bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Assembled Magnetic Dots, Antidots, Dot Chains, and Stripes: Epitaxial Co on Ru(0001) (INVITED)
Authors: Li Dongqi , Yu Chengtao
Published: April 2011

We have observe a metal-on-metal growth mode in Co/Ru(0001) at elevated temperature, where self-assembled 3D dots and antidots in rather regular truncated pyramidal shapes are mainly attributed to a stress-driven mechanism. While good lattice match has been one of the major criteria to guide epitaxial growth, it is possible that well-chosen lattice mismatched systems could be utilized to fabricate strain-engineered regular magnetic nanostructure arrays with different sizes and periodicity. A linear alignment of self-assembled Co dots and stripes can be created along grooves on a Ru(0001) substrate. Our observations suggest that it may be possible to direct the alignment and positioning in self-assembly of complex patterns by means of substrate templating, which should be of general applicability beyond the Co/Ru system. Magnetically, the dots are ferromagnetic with in-plane single-domain state, while the thick films with antidots exhibit perpendicular stripe domains.
Atomistic Modeling Of Co Growth On Cu(111)
Authors: Khalil Joseph , Bozzolo Guillermo , Farías Daniel , Parga A.L. Vázquez de , Miguel J.J. de , Miranda R.
Published: April 2011

The BFS method for alloys is applied to the study of Co growth on Cu(111). The parameterization of the Co-Cu system is obtained from first-principles calculations, and tested against known experimental features for low coverage Co deposition on Cu(100) and Cu(111). Atomistic simulations are performed to investigate the behavior of Co on Cu(111) as a function of coverage.
Continuum imit of a tep Flow odel of Epitaxial Growth
Authors: Kohn R.V. , Lo T.S. , Yip N.K.
Published: April 2011

We examine a class of step ow models of epitaxial growth obtained from a Burton-Cabrera-Frank (BCF) type approach in one space dimension. ur goal is to derive a consistent contin uummodel for the ev olutionof the lm surface. Away from peaks and valleys, the surface height solves a Hamilton- acobi equation (H E). he peaks are free boundaries for this H E. heir evolution must be speci ed by boundary conditions re ecting the microscopic physics of nucleation. e investigate this boundary condition by numerical simulation of the step ow dynamics using a simple n ucleationlaw. ur results rev ealthe presence of sp ecial structures in the pro le near a peak; we discuss the relationship between these structures and the contin uumequation. e further address the importance of ev aporationfor matching the local behavior near the peak to the solution of the contin uum equation.
An extended Cahn-Hilliard model for interfaces with cubic anisotropy
Authors: Abinandanan T.A. , Haider F.
Published: April 2011

For studying systems with a cubic anisotropy in interfacial energy σ, we extend the CahnHilliard model by including in it a fourth rank term, which leads to an additional linear term in the evolution equation for the composition field. It also leads to an orientation-dependent effective fourth rank coeficient γ(hkl) in the governing equation for the one-dimensional composition profile across a planar interface. The main effect of a non-negative γ(hkl) is to increase both σ and interfacial width w, each of which, upon suitable scaling, is related to γ(hkl) through a universal scaling function. The anisotropy in the interfacial energy can be large enough to give rise to corners in the Wulff shapes in two dimensions. In particles of finite sizes, the corners get rounded, and their shapes tend towards the Wulff shape with increasing particle size. In the study of unmixing of concentrated alloys, the anisotropy nt only leads to non-spherical particle shapes, but also to strongly elongated morphologies.
Chemical Vapor Deposition by Pulsed Ultrasonic Direct Injection of Liquid Precursors Produces Versatile Method for Creation of Thin Film Circuits and Devices.
Authors: Leiby Mark W.
Published: April 2011

We demonstrate a unique, ultrasonic direct injection method that employs nanophase materials (e.g. polymers, metal-organic and ceramic precursors). By use ofin situprocess control, and modification of process parameters, morphology, and structure may be varied to produce desired characteristics. By sequential application of these strategies one may fabricate MEMS, OLED's, deposit conformal coatings, create surface acoustic wave (SAW) chemical sensors, and many other thin film circuits and devices.
An Integrated Tool for Rapid Prototyping of Electronic Circuits Using a Laser Direct Write Technique
Authors: Mathews Scott A. , Duignan Michael
Published: April 2011

A laser-based tool has been developed for the fabrication of electronic circuits. The tool integrates three separate functions on a single platform. These functions are deposition, laser processing, and laser micromachining. Deposition is accomplished by dispersing a target material in a thin layer over a transparent backing layer, holding the target material in close proximity to a receiving substrate, and irradiating the target material from behind with a short pulse UV laser. The UV pulse vaporizes a small amount of the material at the material/backing interface, thereby propelling the remainder of the target material toward the receiving substrate. Patterning is achieved either by translating the receiving substrate, scanning the laser beam, or a combination of the two. After transfer, most materials require some thermal processing: either oven baking or laser sintering. Fabricated circuits have included conductors (Ag, AgPd, AgPt, Cu), resistors (cermet and polymer thick film), and dielectrics (ceramic and polymer thick film). These materials have been patterned with feature sizes as small as 10 m and linear write speeds as high as 1 meter per second. The tool includes an integrated, near IR laser which can be operated both CW and pulsed for thermal processing. Laser sintering of metals, cermet resistors, and ceramic dielectrics has been demonstrated on low temperature, polymer substrates. The localized heating achievable with the laser allows the sintering or annealing of high temperature materials without damaging the underlying substrate. The tool includes a complete, state-of-the-art laser micromachining system, capable of milling recesses, drilling vias, trimming components, and excising circuits. No masks or phototools are required. No photoresists or wet chemistries are needed. The tool does not require a clean room environment. The combined functionality and speed result in a flexible and powerful tool for the rapid prototyping of circuits, and potentially, small scale production.
Direct Write Microbatteries for Next-Generation Microelectronic Devices
Authors: Swider-Lyons Karen E. , Piqué Alberto , Arnold Craig B. , Wartena Ryan C.
Published: April 2011

Microbatteries and integrated microbattery systems are likely to be the sole power source or a power-source component for the next generation of microelectronic devices. As part of the LEAPS (Laser Engineering of Advanced Power Sources) program, custom-designed microbatteries and ultracapacitors will be integrated in microelectronic circuits for optimum performance. The Naval Research Laboratory's Matrix-Assisted Pulsed-Laser Deposition Direct-Write (MAPLE DW) process is used to rapidly fabricate various primary and secondary (non-rechargeable and chargeable) electrochemical power sources. This laser forward-transfer process can be used to transfer any type of battery material and battery material mixtures, including polymers, hydrated oxides, metals, and corrosive electrolytes. Additional laser micromachining capabilities are used to tailor the battery sizes, interfaces, and configurations. Examples are given for planar RuO2 ultracapacitors and stacked alkaline batteries.
Direct-Write Processes as Enabling Tools for Novel Antenna Development
Authors: Irwin Bryan S. , Taylor Robert M. , Wilhelm Michael J. , Church Kenneth H. , Culver James W. , Werner Douglas H.
Published: April 2011

Significant research effort is regularly applied to the goal of reducing the size of radio-frequency antennas while maintaining the entire set of positive attributes of proven but relatively large antennas. Such parameters as frequency response (multiple or single), bandwidth, and complexity of the antenna-driver balun structures require iterative optimization. The direct-write processes now available have enabled the insertion of reactive-loading elements as integral parts of the antenna structure, especially into new conformal designs. These reactive-loading elements were used in conjunction with modern design techniques to achieve antenna devices that were reduced in size to as much as half that of traditional counterparts. The performances of the miniaturized antennas constructed by direct-write methods were evaluated and compared to those of traditional antenna structures.
Microstructural Study and Thermal Modeling of Laser Formed Ti-6Al-4V
Authors: Kelly S.M. , Kampe S.L.
Published: April 2011

A two-dimensional thermal model for a commercial laser additive manufacturing (LAM) process has been developed to predict the thermal history of Laser Formed Ti-6Al-4V single line (rib-on-web) builds. The thermal model has been developed to assist in the prediction and interpretation of the as-processed microstructure, which evolves as a result of the complex thermal history that develops as a result of the deposition of multiple layers of material. In the current work, the model is used to show that the presence of layer bands is a result of different regions in the build experiencing varying super b transus time, temperature, and cooling rate conditions within different regions in the build.
Scanning Impedance Microscopy: From Impedance Spectra to Impedance Images
Authors: Kalinin Sergei V. , Bonnell Dawn A.
Published: April 2011

Abstract:Impedance spectroscopy has long been recognized as one of the major techniques for the characterization of ac transport in materials. The primary limitation of this technique is the lack of spatial resolution that precludes the equivalent circuit elements from being unambiguously associated with individual microstructural features. Here we present a scanning probe microscopy technique for quantitative imaging of ac and dc transport properties of electrically inhomogeneous materials. This technique, referred to as Scanning Impedance Microscopy (SIM), maps the phase and amplitude of local potential with respect to an electric field applied across the sample. Amplitude and phase behavior of individual defects can be correlated with their transport properties. The frequency dependence of the voltage phase shift across an interface yields capacitance and resistance. SIM of single interfaces is demonstrated on a model metal-semiconductor junction. The local interface capacitance and resistance obtained from SIM measurements agrees quantitatively with macroscopic impedance spectroscopy. Superposition of a dc sample bias during SIM probes the C-V characteristics of the interface. When combined with Scanning Surface Potential Microscopy (SSPM), which can be used to determine interface I-V characteristic, local transport properties are completely determined. SIM and SSPM of polycrystalline materials are demonstrated on BiFeO3 and p-doped silicon. An excellent agreement between the properties of a single interface determined by SIM and traditional impedance spectra is demonstrated. Finally, the applicability of this technique for imaging transport behavior in nanoelectronic devices is illustrated with carbon nanotube circuit.
Incentives for Using LEIM in the Investigation of Corrosion Initiation on Organic Coated Alloys
Authors: Taylor S. R. , Mierisch A.M.
Published: April 2011

Local electrochemical impedance mapping and spectroscopy (LEIM/S) have become important tools for the investigation of local electrochemical breakdown events associated with the degradation of organically coated metals in aqueous environments. LEIM/S of organic coated metal substrates has revealed local degradation events that are distributed spatially and temporally. These observations provide support to a number of long-standing theories, as well as provide new insight into the damage process. The local changes in impedance observed at early stages of immersion support the presence of virtual pores, while the metastability of impedance peaks representing the local changes provide evidence of healing via corrosion product formation. Each of these are long-standing theories used to explain global electrochemical impedance measurements. This paper will provide an overview of some of the events observed using LEIM and examine these results in the context of recent analytical and numerical models. Models used to predict the electric field above an equipotential disk electrode support the interpretation of most experimental LEI data as being representative of chemical and physical phenomenon and not a result of measurement artifact. However, certain features may be an artifact of the finite nature of the experimental process. The interpretation of LEIM events in view of current experimental and modeling results will be discussed.
Structure and Electronic Properties of Diamond-Like Carbon and its Heat-Treatment Effect
Authors: Takai Kazuyuki , Oga Meigo , Sato Hirohiko , Enoki Toshiaki , Ohki Yoshimasa , Taomoto Akira , Suenaga Kazutomo , Iijima Sumio
Published: April 2011

Diamond-Like Carbon (DLC) was gradually converted to the disordered graphite by means of heat-treatment (HT). According to Raman spectroscopy and x-ray diffraction (XRD), the disorder nature of the structure is modified from atomic scale sp2/sp3 disorder to disordered sp2-domain network by the migration of sp3-defects induced by HT at temperatures 200 - 400°C. The structural change increases conductivity and modifies the hopping conduction mechanism at low temperatures. The slight positive thermoelectric power for samples with graphitic domains is suggestive of carrier compensation by the competition of hole and electron carriers that originates from the inhomogeneous charge distribution caused by the difference of Fermi levels among the sp2-domains.
Microstructural Development and Properties of (1-x) wt% Ba0.55Sr0.45TiO3-x wt% MgO Bulk Ferroelectrics
Authors: Fountzoulas Costas G.
Published: April 2011

A study was made of the relationship between the microstructure and electrical properties of the bulk ferroelectric composite materials: (100-x) wt% Ba0.55Sr0.45TiO3-x wt% MgO. The ferroelectric composites (x= 40, 60) were fabricated by dry pressing from two powder precursors: 1) Ba0.55Sr0.45TiO3 (BST) calcined in the solid state with sol-gel MgO (Sg-MgO), and 2) hydrothermal BST and MgO calcined in the solid state. The pellets were sintered at 1250, 1350 and 1450°C. The sintered microstructure, chemistry, and phase with crystallinity was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), respectively. The density and porosity were determined by the Archimedes technique. Dielectric properties of permittivity and loss tangent were characterized by the parallel plate capacitor method.
Impedance Spectroscopy in Ferromagnetic Materials
Authors: Valenzuela Raul
Published: April 2011

Impedance spectroscopy (IS) is a powerful characterization methodology for a wide range of electric materials such as ceramics, ferroelectrics, ion conductors, piezoelectrics, etc. In this paper, an extension of IS to the case of ferromagnetic materials is presented. In particular, the resolution of the most common magnetization processes (domain wall bulging, domain wall displacement and spin rotation) is analyzed. IS is applied to ferrites and giant magnetoimpedance in amorphous wires.
Scaling Effects in Al72Mn22Si6 Quasicrystals Deduced from the Pressure and Temperature Dependence of the Resistance
Authors: Vassiliou John K. , Otto Jens W. , Pothireddy A. , Simons E. A.
Published: April 2011

X-ray diffraction and resistivity measurements on the Al72Mn22Si6 (Al-Mn-Si) rapidly quenched alloy are reported. The x-ray pattern shows that the alloy is essentially single phase, with a little mixture of unreacted Al. The peaks can be indexed using icosahedral vectors in the six dimensional space Z6. The resistance of thin ribbons of Al72Mn22Si6 quasicrystals has been measured as a function of temperature between 1.4 and 300 K at fixed pressures in the range 0 to 15 Kbar. Below 40 K, the resistance increases with decreasing temperature, and below 14 K, the conductivity varies as T1/2. This result is in agreement with the scaling and localization models in which spatial disorder and electron-electron correlation effects determine the electronic transport properties of the material. The value of the magnetoresistance measured at 60 KGauss and 0.34 K agrees qualitatively with the predictions of the above models. The pressure dependence of the correlation gap and the resistivity suggests that the system is in the strong coupling limit. In this regime, the functional dependence of the correlation energy on resistivity is Δ ~ ρ-2.
Electrically Active Deep Levels in ScN
Authors: Perjeru Florentina , Bai Xuewen , Kordesch Martin E.
Published: April 2011

We report the electronic characterization of n-ScN in ScN-Si heterojunctions using Deep Level Transient Spectroscopy of electrically active deep levels. ScN material was grown by plasma assisted physical vapor deposition and by reactive sputtering on commercial p+ Si substrates. Deep level transient spectroscopy of the junction grown by plasma assisted physical vapor deposition shows the presence of an electronic trap with activation energy EC-ET= 0.51 eV. The trap has a higher concentration (1.2–1.6 1013cm−3) closer to the ScN/Si interface. Junctions grown by sputtering also have an electronic trap, situated at about EC-ET= 0.90 eV.
Refractory Thin-Film Metallizations with Controlled Stress and Electrical Resistivity
Authors: Golecki Ilan , Eagan Margaret
Published: April 2011

Rhodium and iridium are refractory metals which possess intrinsically high electrical conductivity, and their chemical inertness enables their use at relatively high temperatures in microelectronics. However, due to the high Young's modulus of these materials, a residual tensile stress of hundreds of MPa is measured in evaporated thin films. New data is presented, demonstrating control over both the magnitude and the sign of the residual stress in such refractory thin films formed by means of ion-beam-enhanced physical vapor deposition on oxidized Si substrates. The electrical resistivity and stress are determined by controlling the substrate temperature, deposition rate and ion beam parameters. Thicker films are achieved in this manner, including films with near-zero residual stress.
Radio-Frequency Impedance Analysis of Anodic Tantalum Pentoxide Thin Films
Authors: Due~as S. , Castãn H. , Barbolla J. , Kola R.R. , Sullivan P.A.
Published: April 2011

Anodic tantalum pentoxide is studied up to 3 GHz by using for the first time the Radio-Frequency Impedance Analysis. Over this broad frequency range we extract a better knowledge on the very physical nature of this dielectric. From impedance analysis we obtain the value of the leakage conductance in parallel to the pure capacitance. At frequencies higher than 1 MHz capacitance vanishes to zero. This behaviour appears for all the samples, independently of thickness, anodization precursor or electrode metals, suggesting that it should be due to some intrinsic property of the dielectric. The electrical response of amorphous tantalum oxide is due to dipole oscillations characterized by a constant time; when frequency is high enough, dipoles do not have time to follow the field oscillations and, as a consequence, there is not any capacitive behaviour.
Influence of Confinement on Molecular Reorientational Dynamics of Liquid Crystals: Broadband Dielectric Spectroscopy Investigations
Authors: Aliev Fouad M.
Published: April 2011

Broadband dielectric spectroscopy has been applied for investigations of the dynamic behavior of liquid crystals (LCs) confined in porous matrices with random pores as well as in parallel cylindrical pores. We observed deep supercooling of LC in random pores. The relaxation times of the process due to the molecular rotation in deeply supercooled state are slower than at the temperatures corresponding to nematic phase by a factor of 106. This slowing down is accompanied by anomalous broadening of the dielectric spectra. For LC confined in cylindrical pores with homeotropic orientation on the pore walls we have investigated the relaxation of the librational mode. The dynamics of this mode is different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependencies of relaxation times of the librational mode needs the involvement of the temperature dependence of orientational order parameter. The investigations of the relaxation in thin LC layers formed on cylindrical pore walls show that the process due to rotation of molecules around their short axis (with single relaxation time for bulk LC) is the process with a distribution of relaxation times in thin layers and this process broadens with decreasing thickness of the layers.
The use of XANES and ELNES for the Characterisation of Stabilised Zirconia
Authors: McComb David W. , Ostanin Sergei , Vlachos Dimitris , Craven Alan J. , Finnis Michael W. , Paxton Anthony T. , Alavi Ali
Published: April 2011

The electron energy-loss near-edge structure (ELNES) and x-ray absorption near-edge structure (XANES) at the oxygen K-edge has been investigated in a range of yttria-stabilised zirconia (YSZ) materials. Analysis of near-edge structure reveals that both the crystallographic phase and the metal fraction of yttrium present can be determined directly from the oxygen K-edge data. Simulation of the ELNES/XANES was achieved using a pseudopotential based method to obtain the relaxed atomic coordinates combined with full-potential LMTO method to calculate the electronic structure.
Impedance spectroscopy study of ionic diffusion in polycrystalline ZrO2:Y2O3 solid solution
Authors: Fonseca Fábio C. , Muccillo Eliana N. S. , Muccillo R.
Published: April 2011

The ZrO2:Y2O3 solid solution formation has been followed by impedance spectroscopy and X-ray analysis. The experimental sequence, after mixing 8 mol% Y2O3 to ZrO2, was: attrition milling the mixture, drying, weighing, cold pressing, thermally treating at several different temperatures and times, performing the X-ray diffraction measurements at room temperature, applying metallic electrodes, and performing the impedance spectroscopy measurements in the 300°C-600°C temperature range. A good correlation was found between the decrease of the yttria main diffraction line and the increase of the stabilized zirconia main diffraction line, showing that solid solution is attained at the expenses of yttria, as expected. The impedance spectroscopy data Z(ω, T, t) show that the bulk response follows a t1/2 law, an evidence of yttrium diffusion to zirconia. Moreover, a relationship is found between the bulk resistivity and the elimination of ion blockers for increasing sintering times. The result allowed for the determination of the activation energy for the diffusion of the slowest diffusing species (Zr4+) in ZrO2:Y2O3.
The influence of filler properties on the strong PTC effect of resistivity in polymer based conducting composites
Authors: Glatz-Reichenbach Joachim , Strümpler Ralf
Published: April 2011

Polymer based composites are very attractive materials for a plurality of technical applications. For electrical purposes the resistivity of such materials can be tuned over many orders of magnitude from highly insulating (1014&cm) to well conducting (10-3&cm) states. One particular class of polymer based composites even show a strong non-linear reversible change in resistivity with temperature between conduction and insulation. Such a pronounced effect of positive temperature coefficient of resistivity (PTCR) can be technically used, for example, in self regulating heating devices, for temperature sensing or, as a very challenging and important task, for current (i.e. over- as well as short-circuit currents) limiting and interrupting devices. The PTCR-devices act similar like fuses but repetitively, which offers technical and economical benefits.

In the present work we investigate how the physical properties of the conducting filler influence the switching characteristics of the PTC material. Experimental results on resistivity and its change under active heating by Joule's losses during current flow are presented and discussed for different composites, compounded with fillers like carbon black, Ni/Ag, TiB2 or WC/Co. The strong resistance change caused by break-off and separation of particle-particle micro-contacts is driven by the very different thermal expansion coefficients of filler and matrix. It is in particular demonstrated how the heat capacity of filler-particles influences the dynamics of the micro-contact separation.
Combinatorial Molecular Layer Epitaxy of Hf Based Phosphor Oxides
Authors: Arai N. , Kim T. W. , Kubota H. , Matsumoto Y. , Koinuma H.
Published: April 2011

A series of MHfO3: Tm (M =Ca, Sr and Ba) composition spread films and superlattices (SLs) were quickly fabricated on SrTiO3 (001) substrate in the molecular layer-by-layer growth using combinatorial pulsed laser deposition (PLD) under in-situ reflection high-energy electron diffraction (RHEED) monitoring. Crystal structures and luminescence properties of composition-spread and SLs were evaluated by the concurrent X-ray diffractometer and cathode luminescence (CL), respectively. CL properties of the films were found strongly dependent on their composition and stacking sequence. Possible effect of the stress due to the film-substrate interaction on the CL property is discussed.
Combinatorial Search for Transparent Oxide Diluted Magnetic Semiconductors
Authors: Fukumura T. , Kawasaki M. , Jin Zhengwu , Kimura H. , Yamada Y. , Haemori M. , Matsumoto Y. , Inaba K. , Murakami M. , Takahashi R. , Hasegawa T. , Koinuma H.
Published: April 2011

Diluted magnetic semiconductor (DMS) possesses charge and spin degrees of freedom leading to their interplay promising for novel devices. DMSs based on II-VI and III-V compound semiconductors have been extensively studied so far. Recently, the oxide semiconductors doped with transition metal magnetic impurity have attracted much attention for the possible high ferromagnetic Curie temperature. Here, we overview recent studies of the transparent oxide based DMSs, ZnO, TiO2, and SnO2 doped with 3d transition metals, by using the combinatorial materials synthesis and the high throughput screening.
High Throughput X-ray Diffractometer for Combinatorial Epitaxial Thin Films
Authors: Ohtani M. , Fukumura T. , Ohtomo A. , Kikuchi T. , Omote K. , Koinuma H. , Kawasaki M.
Published: April 2011

We report on the development of a high throughput x-ray diffractometer that concurrently measures spatially resolved x-ray diffraction (XRD) spectra of epitaxial thin films integrated on a substrate. A convergent x-ray is focused into a stripe on a substrate and the diffracted beam is detected with a two-dimensional x-ray detector, so that the snapshot image represents a mapping of XRD intensity with the axes of the diffraction angle and the position in the sample. High throughput characterization of crystalline structure is carried out for a BaxSr1-xTiO3 composition-spread film on a SrTiO3 substrate. Not only the continuous spread of the composition (x), but also the continuous spread of the growth temperature (T) are given to the film by employing a special heating method. The boundary between the strained lattice and relaxed lattice is visualized by the concurrent XRD as functions of x and T in a high throughput fashion.
Information-rich High-Throughput Screening of Curing Formulations Via the Large Sample Array Calorimeter
Authors: Stirn Pamela J. , Hofelich Tom C. , Tamilarasan Ramasamy R.
Published: April 2011

This paper describes the use of an automated Large Sample Array Differential Scanning Calorimeter (LSA-DSC or LSA) for process optimization. The LSA was designed specifically for screening studies of multi-variable arrays where a large number of samples need to be examined simultaneously. It is ideal for kinetic evaluation of both biological and chemical reactions. The LSA can be used in either a temperature scanning (DSC) or isothermal (IMC) mode. An example where this equipment was used to optimize epoxy formulations will be presented. These formulations were prepared with high throughput techniques and evaluated using the LSA-DSC to determine the cure kinetics.
Combinatorial Mapping of Polymer Film Wettability On Gradient Energy Surfaces
Authors: Ashley Karen , Sehgal A. , Amis Eric J. , Raghavan D. , Karim A.
Published: April 2011

Combinatorial methods were used for studying dewetting of thin hydrophobic polystyrene (PS) and hydrophilic poly(DL-lactic acid) (PDLA) films on chemically modified gradient energy surfaces. Substrate libraries were prepared by immersing passivated Si (Si-H surface functionality) in Piranha solution (H2SO4/H2O2/H2O) at acontrolled rate, yielding a systematic variation of solvent contact angles across the surface. Additionally, chlorosilane-treated Si surfaces were exposed to UV radiation in a gradient fashion under ozone atmosphere such that a range from hydrophobic to hydrophilic conditions was obtained across the surface (≈ 3 cm). Solvent droplet contact angles of water and diiodo methane were used to quantify the spatial variation of surface energy along one axis across the surface. Libraries of thin films of PS or PDLA coatings on gradient energy surfaces orthogonal to gradients in film thickness were screened for dewetting behavior using automated optical microscopy. Contrasting trends in the wettability of PS and PDLA were visibly apparent as a function of surface energy of the substrate. The number density of polygons of the dewet PS films was found to obey a power law relationship with both film thickness and substrate surface hydrophilicity.
Flash Photolysis of Polystyrene with Laser
Authors: Hongwei Ma , Yongjian Tang , Baoshun Cui , wende Gao , Weiming Liu , Shouwen Wang , Hong Ma
Published: April 2011

This paper describes the photolysis of polystyrene with 1.06μm laser. The laser dissociation is measured with mass spectrum method. It gives the mean mass value of particles, quantum value and percentage of m/e=104 vs time.
Energy Landscapes: An Overview
Authors: Wales David J.
Published: April 2011

The goal of energy landscape theory is to relate observable thermodynamic and dynamic properties to features of the underlying potential energy surface. Here we illustrate the approach with reference to the annealing of C60and indicate how it may be used to design improved global optimisation algorithms.
Going through Rough Times: from Non-Equilibrium Surface Growth to Algorithmic Scalability
Authors: Korniss G. , Novotny M.A. , Rikvold P.A. , Guclu H. , Toroczkai Z.
Published: April 2011

Effcient and faithful parallel simulation of large asynchronous systems is a challenging computational problem. It requires using the concept of local simulated times and a synchronization scheme. We study the scalability of massively parallel algorithms for discrete-event simulations which employ conservative synchronization to enforce causality. We do this by looking at the simulated time horizon as a complex evolving system, and we identify its universal characteristics. We find that the time horizon for the conservative parallel discrete-event simulation scheme exhibits Kardar-Parisi-Zhang-like kinetic roughening. This implies that the algorithm is asymptotically scalable in the sense that the average progress rate of the simulation approaches a non-zero constant. It also implies, however, that there are diverging memory requirements associated with such schemes.
Atomistic Modeling of III-V Semiconductors: Thermodynamic Equilibrium and Growth Kinetics
Authors: Grosse Frank , Barvosa-Carter William , Zinck Jennifer J. , Gyure Mark F.
Published: April 2011

Growth kinetics and thermodynamic equilibrium can both be determining factors at different stages of III-V semiconductor heteroepitaxy. We study their interplay, employing kinetic Monte Carlo simulations for the InAs(001) surface. The simulation contains atomistic details of both species, including the stability of different reconstructions and their kinetics. The behavior of the surface in thermodynamic equilibrium, including different reconstructions, is determined exclusively by extensive total energy calculations employing ab initio density functional theory. The continuous phase transition between the α2(2x4) and β2(2x4), predicted by theory, is confirmed by experiment. At full layer coverage, a recovery of the stable reconstruction is observed. The different time scales associated with As2 and In are discussed with respect to equilibrium and kinetics.
Design of Functionally Graded Composite Structures for Control of Stress
Authors: Lipton Robert , Velo Ani
Published: April 2011

In this paper a methodology is introduced for the design of structural components made from composite materials for the control of stress. A numerical method is developed for designing functionally graded materials with minimum stress in prescribed sub-domains inside the structure.
Value-In-Use of Composite Reinforcing Fibers
Authors: Wallenberger Frederick T.
Published: April 2011

This paper analyzes the value-in-use of advanced fibers, especially of those, which are used to reinforce polymer matrix composites. Of particular interest in this regard are some recent fibers, such as (1) pure silica fibers derived from water glass, (2) oxynitride glass fibers, having the same high elastic modulus as SM carbon fibers, and (3) Kenaf, as well as other natural plant fibers, which are beginning to find commercial use in selected automotive composites.
Glass Fibers from High and Low Viscosity Melts
Authors: Wallenberger Frederick T. , Weston Norman E.
Published: April 2011

Typical commercial and experimental oxide glass fibers are made from silicate melts, which have viscosities of log 2.5 to log 3.0 poise at the forming temperatures. But, strong fibers were recently also made from melts having viscosities of 0.5 to 2.0 poise, and a sharp melting point rather than a viscosity that gradually changes with temperature. This paper analyzes the various mechanisms of fiber formation, and proposes an answer to the apparent inconsistencies. In this context, the present paper bridges recent advances in the disciplines of advanced inorganic fibers [1], composite reinforcing fibers [2, 3, 4], and fiber glass reinforcements [5].
Theory and Simulation of Texture Formation in Mesophase Carbon Fibers
Authors: Yan J. , Rey A. D.
Published: April 2011

Carbonaceous mesophases are spun into high performance carbon fibers using the melt spinning process. The spinning process produces a range of fiber textures whose origins are not well understood. Planar polar (PP) and planar radial (PR) textures are two ubiquitous ones. A model that describes the formation process of the PP texture based on the Landau-de Gennes mesoscopic theory for discotic liquid crystals, including defect nucleation, defect migration, and overall texture geometry, is presented, solved, and validated. The computed PP and PR textures phase diagram, given in terms of temperature and fiber radius, is presented to establish the processing conditions and geometric factors that lead to the selection of these textures. The influence of elastic anisotropy to the textures formation and structure is also characterized.
Characterizing the Thermomechanical Degradation of a Filled Elastomer by Morphology and X Ray Photoelectron Spectroscopy
Authors: Crosta Giovanni F , Nelson Art J , Camatini Marina C
Published: April 2011

Three types of debris particles, denoted by L2, H2 and K3 respectively, originated from the abrasion of silica-filled, vulcanized rubber under different test conditions (severity) were analyzed and compared. The structural fractal dimension, DFS, of the particle perimeter was chosen as a morphological descriptor (but not necessarily as an intrinsic property of the fractured material !). Said dimension was estimated by processing light microscopy images. A value of the morphological threshold, TST, which separates the textural from the structural domain in the RICHARDSON plot was determined in order to maximize discrimination between the three particle types and rank them by increasing values of DFS. Particles from the highest severity test (K3) exhibited the highest value of DFS. X ray photoelectron spectroscopy (XPS) provided elemental composition, core level binding energies and the speciation of C, N, O, Si and S. As a result, L2 debris was found to originate from two processes: fracture of rubber and segregation of extender oil. Evidence has come both from morphology and XPS. Particles of H2 and K3 were ascribed to fracture alone. Comparison between K3 and the reference material, rasped rubber (RAS), shows the following: a) increase of the [S]/[C] surface atomic concentration ratio from RAS to K3; b) existence of multiple bonding states of S in K3 with energy peaking at 162.9 ± 0.3 eV ([-S-S-]n); c) weak contribution of R-S-O-R oxidized S species in K3 at 165 eV, not seen in RAS; d) no evidence of either SO3 or SO4 groups in any material. Although preliminary, these results prove the ability of morphological analysis and XPS to characterize the surface properties of debris particles non destructively.
Monotonic and Cyclic Fatigue Behavior of a High Performance Ceramic Fiber
Authors: Kerr M. , Williams J.J. , Chawla N. , Chawla K.K.
Published: April 2011

Monotonic and cyclic fatigue behavior of fibers are of general interest, regardless of the end use of the product whether in a composite or in a fabric. Study of cyclic fatigue behavior of fibers is particularly difficult because of their small diameter (∼10 μm) and high aspect ratio. In this paper, we report some preliminary results of monotonic tension and tension – tension fatigue behavior of a ceramic fiber: Nextel 312 (Al2O3-SiO2-B2O3) fiber. This fiber has a nanocrystalline structure with B2O3mostly in the form of a glassy phase. The tensile strength data of this fiber showed a Weibull modulus of 4.6, indicating a large degree of variability. Our experiments show clear indication of cyclic loading being more damaging than static loading for Nextel 312. The fracture surface observations of fatigues samples showed some distinctly different features from those observed in fibers subjected to monotonic tension.
Novel Templated Polyphenol for Ionic Conductivity
Authors: Bruno Ferdinando F. , Nagarajan Ramaswamy , Kumar Jayant , Samuelson Lynne A.
Published: April 2011

Phenolic polymers and phenol formaldehyde resins are of great interest for a number of electronic and industrial applications. Unfortunately, the toxic nature of the starting materials (formaldehyde) and harsh reaction conditions required for the synthesis of these polymers have severely limited their use in today’s markets. We present here an alternative, biocatalytic approach where the enzyme horseradish peroxidase is used to polymerize phenol in the presence of a template such as polyethylene oxide. Here the template serves as a surfactant that can both emulsify the phenol and polyphenol chains during polymerization and maintain water/solvent solubility of the final polyphenol/template complex. The reactants and the reaction conditions of this approach are mild and result in high molecular weight, electrically and optically active, water-soluble complexes of polyphenol and the template used. High molecular weight water-soluble polyphenol/polyethylene oxide complexes were formed. The ionic conductivity and potential use of these polymers as polyelectrolytes for battery and solution cell applications will be discussed.
Insights into Toughening Particulate Brittle Composites
Authors: Merchant I.J. , Chandler H.W. , Henderson R.J. , Stebbings T. , Macphee D.E.
Published: April 2011

A conventional approach to the toughening of brittle materials has been to incorporate fibrous inclusions. These toughen the composite by acting as crack bridges, with energy being dissipated by frictional losses during pull-out of the fibre or by matrix failure on the scale of fibre surface roughness. In all cases, toughening has been achieved only where propagating macrocracks have interacted with an appreciable number of reinforcing inclusions. This paper considers the probability that toughening via crack-bridging in these fibrous and especially particulate toughened materials has not been optimised and proposes the idea that the frequency of interaction between crack and inclusion is strongly increased by un-bonding the inclusion from the matrix. Results from studies on cement-mortars are presented in support of this and show significant improvements in toughness associated with samples in which inclusions are deliberately un-bonded from the matrix in advance of the crack arriving.
Infiltration of Al-Mg Alloy into SiC Preform in the Production of Metal Matrix Composites by Pressureless Infiltration
Authors: Zulfia A. , Hand R.J.
Published: April 2011

Molten Al-Mg alloys has been infiltrated into SiC to produce Al matrix composites at 900oC for different infiltration times under N2. The wettability of the ceramic reinforcement by the Al-Mg alloy is crucial in determining whether Al can be infiltrated into ceramic preform. Sessile drop results showed that Al alloys with Mg contents greater than 8wt-% had a contact angle lower than 90o, after 5 minutes contact time, this was associated with the infiltration of Al-Mg alloys into SiC preform occurred after 30 minutes. Sessile drop experiments also show that SiC is similarly wetted by Al-Mg alloys under N2. It is concluded that the infiltration process does not involve the intermediate nitride phase suggested by other authors. These materials were also charaterised both mechanical properties and microstructure.
The Coercivity – Remanence Tradeoff in Nanocrystalline Permanent Magnets
Authors: Lewis Laura H. , Crew David C.
Published: April 2011

The energy product (BH)maxis a figure of merit quantifying the maximum amount of useful work that can be performed by the magnet. The energy product is determined by the magnetic remanence and the coercivity which, as extrinsic properties, are determined by the magnets' microstructure. Thus, in principle, magnetic material microstructures may be tailored to obtain defined parameters to produce optimal permanent magnets. However, as asserted by the eponymous Murphy, “Nature favors the hidden flaw”. While there is still much undeveloped potential in nanomagnetic materials, with relevant length scales on the order of 100 Å, accumulating evidence strongly suggests that maximum remanence and maximum coercivity are mutually exclusive in nanocrystalline magnetic materials. Diverse experimental and computational results obtained from nanocrystalline Nd2Fe14B-based magnets produced by melt-spinning techniques and subjected to various degrees of thermomechanical deformation confirm this conclusion. Recent results obtained from temperature-dependent magnetic measurement, magnetic force microscopy and simple micromagnetic modeling will be reviewed and summarized. The results, while somewhat discouraging, do hint at possible materials design routes to sidestep the inherent performance limitations of the magnetic nanostructures.
Silver-Polyimide Nanocomposite Films Yielding Highly Reflective Surfaces
Authors: Southward Robin E. , Dean C. J. , Scott J. L. , Broadwater S. T. , Thompson D. W.
Published: April 2011

Highly reflective surface-metallized flexible polyimide films have been prepared by the incorporation of the soluble silver ion complex (1,1,1-trifluoroacetylacetonato)silver(I) into dimethylacetamide solutions of the poly(amic acid) prepared from 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoro-propane (4-BDAF). Thermal curing of solution cast silver(I)-poly(amic acid) films leads to cycloimidization of the amic acid with concommitant silver(I) reduction and formation of a reflective surface-silvered film at 8 and 13 weight percent silver. The metallized films are thermally stable and flexible with mechanical properties similar to those of the parent polyimide. TEM reveals that the bulk (interior) of the polyimide composite films have 5-20 nanometer-sized silver particles with a surface layer of silver metal ca. 80 nm thick. Neither the bulk nor the surface of the films is electrically conductive. Adhesion of the surface metal to polyimide is excellent.
What Xe Nanocrystals in Al Can Teach us in Materials Science
Authors: Allen C. W. , Birtcher R. C. , Dahmen U. , Furuya K. , Song M. , Donnelly S. E.
Published: April 2011

Noble gases are generally very insoluble in solids. For example, Xe implanted into Al at 300 K forms a fine dispersion of crystalline precipitates and, at large enough fluence, fluid precipitates, both of which are stabilized, relative to the gas phase, by the Laplace pressure due to precipitate/matrix interface tensions. High resolution electron microscopy has been performed to determine the largest Xe nanocrystalline precipitate in local equilibrium with fluid Xe precipitates within the Al matrix. From the shape and size of the largest crystal and the Laplace pressure associated with its interface, we show that the interface tensions can be derived by setting the Laplace pressure equal to the pressure for solid/fluid Xe equilibrium derived from bulk Xe compression isotherms at the temperature of equilibration and observation. The Xe/Al interface tensions thus derived are in the range of accepted values of surface tensions for the Al matrix. Furthermore, it is suggested that this same technique may be employed to estimate unknown surface tensions of a solid matrix from the size and shape of maximal nanocrystals of a noble gas element, which have been equilibrated in that matrix at the temperature of observation.
H3PO4 / oxide nanoparticles / polymer composites as proton conducting membranes
Authors: Carrière D. , Barboux P. , Moreau M. , Boilot J.-P.
Published: April 2011

Stable sols of 60 nm colloidal zirconia have been prepared by thermolysis of zirconium acetate. The surface complexing acetate groups have been replaced by phosphoric acid groups. Phosphate grafting has been characterized by dynamic light scattering, infrared spectroscopy, 31P nuclear magnetic resonance and impedance spectroscopy measurements. These systems give acid and proton conductive particles (4.10-5 S.cm-1 at 70 % relative humidity).

H3PO4/ZrO2/PVDF-co-HFP composite membranes have been synthesized. Impedance spectroscopy measurements allow discrimination between proton conduction at the surface of the phosphated particles and within free H3PO4 in the polymer. For the highest H3PO4/ZrO2 ratios, the latter phenomenon prevails, giving a proton conductivity of 6.10-4 S.cm-1 at 70 % R.H.