ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Christos G. Aneziris
In this work the wetting behaviour of amorphous and crystalline silicon dioxide in contact with a silicate slag based on fayalite is demonstrated as a function of contact angles, activation energies of the kinetic stages of wetting. In addition the dynamic adhesion work has been calculated as a function of the inclination angle. The amorphous silicon dioxide in contact with the slag presents lower contact angles accompanied also by higher dynamic adhesion works in comparison to crystalline porous ceramics with the same chemistry. [source]

The Implications of Polymer Selection in Regenerative Medicine: A Comparison of Amorphous and Semi-Crystalline Polymer for Tissue Regeneration

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Michelle D. Kofron
Abstract Biodegradable polymeric scaffolds are being investigated as scaffolding materials for use in regenerative medicine. While the in vivo evaluation of various three-dimensional (3D), porous, biodegradable polymeric scaffolds has been reported, most studies are ,3 months in duration, which is typically prior to bulk polymer degradation, a critical event that may initiate an inflammatory response and inhibit tissue formation. Here, a 6,month in vitro degradation and corresponding in vivo studies that characterized scaffold changes during complete degradation of an amorphous, 3D poly(lactide- co -glycolide)(3D-PLAGA) scaffold and near-complete degradation of a semi-crystalline3D-PLAGA scaffold are reported. Using sintered microsphere matrix technology, constructs were fabricated in a tubular shape, with the longitudinal axis void and a median pore size that mimicked the architecture of native bone. Long-term quantitative measurements of molecular weight, mechanical properties, and porosity provided a basis for theorization of the scaffold degradation process. Following implantation in a critical size ulnar defect model, histological analysis and quantitative microCT indicated early solubilization of the semi-crystalline polymer created an acidic microenvironment that inhibited mineralized tissue formation. Thus, the use of amorphous over semi-crystalline PLAGA materials is advocated for applications in regenerative medicine. [source]

Water sorption, glass transition, and protein-stabilizing behavior of an amorphous sucrose matrix combined with various materials

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2010
Koreyoshi Imamura
Abstract The effects of various additives on the physical properties of an amorphous sugar matrix were compared. Amorphous, sugar,additive mixtures were prepared by freeze-drying and then rehumidified at given RHs. Sucrose and eighteen types of substances were used as the sugar and the additive, respectively, and water sorption, glass-to-rubber transition, and protein stabilization during freeze-drying for the various sucrose,additive mixtures were examined. The additives were categorized into two groups according to their effects on Tg and water sorption. Presence of polysaccharides, cyclodextrins, and polymers (large-sized additives) resulted in a decrease in equilibrium water content from the ideal value calculated from individual water contents for sucrose and additive, and in contrast, low MW substances containing ionizable groups (small-ionized additives) resulted in an increase. The increase in Tg by the addition of large-sized additives was significant at the additive contents >50,wt.% whereas the Tg was markedly increased in the lower additive content by the addition of small-ionized additives. The addition of small-ionized additives enhanced the decrease in Tg with increasing water content. The protein stabilizing effect was decreased with increasing additive content in the cases of the both groups of the additives. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4669,4677, 2010 [source]

Gradient graft copolymers derived from PEO-based macromonomers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2006
Dorota Neugebauer
Abstract Atom transfer radical polymerization (ATRP) of two poly(ethylene oxide) (PEO) macromonomers, with different polymerization degrees (DPn) and different end groups, was conducted in solution via the grafting through method. Selection of a PEO methacrylate with a methyl end-group (PEOMeMA, DPPEO = 23) and a PEO acrylate end-capped by a phenyl ring (PEOPhA, DPPEO = 4) for the copolymerization led to a spontaneous gradient of PEO grafts along the copolymer backbone. Such a composition was formed because of significantly different reactivities of the two PEO macromonomers. The resulting copolymer has PEOMeMA at one end of the polymer chain, gradually changing through hetero-sequences of PEOPhA at the other chain end. An increase in the initial feed ratio of PEO acrylate reduced the rate of change in the shape of the gradient. Amorphous,crystalline structure in the copolymers was demonstrated by DSC and WAXS. The mechanical measurements of copolymers consisting of an amorphous PEOPhA and crystallizable PEOMeMA segments indicated elastomeric properties in the range of a soft rubber (G, , 104 Pa, G, , G,). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1347,1356, 2006 [source]

Optical and Electrical Properties of Amorphous and Nanocrystalline (La0.8Sr0.2)0.9MnO3 Thin Films Prepared from Low-Temperature Processing Technique

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006
Toshio Suzuki
The results of a study on the optical and electrical properties of (La0.8Sr0.2)0.9MnO3 (LSM) thin films obtained by a polymeric precursor spin coating technique were presented. This method allowed preparation of optical quality thin films at annealing temperatures around 800°C. Amorphous and crystalline LSM thin films were studied by optical and electrical conductivity measurements. The energy-dependent absorption coefficients for the crystalline specimen were calculated from optical spectra and extra absorption was observed in the range of 1.8,2.5 eV with the exchange-gap excitation behavior in the 3,5 eV range. In comparison to the amorphous specimens, the electrical conductivity of the nanocrystalline specimen increased two to three orders of magnitude with decreasing activation energy. The charge carrier absorption model suggested an increase of the carrier concentration in the nanocrystalline specimen which may be a reason for the change in the electrical conductivity. [source]

Incorporation of Multi-Walled Carbon Nanotubes into Biodegradable Telechelic Prepolymers

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2008
Wenhui Song
Abstract Biodegradable lactic-acid-based telechelic prepolymers incorporating CNTs were prepared. The products were characterized by FTIR, TGA, DSC, POM, 1H and 13C NMR, TEM, and FESEM. The results indicated that hydroxy-terminated telechelic prepolymers were obtained. According to the TGA curves, the initial thermal decomposition temperatures of the prepolymers incorporating carboxylic CNTs were higher than those of the pure prepolymers. Amorphous and crystalline prepolymers incorporating CNTs were obtained, while the spherocrystal morphologies were not changed by the addition of the CNTs. The carboxylic CNTs were coated with PLA polymers after polymerization and well dispersed in the prepolymer matrix. [source]

Preparation and optical properties of amorphous and crystalline BLT thin films grown on SiO2/Si(100) substrates by a CSD process

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2004
Ziping Cao
Abstract Amorphous and crystalline Bi3.25La0.75Ti3O12 thin films deposited on SiO2/Si(100) substrates have been prepared by a chemical solution deposition (CSD) process. X-ray diffraction shows that the crystal structure is a bismuth-layered perovskite structure with some preferred (117) orientation. The refractive indices and extinction coefficients of the amorphous and crystalline films were obtained by spectroscopic ellipsometry as a function of photo energy in the range from 1.8 to 4.0 eV. The dispersion of refractive indices was fitted by the Wemple,Didomenico single electronic oscillator dispersion mode. An interesting exponential absorption was found in the amorphous and crystalline BLT films, which may be ascribed to the substitution of lanthanum for bismuth. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Amorphous and Microcrystalline Silicon , Materials Science and Devices,

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2004
Norbert H. Nickel
This Special Issue reviews the latest experimental and theoretical studies in the field of amorphous, nano- and microcrystalline silicon covering materials preparation, electrical and optical properties, characterization of defects, the role of hydrogen, device fabrication and characterization, and novel device applications. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

ChemInform Abstract: Single-Crystal Structure Determination and Solid-State NMR Investigations of Lithium Nitridosilicate Li2SiN2 Synthesized by a Precursor Approach Employing Amorphous "Si(CN2)2".

CHEMINFORM, Issue 28 2009
Sandro Pagano
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Effect of annealing on the structural, electrical and optical properties of nanostructured TiO2 thin films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2009
S. Sankar
Abstract Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO2 films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV-Visible spectroscopy and electrical studies. X-ray diffraction studies showed that the as-deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator-Wemple and Didomenico model. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of annealing on structural, electrical and optical properties of AgGa(Se0.5S0.5)2 thin films deposited by using sintered stoichometric powder

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2009
H. Karaagac
Abstract The structural, electrical and optical properties of AgGa(Se0.5S0.5 )2 thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450,600 °C. X-ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started at 450 oC with mixed binary phases of Ga2Se3, Ga2S3, ternary phase of AgGaS2 and single phase of S. The compositional analysis with the energy dispersive X-ray analysis (EDXA) revealed that the as-grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 13.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as-grown, annealed at 450, 500, 550, and 600 °C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250-430 K for all samples. The room temperature resistivity value of as-grown film was found to be 0.7x108 (,-cm) and reduced to 0.9x107 (,-cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Crystallization behaviors of carbon fiber reinforced BN-Si3N4 matrix composite

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2007
Bin Li
Abstract The crystallization behaviors of a new carbon fiber reinforced composite with a hybrid matrix comprising BN and Si3N4 prepared by precursor infiltration and pyrolysis were investigated by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the as-received composite is almost amorphous, and its main composition is BN and Si3N4. When heat treated at 1600°C, the composite is crystallized and shows a much better crystal form. When heat treated at 2100°C, Si3N4 in the matrix is decomposed, and BN exhibits a relatively complete crystallization. The existence of B4C and SiC is detected, which indicates the interfacial chemical reactions between nitride matrices and carbon fibers. The surface morphology of carbon fibers in the composite changed significantly when heated from 1600 to 2100°C, which also proved the occurrence of interfacial chemical reactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photoelectrical properties of crystalline titanium dioxide thin films after thermo-annealing

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007
R. Sathyamoorthy
Abstract This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO2) thin films annealed at different temperatures (425-900°C). The structure of the as-grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin films

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005
C. Viswanathan
Abstract Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (Tsb = 30°, 400°C). X-ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 , 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (Egopt) 1.56 eV; where as the films formed at 400°C were found to have a Egopt of 1.92 eV. The increase in the value of Egopt with Tsb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current -Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Influence of nanocrystalization on magnetoelastic Villari effect in Fe73.5Nb3Cu1Si13.5B9 alloy

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3-5 2003
R. Szewczyk
Abstract The results of an investigation of the influence of thermal annealing on the magnetoelastic properties of Fe73.5Nb3Cu1Si13.5B9 soft magnetic alloy in both amorphous and nanocrystalline state are presented. A new method developed was used to apply uniform compressive stresses to the investigated ring core made of the alloy. The compressive stresses produced by external mechanical forces were applied perpendicularly to the direction of the magnetizing field. Due to the uniform distribution of stresses in the core brittle nanocrystalline alloys may be tested for stresses up to 10 MPa. The results revealed, that process of nanocrystallisation causes significant increase in the stress sensitivity of the Fe73.5Nb3Cu1Si13.5B9 alloy. Moreover the influence of stresses caused by external forces is more significant at relatively low values of the magnetizing field suggesting that these nanocrystalline soft magnetic materials are stress sensitive in the range of technical operation of inductive components based on such materials. [source]

Applying the Collective Causal Mapping Methodology to Operations Management Curriculum Development,

DECISION SCIENCES JOURNAL OF INNOVATIVE EDUCATION, Issue 2 2007
Julie M. Hays
ABSTRACT Although the field of operations management has come a long way since its beginnings in scientific management, the field still appears somewhat amorphous and unstructured to many. Introductory operations management textbooks usually include a number of largely disjointed topics, which leave many students (and their instructors) without a coherent framework for understanding the field. As a result, the importance and sequencing of topics varies widely between courses and instructors, even within the same university. This article applies the newly developed Collective Causal Mapping Methodology to create a causal map for the entire field of operations management. The causal map is built on expert opinions collected from over 250 academics and practitioners representing many areas of expertise, schools, organizations, and countries. This collective causal map is then used to create a new framework for understanding and teaching operations management. This framework can aid instructors in determining which topics should be taught in an operations management course, how these topics might be grouped and sequenced, and the important interrelationships among the topics that should be stressed to students. [source]

Epidermoid cyst of the intrapancreatic accessory spleen producing CA19-9

DIGESTIVE ENDOSCOPY, Issue 3 2004
Hiroyuki Watanabe
We report a rare case of an epidermoid cyst in an accessory spleen at the pancreatic tail with producing CA19-9. A 55-year-old female was admitted to our hospital, Cancer Research Institute, Kanazawa University, for close examination of a cystic lesion at the pancreatic tail and a high serum CA19-9-value (176 U/mL). There were almost no abdominal symptoms related to the cystic lesion. A cystic tumor approximately 3 cm in diameter and composed of multilocular cysts without a protruding portion of the inner surface was found at the pancreatic tail by ultrasound sonography, computed tomography, and magnetic resonance imaging. Endoscopic retrograde pancreatography revealed that the main pancreatic duct shifted at the pancreatic tail and there was no communication between the main pancreatic duct and cystic lesion. Based on a preoperative diagnosis of mucinous cystic tumor, distal pancreatectomy with splenectomy was performed. Histological ,ndings suggested an epidermoid cyst (3.5 × 3.0 cm) originating from an intrapancreatic accessory spleen. Immunohistochemical analysis of CA19-9 in the epidermoid cyst showed clear staining of the inner epithelium of the cyst and amorphous or hyalinous cystic contents. The serum CA19-9 value was con,rmed to decline to normal 2 months after resection. Physicians should not forget this disease during differential diagnosis related to pancreatic cystic lesions with elevated levels of serum tumor markers, such as CA19-9 or carcinoembryonic antigen, although this disease is extremely rare. [source]

Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology, limb reduction and postnatal skeletal ontogeny

ACTA ZOOLOGICA, Issue 1 2009
Adriana Jerez
Abstract The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor, a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4,3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X-2-2-2-2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features. [source]

Ultrastructure of the spermatozoon of Apus apus (Linnaeus 1758), the common swift (Aves; Apodiformes; Apodidae), with phylogenetic implications

ACTA ZOOLOGICA, Issue 4 2005
Barrie G. M. Jamieson
Abstract The spermatozoon of Apus apus is typical of non-passerines in many respects. Features shared with palaeognaths and the Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around an elongate distal centriole; and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. The perforatorium and endonuclear canal are lost in A. apus as in some other non-passerines. All non-passerines differ from palaeognaths in that the latter have a transversely ribbed fibrous sheath whereas in non-passerines it is amorphous, as in Apus, or absent. The absence of an annulus is an apomorphic but homoplastic feature of swift, psittaciform, gruiform and passerine spermatozoa. The long distal centriole, penetrating the entire midpiece, is a remarkably plesiomorphic feature of the swift spermatozoa, known elsewhere only in palaeognaths. The long centriole of Apus, if not a reversal, would be inconsistent with the former placement of the Apodiformes above the Psittaciformes from DNA,DNA hybridization. In contrast to passerines, in A. apus the microtubules in the spermatid are restricted to a transient single row encircling the cell. The form of the spermatozoon fully justifies the exclusion of swifts from the passerine family Hirundinidae. [source]

The trouble with drink: why ideas matter

ADDICTION, Issue 5 2010
Griffith Edwards
ABSTRACT This paper builds upon the work of previous authors who have explored the evolution of ideas in the alcohol arena. With revisions in the relevant sections of ICD and DSM forthcoming, such matters are of considerable contemporary importance. The focus here will be upon the history of the last 200 years. The main themes to be explored include the flux of ideas on what, over time, has counted as the trouble with drink, ideas on the cause of the problem and the impact of this thinking on public action. Medical authorities of the late Enlightenment period made the revolutionary suggestion that habitual drunkenness constituted a disease, rather than a vice. The thread of that idea can be traced to the present day, but with an alternative perception of drink itself or alcohol-related problems generally, as cause for concern, also having a lineage. There are several inferences to be drawn from this history: the need for vigilance lest disease formulations become stalking-horses for moralism and social control, the need to integrate awareness of alcohol dependence as a dimensional individual-level problem, with a public health understanding of the vastly amorphous and at least equally important universe of alcohol-related problems; the dangers lurking in scientific reductionism when the problems at issue truly require a multi-disciplinary analysis; and the need for global consensus rather than cultural imposition of ideas on what counts as the problem with drink. [source]

Ba6Si6N10O2(CN2) , A Nitridosilicate with a NPO-Zeolite Structure Type Containing Carbodiimide Ions

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2009
Sandro Pagano
Abstract A new precursor approach leading to NPO-zeolite analogous nitridosilicates with cavities containing carbodiimide ions is presented. The reaction of amorphous "Si(CN2)2" and barium in liquid sodium afforded Ba6Si6N10O2(CN2) as yellow crystals. The structure is a rare example of the NPO-zeolite framework type and the first nitridosilicate incorporating carbodiimide ions. The partially ordered integration of carbodiimide moieties in the channels leads to the formation of a superstructure (P, no. 174, a = 16.255(2), c = 5.4690(11) Å, Z = 3, R1 = 0.0299, 2139 data, 100 parameters) and merohedral twinning. A comprehensive structure solution is presented, taking all possible ordering variants and twin laws into account.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Wetting Behavior of Amorphous and Crystalline Silicon Dioxide in Contact with a Silicate Slag Based on Fayalite

Hydroxyapatite/Bioactive Glass Films Produced by a Sol,Gel Method: In Vitro Behavior

ADVANCED ENGINEERING MATERIALS, Issue 11 2009
Nihat C. Köseo
Abstract Hydroxyapatite (HA) and HA/bioactive glass (49S) films were deposited on Si(100) substrates by a sol,gel dip-coating method. The microstructure and in vitro bioactivity of the films were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Polycrystalline HA and amorphous bioactive glass films were obtained after annealing at 600 and 400,°C, respectively. The crystallization temperature of HA was determined to be around 568,°C. The surfaces of the HA films were covered with an apatite layer consists of spherulites formed by nanosized needle-like aggregates after the soaking in simulated body fluid (SBF) for 10 days, while amorphous HA/bioactive glass surface was covered with larger spherical crystallites. Both XPS and EDS results obtained from HA/bioactive glass film, after soaking in SBF, showed increasing P amounts on the surface at the expense of Si. The higher density of the newly formed layer on HA/bioactive glass surface than that of the HA surface after 10 days of soaking was evidence of increased reaction rate and apatite forming ability when bioactive glass layer is present on the HA films. [source]

Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Harald Schmidt
Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source]

In situ Grazing Incidence Scattering Investigations During Magnetron Sputtering Deposition of FePt/Ag Thin Films,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Valentina Cantelli
Using in situ synchrotron X-ray grazing incidence scattering experiments we investigated FePt islands mediated by Ag. FePt has been deposited by DC-magnetron sputtering on amorphous Si/SiO2 substrate at 400,°C, to support the formation of the hard ferromagnetic L10 -FePt phase during growth. The sequential Ag/FePt deposition provides separated FePt nanoislands without magnetic property degradation. We obtained magnetic moments preferentially oriented parallel to layer surface. [source]

Fundamentals of Metal-induced Crystallization of Amorphous Semiconductors

ADVANCED ENGINEERING MATERIALS, Issue 3 2009
Zumin Wang
Abstract A general, quantitative model has been developed that provides fundamental understanding of the metal-induced crystallization (MIC) of amorphous semiconductors. Interface thermodynamics has been shown to play a decisive role for the whether or not occurrence of MIC. The model has been employed to predict the MIC temperature for various metal/amorphous-semiconductor systems. A consequence of the model is the prediction that the thickness of an ultrathin, pure Al film put on the top of an amorphous Si layer can be used as a very accurate tool to tune the crystallization temperature of amorphous Si. These theoretical predictions have been confirmed experimentally. The fundamental understanding reached may lead to pronounced technological progress in the low-temperature manufacturing of crystalline-Si-based devices deposited on cheap and flexible substrates such as glasses, plastics, and possibly even papers. [source]

Pollution of carbonate soils in a Mediterranean climate due to a tailings spill

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002
M. Simón
Summary The retention walls in a pond containing the residues from the pyrite mine of Aznalcóllar (southern Spain) broke open on 25 April 1998, spilling approximately 6 × 106 m3 of polluted water and toxic tailings, which affected some 55 km2. Drying and aeration of the tailings resulted in oxidation, forming an acidic solution with high pollutant contents, the effects of which were studied in a calcareous soil. The infiltration of this solution markedly affected only the first 12 mm of the soil, where strong acidification caused the weathering of the carbonates, and where the fine mineral particles were hydrolysed. The SO42, ions in the acidic solution precipitated almost entirely at this depth, forming gypsum, hydroxysulphates and complex sulphates. The Fe3+ ions also precipitated there, mainly in amorphous or poorly crystallized forms, adsorbing to As, Sb, Tl and Pb dissolved in the acidic solution. The Al3+ ions, though partly precipitating in the acidic layer, accumulated mostly where the soil pH exceeded 5.5 (12,14 mm in depth). They did so primarily as amorphous or poorly crystallized forms, adsorbing to Cu dissolved in the acidic solution. The Zn2+ and Cd2+ ions accumulated mainly at pH > 7.0 (19,21 mm in depth), being adsorbed chiefly by clay mineral. After 15 months, only the first 20 mm of the soil were acidified by the oxidation of the tailings and most of the pollutants did not penetrate deeper than 100 mm. Consequently, the speed of the cleanup of the toxic spill is not as important as a thorough removal of tailings together with the upper 10 cm of the soil. [source]

Nitrided Amorphous Stainless Steel Coatings Deposited by Reactive Magnetron Sputtering from an Austenitic Stainless Steel Target

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009
Salvatore Cusenza
Abstract Stainless steel films were reactively magnetron sputtered in argon/nitrogen gas flow onto oxidized silicon wafers using austenitic AISI 316 stainless-steel targets. The deposited films of about 300,nm thickness were characterized by conversion electron Mö-i;ssbauer spectroscopy, magneto-optical Kerr-effect, X-ray diffraction, Rutherford backscattering spectrometry, and resonant nuclear reaction analysis. These complementary methods were used for a detailed examination of the nitriding effects for the sputtered stainless-steel films. The formation of an amorphous and soft ferromagnetic phase in a wide range of the processing parameters was found. Further, the influence of postvacuum-annealing was examined by perturbed angular correlation to achieve a comprehensive understanding of the nitriding process and phase formation. The amorphous phase is not very stable and crystallization can be observed at 973,K. [source]

Soft magnetic materials for electrical engineering: state of the art and recent advances

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2005
F. Alves
Abstract This article gives a brief description of the essential characteristics and principal applications of amorphous, crystalline and nanostructured soft magnetic materials in electrical engineering. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Coaxial Nanorods of MgO Core with Si Shell Layers

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2007
W. Kim
This article demonstrates an approach to the synthesis of MgO/Si core-shell nanorods. The Si shell was close to amorphous, whereas the MgO core was crystalline with a cubic structure. The PL of the Si-coated products under excitation at 325 nm exhibited a visible light emission, which was almost identical to that of the uncoated ones. [source]