bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Nitrogen Ion Implantation on the Abrasive Wear Resistance of the Ti-6Al-4V/UHMWPE Couple
Authors: Matthews Frank D. , Greer Keith W. , Armstrong Douglas L.
Published: June 2019

Nitrogen ion implantation was investigated as a means of improving the wear resistance of Ti-6Al-4V alloy and the performance of the Ti-6Al-4V/ultra high molecular weight polyethylene (UHMWPE) wear couple. Included in the pin-on-disc wear study were cobalt-chromium and stainless steel controls as well as non-ion-implanted Ti-6Al-4V. Ion implanted Ti-6Al-4V and the control alloys exhibited minor scratching whereas non-ion-implanted Ti-6AI-4V exhibited definite wear scars. Gravimetric analysis of the UHMWPE discs revealed no significant difference between those worn against ion implanted Ti-6Al-4V and the control alloys. Discs worn against non-ionimplanted Ti-6Al-4V, however, exhibited significantly more weight loss than the other couples. The results of this testing indicate that nitrogen ion implantation improves the wear resistance of Ti-6Al-4V with an attendant decrease in the amount of polyethylene abrasive wear.
Preparation and Characterization of Insulating Polyphenylene Oxide Films on Platinum Electrodes
Authors: Langmuir Margaret E. , Koch V. R.
Published: June 2019

Polyphenylene oxide (PPO) polymer films were electrogenerated on Pt substrates from solutions of o-allylphenol (OAP), 2-allyl-4-methylphenol (2A4MP), and 2-allyl-6-methylphenol (2AGMP). Relatively thick (l–20μm) films of the corresponding PPO films were generated from 50 v/o methanol/water solutions of the monomers or at low phenol:KOH concentration ratios. The film thickness depended on the maximum anodic potential to which the electrode was cycled. Films prepared from these solutions were found to be microporous with respect to ion permeability, allowing the oxidation of Br− and reduction of Fe3+ to take place at the Pt surface. Competing oxidation of methoxide ion was found to be the cause of the film porosity and thickening.

On the other hand, thin (500–1000Å) coherent insulating films which were impervious to Br− and Fe3+ ions could be deposited from aqueous KOH solutions and from methanolic solutions at high phenol:KOH concentration ratios. The thin films were found to decrease the diffusion rates of hydronium and hydrox hydroxide ions to the electrode surface to a significant degree. As a result, the filmed electrodes could be cycled in neutral saline between +1.5 and −0.2 V vs. SCE with no damage to the film.
Artificially Induced Biological Organs: A New Concept
Authors: Wildevuur Ch. R. H. , van der Lei B.
Published: June 2019

The biological repair process tends to cover a vascular prosthesis by normal arterial wall tissue. This process was successfully utilized in rats to form eventually a neo-artery induced by a temporary physiologically functioning prosthetic scaffold. Essential for the regeneration of a normal compliant neo-artery was the initial physiological campliance and the gradual degradation of the prosthetic grafts. Only then the regenerating neo-media was effectively stimulated by the pulsatile flow to produce elastic laminae. Regeneration of the arterial wall could be enhanced by seeding smooth muscle cells. The same concept was successfully applied to replace the trachea and oesophagus in rabbits. These results demonstrate that regeneration of biological organs can be induced by temporary acting artificial organs, which are anatomically correct and superior to permanently implanted artificially organs.
Fracture Toughness Testing of In Vivo Aged Biomaterials
Authors: Pilliar R. M. , Williams D. F. , Vowles R.
Published: June 2019

Although mechanical property characterization of materials for loadbearing implant applications is recognized as a necessary prerequisite to theirin vivouse, tests are usually restricted toin vitrosituations becaus-of specimen size and cost limitation. Thisstid7'Jescribes a fracture toughness test that uses small specimens that can be conveniently placed in intermuscular positions in laboratory rats. The method is illustrated for the evaluation of two orthopaedic biomaterials namely bone cement and a filled composite (hydroxyapatite-filled polyethylene). The results indicated little mechanical degradation of the bone cement after 120 daysin vivobut a significant change in the filled polyethylene composite after only 70 days in vivo.
Role of Plasma Proteins in Corrosion of 316L Stainless Steel In Vitro
Authors: Bence J. L. , Black J. , Mitchell S. N.
Published: June 2019

Plasma proteins have been recognized as playing a role in the corrosion of metals used as medical implants. In this study, we examined the early events of anodic corrosion of 316L stainless steel in saline/plasma mixtures. Polished, annealed, cleaned and passivated 316L electrodes with a surface area/body fluid volume (SA/BFV) ratio of 23X were driven anodically in a 100 ml acid cleaned cell at 950 and 1150 mV (vs. SCE). Electrolyte solutions of isotonic saline (pH = 7.4) containing 0, 5, 10 and 25 volume percent human plasma were used. Aliquots of solution were taken at intervals and analyzed for Cr, Ni and Fe by atomic absorption spectrophotometry. Corrosion continued until a total charge of 1.0 to 1.5 C was passed. Plots of solution metal concentration versus electrolyte solution composition, calculated at an isocoulombic point (Q = 0.5 C) and adjusted for initial concentration, were prepared to test for effects of the presence of plasma proteins. Increases in elemental release rates of up to 3x (p 0.05) were found, with peak effects in 5 and 10 volume percent plasma solutions. The effects depend upon anodic potential, metal species, plasma protein concentration and possibly plasma composition.
Microstructure and Friction of Ion Beam Induced Amorphous Ti-Pd Alloys
Authors: Hirvonen J-P. , Nastasi M. , Phillips J. R. , Mayer J. W.
Published: June 2019

Multilayered samples of Ti-Pd with linearly varying compositions were irradiated by Xe ions at 600 keV. The induced microstructures were studied by using transmission electron microscopy and Rutherford backscattering. Mixing was found to be complete over the entire composition range, resulting in amorphous or amorphous plus crystalline structures except at the palladium-rich end, where a crystalline Pd-Ti solid solution was obtained. This is consistent with the high equilibrium solubility of Ti in Pd. In addition, significant coarsening of the microstructure caused by irradiation was found in this solid solution region.

Friction measurements were carried out in air and water by using a polytetrafluoroethylene pin as a counterpart. In air the friction coefficient was independent of composition and microstructure after about 2000 passes. In water, however, after 600 passes the friction coefficient reached a steady-state value with a pronounced minimum over the amorphous region. This property was unchanged throughout the remaining 10000 passes.
Ftir and Resolved Esca Studies of Segmented Polyether Polyurethanes
Authors: Grobe G. L. , Gardella Joseph A. , Chin Roland L. , Salvati Lawrence
Published: June 2019

Surface analysis of biomedical materials is necessary for determination of surface structure/biological property relationships. Previous studies [3,6] have demonstrated the applicability of Angle Resolved X-Ray Photoelectron Spectroscopy (ARXPS or ARESCA) and Fourier Transform Infrared Spectroscopy (FT-IR) with Attenuated Total Reflectance (ATR) sampling. Using these surface sensitive techniques on currently marketed segmented polyurethanes (SPU) (Biomer TMand Cardiothane-51TM), we have investigated chemical and morpholgical differences between polymeric mixtures cast from solvents of varying polarity. These materials are used because of their resistance to degradation and hydrolysis.

Results will show: (1) Selective casting of different constituents of the mixture as monitored by FT-IR, where polymers can be represented as opposed to block copolymers; (2) Correlation between the Hildebrand solubility parameter of the casting solvent and the portion of the polymer selectively cast; (3) Models of solution cast polymers will be presented including (concentration gradient) of the constituents; (4) SEM micrographs will provide information on domain size and the formation of these solution cast films; (5) Depths and concentration gradients will be estimated by comparing results from AHXPS and variable angle FT-IR/ATR.
Biomedical Materials to Repair Retinal Detachments
Authors: Refojo Miguel F.
Published: June 2019

Implants are essential for the repair of retinal detachments. The implant buckles the wall of the eye and apposes the detached retina with the choroid, thus restoring light sensitivity to the retina. The scleral buckling also relieves traction on the retina from a shrinking vitreous body. The implant materials most commonly used are solid silicone rubber and silicone sponges, but both types have some disadvantages. A poly(hydroxyethyl acrylate-co-methyl acrylate) hydrogel implant with improved properties of softness and antibiotic absorption is also available for retinal detachment surgery. Proliferative vitreoretinopathy involves various conditions of retinal detachment complicated by vitreous fibrosis, which, after vitrectomy, may be treated with intraocular injection of fluids that support the retina against the choroid. For conditions requiring a long-term implant, silicone oil although controversial is the material of choice. Many other substances have been investigated but none better has yet been found.
Bioactive Materials
Authors: Hench L. L. , Wilson June
Published: June 2019

Biomaterials can be classified in terms of their interfacial response with tissues: 1) nearly inert, 2) nearly inert microporous, 3) resorbable, and 4) surface active. Surface active biomaterials include bioactive glasses such as Bioglass®, bioactive glass-ceramics such as Ceravital® or A/W Glass-Ceramic, hydroxylapatite such as Calcitite® or bioactive composites such as Palavital® or stainless steel fiber reinforced Bioglass®. All of the above surface active biomaterials form an interfacial bond with adjacent tissue. However, the time dependence of bonding, strength of bond, mechanisms of bonding, and thickness of bonding zone differ. Depending upon composition, type of tissue, and type of load applied, and explanation for the compositional dependence is presented together with various medical and dental implant applications, including middle ear prostheses, maxillofacial reconstruction, endosseous ridge maintenance and augmentation, periodontal packing, and fixation of orthopedic joint prostheses.
Composite Plaster/Hydroxylapatite Implants for Jaw Bone Restoration
Authors: Hanker Jacob S. , Tucker Myron R. , Terry Bill C. , Carnevale Reynolds A. , Giammara Beverly L.
Published: June 2019

Sintered ceramic, nonresorbable hydroxylapatite (HA) is a calcium phosphate biomaterial widely employed alone for augmentation or maintenance of the mandibular ridge and for filling alveolar bony defects. The small particles used for ridge augmentation or periodontal defects tend to scatter and the larger blocks used for extraction sockets don't fit well. Our recent studies suggest that these problems can be circumvented by composite plaster of Paris/HA implants. In addition to binding the HA particles, the plaster makes the implants easier to shape. Plaster is not only very biocompatible but may actually help prevent infection. It appears to act as a scaffold for incorporation of the HA particles into osseous tissue. In several days the plaster is resorbed but it is replaced at the same rate by infiltrating fibrovascular tissue; plaster definitely promotes the filling of osseous defects initially by connective tissue. This tissue not only maintains the form and integrity of the implant, but its vascular and collagen components promote healing and contribute to subsequent filling of the defects and approximation of the HA particles by new cancellous bone. These composite implants can be preformed on casts prior to surgery or tailored during the surgical procedure. Their use precludes the difficulties encountered when plaster alone is implanted (resorption) or when HA alone is used (particle scatter or nonpenetration of the material by host vascular and connective tissues). By having a resorbable component which permits penetration by fibrovascular tissue and a nonresorbable component which can act as a nidus for new cancellous bone formation, these composite alloplasts act like artificial bone. Their use to support a denture, or for immobilizing teeth and reducing pocket depths in advanced periodontal disease, gives better results than HA alone.
The Use of the Four-Point Bending Technique for Determining the Strength of Low K Dielectric/Barrier Interface
Authors: Tsui Ting , Goldberg Cindy , Braeckelman Greg , Filipiak Stan , Ekstrom Bradley M. , Lee J.J. , Jackson Eric , Herrick Matthew , Iacoponi John , Martin Jeremy , Sieloff David
Published: June 2019

One of the important reliability challenges in integrating copper/Low-K dielectric technology has been adhesion between the Low-K dielectric and barrier metal. This investigation explored the applicability of the four-point bend technique for determining the adhesion strength of a fluorine doped low dielectric constant oxide in contact with tantalum barrier layer. Time of flight secondary ion mass spectroscopy (ToFSIMS) was used for surface chemical analyses of the delaminated surfaces to identify the fractured interface and its chemical compositions. The effect of annealing on mechanical strength was coupled with chemical analysis to discern the adhesion properties. Experimental results suggested that fluorine rich interfacial layer formation was associated with degraded adhesion characteristics between Low-K dielectric and tantalum barrier metal.
Microtexture and Strain in Electroplated Copper Interconnects
Authors: Spolenak R. , Barr D. L. , Gross M. E. , Evans-Lutterodt K. , Brown W. L. , Tamura N. , Macdowell A. A. , Celestre R. S. , Padmore H. A. , Valek B. C. , Bravman J. C. , Flinn P. , Marieb T. , Keller R. R. , Batterman B. W. , Patel J. R.
Published: June 2019

The microstructure of narrow metal conductors in the electrical interconnections on IC chips has often been identified as of major importance in the reliability of these devices. The stresses and stress gradients that develop in the conductors as a result of thermal expansion differences in the materials and of electromigration at high current densities are believed to be strongly dependent on the details of the grain structure. The present work discusses new techniques based on microbeam x-ray diffraction (MBXRD) that have enabled measurement not only of the microstructure of totally encapsulated conductors but also of the local stresses in them on a micron and submicron scale. White x-rays from the Advanced Light Source were focused to a micron spot size by Kirkpatrick-Baez mirrors. The sample was stepped under the micro-beam and Laue images obtained at each sample location using a CCD area detector. Microstructure and local strain were deduced from these images. Cu lines with widths ranging from 0.8 [.proportional]m to 5 [.proportional]m and thickness of 1 [.proportional]m were investigated. Comparisons are made between the capabilities of MBXRD and the well established techniques of broad beam XRD, electron back scatter diffraction (EBSD) and focused ion beam imagining (FIB).
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

Neutron 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

The 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

The “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

Poly(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

The 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

Confocal 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

The 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

Molecular 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

The 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

Nuclear 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

Thin 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

One 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

Laser 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

High-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

Highly (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

A 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

We 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

A 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

Thin 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.
The Ferroelectric Slab Waveguide: a Geometry for Microwave Components that Incorporate Ferroelectric Materials
Authors: Crowne Frank J. , Tidrow Steven C.
Published: June 2019

A slab geometry, in which ferroelectric is inserted between two “cladding” layers with a microstrip electrode placed on top, is proposed as a way to integrate the properties of ferroelectric materials into microwave components. This structure distributes the propagating microwave fields between the ferroelectric and the cladding, so that the microwave dielectric constant is a weighted average of the dielectric constants of the two materials. It is shown that this geometry drastically reduces dissipation due to dielectric losses in the ferroelectric. In addition, by applying a dc bias to the microstrip line, the dielectric constant of the ferroelectric layer can be varied and with it the microwave properties of the structure.
Rapid Gel Cast Prototyping of Complex Paraelectric (Ba,Sr)TiO3/MgO Composites
Authors: Synowczynski Jennifer , Hirsch Samuel , Gersten Bonnie
Published: June 2019

A rapid prototyping process for manufacturing complex three-dimensional RF structures in ceramic systems was developed. The process combines fundamentals from lost wax investment casting and ceramic gelcasting. The first step is to directly deposit a mold made of a low melting point wax using a high precision inkjet rapid prototyper. Then, a gelcasting slurry containing polymeric precursors, a high solids loading of ceramic powders and a free radical initiator is cast into the mold and polymerized to lock in the structure. Finally, the mold is melted and the remaining green part is sintered. Aqueous gelcasting slurries were developed for MgCO3, (Ba,Sr)TiO3, and a composite of (Ba,Sr)TiO3 and MgO. The maximum solids loading attained for each of the powders was 22 V%, 50 V%, and 25 V% respectively. The 50V% gelcast part had a more uniform microstructure, higher sintered density, less open porosity and smaller grain size than parts produced through dry pressing. The microstructural improvements resulted in a high dielectric permittivity.
Honeycomb Films of Biodegradable Polymers for Tissue Engineering
Authors: Nishikawa Takehiro , Arai Keiko , Hayashi Junko , Hara Masahiko , Shimomura Masatsugu
Published: June 2019

We report that microporous films (honeycomb films) can lead various types of cells to tissue formation. The honeycomb films were fabricated by applying a moist air to a spread polymer solution containing biodegradable polymers (poly(L-lactic acid) (PLLA) and poly (ε-caprolactone) (PCL)) and an amphiphilic polymer. Hepatocytes were cultured on a self-supporting honeycomb film of PLLA. The hepatocytes formed a single layer of columnar shape cells with a thickness of 20 μm. The tissue formation of hepatocytes specifically occurred on the honeycomb film of PLLA, not on a flat film of PLLA. Three dimensional tissue structures were formed, when cells were cultured on both sides of the self-supporting honeycomb film. Double layers of hepatocytes were obtained by the method. Striated tissues such as heart and blood vessel could be reconstructed by utilizing a stretched honeycomb film of PCL.
Biologically-Based Self-Assembling Hydrogels
Authors: Seal Brandon L. , Panitch Alyssa
Published: June 2019

We have developed polymers, which borrowing from biology, assemble into networks. The self-assembly regions of fibrinogen were cloned to form a scaffolding that either interacts with fibrin or assembles independently. Peptides consisting of a binding pocket (BP), ligand (L), and/or a Factor XIIIa substrate were synthesized and conjugated to methacroylated dextran or acrylated poly(ethylene glycol). Peptide-conjugated dextran was added to polymerizing fibrin, and the resulting hydrogels were evaluated rheologically. These conjugates significantly affected the mechanical properties of fibrin while the addition of unconjugated dextran did not. The BP and L peptides were conjugated to PEG star polymer. Mixtures of conjugated PEG-BP and PEG-L were found to assemble. This work shows that peptides directing assembly can be designed using motifs found in proteins. The peptides in this study not only alter the mechanical properties of fibrin, but also allow a mechanism for creating a self-assembling network.
Self-Assembly of a Modular Polypeptide based on Blocks of Silk-Mimetic and ElastinMimetic Sequences
Authors: Cazalis Chrystelle S. , Conticello Vincent P.
Published: June 2019

Spider dragline silk fiber displays a unique and technologically significant combination of high tensile and compressive strength. The structural origin of these properties arises from the alternating sequence of crystalline alanine-rich domains and amorphous glycine-rich domains, which undergo microscopic phase separation in the silk fiber. We previously reported the synthesis and the self-assembly of a novel polypeptide 1, which emulates the modular structure of crystalline and amorphous elastomeric domains in dragline silk proteins. The sequence of this polypeptide comprises an alternating arrangement of a self-complementary, amphiphilic silk-mimetic oligopeptide (Ala-Glu-Ala-Glu-Ala-Lys-Ala-Lys) and environmentally-responsive elastin-mimetic segment (Val-Pro-Gly-Val-Gly). We report herein the synthesis and the self-assembly of an analogous polypeptide (2) with an higher content of elastin mimetic pentapeptides. A synthetic gene encoding four repeats of the alternating sequence was expressed in E. coli strain BL21(DE3) as a C-terminal fusion to a decahistidine leader sequence to afford a polypeptide with a molar mass of approximately 39 kDa. The regularly alternating pattern of elastin-mimetic and silk-mimetic blocks within the protein allowed the copolymer to spontaneously self-assemble upon heating above the phase transition of the elastin-mimetic block. The self-assembly process was studied using a combination of CD and solid-state NMR spectroscopy, which suggested that the alanine-rich domains undergo a conformational rearrangement from α-helix to β-sheet. This rearrangement coincides with the macromolecular phase transition of the elastin-mimetic domains, which resulted in irreversible aggregation of the polypeptide above the Tt of the elastin-mimetic domains.
Helical, Disordered, and What that Means: Structural Characterization of a New Series of Methyl 1-Thiaoligo(ethylene Oxide) Self-Assembled Monolayers
Authors: Vanderah David J. , Arsenault Jennifer , La Hongly , Silin Vitalii , Meuse Curtis W. , Gates Richard S.
Published: June 2019

Self-assembled monolayers (SAMs) of a series of linear thiols containing a 1-thiaoligo(ethylene oxide) [TOEO] moiety, i.e., HS(CH2CH2O)xCH3, where x = 3 - 6, were prepared on polycrystalline gold (Au) and characterized by reflection absorption infrared spectroscopy (RAIRS) and spectroscopic ellipsometry (SE). For x = 5 and 6, the RAIRS data show that the TOEO segment, oriented normal to the substrate, adopts the highly ordered 7/2 helical structure of the folded-chain crystal polymorph of poly(ethylene oxide). For x = 3 and 4, the RAIRS and SE data indicate disordered, “amorphous” SAMs with essentially no evidence of the helical conformation in the TOEO segment. These data suggest that, for SAMs with TOEO segments, a minimum of five ethylene oxide units is required to adopt a helical conformation.
Selectivity of Polypeptide Binding to Nanoscale Substrates
Authors: Lustig Steven R. , Jagota Anand
Published: June 2019

We present new computational methodology for designing polymers, such as polypeptides and polyelectrolytes, which can selectively recognize nanostructured substrates. The methodology applies to polymers which might be used to: control placement and assembly for electronic devices, template structure during materials synthesis, as well as add new biological and chemical functionality to surfaces. Optimization of the polymer configurational sequence permits enhancement of both binding energy on and binding selectivity between one or more atomistic surfaces. A novel Continuous Rotational Isomeric State (CRIS) method permits continuous backbone torsion sampling and is seen to be critical in binding optimization problems where chain flexibility is important. We illustrate selective polypeptide binding between either analytic, uniformly charged surfaces or atomistic GaAs(100), GaAs(110) and GaAs(111) surfaces. Computational results compare very favorably with prior experimental phage display observations [S.R. Whaley et al., Nature, 405, 665 (2000)] for GaAs substrates. Further investigation indicates that chain flexibility is important to exhibit selective binding between surfaces of similar charge density. Such chains begin with sequences which repel the surfaces, continue with sequences that attract the surface and end with sequences that neither attract nor repel strongly.