Narrow Results

Two chemical solutions NH₄F:H₂O:C₃H₈O₃(sol${}_1)$ and NH₄F:H₂O:C₂H₆O₂(sol${}_2)$ with different fluoride ratios were used separately in an anodic process to study the morphological characteristics of the produced copper oxides. Glycerol and ethylene glycol were utilized as inhibitions to slow down the activity of fluoride ions. The rest of the anodization process parameters were constant. Scanning electron microscope (SEM) images showed the formation of Cu₂O microcubes when sol₁ was used. The utilization of sol₂ produced octahedral Cu₂O as well as cubes and spherical structures. The increase of NH₄F in sol₁ led to a reduction in the volumes of Cu₂O microcubes, and in sol₂, it produced incomplete octahedral Cu₂O. Since ethylene glycol has a lower viscosity than glycerol, copper corrodes more quickly in the presence of the former than in the latter. The findings indicate that sol₁ is experiencing a higher current flow than sol₂. The relationship between current and time is semi-constant at low applied voltage, but the two curves behave differently when applying high voltage in the early stages.

High-orderly nanotubes of titania were fabricated by anodic oxidation of pure titanium substrate in different electrolytes containing fluoride. Different morphological nanotubes of titania were obtained through controlling the different pH value of inorganic electrolytes, and it was found that nanotubes of titanium oxide would not formed when pH value was above 6. The morphological and structural properties of nanotublar products were characterized by SEM. The synthesized nanotubes of titania in organic electrolytic solutions containing fluoride was of 60 μm in length. The experiments demonstrated the length and orderliness of nanotubes of titanium oxide in organic solutions were much better than those in inorganic solutions.

The micro-pores with size of 0.2 to 1.8 µm, which randomly distribute in a 316L stainless steel substrate, were fabricated by the transfer of the porous structure of anodic porous alumina. The mask anodic porous alumina was directly prepared by anodizing of aluminum film, which was deposited on 316L substrate by DC magnetron sputtering. The transfer of the porous structure of anodic alumina into the 316L substrate could be achieved without the additional through-hole treatment to the barrier layer. The localized priority dissolution on porous alumina is observed during the anodizing. And this process is considered to lead to the micro-pores formation on 316L substrate. In addition, the effect of anodizing time on the pores size and number on 316L substrate also was discussed.

In this work, Ag nanoparticles were deposited in the TiO${}_{2-X}$ nanotube films through magnetron sputtering to form Ag-TiO${}_{2-X}$ nanocomposite. Scanning electron microscopy (SEM) was used to study microstructure and surface morphology. Rhodamine B (RhB) was deposited on the surface of Ag-TiO${}_{2-X}$ substrate for Raman spectroscopy test. The size of Ag nanoparticles can be controlled by changing the magnetron sputtering time. The result indicated that sputtering for 30 s obtained the highest Raman enhancement.

Alumina nanowires have been synthesized by a simple electrochemical route, by tailoring the anodization process of aluminum. Two-stage anodization of pure aluminum foils were carried out in 0.3 M oxalic acid electrolyte by maintaining a constant current density of 250 A/m² and suitably controlling the other anodization parameters: anodization voltage, bath temperature and anodization time. The fabricated alumina nanowires were investigated by field-emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Moreover, the X-ray diffraction (XRD) study on the prepared nanowires shows that they are non-crystalline in nature. The photoluminescence (PL) spectra of alumina nanowires exhibit two stable emission bands at 438 and 581 nm. The blue luminescence behavior of the alumina nanowires are attributed to the oxygen-deficient defect centers. PL study of alumina nanowires shows that they have potential applications in light emission devices.

In this article, titanium oxide nanotube arrays (TiO₂–NTAs) were fabricated by anodic oxidation in an ethylene glycol (EG) electrolyte solution containing 0.25 wt.% NH₄F. By varying anodized time and annealed temperature, the obtained nanotube arrays behaved different photocatalytic (PC) activities and photocurrent properties. These samples were characterized by scanning electronic microscope (SEM), X-ray powder diffraction (XRD). It was indicated in SEM images that TiO₂ nanotube manifests highly ordered structure which, however, has been completely destroyed when the temperature comes to 800°C. XRD manifested that TiO₂ nanotubes with various kinds of length all possessed anatase crystallite when annealed at 500°C; meanwhile, with certain length, TiO₂–NTAs annealed at series calcination temperature range of 300–600°C also presented anatase crystallite, which is gradually enhanced with the increment of temperature. At 700°C, mixed structure was observed which was made up of proportions of overwhelming anatase and toothful rutile. Methyl blue (MB) degradation and photocurrent measurement testified that TiO₂–NTAs under 4 h oxidation and 3 h of 600°C calcination manifested the highest activity and photocurrent density.

In this paper, a new environmental-friendly electrolyte containing sulfuric acid and tartaric acid has been used as the substitute of chromic acid for anodization. The work discussed the influence of anodizing voltages on the fatigue life of anodized Al 2024-T3 by performing fatigue tests with 0.1 stress ratio (R) at 320 MPa. Meanwhile the fatigue cycles to failure, yield strength, tensile strength and fracture surface of anodic films at different conditions were investigated. The results showed that the fatigue life of anodized and sealed specimens reduced a lot compared to aluminum alloy, which can be attributed to the crack sites initiated at the oxide layer. The fracture surface analyses also revealed that the number of crack initiation sites enlarged with the increase of anodizing voltage.

Anodized aluminum oxide (AAO) templates with an average diameter of $D_1\sim 20$nm and $D_2\sim 200$nm are synthesized by two-step anodization. Nickel nanowires are fabricated by AC electro deposition with less microstructure defects at low voltage in AAO templates. Magnetic properties of compact nickel (Ni) nanowires show that easy axis is parallel to nanowire axis for diameter $D_1\sim 20$nm while by varying diameter from $D_1\sim 20$nm to $D_2\sim 200$nm, easy axis shifts to perpendicular direction of nanowire axis. This shifting of magnetic easy axis from parallel to perpendicular direction is mainly due to shape anisotropy and interactive fields between the wires. The competition between shape anisotropy (due to individual wire) and interactive fields by varying diameter of nanowires could result in tailoring of the direction of magnetic easy axis of nanowires.

We report on the influence of stirring of electrolyte (glycerol$+$ H₂O $+$ NaCl) on anodic growth of Ni-Ti-O nanopores (NPs) on nearly equiatomic NiTi alloy at different applied voltages. The results show that anodization is a diffusion-controlled process. The stirring has little influence on the NP diameter, but shortens its length. High stirring speed of electrolyte yields high Ni content in the NPs, which is promising in electrocatalysis, biosensor, supercapacitor, and other related fields.

The development of new nanomaterials with controlled characteristics for nanophotonics is of great relevance. In this work, photonic crystals with reflectance at the wavelength of 690nm and the value of 28% were formed by porous-alumina-assisted-anodizing of system Al/Ta on Si wafer. By selecting improved anodizing modes of system Al/Nb on glass, the reflectance was increased to 42% at the wavelength of 340nm. This result shows the high promise of the proposed methods and in the future will significantly improve the result by trying two- or three-stage methods of porous-alumina-assisted-anodizing, nanoimprint stamps and optimization of the anodizing modes for any wavelengths.

In this paper we present a study on the application of nanoporous silicon to an optoelectronic device called a nanoporous silicon metal-semiconductor-metal (MSM) visible light photodetector. This device was fabricated on a nanoporous silicon layer which was formed by electrochemical etching of a silicon wafer in a hydrofluoric acid solution under various anodization conditions such as the resistivity of the silicon wafer, current density, concentration of the hydrofluoric acid solution and anodization time. The structure of this device has two square Al/nanoporous silicon Schottky-barrier junctions on the silicon substrate and the electrode spacing is 500 μm. The experiment will study photoresponse and the response time of a nanoporous silicon MSM photodetector which was fabricated on the various porosity of a nanoporous silicon layer. It is found that when devices are fabricated on a higher porosity nanoporous silicon layer, the photoresponse of the device will expand toward the short-wavelength and the bandwidth of the spectrum response will cover visible light. In addition, it is found that the response time of the device in terms of rise time will decrease.

We investigated the Raman spectra as a function of the total electric charge consumed in forming porous silicon. It was found that the Raman peak shifted to the lower wave number side as the total electric charge increased. However, the width of the Raman line was insensitive to the total electric charge. It shows the size of nanocrystallites can be widely ranged regardless of the degree of electrochemical reactions during anodization.

Porous anodic alumina formation on silicon substrate is an example of a nanostructured porous array that is well-suited as a template for growing metallic nanowires. Commercial silicon wafer deposited with aluminum is used as substrate. Prior to anodization, the aluminum film is cleaned with mixture of acids solution to remove its native oxide growth. Anodization of aluminum film on silicon wafer is performed in oxalic acid solution to generate uniform and self-organized nanoporous alumina film. The pores are in the range of 60 nm diameter and pore density is about 9 × 10⁹/cm². The nanoporous alumina template is filled with nickel nanowires by wet electrodeposition process. After nanowire is grown on silicon wafer, the alumina template is etched and the as grown nickel nanowire forest is patterned using laser pruning method. The crystallinity pattern of the as grown nickel naowire forest is characterized using X-ray diffraction technique.

The temperature of alumina barrier layer during a high electric field anodization of aluminum (the current density more than 50mA/cm${}^2)$ has been studied by analyzing the aluminum film resistance. In the case of Joule heat power density to be larger than 20W/cm², the temperature inside the barrier layer can exceed $660^{\circ }$C, which leads to the local melting of aluminum. Scanning electron microscopy has shown the location of molten aluminum droplets and their movement during the anodization process.

Porous anodic alumina (PAA) thin films, having interconnected pores, were fabricated from Cu-doped aluminum films deposited on $p$-type silicon wafers by anodization. The anodization was done at four different anodizing voltages (60V, 70V, 80V and 90V) in phosphoric acid and two voltages (60V and 70V) in oxalic acid. The aluminum and PAA samples were characterized by SEM and XRD while the pore arrangement, pore density, pore diameter, pore circularity and pore regularity were also analyzed. XRD spectra confirmed the aluminum to be crystalline with the dominant plane being (220), the Cu-rich phase have an average particle size of $15\pm 5$nm uniformly distributed within the Al matrix of 0.4-$\mu$m grain size. The steady-state current density through the anodization increased by 117% and 49% for oxalic and phosphoric acids, respectively, for 10V increase (from 60 to 70 V) in anodization voltage. Similarly, the etching rate increased by 100% for oxalic acid and by 40% for phosphoric acid which are responsible for 47% and 29% decreases in anodization duration, respectively. The highest value of circularity obtained for anodized Al–0.5wt.% Cu formed in oxalic acid at 60V was 0.86, and it was 0.80 for the phosphoric acid at 90V. Anodization of Al–0.5wt.% Cu films allows the formation of circular pores directly on $p$-type silicon wafers which is of importance for future nanofabrication of advanced electronics. The results of anodized Al–0.5wt.% Cu thin film were compared with other anodized systems such as anodized pure Al and Al doped with Si.

“Multi-layer” walled TiO₂ nanotube array has been prepared by anodization with post-treatment of ethanol. Two post-treatment methods, which were ethanol and water treatment respectively, exerted a marked and different effect on the structure of nanotube. With ethanol immersion, the “multi-layer” walled nanotube can be obtained, while water treatment cannot produce the “multi-layer” walled structure. The main reason could be the uptake of carbon and fluoride during anodization process. Compared with “single-layer” walled TiO₂ nanotube, “multi-layer” walled TiO₂ nanotube demonstrated higher photocatalytic activity.

The anodization with different cathodes (i.e., point cathode, linear cathode or planar cathodes with different areas) was performed to determine the effect of the cathode area on TiO₂ nanotube (TiNT) yield. Results show that proper planar cathode, but not point or linear cathode, is necessary for the production of TiNT, and 8:3 (S_(-)/S₍₊₎) is regarded as the optimal electrode area ratio. The anodization with three electrodes would help to further enhance the unit yield. And the unit yield by one cathode and two anodes is higher than that by two cathodes and one anode, but the product of the latter featured with more uniform structure. Our work would help in guiding the further exploration of high yield TiNT.