bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of Phase Transformation During Homogenization of Ternary Aluminum Alloys
Authors: Hofmeister Thorsten , Greven Klaus , Ludwig Andreas , Sahm Peter R.
Published: April 2011

The microstructure determines for the most part mechanical properties of castings. This is the case especially with age-hardening aluminum alloys. To predict the phase transformation in cast parts during and after solidification a sophisticated approach to a coupled modeling of various simulation phenomena is presented. This approach couples a diffusion equation solver which considers the online estimation of thermodynamic equilibria with a macroscopic model for temperature calculation. The coupled micro-model predicts the dendrite solidification of ternary alloys. To simulate the phase transformation in temperature zones below solidification a homogenization model is added. Permanent mould casting experiments with ternary aluminum alloys are used to validate these models.
Influence of Dislocations on Deuteride Formation in Single Crystal Palladium
Authors: Chen W.C. , Heuser Brent J.
Published: April 2011

The effect of dislocations on deuteride formation in the Pd-D system has been investigated with small-angle neutron scattering (SANS). Deuteride precipitation morphologies in well-annealed single crystal Pd and deformed single crystal Pd have been determined with SANS. High densities of dislocations were introduced into the deformed sample by cycling across the deuteride miscibility gap. The characteristic response from small, 20-30 Angstrom thick, plate-like particles has been observed in the SANS measurement of both sample types. We believe these small plates act as precursors to the formation of much larger, tens-of-microns thick incoherent plate-like particles. These much larger deuteride plates have a preferred habit plane that depends on sample type; (100) for the well-annealed matrix and (110) for the deformed matrix.
The Origin of Electrical Activity at Grain Boundaries in Perovskites and Related Materials
Authors: Pennycook S. J. , Kim M. , Duscher G. , Browning N. D. , Sohlberg K. , Pantelides S. T.
Published: April 2011

In the last few years, the combination of atomic-resolution Z-contrast microscopy, electron energy loss spectroscopy and first-principles theory has proved to be a powerful means for structure property correlations in complex materials1. Here we demonstrate the effectiveness of this combined approach by demonstrating the origins of electrical activity at grain boundaries in the prototypical perovskite SrTiO3 and the high-temperature superconductor YBa2Cu3O7-x, materials that are closely related in structure. We show, both experimentally and theoretically, that grain boundaries in SrTiO3 are intrinsically non-stoichiometric. Electron energy-loss spectroscopy (EELS) provides direct evidence of non-stoichiometry, in agreement with total- energy calculations that predict non-stoichiometric grain boundaries to be energetically favorable. The predicted structures are consistent with atomic-resolution Z-contrast micrographs. These results provide a consistent explanation of the grain boundary charge that was previously inferred from electrical measurements, and provides a microscopic explanation of the resulting “double-Schottky barriers”. We also present experimental evidence for non-stoichiometry at grain boundaries in the high-temperature superconductor YBa2Cu3O7-x, where the same phenomenon explains the observed exponential reduction of critical currents with grain boundary misorientation.
Origin of Voids at the Interface of Wafer Bonded Sapphire on Sapphire
Authors: Senz Stephan , Kopperschmidt Pascal , Zakharov Nikolai Dimitri
Published: April 2011

Two sapphire (Al2O3, r-cut) wafers were bonded at room temperature. The bonding energy increased during heating up to 1100 °C. The interface was investigated by plan-view and cross-section TEM. The bonding strength after heating to 1100 °C is similar to the bulk bonding strength. A high density of voids at the bonded interface was observed. The voids are elongated along the interface in a pancake shape. The surfaces are low index planes. The volume inside the voids is higher than expected from a model, where a hydrophobic initial bonding is assumed. The strength of initial bonding and the free volume at the interface can be understood, if the sapphire surfaces are hydrophilic and covered by several monolayers of water during initial bonding. During annealing the water diffuses out along the bonded interface and a free volume remains.
In-Situ Tem Analysis of Nanometre-Sized Oxide Precipitates in a Metal Matrix
Authors: Kooi Bart J. , De Hosson Jeff Th.M.
Published: April 2011

The objective of the present work is the in-situ study of the transformation of small oxide precipitates in a metal matrix by conventional and high-resolution transmission electron microscopy (HRTEM). As an example the reduction of Mn3O4 into MnO for nano-sized oxide precipitates in a silver matrix was studied in detail. A convenient method for monitoring the reduction process is shown for a large number of precipitates simultaneously. It is based on two-beam dark-field images showing distinct Moiré patterns for the MnO and the various types of Mn3O4 precipitates embedded within an Ag matrix. A controlling factor of the transformation kinetics appeared to be the rate in which the system can relax the strains due to the accompanying volume reduction of the precipitates. Other interesting aspects of the Mn3O4 to MnO transformation scrutinized and explained were the shape change of the precipitates upon reduction and the fact that mixed Mn3O4/MnO precipitates were only detected within a small temperature/time interval. Ostwald ripening of the MnO precipitates was observed as well.
Structure-Property Relationships of Tin Dioxide Thin Films Grown on Sapphire Substrates by Femtosecond Pulsed Laser Deposition
Authors: Dominguez J. E. , Fu L. , Pan X. Q.
Published: April 2011

The sensitivity of semiconductive tin dioxide (SnO2) to reducing gases is determinedby the electrical conductivity change in the material. This change in conductivity strongly dependson the thickness of the electron depletion layer near the oxide film surface. In this paper we study the effect of crystal defects and interfaces on the electrical properties and the gas sensing performance of SnO2 thin films. SnO2 thin films with the thickness varying from 15 nm to 100 nm were deposited on sapphire substrates with different surface crystallographic orientations by femtosecond pulsed laser deposition. Films grown on the (1012) sapphire (R-cut) are epitaxial, single crystal. High resolution transmission electron microscopy studies showed the existence of a large number of crystal defects including crystallographic shear planes and misfit dislocations at the film/substrate interface. Films grown on the (0001) sapphire substrates (Ccut) are nanocrystalline with (200) texture. The gas sensitivity of the films was measuredin a gas reactor at high temperature. It was found that the sensitivity to reducing gases increases with decreasing film thickness. Electrical transport properties of the SnO2 thin films were investigated byHall effect measurements. Models correlating the microstructures of thin films to electrical properties are proposed.
Nanoscale electromechanical phenomena in ferroelectric thin films
Authors: Ganpule C. S. , Roytburd A. L. , Nagarajan V. , Stanishevsky A. , Melngailis J. , Williams E. D. , Ramesh R.
Published: April 2011

Focused ion beam milling was used to fabricate ferroelectric islands in Pb-Zr-Ti-O thin films. The islands ranged in size from 200μm×200μm to 0.3μm×0.3μm. The inverse piezoelectric effect was studied in these islands as a function of their size by tracking the surface displacement of the top electrode of the island (under an applied electric field) using an atomic force microscope (AFM). It was found that there was a substantial increase in the piezoresponse as the size of the island decreased below 100μm×100μm. This increase was attributed to the elastic deformation of the substrate.
Preparation of sub-100nm Thickness PZT thin Films with Chemical Solution Deposition Method for low Voltage Operation
Authors: Lee Yong Kyun , Lee June Key , Kim Chang Jung , Yi Insook , Chung Ilsub
Published: April 2011

PZT thin films with a thickness of 70 nm were successfully fabricated using a modified solution combined with PbTiO3 seed layer. Throughout various approaches, we found that the microstructure of PZT thin film plays an important role in determining the electrical properties such as hysteretic properties and leakage currents, particularly when the thickness is below 100 nm. We modified the precursor system to improve the microstructure in PZT thin film. In addition, we also adopted a thin PbTiO3 seed layer to enhance the initial nucleation density. Finally, we could obtain good electric properties similar to those obtained from 240 nm thick PZT film. The hysteretic properties is excellent enough to operate at a low voltage (2V) for a high density FRAM application.
Characterization of Ferroelectric Property of c-axis and non-c-axis Oriented Epitaxially Grown Bismuth Layer-Structured Ferroelectric Thin Films with Different m-numbers Prepared by MOCVD
Authors: Watanabe Takayuki , Sakai Tomohiro , Saiki Atsushi , Saito Keisuke , Chikyo Toyohiko , Funakubo Hiroshi
Published: April 2011

Epitaxial thin films of bismuth layer-structured ferroelectrics (BLSF) with different m-numbers, i.e., Bi2VO5.5 (BVO) (m=1), SrBi2Ta2O9 (SBT) (m=2), and Bi4Ti3O12 (BIT) (m=3), were grown by metalorganic chemical vapor deposition (MOCVD). (00l)-oriented films were deposited on (100)SrTiO3. (114)-oriented BVO, (116)-oriented SBT, and (118)-oriented BIT films were deposited on (110)SrTiO3. Moreover, (102)-oriented BVO, (103)-oriented SBT, and (104)-oriented BIT films were deposited on (111)SrTiO3. On (100), (110), and (111)SrTiO3 substrates, c-axis of the deposited films was tilted about 0°, 45°, and 56°, respectively, against perpendicular to the surface of the substrates irrespective of m-number. This suggests the growth of crystallographic equivalent orientation. The distinctive surface morphology originated to the feature of the film orientation was observed. The dielectric constant and the leakage current of c-axis-oriented film was smaller than that of non-c-axis-oriented one, indicating smaller dielectric constant and leakage current along c-axis than a- or b-axes. A larger ferroelectric anisotropy was ascertained for SBT and BIT films. Furthermore, the evaluated spontaneous polarization along a- and c- axes of BIT from the data of the epitaxially grown BIT films well agreed with the reported one for the single crystal. This suggests the ferroelectric property was not strongly affected by the strain in the films.
Ferroelectric and Piezoelectric Properties of Epitaxial Pb(Yb1/2Nb1/2)O3-PbTiO3 Films
Authors: Yoshimura Takeshi , Trolier-McKinstry Susan
Published: April 2011

(1°x)Pb(Yb1/2Nb1/2)O3划xPbTiO3 (PYbN-PT, x=0.5) epitaxial films were grown on (001)SrRuO3/(001)LaAlO3 and (111)SrRuO3/(111)SrTiO3 substrates by pulsed laser deposition. (001)PYbN-PT epitaxial films with high phase purity and good crystalline quality were obtained for a wide range of deposition rates (60-90 nm/min) and temperatures (620-680 °C). (111)PYbN-PT films were also obtained at temperatures in the range of 600 °C to 620 °C. The ferroelectric and piezoelectric properties were investigated on both (001) and (111) PYbN-PT films. The remanent polarizations of (001)PYbN-PT and (111)PYbN-PT films were as high as 34 μC/cm2 and 26 μC/cm2, respectively. On (001)PYbN-PT films with a thickness of 900 nm, an e31 coefficient of -13 C/m2 and an aging rate of 2.5% per decade were observed.
Electrophoretic Deposition of Ferroelectric Composites for Applications in Electronic Scanning Systems
Authors: Ngo E. , Joshi P.C. , Cole M. W. , Hubbard C. W.
Published: April 2011

We have investigated the electrophoretic deposition (EPD) as a low cost and conformal method of fabricating barium strontium titanium (BST) based composite thick films. The films were deposited at a controlled rate on platinum substrate in acetone-based slurry under electric bias. Acetone-aerosol OTS surfactant dispersion was used as dispersive medium. Conformal BST based thick films of 10-80 μm were obtained. The dielectric constant and dielectric loss factor of Ba0.60Sr0.40TiO3 and Ba0.60Sr0.40TiO3 – 20wt% compositions were 603.3 and 0.029 and 327.0 and 0.002, respectively. The low frequency electronic properties of the electrophoretic films were also compared with those of the bulk BST ceramics. In addition, the optical and the structural properties of the films are also discussed. The various techniques employed include x-ray diffraction, SEM and surface profilometer.
Macroscopic Actuators Using Thick Piezoelectric Coatings
Authors: Sayer M. , Lockwood G.R. , Olding T.R. , Pang G. , Cohen Lester M. , Ren W. , Mukherjee B.K.
Published: April 2011

Large scale actuated structures often require piezoelectric elements in the thickness range 10-50μm. For manufacturing purposes, the chemical solution deposition of sol gel composites can create such structures using methods compatible with semiconductor fabrication technology. The piezoelectric characteristics of structures fabricated by patterning methods based on the lapping and dicing of bulk ceramic, spray coating and laser machined and micromolded sol gel composites are compared. Laser interferometer measurements on PZT/PZT composites give d33 = 200 pC/N and d31 = 24 pC/N. The design and fabrication of large area voltage actuated mirrors and annular and linear ultrasonic arrays in the frequency range of 50 MHz are demonstrated.
Effect of Laser Energy and Laser Pulses on the Microstructure, Composition and Properties of Barium Strontium Titanate Thin Films Synthesized by Pulsed Laser Deposition
Authors: Fountzoulas Costas G. , Demaree J. D. , McKnight Steven H.
Published: April 2011

Barium strontium titanate (BSTO) films were synthesized by the pulsed laser deposition technique (PLD) on silicon substrates at room temperature. The thin films were synthesized at ambient temperature and 30 mT oxygen partial pressure, with 300, 400 and 500 mJ/cm2 laser fluence at 5, 10 and 20 pulses per second on silicon wafer substrates. All films were subsequently post-annealed at 750°C in an continuous oxygen stream. The microstructure, crystallinity and lattice constant of the BSTO films were studied with the aid of atomic force microscopy (FEM) and Glancing Angle X-ray Diffraction analysis (GAXRD). The hardness and modulus of elasticity of the films were studied with the aid of a nanohardness indenter. The film stoichiometry was determined with the aid of Rutherford Backscattering Spectrometry (RBS). The results of this research will be combined with the results of our previous work [1, 2] on the effect of substrate temperature and oxygen partial pressure on the microstructure and properties of the BSTO films in order to construct a structural zone model (SZM) of the BSTO films synthesized by PLD.
Cellular Domain Architecture of Stress-free Epitaxial Ferroelectric Films
Authors: Alpay S. P. , Roytburd A. L. , Nagarajan V. , Bendersky L. A. , Ramesh R.
Published: April 2011

Epitaxial ferroelectric films undergoing a cubic-tetragonal phase transformation relax internal stresses due to the structural phase transformation and the difference in the thermal expansion coefficients of the film and the substrate by forming polydomain structures. The most commonly observed polydomain structure is the c/a/c/a polytwin that relieves the internal stresses only partially. Relatively thicker films may completely reduce internal stresses if all three variants of the ferroelectric phase are brought together such that the film has the same in-plane size as the substrate. In this article, we provide experimental evidence on the formation of the 3-domain structure based on transmission electron microscopy in 450 nm thick (001) PbZr0.2Ti0.8O3 films on (001) SrTiO3 grown by pulsed laser deposition. X-ray diffraction studies show that the film is fully relaxed. Experimental data is analyzed in terms of a domain stability map.
Growth of (Ba,Sr)TiO3 Thin Films in a Multi-wafer MOCVD Reactor
Authors: Ehrhart P. , Fitsilis F. , Regnery S. , Jia C. L. , Jin H.Z. , Waser R. , Schienle F. , Schumacher M. , Juergensen H.
Published: April 2011

We report on the performance of a planetary multi-wafer MOCVD reactor which handles 5 six inch wafers simultaneously. The reactor is combined with a liquid delivery system which mixes the liquid precursors from three different sources: 0.35 molar solutions of Ba(thd)2 and Sr(thd)2 and a 0.4 molar solution of Ti(O-i-Pr)2(thd)2. The microstructure and the film stress were investigated by X-ray diffraction and the composition of the films was determined by X-ray fluorescence analysis. As a direct consequence of the reactor design we obtain a high uniformity of the films over 6 inch wafers, as well as high efficiencies for the precursor incorporation. Film growth is discussed within a wide parameter field and the finally achieved electrical properties, e.g., permittivity, loss tangent, leakage current, are discussed in relation to the microstructural properties.
Evaluation of Ferroelectric BaxSr1−xTiO3 Thin Films Driven by Phase Shifters for Reflectarray Applications
Authors: Miranda F. A. , Mueller C. H. , Keuls F. W. Van , Romanofsky R. R.
Published: April 2011

The application of ferroelectric thin films for the development of frequency and phase agile microwave components has been the reason behind very encouraging demonstrations of tunable microwave devices in recent years. Thus, one could conclude with basically a general consensus, that the question of the suitability of thin film ferroelectric technology for the fabrication of superior tunable microwave components has been already answered in a favorable way. However, what is still pending in regards to the validation of this technology is the development of evaluation methodologies to set forth the standards for the material quality and subsequent performance criteria of specific components and devices based on this technology. In this paper we discuss the evaluation methodology under implementation at NASA Glenn Research Center aimed at identifying and optimizing the most relevant parameters of BaxSr1−xTiO3 (BSTO) ferroelectric thin films (i.e., tunability, losses, thickness, crystalline quality, etc.) as defined by a specific microwave application (in our case, phase shifters for reflectarray antennas). Results of our material analysis based on X-ray diffraction and ellipsometry, and how these properties correlate with RF performance for a targeted circuit, will be presented.
On the Evolution of Surface Morphology of Polysilicon Mems Structures During Fatigue
Authors: Allameh S. M. , Gally B. , Brown S. , Soboyejo W.O.
Published: April 2011

This paper presents the results of an atomic force microscopy (AFM) study of the evolution of surface topology in notched polysilicon MEMS structures deformed under cyclic loading at room temperature. The in-situ and ex-situ AFM studies reveal changes in surface topology after cyclic actuation at a relative humidity of ∼70%. These lead ultimately to large wavelength modulations close to the bottom of the notch, in the areas where the tensile stresses are maximum. This is in contrast with the wavelength of the surface modulations away from the notch, which remain relatively unchanged. The results are discussed in terms of possible chemical/surface processes that can occur in the presence of water vapor.
Annealing Effects on the Microstructure and Mechanical Properties of Liga Nickel for Mems
Authors: Cho H. S. , Babcock W. G. , Last H. , Hemker K. J.
Published: April 2011

The emergence of elevated temperature applications for microelectomechanical systems (MEMS) has resulted in the need for an understanding of the relation between the microstructural stability and the mechanical properties of their structural elements. Hardness and tensile tests and microstructural observations have been conducted with as-deposited and annealed conditions of LIGA-Ni microsamples that were deposited with current densities of 6mA/cm2 and 50mA/cm2. The Young's modulus was found to be independent of the annealing temperature, but the hardness and yield strength decreased dramatically at temperatures above 400°C. The microsamples deposited at a current density of 6mA/cm2 showed much higher strength and hardness than those deposited at 50mA/cm2. This increased strength has been related to the observation that the microstructure of the 6mA/cm2 microsamples is much finer than was observed for 50mA/cm2.
Unstable Etching Of Si(110)with Potassium Hydroxide
Authors: Moktadir Z. , Sato K. , Shimizu T. , Shikida M.
Published: April 2011

We present the experimental data for the morphological evolution of Si(110) etched with Potassium Hydroxide. The observed results are interpreted using a continuum equation. The results reveal the presence of unstable etching, which leads to the formation of a columnar structure on the surface. The early stage of the formation of this columnar structure can be explained by a linear theory. This instability is caused by anisotropic surface tension.
Wet-Etch Patterning of Lead Zirconate Titanate (PZT) Thick Films for Microelectromechanical Systems (MEMS) Applications
Authors: Wang L.-P. , Wolf R. , Zhou Q. , Trolier-McKinstry S. , Davis R. J.
Published: April 2011

Lead zirconate titanate (PZT) films are very attractive for microelectromechanical systems (MEMS) applications because of their high piezoelectric coefficients and good electromechanical coupling. In this work, wet-etch patterning of sol-gel PZT films for MEMS applications, typically with film thicknesses ranging from 2 to 10 microns, was studied. A two- step wet-etch process was developed. In the first step, 10:1 buffered HF is used to remove the majority of the film at room temperature. Then a solution of 2HCl:H2O at 45°C is used to remove metal-fluoride residues remaining from the first step. This enabled successful patterning of PZT films up to 8 microns thick. A high etch rate (0.13μm/min), high selectivity with respect to photoresist, and limited undercutting (2:1 lateral:thickness) were obtained. The processed PZT films have a relative permittivity of 1000, dielectric loss of 1.6%, remanent polarization (Pr) of 24μC/cm2, and coercive field (Ec) of 42.1kV/cm, all similar to those of unpatterned films of the same thickness.
Characterization of Silicon Fusion Bonds Using a Four-Point Bend Specimen
Authors: Turner Kevin T. , Ayon Arturo A. , Choi Dongwon , Miller Bruno , Spearing S. Mark
Published: April 2011

The increased number of MEMS devices that are fabricated by bonding two or more bulk micromachined silicon wafers has highlighted the need to produce reliable silicon fusion bonds. The current study focuses on employing a four-point bend delamination specimen to measure silicon fusion bond strength as a function of processing conditions. The specimen, which is composed of two bonded layers and an initial notch, permits the measurement of a mixed-mode critical strain energy rate, GC, at the interface. This specimen geometry is advantageous because it does not require measurement of crack length to calculate the strain energy release rate and is insensitive to damage near the specimen edges. The fact that the interface is loaded under mixed-mode conditions presents difficulties in achieving stable crack propagation in well bonded specimens. Attempts were made to eliminate this problem by reducing the effective bond toughness by etching shallow grooves in the wafer surfaces to reduce the bonded area. Testing revealed that while this approach reduced the effective toughness of the interface, it did not prevent crack deflection in well bonded samples. Despite the limitations of the specimen, data was obtained for silicon fusion bonds fabricated under various annealing and contacting conditions. Test results indicate an increase in bond toughness with annealing temperature and time. The data also suggests that the contacting pressure and duration have little effect on bond quality. The specimen, while limited to characterizing bonds with lower toughness, proved straightforward to fabricate and test.
Structural and Electrical Properties of Biaxially Textured YBa2Cu3O7-x Thin Films on Buffered Ni-based Alloy Substrates
Authors: Li M. , Ma B. , Jee Y. A. , Fisher B. L. , Balachandran U.
Published: April 2011

Oxide high-Tc superconducting wires and tapes with high critical current density (Jc) are essential to future electrical power applications. Recently, YBa2Cu3O7−x (YBCO) thin films grown on Ni-based alloy tapes have attracted intense interest because of their promise for these applications. To achieve high Jc, buffer layers are necessary for fabricating biaxially aligned YBCO thin films. In our studies, yttria-stabilized zirconia (YSZ) layers were deposited on Ni- based alloy substrates by ion-beam assisted deposition, and CeO2 buffer layers were subsequently deposited on the YSZ layer by pulsed laser deposition (PLD) or electron beam evaporation. In addition, MgO layers were deposited on Ni-based alloy substrates by inclined substrate deposition. Finally, biaxially textured YBCO thin films were deposited on these buffered metallic substrates by PLD under optimized conditions. The orientation and in-plane textures of YBCO and the buffer layers were characterized by X-ray diffraction Ø/2Øscans, ø- scans, and pole figure analysis. The superconductive transition features were examined by measuring inductive Tc and transport Jc.
Nd/Ba substitution and oxygen deficiency effects on the pinning properties of NdBa2Cu3O7-σ single crystals
Authors: Shibata S. , Nakao K. , Yamamoto A. , Feng Y. , Pradhan A.K. , Machi T. , Koshizuka N.
Published: April 2011

We studied the origin of peak effect in the magnetic field dependence of Jc in NdBa2Cu3O7-σ single crystals. The single crystals were grown by the slow cooling method under various partial O2 pressures(PO2) (0.04∼1%) in Ar atmosphere. We found that the peak effect depends on PO2 and it disappears for the crystals grown under low PO2∼0.04%. This result demonstrates the important role of Nd/Ba substitution for the peak effect because it is known that the Nd/Ba substitution decreases with lowering PO2. We also investigated the role of oxygen vacancies in the peak effect for the crystals with different amount of Nd/Ba substitution. We found that the main cause of peak effect in fully oxygenated crystals is due to local low Tc regions caused by the Nd/Ba substitution rather than those by the oxygen vacancies.
Simulations of Filled Polymers on Multiple Length Scales
Authors: Starr Francis W. , Glotzer Sharon C.
Published: April 2011

We present simulation results of the effect of nanoscopic and micron-sized fillers on the structure, dynamics and mechanical properties of polymer melts and blends. At the smallest length scales, we use molecular dynamics simulations to study the effect of a single nano-filler on the structure and dynamics of the surrounding melt. We find a tendency for polymer chains to be elongated and flattened near the filler surface. Additionally, the simulations show that the dynamics of the polymers can be dramatically altered by the choice of polymer-filler interactions. We use time-dependent Ginzburg-Landau simulations to model the mesoscale phase-separation of an ultra-thin blend film in the presence of an immobilized filler particle. These simulations show the influence of filler particles on the mesoscale blend structure when one component of the blend preferentially wets the filler. Finally, we present some preliminary finite element calculations used to predict the effect of mesoscale structure on macroscopic ultrathin film mechanical properties.
Comprehensive Structural Study of Pre- and Post-Heat Treated Compression Molded Polyurethane Samples of Varying Composition Studied by Scanning Probe Techniques
Authors: Hawley M.E. , Orler E.B. , Wrobleski D.A. , Hjelm R.P. , Brown G.W.
Published: April 2011

Only a limited number of structural studies have been performed on polyurethanes using scanning probe techniques to determine both the microstructure and the corresponding distribution of hard and soft segments within samples. This type of information is needed to better understand the mechanical properties of these materials and to facilitate modeling. In order to address these issues, we have fabricated a series of compression molded segmented poly(ester urethane) samples with hard (HS) to soft segment ratios from 19 to 100%. Samples were examined using scanning probe phase imaging techniques to obtain the topography and corresponding distribution of hard domains before and after heating at 100°C.

A number of significant differences were observed between the pre- and post-heat treated samples. Variations in structure and heat-induced morphological changes were directly related to HS content. Fine strand- or fibril-like structures were most prominent in the 23 and 19% HS sample but first appeared at 30% HS. Harder, thicker elongated structures dominated the surface of the100% HS sample and were seen to a limited extent on all samples, especially after annealing and quenching. The 23% HS sample surface structure depended on quenching rate and time after treatment.
ToF-SIMS Study of Polymer Nanocomposites.
Authors: Zaitsev Vladimir S. , Seo Young-Soo , Shin Kwanwoo , Zhang Wenhua , Schwarz Steven A. , Sokolov Jonathan , Rafailovich Miriam H.
Published: April 2011

Films of deuterated polystyrene (dPS) and poly(methyl methacrylate) (PMMA) blends, as well as dPS and PMMA and poly(ethylene-co-propylene) (PEP) blends have been spin-cast from toluene solution and annealed at temperatures above their glass transition temperatures for up to 72 hours. Surface topography of the cast and annealed films was measured by atomic force microscopy (AFM). Dynamic secondary ion mass spectrometry (SIMS) was used to study microphase segregation of the polymer films. A series of two-dimensional (2D) images of the films were acquired during sample sputtering. A reconstruction of the sample three-dimensional (3D) structure from 2D data was performed. Spatial distributions of H, D, C, O, and higher mass fragments revealed microphases with dimensions on the order of a few microns. We describe the method that corrects height distortion to 3D SIMS images. After sputtering, AFM is used to produce a topographic image of the area analyzed by SIMS. The surface height variation array from SIMS data was compared with that observed by AFM. A limitation of the correction method is discussed.
The Influence of Humidity on the Structure of MoS2(PEO)1.3 Nanocomposites
Authors: Westreich Philippe , Yang Datong , Frindt Robert F.
Published: April 2011

Layered nanocomposites of molybdenum disul.de (MoS2) andp oly (ethylene oxide) (PEO) were studied using x-ray di.raction of powder and oriented thin.lm samples. Thermal gravimetric analysis provided information on the composition of the material. The e.ects of the molecular weight of PEO andthe atmospheric relative humidity on the structure were also investigated. A basal plane spacing of 14.3 °, corresponding to an expansion of 8.1 ° between MoS2 layers, was foundfor dry samples, in agreement with the literature. At about 30% humidity, the expansion increases to 10.6°. This increase corresponds approximately to the thickness of one monolayer of water. The spacing is constant until around80% humidity, when the expansion begins to increase again, reaching up to 25 ° near 100% humidity. X-ray coherence lengths in the direction perpendicular to the planes averaged13, 7 and 2 MoS2 layers for the dry, 58% humid and nearly 100% humid samples, respectively.
Evaluation of a Collagen-Hyaluronate Bilayer Matrix for Bone and Cartilage Repair
Authors: Liu Lin-Shu , Thompson Andrea , Daverman Robin , Poser James W. , Spiro Robert C.
Published: April 2011

We have developed a novel bilayer matrix composed of a porous type I collagen layer that transitions into a hyaluronate gel layer. This study evaluates the potential of the bilayer matrix to support the in vitro and in vivo formation of both bone and cartilage tissue. In the presence of recombinant human growth and differentiation factor-5, fetal rat calvarial cells cultured in the HA layer grew in a round, aggregated, chondrocyte-like morphology, while those in the collagen layer grew flattened and spread. Biochemical analysis demonstrated that cells in the collagen layer expressed higher levels of alkaline phosphatase activity, and lower levels of sulfated glycosaminoglycans and type II collagen when compared to cells in the HA layer. Intramuscular implants of the bilayer matrix with growth factor retrieved at 28 days revealed the presence of bone and cartilage tissue in the collagen and hyaluronate layers, respectively. These results demonstrate that the differentiation of cells in response to a single growth factor can be guided by specific compositional changes of the extracellular matrix.
Apatite Growth on Bioactive Glass in Artificial Saliva
Authors: Efflandt Sarah E. , Cook Robert F. , Francis Lorraine F.
Published: April 2011

Bioactive glass disks from the MgO-CaO-P2O5-SiO2 system were placed in artificial saliva for time periods varying from 1 to 42 days. Surfaces were then analyzed using scanning electron microscopy (SEM) and x-ray diffraction to investigate surface morphologies and crystallinity. SEM examination exhibited dramatic surface changes as early as 2 d. X-ray results showed crystallinity in the form of apatite at 10 d, which became more developed though 42 d. The bioactive glass in water and non-bioactive glass in artificial saliva were used as controls; both exhibited no evidence of apatite formation on their surfaces through the 42 d time period. This study shows that bioactive glass reacts in artificial saliva to form apatite and that the apatite layer becomes better crystallized over an extended time period. These results give a better understanding of the surface changes and mineralization that occur over time and can be used to interpret results from in vitro and in vivo studies done on bioactive glass in the oral environment.
Bioactivity of Vitronectin Adsorbed on Nanophase Alumina Promotes Osteoblast Adhesion
Authors: Webster Thomas J. , Schalder Linda S. , Siegel Richard W. , Bizios Rena
Published: April 2011

The role of the conformation and bioactivity of adsorbed vitronectin in enhancing osteoblast (the bone-forming cells) adhesion on nanophase (that is, grain sizes less than 100 nm) alumina was investigated in the present in vitro study. Results obtained from surface-enhanced Raman scattering (SERS) provided the first evidence of increased unfolding of vitronectin adsorbed on nanophase alumina. This conclusion was further supported by dose-dependent inhibition of cell adhesion on nanophase alumina pretreated with vitronectin following preincubation of osteoblasts with either Arginine-Glycine-Aspartic Acid-Serine (RGDS) or Lysine-Arginine-Serine-Arginine (KRSR) to block respective cell-membrane receptors. These events, namely enhanced unfolding of vitronectin that leads to exposure of bioactive epitopes (such as RGDS) in adsorbed vitronectin may explain the observed increased osteoblast adhesion on nanophase alumina.
Ammonia RF-Plasma on PTFE Surfaces: Quantification of the Species Created on the Surface by Vapor - Phase Chemical Derivatization
Authors: P. Chevallier , M. Castonguay , D. Mantovani , G. Laroche
Published: April 2011

A cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used with the aim of modifying the internal surface of ePTFE arterial prostheses to improve their biocompatibility. In order to understand the effects of this treatment on the PTFE polymer surface, we have first realized RF-plasma treatment experiments on PTFE films. Preliminary XPS analyses have shown that about 15% of the surface atoms were substituted by nitrogen (N/C ratio of 0.3) whereas the F/C ratio decreased from 2 to 0.6, therefore leading to the conclusion that several chemical species are created onto the surface upon an ammonia plasma treatment. As X-Ray Photoelectron Spectroscopy (XPS) analysis does not allow the direct determination of the nature of the N-species grafted on the surface (chemical shifts are not different enough), vapor phase chemical derivatization was carried out on PTFE films to quantify the concentration of these new surface moities grafted on the polymer surface.
Synthesis and Characterization of Environmentally Responsive Core-Shell Hydrogel Nanoparticles
Authors: Jones Clinton D. , Baker Christina , Lyon L. Andrew
Published: April 2011

We report the synthesis of environmentally responsive hydrogels as nano-sized particles with core-shell morphologies. Composed of co-polymers of N-isopropylacrylamide with various co-monomers, these materials can be designed to render the core and shell responsive to different stimuli or to different magnitudes of the same stimulus. The measured phase transitions reflect the degree to which the two materials interact and thereby modulate the responsivity of the particle as a whole. Characterization of these materials is accomplished via dynamic light scattering and electron microscopy.
Synthesis and Characterization of Water Soluble Block Copolymers for pH-Sensitive Delivery
Authors: Anderson Brian C. , Bloom Paul D. , Sheares Valerie V. , Mallapragada Surya K.
Published: April 2011

A novel, water-soluble AB-block copolymer of diethylaminoethyl methacrylate (DEAEM) and poly(ethylene glycol) (PEG) was synthesized by anionic polymerization. Poly(ethylene glycol) methyl ether (PEGME) was converted into the corresponding potassium salt by reacting with potassium metal. The PEG salt was used as a macroinitiator for the polymerization of DEAEM to yield a PEG-b-PDEAEM block copolymer. Carbon dioxide was used to terminate DEAEM polymerization with a carboxylic acid group. This polymer, loaded with dye, was tested for pH sensitivity by release studies into solutions of various pH.
Characterization and Biocompatibility Studies of Layer-by-Layer Self-Assembled Humic Acid/Fe3+ Films
Authors: Galeska Izabela , Hickey Tammy , Moussy Francis , Papadimitrakopoulos Fotios
Published: April 2011

A semipermeable and non-inflammatory membrane is a prerequisite for the development of an implantable biosensor for continuous pain free monitoring of glucose levels in vivo. Humic acids (HAs) have been reported to have therapeutically relevant characteristics such as antiviral and anti-inflammatory.[1] This encouraged us to investigate the in vivo compatibility of HAs based multilayered films as a potential membrane material for implantable glucose sensors. Electrostatic layer-by-layer self-assembly technique of HAs with oppositely charged ferric ions was utilized to grow these films. Quartz Crystal Microbalance (QCM) and ellipsometric studies have shown repeatable, stepwise increase in mass and in film thickness during self-assembly. The growth of these assemblies exhibited strong dependence on pH and ionic strength of HAs solution and was correlated with the degree of ionization of carboxyl groups and the neutralization induced surface spreading. HAs films used in the biocompatibility study were very well tolerated by the tissue and no difference with silastic tubing, used as control, could be observed. All types of samples, including the controls, induced similar long-term tissue reaction showing almost no inflammation and a light to moderate fibrosis with some blood vessels present.
Diffusion of Dendritic Polymers Through Concentrated Polymer Solutions
Authors: Thomas James L. , Chen Wei , Cheng Yu , Prud'homme Robert K.
Published: April 2011

Diffusional dynamics of polymers can be very sensitive to polymer architecture. Polymers with novel (or time-varying) architectures could facilitate the release of therapeutic compounds from gels or concentrated polymer solutions with unusual or novel kinetic profiles. Towards this end, we are studying the behavior of model dendritic polymers, the poly(amidoamine)(PAMAM) dendrimers, in aqueous solutions and in concentrated solutions of a “matrix” polymer, poly(ethylene oxide)(PEO). Fluorescence measurements of the environmental polarity of the dendrimers provide evidence for pH-induced confomational changes in mid-sized (generation 6), but not in small (generation 2) dendrimers. In aqueous solution, dendrimer diffusion measurements reveal the fractal-like growth of these molecules, but measurements in aqueous PEO solutions failed to detect any pH dependence of the diffusion coefficient. Specific chemical interactions between the PEO and the PAMAM molecules may dominate their dynamic behavior.
Electrokinetic Assembly of Microsphere and Cellular Arrays
Authors: Ozkan Mihrimah , Esener Sadik C. , Bhatia Sangeeta N.
Published: April 2011

We have developed a novel electrochemical system for field assisted, fluidic assembly of objects on a microfabricated silicon substrate by means of electrical addressing. The principle of our technique is based on the movement of charged species in solution to oppositely charged electrodes, as seen commonly in electrophoresis. Here, charged species such as beads and cells are moved electrokinetically through an aqueous solution towards a charged electrode. Micro patterning of the electrodes allows localization of charged species. We present a theoretical framework to predict the electric potential for assembly and disassembly of spherical objects. We correlate theoretical predictions with the motion of negatively charged polystyrene beads of 20 μm diameter on 100 μm feature micro patterned substrates. In addition, we extended these results to arraying of 20-30 μm diameter live mammalian cells by means of electrical addressing. This technique has applications in creation of ‘active’ cellular arrays for cell biology research, drug discovery and tissue engineering.
Energy Level Alignment and Exciton Binding Energies Using Model Interfaces between Metals and Evaporable Organic Electroluminescent Materials
Authors: Alvarado Santos F. , Rieβ Walter
Published: April 2011

We report on a scanning probe spectroscopy study of the electronic properties of model organic/metal interfaces. The experiments allow us to determine parameters that are critical in charge carrier injection and transport, as are the energy gap between positive and negative polaronic states and the height of the barrier for charge carrier injection at metal/organic interfaces. In combination with optical absorption measurements, we gauge the exciton binding energy, a parameter determining energy transport and electroluminescence efficiency. The study was performed on thin films of tris(8-hydroxyquinolato)aluminum (Alq3) deposited on clean and LiF-covered Au(111), and on N,N'-di(naphthalen-1-yl)-N,N'-diphenylbenzidine (NPB) on Ni(111) and substrates.
Synthesis and Characterisation of Polypyridine Derivatives: Towards Regioregular PPY
Authors: Horsburgh Lockhart E. , Monkman Andrew P. , Wang Changsheng , Bryce Martin R.
Published: April 2011

Poly(2,5-pyridinediyl) was prepared from 2-bromo-5-iodopyridine, by a method which combines organomagnesium and organonickel chemistry, and leads to the regioselective formation of poly(2,5-pyridinediyl) (rPPY). The product of the reaction was compared to conventional poly(2,5-pyridinediyl) (PPY), thus enabling us to estimate that rPPY consists of 84±6% head-to-tail linkages. Photophysical properties of rPPY were also measured, and found to be generally similar to those of PPY, although there are some significant differences.
Effects of Inserting Highly Polar Salts Between the Cathode and Active Layer of Bulk Heterojunction Photovoltaic Devices
Authors: Shaheen Sean E. , Brabec Christoph J. , Sariciftci N. Serdar , Jabbour Ghassan E.
Published: April 2011

Thermal deposition of small amounts of various salts at the interface between the active layer and the aluminum cathode was shown to alter the performance of bulk heterojunction photovoltaic devices. LiF and LiBr were found to enhance the power conversion efficiency as compared to devices with no interfacial salt, but Cs and K compounds were found to severely diminish the device performance. It is suggested that the Li compounds preferentially align to produce a bulk dipole moment at the interface, whereas the Cs and K compounds do not.
Preparation of Diarylethene Substituted Polymer Films for Optical Recording
Authors: Cho Song Yun , Kim Eunkyoung
Published: April 2011

Effect of photo-irradiation on the color change of diarylethene polymer films was investigated. Diarylethene polymer films were prepared from photopolymerization of a radical curable mixture of diarylethene compound and a fluoroalkylacrylate containing a photo initiator. 1-[6'-(Methacryloxyethyloxycarbonyl)-2'-methylbenzo[b]thiophene-3'-yl]-2- (2"-methylbenzo[b]thiophene-3"-yl)hexafluorocyclopentene (MMBTF6) was synthesized from 2,3-bis(2-methylbenzo[b]thiophene-3-yl)hexafluorocyclopentene (BTF6) in three steps. 2,2,3,3-Tetrafluoro-1,4-butyldiacrylate (TFBDA) was synthesized from the corresponding diol and acryloyl chloride in the presence of a base. The photocurable mixture was coated on a substrate and subjected to antinic irradiation, to afforded homogeneous transparent film. A mask image was recovered on the film by a light of 365 nm and read by a visible light (λ > 700 nm) without destruction of the image. To erase the recorded image, a white light or a visible light was irradiated. Photochromic quantum yield and photo-induced refractive index change of the diarylethene bound polymer film were determined as 0.12 and 0.0006 respectively.
Synthesis and Optical Properties of a Novel Oligobipyridine
Authors: Fu Y. J. , Wong T.K.S. , Zhang H.X. , Wang G. M. , Hu X. , Gao Z.S. , Jiang M.H.
Published: April 2011

In this paper, 5,5' –bis [ 4'– methyl- ( 2,2'– bipyridin– 4- yl)- ethyl ]- 2,2'– bipyridine (BMBPYBPY), a partially conjugated derivative of oligobipyridine, has been synthesized and found to show strong photoluminescence (PL). Compared with the pyridine-based conjugated polymers, the shortened conjugation length shifts the emission color from green to violet-blue. The effects of morphology on its PL properties have been studied. From its as-precipitated powder state, an emission peak at 418 nm can be observed. However the emission spectra from its diffused states such as doped in KBr, or dissolved in CHCl3, as well as from its amorphous film state fabricated by vacuum evaporation are more complex. Also carried out are preliminary electroluminescent studies. Single layer devices ITO/BMBPYBPY/Al do not emit although current can be observed prominently. Double layer devices ITO/TPD/ BMBPYBPY/Al show emissions both from TPD and BMBPYBPY.
Electrical Conduction Mechanism of Highly Transparent and Conductive ZnO Thin Films
Authors: Minami Tadatsugu , Suzuki Shingo , Miyata Toshihiro
Published: April 2011

In this paper, we describe the underlying theory along with experiments concerning the electrical conductivity of transparent conducting ZnO films with a carrier concentration of 1019-1021 cm−3. The experimentally determined mobility as a function of carrier concentration in the range of 1019-1021 cm−3 could be quantitatively referenced to a theoretically calculated mobility that is dominated by not only grain boundary scattering but also ionized impurity scattering using the Brooks-Herring-Dingle theory with both degeneracy and nonparabolicity of the conduction band taken into account. Concerning nonparabolicity, the conduction band effective mass as a function of carrier concentration was theoretically analyzed and experimentally determined.