bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTAn 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

ABSTRACTThe 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

ABSTRACTPolychromatic 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

ABSTRACTA 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

AbstractA 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

AbstractDiamond 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

AbstractThe 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

AbstractWe 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

AbstractBiaxially 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

AbstractThe 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

AbstractUltrashort-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

AbstractCarbon 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

AbstractSpectroscopic 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

AbstractDiamond 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

AbstractThe 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

AbstractPulsed 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

AbstractRecent 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

AbstractThe 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.