bluuebunny/crossref_metadata_2025 huggingface dataset:
Expansive Reactions in Concrete Observed by Soft X-Ray Transmission Microscopy
Authors: Kurtis K. E. , Monteiro P. J. M. , Brown J. T. , Meyer-Ilse W.
Published: April 2011

Alkali-silica reaction, sulfate attack, and reinforcing steel corrosion can compromise the long-term durability of concrete structures. The anticipated economic impact of an extensive infrastructure repair scheme has produced a renewed interest in the development of advanced characterization methods to assess the degree of deterioration in the concrete experiencing these deleterious reactions. The products of the alkali silica reaction, sulfate attack, and corrosion as well as the cement hydration products are extremely sensitive to humidity. Consequently, characterization techniques that require high vacuum or drying, as many existing techniques do, are not particularly appropriate for the study of these reactions in concrete as artifacts are introduced. A high resolution instrument which allows the examination of these reactions and their products without drying and at normal pressures will promote understanding of the reactions and provide further insight into means of mitigating the damage they cause. Only soft x-ray transmission microscopy provides the required high spatial resolution to observe the reaction process in situ. The alkali-silica reaction can be observed over time, in a wet condition, and at normal pressures, features unavailable with most other high resolution techniques. Soft x-rays also reveal information on the internal structure of the sample. This paper reviews published and ongoing applications of soft x-ray transmission microscopy for the study of expansive reactions that occur in concrete.
Kinetics Of The Growth Of Copper Clusters On The Alumina (0001) Surface : Influence Of Surface Structure
Authors: Gautier-Soyek M. , Gota S. , Douillard L. , Le Fevre P. , Magnan H. , Duraud J. P.
Published: April 2011

The kinetics of the growth of copper clusters on the alumina (0001) surface was studied as a function of surface structure, using EXAFS at the Cu K edge. Equivalent Cu coverages ranging from 0.5 to 4 equivalent monolayers were deposited in situ, at room temperature, on alumina (0001) surfaces exhibiting the (1×1) or the reconstructed structure. The evolution of mean cluster size with deposition time was followed from the mean Cu coordination number in the clusters deduced from the EXAFS data. The increase of the mean cluster radius with deposition time is characteristic of a coalescence mechanism on both surfaces. The growth is quicker on the reconstructed surface, likely due to different surface diffusion properties of both surfaces.
Synchrotron X-ray Absorption Studies of Atomic-Level Alloying in Immiscible Mixtures
Authors: He J.-H. , Schilling P. J. , Ma E.
Published: April 2011

An X-ray absorption beamline has been developed recently at the electron storage ring of the LSU Center for Advanced Microstructures and Devices. Using Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES), we have studied the local atomic environments in immiscible mixtures processed by high-energy ball milling, a mechanical alloying technique involving heavy deformation. By examining the local coordination and bond distances, it is concluded that atomic-level alloying can indeed be induced between Cu and Fe through milling at room temperature, forming substitutional fcc and bcc solid solutions. In addition to single-phase regions, a two-phase region consisting of fcc/bcc solutions has been found after milling at both room temperature and liquid nitrogen temperature. In contrast to the Cu-Fe system, solid solution formation is not detectable in milled Ag-Fe and Cu-Ta mixtures. This work demonstrates the power of synchrotron EXAFS/XANES experiments in monitoring nonequilibrium alloying on the atomic level. At the same time, the results provide direct experimental evidence of the capability as well as limitations of high-energy ball milling to form alloys in positive-heat-of-mixing systems.
Micro-, Meso- and Macro-Texture and Fatigue Crack Roughness in Al-Li 2090 T8E41
Authors: Haase J. D. , Guvenilir A. , Witt J. R. , Stock S. R.
Published: April 2011

The use of synchrotron polychromatic x-ray microbeams in the transmission geometry is described for mapping grain orientation as a function of position and for relating this microtexture to the formation of large asperities on fatigue crack surfaces in Al-Li 2090 T8E41. In common with the centers of rolled plates of many aluminum alloys, Al-Li 2090 T8E41 has a sharp average texture or macrotexture different from that in the outer portions of the plate. The geometry of large asperities in Al-Li 2090 has been related to this macrotexture, and the resulting roughness-induced crack closure is recognized to be responsible for the very low crack propagation rates in certain plate orientations. This report focuses on why asperities form at certain positions and why the crack remains relatively planar elsewhere. The microtexture (i.e., the grain-to-grain orientation variation) seems to be organized into a specific type of mesotexture: multiple adjacent grains have nearly identical orientations and form substantial volumes of near-single-crystal material. Transitions between differently oriented near-singlecrystal volumes or between a near-single- crystal region and more randomly oriented grains appear to bound asperities.
X-Ray Microbeam Quantification of Grain Subdivision Accompanying Large Deformations of Copper
Authors: Butler G. C. , Guvenilir A. , McDowell D. L. , Stock S. R.
Published: April 2011

Polychromatic synchrotron x-ray microbeams offer a very efficient alternative to electron beam methods for quantifying the amount and character of grain subdivision accompanying large deformations. With a 0.01 mm diameter collimator, bending magnet radiation from a 3.0 GeV source and image storage plates, samples of copper with thicknesses greater than 0.1 mm have been studied. Results from an as-received sample and a sample deformed to 100% torsion are compared and illustrate how efficiently grain subdivision can be quantified with polychromatic microbeam diffraction.
Grain Orientation Mapping of Passivated Aluminum Interconnect Lines with X-ray Micro-Diffraction
Authors: MacDowell A. A. , Chang C. H. , Padmore H. A. , Patel J. R. , Thompson A. C.
Published: April 2011

A micro x-ray diffraction facility is under development at the Advanced Light Source. Spot sizes are typically about 1-μm size generated by means of grazing incidence Kirkpatrick-Baez focusing mirrors. Photon energy is either white of energy range 6-14 keV or monochromatic generated from a pair of channel cut crystals. A Laue diffraction pattern from a single grain in a passivated 2-μm wide bamboo structured Aluminum interconnect line has been recorded. Acquisition times are of the order of a few seconds. The Laue pattern has allowed the determination of the crystallographic orientation of individual grains along the line length. The experimental and analysis procedures used are described, as is a grain orientation result. The future direction of this program is discussed in the context of strain measurements in the area of electromigration.
Reduction of Droplet Density onto Hydroxyapatite Films Grown by Pulsed Laser Deposition from Concave-Shaped Targets
Authors: Craciun Valentin
Published: April 2011

A new deposition method, inspired from the crossed fluxes technique, which employs a concave, conic-shaped target is presented here. The rectangular excimer laser beam used for ablation was focused so that the middle of the spot laid exactly on the tip of the concave-shaped target. Each half of the laser spot created a plasma plume on one side of the concave target which was the symmetrical image across the cone axis of that created by the other half of the laser spot. The heavy droplets passed through the plasma interaction region without collisions and, maintaining their direction of motion, moved away from the system axis. The majority of the ablated ions and atoms emitted from one side of the spot collided with those emitted from the other side and, because of the symmetry of the concave-shaped target, acquired a velocity component along the system axis, moving towards the substrate. Scanning electron microscopy investigations showed a significant reduction of droplet density onto the surface of hydroxyapatite layers grown from such concave-shaped targets as compared to films grown from the usual cylindrical targets.
Modifications of Diamond Films Induced by Pulsed Laser Treatment
Authors: Cappelli E. , Mattei G. , Orlando S. , Pinzari F. , Ascarelli P.
Published: April 2011

Diamond thin films promise excellent performance in several application fields such as high temperature and high frequency electronics, but practical applications are presently limited by the polycrystalline morphology of deposited films.

A laser treatment was performed to smooth the surface of diamond films, produced by HFCVD, with the aim to allow a suitable patterning and tayloring of diamond films and their use as coatings on specific tools. Different laser wavelengths (193, 532 nm), times of exposure, and energy densities were employed during the treatments.

A SEM characterization has shown a structural modification of the surface morphology and a noticeable weakening of surface roughness. A microRaman analysis indicated the appearance of a glassy carbon component which, together with the surface smoothing occurring at the treated zone, seems to justify: a) the large reduction of the intensity of Raman spectra (the diamond and silicon optical phonon lines and the photoluminescence emission are about 50 times weaker); b) the enhancement of conductivity and reflectivity.
Does the Subsurface Superheating Effect Really Exist?
Authors: Craciun Valentin , Craciun Doina
Published: April 2011

The existence inside targets during pulsed laser ablation of a sub-surface superheating effect (SSSH) has been predicted by numerical temperature estimations. The experimental evidence has been so far only indirect, based on the modification of the surface morphology caused by the explosive volume boiling induced by the SSSH effect. However, round-shaped micrometer-sized cavities formed by gas release due to volume boiling have been found on several target materials even when the temperature estimations did not predict any SSSH effect. Although the SSSH effect could exist under certain conditions, it seems that it is not a prerequisite for explosive volume boiling which is the actual mechanism responsible for droplets emission. Volume boiling could occur whenever a thick liquid layer, whose temperature is much higher than the equilibrium boiling value is formed and lasts for several tens of nanoseconds on the target surface, a situation usually found when the laser wavelength is poorly absorbed by the target material.
Fabrication of Ferroelectric Fet with Metal/PZT/SiO2/Si Structure
Authors: Yu Jun , Zhou Wenli , Xie Jifan , Zheng Yuankai , Dong Xiaoming , Liu Gang
Published: April 2011

We have fabricated a new ferroelectric memory FET, which consists of the Au/Pb(Zr0.52Ti0.48)O3/SiO2/Si gate structure. Ferroelectric PZT thin film with a thickness of 250~400 nm was prepared by using Excimer Laser Ablation Deposition. Silicon oxide successfully served as a buffer layer between ferroelectric and Si substrate to suppress the charge injection and prevent Pb interdiffusion. Electrical properties of the ferroelectric FET have been characterized through both the Capacitance vs. Voltage(C-V) and Current vs. Voltage(I-V) measurements, showing a typical memory characteristics of FET devices, i.e., the ON state and OFF state were nonvolatile for about thirty minutes and several hours, respectively.
Laser Ablated Buffer Layers for YBCO-Tape Conductors
Authors: Holzapfel B. , Betz V. , Arranz M.A. , Reger N. , Schultz L.
Published: April 2011

Biaxially oriented yttria stabilized zirconia (YSZ) and Pr6O11 buffer layers were grown at room temperature by Ion-Beam Assisted Laser Deposition (IBALD) on metal substrates. Dependent on deposition parameters, IBALD grown films showed in-plane orientations of about 10° FWHM (full-width at half maximum) for both systems. In contrast to the YSZ system, where best in plane alignment is found for a [111] direction oriented parallel to the ion beam, the Pr6O11 system shows best in-plane alignment at nearly gracing incidence of the ion beam. An additional thin intermediate CeO2 layer improves the heteroepitaxial growth of YBCO on highly biaxially oriented YSZ films. Pulsed Laser Deposition (PLD) was also used to grow epitaxial CeO2 buffer layers directly on biaxially textured Ni-tapes. SIMS investigations showed an interdiffusion zone of about 0.5μm at standard deposition conditions, but no enhanced grain boundary diffusion could be observed.
Atomic Structure and Property Correlation in Pulsed Laser Deposited High -Tc Films
Authors: Kalyanaraman R. , Oktyabrsky S. , Jagannadham K. , Narayan J.
Published: April 2011

The atomic structure of grain boundaries in pulsed laser deposited YBCO/MgO thin films have been studied using transmission electron microscopy. The films have perfect texturing with YBCO(001)//MgO(001), giving rise to low-angle [001] tilt boundaries from the grains with the c-axis normal to substrate surface. Low angle grain boundaries have been found to be aligned preferentially along (100) and (110) interface planes. The energy of (110) boundary planes described by an alternating array of [100] and [010] dislocation is found to be comparable to the energy of a (100) boundary. The existence of these split dislocations is shown to further reduce the theoretical current densities of these boundaries indicating that (110) boundaries carry less current as compared to (100) boundaries of the same misorientation angle. Further, Z-contrast transmission electron microscopy of a 42° asymmetric high-angle grain boundary of YBCO shows evidence for the existence of boundary fragments and a reduced atomic density along the boundary plane
Surface Modification and Ablation of Insulators Using a Tunable, Picosecond Mid-Infrared Laser
Authors: Haglund R. F. , Ermer D. R. , Lines A. H. , Papantonakis M. R. , Park H. K. , Yavas O.
Published: April 2011

Ultrashort-pulse lasers with fundamental wavelengths ranging from near-infrared to near-ultraviolet are increasingly being used for laser-induced surface modification of non-metallic solids. The relaxation of the initial electronic excitation into vibrational relaxation modes can produce efficient ablation and other desirable surface modifications with little collateral damage because the laser energy is deposited on a time scale much shorter than thermal diffusion times. Little is known, however, about how ultrashort pulses interact with insulators at wavelengths in the vibrational infrared. This paper describes surface modifications achieved by picosecond laser irradiation in the 2-10 lim range. The laser source was a tunable, free-electron laser (FEL) with I-ps micro-pulses spaced 350 ps apart in a macropulse lasting up to 4 μs, with an average power of up to 3 W. This unusual pulse structure makes possible novel tests of the influences vs fluence and intensity, as well as the effects of resonant vibrational excitation. As model materials systems, we studied calcium carbonate, its isoelectronic cousin sodium nitrate, and fused silica. Particularly intriguing are surface modifications achieved by tuning the laser into vibrational resonances and overtones of the target materials, or by tailoring the energy content of the pulse. The mechanisms underlying these effects, and their implications for materials-modification strategies, are discussed.
Studies of Carbon Nitride Thin Films Synthesized by KrF Excimer Ablation of Graphite in Nitrogen Atmosphere
Authors: Ren Z.M. , Lu Y.F. , Song W.D. , Chan D.S.H. , Low T.S. , Gamani K. , Chen G. , Li K.
Published: April 2011

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite in nitrogen atmosphere. Different fluences of the excimer laser and pressures of the nitrogen atmosphere were used in order to achieve a high nitrogen content in the deposited thin films. Fourier Transform Infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The highest N/C ratio 0.42 was achieved at an excimer laser fluence of 0.8 Jcm -2with a repetition rate of 10 Hz under the nitrogen pressure of PN=100 mTorr. A high content of C=N double bond instead of C-N triple bond was indicated in the deposited thin films. Ellipsometry was used to analyze the optical properties of the deposited thin films. The carbon nitride thin films have amorphous-semiconductor-like characteristics with the optical band gap Eop, as high as 0.42 eV.
Characterization of Pulsed-Laser Deposited Amorphous Diamond Films by Spectroscopic Ellipsometry
Authors: Jellison G. E. , Geohegan D. B. , Lowndes D. H. , Puretzky A. A. , Merkulov V. I.
Published: April 2011

Spectroscopic ellipsometry is used to characterize amorphous diamond, also known as tetrahedral amorphous carbon, (ta-C) films grown by pulsed laser ablation. The ellipsometry data is collected with the two-modulator generalized ellipsometer, which measures all three parameters required to characterize isotropic samples, as well as additional parameters used to characterize strain-induced birefringence of the focusing optics. Lenses are used to focus the light spot to an ellipse 0.7 × 2.0 mm2, allowing us to perform several ellipsometric measurements across the profile of ta-C films grown on 7.5 cm diameter Si wafers. The spectroscopic ellipsometry data are fit using a model of the ta-C dielectric function based on the Tauc band edge and the Lorentz expression of the dielectric function for an ensemble of atoms. These fits are used to determine the thicknesses of the rough surface layer, the ta-C film, and the interface layer, as well as the energy gap of the film. Comparisons are made with fits to an earlier formulation due to Forouhi and Bloomer [Phys. Rev. B 34, 7018 (1986).]. In addition to being Kramers-Kronig consistent, the Tauc-Lorentz formulation fits the ta-C data better.
Pulsed Laser Treatment of WC, Co Tool Substrates to Improve Co Removing and Diamond Nucleation
Authors: Cappelli E. , Orlando S. , Pinzari F. , Ascarelli P.
Published: April 2011

Diamond coated cutting tools seem to be one of the most promising system to machine non ferrous, very hard materials, like metal matrix composites (MMC), carbon fibers, hypereutectic Al/Si alloys. The widespread used and cheaper bulk material for tool inserts, the WC,Co hard metal, is convenient and profitable as a substrate for diamond film coatings. Unfortunately, the Co-rich binder phase constitutes a severe obstacle for diamond deposition. Because of the catalytic effect for amorphous carbon or soot formation, the presence of Co actually results in a detrimental effect both on diamond nucleation and adhesion to substrate. Several chemical and physical methods have been developed to etch Co from the surface, no conclusive and perfectly reliable procedure, however, has been achieved, as far as a strong adhesion is concerned.

In our experiments, we used ArF (λ = 193 nm, hv ≅ 6.4 eV) and Nd:YAG (λ= 532 nm, hv ≅ 2.3 eV) pulsed laser treatment to selectively remove Co from the surface and to seal the structural voids, coming out after Co chemical etching from the substrate, and responsible of surface segregation of Co from the bulk, during CVD diamond deposition. The sealing efficiency, after a thermal treament (3h, 800°C) in an inert atmosphere, resulted to be quite good, compared to the untrated surface. The morphological and chemical effects have been studied by SEM/EDAX microscopy.
Deposition of Ablation Products from UV-Laser Irradiated Polymer Surfaces
Authors: Arenholz E. , Kirchebner A. , Klose S. , Heitz J. , Bäuerle D.
Published: April 2011

The growth and structure of surface dendrites observed after UV-Iaser irradiation of polyethylene-terephthalate (PET) have been investigated. The lateral size and structure of dendrites is strongly influenced by the laser wavelength and ambient pressure. Pressure-dependent experiments demonstrate the importance of redeposition of ablation products onto the laser-modified surface. Different possible growth mechanisms are discussed.
Pulsed Laser Ablation of Low-Density Nanoporous Metal Oxides
Authors: Gimon-Kinsel Mary E. , Muñoz Trinidad , Balkus Kenneth J.
Published: April 2011

Pulsed laser ablation has been employed to generate thin films of low density metal oxides, including nanoporous molecular sieves. An excimer laser (KrF*, 248 nm) was used to deposit molecular sieve films onto a variety of substrates including polished silicon, platinum, tantalum, titanium nitride, glass, indium-doped tin oxide, copper and Mylar. Recent results for the deposition of microporous UTD-1 and FeAPO-5 as well as mesoporous aluminosilicate MCM-41 and Nb-TMSI molecular sieve films are presented. The order (crystallinity) of the laser deposited films has been shown to be enhanced by a brief post hydrothermal treatment. A vapor phase treatment of the laser deposited FeAPO-5 films allows for increases in film crystallinity without an increase in film thickness. Hydrothermal treatment of laser deposited Nb-TMSI results in “worm hole” pore motif which is new for this composition. Silicate based molecular sieves such as UTD-1 and aluminosilicate MCM-41 require a UV-absorbing guest molecule for laser ablation giving rise to a phenomenon referred to as guest assisted laser ablation (GALA). The molecular sieve films were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy.
In Situ Synthesis of Single-Phase Skutterudite Thin Films (CoSb3 and IrSb3) by Pulsed Laser Deposition
Authors: Caylor J.C. , Stacy A.M. , Bandaru P. , Sands T. , Gronsky R.
Published: April 2011

Recent advances in doping and substitutional alloying of bulk skutterudite phases based on the CoAs3 structure have yielded compositions with high thermoelectric figures-of-merit (“ZT”). It is postulated that further enhancements in ZT may be attained in artificially-structured skutterudites by engineering the microstructure to enhance carrier mobility while suppressing the phonon component of the thermal conductivity. This work describes the growth of single-phase skutterudite thin films (CoSb3 and IrSb3) by pulsed laser deposition. A substrate temperature of 250°C has been found to be optimal for the deposition of the skutterudites from stoichiometric targets. Above this temperature, the film is depleted of antimony due to its high vapor pressure. However, when films are grown from antimony-rich targets, the substrate temperature can be increased to at least 350°C without losing the skutterudite phase. Films from both target types were characterized with X-ray diffraction and Rutherford-Back-Scattering (RBS) to reveal structure and stoichiometry. Some preliminary electrical measurements will also be shown.
Time-Resolved Imaging and Photoluminescence of Gas-Suspended Nanoparticles Synthesized by Laser Ablation: Dynamics, Transport, Collection, and Ex Situ Analysis
Authors: Geohegan D. B. , Puretzky A. A. , Duscher G. , Pennycook S. J.
Published: April 2011

The dynamics of gas phase nanoparticle formation by pulsed laser ablation into background gases are revealed by imaging photoluminescence and Rayleigh-scattered light from gas-suspended SiOx nanoparticles following ablation of c-Si targets into 1-10 Torr He and Ar. Two sets of dynamic phenomena are presented for times up to 15 s after KrF-laser ablation. Ablation of Si into heavier Ar results in a uniform, stationary plume of nanoparticles while Si ablation into lighter He results in a turbulent ring of particles which propagates forward at 10 m/s. The effects of gas flow on nanoparticle formation, photoluminescence, and collection are described. The first in situ time-resolved photoluminescence spectra from 1-10 nm diameter silicon particles were measured as the nanoparticles were formed and transported. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to photoluminescence from oxidized porous silicon were measured, but with a pronounced vibronic structure. The size and composition of individual gas-condensed nanoparticles were determined by scanning transmission electron microscopy and correlated with the gas-phase photoluminescence. Weblike-aggregate nanoparticle films were collected at room temperature and 77K on c-Si substrates. After standard passivation anneals, the films exhibited strong room temperature photo-luminescence consisting of 3 spectral bands in agreement with the gas-phase measurements, however lacking the vibronic structure. These techniques demonstrate new ways to study and optimize the luminescence of novel optoelectronic nanomaterials during synthesis in the gas phase, prior to deposition.
Fabrication of Iron Oxide Nanoparticles by Pulsed-Laser Ablation
Authors: Sasaki Takeshi , Zeng Xiaoyan , Koshizaki Naoto
Published: April 2011

Nanoparticles of iron oxide were prepared by pulsed laser ablation on carbon coated mica substrates. An ArF excimer laser was used to irradiate a Fe2O3 target in atmospheres of Ar at room temperature. The effects of ambient pressure on size and morphology of nanoparticles were investigated using transmission electron microscopy. The morphology of the deposited nanoparticles was strongly dependent on the ablation pressure. The formations of nanoparticles and their aggregates were observed at pressures higher than 46.7 Pa and 267 Pa of Ar, respectively. The size of the primary nanoparticles ranged from 2 – 9 nm and their size distribution agreed with a log-normal distribution function. The aggregate size increased with ambient pressure and the primary particle size was independent of ambient pressure.
Aerosol Formation and Evolution During Laser Ablation
Authors: Camata Renato P. , Hirasawa Makoto , Okuyama Kikuo , Takeuchi Kazuo
Published: April 2011

Low pressure differential mobility analysis and transmission electron microscopy were used to study the aerosol formed during 1064-nm pulsed Nd3+:YAG laser ablation of a solid cesium iodide (CsI) target. Measurements reveal that the aerosol is comprised of particles in three size regimes: particles with approximately log-normal size distributions and Dpg ~ 10 nm, compact spherical CsI particles with Dpg ~ 80 nm, and fractal-like agglomerates with Dpg ~ 1-3 μm.
Analysis of Impurity Diffusion in Ordered Alloys and Intermetallic Compounds of the L12 Type
Authors: Belova I.V. , Murch G.E.
Published: April 2011

In this paper we present a new formalism for impurity diffusion in A3B alloys taking the L12 structure. We analyse two limiting cases, where impurities remain entirely on the α sublattice and where the impurities are distributed between the two sublattices but the actual mobility is largely confined to the α sublattice. Application is made to In diffusion in Ni3Al and Al diffusion (which may itself act like an impurity on the α sublattice) in Ni3Al.
Mechanisms of Al Self- and Al-Substituting Solute Diffusion in Ni3Al
Authors: Frank St. , Divinski S. , Herzig Chr.
Published: April 2011

Diffusion of the Al-substituting elements Ga, Ge, Ti and Nb has been investigated in Ni3Al single crystals by the secondary ion mass spectrometry (SIMS). A model for the minority component diffusion by anti-structure defects has been suggested for the Ll2 structure. It involves both nearest neighbor jumps of the solute atoms on the Ni sublattice as anti-structure atoms and the formation of so-called anti-structure bridges which correspond to jumps between different sublattices. The model under consideration was shown to agree with the experimental data on the Al-substituting solute diffusion (X = Ga, Ge, Ti, Nb) in Ni3Al and it allows to explain also the observed ratio of the diffusivities DNi/DX, which may be higher and/or lower than unity in dependence on the solute and temperature.
Measurements of the Diffusion of Iron and Carbon in Single Crystal NiAl using Ion Implantation and Secondary Ion Mass Spectrometry
Authors: Hanrahan R. J. , Withrow S. P. , Puga-Lambers M.
Published: April 2011

Classical diffusion measurements in intermetallic compounds are often complicated by low diffusivities or low solubilities of the elements of interest. Using secondary ion mass spectrometry for measurements over a relatively shallow spatial range may be used to solve the problem of low diffusivity. In order to simultaneously obtain measurements on important impurity elements with low solubilities we have used ion implantation to supersaturate a narrow layer near the surface. Single crystal NiAl was implanted with either 12C or both 56Fe and 12C in order to investigate the measurement of substitutional (Fe) versus interstitial (C) tracer diffusion and the cross effect of both substitutional and interstitial diffusion. When C alone was implanted negligible diffusion was observed over the range of times and temperatures investigated. When both Fe and C were implanted together significantly enhanced diffusion of the C was observed, which is apparently associated with the movement of Fe. This supports one theory of dynamic strain aging in Fe alloyed NiAl.
Diffusion in Metals and Intermetallic Compounds: The Impact of AB-INITIO Calculations
Authors: Fähnle M. , Meyer B. , Mayer J. , Oehrens J.S. , Bester G.
Published: April 2011

By means of statistical mechanics the relations between the effective formation energies, entropies and volumes of atomic defects in ordered compounds which may be obtained experimentally and the parameters characterizing the microscopic properties of the single defects are derived, and the microscopic parameters are determined by the ab-initio electron theory. In a second step, the migration energies for possible self-diffusion paths are calculated by the transition-state theory in combination with the ab-initio electron theory. Results are reported for B2-FeAl and for Fe3Al, Ni3Sb and Fe3Si with D03 structure, and the impact of the calculations on the interpretation of experimental data is discussed.
Fermi-Level Effect, Electric Field Effect, and Diffusion Mechanisms in GaAs Based III-V Compound Semiconductors
Authors: Tan T. Y. , Chen C.-H. , Gösele U. , Scholz R.
Published: April 2011

Diffusion mechanisms and point defects in GaAs and related III-V compounds are discussed. An understanding of the As sublattice situation has been arrived at fairly recently and is presently tentative. Understanding of the Ga sublattice situation has become more acceptable in that experimental results are consistently explained by the Fermi-level effect and the As4 pressure effect. On the Ga sublattice, though controversies still exist, some are readily resolved by noting the role of the electric field produced by semiconductor electrical junctions, physical junctions, and surfaces.
Arsenic Diffusion in Intrinsic Gallium Arsenide
Authors: Bösker G. , Stolwijk N.A. , Mehrer H. , Södervall U. , Thordson J.V. , Anderson T.G. , Burchard A.
Published: April 2011

Self-diffusion on the As sublattice in intrinsic GaAs was investigated in a direct way by As tracer diffusion measurements using the radioisotopes 73As and 76As and in an indirect way by annealing of buried nitrogen doping layers in epitaxially grown GaAs/GaAs:N heterostructures. The latter experiments were analyzed by secondary ion mass spectroscopy and interpreted within the framework of the kick-out mechanism yielding the As diffusivities mediated by As interstitials IAs. Comparison of with tracer diffusion coefficients – including data reported in the literature–points to a substantial contribution of IAs to As diffusion in intrinsic GaAs under As-rich ambient conditions.
Impurity Diffusion in SiGe Alloys: Strain and Composition Effects
Authors: Larsen Arne Nylandsted
Published: April 2011

The advent of epitaxial-growth techniques dedicated to the growth of epitaxial layers of group-IV semiconductors and their alloys has opened up new possibilities for novel types of diffusion experiments and thus for critical tests of existing diffusion theories. It is now possible to grow test structures for diffusion consisting of well-defined narrow distributions of tracer impurities in epitaxial layers of biaxial-strained or relaxed alloys of different compositions. This enables studies of alloy effects and/or strain effects on diffusion with varying strain energy for a well-defined type of strain (tensile or compressive). A review is presented on recently published results on impurity diffusion in strained and relaxed, epitaxial SiGe alloy layers. As almost all these studies have focused on boron and antimony diffusion, these two impurities will have the leading roles in this review.
Time Dependence of Arsenic Precipitates' Size Distribution in Low Temperature GaAs
Authors: Hung C.Y. , Harris J.S. , Marshall A.F. , Kiehl R.A.
Published: April 2011

The time dependence of the size distribution of arsenic precipitates during annealing for both large (~10nm) and small size (~4nm) regimes is investigated. A narrowing of the size distribution is observed in the small size regime. This improvement in size uniformity is in marked contrast to what is observed for larger precipitates, which coarsen with a widening distribution similar to that of classical Ostwald ripening. Inverse coarsening caused by an elastic interaction between small precipitates due to coherency strain is a possible mechanism for this interesting and potentially useful behavior.
Ultra-Fast NiSi2 Formation in p+-Si by High Current Densities
Authors: Huang J.S. , Tu K.N.
Published: April 2011

An ultra-fast lateral formation of epitaxial NiSi2 line in heavily doped p+-Si diffused tub was created at room temperature ambient under the application of current densities of 106 A/cm2. A NiSi2 line of 140 μm long and I μm wide linking the cathode and anode contacts to p+-Si was formed within 1 second. Shorter lines were formed with lower current densities. The formation of shorter lines was again completed within 1 second and there was very little subsequent growth upon further stressing. The line length strongly depends upon applied current which tend to suggest that the line formation is limited by driving force rather than by kinetics. We propose that the ultra-fast silicide formation is a result of Ni interstitial diffusion in Si induced by electron-hole recombination heating and electromigration.
Enhanced Oxide Ion Diffusion in the Interlanthanide Perovskite LaTmO3
Authors: Deepa M. , Varadaraju U.V.
Published: April 2011

Recent studies on Perovskites type compounds revealed an oxide ion conductivity, higher than that of Fluorite structures. The most recent one is doped Lanthanum Gallate, which exhibits a maximum ionic conductivity of 0.14 S cm-1 and is a promising new ion conductor. The objective of this study is to synthesize and investigate the ionic conductivity of a similar compound, namely doped LaTmO3. Single phase compounds of the system La1-xSrxTm1-yMgyO3(X=0-0.2,y=0.1&0.2) were synthesized and the ionic conductivity measured at various temperatures. The results showed that ionic conductivity improved significantly with Sr doping. It showed highest oxygen ion diffusion and catalytic activity for Sr doped LaTmO3.
Localized Diffusional Motion of Hydrogen and Deuterium in Crystalline Pd9Si2
Authors: Karmonik C. , Huang Q. , Udovic T.J. , Rush J.J. , Andersson Y. , Flanagan T.B.
Published: April 2011

Using quasielastic neutron scattering, we have studied the dynamics of hydrogen and deuterium in crystalline Pd9Si2. For both isotopes, a localized motion was found which takes place between two energetically different sites. For the hydrogenated sample, the spatial and temporal parameters characterizing this motion are derived. The results are in agreement with neutron powder diffraction and neutron vibrational spectroscopic measurements.
Diffusion of Carbon into RE2Fe17(RE=RARE Earth) Lattice: A High Temperature Approach
Authors: Venkatesan M. , Varadaraju U.V. , Rao K.V.S. Rama
Published: April 2011

The interstitial carbides HoErFe15Ga2Cy (y=0,0.5,1.0,1.5,2.0) were synthesized by are melting technique and characterized by X-ray diffraction and magnetization measurements. The hexagonal Th2Ni17 type structure persisted in all compounds. Both the Curie temperature TC and unit cell volume v are found to increase monotonically with increasing carbon concentration. The unit cell volume increase of Ga substituted carbide HoErFe15Ga2C2.0 is around 6.1% compared to HoErFe17. The Curie temperature increase is mainly due to the strengthening of exchange interaction. The Ga substitution is found to not only help the formation of single phase but also enhance the uniaxial anisotropy.
Stress Effects and Non-Linearities in Dwfusional Mixing of Multilayers
Authors: Beke D.L. , Nemes P. , Erdélyi Z. , Szabó I.A. , Langer D.G.
Published: April 2011

In classical treatments of diffusional mixing of multilayers it is usually supposed that i) the intrinsic diffiision coefficients, Di, are independent of concentration, and they are equal (the Kirkendall shift is zero) [1]; ii) the stress effects are discussed in the framework of the CahnHilliard--theory [1,2]; iii) the deviation from the continuum description can be analysed for a sinusoidal concentration distribution in the discrete Fick equations. These limitations are discussed here and numerical simulations are used to show the effects of the strong concentration dependence of Di. The role of stresses are discussed in the framework of the treatment given by Stephenson [3], which contains the effect of simultaneous stress relaxation (Kirkendall-shift) as well. For the correct description of the Kirkendall-effect a generalised analytical expression for the gradient energy term is also given. The consequences of above effects on the decay of the intensity of the first small angle Bragg peak, due to the concentration modulation, is illustrated.
Modification of Fibroin Film with A Chimera Fibroin Fragment for Improvement of Cell Adhesion
Authors: Tamada Yasushi
Published: April 2011

Silk fibroin is a naturally occurring structural protein with good mechanical properties used in a variety of forms, such as powder, fiber, film, and gel. Although silk fibroin is potentially suitable for use in tissue engineering, it lacks cell regulation functions such as cell adhesion, growth, metabolism, and differentiation. The immobilization of biologically active molecules such as proteins and peptides has been reported as promising in controlling cell behavior. Silk fibroin's phase transition is characterized by a conformational change of protein from a random coil to a beta sheet. During phase transition, biological molecules can be stably entrapped in silk fibroin without the use of chemicals. We designed a novel immobilization using this phase transition mechanism with a chimera fibroin fragment. The chimera fibroin fragment was constructed by linking a bioactive peptide to fibroin fragments including crystal regions. In the first study, a synthetic oligonucleotide encoding Arg-Gly-Asp peptide which promotes cell adhesion, was fused to the fibroin fragment gene through inframe gene fusion, and the chimera fibroin (RGD-fibroin) gene was expressed by E.coli. This paper discusses RGD-fibroin construction, and the results of cell adhesion on fibroin films containing RGD-fibroin.
Positron Annihilation Lifetime Measurements in Collagen Biopolymer
Authors: Siles S. , Moya G. , Li X.H. , Kansy J. , Moser P.
Published: April 2011

Lifetime measurement in Positron Annihilation Spectroscopy (PAS) is applied to the study of free-volume collagen characteristics as a function of concentration. The lifetimes of positrons were obtained by a conventional fast-fast coincidence system. All lifetime data are fitted in three components by using the computer program POSITRON FIT and resolved. For each concentration, lifetime distributions were analyzed in order to obtain the different components, thus we have observed three components of which a long component τ3. This long lived component can be associated with a pick-off annihilation of ortho-positronium (o-Ps) trapped in free volumes of amorphous region. This investigation shows the potential of the positron annihilation spectroscopy technique in the study of biopolymer microstructures.
Neuronal Outgrowth Guidance on Patterned Organic Films
Authors: Matsuzawa M. M. , Krauthamer V. , Potember R.S.
Published: April 2011

Glass substrates were modified with organic thin films to guide the outgrwoth of cultured neurons dissociated from the central nervous system. Embryonic hippocampal neurons, grown on these modified substrates, developed a morphology by following the surface geometries and they formed contacts with each other. We are now investigating technical procedures for forming physiological synapses using goldfish retinal neurons in culture.
Development of A Flexible Cell Targeting System Based on Silica Nanoparticles
Authors: Schiimstel T. , Schirra H. , Gerwann J. , Lesniak C. , Kalaghi-Nafchi A. , Sametik M. , Borchard G. , Haltner E. , Lehr C.-M. , Schmidt H.
Published: April 2011

Commercially available and synthesized silica particles were fluorescently labeled with FITC and modified to get a wide variety of particle systems with defined size and surface charge. By a variation of reaction conditions particles with diameters of 10 and 80 nm determined with TEM and with zetapotentials between -50 to +30 mV under physiological conditions (pH: 7.4, PBS-buffer) were available.

A further molecular shell consisiting of avidin was obtained by binding the molecules to negatively charged particle surfaces through electrostatic interactions. The amount of avidin coupled to the silica particles was 1.7 μg per mg particle. Starting with particles with an hydrodynamic diameter determined with PCS of 260 nm, the size increased to 500 nm, while the zeta potential was altered to -8 mV under physiological conditions.

Biotinylated wheat germ agglutinin (bio-WGA) can be bonded to such particles through avidin / biotin complex formation. Up to 2.8 μg lectin per mg particles could be coupled to the particle surface. This leads to a further increase of hydrodynamic diameter to 650 nm. It could be shown by hemagglutination test, that the bonded lectin is still active. No toxic effects of the silica particles were found at 1 wt.-% particle concentration with various cell types (Caco-2, L132). The binding of lectin-particle complexes to cells was increased by a factor of 4.4 in comparison to uncoated particles.

In addition it was found that WGA can directly be coupled to the particle surface. An amount of 1.8 μg Lectin per mg particle was determined. The hydrodynamic diameter increases from 260 nm to 432 rm, while a zetapotential of-28 mV was found under physiological conditions.

It could be shown, that negatively charged silica nanoparticles are suitable systems to couple various biomolecules retaining their biological function.
Tailoring Polymer Surfaces for Controlled Cell Behavior
Authors: Mayes A.M. , Irvine D.J. , Griffith L.G.
Published: April 2011

An ideal surface for many biomaterials applications would resist nonspecific protein adsorption while at the same time providing a means for specifically signaling cells to guide survival, growth, migration, and differentiation. This work was directed towards the investigation of model systems and clinically-applicable materials which provide both of these surface requirements. Model systems were prepared by chemically grafting end-functionalized star poly(ethylene oxide) (PEO) to surfaces. The end-grafted polymers provide a means for cell-signaling through coupling of peptides to the free chain ends. Protein adsorption on star vs. linear grafted layers was compared. To further understand these results, neutron reflectivity studies were carried out in situ for solvated PEO surfaces to determine the concentration profiles of the swollen grafted layers. Surprisingly, grafted PEO layers which resist protein adsorption have low concentrations of polymer segments throughout the swollen layer. We find that dense star architectures which might be expected to impart improved protein resistance in fact allow small proteins to adsorb. For clinical materials, a novel approach to the surface modification of poly(lactide) (PLA) has been taken by surface segregating a comb copolymer containing a PLA backbone and poly(ethylene glycol) teeth. The ends of the teeth provide sites for surface tethering of peptide ligands. Comb surfaces without tethered ligands are cell adhesion resistant, indicating strong protein adsorption resistance. By then incorporating an adhesion ligand, modulation of cell morphology on comb surfaces has been demonstrated. Finally, the surface segregation of the comb to the surface of PLA was shown via cell attachment assays and XPS measurements.
Determining the Enthalpy of Formation of A Si Interstitial Using Quantitative Tem and Sims
Authors: Bharatan S. , Haddara Y. M. , Law M. E. , Jones K. S.
Published: April 2011

Some of the key parameters used in process simulators are formation energy, diffusivity and the concentration of Si self-interstitials. Unfortunately, experimental verification of these parameters is lacking. This work is therefore designed to determine the equilibrium concentration of self-interstitials at various temperatures and thus compute the formation energy for selfinterstitials in Si. Samples with thin (10 nm) buried boron layers were grown by MBE and samples with a buried type II dislocation loop layer were produced by Ge+ implantation into undoped MBE. These samples were subjected to a 40 KeV 1E14 /cm2 Si+ implant followed by anneals at temperatures between 685°C and 815°C for varying times. The loop layer was investigated to monitor the total flux of the interstitials as a function of time while the broadening of the B layer profile was analyzed by SIMS to determine the interstitial supersaturation. A combination of these two values provides an estimate of the equilibrium concentration of the Si interstitials. The results at various temperatures are then used to extract the enthalpy of formation of the Si interstitial.
Investigation of the Growth and Chemical Stability of Composite Metal Gates on Ultra-thin Gate Dielectrics
Authors: Claflin B. , Binger M. , Lucovsky G. , Yang H.-Y.
Published: April 2011

The growth of reactively sputtered TiNx and WNx compound metal films on ultra-thin, remote plasma enhanced chemical vapor deposited SiO2 and SiO2/Si3N4 (ON) stack dielectrics is investigated from initial interface formation to bulk film by interrupted growth and on-line Auger electron spectroscopy (AES). Growth of both metals occurs uniformly without a seed layer on both dielectrics. The chemical stability of these metal/dielectric interfaces is studied by sequential on-line rapid thermal annealing treatments up to 850 °C and AES. TiNx reacts with SiO2 above 850 °C but the addition of a Si3N4 dielectric top-layer makes the TiNx/ON interface chemically stable at 850 °C. WNx/SiO2 and WNx/Si3N4 interfaces are both stable below 650 °C. MOS capacitors using TiNx or WNx metal gates and thermal SiO2 gate dielectrics exhibit excellent capacitance-voltage characteristics. The work function for TiNx lies near midgap in Si while for WNx it lies closer to the valence band.
Properties of Vacancies in Silicon Determined by Out-Diffusion of Zinc from Silicon
Authors: Giese A. , Bracht H. , Walton J. T. , Stolwijk N. A.
Published: April 2011

We present out-diffusion of Zn in Si as a new method to study properties of Si vacancies. Out-diffusion experiments were performed on homogeneously Zn-doped Si samples at 1107°C and 1154°C. The resulting concentration-depth profiles were measured by means of spreading-resistance profiling. Based on a diffusion model in which Zn migrates simultaneously via the kick-out and the dissociative mechanism all experimental profiles were modeled by computer simulations. The calculations reveal that out-diffusion of Zn from Si occurs to a considerable extent via the dissociative mechanism. Hence, vacancy properties like the equilibrium concentration CVeq and the transport capacity CveqDV can be extracted from profile fittings. The results are compared with literature data deduced from in-diffusion experiments.