bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neutron Reflectivity Measurements of Molecular Weight Effects on Polymer Mobility near the Polymer/Solid Interface
Authors: Lin Eric K. , Pochan Darrin J. , Wu Wen-li , Satija Sushil K. 
Published: June 2019

ABSTRACTNeutron reflectometry is used to measure the rate of interdiffusion between bilayer samples of deuterated and hydrogenated poly(methyl methacrylate) (PMMA) films with the polymerpolymer interface near the native oxide surface of a silicon wafer. In this work, the effects of a favorable substrate interaction and the molecular weight of each polymer layer are determined. Both the film thickness and the molecular weight of the lower d-PMMA layer are kept constant with a thickness of approximately one radii of gyration (Rg) of the polymer and the molecular weight of the upper hydrogenated layer is varied. Earlier experiments show that the mobility of the polymer chains within Rg of the substrate is much lower than that of the bulk, suggesting that the mobility of surface-pinned polymers controls the interdiffusion rate. In this study, we find that the rate of interdiffusion is strongly dependent upon the molecular weight of the top layer.
The Reactive Formation of Diblock Copolymer at a Polymer/Polymer Interface and its Effect on Interfacial Structure
Authors: Schulze Jonathan S. , Lodge Timothy P. , Macosko Christopher W. 
Published: June 2019

ABSTRACTThe reaction of perdeuterated amino-terminal polystyrene (dPS-NH2) with anhydrideterminal poly(methyl methacrylate) (PMMA-anh) at a PS/PMMA interface has been observed with forward recoil spectrometry (FRES). Bilayer samples were constructed by placing thin films of PS containing ∼8.5 wt % dPS-NH2 on a PMMA-anh layer. Significant reaction was observed only after annealing the samples at 174°C for several hours, a time scale at least two orders of magnitude greater than the time required for the dPS-NH2 chains to diffuse through the bulk PS layer. The topography of the interfacial region as copolymer formed was measured using atomic force microscopy (AFM). Roughening of the PS/PMMA interface was observed to varying degrees in all annealed samples. Furthermore, the extent of this roughening was found to depend on the PS matrix molecular weight. Reaction in the samples with a high molecular weight PS matrix resulted in a root mean square roughness approximately equal to the radius of gyration Rg of the copolymer. However, approximately twice as much roughening was observed in the low molecular weight PS matrix. This study reveals how the molecular weight of one of the phases can affect the rate of reaction at a polymer/polymer interface.
Molecular Drag-Strain Coupling in Branched Polymer Melts
Authors: Blackwell Richard J. , McLeish Tom C. B. , Harlen Oliver G. 
Published: June 2019

ABSTRACTThe “pom-pom” model of McLeish and Larson (J. Rheol. 42, 81, 1998) provides a simple molecular theory for the nonlinear rheology of long chain branched polymer melts. The Edwards-de Gennes tube concept is used to derive a constitutive equation for a simple branched molecule composed of two star polymers linked by a single backbone chain. A feature of this model is that the backbone section of tube can stretch up to maximum length given by the maximum entropic drag-force from the arms, after which the star arms are withdrawn into the backbone tube. This produces a sharp transition in the extensional viscosity at this maximum stretch. This unphysical feature results from an over-simplification of the behaviour near the branch points.In this paper we introduce a simple treatment of the coupling between relaxed and unrelaxed polymer segments at branch-points. This allows for localised displacements of branch-point within a quadratic potential before maximum extension is reached. Displacing the branch-point reduces the length of arm outside the tube and so reduces in the drag on the star arms. This smoothes out the sharp transitions in extensional viscosity in the original “pom-pom” model at the cost of introducing an extra unknown parameter.This modification improves the prediction of the nonlinear rheology of H-polymers whose molecular structure is known. Alternatively, for polymers of unknown structure such as commercial Low Density Polyethylene, the model parameters may be fitted from linear viscoelastic and uniaxial extension data, to provide predictions for the behaviour in transient nonlinear shear and planar extension. By including local branch-point displacement we find improved agreement with the data for Low-Density Polyethylene.
Grafted Poly(acrylic acid) Brushes for Cell-Surface Interactions
Authors: Hilborn Jöns , Gupta B. , Garamszegi L. , Laurent A. , Plummer C.J.G. , Bisson I. , Frey P. , Hedrick J.L. 
Published: June 2019

ABSTRACTPoly(acrylic acid) (PAA) was grafted onto RF plasma treated PET films and onto SiO2 covered glass surfaces. PET films with various amounts of grafted PAA (0.4, 5, 11 and 19 μm/cm2) were immersed into a solution of collagen to allow for polyionic complex formation as a method for protein immobilization. It was found that the amount of complexed collagen was close to proportional to the amount of PAA. A closer investigation of the optical density of the PAA brushes close to the glass surface wa was performed using Reflectometric Inteference Spectroscopy. The supression of possibilities of extension and collaps of the brushes upon variation in pH is suggested to be caused by polyionic crosslinking between protonated collagen and deprotonated PAA. Such PAA-collagen surfaces with PAA concentrations lower that 10 μm/cm2 were shown to be suitable substrates for growth of human bladder smooth muscle cells.
Structure evolution during polymer blend dewetting and demixing
Authors: Gutmann J. S. , Müller-Buschbaum P. , Wunnicke O. , Stamm M. 
Published: June 2019

AbstractThe paper investigates the structure formation in thin polymer blend films. Such a control of the structure formation is of great importance in many industrial applications. In this paper we follow two different routes in order to control the surface structures. One is the creation of surface structured through a dewetting of the thin films. The dewetting is archived through a plastification of the film either annealing or by swelling in a solvent atmosphere. As a result the control of this process allows to form very small and regular structures. The second route utilizes the demixing of an strongly immiscible polymer blend during preparation and yields much less defined structures. To allow a quantitative comparison if the evolving surface structures are statistically analyzed in terms of their rms-roughness and Fourier spectrum and compared with predictions from existing growth models.
The influence of interfacial mechanical behaviour upon deformation and fracture of composite biopolymer gels
Authors: Plucknett K.P. , Normand V. , Pomfret S.J. , Ferdinando D. , Frith W.J. , Norton I.T. 
Published: June 2019

ABSTRACTConfocal Laser Scanning Microscopy (CLSM) has been used to follow the dynamic structure evolution of two protein/polysaccharide mixed biopolymer gel systems during large strain deformation. Gelatin/maltodextrin composites exhibited a ‘;pseudo-yielding’ stress-strain response in both tension and compression, when the gelatin-rich phase is continuous, which was attributed to debonding of the particle/matrix interface. This behaviour was significantly less apparent for gelatin/agarose mixed gels. The interfacial fracture energy of the two systems was determined using an elastomer composite debonding model. The gelatin/maltodextrin interfacial fracture energy (∼0.2 J.m-2) was found to be an order of magnitude less than for gelatin/agarose, leading to the observed variation for the two systems.
The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics
Authors: Emerson John A. , Giunta Rachel K. , Miller Gregory V. , Sorensen Christopher R. , Pearson Raymond A. 
Published: June 2019

ABSTRACTThe contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.
Modelling Surface Properties of Linear Amorphous Polymers
Authors: Goudeau S. , Galy J. , Gerard J.F. , Fulchiron R. , Barrat J.L. 
Published: June 2019

ABSTRACTMolecular dynamics simulations have been carried out on fully atomistic models of amorphous polymers. Both bulk structures and thin films were simulated for a wide range of thermoplastics such as PS, PMMA, poly (phenylene-ether) (PPE), poly (etherimide) (PEI). The influence of molecular weight and functional end-groups was investigated. The comparison between “bulk” and “surface” models clearly shows the increase of molecular mobility and a strong decrease in density at the vicinity of free surfaces. Simulated surface tensions, computed by different methods, are generally overestimated as compared to the experimental ones.PVT (Pressure-Volume-Temperature) measurements have been conducted, as another method to compute physical properties of amorphous polymers. From such measurements, cohesive energy densities, interaction parameters, and then interfacial properties, were obtained for various thermoplastics and the corresponding incompatible melts. Such a tool could be used for designing polymer surfaces and interfaces in polymer blends.
Infrastructure and Architectural SuretySM
Authors: Matalucci Rudolph V. , O'Connor Sharon 
Published: June 2019

ABSTRACTThe mission of the Architectural SuretySM program at Sandia National Laboratories is to assure the performance of buildings, facilities, and other infrastructure systems under normal, abnormal, and malevolent threat conditions. Through educational outreach efforts in the classroom, at conferences, and presentations such as this one, public and professional awareness of the need to defuse and mitigate such threats is increased. Buildings, airports, utilities, and other kinds of infrastructure deteriorate over time, as evidenced most dramatically by our crumbling cities and aging buildings, bridges, and other facility systems. Natural disasters such as tornadoes, earthquakes, hurricanes, and flooding also stress the materials and structural elements of our built environment. In addition, criminals, vandals, and terrorists attack our federal buildings, dams, bridges, tunnels, and other public and private facilities. Engineers and architects are beginning to systematically consider these threats during the design, construction, and retrofit phases of buildings and infrastructures and are recommending advanced research in new materials and techniques. Existing building codes and standards do not adequately address nor protect our infrastructure or the public from many of these emerging threats.The activities in Sandia National Laboratories' Architectural SuretySM efforts take a risk management approach to enhancing the safety, security, and reliability of our constructed environment. The technologies and techniques developed during Sandia's 50 years as the nation's lead laboratory for nuclear weapons surety are now being applied to assessing and reducing the vulnerability of dams, to enhancing the safety and security of our staff in foreign embassies, and assuring the reliability of other federal facilities. High consequence surety engineering and design brings together technological advancements, new material requirements, systems integration, and risk management to improve the safety, security, and reliability of our as-built environment. The thrust of this paper is the role that new materials can play in protecting our infrastructure. Retrofits of existing buildings, innovative approaches to the design and construction of new facilities, and the mitigation of consequences in the event of an unpreventable disaster are some of the areas that new construction materials can benefit the Architectural SuretySM of our constructed environment.
Materials Issues In Modern Reactor Safety
Authors: Powers D. A. 
Published: June 2019

ABSTRACTNuclear power currently supplies about 20% of the nation's electrical power needs. The nuclear power industry is going through evolutions that will lead to greater efficiency and competitiveness. Many changes in the nuclear power industry are limited by materials issues. This paper discusses a representative range of the materials issues that are arising in the industry. Materials issues are associated with prolonged use of reactor fuel, extended operation of power plants and realistic analyses of power plant safety. The issues include questions of fuel stability at high burnups, metallurgical issues of fuel cladding, embrittlement of pressure boundaries, detecting and sizing flaws in steam generators and issues of environmental qualification of reactor control and instrumentation systems. The paper concludes with a discussion of the future of nuclear power and the continuing need for better materials for power plants.
Deposition of Al65Cu23Fe12 and Composite Quasicrystalline Pvd Thin Film Coatings
Authors: Sordelet Daniel J. , Besser Matthew F. , Kustus Frank M. 
Published: June 2019

AbstractThin film coatings of Al-based quasicrystals were deposited by magnetron sputtering. Sputtering targets of Al65Cu23Fe12 and Al65Cu23Fe12+5v/o Fe-Al were prepared with plasma arc spraying by forming thick (∼5mm) coatings onto Cu substrates. By incorporating a controlled fraction of porosity and micro-cracks within the plasma sprayed target, cracking or delamination of the target during magnetron sputtering could be avoided. Compositions of the as-deposited PVD films were close to the sputtering target composition when the bias voltage was kept around –40V; higher bias voltages (e.g., -100 to -200V) lead to coatings that were deficient in Al. As-deposited coatings prepared with the lower bias voltage could be subsequently annealed at 700°C for two hours to yield a nearly single-phase icosahedral structure. After annealing, composite coatings indicate the presence of an Fe-Al phase along with the icosahedral phase.
Electrical and Structural Characterization of Boron Implanted Silicon Following Laser Thermal Processing
Authors: Gable K. A. , Jones K. S. , Law M. E. , Robertson L. S. , Talwar S. 
Published: June 2019

AbstractOne alternative to conventional rapid thermal annealing (RTA) of implants for ultra-shallow junction formation is that of laser annealing. Laser thermal processing (LTP) incorporates an excimer pulsed laser capable of melting the near surface region of the silicon (Si) substrate. The melt depth is dependent upon the energy density supplied by the irradiation source and the melting temperature of the substrate surface. A process window associated with this technique is able to produce similar junction depths over a range of energy densities due to the melting temperature depression established with pre-amorphization of the substrate surface prior to dopant incorporation. The process window of germanium (Ge) preamorphized, boron (B) doped Si was investigated. 200 mm (100) n-type Si wafers were preamorphized via 18 keV Ge+ implantation to 1x1015/cm2 and subsequently implanted with 1 keV B+ to doses of 1x1015/cm2, 3x1015/cm2, 6x1015/cm2, and 9x1015/cm2. The wafers were laser annealed from 0.50 J/cm2 to 0.88 J/cm2 using a 308 nm XeCl excimer irradiation source. Transmission electron microscopy (TEM) was used to determine the process window for each implant condition, and correlations between process window translation and impurity concentration were made. Four-point probe quantified dopant activation and subsequent deactivation upon post-LTP furnace annealing.
Effect of Laser Thermal Processing on Defect Evolution in Silicon
Authors: Kuryliw Erik , Jones Kevin S. , Sing David , Rendon Michael J. , Talwar Somit 
Published: June 2019

AbstractLaser Thermal Processing (LTP) involves laser melting of an implantation induced preamorphized layer to form highly doped ultra shallow junctions in silicon. In theory, a large number of interstitials remain in the end of range (EOR) just below the laser-formed junction. There is also the possibility of quenching in point defects during the liquid phase epitaxial regrowth of the melt region. Since post processing anneals are inevitable, it is necessary to understand both the behavior of these interstitials and the nature of point defects in the recrystallized-melt region since they can directly affect deactivation and enhanced diffusion. In this study, an amorphizing 15 keV 1 x 1015/cm2 Si+ implant was done followed by a 1 keV 1 x 1014/cm2 B+ implant. The surface was then laser melted at energy densities between 0.74 and 0.9 J/cm2 using a 308 nm excimer-laser. It was found that laser energy densities above 0.81 J/cm2 melted past the amorphous-crystalline interface. Post-LTP furnace anneals were performed at 750°C for 2 and 4 hours. Transmission electron microscopy was used to analyze the defect formation after LTP and following furnace anneals. Secondary ion mass spectrometry measured the initial and final boron profiles. It was observed that increasing the laser energy density led to increased dislocation loop formation and increased diffusion after the furnace anneal. A maximum loop density and diffusion was observed at the end of the process window, suggesting a correlation between the crystallization defects and the interstitial evolution.
Characterization and Monitoring of Silicon-on-Insulator Fabrication Processes by High-Resolution X-ray Diffraction
Authors: Cohen G. M. , Mooney P.M. , Park H. , Cabral C. , Jones E.C. 
Published: June 2019

AbstractHigh-resolution x-ray diffraction (HRXRD) was used to monitor silicon-on-insulator (SOI) processing steps. The use of HRXRD is attractive since it is non-destructive and can be applied directly to product wafers. We show the usefulness of this technique for the characterization of amorphizing implants for shallow junctions, solid phase re-crystallization of implanted junctions, cobalt-silicide formation, and oxidation; all are critical processes for CMOS fabrication on SOI.
Investigations on Sol-Gel Derived Ba0.5Sr0.5Ti1-δMnδO3 (δ = 0.0 to 5.0 at%) Thin Films for Phase Shifter Applications
Authors: Katiyar R.S. , Jain M. , Majumder S.B. , Romanofsky R.R. , Keuls F.W. van , Miranda F.A. 
Published: June 2019

AbstractHighly (100) oriented Ba0.5Sr0.5Ti1-δMnδO3 thin films were deposited on (100) LaAlO3 (LAO) substrate by sol-gel technique. We have studied systematically the effect of Mn doping on the degree of texturing, surface morphology, dielectric properties and phase transition behavior of barium strontium titanate (BST) thin films. Up to 3 at % Mn doping the degree of (100) texturing and grain size of BST (50/50) thin films were markedly improved, which led to an increased tunability from 29% (undoped) to 39% (3 at % Mn doped); measured at 1 MHz and 2.34V/mm bias field. The transition and Curie-Weiss temperatures of BST (50/50) thin films were found to be about 266 K and 185 K respectively, which confirmed the first order phase transition in the films. The variation of transition temperatures as a function of Mn doping contents in BST (50/50) thin films were influenced by the variation of stress state and surface morphology modifications induced by Mn doping. The bias field dependence of the dielectric constant and loss tangents of undoped and Mn doped films were analyzed in terms of a model based on Devonshire theory. Phase shift measurements showed that the degree of phase shift increases from 239° to 337° with 0 to 3 at% Mn doping. The insertion loss also increases from 5.4 dB (undoped) to 9.9 dB (3 at % Mn doped) with doping content so that there is no effective improvement in the k factor, which remains in the range of 33 - 44°/dB. Modification in surface morphology and film stoichiometry induced by Mn doping is thought to play significant role in observed phase shifter characteristics.
Reliability and Stability of Novel Tunable Thin Film
Authors: Lin G. H. , Fu R. , He S. , Sun J. , Zhang X. , Sengupta L. 
Published: June 2019

AbstractA new process has been developed in Paratek Microwave Inc. to formulate stable tunable (Ba, Sr)TiO3 (BST) based thin film material. Varactors, with a co-planar structure, were fabricated by using the new material. The varactor Q of 105 tested at 2 GHz was observed with average tunability of 58 % at 150V (37.5 V/μm). The lifetime tests indicated that this material is very stable under continuous 100 to 150 V dc bias both at the room temperature and in 70 °C environment. Thus, this novel tunable thin film material opens a new avenue to develop high quality tunable microwave devices. Tunable IF filters have been built by using this novel material for microwave backhaul radios and handset applications. Initial results of a RF phase shifter are also included and demonstrate another application of these films.
Off Axis Growth of Strontium Titanate Films with High Dielectric Constant Tuning and Low Loss
Authors: Kampangkeaw Satreerat , Rogers Charles T. 
Published: June 2019

AbstractWe have measured the nonlinear dielectric properties of strontium titanate (STO) thin films grown on neodymium gallate (NGO) and lanthanum aluminate (LAO) substrates. The films prepared by off-axis pulsed laser deposition were characterized by their dielectric constant and loss tangent at 1 MHz and 2 GHz, and from room temperature down to 4 K. The resulting films show significant variations of dielectric properties with position of the substrates with respect to the plume axis. STO films on LAO substrates show low loss and high dielectric constant in regions near the plume axis. On the other hand, STO on NGO shows this effect only on the films grown far from the plume axis. We also obtained a figure of merit from the relative variation of the dielectric constant divided by the loss tangent in the presence of a DC electric field up to +/- 4 V/μm. Careful mapping of the plume crossection allowed us to improve the quality and reproducibility of the dielectric films, obtaining a best figure of merit at 2 GHz and 4 K close to 100 for NGO substrate but only well off axis.
Application of Ferroelectrics in Low-Cost Microwave Phased-Array Antennas
Authors: Rao J. B. L. , Patel D. P. , Park P. K. , Dougherty T. K. , Zelik J. A. , Prior D. S. , Moffat A. , Sengupta L. C. 
Published: June 2019

AbstractA novel, low-cost, phased-array antenna that uniquely incorporates bulk phase shifting using voltage-tunable dielectric (VTD) material is presented. The array does not contain an individual phase shifter at each radiating element. This paper presents the antenna concept and describes how it can be used as a low-cost phased array. The VTDs that are used in this antenna are described. The measured antenna patterns of a prototype phased array demonstrating electronic beam scanning at 10 GHz are also presented.
Studies of thin film ferroelectrics with charge-compensated substitutions in BST
Authors: Potrepka Daniel , Tidrow Steven , Tauber Arthur , Kirchner Kevin , Rod Bernard , Horwitz James , Chang Wontae , Navi Nissim , Bubb Daniel 
Published: June 2019

AbstractThin films were prepared from bulk targets by pulsed-laser deposition techniques. The targets were composed of Ba0.6Sr0.4TiO3 with charge-compensated substitutions for Ti4+. Results of the dielectric characterization measurements will be discussed and compared to the results of similar measurements in bulk materials with the same composition.