodizing in oxalic acid and their applications in fabrication of nanowire arrays

The nanopore arrays were fabricated by two-step self-organized anodization of aluminum carried out in 0.3 M oxalic acid at the temperature of 20 °C. This relatively high temperature shortens significantly the anodizing time and allows to fabricate quickly thick through-hole membranes without the additional operating cost of a cooling circuit. The structural features of anodic porous alumina such as pore diameter, interpore distance, porosity, pore density and pore circularity were investigated at various durations of pore opening/widening process carried out in 5% H 3PO 4. An excellent agreement of AAO structural features measured in FE-SEM images of the studied samples with results from software calculations was observed. The pore shape can be monitored qualitatively by fast Fourier transforms (FFTs) and quantitatively by calculation the percentage of pore circularity. Additionally, the regularity of the hexagonal arrangement of nanopores in through-hole AAO membranes was compared for various opening/widening time ranging from 40 to 100 min. It was shown that three-dimensional (3D) representations of FE-SEM images and their surface-height distribution diagrams provide interesting information about the surface roughness evolution during the pore opening/widening process. A template-assisted fabrication of Ag and Sn nanowire arrays by electrochemical deposition into the pores of the prepared AAO templates was also successfully demonstrated.

Fabrication of nanoporous TiO 2 by electrochemical anodization

The formation of self-organized porous titania is achieved by electrochemical anodization under a potentiostatic regime. Anodic titanium oxide (ATO) was fabricated by a three-step self-organized anodization of the Ti foil in an ethylene glycol electrolyte containing 0.38 wt% of NH 4F and 1.79 wt% of H 2O. Anodizing was carried out at the constant cell potential ranging from 30 to 70 V at the temperature of 20 °C. It was found that nanoporous TiO 2 arrays can be obtain only after a short duration of the third step (10 min). The influence of anodizing potential on the structural parameters of porous anodic titania including pore diameter, interpore distance, wall thickness, porosity and pore density was extensively studied. The linear dependencies between interpore distance, pore diameter and wall thickness upon the anodizing potential were found. The regularity of pore arrangement was monitored qualitatively by fast Fourier transforms (FFTs) of top-view FE-SEM images. It was found that the best arrangement of nanopores is observed at 40 V. This finding was confirmed by the analysis of pore circularity. The highest circularity of pores was observed once again at 40 V.

Generation of Electron Moiré Fringes on Designed Nanoporous Anodic Alumina Films and Their Replicated Ni Cone Arrays: Exploration of Domain Sizes and Nanopore Arrangements

Here, we demonstrate a new method to measure the domain sizes and the periodicities of the pore arrangements and to find the domain boundaries in the designed PAA film with conical nanopores. Such structural information can be simultaneously obtained by utilizing the electron moiré fringes without direct observation of the nanopores. The electron moiré fringes are generated by overlapping of two patterns on the basis of the principle of the traditional moiré method. The average size of the single domains is estimated to be about 2 μm2. Furthermore, the Ni cone arrays are successfully produced by replication method using the PAA film. Very clear electron moiré fringes can be visualized on the surface of the Ni cone arrays. The domain-shape and the average domain-size in the observed moiré fringes are almost similar to those of the PAA film used as the original template. This fact indicates that the Ni cones are successfully replicated under excellent electrochemical conditions.

Study the effect of striping in two-step anodizing process on pore arrangement of nano-porous alumina

Two-step anodic oxidation of aluminum is generally employed to produce the ordered porous anodized alumina (PAA). Dissolving away (striping) the oxide film after the first anodizing step plays a key role in the final arrangement of nano-pores. In this work, different striping durations between 1 and 6 h were applied to the sample that was initially anodized at a constant voltage of 40 V at 17 °C for 15 h. The striping duration of 3 h was realized as the optimum time for achieving the best ordering degree for the pores. Scanning electron microscopy (SEM) was used during and at the end of the process to examine the cross section and finishing surface of the specimens. Linear-angular fast Fourier transform (LA-FFT), an in-house technique based on MATLAB software, was employed to assess the ordering degree of the anodized samples.

Structural features of self-organized nanopore arrays formed by anodization of aluminum in oxalic acid at relatively high temperatures

Anodic aluminum oxide (AAO) membranes with a highly ordered nanopore arrangement typically serve as ideal templates for the formation of various nanostructured materials. A typical procedure of the template preparation is based on a two-step self-organized anodization of aluminum carried out at the temperature of about 1–3 °C. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30–65 V at a relatively high electrolyte temperature ranging from 20 to 30 °C. Due to a high rate of porous oxide growth, about 5–10-fold higher than in low-temperature anodizing, the process of the template fabrication can be shorten significantly. Similarly to the low-temperature anodization, the best hexagonal pore arrangement is observed for samples anodized at 40 V. With a prolonged duration of the first anodizing step the order degree of triangular nanoporous lattice, observed after the second anodization, improves considerably. The effects of the anodizing potential and the process duration on the structural features of porous anodic alumina such as: pore diameter ( D p), interpore distance ( D c), porosity ( P), pore density ( n) and anodizing ratio ( B U) were investigated in details at various temperatures. The obtained results were compared with theoretical predictions and data reported in the literature.

THE EFFECT OF ALUMINUM ELECTROPOLISHING ON NANO-PORES ARRANGEMENT IN ANODIC ALUMINA MEMBRANES

Surface conditions of aluminum can influence the final arrangement of nano-pores in fabrication of ordered nanoporous anodic alumina membranes (AAMs). This study is mainly focused on the different applied voltages of aluminum electropolishing by keeping all the other parameters constant. After heat treatment (stress relieving and annealing at 500°C) of pure aluminum sheets, the samples were electropolished at different voltages (10-60V) to obtain desirable surface smoothness, while the temperature of the container was kept constant. The current-time curves were recorded during electropolishing process. The surface roughness obtained in each applied voltage was examined using optical microscope and atomic force microscope (AFM). The process was followed by two-step anodization in order to reach ordered nano-pores. Finally, the influence of surface roughness on regularity of nano-pores was observed using scanning electron microscope (SEM). The SEM images were analyzed to investigate the morphology and the degree of self ordering of pores of the samples by using a new designed analytical method aiming MATLAB and fast Fourier transform (FFT) technique. It was concluded that the electropolishing voltage and the resulted surface roughness and also formed defects can competitively affect the arrangement of membrane's nano-pores. A desired smoothness obtained from electropolishing voltage of 30V. Also 40V provided the best order with respect to the other voltages.

Influence of the microstructure of the aluminum substrate on the regularity of the nanopore arrangement in an alumina layer formed by anodic oxidation

We investigated the microstructure of aluminum sheets with different purities (Al 99.999%, Al 99.95%, Al 99.5% and AlMg1) before and after different treatments (polishing and annealing) by X-ray diffraction (phase analysis and pole figures) and high-resolution scanning electron microscopy. In a two-step anodisation process within sulfuric acid a nanoporous alumina layer (with mean diameters of 25 nm and mean distances of 30 nm) was formed on the aluminum sheets. We found that the regularity of the nanopore arrangement correlates with the fraction of aluminum grains with (100) orientation in the aluminum substrate. A correlation with the grain boundary and dislocation densities within the aluminum could not be determined.

Effects of Annealing Treatment of Aluminum Substrate on Nanopore Arrangements in Anodic Alumina

Effects of annealing treatments of aluminum substrate for ordered nanopore arrays formed by self-organized anodization have been investigated. To observe the relationship between microstructures of aluminum substrate and nanopore regularity formed after anodization of the aluminum substrate, aluminum specimens were annealed at 300, 400, and 500 °C. The anodic alumina layer was prepared by two-step anodizing process in oxalic acid at 40 V. The ordered arrays of nanopore on anodic alumina were shown to be strongly dependent on the annealing conditions, and nanopore regularity on alumina template increased with increasing annealing temperature and time.

Defects Analysis in Self-Organized Nanopore Arrays Formed by Anodization of Aluminium at Various Temperatures

The self-organized anodization of aluminium in sulphuric acid was employed for formation of high-density nanostructures at various cell potentials and temperatures. The well-ordered arrangement of nanopores was obtained by two-step anodization process. The qualitative and quantitative analyses of defects were performed from SEM images of nanostructures. The Fourier transform (FFT) analyses showed that the uniformity of the triangular lattice increases gradually with increasing anodising potential independently of temperature. The order in the nanopore arrangement and size of well-ordered domains increase with increasing anodising potential for all studied temperatures. Quantitative analyses of defects, known as Delanuay triangulations, were performed for various anodising potentials and temperatures. The percentage of generated defects is constant at the cell potential between 15 and 23 V. At the temperature of 1 degree C, the percentage of defects equals to 20% while at temperatures of -8 or 10 degrees C reaches a value of about 30%. At the anodising potential of 25 V the percentage of generated defects in porous alumina is drastically reduced to about 10%, independently of the anodising temperature. The perfect nanopore arrangement on the anodised surface with the smallest number of defects can be obtained at 25 V.

Temperature influence on well-ordered nanopore structures grown by anodization of aluminium in sulphuric acid

The nanostructure dimensions and regularity of the hexagonal arrangement of nanopores formed by self-organized anodization of aluminium in a 20 wt.% sulphuric acid was investigated at various cell potentials and temperatures. The quantitative analyses of defects and Fourier transforms (FFT) performed from SEM images showed that regularity of nanopores arrangement can be improved by increasing anodizing potential, independently of the anodizing temperature. The best result in controlled anodization of aluminium can be obtained at 25 V and the temperature of 1 °C. The pore size and interpore distance distribution diagrams constructed for 1000 independent measurements showed that increasing uniformity of pore diameter and interpore distance is directly responsible for improvement of the regularity of hexagonal arrangement of nanopores observed with increasing anodizing potential at temperatures of −8 or 1 °C. At 25 V and independently of the anodizing temperature, the reduced number of generated defects is predominant factor improving regularity of the nanopore arrangement. The temperature influence on the lattice data, porosity of the nanostructure and real current density at the bottom of nanopores have been demonstrated.

Anodizing process of Al films on Si substrates for forming alumina templates with short-distance ordered 25 nm nanopores

Porous alumina templates with short-distance ordered 25 nm nanopores were fabricated by controlling anodizing progress of Al films on Si substrates in sulfuric acid solution. The ordering of nanopore arrangement with a hexagonal symmetry was found to be closely related to thickness of the deposited Al film, growth temperature, applied voltage, and solution concentration. These parameters were explored in detail and proper experimental conditions were obtained to be 0.44 μm, 5 °C, 20 V, and 15 wt.% for the formation of a relatively ordered nanopore array. Anodizing progress of the Al film was monitored through the current–time ( I– t) curve. Infrared transmittance spectral characterization and microstructural observations disclose that a SiO 2 island array has been formed on the surface of Si substrate under our experimental conditions. This kind of SiO 2 island array can be expected to have applications in nanoelectronics and optoelectronics.

Self-assembled growth of C60 nanowhiskers on anodic porous alumina membranes

Unique structured claw-like C60 nanowhiskers were fabricated on an anodic porous alumina membrane. Tips of the C60 nanowhiskers are shaped like cusps, which directly extend into the nanopores of the alumina membrane. It is revealed that the surface stress of the alumina membrane with a highly ordered nanopore arrangement due to thermal treatment is responsible for self-assembled growth of the observed C60 nanowhiskers. The ordering of the nanopore arrangement in the anodic porous alumina membrane helps to form the C60 nanowhiskers along the nanopore channels. The shape and structure of the C60 nanowhiskers are promising characteristics for applications in nanodevices such as field-emission tips and nanoprobes.

A Control of the Nanopore Regularity in Alumina Layer

This study placed a focus on fabrication factors and surface morphology characteristics to obtain anodic alumina layers with ordered nanopore arrays using two-step anodization process. The regularity of nanopore arrangement in anodic alumina was prepared in oxalic acid at 40 V. The regular array was shown to be more strongly dependent on the time of first anodization than that of second anodization. The widening process of oxide surface in H3PO4 solution clearly exhibits that the nanopore diameter of the alumina layer subjected to widening time increased linearly at a rate of 0.6 nm/min at 30°C, and 0.8 nm/min at 40°C. The pore arrays in anodic alumina were analyzed by SEM.

Effect of Tensile Stress on Growth of Self-Organized Nanostructures on Anodized Aluminum

The effect of an applied tensile stress on the pore ordering during anodization of aluminum was studied. A regular arrangement of nanopores was observed at a relatively low external tensile stress. On the contrary, a high tensile stress completely destroys the pore arrangement on anodized surfaces. Under such conditions, huge holes and pits are formed on the surface. The arrangement of nanopores on samples anodized under applied stresses was examined by Fourier transform analysis and Delaunay triangulation and compared with nonstressed samples. The ordering of pores was found to be dependent on the applied tensile stress. The percent of defects in the triangular lattice increases with increasing applied tensile stress. This result suggests that the surface stress has to be taken into account in a future modeling of the growth of porous oxide layer on anodized aluminum. © 2004 The Electrochemical Society. All rights reserved.

Fabrication Parameters for Highly Ordered Nano-Pore Arrays in Alumina Template

The fabrication parameters for highly ordered nanopore arrays formed by self-organized anodization on aluminum have been investigated. To fabricate ordered nanopore arrays in alumina layer a two-step anodization process was used in oxalic acid solution. The regular nanopore arrangement, interpore distance and pore diameter in alumina surface were strongly dependent on the applied potential at anodization. The interpore distance and pore diameter increased with anodic applied potential, and hexagonally ordered pore arrangements in alumina were obtained by anodization at 40V. For the effects of the heat treatment of aluminum substrate on size of domains with same pore orientation, the domain size increased with increasing annealing time.

Distribution and structures of nanopores in YSZ-TBC deposited by EB-PVD

Distribution and arrangement of nanopores in an YSZ (7 wt% Y2O3–ZrO2)-thermal barrier coating (TBC) deposited by an electron beam-physical vapor deposition (EB-PVD) have been investigated by means of transmission electron microscopy. The YSZ-TBC deposited by the EB-PVD showed a typical columnar structure normal to the bond coat surface on the substrate. It has been generally believed that one column is a single crystal and grows continuously from the substrate. In the present study, however, it was found that each column consisted of a number of subcolumns with different misorientations and contained nanopores at the subcolumn boundaries. In addition to the nanopores at the subcolumn boundaries, nanopores with smaller size were observed within subcolumns, and were arranged periodically perpendicular to the growth direction of the subcolumns. Such arrangement and distribution of nanopores may be due to the misorientation of YSZ plate-like grains in the formation and coalescence processes of the YSZ subcolumns.

Determination of the molecular electrical properties of self-assembled monolayers of compounds of interest in molecular electronics.

Determination of the molecular electrical properties of self-assembled monolayers of compounds of interest in molecular electronics.

Doping and Electrochemical Capacitance of Carbon Nanotube-Polypyrrole Composite Films

ABSTRACTComposite films were electrochemically synthesised via the simultaneous deposition of multiwalled nanotubes and polypyrrole, a conducting polymer. Negatively charged functional groups attached to the surface of the acid treated nanotubes enables the tubes to act as a dopant for the PPy in these films. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy revealed that the nano-porous three-dimensional arrangement of PPy coated MWNTs in these films produced specific capacitances per mass and geometric area as high as 192 F g-1 and 1.0 F cm-2, respectively. This value of specific capacitance per geometric area exceeds that of both component materials and other carbon nanotube-conducting polymer composites. The composite films described in this report were also able to charge and discharge more than an order of magnitude faster than similarly prepared pure PPy films. The nano-porosity and small diffusion distances within the composite films, crucial to achieving the superior capacitive performance, were found to be dependent on the concentration of nanotubes and additional dopant anions in the polymerisation electrolyte, offering possibilities for tailoring of the composite structure.

The nanoparticle-coating process: a potential sol-gel route to homogeneous nanocomposites

A sol-gel process was developed for fabricating inherently homogeneous nanocomposites involving: (a) precipitation of nanoparticles; (b) coating the nanoparticles with a film of matrix phase, and; (c) powder forming and sintering. Die-pressed ZrO 2(nanoparticle)–glass(matrix) specimens were pressureless sintered at 1100°C. Scanning electron microscopy (SEM) of these partially sintered specimens revealed a uniform arrangement of nanopores (∼10 −8 m), suggesting homogeneous ZrO 2 nanoparticle distribution.