Self-organized porous alumina nanostructures fabricated by the anodization of aluminum have attracted considerable attention in both scientific and commercial fields as an indispensable part of nanotechnology. This has been fuelled by their versatile applications in fields of electronics or optoelectronics, [1] magnetics, [2,3] energy storage, [4] photocatalysis, [5] photonics, [6] and biosensors. [7] To facilitate various practical applications and nanodevices, fabricating highly ordered porous anodic alumina films with low cost and by a simple process on a large scale is an essential and urgent task and has yet not been solved. Porous anodic alumina (PAA) films with parallel nanopores are known as having a honeycomb-like structure that has short-distance ordering (in several tens to hundreds of nanometers) but long-distance disordering for pore arrangement. [8] To achieve a highly ordered pore arrangement over a large area, many studies have so far elaborated a variety of pretreatments or pretexturing techniques.[9±15] For instance, Masuda and Fukuda [9] first proposed a two-step anodization process, in which the dents on aluminum formed in the first anodization step (several days) worked as the initial sites of pore growth in the second anodization step, thus improving the overall pore arrangement to some extent. To achieve highly ordered PAA films, Masuda and co-workers also invented a pretexturing process, [10,11] i.e., using a textured SiC molder to produce ordered patterns on aluminum by a mechanical indentation prior to anodization. The shallow concaves on aluminum induced the pore initiation during anodization and led to an ideally ordered pore arrangement within the stamped areas (e.g., 4 mm 4 mm). Recently, some modified pretexturing methods, such as pre-patterning on aluminum by optical diffraction grating, [12] atomic force microscope scanning probe, [13] focused-ion-beam, [14] and polystyrene beads, [15] have been also attempted, to perform direct or mold-less patterning on aluminum exclusive of the expensive SiC master fabrication. To facilitate pretexturing, aluminum samples were usually annealed in nitrogen or argon at 400± 500 C to remove mechanical stress and to recrystallize the aluminum. They were then electro-polished in mixed acid solutions (e.g., a mixture of HClO 4 and C 2 H 5 OH) to smooth the surface for precise and uniform imprints. However, all of the pretexturing processes mentioned above, i.e., controlling the initial sites of pore growth, are utilizing external methods or extrinsic factors to achieve ordered PAA films. The decisive method or the intrinsic factor for pore ordering, however, is actually the anodizing process itself, i.e., the optimally combined anodizing conditions such as solution, temperature, and potential or current density. Therefore, raising the self-organizing ability of porous alumina films through an anodizing process, exclusive of any external assistance, is the radical solution for lowering production cost and exploring new applicable fields, which are sig...

Various ordered nanoporous alumina films with arbitrary pore intervals from 130 to 980 nm were fabricated on aluminum by a critical-potential anodization approach with sulfuric, phosphoric, oxalic, glycolic, tartaric, malic, and citric acid electrolytes under 70-450 V. The pore intervals of the porous alumina films were linearly proportional to applied potentials, with corresponding dominated territories to the electrolytes. In addition to pore interval, the self-ordering extent of pore arrangement was also improved with increasing anodizing potentials, leading to highly ordered porous alumina films at critical-high potentials. A cell separation phenomenon occurred for the films formed in sulfuric and glycolic acid solutions at the critical potentials, thus leading to the formation of highly ordered alumina nanotubule arrays. The critical-potential anodization in the other electrolytes produced self-organized porous alumina films with two-layered pore walls and pore bases. The basic principle for achieving porous alumina films with desired pore intervals is controlling the balance of the growth of barrier layer and the pore generation by adjusting the acidity, the concentration, and temperature of electrolytes. The porous alumina films formed in various electrolytes were transparent, and the transmittances of the films were inversely proportional to the applied potentials or the pore intervals.

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A transparent porous alumina nanostructure was formed on a glass covered tin-doped indium oxide (ITO) substrate by anodization of a highly pure sputtered aluminum layer. Details of the fabrication and microstructures of porous anodic alumina films are described and a possible mechanism of anodization is outlined. The variation of anodic current density reflects three processes, i.e., (i) anodization of the sputtered aluminum layer, (ii) transition of electrolysis from aluminum to the underlying ITO film, and (iii) electrochemical reactions on the ITO film beneath the anodic alumina film. As all the aluminum is completely anodized, the resultant oxide films on the ITO/glass substrate possess a parallel porous structure (ϕ80-100 nm, cell size in ∼350 nm) with a thin arched barrier layer (∼80 nm) and exhibit a high transmittance in the ultraviolet-visible light range (75-100% transmittance 300-900 nm). © 2002 The Electrochemical Society. All rights reserved.

Herein, we report the stabilization and modulation of layered-herringbone (LHB) packing, which is known to afford high-performance organic thin-film transistors, based on crystal structure analyses and calculations of intermolecular interaction energies for alkyl-substituted organic semiconductor (OSC) crystals. We systematically investigated the alkyl chain-length dependence of the crystal structures, solvent solubilities, and thermal characteristics for three series of symmetrically and asymmetrically alkyl-substituted benzothieno [3,2-b][1]benzothiophenes (BTBTs). All the series exhibit LHB packing when the BTBTs are substituted with relatively long alkyl chains (−C n H 2n+1 ), i.e., n ≥ 4 for monoalkylated, n ≥ 6 for dialkylated, and n ≥ 5 for phenyl-alkylated BTBTs. LHB packing is also evident in the nonsubstituted and diethyl-substituted BTBTs, although those substituted with short alkyl chains generally did not feature LHB packing because of their lack of interchain ordering. The density functional theory calculations of the intermolecular interactions revealed that the BTBT cores inherently generate LHB packing, and the stability is increasingly enhanced by the alignment of longer alkyl chains. It was also found that the LHB packing is stabilized by keeping the size ratios of the total intermolecular attractive forces between the T-shaped and slipped parallel contacts at about 3:2 for all the LHB compounds, despite the slight structural modifications generated by the substituents. We discuss the effects of alkyl substitutions to modulate the LHB packing of the BTBT cores and thus the two-dimensional carrier transport in layered OSC crystals.

We analyze the constraints on CP-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral CP-even states and the EDMs probing the effect of mixing between the CP-even and CP-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron and diamagnetic atom EDM searches could yield competitive or even more severe constraints. We analyze the quantitative impact of hadronic and nuclear theory uncertainties on the interpretation of the latter systems and conclude that these uncertainties cloud the impact of projected improvements in the corresponding experimental sensitivities.

Titania nanostructures with larger surface areas are fabricated on a glass substrate by anodization of sputtered aluminum and the sol−gel process, and the structural characteristics of the nanostructures are investigated. Highly pure aluminum film (99.99%, ≈2 μm), which is deposited on a glass substrate with a conductive tin-doped indium oxide (ITO) layer, is first anodized potentiostaticly in a phosphoric acid solution to obtain porous alumina structures. The anodic alumina is then used as a host or template to synthesize porous Al2O3/TiO2 composite nanostructures through a sol−gel process. Finally, a TiO2 nanotubules array with contours of porous anodic alumina is fabricated on glass by removing the alumina template selectively. The resultant TiO2 is 4−20 nm polycrystalline of anatase structure with (101) preferential orientation. Titania nanostructures have large surface areas and exhibit a high transmittance in visible light and a strong absorbance within ultraviolet range in UV−vis spectra. Moreover, the fabrication of composite TiO2−xSiO2−xTeO2 (x = 2.5%, 5%) nanostructures is also investigated. Addition of appropriate SiO2 and TeO2 to TiO2 enhances not only the adhesion to the substrate but also the mechanical strength of the nanotubules, while showing little effect on the crystallinity and the UV−vis absorbance of TiO2.

Oxygen-ion conduction in transition-metal oxides is exploited in, for example, electrolytes in solid-oxide fuel cells and oxygen-separation membranes, which currently work at high temperatures. Conduction at low temperature is a key to developing further utilization, and an understanding of the structures that enable conduction is also important to gain insight into oxygen-diffusion pathways. Here we report the structural changes observed when single-crystalline, epitaxial CaFeO₂.₅ thin films were changed into CaFeO₂ by low-temperature reductions with CaH₂. During the reduction process from the brownmillerite CaFeO₂.₅ into the infinite-layer structure of CaFeO₂, some of the oxygen atoms are released from and others are rearranged within the perovskite-structure framework. We evaluated these changes and the reaction time they required, and found two oxygen diffusion pathways and the related kinetics at low temperature. The results demonstrate that oxygen diffusion in the brownmillerite is highly anisotropic, significantly higher along the lateral direction of the tetrahedral and octahedral layers.