bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTThis 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTLead 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

ABSTRACTThe 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

ABSTRACTOxide 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTOnly 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

ABSTRACTFilms 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

ABSTRACTLayered 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

AbstractWe 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

AbstractBioactive 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

AbstractThe 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

AbstractA 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

AbstractWe 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

AbstractA 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

AbstractA 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

AbstractDiffusional 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.