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Structural study of very thin anodic alumina films on silicon by anodization in citric acid aqueous solution.

The formation of thin alumina films on a silicon substrate by anodization in a mild acid, specifically in 1% wt citric acid aqueous solution, is investigated by transmission electron microscopy (TEM). We present a comparative study between two cases of starting material: pure aluminum and an alloy of aluminum with 1% silicon. In both cases the thickness of the Al layer was less than 50 nm. It was observed that under exactly the same conditions, in the first case the anodization was stopping before anodizing the whole film and a remaining non-anodized Al layer was always present, while in the second case, the Al layer was fully anodized, resulting in an alumina matrix with a very high density of silicon nanocrystals of uniform sizes embedded in it. In both cases the alumina film was compact and amorphous.

Aluminum Oxide↗

Fabrication of a one-dimensional array of nanopores horizontally aligned on a Si substrate.

A one-dimensional array of nanopores horizontally aligned on a silicon substrate was successfully fabricated by anodic aluminum oxidation (AAO) using a modified two-step procedure. SEM pictures show clear nanostructures of well-aligned one-dimensional nanopore arrays without cracks at the interfaces of the sandwiched structures. The processes are compatible with the planar silicon integrated circuit processing technology, promising for applications in nanoelectronics. The formation mechanism of a single nanopore array on Si substrates was also discussed.

Aluminum Oxide↗

Nanoscale characterization of carbazole-indole copolymers modified carbon fiber surfaces.

Polycarbazole, carbazole and indole containing copolymers were electrochemically coated onto carbon fiber. The resulting polymers and copolymers were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Characterization of the thin polymer films were performed on the polymer-coated surface of the carbon fiber. Therefore, the results obtained could elucidate the relationship between the initial feed monomer ratio, the resulting polymer/copolymer film morphology and the surface structure formed. The thickness increase (in diameter) was 0.3 and 0.9 microm, for two different composition of carbazole/indole on the carbon fiber. The carbon fibers coated with copolymer thin films were from 6.5 to 8.2 microm in diameter (from AFM measurement).

Carbazoles↗

Templated synthesis, characterization, and sensing application of macroscopic platinum nanowire network electrodes.

Novel platinum nanowire network electrodes have been fabricated through electrodeposition using mesoporous silica thin films as templates. These electrodes were characterized by X-ray diffraction, transmission electron microscope, and scanning electron microscope. The electrochemical properties of the electrodes, such as electrochemical active area and methanol oxidation, have also been studied. Compared with conventional polycrystalline Pt electrodes, these novel nanowire network electrodes possess high electrochemical active areas and demonstrate higher current densities and a lower onset potential for methanol electro-oxidation. Enzymatic Pt nanowire-network-based sensors show higher sensitivity for glucose detection than that using conventional polycrystalline Pt electrode. Such macroscopic nanowire network electrodes provide ideal platforms for sensing and other device applications.

Aspergillus niger↗

Controlled porous pattern of anodic aluminum oxide by foils laminate approach.

A novel, much simpler, and low-cost method to fabricate the porous pattern of the anodic aluminum oxide (AAO) based on the aluminum foils laminate approach was carried out. During our experiments, it was found that the pores of the AAO on the upper foil grew bi-directionally from both the top and the bottom surfaces. Experimental results further indicate that the upward porous pattern of the upper foil is determined by the surface structure of the bottom surface of the upper foil. The porous pattern of AAO can be controlled by a pre-made pattern on the bottom surface. Furthermore, no Aluminum (Al) layer removing process is required in this novel laminate method.

Aluminum Oxide↗

A study of nano-mechanical properties and nano-scratch behavior of boron carbonitride films.

Boron carbonitride (BCN) films were deposited by d.c. unbalanced magnetron sputter deposition where a substrate bias ranging from -50 V to -300 V was applied to the sample. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to confirm the composition and bonding structure of the BCN films. Surface morphology and roughness were analyzed by atomic force microscopy. The nano-mechanical properties and nano-scratch behavior of the prepared films were determined by a nano-indentation system equipped with continuous stiffness measurement and lateral-force measurement attachments. The results indicate that there is little change in the content of B, C, and N. The films deposited are compounds with hybridized B-C-N bonds and the disordered degree of the structure increases with increasing the substrate bias. The substrate biasing can enhance the nanohardness, elastic modulus, nano-scratch resistance, and cohesion strength of the deposited films. During the nano-scratch test, plastic deformation and ploughing wear appears for the BCN films deposited at lower bias. Elastic deformation becomes the dominant deformation mechanism for the films deposited at higher bias. The coefficient of friction between the deposited BCN films and the diamond tip depends on the loading critical load. The increasing of the substrate bias leads to the improvement of the critical load and the elastic deformation proportion.

Adhesiveness↗

Electro-oxidation of methanol on TiO2 nanotube supported platinum electrodes.

TiO2 nanotubes have been synthesized using anodic alumina membrane as template. Highly dispersed platinum nanoparticles have been supported on the TiO2 nanotube. The supported system has been characterized by electron microscopy and electrochemical analysis. SEM image shows that the nanotubes are well aligned and the TEM image shows that the Pt particles are uniformly distributed over the TiO2 nanotube support. A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The electrocatalytic activity of the platinum catalyst supported on TiO2 nanotubes for methanol oxidation is found to be better than that of the standard commercial E-TEK catalyst.

Crystallization↗

Structure and giant magnetoresistance behaviour of Co-Cu/Cu multilayers electrodeposited under various deposition conditions.

Electrodeposited Co-Cu/Cu multilayers were prepared under a variety of deposition conditions on either a polycrystalline Ti foil or on a silicon wafer covered by a Ta buffer and a Cu seed layer. X-ray diffraction (XRD) revealed a strong (111) texture for all multilayers with clear satellite peaks for the multilayers on Si/Ta/Cu substrates, in some cases for up to three reflections. Cross-sectional transmission electron microscopy investigations indicated a much more uniform multilayer structure on the Si/Ta/Cu substrates. The bilayer periods from XRD satellite reflections were in reasonable agreement with nominal values. An analysis of the overall chemical composition of the multilayers gave estimates of the sublayer thickness changes due to the Co-dissolution process during the Cu deposition pulse. The XRD lattice spacing data indicated a behaviour close to a simple "multilayer" Vegard's law which was, however, further refined by taking into account elastic strains as well. In agreement with the structural studies, magnetoresistance data also indicated the formation of more perfect multilayers on the smooth Si/Ta/Cu substrates. An analysis of the magnetoresistance behaviour revealed the presence of superparamagnetic (SPM) regions in the magnetic layers. The contribution of these SPM regions to the total observed giant magnetoresistance was found to be dominating under certain deposition conditions, e.g., for magnetic layer thicknesses less than 1 nm (about 5 monolayers).

Cobalt↗

Electric field modulation of infrared absorption at room temperature in electrochemically self assembled quantum dots.

We report observation of electric-field-modulated infrared absorption at room temperature in electrochemically self-assembled CdS quantum dots produced by electrodepositing the semiconductor in 50-nm pores of an anodic alumina film. The absorption is associated with photoassisted real space transfer of electrons from the CdS dots to surrounding trap sites in the alumina. Similar absorption was observed in the past [Appl. Phys. Lett. 79, 4423 (2001)] and was the basis of a room temperature near infrared photodetector. An electric field modulates this absorption by altering the overlap between the wavefunctions of electronic states in the quantum dots and the trap states in the surrounding alumina, thereby affecting the matrix element for radiative transitions, similar to the quantum confined Stark or Franz-Keldysh effect. The ability to electrically modulate absorption in these structures can result in inexpensive infrared signal processing devices operating at room temperature.

Crystallization↗

Spiral growth of one dimensional titania nanostructures using anodic oxidation.

One dimensional spiral titania nanostructures were obtained by anodization of pure titanium from fluoride containing solutions of phosphoric acid. The formation of nanotubes was found to be dependant on current density. Field Emission Scanning Electron Microscopy (FESEM) shows the diameter of tubes around 70-100 nm which is consistent with the High Resolution Transmission Electron Micrographs (HRTEM) and Atomic Force Microscopy (AFM) images. HRTEM showed the one dimensional growth as spiral in nature which was also supported by AFM images. This anisotropic growth is compared with the possible growth mechanisms.

Crystallization↗

Anodization: a promising nano-modification technique of titanium implants for orthopedic applications.

Anodization is a well-established surface modification technique that produces protective oxide layers on valve metals such as titanium. Many studies have used anodization to produce micro-porous titanium oxide films on implant surfaces for orthopedic applications. An additional hydrothermal treatment has also been used in conjunction with anodization to deposit hydroxyapatite on titanium surfaces; this is in contrast to using traditional plasma spray deposition techniques. Recently, the ability to create nanometer surface structures (e.g., nano-tubular) via anodization of titanium implants in fluorine solutions have intrigued investigators to fabricate nano-scale surface features that mimic the natural bone environment. This paper will present an overview of anodization techniques used to produce micro-porous titanium oxide structures and nano-tubular oxide structures, subsequent properties of these anodized titanium surfaces, and ultimately their in vitro as well as in vivo biological responses pertinent for orthopedic applications. Lastly, this review will emphasize why anodized titanium structures that have nanometer surface features enhance bone forming cell functions.

Coated Materials, Biocompatible↗

Controlled DNA-templated metal deposition: towards ultra-thin nanowires.

In this paper, we report the metallization of a dsDNA template using a novel photography-derived two-step strategy in which dsDNA is first complexed with Ag(I) ions and then irradiated with UV light at 254 nm. The nucleobases act as light harvesters and sensitizers, triggering the photoreduction of the complexed silver ions. This process yields a silver nanoparticles blueprint along the DNA strand. The silver latent image is then developed by depositing metallic nickel through an electroless plating process. This photography-derived procedure generates very homogeneous and evenly distributed strings of silver-core/nickel-shell nanoparticles. Although still discontinuous, we believe that such chains can serve as the base for obtaining continuous metal nanowires. Furthermore, this process can most likely be extended to other plating metals, resulting in a broadly general procedure for metallizing DNA with a variety of different materials. Because of the intrinsic simplicity in using light as the key step, this methodology might be amenable to large-scale development, eventually leading to a very efficient molecular-photolithography process.

Aluminum Silicates↗

Laryngotracheal reconstruction using a Vitallium alloy miniplate.

When stenosis of the larynx and trachea involves loss to anterior support, this is usually corrected by an autograft of costochondral cartilage or of hyoid bone anchored with suture material. This paper describes an alternative technique employing a Vitallium alloy miniplate placed anterior to the airway as a means for providing support. This is placed over a fascial or auricular cartilage graft. Together, they provide a smooth scaffold for mucosal migration. Thirteen patients were treated at Indiana University Medical Center between 1991 and 1993 by means of this technique. Ten of the 13 patients (77%) achieved an adequate airway to allow decannulation. There have been no significant complications related to the use of the miniplate, and specifically, there have been no instances of infection or extrusion. It has been unnecessary to remove any of the miniplates. The Vitallium alloy miniplate offers unique advantages in laryngotracheal reconstruction in that it not only accurately approximates tissues, but it also provides external support to the airway.

Adolescent↗

An alternative method for the treatment of waste produced at a dye and a metal-plating industry using natural and/or waste materials.

The aim of this study was to develop cost-effective, appropriate solidification technologies for treating hazardous industrial wastes that are currently disposed of in ways that may threaten the quality of local groundwater. One major objective was to use materials other than cement, and preferably materials that are themselves wastes, as the solidification additives, namely using wastes to treat wastes or locally available natural material. This research examines the cement-based and lime-based stabilization/solidification (S/S) techniques applied for waste generated at a metal-plating industry and a dye industry. For the lime-based S/S process the following binder mixtures were used: cement kiln dust/ lime, bentonite/lime and gypsum/lime. For the cement-based S/S process three binder mixtures were used: cement kiln dust/cement, bentonite/cement and gypsum/cement. The leachability of the wastes was evaluated using the toxicity characteristic leaching procedure. The applicability and optimum weight ratio of the binder mixtures were estimated using the unconfined compressive strength test. The optimum ratio mixtures were mixed with waste samples in different ratios and cured for 28 days in order to find the S/S products with the highest strength and lowest leachability at the same time. The results of this work showed that the cement-and lime-based S/S process, using cement kiln dust and bentonite as additives can be effectively used in order to treat industrial waste.

Coloring Agents↗

Biological monitoring of nickel.

Measurements of nickel in body fluids, excreta, and tissues from humans with occupational, environmental, and iatrogenic exposures to nickel compounds are comprehensively reviewed. Correlations between levels of human exposures to various classes of nickel compounds via inhalation, oral, or parenteral routes and the corresponding concentrations of nickel in biological samples are critically evaluated. The major conclusions include the following points: Measurements of nickel concentrations in body fluids, especially urine and serum, provide meaningful insights into the extent of nickel exposures, provided these data are interpreted with knowledge of the exposure routes, sources, and durations, the chemical identities and physical-chemical properties of the nickel compounds, and relevant clinical and physiological information, such as renal function. Nickel concentrations in body fluids should not, at present, be viewed as indicators of specific health risks, except in persons exposed to nickel carbonyl, for whom urine nickel concentrations provide prognostic guidance on the severity of the poisoning. In persons exposed to soluble nickel compounds (e.g., NiCl2, NiSO4), nickel concentrations in body fluids are generally proportional to exposure levels; absence of increased values usually indicates non-significant exposure; presence of increased values should be a signal to reduce the exposure. In persons exposed to less soluble nickel compounds (e.g., Ni3S2,NiO), increased concentrations of nickel in body fluids are indicative of significant nickel absorption and should be a signal to reduce the exposures to the lowest levels attainable with available technology; absence of increased values does not necessarily indicate freedom from the health risks (e.g., cancers of lung and nasal cavities) associated with exposures to certain relatively insoluble nickel compounds.

Alloys↗

Epidemiological study of mortality from cancer among chromium platers.

Cancer mortality was studied among 265 male workers in 40 small plating factories (chromium, copper and nickel) where bicycle parts are plated. The study utilized record linkage with the Osaka Cancer Registry file between January 1, 1965 and December 31, 1979. The results showed that seven workers had died of cancer, and the Standardized Mortality Ratio (SMR) calculated for all cancers, stomach cancer and lung cancer were 1.13, 1.23 and 1.11, respectively, with no significant relationship found between the observed and expected values. The SMR for lung cancer among those workers with a high degree of skin ulceration and with perforation of the nasal septum was high, 11.22 and 5.13, respectively, although not statistically significant because of the small sample size in the study. The results suggest that lung cancer occurs in those subjected to a high degree of exposure to chromium.

Adult↗

Preparation and characterization of electrodeposited calcium phosphate/chitosan coating on Ti6Al4V plates.

Electrolytically deposited carbonate apatite coating demonstrates higher strength but weaker support for bone marrow stromal cell attachment than do biomimetically deposited coatings. It is hypothesized that the incorporation of chitosan will increase the biocompatibility of electrolytic coating while maintaining its original strength. To verify this hypothesis, we formed a hybrid calcium phosphate/chitosan coating through electrodeposition. We found that the incorporation of chitosan influenced calcium phosphate formation and crystallization. Moreover, coating thickness and surface roughness decreased with increasing chitosan concentration. Hybrid coating exhibited an increased dissolution rate in both acidic and neutral simulated physiologic solution, whereas no significant difference on adhesive strength was found between the hybrid and original coatings (P > 0.05). Most importantly, the calcium phosphate/chitosan coating proved to be a more favorable surface for goat bone marrow stromal cell attachment than an unincorporated coating (P < 0.01). Considering its economic and simple production, a hybrid calcium phosphate/chitosan coating is thought to be an attractive candidate for future applications.

Alloys↗