bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monolithically Integrated X-Ray Detector Arrays for Computed Tomography
Authors: Sudharsanan R. , Yoganathan M. , Vakerlis G. , Ferekides C. S. , McCandless B. , Birkmire R. , Deych R. , Luhta R. 
Published: April 2011

AbstractThe design and performance of a high sensitivity monolithic X-ray detector array fabricated by depositing CdTe photodiodes on CdWO4 scintillators for computed tomography (CT) are presented. CdTe photodiodes offer improved sensitivity due to the better match to the CdWO4 scintillator emission spectrum than the Si photodiodes used in current CT scanners. A CdTe photodiode fabricated on glass mechanically stacked to a CdWO4 scintillator showed 30% improvement in signal strength over Si photodiodes stacked to CdWO4-. Monolithic X-ray detector arrays were fabricated by depositing a CdTe photodiode structure on CdWO4 using close-spaced sublimation technique. Preliminary results on the detector's X-ray response, signalto- noise ratio and the X-ray temporal response show that monolithic CdTe X-ray detectors are suitable for practical CT scanner applications.
Material Requirements for a Boron Phosphide Thermal Neutron Counter
Authors: Viles T. P. , Brunett B. A. , Yoon H. , Lund J. C. , Hermon H. , Buchenauer D. , McCarty K. , Clifft M. , Dibble D. , James R. B. 
Published: April 2011

AbstractElectrical characterization (current versus voltage and capacitance versus voltage) of nonstoichiometric amorphous boron phosphide Schottky diodes for neutron detection is presented. These results are incorporated in a Monte Carlo model of detector response to determine material requirements for a boron phosphide neutron counter.
Self-Assembled Multilayers and Photoluminescence Properties of a New Water-Soluble Poly(Para-Phenylene)
Authors: Shi Xiaobo , Li DeQuan , Lütt M. , Fitzsimmons M. R. , Van Patten G. P. 
Published: April 2011

AbstractThis paper reports the synthesis and characterizations of a new water-soluble poly(paraphenylene) (PPP) and its applications in preparing self-assembled multi-layer films. This new water-soluble conducting polymer was prepared through the sulfonation reaction of poly(pquarterphenylene- 2,2'-dicarboxylic acid). The incorporation of sulfonate groups has dramatically improved PPP's solubility in water at a wide pH range, whereas previous PPP is only slightly soluble in basic solutions. Dilute aqueous solutions of this polymer with acidic, neutral or basic pH emit brilliant blue light while irradiated with UV light. The sulfonated PPP emits from 350 nm to 455 nm with a maximum intensity at 380 nm. Self-assembled multilayers of this sulfonated PPP were constructed with a positively charged polymer poly(diallyl dimethyl ammonium chloride) and characterized with various surface analyses. Conductive (RuO2 and ITO), semiconductive (Si wafer), and non-conductive (SiO2) substrates were used in the preparation of self-assembled multilayers. Electrical, optical and structural properties of these novel self-assembled thin films will be discussed.
High E-O Coefficient Polymers Based on a Chromophore Containing Isophorone Moiety for Second-Order Nonlinear Optics
Authors: Chen Jinghong , Zhu Jingsong , Todorova Galina , He Mingqian , Dalton Larry R. , Garner Sean M. , Chen Antao , Lee Sang-Shin , Chuyanov Vadim , Steier William H. 
Published: April 2011

AbstractA high -μβ chromophore APII utilizing isophorone as π-conjugation bridge was processed into both PMMA guest host and crosslinked (XL) polyurethane network with various loading densities. High electro -optic coefficients, r33 = 30 pm/V (in PMMA) and r33 = 32 pm/V (in polyurethane) at 1.06 μm were obtained. Alignment temporal stability ranged from 90 to 120°C for XL polymer network. There is virtually no intrinsic absorption loss at 1.3 μm (solution measurement). Also noteworthy is that high optimum loading densities of this chromophore are attainable in both cases without detectable chromophore aggregation due to intermolecular electrostatic interactions.
Synthesis and Nonlinearity of Triene Chromophores Containing the Cyclohexene Ring Structure
Authors: Ermer Susan , Lovejoy Steven M. , Leung Doris S. , Warren Hope , Moylan Christopher R. , Twieg Robert J. 
Published: April 2011

AbstractA series of conjugated donor-acceptor trienes in which the central double bond is incorporated into an unsaturated isophorone, verbenone or chromone ring has been synthesized. In each case, the donor group consists of an amine and an aromatic or heterocyclic ring system, and the acceptor is the dicyanomethylidene group. The nonlinear optical properties of each of the compounds has been measured and correlated with its structure. The dipole moments and molecular hyperpolarizabilities of these compounds, like those of other conjugated polyenes, are large enough to be used as the active components of electro-optic polymers. Unlike other donor-acceptor polyenes, however, these compounds exhibit the thermal stability required for such applications.
Synthesis of Conjugated Polymers by Vapor Deposition Polymerization
Authors: Hsu Chain-Shu , Lin Ting-Li 
Published: April 2011

AbstractThe synthesis of poly(2,5-thienylene vinylene) and poly(4,7-thianaphthene) by vapor deposition polymerization is presented. 2,5-Di(bromomethyl)thiophene was subjected to vapor phase pyrolysis at 550°C to form a reactive intermediate. Upon condensation, the reactive intermediate polymerized spontaneously at a temperature higher than -25°C to produce poly(2,5-thienylene vinylene). The obtained poly(2,5-thienylene vinylene)s were fractionated into THF soluble and insoluble fractions. The number average molecular weights of the THF soluble fractions range from 1500 to 4000 as determined by GPC measurements. The obtained polymer shows no glass transition and melting point on the DSC scans. Doping of a poly(2,5-thienylene vinylene) film with I2 vapor led to a conductivity of 1 × 10−4 S c−1. In the second part of this study, 2,3-diethynylthiophene was subjected to vapor phase pyrolysis at 300°C to yield a reactive intermediate, 4,7- dehydrothianaphthene. Upon condensation, the obtained 4,7-dehydrothianaphthenene was polymerized spontaneously at a temperature higher than -25°C to produce poly(4,7-thianaphthene). The obtained poly(4,7-thianaphthene) was insoluble in common laboratory solvents and shows also no melting point and glass transition on the DSC scans.
Design of Flat Panel Displays Based on Organic Light Emitting Devices
Authors: Gu G. , Burrows P. E. , Forrest S. R. 
Published: April 2011

AbstractWe provide a systematic and quantitative analysis of the design of flat panel displays (FPDs) based on organic light emitting devices (OLEDs). Key performance parameters are estimated for OLED-based displays; system issues, including addressing schemes and strategies required to achieve full color displays, are treated quantitatively. Furthermore, addressing schemes for recently demonstrated, full color, high resolution stacked OLEDs are discussed. Our analysis shows that OLED technology is suitable for many FPD applications, and can provide performance superior to that achieved using alternative display technologies.
Synthesis and Incorporation of Thienylene Vinylene Oligomers in Main-Chain Copolymers
Authors: Madrigal L. G. , Elandaloussi E. H. , Spangler C. W. 
Published: April 2011

AbstractPoly [2,5-thienylene vinylene] (PTV) has been studied extensively over the past decade for both its metallic conductivity behavior upon chemical doping, as well as its interesting third order nonlinear optical properties. PTV oligomers have been synthesized by our group 1, as well as others 2, and the formation of polaron-like radical-cations or bipolaron-like dications by oxidative doping has been demonstrated. In this paper we describe a general synthetic approach to PTV oligomers functionalized for copolymer formation by step-growth reaction.
Femtosecond Pump and Probe Spectroscopy on Poly(Para-Phenylenes)
Authors: Graupner W. , Cerullo G. , Kranzelbinder G. , Lanzani G. , Stagira S. , Nisoli M. , Silvestri S. De , Leising G. 
Published: April 2011

AbstractWe studied the sub-picosecond dynamics of photoexcitations in methyl-substituted poly(para--phenylene)-type ladder polymer (m-LPPP) films in a wide excitation density range up to values typical for the regime of narrow band emission by pump-probe spectroscopy. The singlet excitons relaxation dynamics, monitored at the stimulated emission (SE) peak at 2.53 eV, showed an intensity dependent ultrafast decay component, which occurs on a sub-picosecond time scale, ascribed to the onset of amplified spontaneous emission (ASE). In addition we identified photoinduced absorption (PA) bands of singlet excitons at 1.48 eV and polarons at 1.9 eV respectively. At high excitation density an additional absorption band becomes evident at 2.63 eV.
Optical Characterization of C60 Organic Semiconductor and Bilayers
Authors: Rainho J. P. , Santos L. , Kharlamov A. A. 
Published: April 2011

AbstractPreparation and characterization either by optical absorption, photoluminescence and micro-Raman spectroscopy of individual components as well as bilayers consisting of organic dye semiconductor Zinc Phthalocyanine (ZnPc) and fullerene, C60, thin films are reported. The layers and structures were deposited in vacuum and some fullerene films were also prepared by casting the C60 solution in benzene. The optical absorption and photoluminescence dependencies on film thickness in bilayers C60/ZnPc were observed and may be discussed in a context of interface induced simmetry reduction of C60 molecules.
Hillock Growth at the Surface of Pt/TiN Electrodes for Ferroelectric Capacitors During Annealing in N2/O2 Ambient
Authors: Miura H. , Kumagai Y. , Fujisaki Y. 
Published: April 2011

ABSTRACTThe hillock growth mechanism at the surface of Pt/TiN electrodes is investigated. TEM and SEM observations confirm that local delamination occurs at the Pt/TiN interface first, and then, plastic deformation of the Pt films under compressive stress forms hollow domes, which result in hillocks. Hillocks always start to grow when the internal stress in the Pt films reaches about −1000 MPa during annealing in N2/O2 ambient. Since the initial internal stress of Pt thin films varies from −500 to 500 MPa, depending on their deposition temperature, the hillock growth temperature strongly depends on the deposition temperature of the Pt films. It is very important, therefore, to control the initial internal stress in Pt films in order to eliminate hillock growth at the surface of Pt/TiN electrodes.
Crystallization and Electrical Properties of Bi4TiO12 Films Derived from Bismuth Acetate and Bismuth Nitrate Precursor Solutions
Authors: Kim Chang Jung , Chung C. W. , Lee Kyu Sang 
Published: April 2011

ABSTRACTFerroelectric Bi4Ti3O12 thin films were prepared by the sol-gel method to examine the effect of precursors on the variation of ferroelectric properties. Two kinds of Bi4Ti3O12 sol-gel precursor solutions were synthesized by dissolving bismuth acetate and bismuth nitrate in glacial acetic acid and then adding titanium acetate. The films were deposited on Pt coated Si substrates by the spin-coating method and crystallized by double heat-treatment. The Ps, the Pr, and the Ec values of the film derived from the Bi-acetate were 34.8 μC/cm2, 16.2 μC/cm2, and 128 kV/cm, respectively. The Ps, the Pr, and the Ec of the films from the Bi-nitrate were 14.2 μC/cm2, 5.7 μC/cm2, and 105 kV/cm, respectively. The Bi4T3O12 films prepared from the Bi-acetate revealed better ferroelectricity and resistivity compared to those obtained from the Bi-nitrate.
Large Area PbZr1−xTixO3 (PZT) Thin Films Deposited by MOCVD Processes
Authors: Li Tingkai , Hartford Elliot , Zawadzki Pete , Stall Richard A. 
Published: April 2011

ABSTRACTAn advanced oxide MOCVD tool and processes have been developed to deposit large area PbZr1−xTixO3 (PZT) thin films on 6” Si and Pt/Ti/SiO2/Si substrates. The experimental results show the advanced oxide MOCVD tool can achieve the growth of PZT thin films with thickness uniformity of 2% and composition uniformity better that 3% on both 6” Si and Pt/Ti/SiO,/Si wafers at high deposition rates. X-ray patterns showed a single PZT perovskite phase, and AFM showed homogeneous microstructure and low surface roughness. Typically, 300 nm thick PZT films with a grain size about 0.3 μm have Pr greater than 20 - 30 μC/cm2 at 5V, a dielectric constant around 1000, low coercive field (Ec 50 - 70 kV/cm), and fatigue rate (the normalized polarization is about 0.6 after 1010 cycles at 5 V), and leakage current of 2 - 6×lO−7 A/cm2 at 150 kV/cm and room temperature on Pt electrodes. In addition, the effects of reactor design and process conditions on the thickness and composition uniformity, as well as the m i ero structure and properties were also investigated.
A Study on the Improvement of Characteristics of BST Thin Films Fabricated on Iridium Electrode
Authors: Kil Deok-Sin , Lee Byung-Il , Joo Seung-Ki 
Published: April 2011

ABSTRACTBST thin films have been fabricated by RF magnetron sputtering onto Ir layer as a bottom electrode. When the substrate temperature was maintained at 600 °C during deposition, BST films deposited at that temperature showed very small oxide equivalent thickness of 0.36nm as well as very low leakage current density of about 10−8A/cm2at 1.5V. But as substrate temperature was increased to 700 °C in order to obtain high dielectric constant, oxide equivalent thickness exhibited very low value of about 0.3nm, however, leakage current density drastically increased to 10−4/cm2. BST thin films were fabricated by two step process, which consists of bottom layer deposited at high substrate temperature of 700 °C and top layer deposited at low substrate temperature. In the case of BST thin films which are composed of 20nm thick bottom layer deposited at 700 °C and 30nm thick top layer deposited at 500 °C, we obtained very small oxide equivalent thickness of 0.31nm and low leakage current density of 4 × 10−8A/cm2. at 1.5V.
Sol-Gel Synthesis of Epitaxial Films of (Sr,Ba)Bi2(Nb,Ta)2O9 and Bi4Ti3O12 on [100] SrTiO3
Authors: Morrell Jonathan S. , Xue Ziling B. , Specht Eliot D. , Beach David B. 
Published: April 2011

ABSTRACTAn all-alkoxide sol-gel process utilizing methoxyethoxide complexes in 2-methoxyethanol was used to prepare epitaxial films of SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9, BaBi2Ta2O9, and Bi4Ti3O12 on [100] oriented SrTiO3 single crystals. Films were prepared by spin coating strontium titanate substrates with partially hydrolyzed alkoxide solutions and firing in air at 850 °C for 20 minutes. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002ℓ] reflections. In-plane orientation was determined by pole figures and phi-scans about the [105] plane in the case of the (Sr,Ba)Bi2(Nb,Ta)2O9 complexes and the [117] plane in the case of Bi4Ti3O12. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.
New Type of Advanced Catalytic Material Based Upon Alumina Epitaxially Grown onto Thin Alumina Foil
Authors: Tikhov S. F. , Chernykh G. V. , Sadykov V. A. , Salanov A. N. , Tsybulya S. V. , Alikina G. M. , Lysov V. F. 
Published: April 2011

ABSTRACTFormation of planar layered Al2O3/Al composites via aluminum foil anodic-spark oxidation was studied by using SEM and XRD. A lateral growth of the primary non-porous alumina islands was shown to proceed to an extent where the entire surface was covered, and this layer is responsible for determining the high thermal stability of composite. A washcoating by an alumina suspension substantially increases pore volume and water absorption capacity. Catalysts based on the platinum group metals and transition metal oxides exhibit high activity for the reactions of CO and hydrocarbon oxidations and the selective reduction of nitrogen oxides by hydrocarbons.
Photoconductivity of Diamond-Like Carbon
Authors: Hie A. , Conway N. , Kleinsorge B. , Rattier M. , Robertson J. , Milne W. I. 
Published: April 2011

ABSTRACTWe have studied the photoconductivity in pure tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H). Good photoconductive properties are demonstrated for ta-C:H, showing that the hydrogenated form of ta-C is of a higher electronic quality. Transport and recombination parameters are derived. Ta-C:H are low mobility solids with a μτ product of the order of 10−12 cm2 V−1 and a recombination time τr of about 10−7 s. At low energy excitation, the photoconductivity shows a sublinear dependence on the light intensity over a wide temperature range. The relationship between the photoconductivity and the density of spin defect centers is discussed. UV light is used to excite carriers into the extended states. Competitive recombination centers may be involved at high excitation energy.
Optical & Electronic Properties of Carbon Nitride Thin Films
Authors: Chhowalla M. , Aharonov R. A. , Akiyama M. , Amaratunga G. A. J. 
Published: April 2011

ABSTRACTWe have deposited carbon nitride (CNx) films by magnetron sputtering at varying nitrogen pressures and substrate temperatures. The films were deposited on silicon and quartz substrates simultaneously. The incoming ion energy was controlled by a radio frequency power supply. A magnet in front of the substrate holder was used to enhance the plasma density. The films deposited at room temperature (RT) were found to have nitrogen content of ≥ 40%. These films were semiconducting with an optical bandgap of greater than 2 eV and a RT resistivity of 1012 Ω-cm. Films deposited at low nitrogen pressure (< 7 mtorr), at RT and in the presence of a 15 mtesla magnetic field were found to be hard and also exhibited extremely high elastic recovery. The most interesting result we found was that the hard and elastic CN films were also semiconducting with an optical band gap of 1.7 eV, RT resistivity of 107 Ω-cm and an activation energy of 0.8 eV. In all cases the CN films were almost entirely sp2 bonded.
Ab Initio Investigation of the High Pressure Elasticity of Mg2SiO4 Forsterite and Ringwoodite
Authors: Stixrude Lars , Wentzcovitch R. M. , Da Silva C. , Kiefer B. 
Published: April 2011

ABSTRACTWe discuss the behavior of two minerals of the same composition, Mg2SiO4 but different structures: forsterite and ringwoodite. Ab initio plane-wave pseudopotential results are discussed in terms of the full elastic constant tensors of these phases and their elastic anisotropy. The structures of the two minerals, based on pseudo-hep and pseudo-fee packing of oxygens, respectively, show very different behavior at high pressure. While the elastic anisotropy of olivine depends weakly on pressure between 0 and 25 GPa, the anisotropy of ringwoodite decreases with pressure initially, vanishing at 17 GPa before increasing again at higher pressure. This unusual behavior is understood in terms of a change of sign of the combination of elastic constants c2+2c44-c11, and a resulting interchange of fast and slow directions of acoustic wave propagation. To gain insight into the origin of their elastic behavior, the ab initio results are compared with a simple model based on the O sub-lattice.
Growth of Diamond Anvils for High-Pressure Research by Chemical Vapor Deposition
Authors: Israel Andrew , Vohra Yogesh K. 
Published: April 2011

ABSTRACTGem quality diamond crystals are employed as anvils in high-pressure diamond cell research. Homoepitaxial growth experiments by microwave plasma-assisted chemical vapor deposition (MPCVD) have produced 1.76 mm (diameter) by 0.65 mm (thickness) sized diamonds. We report fundamental studies on diamond growth rate and quality as a function of reactor pressure and methane concentration, in a hydrogen plasma. By varying the growth conditions, large, single crystal diamond can be produced, which is ideal for manufacturing high pressure anvils.Traditional high pressure, high temperature (HPHT) techniques for production of synthetic diamond anvils are extremely expensive and chemical vapor deposition (CVD) provides an economically viable alternative. We report diamond growth rates up to 0.32 mg/hr, which are comparable to HPHT growth rates, and crystal quality approaching that of gem diamond. When perfected, diamond anvils produced from chemical vapor deposition methods could replace those manufactured by high pressure, high temperature synthesis.
Use of Hardness Indentation Coupled with Micro-Raman Spectroscopy in High-Pressure Materials Research
Authors: Kailer A. , Gogotsi Y. G. , Nickel K. G. 
Published: April 2011

ABSTRACTHigh-pressure phase transformations occurring in materials are important for a wide range of problems in materials science and engineering. Most of the results in this field have been obtained using high-pressure cells.In this work, we demonstrate that high-pressure phase transformations also take place during mechanical contact of hard solid materials. These solid-state transformations can be studied by simply combining hardness indentation tests with micro-Raman spectroscopy. In contrast to diamond anvil cell (DAC) experiments, the stress conditions during mechanical contacts are highly non-hydrostatic, i.e. very high shear stresses affect the transformation behavior. Nevertheless, the obtained results can be discussed in the light of the phase transformations as known from DAC experiments. The examples of our research presented here include Si, Ge, SiO2 and ZrO2, and show that phase transformations and amorphization at mechanical contacts are a quite common phenomenon, which has important implications.
A New Pressure Induced Phase in Silica
Authors: Chelikowsky J. R. , Wentzcovitch R. M. , Da Silva C. , Binggeli N. 
Published: April 2011

ABSTRACTWe predict a new pressure induced phase for silica via first principles variable-cell-shape molecular dynamics. The structure results from annealing a-quartz at pressures near a phonon instability. The mechanism which produces this new phase is similar to that proposed for structural transitions in silicate melts. The diffraction pattern of the new phase compares favorably with that of the unidentified intermediate crystal phase found in silica near the pressure induced amorphization transformation.
Image Plate X-Ray Diffraction Study of Distorted FCC Phase in Rare Earth Metals at High Pressures
Authors: Beaver Steven , Chesnut Gary N. , Vohra Yogesh K. 
Published: April 2011

ABSTRACTA high-pressure phase of gadolinium is completely described for the first time. This phase, HR24, is found to exist at 46 GPa. The structure is examined for evidence of delocalization of the f shell, and the evolution of the HR24 phase with increasing pressure is discussed.
Shock-Induced Defects in Bulk Materials
Authors: Gray George T. 
Published: April 2011

ABSTRACTIn this paper examples of the shock-induced defects produced during shock compression which correlate with microstructure / mechanical property changes induced in materials due to shock prestraining are discussed. The characteristics of the shock impulse(peak shock pressure, pulse duration, and rarefaction rate) imparted to the material under investigation and the shock-induced defects produced in numerous metals and alloys are compared with their deformation behavior at ordinary rates of deformation. Examples of the range of defects observed in shock-recovered metals and alloys, include: dislocations, deformation twins, point defects, and residual metastable remnants from pressure-induced phase transformations. Results concerning the influence of interstitial content on the propensity of ω-phase formation and its structure in high-purity and A-70 Ti are presented. The influence of shock-wave deformation on the phase stability and substructure evolution of high-purity (low-interstitial) titanium and A-70 (3700 ppm oxygen) titanium were probed utilizing real-time velocity interferometry (VISAR) and “soft” shock-recovery techniques. Suppression of the α-ω pressure-induced phase transformation in A-70 Ti, containing a high interstitial oxygen content, is seen to simultaneously correspond with the suppression of deformation twinning.