bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rare-Earth Doped Silicon-Rich Silica: Evidence for Energy Transfer between Silicon Microclusters and Rare-Earth Ions
Authors: Kenyon A.J. , Trwoga P.F. , Federighi M. , Pitt C.W. 
Published: April 2011

ABSTRACTWe report the fabrication of rare-earth doped silicon-rich silica thin films by PECVD. The films exhibit absorption edges in the visible region of the optical spectrum consistent with the presence of silicon microclusters. Weak visible photoluminescence due to silicon microclusters is observed. In addition, strong luminescence from the rare-earth ion is obtained even when excited away from characteristic absorption bands; indeed, the luminescence intensity is largely independent of excitation wavelength below 514 nm. We ascribe this to excitation of silicon microclusters followed by an efficient transfer of energy to the rare-earth ions.The very broad absorption of this material opens up the possibility for flashlamp-pumped optoelectronic devices. In addition, we report the fabrication of silicon-rich silica films by PECVD. We show that the optical properties of these films are consistent with the presence of silicon microclusters and show absorption spectra similar to those of the rare-earth doped silicon-rich silica samples. This supports the hypothesis that the principal absorbing species in the rare-earth doped films is microclustered silicon
Generation and Structural Analysis of Silicon Nanoparticles
Authors: Li Ping , Sattler Klaus 
Published: April 2011

ABSTRACTWe have generated 20 to 100 nm sized silicon nanoparticles and analyzed their morphologies using an atomic force microscope (AFM). The particles are formed by deposition of silicon vapor onto silicon wafers and highly oriented pyrolytic graphite (HOPG). On silicon substrates, the particles are close to spherical with relatively narrow size distributions and they are randomly located. On graphite substrates the particles are arranged in chains. Within the chains they show strong deformations in the contact areas. We relate this to covalent inter-particle interactions.
Some Natural Three-and Lower-Dimensional Semiconductor Systems with Metal-Halide Units
Authors: Papavassiliou George C. , Koutselas I.B. , Terzis A. , Raptopoulou C.P. 
Published: April 2011

ABSTRACTThe structural, optical and related properties (i.e. photoluminescence, photoconductivity etc.) of some natural three- and lower-dimensional semiconductor systems based on metal halides are briefly reviewed and some new results are reported. A blue shift of the excitonic bands was observed by decreasing the dimensionality or the size of the materials active part. The results are similar to those obtained from conventional semiconductor systems (e.g. GaAs, CdS, PbI2) by decreasing artificially the dimensionality or decreasing the size.
Photoluminescence Excitation Spectroscopy Of Porous Silicon
Authors: Kux A. , Ben Chorin M. 
Published: April 2011

ABSTRACTWe combine photoluminescence excitation spectroscopy and photoconductivity to extract information about the bandgap and particle size distribution of porous silicon. This allows us to specify the influence of size dispersion and to show that different methods to determine absorption probe different parts of the size distribution.
Structural and Electrical Properties of Undoped Microcrystalline Silicon Grown by 70 MHz and 13.56 MHz PECVD
Authors: Flückiger R. , Meier J. , Crovini G. , Demichelis F. , Giorgis F. , Pirri C.F. , Tresso E. , Pohl J. , Rigato V. , Zandolin S. , Caccavale F. 
Published: April 2011

ABSTRACTMicrocrystalline silicon films deposited by plasma methods have an optical absorption for photon energies above 2.0 eV lower than a-Si:H films and can be efficiently doped with boron or phosphorus. The most widely used deposition technique is the 13.56 MHz PECVD. However quite recently µc-Si:H films were grown at high deposition rates by the 70 MHz PECVD. In this work the authors report on a comparison between µc-Si:H films deposited by both 70 MHz and 13.56 MHz techniques. Particular attention has been devoted to differences and similarities between structural, compositional and electrical properties of the films deposited with the two systems.
Study of Onion-Like Carbon (OLC) Formation from Ultra Disperse Diamond (UDD)
Authors: Kuznetsov Vladimir L. , Chuvilin Andrey L. , Butenko Yurii V. , Mal'kov Igor Yu. , Gutakovskii Anton K. , Stankus Sergey V. , Khairulin Raschid A. 
Published: April 2011

ABSTRACTMeasurements of diamond bulk density change of carbon powder in the annealing of UDD to OLC (293-2400 K) was performed by irradiating the samples with a narrow beam of gamma quanta (137Cs gamma-ray source). The intermediates of UDD to OLC transformation were registered by high resolution TEM. The annealing products were also characterized by true density and specific area adsorption measurements. The structural rearrangement of UDD begins from the surface towards a crystal bulk. UDD annealing proceeds via particles composed of semi-spherical shells enclosed one-to-one with the rest of diamond core and quasispiral carbon shells. The influence of particle size on the temperature of UDD to OLC transformation was found.
Electronic Angular Momentum Effects in the Photophysical Behavior of Fullerenes
Authors: Argentine S. M. , Francis A. H. 
Published: April 2011

ABSTRACTThe intensity of the electronic origin in the emission spectrum of C70 exhibits a strong solvent sensitivity. The intensity of this peak increases relative to the vibronic features as the dielectric constant of the solvent increases. This solvent dependence is explained by an extension of Platt's Perimeter Free Electron Orbital model. The fullerenes, in particular C60 and C70, possess a nearly spherical symmetry that gives rise to the presence of significant electronic orbital angular momentum. The unexpected spectral sensitivity is shown to arise from quenching of the electronic angular momentum by the solvent environment.
Fluorescence of Cyclic Adducts of Fullerene
Authors: Lin Tsung-I , Lin Syh-Kun , Shiu Lung-Lin , Chien Kuo-Ming , Luh Tien-Yau 
Published: April 2011

ABSTRACTFive cyclic adducts C60C4H6, C60C5H6, C60NHCO2, C60NCO2Et, and C60CHCO2Et have been synthesized and their absorption and fluorescence spectral properties investigated and compared with those of the parent. Breaking the structural symmetry of C60 apparently resulted in enhancing the quantum yield two to three-folds in some adducts and thus made fluorescence much easier to be measured at room temperature. New absorption bands and altered fluorescence spectra were observed in the adducts. The Stokes' shifts of the adducts were small, about 4-5 nrm, compared to 68 nm for the parent compound. All the adducts exhibited a single fluorescence lifetime about the same as C60 (ca. 1.3 ns). Aliphatic solvents had little influence on the absorption or fluorescence spectral profile except on the molar absorptivity whereas aromatic and polar solvents strongly interacted with the adducts causing a peak broadening effect.
The Effects of La Concentration on the Properties of PLT Thin Films: From the Perspective of Dram Applications
Authors: Kang Seong Jun , Ryoo Jeong Seon , Yoon Yung Sup 
Published: April 2011

ABSTRACTWe have studied the effects of La concentration on the dielectric and ferroelectric properties of lead lanthanum titanate (PLT) thin films by using sol-gel method. Both the dielectric and ferroelectric properties were greatly affected by the La concentration. The dielectric constants of the films varied from 340 to 870 with varying La concentration in the range from 15 to 33 mol%. Hysteresis loop became slimmer with the increase of La concentration from 15 to 28 mol% and a little fatter again with the increase of La concentration from 28 to 33 mol%. Among the films investigated in this research, PLT(28) thin film showed the best dielectric properties for the application to the dielectrics of ULSI DRAM's. At the frequency of 100 Hz, the dielectric constant and the loss tangent of PLT(28) thin film were 940 and 0.08, respectively. Its leakage current density at 1.5×10 V/cm was 1×10−6 A/cm2. The comparison between the simulated and the experimental curves for the switching transient characteristics showed that PLT(28) thin film behaved like normal dielectrics.
Electrical and Microstructural Properties of Lead Titanate Thin Films Deposited by Metalorganic Chemical Vapor Deposition
Authors: Vellaikal M. , Kingon A. 
Published: April 2011

ABSTRACTLead titanate thin films were deposited on Pt(111)/Ti/SiO2/Si(100) and RuO2/SiO2/Si(100) substrates using metalorganic chemical vapor deposition (MOCVD). Atomic force microscopy revealed that films on ruthenium oxide were rougher than films on platinum. Also the grain size of the film on ruthenium oxide was larger than that on platinum. X-ray analysis revealed that the preferred orientations for films on platinum and ruthenium oxide were different. Hysteresis and fatigue tests were performed to evaluate capacitor structures on these substrates. Films on RuO2 had lower coercive fields than films on platinum. Comparison of polycrystalline and oriented films on platinum indicated that the oriented films were easier to switch and fatigued at a slower rate than the polycrystalline films. But long term property (fatigue, imprint) testing on lead titanate resulted in resistance degradation of these contacts, unlike PZT films.
Electrical Properties of PZT Prepared by Pulsed Laser Ablation on Various Electrodes
Authors: Morimoto Akiharu , Yamanaka Yasuhiro , Minamikawa Toshiharu 
Published: April 2011

ABSTRACTThe effect of various electrodes on the ferroelectric properties of lead-zirconate-titanate (Pb(Zr0.52Ti0.48)O3 PZT) films through the film structure is presented. All the PZT films were deposited by pulsed laser ablation (PLA) using an ArF excimer laser. For electrode materials, YBa2Cu3O7 (YBCO) and Ni-alloy were deposited by pulsed laser ablation and sputtering, respectively. As a result various kinds of PZT films with various film structures were obtained. These experiments revealed that there is no simple correlation between the film structure and the fatigue resistance. The fatigue resistance is, however, found to be improved primarily by decreasing the switched-charge density, although the correlation shows some ambiguity. This suggests that the large polarization reversal accelerates the fatigue but there remained the possibility that the fatigue resistance is improved by the optimization of the film structure and film-substrate interface.
Strontium Barium Niobate Thin Films Prepared by Pulsed Laser Deposition
Authors: Liu Y. , Ong C.W. , Chan P.W. , Choy C.L. 
Published: April 2011

ABSTRACTStrontium barium niobate Sr0.55Ba0.45Nb2O6 thin films were prepared on Si (111) substrates by pulsed laser deposition (PLD). The film composition was determined as a function of the fluence φ and wavelength λ of the laser beam, the oxygen ambient pressure Po2 and the substrate temperature Ts. The results show that the film composition is very close to that of the target, and is almost independent of φ from 1 to 8 J cm−2, λ = 355, 532 and 1064 nm, Po2 from 0 to 150 mTorr, and Ts from 25 to 700°C. These results suggest that PLD is excellent for preparing SBN films with compositions congruent to that of the target. The x-ray diffraction data show that all the samples deposited at room temperature are amorphous. The x-ray diffraction results also indicate that the samples deposited at 700°C have a tungsten-bronze-(TB-) type structure with preferred crystallite orientation, while the room-temperature-deposited samples after annealing at 800°C for 30 minutes are polycrystalline and have random crystallite orientation.
Preparation and Mechanical Properties of Si3N4 Ceramics With Dispersed NANO Sic Particles
Authors: Yanail Tomohiro , Ishizaki K. 
Published: April 2011

AbstractThe purpose of the present work is to toughen the grain boundary phase of Si3N4 ceramics by forming a nano composite grain boundary phase of SiC particles. The nano SiC particles form through a reaction between the coated carbon and the surface oxidation phase in Si3N4. The carbon is coated through thermal decomposition of CH4 gas. The sintcred bodies arc obtained by hot-pressing at 1800 °C for one h. By increasing the carbon content, both fracture toughness and bending strength initially increase, then reach the maximum value at the same amount of carbon content, and decrease. The carbon content at which the fracture toughness and bending strength exhibit the maximum value increases with the increase in the surface oxygen content. The precipitated SiC particles dispersed in a grain boundary phase, at a Si3N4-Si3N4 interface or in a Si3N4 grain. The locations and size (less than 30 nm) of the SiC particles are examined by TEM and HREM observations. As the grain boundary is toughened by the precipitated nano SiC particles in the grain boundary phase or at the Si3N4-Si3N4 interface to help Si3N4 grain bridging without any glassy phase, these SiC particles block or resist the intergranular fracture.
Fragmentation of Highly Charged Metallic Clusters
Authors: Blaisten-Barojas Estela , Li Yibing , Belenki A. 
Published: April 2011

ABSTRACTMultiply charged metal clusters undergo fission at a certain size. This critical size can be predicted by the liquid drop model when some modifications are taken into consideration. In this work we revise the asymmetric liquid drop model (ALD) and modify it for the alkali metals. This modification addresses those fragmentation channels in which a parent cluster with charge Ze fissions into two fragments. One of the fragments is small and singly charged whereas the second fragment is large and carries the rest of the charge. A different energetic balance equation is presented in which the ionization energy of a single atom and the energy of formation of a small cluster are included. Results and comparison to experiments is provided for Na and Cs clusters. Prediction of the critical size of Na and Cs clusters with Ze>7 is part of the discussion.
Oxidative Catalytic Decomposition of Toxic Gases Using Hydroxyapatite and Fluorhydroxyapatite
Authors: Palucka Timothy P. , Eror Nicholas G. , Mcnamara Thomas A. 
Published: April 2011

ABSTRACTAn oxidative catalytic route for the decomposition of nerve gases was investigated using hydroxyapatite (HA, chemical composition Ca10(PO4)6(OH)2) and its partially fluorinated analog fluorhydroxyapatite (FHA, Ca10(PO4)6Fx(OH)2−x). Samples were prepared with surface areas ranging from 34 to 238 m2/g to study surface area effects; 1.2 wt. % platinum was deposited on one substrate to investigate the effect of a transition metal on activity and selectivity. Reaction studies were performed using dimethyl methylphosphonate (DMMP), a nerve gas simulant, in a stream of 80 percent nitrogen and 20 percent oxygen at 573 K and atmospheric pressure. High surface area FHA samples showed an increase in the "protection period" (period of 100% conversion) with increasing fluorine substitution; such an increase was not seen for low surface area FHA samples. In the absence of platinum, the reaction products were methanol and dimethyl ether; with platinum, CO2 was also obtained.
Computer Simulation of Diffusion and Adsorption in Pillared Clays
Authors: YI Xiaohua , Sahimi Muhammad , Shing Katherine S. 
Published: April 2011

ABSTRACTWe developed a model to describe the morphology and energetics of pillared clays. Grand- Canonical Ensemble Monte Carlo and Molecular Dynamics simulations are used to study diffusion and adsorption of finite-size molecules in such systems, and the effect of various factors on these processes is investigated.
Point Defects and Cation Tracer Diffusion in (CrxFe1-x)3-δO4 Spinels
Authors: TÖpfer J. , Dieckmann R. 
Published: April 2011

AbstractThe cation diffusion in the spinel solid solution (CrxFe1-x)3-δO4 (0 ≤ x ≤ 0.5) was experimentally investigated at 1200 °C as a function of oxygen activity, aO2 (= PO2/P°with P° = 1 bar) and cationic composition, x. Cation tracer diffusion coefficients, DMe' of Me = Co, Cr, Fe and Mn, were determined using the radioactiveisotopes Co-60, Cr-51, Fe-59 and Mn-54. For each cationic composition V-shaped log DMe vs. log aO2 plots were obtained. The observed oxygen activity dependences indicate that the cation diffusion is determined by different point defect species prevailing at high and low oxygen activities, respectively. The observed oxygen activity dependences, in comparison with considerations based on point defect thermodynamics, suggest that cations diffuse via cation vacancies at high aO2' while at low aO2 cation interstitials prevail in the cation diffusion. In addition, new experimental data for tihe deviation from stoichiometry ≤in (CrxFe1-x)3-≤O4 are presented and discussed.
Cation Conductivity in Mixed Sulfate-Based and Mixed Iodide-Based Solids with Phase Transitions
Authors: Secco E. A. 
Published: April 2011

AbstractThe ac electrical conductivity versus temperature dependence of solids undergoing phase transitions incorporating various guest ions, viz isovalent cations and anions, ions with different ionic radius, ions with different polarizability, in Na2SO4-based, Ag2SO4-based, Li2SO4-based and U02SO4-based compositions along with MxTl(1x)I compositions for 1 ≤ x ≤ 0.13, whose M = K, Rb, Cs, are reported. An overview is given of the interplay of various factors, structural and non-structural, with their contribution limits impacting on locking-in the fast cation conductivity phase and the interpretation of fast-ion conductivity in the context of a percolation-type of ionstransport mechanism.
Interfacial Zone Percolation in Concrete: Effects of Interfacial Zone Thickness and Aggregate Shape
Authors: Bentz D.P. , Hwang J.T.G. , Hagwood C. , Garboczi E.J. , Snyder K.A. , Buenfeld N. , Scrivener K.L. 
Published: April 2011

AbstractPreviously, a hard core/soft shell computer model was developed to simulate the overlap and percolation of the interfacial transition zones surrounding each aggregate in a mortar or concrete. The aggregate particles were modelled as spheres with a size distribution representative of a real mortar or concrete specimen. Here, the model has been extended to investigate the effects of aggregate shape on interfacial transition zone percolation, by modelling the aggregates as hard ellipsoids, which gives a dynamic range of shapes from plates to spheres, to fibers. For high performance concretes, the interfacial transition zone thickness will generally be reduced, which will also affect their percolation properties. This paper presents results from a study of the effects of interfacial transition zone thickness and aggregate shape on these percolation characteristics.
Surface Core-Level Photoelectron Diffraction of Surface Reconstructions
Authors: Rotenberg Eli , Denlinger J. D. , Kevan S. D. , Tonner B. P. 
Published: April 2011

AbstractExperimental surface core-level shifts (SCLSs) aid in understanding the roles of altered electronic and screening properties at reconstructed semiconductor surfaces.1 Because of unresolved theoretical issues, the assignment of SCLSs has often remained controversial even though the surface geometry has been completely determined with traditional probes.Angular- and energy-dependent x-ray photoelectron diffraction (XPD) of each chemically resolved surface core-level electron can be used to discriminate the structure around each chemically shifted species. However, this technique requires tunability, high energy resolution to separate the SCLSs from the bulk core-levels, and high photon flux in order to gather large amounts of data in a reasonable time. Using the newly commissioned spectromicroscopy beamline 7.0 at the Advanced Light Source, we have acquired chemically-resolved XPD data for Si(111) 7×7 for several photon energies, and by examination of forward-focusing peaks we can draw tentative conclusions about the atomic origins of each core-level shifted peak.
Modeling Valence-Band Images from Synchrotron-Radiation Studies Using Display Analyzers: Lithium Fluoride and Graphite
Authors: Shirley Eric L. , Terminello Louis J. , Klepeis John E. , Himpsel F. J. 
Published: April 2011

AbstractWe present simulated photoelectron angular distributions (PAD's) for LiF and graphite. The results describe electron photocurrent versus photon energy, electron initial-state energy, and emission angles (leading to identification of two, or three, components of a valence electron's initial crystal momentum). Results are displayed in a fashion greatly facilitated by display analyzers. Earlier experimental results for LiF are confirmed in great detail. We discuss statistical comparison of theoretical and experimental PAD's. Effects of Bragg- diffraction on outgoing photoelectrons and uncertainty in crystal momentum normal to a surface are analyzed. In graphite, the observed lowering of symmetry, from that in a periodic-zone band structure to that seen in the PAD's, is modeled and explained.
Synchrotron X-ray Scattering Studies at Mineral-Water Interfaces
Authors: Chiarello Ronald P. , Sturchio Neil C. 
Published: April 2011

AbstractSynchrotron X-ray scattering techniques provide a powerful tool for the in situ study of atomic scale processes occurring at solid-liquid interfaces. We have applied these techniques to characterize and study reactions at mineral-water interfaces. Here we present two examples. The first is the characterization of the calcite (CaCO3) (1014) cleavage surface, in equilibrium with deionized water, by crystal truncation rod measurements. The second is the in situ study of the heteroepitaxial growth of otavite (CdCO3) on the calcite (1014) cleavage surface. The results of such studies will lead to significant progress in understanding mineral-water interface geochemistry.
A Quantitative Crystallization Study of Thin Amorphous Fe80B20 Films Via Empirical Modeling of Exafs Data
Authors: Harris V. G. , Oliver S. A. , Ayers J. D. , Das B. N. , Koon N. C. 
Published: April 2011

AbstractThin amorphous films (t=200Å) of Fe80B20 were annealed at temperatures ranging from 473K–823K and studied using extended X-ray absorption fine structure to investigate the evolution of local structure around the Fe atoms during crystallization. Modeling of the local environment around Fe using empirical standards was employed to determine the relative fraction of the crystalline phases present in annealed samples. Results illustrate the sensitivity of EXAFS in detecting the onset of crystallization in thin amorphous films and its ability to quantitatively measure the relative fraction of crystalline phases present in partially crystallized thin film samples.