bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation Between Structural Parameters, Polarisabilities and Dielectric Properties in Non-Ferroelectric Complex Perovskites
Authors: Colla E. L. , Setter N.
Published: April 2011

A combination of different empirical methods which allow the prediction of the dielectric properties of non-ferroelectric complex perovskites has been proposed and its present limits verified. The long term purpose is to engineer new microwave materials with increased relative permittivity ε0 and low thermal coefficient of the resonant frequency τf.

The estimation of the dielectric properties has been accomplished by means of structural predictions based on the tolerance factor and a microscopic model. Furthermore, the optical permittivity based on the Gladstone-Dale relation and the total polarisability according to the molecular/ion additivity rule were also estimated. Ceramics of new compositions were then fabricated and analysed to verify the dielectric properties predicted by the empirical methods. Results show good agreement with the expected structural features and optical permittivities, and the method is sufficiently reliable to estimate the end values, or at least to estimate trends of the dielectric properties induced by partial substitution of cations on site A. The importance of the electronic polarisability on the end value of τε has been demonstrated.
Effect of Divalent Dopants on Properties of Ba3.75Nd9.5Ti18O54 Microwave Dielectric Resonators
Authors: Ubic R. , Reaney I. M. , Lee W. E. , Samuels J. , Evangelinost E.
Published: April 2011

Pellets in the ternary solid-solution Ba6–3xNd8+2xTi18O54 (x=0.75) have been processed to near theoretical density by mixed-oxide synthesis, and their dielectric properties determined to be εr≈89, Qf> 10,000, and τf≈+60ppm/°C at microwave frequencies. Similar ceramics with Ca, Sr, and Pb partially substituted for Ba were also processed and analysed. Both Ca and Sr were found to increase εr to 100–105 but significantly lower Qf and inflate τf. While Pb substitution also lowered Qf, it had no significant effect on εr and beneficially suppressed τf to values from -16 to +8ppm/°C, tunable with Pb content, strongly suggesting that these materials may be useful for commercial applications.
On the Structures of Mo2O5(OCH3)2 and Mo2O5(OCH3)2 ·2CH3OH
Authors: McCarron E. M. , Harlow R. L. , Li Z. G. , Suto C. , Yuen Y.
Published: April 2011

The reaction of molybdenum trioxide dihydrate, MoO3·2H2O, with methanol produces the title compounds. That these molybdenum oxy-methoxides decompose with liberation of CH2O suggests that they represent exquisite models for selective oxidation of methanol to formaldehyde over molybdate catalysts. While a number of physical techniques have been employed to elucidate certain of their structural aspects, unfortunately, the detailed structures of these materials remain unknown. Problems, both physical and crystallographic, encountered in attempts to determine these structures are discussed. Also discussed is the recent progress made by employing the complimentary nature of electron and powder diffraction techniques.
Electrochemical Characterization of Mixed Conducting Ba(Ce1-(x+y)PryGdx)O3-x/2 Cathodes
Authors: Mukundan R. , Davies P. K. , Worrell W. L.
Published: April 2011

The high protonie conductivities of barium cerium gadolinium perovskites (Ba(Ce1-xGdx)O3-x/2, O < x < 0.2) has led to their incorporation as electrolytes in fuel cells operating at 873–1073K. In an effort to develop new mixed-conducting electrodes that are compatible with the cerate electrolyte, we have examined the electrochemical properties of Pr-doped barium gadolinium cerate. The Pr doping increases the electronic contribution to the total conductivity and for Ba(Ce0.5Pr04Gd0.1)O2.95, a conductivity exceeding ≈ 0.1 S/cm at 1173K in dry air has been obtained. EMF measurements indicate the presence of both protonie and oxygen ionic contributions to the conductivity in the Pr substituted samples. The cathodic overpotentials of Ba(Ce1-(x+y)PryGdx)O3-x/2 mixed conductors on a Ba(Ce0.8Gd0.2)O2.9 electrolyte have been measured. Ba(Pr0.8Gd0.2)O2.9 has the best cathodic performance and could be a viable alternative to Pt cathode for a barium cerate based fuel cell.
Conduction Properties of Na+-ion Implanted Glass-Ceramics in the System Na2O-R2O3-P2O5-SiO2 (R=Rare Earth)
Authors: Okura Toshinori , Tanaka Miki , Sudoh Giichi
Published: April 2011

The glass-ceramics of the phosphorus containing Na5RSi4O12type (R=rare earth) Na+-superionic conductors (Narpsio-V) in the system Na2O-Sm2O3-P2O5-SiO2 were prepared by crystallization of glasses with the composition Na3+3x-ySm1-xPySi3-yO9. The optimum conditions for crystallization were discussed with reference to the conduction properties and the preparation of uncracked bulky glass-ceramic Narpsio-V. The ionic conductivity of the glass-ceramic Na3.9Sm0.6P0.3Si2.7O9 at 300°C was drastically enhanced from 2.38×10-2 S/cm to 7.15×10-2 S/cm upon implantation of 200 keV Na+ ions to a fluence of 1 × 1015 cm-2.
Predominant Factors of Lithium Ion Conductivity in Perovskite-Type Oxides
Authors: Inaguma Y. , Katsumata T. , Yu J. , Itoh M.
Published: April 2011

The relation between the structure and the lithium ion conductivity in perovskite-type oxides ABO3was investigated from the viewpoint of the the arrangement of A-site ions. It was showed that the conductivity in La2/3-xLi3x□1/3–2xTiO3is strongly influenced by not only the concentration but also the ordered arrangement of skeletal A-site ions. Further the activation energy for ion conduction was found to be dominated by the covalency of B-O bond in addition to the bottleneck size.
New Manganese Oxides by Hydrothermal Reaction of Permanganates
Authors: Chen Rongji , Zavalj Peter , Stanley Whittingham M.
Published: April 2011

The mild hydrothermal decomposition of aqueous permanganate solutions has been found to lead to new layered manganes oxides. In the case of alkali permanganates, AMnO4, layered birnessite-type compounds are formed with the general formula - AxMnO2•nH2O. These compounds have R 3 m rhombohedral structures analogous to the layered disulfides. The water is reversibly lost on heating, and the compounds readily intercalate lithium ions in a reversible manner. In the case of the hydrothermal decomposition of tetramethylammonium permanganate in the presence of nickel, the new compound NiMnO3is formed that has a novel structure. This compound also has interesting magnetic properties, being a paramagnet above 111K and a ferromagnetic below that temperature.
The Preparation of Kinetically Stable Crystalline Compounds from Modulated Elemental Reactants
Authors: Hornbostel Marc D. , Noh Myungkeun , Johnson Christopher D. , Johnson David C.
Published: April 2011

Diffusion distances within elementally modulated reactants can be controlled on an Angstrom length scale. Below a critical repeat thickness, elementally modulated reactants interdiffuse without nucleating crystalline compounds. Using this amorphous intermediate, we can prepare metastable compounds by controlling nucleation: Above this critical repeat thickness, crystalline compounds nucleate at the reacting interfaces. Using the architecture of the initial reactant to control the diffusion distances in the initial reactant, we have found that we can prepare crystalline superlattices. Crystalline superlattice compounds containing integral numbers of inter grown transition metal dichalcogenide layers and alternating layers of transition metal carbides have been prepared through controlled crystallization of superlattice reactants with designed compositional modulation. High quality c-axis oriented dichalcogenide crystalline superlattices result from extended annealing at relatively low temperatures. A large number of [00l] diffraction orders and off-axis [10l] diffraction peaks are observed indicating that these compounds are crystalline in three dimensions. Similar annealing conditions were used to prepare carbide superlattices, however the limited low temperature diffusion rates of the carbides limit the crystallite size to approximately 300Å. The rational synthesis of these intergrowth compounds from superlattice reactants permits the exploratory synthesis of a new class of compounds and the tailoring of physical properties as a function of compositional layer thicknesses and native properties of the parent compounds.
V2O5 and β-CuxV2O5 Thin Films Grown by Mocvd
Authors: Gleizes A. , Bufforn J.-M. , Salzman C. , Virette E. , Senocq F.
Published: April 2011

Thin films of V2O5 and β-CuxV2O5 have been grown by MOCVD using VO(OiPr)3 and Cu(tmhd)2 (tmhd = tetramethylheptanedionato) as precursor molecules. Films were grown on chips of Si3N4 coated silicon wafers in a cold wall reactor using a H.F. heater. A mixture of helium and oxygen was used as a reactive carrier gas, and depositions were performed at low pressure. The films were examined by SEM, characterized by XRD, and analyzed by EDS and EMPA techniques. All the films proved to be carbon free.

For V2O5, the substrate temperature was varied from 450 to 630°C. The films are highly caxis oriented for both ends of the temperature range, and less oriented for intermediate temperatures. For 630°C, the XRD pattern consists almost entirely of reflections (001) and (002).

For β-CuxV2O5, the substrate temperature was varied from 450°C to 650°C. Pure β-phase films with x varying from 0.25 to 0.55 have been obtained above 500°C, by using well chosen gas phase composition. Morphology and texture depend dramatically on the temperature. The most oriented films exhibit a strong anisotropy of electrical surface conductivity.
Synthesis Optimization of Mesoporous MCM-41 Materials in Acidic Media
Authors: Karlsson A. , Schmidt R. , Stocker M.
Published: April 2011

The synthesis of MCM-41 in a highly acidic medium has been optimised. It was found that the relatively low-cost synthesis gave a material with extremely high surface areas (more than 1500 m2/g) compared to that obtained in conventional alkaline synthesis (ca 1100 m2/g). Judged by the short synthesis time, high yield, enhanced adsorption capacity, large particle size and thermal stability, the acid route to MCM-41 appears promising from an industrial point of view. Additional cost-reducing steps, such as the recycling of the “acid matrix” and the reduction of the volume of the water/acid mixture were successfully applied.
Synthesis and Catalytic Applications of Novel Mesoporous Aluminosilicate Molecular Sieves
Authors: Reddy Kondam Madhusudan , Song Chunshan
Published: April 2011

This paper reports on the synthesis of four series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different aluminum compounds were examined as Al source in the hydrothermal synthesis of the mesoporous aluminosilicates of MCM-41 type, including pseudo boehmite (alumina), aluminum sulfate, aluminum isopropoxide, and sodium aluminate. Each Al source was examined at three different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the dioo-spacings for the samples prepared with different Al sources: sodium aluminate > Al isopropoxide > Al sulfate > pseudo boehmite. Such differences reveal that Al incorporation in the framework increases in the following order: pseudo boehmite < Al sulfate < Al isopropoxide < sodium aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. 27Al NMR and 29Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and sodium aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. We also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.
Alumoxane Precursors to Designer Catalysts and Catalyst Supports: Catalytic Oxidation of Dichloromethane
Authors: Cook Ron L. , Wong Cynthia , Harlan C. Jeff , Kareiva Aivaras , Barron Andrew R.
Published: April 2011

Carboxylato-alumoxanes are aluminum-oxygen macromolecules consisting of a boehmite-like core surrounded by a sheath of carboxylate groups. The alumoxanes may be processed like organic polymers yet when fired are readily transformed into ceramic oxides. The alumoxanes can be precisely doped at room temperature in aqueous solution with a range of metal cations to prepare novel catalyst and catalyst support materials. The ease of introduction of multiple cations into the alumina lattice via the alumoxane approach provides a method for fine-tuning catalyst support properties and the fabrication of new catalyst materials themselves. Manganese-doped alumina (Mn-Al2O3), formed via the doping of an alumoxane with Mn at room temperature, is presented as an example where the alumoxane route provides enhanced catalytic performance over traditional approaches for the low temperature catalytic oxidation of chlorinated hydrocarbons (CHCs). The Mn-Al2O3 formed from the Mn-doped alumoxane is compared with MnO2/Al2O3 prepared by the incipient wetness method, and commercial Pt/Al2O3 for the oxidation/destruction of dichloromethane (CH2Cl2).
Ion-Exchangeable Oxides with Layered Perovskite Structures as Photocatalysts for Overall Water Splitting
Authors: Takata T. , Shinohara K. , Tanaka A. , Hara M. , Kondo J. N. , Domen K.
Published: April 2011

A novel series of photocatalysts for an overall water splitting is reported. The catalysts have a layered perovskite type structure with a general formula of A2−xLa2Ti3−xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0). The catalysts, except for the one with x=1.0, are spontaneously hydrated, and the band gap irradiation induced efficient evolution of H2 and O2 in a stoichiometric ratio from an aqueous alkaline solution when a proper amount of Ni loading was made. The reaction mechanism of water splitting on these catalysts is discussed on the bases of the structural study of the catalysts.
FT-IR Characterization of the Acidic and Basic Sites on a Nanostructured Aluminum Nitride Surface
Authors: Baraton M.-I. , Chen X. , Gonsalves K. E.
Published: April 2011

A nanostructured aluminum nitride powder prepared by sol-gel type chemical synthesis is analyzed by Fourier transform infrared spectrometry. The surface acidic and basic sites are probed out by adsorption of several organic molecules. Resulting from the unavoidable presence of oxygen, the aluminum nitride surface is an oxinitride layer in fact, and its surface chemistry should present some analogies with alumina. Therefore, a thorough comparison between the acido-basicity of aluminum nitride and aluminum oxide is discussed. The remaining nitrogen atoms in the first atomic layer modify the acidity-basicity relative balance and reveals the specificity of the aluminum nitride surface.
Fast Dynamics in Glass-Forming Polymers Revisited
Authors: Colmenero J. , Arbe A. , Mijangos C. , Reinecke H.
Published: April 2011

The so called “fast-dynamics” of glass-forming systems as observed by time of flight (TOF) neutron scattering techniques is revisited. TOF-results corresponding to several glass-forming polymers with different chemical microstructure and glass-transition temperature are presented together with the theoretical framework proposed by us to interpret these results. The main conclusion is that the TOF-data can be explained in terms of quasiharmonic vibrations and the particular short time behavior of the segmental dynamics. The segmental dynamics display in the very short time range (t ≈ 2 ps) a crossover from a simple exponential behavior towards a non-exponential regime. The first exponential decay, which is controlled by C-C rotational barriers, can be understood as a trace of the behavior of the system in absence of the effects (correlations, cooperativity, memory effects…) which characterize the dense supercooled liquid like state against the normal liquid state. The non-exponential regime at t > 2 ps corresponds to what is usually understood as α and β relaxations. Some implications of these results are also discussed.
Fragility of Polymeric Liquids: Correlations between Thermodynamic and Dynamic Properties
Authors: Colucci Dina M. , McKenna Gregory B.
Published: April 2011

The effect of polymer structure on fragility was determined by relating the apparent fragility to the relaxation response, heat capacity, and thermal expansion. For the 14 polymers studied, the fragility estimates based on the relaxation behavior (log aT) correlated well with the thermodynamic estimates of ΔCp/Mo, and Δα. In general, polymers with less sterically hindered repeat unit structures exhibited strong behavior. Polymers with sterically hindered backbones containing oxygen or ringed structures in the backbone were consistently fragile using log aT, ΔCp/Mo, and Δα as measures of fragility. On the other hand, using Cp1/Cpg as a fragility criterion resulted in very different fragility classifications.
Spectroscopic Investigations of the Network Structure in Borovanadate Glasses
Authors: Attos O. , Massot M. , Mavi H. S. , Julien C.
Published: April 2011

Borovanadate glasses with mixed conductivity, i.e., simultaneous ionic and electronic carriers have been obtained in the system (100−x)[B2O3-Li2O]-xV2O5 (0 ≤ x ≤ 30 mole%). To understand the origin of the conductivity in these glasses, the compositional dependence of the network structure has been studied by Raman and infrared spectroscopy.
New Fe-Ni Based Metal-Metalloid Glassy Alloys Prepared by Mechanical Alloying and Rapid Solidification
Authors: Suñol J. J. , Clavaguera-Mora M. T. , Clavaguera N. , Pradell T.
Published: April 2011

Mechanical alloying and rapid solidification are two important routes to obtain glassy alloys. New Fe-Ni based metal-metalloid (P-Si) alloys prepared by these two different processing routes were studied by differential scanning calorimetry and transmission Mössbauer spectroscopy. Mechanical alloyed samples were prepared with elemental precursors, and different nominal compositions. Rapidly solidified alloys were obtained by melt-spinning. The structural analyses show that, independent of the composition, the materials obtained by mechanical alloying are not completely disordered whereas fully amorphous alloys were obtained by rapid solidification. Consequently, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. The P/Si ratio controls the magnetic interaction of the glassy ribbons obtained by rapid solidification. The experimental results are discussed in terms of the degree of amorphization and crystallization versus processing route and P/Si ratio content.
Fast Dynamics in Glass-Formers: Relation to Fragility and the Kohlrausch Exponent
Authors: Ngai K. L. , Roland C. M.
Published: April 2011

From the Raman spectra and related inferences from low temperature specific heat data, Sokolov and coworkers have established that the ratio of the quasielastic and vibrational contributions at low temperatures (5∼10K) up to Tg correlates well with the degree of fragility and β of the glass-former. As pointed out by Sokolov (see his contribution in this Volume) such a correlation between the fast dynamics and structural a-relaxation at Tg(i.e., m and β) is intriguing, since at and below Tg, the α-relaxation time τα is more than twelve orders of magnitude longer than the quasielastic contribution and the boson peak. We show in this paper how the Coupling Model (CM) may provide an explanation for this correlation.
Electrostatic Potentials at θ = 24° [001] Tilt Boundaries in Undoped and Doped Strontium Titanate Bicrystals
Authors: Mao Z. , Dunin-Borkowski R. E. , Boothroyd C. B. , Knowles K. M.
Published: April 2011

Phase contrast techniques in the transmission electron microscope are used to measure directly the electrostatic potentials at θ = 24° [001] symmetrical tilt grain boundaries in both undoped and Nb-doped SrTiO3 bicrystals. The boundaries are all found to have significantly lower scattering potentials than the surrounding bulk material. The depths and the shapes of the potential wells at the boundaries are discussed in the light of both theoretical models of the grain boundary chemistry of pure and doped strontium titanate and other experimental data that we have acquired on these boundaries from high resolution transmission electron microscopy, diffuse dark field imaging, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.
Interface Effects on the Tensile and Fatigue Crack Growth Behavior of Fiber-Reinforced Metal Matrix Composites
Authors: Majumdar B. S. , Warrier S. G. , Miracle D. B.
Published: April 2011

The effects of the interface on the tension and fatigue crack growth behavior of fiber-reinforced titanium matrix composites were studied using single-ply and single-fiber SiC/Ti-6Al-4V mini-composites with different SiC fibers and coatings. Attention was focused on fiber failure mechanisms in the absence of a matrix crack (tension loading), and on fatigue crack deceleration mechanisms. In contrast to established models of tensile failure, local load sharing behavior was observed for very weak interfaces, with plasticity playing a major role in enhancing stress concentration effects. The approach included statistical evaluation of fiber breaks, their locations, and comparisons between single-fiber and single-ply composites. Under fatigue loading, crack deflection behavior was found to be consistent with a strength based interface debonding model. Crack shielding through modulus mismatch was found to have a significant effect on crack growth rates, independent of bridging conditions, with a stronger interface performing better under such conditions. The ramifications of the different mechanisms on interface optimization for longitudinal and transverse properties of composites are indicated.
Structure of Interfaces in Multilayers
Authors: Fedorenko A. I. , Pershin Yu.P. , Poltseva O. V. , Ponomarenko A. G. , Voronov D. L. , Yulin S. A.
Published: April 2011

Structure of interfaces in as-deposited state and after annealling at elevated temperatures was studied in variety of dc-magnetron sputtered multilayers by X-ray diffraction and high resolution electron microscopy. Interfaces in multilayers from materials without phase equilibrium (Mo/Si, W/Si, MO/B4C, Cr/C, Mo/(B+C)) are unstable and has the trend to evolution due to interlayer redistribution of chemical elements. Formation of the extended intermixed transition zones at interfaces is characteristic for multilayers from materials without phase equilibrium with each other. Unhomogeneous structure of materials along and across layers is responsible for nonuni-form proceeding of layer intermixing, development of interface roughness and differences of neighbour interfaces. It was shown that thickness asymmetry of intermixed transition zones at Mo/Si and Si/Mo interfaces in large-period Mo/Si multilayers is caused by different mechanisms of growth of Mo and Si on each other and by different structure of lower and upper parts of polycrystalline Mo-layers. Interfaces in multilayers from materials with phase equilibrium MoSi2/Si, WSi2/Si, OB2/C, TiC/C, Ni/C, MO2B5/B4C) are sharp and stable at elevated temperatures which gives the possibility to treat them for modification of their structure (smoothening, restoring sharp profiles of chemical elements). Multilayers W/Ti and W/TiN showed trend to formation of epitaxial superlattices with coherent or partially coherent (with misfit dislocations) interfaces and pseudomorphic state of layers.
Interfaces and fatigue Damage in a Ti-15–3/SCS-6 [0/90]2s Composite
Authors: Soboyejo W. O. , Rabeeh B. , Li Y. , Rokhlin S.
Published: April 2011

The key role of interfaces in the initiation and propagation of fatigue damage is elucidated for a model eight ply [0/90]2s Ti-15V-3Cr-3Al-3Sn (Ti-15–3) composite reinforced with SiC (SCS-6) fibers. Interfacial strengths obtained from fiber push-out tests are used in the quantification of shielding due to crack bridging. Composite fatigue tests are predicted using an idealized fracture mechanics model. The possible effects of interfacial strength variation on the predicted fatigue lives are also elucidated.
Characterization of Interphase Regions Using Atomic Force Microscopy
Authors: Vanlandingham M. R. , McKnight S. H. , Palmese G. R. , Bogetti T. A. , Eduljee R. F. , Gillespie J. W.
Published: April 2011

The use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation. In this paper, a novel technique is used to probe local property changes in multi-component polymer systems. Changes in indentation response in interphase regions are investigated for an adhesive system involving a diffuse polymer-polymer bond and for two composite systems. To date, diamond-tipped probes with effective spring constants of 150 and 310 N/m have been used to investigate polyimide and epoxy resin matrices reinforced by carbon fibers.
Mo-W Interdiffusion and the Influence on Potassium Bubbles in W Lamp Wire
Authors: Bewlay B. P. , Briant C. L. , Murray M. L.
Published: April 2011

The effects of Mo contamination on the microstructure of lamp-grade tungsten wire are investigated in this study. Mo is often used as the mandrel material in the coiling of lamp filaments, and when utilized during high temperature heat treatments significant amounts of Mo can diffuse into the W. In this study, W-Mo diffusion couples were prepared and heat treated at temperatures of 2500°C and above to intentionally contaminate the W with Mo. After dissolution of the Mo and additional high temperature heat treatments of the W, equiaxed grains were observed in the W and excessive porosity was also observed. Explanations for these microstructural changes are discussed. Microprobe data were also obtained to quantify interdiffusion between the W and Mo.
Toward Optimization of the Grain Boundary Character Distribution in Copper by Strain Annealing
Authors: King Wayne E. , Schwartz Adam J.
Published: April 2011

We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy (OIM)[1–4] has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries, “special fraction,” was ∼70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special grain boundaries while both of the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.
Stacking Fault Energies in TiCx
Authors: Harris R. M. , Bristowe P. D.
Published: April 2011

We have used a Tight Binding model to calculate the surface energies of various (111) stacking faults in TiC1.0 and TiC0.5. Based upon our preliminary results we have identified the stable stacking faults and have examined possible dislocation dissociation reactions.
Applications of Active Thin Film Coatings on Optical Fibers
Authors: Fox G. R. , Muller C.A.P. , Wüthrich C. R. , Kholkin A. L. , Setter N. , Costantini D. M. , Ky N. H. , Limberger H. G.
Published: April 2011

Active thin film coatings on optical fibers provide a variety of functions that are being used to develop active all-fiber optical devices. Two types of active coatings that are of interest for device development include resistive and piezoelectric coatings. Resistive coatings can be used to heat an optical fiber, while piezoelectric coatings can be used to strain the fiber. Localized changes in the fiber waveguiding properties can be achieved by electrically activating the fiber coating. These coated fibers show promise for applications such as optical phase shifters and modulators.

Recent developments in the fabrication of diffraction gratings within the core of an optical fiber have provided the means for making a variety of intra-core reflection and band pass filters. By combining these passive intra-core fiber devices with active coatings, wavelength tunable devices have been demonstrated. Wavelength tunable devices are expected to have a variety of applications in telecommunications and sensing networks. A review of recent developments in fiber coating and analysis techniques, device fabrication, and applications of active all-fiber devices are presented along with a discussion of which coating materials are of interest in active devices.
Change of Ms Temperatures and its Correlation to Atomic Configurations of Offstoichiometric NiTi-Cr and NiTi-Co Alloys
Authors: Hosoda Hideki , Fukul Toshihiko , Inoue Kanryu , Mishima Yoshlnao , Suzuki Tomoo
Published: April 2011

Effects of compositional deviation from the stoichiometry and Cr and Co additions on martensitic-transformation-slart and auslenite-start temperatures (Ms and As) of offstoichiometric NiTi alloys are investigated. Ms and As are determined using conventional differential thermal analysis (DTA), where the temperature range investigated is between 77K and 423K. Alloys are widely chosen with both Ni- and Ti-rich compositions, to which ternary elements, Cr and Co, are added. It is clearly shown that Ms and As in single phase regions are reduced with increasing amount of constituent element, Ni, and ternary elements, Cr and Co. On the other hand, Ms and As do not depend on Ti concentration when Ti concentration is more than 52mol.%. NiTi alloys are in two phase region in the case. Ms changes by Co at offstoichiometry are evaluated to be -15K / mol.% in Ni poor side and -30K / mol.% in Ni rich side. These values correspond to -22K / mol.% for the stoichiometric NiTi alloys. Also, effects of Cr on Ms are evaluated to be -65K / mol.% in Ni poor side and -45K / mol.% in Ni rich side. The former is similar to the Ms change in stoichiometric alloys, and the latter is close to our prediction of -30K / mol.% in comparison with the reported value of -120K / mol.% for stoichiometric alloys. It is concluded for offstoichiometric NiTi alloys that effects of ternary additions on Ms can be explained using electronic structures of ternary elements by taking atomic configurations into account, as well as the stoichiometric NiTi alloys. Effect of degree of order is also discussed.
Pseudoelasticity in High Strengthening Fcc Single Crystals
Authors: Chumlyakov Yu.I. , Kireeva I. V. , Kapasova G. S. , Litvinova E. I.
Published: April 2011

It was experimentally shown that the achievement of a high deforming stress level due to dispersion hardening and solid solution strengthening of FCC single crystals with a low stacking-fault energy leads to the deformation mechanism changing from slip to twinning, the dependence of mechanical properties on a crystal orientation and a sign of applied stresses. During deformation by twinning at T<150–300K effects of pseudoelasticity associated with elastic twinning is observed.
Dynamic Aspects of Formation of Synthetic Membranes
Authors: Thies M. , Paradies H. H. , Clancy S. F.
Published: April 2011

A detailed physical analysis of data obtained from static light and dynamic light scattering experiments with polymer-like distearyldimethylammonium OH (DSDMA X) micelles has been undertaken at dilute and semidilute concentrations, and compared with those in the presence of racemic and enantiomeric anions, e.g. S-(+)-lactate or the R-(-)-enantiomer.
DNA Sequence Alignment and Critical Phenomena
Authors: Drasdo Dirk , Hwa Terence , Lässig Michael
Published: April 2011

Alignment algorithms are commonly used to detect and quantify similarities between DNA sequences. We study these algorithms in the framework of a recent theory viewing similarity detection as a geometrical critical phenomenon of directed random walks. We show that the roughness of these random walks governs the fidelity of an alignment, i.e., its ability to capture the correlations between the sequences compared. Criteria for the optimization of alignment algorithms emerge from this theory.
The Structural Changes Induced by Anchored Polymers on Droplet and Bicontinuous Microemulsion
Authors: Lal Jyotsana , Auvray Loic
Published: April 2011

Macroscopically, phase changes (induced due to change of curvature) were observed on the introduction of PEG (polyethyleneglycol) grafted on lipids (anchored polymers) in the Winsor phases of microemulsion. Replacing some of the surfactant in the monolayers of the micro-emulsion with polymer grafted lipids changes the interaction between droplets of micro- emulsion and a greater increase in the percentage of anchored polymer in the monolayer might even bring about structural changes. The results on winsor phases, droplet microemulsions and bicontinous phases with anchored polymers as studied by Small Angle Neutron Scattering (SANS) are reported below, together with the contrast variation techniques used to characterize average curvature in the system.
Coherent and Incoherent Ripples in Dipalmitoylphosphatidylcholine
Authors: Mason P. C. , Gaulin B. D. , Epand R. M. , Wignall G. D. , Lin J. S.
Published: April 2011

The rich phase behaviour displayed by phospholipid bilayers and their structural relationship to biological membranes have made them fascinating objects of study. Despite being one of the most often examined of these model membrane systems, dipalmitoylphosphatidylcholine (DPPC) continues to be a source of interest for scientists. In particular, the ripple phase, Pβ′, of fully hydrated DPPC has generated a great deal of attention over the years as scientists have tried to understand the structural details of this novel phase1–5.
Interfacially Confined Polymeric Systems Studied by Atomic Force Microscopy
Authors: Overney René M. , Guo Lantao , Totsuka Hirono , Rafailovich Miriam , Sokolov Jonathan , Schwarz Steven A.
Published: April 2011

Within the last few years, a surface science technique, the atomic force microscopy (AFM), has evolved to be capable of simultaneously measuring tribological (friction, wear, adhesion) and rheological (elastic moduli, viscosity, hardness) properties and topography on the nanometer scale. Particularly for thin polymeric films, the AFM can be efficiently used for studying surface mechanical properties which are of fundamental importance to help predict stress and frictional behavior of interfacially confined ultrathin films.

In this paper, the following aspects will be discussed: (a) mechanical properties of ultrathin homopolymer and copolymer films, (b) dewetting dynamics of interfacially confined phase-separated homopolymers, and (c) the influence of graft-copolymers on the wetting and dewetting characteristics of homopolymers.
Monte Carlo Study of A+A+A→0 and A+2B→0 Reactions
Authors: Yen Andrew , Kopelman Raoul
Published: April 2011

The diffusion-limited annihilation reactions A+A→products and A+B→products havebeen subject to theoretical, numerical, and experimental study over the past decade. “Anomalous” behaviors have been reported for both reactions, but with different upper critical dimensions (d=2 and d=4 respectively). The critical dimensions and the scaling of the exponents for the generalized reaction nA+mB→products depends on n and m. We present Monte Carlo simulations for two different types of third-order reactions, A+A+A→0 and A+2B→0, on both one and two dimensional lattices. Our numerical results show that for the two-dimensional case the behavior of the reaction follows mean-field theory while in one dimension the result is“anomalous”. Our numerical results are in good agreement with theory based on microscopic arguments and scaling analysis.
Line Tension Effect on Alkane Droplets Near the Wetting Transition
Authors: Dussaud A. D. , Vignes-Adler M.
Published: April 2011

We have investigated n-octane droplets resting on the surface of sodium chloride solutions as a function of the salt concentration in a saturated, closed cell. For high salt concentration, the system approaches a wetting transition : the contact angles are very small (∼ 1°), the macroscopic droplet is unstable, and it breaks up spontaneously into microdroplets. The stable polydisperse population of microdroplets (5 μm < r < 250 μm) allowed us to analyze the dependence of the contact angle on droplet size. Because of the low contact angle values, accurate measurement ofcontact angles was obtained by interferometry. Moreover the accuracy of the classical method was significantly improved through the systematic use of three wavelengths. The relationship between the contact angle and the size droplet size indicated a positive line tension, τ, and the order of magnitude of τ was in good agreement with the theoretical prediction, τ, varies between (8.6 ± 0.9). 10−11 N and (1 ± 0.1).10−9 N and was dependent on the salt concentration. The positive sign of τ and its significant effect on droplet shape were related to the fact that the system was approaching the wetting transition.
Imaging Complex Fluids Under Confinement and Flow: Development of Bragg-Fresnel Optics for X-ray Microdiffraction
Authors: Li Youli , Idziak Stefan H.J. , Caine Ernie , Subramanian G. , Hu Evelyn , Safinya Cyrus R.
Published: April 2011

We present results of simultaneous efforts to develop: 1.) Bragg-Fresnel Optics(BFO) to be used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions; and 2.) Methodologies for confining complex fluids and biomaterials for in-situ structural studies. Using microelectronics process technology, we have fabricated linear and circular Bragg-Fresnel Lenses (BFL) in Si and III-V compound semiconductor substrates such as InP, GaAs and GaAs heterostructures with outermost zone width to 0.25 μm. X-ray characterization of linear BFLs were performed on a wiggler beamline at Stanford Synchrotron Radiation Laboratory (SSRL) at x-ray energies of 8 keV and 16 keV. A ∼5 μm focal spot size was obtained with a 50 μm incident beam, which was determined by the partial coherence of the source. On the confinement techniques, we have developed the X-ray Surface Force Apparatus (XSFA) which allows in-situ x-ray diffraction measurements to be made on fluid thin films confined between two atomically smooth surfaces. A new approach is being pursued to study the effects of confinement and flow on complex fluids and biological materials using microchannels fabricated on glass substrates.
Discontinuity in Particle Granular Temperature Observed in Gas Fluidized Beds Across The Geldart B/A Boundary - Implications for Stability and Properties of the Geldart A Phase
Authors: Cody George D. , Goldfarb David J.
Published: April 2011

We present new experimental data on the properties of monodispersed glass spheresas a function of sphere diameter and gas flow in a gas fluidized bed. The data obtained by a novel non-intrusive probe of the average particle kinetic energy, or granular temperature, at thewall is used to explore and understand the well known empirical distinction between fluidized particles which exhibit a single phase state at initial fluidization (Geldart A powders) and fluidized particles that exhibit gas bubbles at initial fluidization (Geldart B powders). Specifically we show that the experimental “jump” we observe in the granular temperature atthe Geldart / transition is sufficient to account for the initial stability of the Geldart A phase on the basis of the one dimensional, first order, two wave, stability theory first introduced by Jackson in the early sixties. We present new data on the diameter dependent properties of the glass spheres during bed collapse and bed expansion, which demonstrate the distinctionbetween Geldart A and B behavior for these monodispersed glass spheres. Finally we present a simple Langevin model to account for the dependence of the granular temperature on sphere diameter and gas flow, and discuss the implications of these new experimental data for the fundamental physics of the Geldart A phase.
Numerical Simulation of the Transient Photoconductivity in A-SI:H as a Function of the Excitation Density
Authors: Feist H. , Kunst M.
Published: April 2011

The dependence of the transient photoconductivity induced by pulsed excitation (TPC) on the excitation density is discussed with the help of numerical simulations. It is shown that recombination between excess mobile electrons and all excess holes (mainly localized) can explain the excitation density dependence of the TPC amplitude of standard a-Si:H at room temperature using a rate parameter kBB of 10−8cm3/s. This model leads to a decay faster than experimentally observed in the time range from 40ns to 1 μs. A variation of the recombination model is presented that gives a better fit for the longer time range still showing the correct excitation density dependence in the short time range. Moreover comparison of the simulations with experimental data yields limits for the parameters of the conduction band tail. In particular, the time necessary to establish a dynamic equilibrium of excess electrons between delocalized states in the conduction band and localized states in the tail appears to be very informative.
Optically Induced Conductivity Changes in Amorphous Silicon: A Historical Perspective
Authors: Staebler David L.
Published: April 2011

A historical perspective of the discovery of optically induced changes in amorphous silicon is presented in this paper from my personal point of view. It includes the story of how Chris Wronski and I discovered the effect, the key elements in our R&D environment that lead to our quick realization that the effect was reversible and reproducible, how our research environment supported the rapid publication of our first paper, and a brief look at the effect from today's perspective.
Pulsed-Laser Crystallized Highly Conductive boron-doped Microcrystalline Silicon
Authors: Nebel C. E. , Dahlheimer B. , Karrer U. , Stutzmann M.
Published: April 2011

The preparation of seed lattices, using three interfering beams (TIB) from a pulsed Nd:YAG laser in a-Si layers of 100 to 400 nm thickness is introduced and applied for seeded laser or thermally induced crystallization of a-Si on Corning 7059 glass. The structural and electronic properties of the μc-Si layers are investigated by X-ray, electron- and atomic force microscopy, Hall and conductivity measurements. In highly boron-doped μc-Si, grains up to 1.3 μm in diameter are detected, giving rise ti conductivities of ≃ 2000 S/cm and hole mobilities of ≃ 10cm2/Vs.
Growth of Micro-Crystalline SI:H and (SI,GE):H on Polyimide Substrates using ECR Deposition Techniques
Authors: Erickson Karl , Dalal Vikram L. , Chumanov George
Published: April 2011

We report on the growth of good quality micro-crystalline Si:H and (Si,Ge):H films on polyimide substrates using a remote plasma ECR deposition technique. We find that under conditions that lead to significant ion bombardment of the substrate, the films are microcrystalline even at relatively low deposition temperatures of about 250 C. A critical factor in inducing micro-crystallinity is the presence of a metal coating layer on polyimide. In the absence of such a coating, the films are amorphous, probably because the uncoated polyimide substrate charges up and prevents any further ion bombardment. The quality of the films was measured using both Raman spectroscopy and by studying the activation energy and low-energy absorption coefficient of the films. The sub gap absorption coefficient was found to follow the crystalline Si absorption curve quite well. The addition of germane to the gas phase shifted the absorption curve to smaller energies.
Laser Induced Melting and Crystallization of Boron Doped Amorphous Silicon
Authors: Nebel C. E. , Schöniger S. , Dahlheimer B. , Stutzmann M.
Published: April 2011

Transient reflectivity experiments have been performed to measure the dynamics of laser-induced melting of amorphous silicon (a-Si) and the crystallization to μ-Si of films with different thicknesses on Corning 7059 glass. The laser-induced melting takes place with a velocity of 13 to 24 m/s, while the solidification is about a factor 10 slower. The crystallization starts at the Si/glass interface and at the surface. In the center of the films, Si remains liquid for an extended period of time. The crystallization dynamics point towards an heterogeneous morphology of laser-crystallized Si, where the surface and the interface layers are composed of small grains and the bulk of larger grains.
Photoluminescence and Optical Characterization of a-SixN1-x:H based Multilayers Grown by PECVD
Authors: Giorgis F. , Giuliani F. , Pirri C. F. , Tresso E. , Galloni R. , Rizzoli R. , Summonte C. , Desalvo A. , Zignani F. , Rava P. , Cacca Vale F.
Published: April 2011

High room temperature photoluminescence efficiency (PLE) was observed for the first time in a-SixN1-x:H based nanometric multilayers deposited by plasma enhanced chemical vapour deposition (PECVD). The structure consists of alternate stoichiometric a-Si3N4:H barrier layers (E04=5.0 eV) and well layers in which E04 is varied between 2.11 eV and 2.64 eV. The peak of PL spectra and the absorption coefficient edge exhibits a blue shift up to 0.5–0.6 eV by decreasing the well thickness from 30 Å down to 5–10 Å. A strong increase in the PLE of multilayers, with well thickness around 5–10 Å, with respect to the PLE of bulk material was obtained.

A p-i-n light emitting device (LED) with a multilayered structure as i-layer, having well layers with E04=2.64 eV and thickness 10 Å, is presented. The LED under forward bias shows an emission visible with the naked eye, with limited degradation after 8 hours of continuous operation.
Structure and Electronic Parameters of A-Si:H Deposited by DC-MASD
Authors: Golikova O. A. , Kuznetsov A. N. , Kudoyarova V. Kh. , Kazanin M. M. , Adriaenssens G. J. , Herremans H.
Published: April 2011

A systematic study of structure and electronic parameters of a-Si:H deposited by dc-magnetron assisted SiH4 decomposition (MASD) depending on substrate temperature, gas pressure, gas flow and grid mounting has been carried out. Correlation between the film microstructure, dangling bond density and electron mobility-life time product were established. The photoconductivity changes under light soaking were shown to be minimal when the films contained hydrogen in the (SiH2)n chains.