CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2008
Shaojun Guo
Abstract We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100,°C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the ,6,nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57,V for oxygen reduction, which is about 200,mV more positive than that obtained by using a ,6,nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that ,6,nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O2 to H2O in air-saturated H2SO4 (0.5,M). Finally, compared to the ,6,nm Pt nanoparticle catalyst, the ,6,nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings. [source]

Preferred Functionalization of Metallic and Small-Diameter Single-Walled Carbon Nanotubes by Nucleophilic Addition of Organolithium and -Magnesium Compounds Followed by Reoxidation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2008
David Wunderlich Dipl.-Chem
Abstract Covalent sidewall addition to single-walled nanotubes (SWNTs) of a series of organolithium and organomagnesium compounds (nBuLi, tBuLi, EtLi, nHexLi, nBuMgCl, tBuMgCl) followed by reoxidation is reported. The functionalized Rn -SWNTs were characterized by Raman and NIR emission spectroscopy. The reaction of SWNTs with organolithium and magnesium compounds exhibits pronounced selectivity: in general, metallic tubes are more reactive than semiconducting ones. The reactivity of SWNTs toward the addition of organometallic compounds is inversely proportional to the diameter of the tubes. This was determined simultaneously and independently for both metallic and semiconducting SWNTs. The reactivity also depends on the steric demands of the addend. Binding of the bulky t- butyl addend is less favorable than addition of primary alkyl groups. Significantly, although tBuLi is less reactive than, for example, nBuLi, it is less selective toward the preferred reaction with metallic tubes. This unexpected behavior is explained by fast electron transfer to the metallic SWNTs having low-lying electronic states close to the Fermi level, a competitive initial process. The NIR emission of weakly functionalized semiconducting SWNTs, also reported for the first time, implies interesting applications of functionalized tubes as novel fluorescent reporter molecules. [source]

Circular Dichroism Study of the Mechanism of Formation of DNA Templated Nanowires

CHEMPHYSCHEM, Issue 15 2008
Hamsa Jaganathan
Abstract In order to control the fabrication method, the mechanism used in the formation of DNA templated nanowires is investigated through circular dichroism (CD) spectroscopy. Metallic (Au) and magnetic (Fe2O3 and CoFe2O4) nanoparticles (NP) are aligned along the DNA strand at various mass ratios. The DNA templated nanowires are compared to the structure of B-form dsDNA through CD experiments. Absorbance and thermal melting tests are performed to verify the structural changes of DNA templated nanowires. Low concentrations of nanoparticles preserve the DNA B-form through electrostatic interactions. Conversely, at higher concentrations of nanoparticles aligned along the DNA strand, the template is denatured. Information on the mode of nanoparticle binding and DNA helix alterations are explored for metallic and magnetic nanowires based upon the results. [source]

Characterisation of Nanohybrids of Porphyrins with Metallic and Semiconducting Carbon Nanotubes by EPR and Optical Spectroscopy

CHEMPHYSCHEM, Issue 13 2008
Sofie Cambré
Abstract Single-walled carbon nanotubes (SWCNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of cobalt(II)OEP, adsorbed on the nanotube walls by ,,,-stacking, demonstrates that the CNTs act as electron acceptors. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Moreover, molecular oxygen is shown to bind selectively to nanohybrids with semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99,% of the porphyrins are interacting with the CNTs. Due to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red-shifted compared to the free porphyrin absorption. In addition a quasi-complete quenching of the porphyrin fluorescence is also observed. [source]

A new endoscopic technique for suspension of esophageal prosthesis for refractory caustic esophageal strictures

DISEASES OF THE ESOPHAGUS, Issue 3 2008
E. Ancona
SUMMARY., There is no clear consensus concerning the best endoscopic treatment of benign refractory esophageal strictures due to caustic ingestion. Different procedures are currently used: frequent multiple dilations, retrievable self-expanding stent, nasogastric intubation and surgery. We describe a new technique to fix a suspended esophageal silicone prosthesis to the neck in benign esophageal strictures; this permits us to avoid the frequent risk of migration of the expandable metallic or plastic stents. Under general anesthesia a rigid esophagoscope was placed in the patient's hypopharynx. Using transillumination from the optical device, the patient's neck was pierced with a needle. A n.0 monofilament surgical wire was pushed into the needle, grasped by a standard foreign body forceps through the esophagoscope and pulled out of the mouth (as in percutaneous endoscopic gastrostomy procedure). After tying the proximal end of the silicone prosthesis with the wire, it was placed through the strictures under endoscopic view. This procedure was successfully utilized in four patients suffering from benign refractory esophageal strictures due to caustic ingestion. The prosthesis and its suspension from the neck were well-tolerated until removal (mean duration 4 months). A postoperative transitory myositis was diagnosed in only one patient. One of the most frequent complications of esophageal prostheses in refractory esophageal strictures due to caustic ingestion is distal migration. Different solutions were proposed. For example the suspension of a wire coming from the nose and then fixed behind the ear. This solution is not considered optimal because of patient complaints and moreover the aesthetic aspect is compromised. The procedure we utilized in four patients utilized the setting of a silicone tube hanging from the neck in a way similar to that of endoscopic pharyngostomy. This solution is a valid alternative both for quality of life and for functional results. [source]

Working Electrodes from Amalgam Paste for Electrochemical Measurements

ELECTROANALYSIS, Issue 4 2008
Bogdan Yosypchuk
Abstract Paste electrode with paste amalgam as an active electrode material is described here for the first time. Designed electrode from silver paste amalgam (AgA-PE) is solely metallic and does not contain any organic binder. Mechanical surface regeneration of AgA-PE is performed in the same way as for classical carbon paste electrodes and reproducibility of such regeneration is about 10%. Electrochemical surface regeneration appeared very efficient for most measurements. In dependence on paste metal content, the electrode surface can be liquid (resembling a film) or rather solid. The hydrogen overvoltage on AgA-PE is high, and the electrode allows measurements at highly negative potentials. AgA-PE is well suited for study of reduction or oxidation processes without an accumulation step. Anodic stripping voltammetry of some metals tested on the electrode is influenced by formation of intermetallic compounds. The measurement based on cathodic stripping voltammetry (adenine, cysteine) and on catalytic processes from adsorbed state (complex of osmium tetroxide with 2,2,-bipyridine) can be performed on AgA-PE practically under the same conditions as found earlier for HMDE and for silver solid amalgam electrode. The working electrode from paste amalgam combines the advantages of paste and metal electrodes. [source]

Fixation of heavy contaminants of a dirty bomb attack: Studies with uranium and metal simulants

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2007
Thomas L. McGehee
Abstract Asphalt emulsions were evaluated as a means to immobilize radiological contaminants deposited on urban surfaces after a dirty bomb attack. Contaminated surfaces would be sprayed with thin coatings of asphalt emulsion to encapsulate the radioactive particles until the site can be safely remediated. This research investigated applications of an asphalt emulsion (Topein C, Encapco Technologies, LLC, Napa, CA) to treat (zero-valent) iron, lead, and uranium powders on various building material surfaces. Initial studies found that some of the building materials (limestone, concrete, and metal) reacted with the emulsion producing gas bubbles, which formed 0.001 to 1 cm vesicles in the cured asphalt emulsion. These vesicles, however, did not expose the building material surface, and the reaction appeared to aid in the setting of the emulsion. Powdered lead did not react with the asphalt emulsion, but iron powder and uranium did. Iron powder and the emulsion formed vesicles up to 0.5 mm (but not exposing the building material surface), while the uranium (U3O8) had a moderate reaction when compared with to the lead and iron powders. Scanning electron micrographs showed that the lead powder formed nonreactive layers adjacent to the concrete surface while iron particles were evenly distributed in the asphalt matrix due to the reaction with the asphalt, indicating that the physical and chemical reactions between the iron metal particles, asphalt, and concrete affected particle distribution in the asphalt matrix. A vertical operation sediment tube was used to determine the flowing shear stress durability of the asphalt/metal/substrate complex. The asphalt treatment with iron had no loss at the shear range tested (0.1,2.5 Pa), while the asphalt stabilized powdered lead lost 8% asphalt and lead at 2.5 Pa mean shear stress applied for 5 h. The chemical reaction between asphalt emulsion and iron increased the resistance of the asphalt/metal/substrate complex to shear when compared with lead. Some hydrogen was formed in reactions with iron, but the amount formed was well below the lower flammability limit. Treatment of uranium indicated that the emulsion was effective at reducing leaching of the uranium 10 fold. These experiments indicate that asphalt emulsions may be a viable means for containing metallic or dense radiological contaminants on common building materials. © 2007 American Institute of Chemical Engineers Environ Prog 26:94,103, 2007 [source]

Conductive Nanostructures of MMX Chains

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2010
Alejandro Guijarro
Abstract Crystals of [Pt2(n -pentylCS2)4I] show a transition from semiconductor to metallic with the increase of the temperature (conductivity is 0.3,1.4,S,·,cm,1 at room temperature) and a second metallic,metallic transition at 330,K, inferred by electrical conductivity measurements. X-ray diffraction studies carried out at different temperatures (100, 298, and 350,K) confirm the presence of three different phases. The valence-ordering of these phases is analyzed using structural, magnetic, and electrical data. Density functional theory calculations allow a further analysis of the band structure derived for each phase. Nanostructures adsorbed on an insulating surface show electrical conductivity. These results suggest that MMX-polymer-based nanowires could be suitable for device applications. [source]

Fabrication of CdSe-Nanofibers with Potential for Biomedical Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2010
Amir Fahmi
Abstract The design and synthesis of nanostructured functional hybrid biomaterials are essential for the next generation of advanced diagnostics and the treatment of disease. A simple route to fabricate semiconductor nanofibers by self-assembled, elastin-like polymer (ELP)-templated semiconductor nanoparticles is reported. Core,shell nanostructures of CdSe nanoparticles with a shell of ELPs are used as building blocks to fabricate functional one-dimensional (1D) nanostructures. The CdSe particles are generated in situ within the ELP matrix at room temperature. The ELP controls the size and the size-distribution of the CdSe nanoparticles in an aqueous medium and simultaneously directs the self-assembly of core,shell building blocks into fibril architectures. It was found that the self-assembly of core,shell building blocks into nanofibers is strongly dependent on the pH value of the medium. Results of cytotoxicity and antiproliferation of the CdSe-ELP nanofibers demonstrate that the CdSe-ELP does not exhibit any toxicity towards B14 cells. Moreover, these are found to be markedly capable of crossing the cell membrane of B14. In contrast, unmodified CdSe nanoparticles with ELPs cause a strong toxic response and reduction in the cell proliferation. This concept is valid for the fabrication of a variety of metallic and semiconductor 1D-architectures. Therefore, it is believed that these could be used not only for biomedical purposes but for application in a wide range of advanced miniaturized devices. [source]

A General Approach for Fabricating Arc-Shaped Composite Nanowire Arrays by Pulsed Laser Deposition

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
Yue Shen
Abstract Here, a new method is demonstrated that uses sideways pulsed laser deposition to deliberately bend nanowires into a desired shape after growth and fabricate arc-shaped composite nanowire arrays of a wide range of nanomaterials. The starting nanowires can be ZnO, but the materials to be deposited can be metallic, semiconductor, or ceramic depending on the application. This method provides a general approach for rational fabrication of a wide range of side-by-side or "core,shell" nanowire arrays with controllable degree of bending and internal strain. Considering the ZnO is a piezoelectric and semiconductive material, its electrical properties change when deformed. This technique has potential applications in tunable electronics, optoelectronics, and piezotronics. [source]

Observation of a 2D Electron Gas and the Tuning of the Electrical Conductance of ZnO Nanowires by Controllable Surface Band-Bending

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2009
Youfan Hu
Abstract Direct experimental evidence for the existence of a 2D electron gas in devices based on ZnO nanowires (NWs) is presented. A two-channel core/shell model is proposed for the interpretation of the temperature-dependent current,voltage (I,V) characteristics of the ZnO NW, where a mixed metallic,semiconducting behavior is observed. The experimental results are quantitatively analyzed using a weak-localization theory, and suggest that the NW is composed of a "bulk" semiconducting core with a metallic surface accumulation layer, which is basically a 2D electron gas in which the electron,phonon inelastic scattering is much weaker than the electron,electron inelastic scattering. A series of I,V measurements on a single NW device are carried out by alternating the atmosphere (vacuum, H2, vacuum, O2), and a reversible change in the conductance from metallic to semiconducting is achieved, indicating the surface accumulation layer is likely hydroxide-induced. Such results strongly support the two-channel model and demonstrate the controllable tuning of the ZnO NW electrical behavior via surface band-bending. [source]

Magnetic and viscous coupling at the core,mantle boundary: inferences from observations of the Earth's nutations

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2007
B. A. Buffett
SUMMARY Dissipative core,mantle coupling is evident in observations of the Earth's nutations, although the source of this coupling is uncertain. Magnetic coupling occurs when conducting materials on either side of the boundary move through a magnetic field. In order to explain the nutation observations with magnetic coupling, we must assume a high (metallic) conductivity on the mantle side of the boundary and a rms radial field of 0.69 mT. Much of this field occurs at short wavelengths, which cannot be observed directly at the surface. High levels of short-wavelength field impose demands on the power needed to regenerate the field through dynamo action in the core. We use a numerical dynamo model from the study of Christensen & Aubert (2006) to assess whether the required short-wavelength field is physically plausible. By scaling the numerical solution to a model with sufficient short-wavelength field, we obtain a total ohmic dissipation of 0.7,1 TW, which is within current uncertainties. Viscous coupling is another possible explanation for the nutation observations, although the effective viscosity required for this is 0.03 m2 s,1 or higher. Such high viscosities are commonly interpreted as an eddy viscosity. However, physical considerations and laboratory experiments limit the eddy viscosity to 10,4 m2 s,1, which suggests that viscous coupling can only explain a few percent of the dissipative torque between the core and the mantle. [source]

Preparation of Metallic Films on Elastomeric Stamps and Their Application for Contact Processing and Contact Printing,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2003
H. Schmid
Abstract The formation of permanent or reversible metallic patterns on a substrate has applications in microfabrication and analytical techniques. Here, we investigate how to metallize an elastomeric stamp, either for processing of a substrate mediated by the proximity between the metal on the stamp and an active layer on the substrate, or for contact printing of the metal from a stamp to a substrate. The stamps were made from poly(dimethylsiloxane) (PDMS) and were modified before metallizing them with Au by adding to or removing from their bulk mobile silicone residues, by oxidizing their surface with an O2 -plasma, by surface-fluorination via silanization, or by priming them with a Ti layer. The interplay between the adhesion of the different layers defines two categories of application: contact processing and contact printing. Contact processing corresponds to keeping the metal on the stamp after contacting a substrate; it is reversible and nondestructive, and useful to define transient electrical contacts or quench fluorescence on a surface, for example. Contact printing occurs when the metal on the stamp adheres to the printed surface. Contact printing can transfer a metal, layers of metals, or an oxide onto a substrate with submicrometer lateral resolution. The transfer can be total or localized to the regions of contact, depending on the morphology of the metal on the stamp and/or the surface chemistry of the substrate. [source]

Printed Origami Structures (Adv. Mater.

ADVANCED MATERIALS, Issue 20 2010
20/2010)
Bok Y. Ahn, Jennifer Lewis, and co-workers report on p.,2251 a new method for creating complex 3D structures that combines direct-write assembly with a wet-folding origami technique. Planar lattices composed of a titanium hydride ink are printed, and then folded, rolled, or molded into the desired shape. These 3D objects are then transformed into metallic or ceramic structures by thermal annealing. [source]

A survey of the behavior of the hydroxybisphosphonic function in crystallized acids, metallic salts, and some related compounds

HETEROATOM CHEMISTRY, Issue 2 2001
J.-P. Silvestre
The flexibility and the different degrees of ionization of the hydroxybisphosphonic function provide numerous possibilities for the complexation of metallic and organic cations to molecules possessing these functions. The properties of this class of compounds are very interesting for different industrial and medical applications. They depend in a large part on the nature of the hydrocarbonated chain substituted to CH3 in hydroxyethylidenebisphosphonic acid and of the number and the position of the bisphosphonic groups grafted on this chain. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:73,89, 2001 [source]

Bulk Metallic Glasses with Functional Physical Properties

ADVANCED MATERIALS, Issue 45 2009
W. H. Wang
Abstract In this review, we report on the formation of a variety of novel, metallic, glassy materials that might well have applications as functional materials. The metallic glasses, with excellent glass-forming ability, display many fascinating properties and features such as excellent wave-absorption ability, exceptionally low glass-transition temperatures (,35,60,°C) approaching room temperature, ultralow elastic moduli comparable to that of human bone, high elasticity and high strength, superplasticity and polymer-like thermoplastic formability near room temperature, an excellent magnetocaloric effect, hard magnetism and tunable magnetic properties, heavy-fermion behavior, superhydrophobicity and superoleophobicity, and polyamorphism, all of which are of interest not only for basic research but also for technological applications. A strategy based on elastic-moduli correlations for fabrication of bulk metallic glasses (BMGs) with controllable properties is presented. The work has implications in the search for novel metallic glasses with unique functional properties, for advancing our understanding of the nature and formation of glasses, and for extending the applications of the materials. [source]

Photocatalytic Carbon-Nanotube,TiO2 Composites

ADVANCED MATERIALS, Issue 21 2009
Karran Woan
Abstract The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixtures and chemically bonded CNT,TiO2 composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with organic, inorganic, and biological agents. Finally, various applications and challenges for these composite materials are reported. [source]

Physics-based preconditioner for iterative algorithms in multi-scatterer and multi-boundary method of moments formulations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002
Jürgen v. Hagen
Abstract An efficient method to solve electromagnetic scattering problems involving several metallic scatterers or bodies composed of dielectric and metallic regions is proposed. So far, the method of moments has successfully been applied to large arrays of identical scatterers when it was combined with preconditioned iterative algorithms to solve for the linear system of equations. Here, the method is generalized to geometries that are composed of several metallic elements of different shapes and sizes, and also to scatterers that are composed of metallic and dielectric regions. The method uses in its core an iterative algorithm, preferably the transpose-free quasi-minimum residual (TFQMR) algorithm, and a block diagonal Jacobi preconditioner. For best performance, the blocks for the preconditioner are chosen according to individual scatterers or groups of scatterers for the array case, and according to the electric and magnetic current basis functions for dielectric/metallic scatterers. The iterative procedure converges quickly for an optimally chosen preconditioner, and is robust even for a non-optimal preconditioner. Reported run times are compared to run times of an efficiently programmed LU factorization, and are shown to be significantly lower. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Influence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal Composites

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008
Tatsuo Kumagai
Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source]

Fracture Toughness Enhancement for Alumina Systems: A Review

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2008
Osayande L. Ighodaro
Investigations have been carried out to determine ways of tailoring ceramic materials in order that one or more toughening mechanisms are activated in service. Microstructural manipulations, as well as composite formulations involving metallic, intermetallics, and ceramic phases have been used with ceramic matrices. Macrostructurally, laminated structures and functional gradient materials (FGMs) have also been formulated to enhance mechanical properties. Although significant improvements in material properties have been reported, ceramics are still below their projected positions on the materials map. This article presents a review of research activities pursuant to improving fracture toughness of alumina matrix systems and the enhancements achieved. [source]

Self-Repairing Function in the Carbon-Containing Refractory

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2007
Akira Yamaguchi
Self-repairing function is observed in carbon-containing refractory such as MgO,C, Al2O3,C, and so forth. Non-oxides such as pure metallic, alloys, carbides, and nitrides are intentionally added to the refractory composition to bring about this function. As a basis of the development of a self-repairing refractory, the self-repairing mechanism in the carbon-containing refractory is described. [source]

Metallodielectric Photonic Crystals Assembled from Monodisperse Spherical Colloids of Bismuth and Lead,

ADVANCED MATERIALS, Issue 4 2006
Y. Wang
Monodisperse metallic and metallodielectric spherical colloids have been synthesized in large quantities and explored as building blocks for fabricating three-dimensional metallodielectric photonic crystals. Both measurements and calculations revealed large photonic bandgaps covering optical wavelengths from the visible up to the near-IR region for the metallic (Bi and Pb) and metallodielectric (with a silica coating) colloids (see Figure). [source]

Nanoporous Gold Leaf: "Ancient Technology"/Advanced Material,

ADVANCED MATERIALS, Issue 21 2004
Y. Ding
A free-standing nanoporous gold (NPG) membrane is made by dealloying commercially available white-gold leaf in nitric acid (see Figure). This porous material has an unusual combination of characteristics in that it is metallic with a continuous crystal lattice throughout the porous network, and has a pore size that is adjustable via simple room-temperature post-processing. This ultra-high-surface-area material is potentially very useful for applications such as electrocatalysis and sensing. [source]

Modification of Electronic Structures of a Carbon Nanotube by Hydrogen Functionalization

ADVANCED MATERIALS, Issue 24 2002
K.S. Kim
A rigorous method to engineer the electronic structure of carbon nanotubes from metallic to semiconducting is reported (see inside front cover). An intramolecular junction in carbon nanotube is fabricated, where half of the nanotube is masked by a silicon oxide thin film. Functionalization of the nanotube by atomic hydrogen leads to the formation of an intramolecular junction, resulting in clear rectifying behavior at room temperature. This represents an important step towards the practical realization of nanotube-based nanotransistors. [source]

Endohedral carbon chains in chiral single-wall carbon nanotubes

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2006
Ravi K. Vadapalli
Abstract Using a first-principles, local density functional approach, we report the bond length optimization of endohedral linear carbon chains. In these calculations, all-carbon nanowire structures were constructed by inserting cumulenic linear carbon chains inside the semiconducting (7,3) and metallic (7,4) single-wall carbon nanotubes with radii of ,0.35 nm. Our calculations show that the total energy results for the endohedral chains inside both (7,3) and (7,4) nanotubes are well described with a common total energy curve having an equilibrium bond length of ,0.129 nm. The electronic band structures of the carbon nanowires are described in terms of a rigid-band model, with the Fermi level for the carbon nanowire effectively pinned near the top of bands originating from the valence band of the single-wall nanotube. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]

FWCIP method for PGB planar structures

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 3 2002
T. P. Vuong
Abstract The fast wave concept iterative process (FWCIP) and the boundary element method (BEM) are combined to evaluate the characteristic impedance of a microstrip filter, which is composed of (8×8) metallic via holes array. Simulations, measurements, and previous publications are in good agreement. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 236,246, 2002. [source]

Virulent spores of Bacillus anthracis and other Bacillus species deposited on solid surfaces have similar sensitivity to chemical decontaminants

JOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2007
J-L. Sagripanti
Abstract Aims:, To compare the relative sensitivity of Bacillus anthracis and spores of other Bacillus spp. deposited on different solid surfaces to inactivation by liquid chemical disinfecting agents. Methods and Results:, We prepared under similar conditions spores from five different virulent and three attenuated strains of B. anthracis, as well as spores of Bacillus subtilis, Bacillus atrophaeus (previously known as Bacillus globigii), Bacillus cereus, Bacillus thuringiensis and Bacillus megaterium. As spore-surface interactions may bias inactivation experiments, we evaluated the relative binding of different spores to carrier materials. The survival of spores deposited on glass, metallic or polymeric surfaces were quantitatively measured by ASTM standard method E-2414-05 which recovers spores from surfaces by increasing stringency. The number of spores inactivated by each decontaminant was similar and generally within 1 log among the 12 different Bacillus strains tested. This similarity among Bacillus strains and species was observed through a range of sporicidal efficacy on spores deposited on painted metal, polymeric rubber or glass. Conclusions:, The data obtained indicate that the sensitivity of common simulants (B. atrophaeus and B. subtilis), as well as spores of B. cereus, B. thuringiensis, and B. megaterium, to inactivation by products that contain either: peroxide, chlorine or oxidants is similar to that shown by spores from all eight B. anthracis strains studied. Significance and Impact of the Study:, The comparative results of the present study suggest that decontamination and sterilization data obtained with simulants can be safely extrapolated to virulent spores of B. anthracis. Thus, valid conclusions on sporicidal efficacy could be drawn from safer and less costly experiments employing non-pathogenic spore simulants. [source]

Half metallic properties of LaSrVMoO6

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2010
Weiyu Song
Abstract The recent synthesized LaSrVMoO6 was speculated to be compensated half metal, i.e., half metal with zero magnetic moment. Based on the experimental structure, our first principles study indicates that it is ferrimagnetic and half metallic with the magnetic moment 2.0 ,B when the electron correlation of Mo 4d electrons is larger than 2.72 eV. This indicates the strong electron correlation effect of Mo 4d electrons. Nonetheless, the obtained large magnetic moment (2.0 ,B) contradicts with the experimental observed nearly zero magnetic moment. Although the large antisite defects of the experimental sample might be the reason to reduce the saturated magnetic moment, further physical insights need to be investigated. The spin-orbit coupling effect has minor effect on the studied properties. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

Roles of cations, electronegativity difference, and anionic interlayer interactions in the metallic versus nonmetallic character of Zintl phases related to arsenic

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008
Pere Alemany
Abstract A first-principles Density Functional Theory study of several layered solids structurally related to rhombohedral arsenic has been carried out. The electronic structures of rhombohedral arsenic, CaSi2, CaAl2Si2, KSnSb, and SrSn2As2 are discussed in detail, emphasizing on the origins of their metallic or nonmetallic behaviours. It is found that all of these systems are metallic except KSnSb. Electronegativity differences between the elements in the anionic sublattice and/or direct interlayer interactions play the main role in controlling the conductivity behavior. CaSi2 exhibits a peculiar feature since the cation directly influences the conductivity but is not essential for its appearance. Cation-anion interactions are shown to have an important covalent contribution, but despite this fact and the metallic character found for most of these phases, the Zintl approach still provides a valid approximation to their electronic structure. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source]

Wear mechanisms in metal-on-metal bearings: The importance of tribochemical reaction layers

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2010
Markus A. Wimmer
Abstract Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:436,443, 2010 [source]