bluuebunny/crossref_metadata_2025_split huggingface dataset:
A mesoscale strength model for silica-filled PDMS
Authors: Hanson D. E. 
Published: April 2011

ABSTRACTWe present a mesoscale model that describes the tensile stress of silica-filled polydimethylsiloxane (PDMS) under elongation. Atomistic simulations of a single chain of PDMS, interacting with itself and/or a hydroxylated silica surface provide estimates of the microscopic forces required to stretch or uncoil a chain of PDMS, or detach it from a silica surface Using these results, we develop a mesoscale, inter-particle strength model for uncrosslinked, silica-filled PDMS. The strength model includes these atomistic forces, as determined from the simulations, a small entropic component, and a Gaussian probability distribution to describe the distribution of chain lengths of PDMS strands connecting two silica particles and the chain lengths in the free ends. We obtain an analytic stress/strain expression whose predictions agree with experiment.
Fractal Shape Analysis of Tire Debris Particles: Preliminary Results and Applications
Authors: Camatini Marina , Crosta Giovanni F , Corbetta Gaia M , Ottin-Bocat Mara , Ambrosio Stefano , Giuliani Gianpaolo , Cencetti Simone , Regazzoni Claudia 
Published: April 2011

ABSTRACTParticles of tread rubber debris produced by laboratory wear tests are imaged by light microscopy. The fractal dimension, DF, of the image perimeter is estimated. The sensitivity of DF with respect to the image acquisition and processing parameters is determined. Particles belonging to two types of undifferentiated debris, low severity (LS) and rasping (R), respectively, are analyzed. The values of DF have distributions, which, if suitably interpreted, allow the identification of either debris type with the following conditional probabilities: pLS|LS = 0.71 and pR|R = 0.81. The procedure can be eventually applied to environmental impact studies.
Design of pH Sensitive Materials for On/Off Release of Thrombolytic and Anticoagulant Drugs
Authors: Thornton Angela M. , Brazel Christopher S. 
Published: April 2011

AbstractAn experimental study was conducted to determine the mechanisms of transport for delivery of cardiovascular agents using a pH-sensitive hydrogel as the carrier. Copolymer gels based on hydrophilic (2-hydroxyethyl methacrylate) and polybasic (N,N-diethylaminoethyl methacrylate) monomers were formed as membranes and analyzed for their potential to control the diffusion of model solutes as well as heparin and streptokinase. The polybasic materials were selected because they would allow drug delivery to be triggered by microenvironmental pH fluctuations around the site of a blood clot. In slightly basic solutions, the polymers remained in a thermodynamic state of phase-separation, while the polymer absorbed more solution and the mesh size increased once the pH was less than the pKb of the polybasic moiety. The hydrogels' equilibrium swelling ratios were determined as a function of pH, and the mesh sizes were determined by rubber elasticity measurements. Diffusion of model solutes, as well as heparin, was studied using side-by-side diffusion cells to determine the influence of gel morphology and mesh size on the screening of the solutes. Streptokinase release from these gels was modulated by environmental pH.
Microstructural Characterization of Polyanhydride Blends for Controlled Drug Delivery
Authors: Shen Elizabeth E. , Chen Hsin-Lung , Narasimhan Balaji 
Published: April 2011

AbstractThis research examines the microstructure of polyanhydride blends for use in drug delivery devices. Atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) studies were performed on the homopolymers and blends of the polyanhydrides poly(1,6-carboxyphenoxy hexane) (CPH) and poly(sebacic anhydride) (SA). AFM of the CPH/SA blends 20:80, 50:50, and 80:20 showed distinct patterns indicating spinodal decomposition and phase separation on the micron-scale. Because it has been shown that incorporated drugs will thermodynamically partition into phase-separated domains depending on their hydrophobicity, polyanhydride blends will be able to encapsulate larger bioactive compounds including nucleotides, proteins, and vaccines. Preliminary SAXS studies of the CPH/SA blend systems provide information on the crystalline morphology of the polymer. A peak shift to a lower q from poly(SA) to the blends indicates that the poly(CPH) is incorporated into and causes swelling of the interlamellar amorphous regions of poly(SA).
Functional Recovery Following Spinal Cord Hemisection Mediated by a Unique Polymer Scaffold Seeded with Neural Stem Cells
Authors: Lavik Erin , Teng Yang D. , Zurakowski David , Qu Xianlu , Snyder Evan , Langer Robert 
Published: April 2011

AbstractA dual scaffold structure made of biodegradable polymers and seeded with neural stem cells has been developed to address the issues of spinal cord injury including axonal severance and the loss of neurons and glia. The general design of the scaffold is derived the structure of the spinal cord with an outer section which mimics the white matter with long axial pores to provide axonal guidance and an inner section seeded with neural stem cells to address the issues of cell replacement and mimic the general character of the gray matter. The seeded scaffold leads to improved functional recovery as compared with the lesion control or cells alone following spinal cord injury.
Tunable Optical Gain from Soluble Thiophene-Based Oligomers
Authors: Anni M. , Gigli G. , Zavelani-Rossi M. , Gadermaier C. , Lanzani G. , Barbarella G. , Favaretto L. , Cingolani R. 
Published: April 2011

ABSTRACTTunable optical gain is demonstrated, through pump and probe measurements, in spin coated neat films of soluble S,S-dioxide oligothiophenes with different functionalization pattern. The molecular functionalization with alkyl and aryl groups allows us to obtain photoluminescence efficiency up to 70%, good chemical stability, high solubility and tunable gain along the visible range from 470 nm to 660 nm. The gain cross section is up to 9*10-18 cm2. The gain relaxation dynamic is studied through time resolved pump and probe measurements. A comparison with some of the best organic materials for laser application is presented. From these results we conclude that thienyl-S,S-dioxide oligothiophenes are interesting materials for applications to organic lasers and amplifiers.
The Effect of Surface Preparation on the Structure and Electrical Transport in an Organic Semiconductor
Authors: Kosbar Laura L. , Dimitrakopoulos Christos D. , Mascaro Debra J. 
Published: April 2011

ABSTRACTSelf-assembled monolayers (SAMs) with a variety of structures and terminal groups were evaluated as underlayers for pentacene deposition. It was found that the most critical factor in the formation of highly oriented thin film pentacene with large grain size was the geometric structure of the monolayer. Monolayers with terminal bonds parallel to the surface produce large pentacene grains with an angular rather than the dendridic structure normally observed on octadecyltrichlorosilane (OTS) coated substrates. The grain size, X-ray scattering, carrier mobility, and current on/off ratios are all improved with monolayers of the appropriate geometry.
The First Example of a Polythiophene Bearing Fused Tetrathiafulvalene Units
Authors: Skabara Peter J. , Roberts Donna M. , Ray Asim K. , Umare Suresh S. , Hassan Aseel K. , Nabok Alexey V. , Müllen Klaus 
Published: April 2011

ABSTRACTThe polymerization of a fused 2,5-dibromothieno-TTF derivative by Yamamoto procedures gave a highly electroactive polymer; doping the material with TCNQ increased the conductivity of the polymer by approximately two orders of magnitude.
Polarized Electroluminescence in Double Layer LEDs with Perpendicularly Oriented Polymers
Authors: Bolognesi A. , Botta C. , Facchinetti D , Jandke M. , Strohriegl P. , Kreger K. , Blumstengel S. 
Published: April 2011

ABSTRACTWe have prepared and characterized a light emitting diode (LED) with the active film formed by two polymers emitting in two different regions: in the yellow-green and in the red range of the visible spectrum. The two polymers are polyparaphenylenevinylene (PPV) and poly[3-(6-methoxyhexyl)thiophene] (P6OMe) respectively. P6OMe was spin coated on a PPV layer previously oriented and was also oriented by means of the rubbing technique in the direction perpendicular to the PPV orientation. The polarized electroluminescence obtained from this device shows yellow-green emission from PPV, or red from P6OMe depending on the orientation of the analyzer.
Synthesis and Characterization of Poly(N-alkyl-2,7-carbazole)s: Blue Light-Emitting Materials
Authors: Morin J.-F. , Leclerc M. , Lévesque I. , D'Iorio M. 
Published: April 2011

ABSTRACTThe synthesis of a new class of π-conjugated based on N-alkyl-2,7-carbazole is reported. Two different synthetic pathways were used to obtain 2,7-functionalized carbazole units. The first pathway leads to N-alkyl-2,7-dichlorocarbazole which undergoes a Yamamoto coupling to obtain the homopolymer. The second synthetic method provides N-alkyl-2,7-diiodocarbazole. This monomer allows the utilization of more versatile synthetic tools such as Suzuki and Stille couplings to obtain highly regioregular copolymers. Poly(N-(2-ethylhexyl)-2,7-carbazole) (PEHC) prepared using Yamamoto coupling shows strong pure blue photoluminescence (437 nm) and electroluminescence (432 nm, 225 cd/m2) with no excimer formation.
Silole Derivatives with a High and Non-dispersive Electron Mobility, and a 100 % Photoluminescence Quantum Efficiency
Authors: Murata H. , Malliaras G. G. , Uchida M. , Shen Y. , Kafafi Z. H. 
Published: April 2011

ABSTRACTNon-dispersive and fast electron transport was realized for an amorphous, vapor deposited film of 2,5-bis(2',2''-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene in ambient and inert atmospheres. An electron mobility of 2×10−4cm2/Vs was measured by time-of-flight at an electric field of 6×105V/cm. This mobility is more than two orders of magnitude larger than that of the most widely used electron transporter, tris(quinolin-8-olato) aluminum (III), in molecular organic light-emitting devices (MOLEDs). Another silole derivative, namely 1,2-bis (1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl)ethane, exhibits bright fluorescent blue-green light with an absolute quantum yield close to 100 % in the solid state. MOLEDs composed of stacked neat films of these two silole derivatives and a hole transporter show a significantly low operating voltage and an external quantum efficiency of 4.8 %, close to the theoretical limit.
Role of Surfaces and Interfaces for the Electronic Properties of Conducting Oxides
Authors: Klein Andreas 
Published: April 2011

ABSTRACTTransparent conductive oxides (TCOs) are generally considered as degenerate semiconductors doped intrinsically by oxygen vacancies and by intentionally added dopants. For some applications a high work function is required in addition to high conductivity and it is desired to tune both properties independently. To increase the work function, the distance between the Fermi energy and the vacuum level must increase, which can be realized either by electronic surface dipoles or by space charge layers. Photoelectron spectroscopy data of in-situ prepared samples clearly show that highly doped TCOs can show surface band bending of the order of 1 eV. It is further shown that the band alignment at heterointerfaces between TCOs and other materials, which are crucial for many devices, are also affected by such band bending. The origin of the band bending, which seems to be general to all TCOs, depends on TCO thin film and surface processing conditions. The implication of surface band bending on the electronic properties of thin films and interfaces are discussed.
A Combinatorial Approach to TCO Synthesis and Characterization
Authors: Perkins John , Readey Dennis , Alleman Jeff , del Cueto Joe , Li Xiaonan , Coutts Tim , Stauber Renaud , Duncan Chris , Young David , Parilla Phil , Keyes Brian , Gedvilas Lynn , Balzar Davor , Wang Qi , Ginley David 
Published: April 2011

ABSTRACTWe have developed the deposition, characterization and analysis tools necessary for a combinatorial approach to thin film metal oxides, with a special focus on transparent conducting oxides (TCOs). We are presently depositing compositionally graded libraries using mutli-target sputtering and CVD. The initial collection of characterization tools includes UV/VIS/NIR transmission/reflection, FTIR reflectance, Raman scattering, 4-point conductivity, thickness, xray diffraction and electron microprobe. In addition to allowing for a more complete empirical optimization of TCO properties, we expect to develop an improved basic understanding of TCOs, especially in the area of p-type TCOs. This paper provides an overview of our current combinatorial material science program as applied specifically to TCOs.
An X-ray Diffraction Investigation of Tin Oxide Deposition and Annealing
Authors: Robbins Joshua J. , Huang Yen-Jung , Bai Mailasu , Vincent Tyrone , Wolden Colin A. 
Published: April 2011

ABSTRACTTin oxide thin films were deposited by plasma-enhanced chemical vapor deposition (PECVD) for applications as a transparent conductor. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to quantify the crystal structure and morphology of these films both as-deposited and after annealing conditions. Annealing was performed in an argon environment as a function of time and temperature. Although annealing was found to significantly improve electrical properties, the structure as measured by XRD remained largely unchanged. Hall effect measurements show that the improvements in resistivity are due to increases in carrier concentration. XRD did reveal that films deposited on the powered electrode had a film orientation that was distinctly different than films deposited on the grounded electrode. These changes suggest the importance of ion bombardment energy. The structural changes were correlated with improved electrical properties.
A Theoretical Study of p-Type Doping of ZnO: Problems and Solutions
Authors: Yan Yanfa , Zhang S.B. , Pennycook S.J. , Pantelides S.T. 
Published: April 2011

ABSTRACTWe present results of a comprehensive set of first-principles total-energy calculations of native and impurity-defect complexes in ZnO and use these results to elucidate the problems that occur in efforts to achieve p-type doping. The analysis naturally leads to new approaches that are likely to overcome the difficulties. The results provide detailed explanations of recent puzzling observations made in attempts to produce p-type ZnO.
Deep-UV Transparent Conductive β-Ga2O3 Film
Authors: Orita Masahiro , Ohta Hiromichi , Hirano Masahiro , Hosono Hideo 
Published: April 2011

ABSTRACTDeep ultraviolet transparent and electrical conductive β-Ga2O3 film was prepared on SiO2 glass substrate. The film had electric conductivity of 1 Scm−1, carrier density of 1.4 × 1019cm−3 and mobility of 0.44 cm2V−1s−1. Internal transmittance at wavelength of 248 nm exceeded 50 %. Conductivity was enhanced at an oxygen pressure less than 10−4 Pa, and transparency appeared at a substrate temperature over 800 °C.
Structural, Optical, and Electron Transport Qualities of Zinc-Stannate Thin Films
Authors: Young David L. , Coutts Timothy J. , Williamson Don L. 
Published: April 2011

ABSTRACTSingle-phase, spinel zinc stannate (ZTO = Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10−2 -10−3 ωcm, mobilities of 16 - 26 cm2/V-s, and n-type carrier concentrations in the low 1019 cm−3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. 119Sn Mössbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn+4. A pronounced Burstein-Moss shift moved the optical bandgap from 3.35 eV to as high as 3.89 eV.Density-of-states effective mass, relaxation time, mobility, Fermi energy level, and a scattering parameter were calculated from transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 me as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. First-order nonparabolic conduction-band theory was applied to extrapolate a bottom-of-the-band effective mass of 0.15 me. Calculated scattering parameters and temperature-dependent transport measurements correlated well with ionized impurity scattering with screening by free electrons for highly degenerate films.
Niobate Films for Microwave Applications
Authors: Cho C.-R. , Koh J.-H. , Grishin A.M. , Abadei S. , Gevorgian S. 
Published: April 2011

ABSTRACTSubmicron thick niobate films, Na0.5K0.5NbO3 (NKN) and Ag0.9Ta0.42Nb0.58O3-δ (ATN), have been pulsed laser deposited on MgO, Pt80Ir20, and Si substrates for microwave device applications. Strong bi-axial (001)-(011) texture observed in both films on MgO substrates indicates that there are major similarities in the growth mechanisms in these films. The dielectric permittivity ε′ of NKN film increases monotonously with temperature, while that of ATN shows a weak temperature dependence (about 21% of variation) in a wide temperature range from 77 K to 400 K. Measured tunability Δε′/ε′ and dielectric loss tanδ for niobate/MgO interdigital capacitors have been found to be (Δε′/ε′)NKN = 40%, tanδNKN = 1.4-2.3% and (Δε′/ε′)ATN = 4.3%, tanδATN = 0.23-0.25% at 1 MHz under maximum electric field of 100 kV/cm. Microwave spectroscopy studies for NKN/Si varactors show (Δε′/ε′)NKN/Si of 13% and tanδNKN/Si = 1.2-6.6% at 40 GHz @ 200 kV/cm.
Thin PZT Film Pressure Microsensor
Authors: Khartsev S.I. , Grishin M.A. , Nilsson Kenth , Grishin A.M. 
Published: April 2011

ABSTRACTWe report on a ferroelectric film pressure sensor fabricated on the top of 4 mm long and 1.4 mm in diameter Pt80Ir20 (PtIr) rod-shaped tip. It consists of a PZT(0.5μm)/LSMO(0.1μm) film heterostructure, deposited by pulsed laser ablation of stoichiometric ceramic targets PbZr0.52Ti0.48O3 and La0.67Sr0.33MnO3, and a circular, ø= 1.2 mm, Au electrode on the top of the PZT film. The Au/PZT/LSMO/PtIr thin-film capacitor demonstrates good ferroelectric properties: dielectric constant of 762 and loss tanσ =0.008 @ 5 kHz, induced polarization as high as 32 μC/cm2 at electric field of 250 kV/cm. Piezoelectric test, performed in a hydrostatic pressure chamber, exhibits the piezoelectric constant to be as high as 67 pC/N. This is 20% higher than 56 pC/N shown by a polarized bulk PZT sensor fabricated from the ceramics used as the target in the pulsed laser deposition process. Such an increase of the piezoelectric constant we attribute to the preferential (001) orientation of the PZT film grown on the PtIr bulk substrate. The resolution of the thin PZT film pressure microsensor was found to be about 1 mbar.
Computer Modeling of Luminescence in ABO3 Perovskites
Authors: Eglitis R. I. , Kotomin E. A. , Borstel G. 
Published: April 2011

ABSTRACTWe suggest theoretical interpretation to a long-debated discussion on a nature of the intrinsic “green” luminescence observed in many ABO3 perovskites. For this purpose we performed quantum chemical calculations using the Intermediate Neglect of the Differential Overlap combined with the Large Unit Cell periodic model. Triplet exciton which is very likely responsible for the “green” luminescence is shown to be in a good approximation a pair of nearest Jahn-Teller electron and hole polarons (a bipolaron).
Analysis of Tungstates and Sesquioxides, Two of the Best Yb3+-Doped Laser Crystals According to Different Evaluations.
Authors: Boulon Georges , Brenier Alain , Laversenne Laetitia , Guyot Yannick , Goutaudier Christelle , Cohen-Adad Marie-Thérèse , Métrat Gérard , Muhlstein Noelle 
Published: April 2011

ABSTRACTThe development of reliable InGaAs laser diode pump sources emitting in the 900-980 nm spectral range is stongly influencing the field of lasers based on Yb3+-doped solid state crystals. Ca5(PO4)3F (C-FAP) and S-FAP (Sr5(PO4)3F) were soon recognized to be favourable hosts for Yb3+ lasing in the nanosecond pulse regime. This fact was supported by an evaluation of the spectroscopic properties of several Yb3+-doped crystals useful for laser action. This evaluation is based on two parameters known from spectroscopy, the emission cross-section at the laser wavelength and the minimum pump intensity required to achieve transparency at the laser wavelength.We think there is a need of a new evaluation of Yb3+-doped crystals in order to predict the laser efficiency in a more realistic manner in different kinds of regimes. We present here the main spectroscopic properties of two Yb3+-doped laser crystals which are grown in our Group: (i) KY(WO4)2 double tungstates by the Floating Crystal method and (ii) Y2O3sesquioxides by the Laser Heated Pedestal Growth method. The approach, based on a quasi-three level laser model, leads to compare all known Yb3+-doped crystals in a two-dimensional diagram considering the laser extracted power and the slope efficiency. We shall show that tungstates and sesquioxides belong to the highest laser crystal potential in CW-end pumping configuration.
High Pressure Studies of Sm2+-Doped Sol-Gel Glasses
Authors: Costa Vilma C. , Shen Yongrong , Bray Kevin L. , Santos Ana M. M. 
Published: April 2011

ABSTRACTGlasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 were prepared from metal alkoxide solution using the sol-gel process. After low temperature heat treatment in air, the glasses were heated up to 800 °C under a flowing H2 atmosphere to reduce Sm3+ into Sm2+. Samarium ions in the divalent and trivalent states were identified by fluorescence measurements. The fluorescence properties of Sm2+ions are discussed in relation to concentration of Sm2O3 and the glass matrix composition. Preliminary results of pressure studies on the luminescence spectra and lifetime of Sm2+ in the glasses are presented as well.
InGaAs-InP Quantum Wire Stark Effect Modulators: Effect of Wire Width in the Optimization of Changes in Excitonic Absorption and Index of Refraction
Authors: Xu M. , Huang W. , Jain F. 
Published: April 2011

ABSTRACTQuantum wire/dot modulators offer superior performance over their quantum well counterpart due to enhanced excitonic binding energy. This paper presents simulations on InGaAs-InP quantum wire Stark effect optical modulators showing a novel trend. While the excitonic binding energies and absorption coefficients increase as the width of the wire is decreased, the refractive index change Δn is maximized at a wire width depending on the magnitude of the applied electric field. For example, Δn is maximized at a width of about 100Å for an external electric field of 120kV/cm in an InGaAs quantum wire. This behavior is explained by considering the opposing effects of the wire width on binding energy and changes in the electron-hole overlap function in the presence of an external electric field. Practical InGaAs-InP modulators using V-groove structures are also presented.