bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical Response of Porous and Dense NiTi-TiC Composites
Authors: Burkes Douglas E. , Gottoli Guglielmo , Moore John J. , Ayers Reed A. 
Published: April 2011

ABSTRACTThe Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines is currently using combustion synthesis to produce several advanced materials. These materials include ceramic, intermetallic, and metal-matrix composites in both porous and dense form. Currently, NiTi – TiC intermetallic ceramic composites are under investigation for use as a bone replacement material. The NiTi intermetallic has the potential to provide a surface that is capable of readily producing an oxide layer for corrosion resistance. The TiC ceramic has the potential to increase the hardness and wear resistance of the bulk material that can improve the performance lifetime of the implant. Processing parameters are critical to the production of the NiTi – TiC composite and will be discussed. These parameters can lead to the formation of substoichiometric TiC and nickel rich NiTi that changes the overall mechanical and material properties. In addition, the size of the TiC particles present within the bulk product varies with porosity. Both porous and dense samples have been mechanically analyzed employing micro-indentation techniques as well as compression tests in an attempt to characterize the mechanical response of these composites. The effects of the TiC particles, the formation of Ni3Ti intermetallic and the effects of porosity on the overall mechanical and material properties will be discussed.
Mechanical Properties of Nacre Constituents: An Inverse Method Approach
Authors: Barthelat Francois , Espinosa Horacio D. 
Published: April 2011

ABSTRACTNacre, also known as mother-of-pearl, is the iridescent layer found inside some mollusk species such as oyster or abalone. It is made of relatively weak materials, but its hierarchical microstructure is so well optimized that its macroscopic mechanical properties are far superior to those of its constituents. For this reason there is a great interest in nacre as a source of inspiration for novel designs of composites. Despite many years of research on nacre, an accurate characterization of its constituents is lacking. In this work nacre was tested as a layered composite material using low depth indentation and uniaxial compression. The first test was modeled using finite element analysis and the second test was modeled as a Reuss composite in compression. A micromechanical model of the interface was also pursued to gain insight on the relevance of the interface features such as tablet roughness and biopolymer hydrated response. The results of the two experiments were combined to solve an inverse problem that yielded the needed properties for tablets and interfaces. These findings are expected to make possible computational models of nacre with a new degree of accuracy and therefore contribute to a better understanding of the mechanisms leading to its remarkable properties.
Spectral profiles of two-photon absorption: Coherent versus two-step two-photon absorption
Authors: Polyutov S. , Minkov I. , Gel'mukhanov F. , Kamada K. , Baev A. , Ågren H. 
Published: April 2011

ABSTRACTWe present a theory of two-photon absorption in solutions which addresses the formation of spectral shapes taking account of the vibrational degrees of freedom. The theory is used to rationalize observed differences between spectral shapes of one- and two-photon absorption. We elaborate on two underlying causes, one trivial and one non-trivial, behind these differences. The first refers simply to the fact that the set of excited electronic states constituting the spectra will have different relative cross sections for one-and two- photon absorption. The second reason is that the two-step and coherent two-photon absorption processes are competing, making the one-and two-photon spectral bands different even considering a single final state. The theory is applied to the N-101 molecule [di-phenyl-amino-nitro-stilbene] which was recently studied experimentally in the paper [ T.-C. Lin, G.S. He, P.N. Prasad, and L.-S. Tan, J. Mater. Chem., 14, 982, 2004.]
Effects of Deposition Angle on the Optical Properties of Helically Structured Films
Authors: Sorge Jason B. , van Popta Andy C. , Sit Jeremy C. , Brett Michael J. 
Published: April 2011

ABSTRACTGlancing-angle deposition (GLAD) is a fabrication method capable of producing thin films with variable porosity. The GLAD process exploits substrate shadowing and limited adatom diffusion to create isolated columns of material that collectively comprise a highly porous thin film. GLAD can be used to create chiral or helical structures with a wide range of porosity through variation of the substrate tilt angle and controlled substrate rotation. We present the effect of the deposition angle on the selective transmittance of circularly polarized light in helical thin films fabricated with the GLAD process. Transmission measurements of titanium dioxide helical films reveal two regimes of enhanced selective transmittance: one corresponding to a substrate tilt angle that produces a maximum circular birefringence and another corresponding to strong anisotropic scattering.
Degradation of Ru(bpy)32+-based OLEDs
Authors: Goldberg Velda , Kaplan Michael , Soltzberg Leonard , Genevich Joseph , Berry Rebecca , Bukhari Alma , Chan Sherina , Damour Megan , Friguglietti Leigh , Gunn Erica , Ho Karen , Johnson Ashley , Lin Yin Yin , Lowenthal Alisabet , Suth Seiyam , To Regina , Yopak Regina , Slinker Jason D. , Malliaras George G. , Flores-Torres Samuel , Abruña Hector D. 
Published: April 2011

ABSTRACTAnalysis of the possible mechanisms of degradation of Ru(bpy)32+-based OLEDs has led to the idea of quencher formation in the metalloorganic area close to the cathode. It has been suggested that the quencher results from an electrochemical process where one of the bipyridine (bpy) groups is replaced with two water molecules [1] or from reduction of Ru(bpy)32+ to Ru(bpy)30 [2]. We have tested these and other degradation ideas for Ru(bpy)32+-based OLEDs, both prepared and tested with considerable exposure to the ambient environment and using materials and procedures that emphasize cost of preparation rather than overall efficiency. In order to understand the mechanisms involved in these particular devices, we have correlated changes in the devices' electrical and optical properties with MALDI-TOF mass spectra and UV-vis absorption and fluorescence spectra.
Fast-Switching, High-Contrast Electrochromic Thin Films Prepared Using Layer-by-Layer Assembly of Charged Species
Authors: Grunlan Jaime C. 
Published: April 2011

ABSTRACTThin films were prepared by depositing alternating layers of tungstate anion (WO42-) and poly(4-vinylpyridine-co-styrene) (PVP-S) onto an electrode from aqueous solutions. These films have very high contrast (CR > 8) relative to equivalent films prepared using poly(ethylene dioxythiophene) (PEDOT), but suffer from slow color change due to poor electrical conductivity. The switching time of the tungstate-based films was decreased by an order of magnitude, from 30 seconds down to three, by adding layers of indium tin oxide (ITO) particles stabilized with poly(diallyldimethylammonium chloride) (PDDA). In this case, a four-layer repeating structure was created (i.e., PVP-S and PDDA-ITO were each deposited every fourth layer). Unlike tungstate, ITO has a high intrinsic conductivity (∼ 104 S/cm) that accounts for the dramatic increase in the switching speed. It is only through the nanometer-scale control of film architecture, provided with the layer-by-layer (LbL) deposition process, that switching speed and contrast ratio can be optimized simultaneously.
Optical Responses of Conjugated Polymers by TDDFT in Real-Space and Real-Time Approach
Authors: Akino Nobuhiko , Zempo Yasunari 
Published: April 2011

ABSTRACTThe time dependent density functional theory (TDDFT) has applied to study the optical responses of the conjugated polymers such as poly(p-phenylenevinylene) and poly(9, 9-dialkyl-fluorene). In our study, the real-space grid representation is used for the electron wavefunctions in contrast to a conventional basis set on each atom. In the calculations of the optical responses, the real-time approach is employed, where we follow the linear responses of the systems under externally applied perturbations in the real time. Since a real polymer is too large to handle, we have calculated the oligomers with different length and observed the spectrum peak is redshifted as the length of oligomer increases. The property of the polymer is extrapolated as the infinitely long oligomer. The estimated polymer spectra agree with the experiments reasonably well.
Linear and Nonlinear Transmission of Surface Plasmon Polaritons in an Optical Nanowire
Authors: Panoiu N. C. , Osgood R. M. 
Published: April 2011

ABSTRACTPolymer-metal composites offer the possibility of strongly enhanced nonlinear optical properties, which can be used for ultrasmall photonic devices. In this paper, we investigate numerically, by means of the finite-difference time-domain (FDTD) method, the propagation characteristics of surface plasmon polariton (SPP) modes excited in an optical nanowire consisting of a chain of either metallic cylinders or metallic spheres embedded in dielectric shells made of polymers (or other material) with optical Kerr nonlinearity. Our FDTD calculations incorporate both the nonlinear optical response of the dielectrics as well as the frequency dispersion of the metals, which is considered to obey a Drude-like model. It is demonstrated that, in the linear limit, the nanowire supports two SPP modes, a transverse and a longitudinal one, separated by Δλ = 20 nm. Furthermore, the dependence of the transmission of these SPP modes, on both the pulse peak power and Kerr coefficient of the dielectric shell, is investigated. Nonlinear optical phenomena, such as power-dependent mode frequency, switching, or optical limiting, are observed.
Coherent Oscillations of Breathing Modes in Metal Nanoshells
Authors: Kirakosyan Arman S. , Shahbazyan Tigran V. 
Published: April 2011

ABSTRACTWe study coherent oscillations of radial breathing modes in metal nanoparticles with a dielectric core. Vibrational modes are impulsively excited by a rapid heating of the particle lattice that occurs after laser excitation, while the energy transfer to a surrounding dielectric leads to a damping of the oscillations. In nanoshells, the presence of two metal surfaces leads to a substantially different energy spectrum of acoustic vibrations. The lowest and first excited modes correspond to in-phase (n=0) and anti-phase (n=1) contractions of shell-core and shell-matrix interfaces respectively. We calculated the energy spectrum as well as the damping of nanoshell vibrational modes in the presence of surrounding medium, and found that the size-dependences of in-phase and anti-phase modes are different. At the same time, the oscillator strength of the symmetric mode is larger than that in solid nanoparticles leading to stronger oscillations in thin nanoshells.
Current-voltage characteristics in organic semiconductor crystals: space charge vs. contact-limited carrier transport
Authors: Reynaert J. , Arkhipov V. I. , Genoe J. , Borghs G. , Heremans P. 
Published: April 2011

ABSTRACTNumerous experimental studies, mostly based on the time-of flight (TOF) technique, showed that the conductivity in organic crystals can be analysed in terms of (trap-controlled) band transport. However, recent comparative studies of TOF signals and space charge limited currents (SCLCs) in tetracene crystals revealed a striking difference in carrier mobilities estimated from TOF current transients and from SCLC curves. The analysis of the SCLC curves yielded the mobilities wildly varying within 6 orders of magnitude. Therefore, it is not always clear whether the measured current-voltage (IV) device characteristics are controlled by charge injection or by transport in the bulk. In this work, we formulate a model of dopant-assisted carrier injection across a metal/organics interface and use this model for the analysis of IV curves measured on a tetracene and perylene crystal. The model suggests the occurrence of an energetically disordered layer at the surface of an organic crystal. This might be either an amorphous phase of the same material or a crystalline layer with a high density of defects and/or impurities. Since, at variance with bulk properties, the surface of an organic crystal is poorly controlled and can be strongly modified upon the contact deposition, the model of injection-controlled IV characteristics can explain the striking difference between the TOF mobility and the apparent ‘SCLC mobility’ measured in tetracene crystals. In order to give more credence to the role of surface defects states in the dark charge transport, we compare IV characteristics measured on sandwich and coplanar structures. In the latter structure, surface states show a major contribution to the conductivity.
Luminescence properties of Eu3+:Y2O3 and Eu3+:Lu2O3 nanoparticles, ceramics and thin films
Authors: Zhang Kai , Hunter D. , Mohanty S. , Dadson J. B. , Barnakov Y. , Pradhan A. K. 
Published: April 2011

ABSTRACTEu3+ doped Y2O3 and Lu2O3 nanocrystalline powders were synthesized via combustion technique using urea as a fuel and the metal nitrates as oxidants. The compacted nanopowders were vacuum sintered in order to form the translucent ceramics. A significant enhancement of emission characteristics was observed from the ceramics synthesized from the nanoparticles by controlling the vacuum-sintering conditions. Although the processed ceramics display superior emission characteristics, the nanocrystalline phosphor powders also display reasonably good emission characteristics. Highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films were deposited on various substrates under different growth and optimization conditions using pulsed-laser deposition technique using high-density translucent ceramic target. Superior spectroscopic performance was obtained on films grown on sapphire substrates due to high-quality and epitaxial nature of the film.
Synthesis of nanomaterials in Highly Swollen Liquid Crystals
Authors: Tokumoto Myriam , Surendran Geetarani , Santos Eduardo Pena dos , Kooyman Patricia , Remita Hynd , Ramos Laurence , Prouzet Eric 
Published: April 2011

ABSTRACTHighly Swollen Liquid Crystals (SLC) that exhibit hexagonal, cubic or lamellar symmetry have been demonstrated to form a new type of soft nanoreactors. These mesophases are formed by a quaternary mixture combining a surfactant, an aqueous solution of inorganic salt, cyclohexane as a hydrophobic swelling solvent and pentanol-1 as a co-surfactant. Unlike previous works that used a “nanocasting” approach in a binary liquid crystal, the composition of these SLC allows syntheses to be proceeded inside the aqueous and/or the organic phase. Therefore inorganic, metallic or organic materials can be prepared and the geometry of the SLC controls the final shape of the prepared by this approach. We will describe various materials that were obtained by different processes in these SLCs: rod-like nanoaggregates of metal nanoparticles were synthesized by chemical reduction in the aqueous part of the hexagonal mesophase, microrods of zirconia were obtained by slow crystallogenesis from hydrated zirconium oxychloride, mesoporous zirconia was prepared by a faster hydrolysis and polymer micro- and nano-fibers were obtained in the organic phase by photopolymerization or radiolysis. We will show how the changements in the SLC structure can modify the structure of the compounds synthesized inside and that this system constitutes a quite universal medium for the preparation of nanomaterials or nanostructured systems.
Electrochemical Characterization of Phosphosilicate-modified Nafion Membranes
Authors: Klein L. C. , Aparicio M. 
Published: April 2011

ABSTRACTHybrid membranes containing Nafion and phosphosilicate gels were prepared using infiltration and recasting methods. The hybrid membranes were investigated using complex impedance spectroscopy. Conductivities were determined as a function of relative humidity. Infiltrated membranes, which contained gel in more or less discrete particles, were compared with recast membranes where the gel was more evenly distributed. Both of the modified membranes were compared to unmodified Nafion. The impedance spectra were analyzed to distinguish electrode interface effects from bulk transport phenomena.
Two Synthetic Routes to The Formation of Tungsten Oxide Hybrid Compounds
Authors: Chong S.V. , Ingham B. , Tallon J.L. 
Published: April 2011

ABSTRACTThe syntheses of tungsten oxide-organic amine hybrids via homogenous and heterogeneous routes were explored and compared. In the former case, tungstic acid (H2WO4) and an appropriate amine were dissolved in ammonia solution under nitrogen atmosphere, and the product was precipitated out via evaporation of the solvent. In heterogeneous synthesis, a non-aqueous approach was employed in which H2WO4 powder was aged in a solution consisting of the amine dissolved in an appropriate organic solvent. XRD and FTIR showed that the hybrid materials obtained from the two different methods are identical. Based on these findings, we were able to prepare tungsten oxide hybrid films for the first time, by dip-coating tungstic acid films prepared from sol-gel techniques, in a non-aqueous diamine solution. The XRD spectra of these films exhibit a series of harmonic peaks, indexed as [00k ], which correspond to the Bragg peaks for the hybrid compounds. SEM shows the morphology of tungstic acid changes from the irregularly shaped platelets to a needle-like structure of the hybrids and resulted in a loosely packed coating.
Fabrication of Organic/Inorganic Nanocomposites Using Pulsed Laser Ablation of Zinc in Aqueous Solutions
Authors: Sasaki Takeshi , Liang Changhao , Usui Hiroyuki , Shimizu Yoshiki , Koshizaki Naoto 
Published: April 2011

ABSTRACTHybrid organic/inorganic nanocomposites composed of zinc hydroxide and surfactant molecule, and/or zinc oxide nanoparticles were fabricated using pulsed laser ablation of zinc in aqueous solutions of various surfactants. A Zn plate was ablated by a pulsed Nd:YAG laser in four types of surfactant solutions with different concentrations. Zinc oxide nanoparticles with average diameter of 10–40 nm were obtained in cationic, amphoteric and nonionic surfactant solutions. Unique layered organic/inorganic nanocomposites composed of zinc hydroxide layers and surfactant molecules were obtained in aqueous solutions of the anionic surfactants, sodium alkyl sulfate (CnH2n+1SO4-·Na+). The carbon number, n, in the alkyl sulfate family is very important for the formation and structure of the layered nanocomposites. The layered organic/inorganic nanocomposite can be obtained only in the specific sodium alkyl sulfates (n = 12, 13, 14 and 16) and the layer spacing of the nanocomposites increased with n from 26.8 Å to 42.0 Å. It is shown that the structures of ZnO nanoparticles and layered organic/inorganic nanocomposites can be controlled by the type of surfactants in solution.
Self-Assembled Monolayers of 12-Mercaptododecylphosphonic Acid on Titania Particles; Application to the Extraction of Heavy Metals
Authors: Anthérieu Sébastien , Brodard-Séverac Florence , Guerrero Gilles , Hubert Mutin P. 
Published: April 2011

ABSTRACTTitania particles (P25 DEGUSSA AG) were treated by a solution of 12-mercaptododecyl-phosphonic acid (MDPA) in toluene to obtain an organic-inorganic hybrid material with thiol functions at the surface. This material was characterized by chemical analysis, solid state 31P MAS NMR and FTIR spectroscopies, and XPS. Reaction of the phosphonic acid end of MDPA with the TiO2 surface led to the formation of a relatively dense and well-ordered self-assembled monolayer (SAM), with a density of about 3.9 SH functions per nm2. This material was tested for the extraction of mercury in water at pH 7, 9, and 11. Chemical analysis indicated no loss of SH functionality, even at pH 11. The best extraction results were obtained at pH 9 and 11, with a metal extraction ability between 85 and 90%.
B and P Glass Formers as Stabilizers of Luminescent Ce(III) in Silica-Based Glasses
Authors: Canevali C. , Mattoni M. , Morazzoni F. , Scotti R. , Krsmanovic R. , Polizzi S. , Bettinelli M. , Speghini A. 
Published: April 2011

ABSTRACTCe3+-doped boro, phospho and borophosphosilicate monolithic glasses (BSG, PSG and BPSG) were prepared by sol-gel method. The inclusion of the glass formers P and B in silica lowered the tendency of rare earth (RE) to segregate as CeO2 with respect to pure SiO2 matrix (SG). In PSG and BPSG, Ce3+ co-ordination to P=O groups was responsible for the inhibition of both CeO2 segregation and oxidation of isolated Ce3+ ions to Ce4+. The better ion dispersion in the host matrix and the stabilization of Ce3+ oxidation state improved PSG and BPSG luminescence properties with respect to BSG and SG.
Molybdenum Dioxide and Vanadium-Doped Molybdenum Dioxide Microcrystals in a Polymer Container.
Authors: Pavel Alexandru C. , Romanovicz Dwight K. , McDevitt John T. 
Published: April 2011

ABSTRACTMolybdenum dioxide and vanadium-doped molybdenum dioxide microcrystals were synthesized by a totally new method involving a redox-active monomer route. The two related dioxides had virtually identical crystal structures and the three precursors used in the process could be subsequently divided in two subgroups of two members each, based on their strong similarities in composition and crystal structure, respectively. Molybdenum trioxide (orthorhombic and hexagonal forms) and the vanadium-doped (10%, molar) molybdenum trioxide (hexagonal form) were used in the redox process with excess pyrrole, and at relatively high temperature (325°C) and long reaction time (12 days), formed a heterogeneous new type of organic-inorganic microcomposite. The new material could be described as a molybdenum dioxide crystal in a polymer box, with the size of the crystallite grain depending on the dimensions of the initial molybdenum trioxide grain and the ratio between the unit cell volumes of the initial and final oxide. The procedure took advantage of the relatively high reduction potentials of the Mo6+and V5+oxide surface centers towards the oxidative polymerization of pyrrole at intermediate temperatures, and the high catalytic activity of the metal cations in the molybdenum trioxide-based materials towards the total oxidation of the carbon atoms in the organic moiety, at elevated temperatures. This new synthetic route offers good perspectives as precursor composites for nanocrystal engineering in practical applications like heterogeneous catalysis, chemical sensing, nanostructured metallic catalysts, etc.
Preparation of Particulate Core-Shell Metal Oxide-Polymer Nanocomposites by a Sol-Gel Approach
Authors: Kickelbick Guido , Holzinger Dieter 
Published: April 2011

ABSTRACTTwo general microemulsion-based routes towards surface-functionalized metal oxide nanoparticles serving as macroinitiators in “grafting from” atom transfer radical polymerization (ATRP), are presented. Metal alkoxides modified with several β-diketone derivatives carrying potential ATRP-initiating sites served as precursors for the particle formation leading in an solgel process to in situ-functionalized titanium-, zirconium-, tantalum-, vanadium-, yttrium-, and iron oxide nanoparticles. The obtained systems were compared with metal oxide nanoparticles prepared by using metal salts as precursors which were functionalized in a second step with ATRP-initiator containing silane coupling agents. The obtained particles had diameters between 5 nm and 640 nm and served as multifunctional polymerization initiators in ATRP using styrene and methyl methacrylate as monomers.