bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the Sputtering Parameters on the Properties of A12O3 and Ain Insulators in Spin Tunneling Junctions
Authors: Plaskett T.S. , Freitas P.P. , Sun J.J. , Sousa R.C , da Silva F. F. , Galvão T.T.P. , Pinho N.M. , Cardoso S. , da Silva M.F. , Soares J. 
Published: April 2011

ABSTRACTThe role of the sputtering parameters on the properties of thin A12O3 and A1N insulator layers for spin dependent tunneling junctions was studied. A12O3 insulators were prepared by rf sputtering from an A12O3 target in an Ar or Ar-O2 atmosphere and also by plasma oxidation in an O2 atmosphere of a thin Al layer. The thin Al layer was deposited by rf sputtering at room temperature. A1N was prepared by reactive sputtering from an Al target in a Ar-N2 atmosphere. The index of refraction n measured by ellipsometry, was used to optimize the sputtering parameters, and chemical etch rates were used for information on pin-hole density. The aimed values were n=1.75 for A12O3 (corundum structure) and n=2.2 for A1N. For reactively sputtered A12O3, under optimized deposition conditions, n reaches 1.65 for films 300 Å thick. A12O3 thin layers fabricated by plasma oxidation of a thin Al film were also prepared but the oxide layer was too thin for ellipsometry characterization. A1N insulating films show a constant n value of 1.92 from 400 Å down to 60 Å thick films. Rutherford backscattering analysis show that the ratio of Ar to N2 must be less than 1 to avoid O2 incorporation in the film. Junctions of the type glass/buffer/FM/insulator/FM, where FM is either Co or NiFe, were made by contact metal masks with a junction area of 0.25 mm.2 The A12O3 deposited by sputtering from an A12O3 target under conditions expected to give n>1.5 had a magnetoresistance at room temperature MR(RT) of 2.5% with a junction resistance Rj of 2.2 m Ω and by fitting the I-V curve to existing tunneling theory gave an effective barrier thicknesst of 20 Å and a barrier heightΦ of 2.2 eV. These occurred in only one sample (9 junctions) and were not reproducible. The A12O3 insulators prepared by plasma oxidation of a thin Al layer gave a MR(RT)= 4%, tj = 22 Å, Rj=250 k,Ω and Φ =1.4 eV. The A1N insulator with n =1.9 gave a MR(RT)= 1.6 %, t = 20 A, Rj = 4.8 kΦ and barrier height 1.2 eV. In the last two cases junctions with MR at room temperature can be produced with reasonable reproducibility, Al2O3 samples showed a 15–20% increase in MR as the temperature was lowered to 17 K, while AIN junctions show an increase of a factor of 2 in MR at 77 K.
Effect of Ru Impurities on Magnetoresistance in Co/Ru/Co(Ru) Sandwiches
Authors: Dinia A. , Rahmouni K. , Persat N. , Stoeffler D. , Ounadjela K. , van den Berg H.A.M. 
Published: April 2011

ABSTRACTMagnetoresistance (MR) measurements have been performed on two series of Co(3.2 nm)/Ru(x=0.5 to 3 nm)/Co(3.2 nm) and Co(3.2 nm)/Ru(x)/Co.92Ru.08 (3.2 nm) sandwiches prepared by ultra high vacuum evaporation onto mica substrates. At 300 K, all samples of the first series present giant magnetoresistance (GMR) whereas the samples of the second series, and with the same Ru spacer thickness, show an inverse GMR. This inverse GMR is induced by alloying the second Co layer with 8 at% Ru and can be attributed to the change of the scattering coefficients ratio (α) between the two magnetic layers. Indeed, for the first Co layer the scattering coefficient ratio a1 = p↓/↑> 1. However, for the second magnetic layer, alloying Co and Ru may induce an increase of the density of states at the Fermi level for majority spin electrons and as a consequence 0C2 = p↓/↑< 1
Magnetic Properties of Thin Eu Films on Gd(0001) Studied by Magnetic Circular Dichroism in Photoemission
Authors: Arenholz E. , Starke K. , Kaindl G. 
Published: April 2011

ABSTRACTThe magnetic order of ultra-thin Eu films on Gd(0001) was studied in an element-specific and layer-resolved way using magnetic circular dichroism (MCD) in 4ƒphotoemission (PE). It was found that Eu films up to 2 monolayers (ML) exhibit a high net magnetization parallel to that of the Gd substrate. For Eu coverages exceeding 2 ML, the ferromagnetic alignment of the Eu moments breaks down, except for the Eu interface layer. A comparison of the temperature dependences of the Eu-4/ and Gd-4/ MCD-PE signals for 1-ML-Eu/Gd(0001) with the results of a layer-resolved mean-field calculation results in values for the exchange-coupling constants within the Eu monolayer as well as between Eu and the Gd substrate.
Formation and Properties of Nanosize Ferromagnetic MnAs Particles in Low Temperature GaAs by Manganese Implantation
Authors: Wellmann P.J. , Garcia J.M. , Feng J.-L. , Petroff P.M. 
Published: April 2011

AbstractThe synthesis of ferromagnetic particles of the size of several nm (10… 100nm) imbedded in semiconductors is of particular interest for device applications such as magnetic sensors, switches or memories based on integrated semiconductor devices. We have investigated the formation as well as the structural and magnetic properties of MnAs nanomagnets (size ≈ 20nm) in low temperature grown GaAs (LT-GaAs). The MnAs nanomagnets which show ferromagnetism at room temperature have been synthesized using ion implantation with Mn and subsequent rapid thermal annealing (RTA). To characterize these nanomagnets, we present SQUID measurements (superconducting quantum interference device), TEM analysis (transmission electron microscopy) and EDX analysis (electron beam induced x-ray fluorescence).
Tight Binding KKR - Application to CoCu(001): Electronic Structure and Transport
Authors: Zahn P. , Mertig I. , Zeller R. , Dederichs P.H. 
Published: April 2011

AbstractStarting from a tight binding formulation of the KKR (Korringa-Kohn-Rostocker) Green function method we developed a self consistent band structure code. By using a reference system containing repulsive muffin tin potentials we obtain structure constants which decay exponentially with distance. In the case of multilayered systems the numerical effort scales linearly with the number of monolayers in a unit cell. We report about calculations of CoCu(001) systems. With our method we are able to consider the electronic structure, the interlayer exchange coupling, and the transport properties (conductivity, giant magnetoresistance = GMR) on an equal footing.
Effect of Cap-Layers on Interlayer Exchange Coupling
Authors: Kudrnovský J. , Drchal V. , Bruno P. , Coehoorn R. , De Vries J.J. , Wildberger K. , Dederichs P.H. , Weinberger P. 
Published: April 2011

ABSTRACTThe effect of non-magnetic cap-layers on the amplitudes and the phases of the oscillations of interlayer exchange coupling (IEC) is studied theoretically on ab initio level. We employ a spin-polarized surface Green function technique within the tight-binding linear muffin-tin orbital method and the Lloyd formulation of the IEC. Application is made to Co/Cu/Co(001) trilayers with Cu-cap layers interfacing vacuum through the dipole barrier.
Study of perpendicular induced magnetic moments in the Ag of Ag/Fe multilayers
Authors: Phale T. , Dekoster J. , De Moor P. , Schuurmans P. , Severijns N. , Trhlik M. , Van Geert A. , Vanneste L. , Vereecke B. , Brewer W.D. 
Published: April 2011

AbstractWe investigated the induced magnetic behaviour of the Ag of Fe/Ag multilayers with low temperature nuclear orientation. The experiments show induced magnetic moments in all samples. Furthermore, multilayers with 2ML and 4ML of Ag, these moments do not lie in the plane of the multilayer at low external magnetic fields.
Electrical Extraction of The in-Plane Dielectric Constant of Fluorinated Polyimide
Authors: Loke Alvin L.S. , Wetzel Jeffrey T. , Stankus John J. , Simon Wong S. 
Published: April 2011

AbstractFluorinated polyimide can potentially replace TEOS as an interlevel dielectric in future ULSI interconnect technologies because its lower dielectric constant offers reduced crosstalk, signal propagation delay, and dynamic power dissipation. One issue associated with polyimides is the anisotropy in dielectric constant, where the smaller out-of-plane dielectric constant, typically measured using parallel-plate capacitors, can misleadingly exaggerate the advantage in reducing crosstalk. In this paper, we present a novel electrical technique to estimate the in-plane dielectric constant of DuPont FPI-136M fluorinated polyimide without requiring dielectric gapfill.A blanket FPI-136M film is deposited over interdigitated inlaid Al(0.5%Cu) structures and the crosstalk capacitance is measured. Identical inlaid structures with air and TEOS passivations are also measured for capacitance calibration. Differences in measured capacitances reflect electric fields fringing in the various passivation dielectrics above the inlaid metal. With the known dielectric constants of air and TEOS, the effective dielectric constant of FPI-136M is interpolated to be 2.8. Interconnect simulations confirm that the effective dielectric constant extraction technique is valid and accurate provided that the passivation layer is sufficiently thick to contain the fringing fields.To estimate the in-plane dielectric constant, we use simulations to determine the combination of in-plane and out-of-plane dielectric constants that is equivalent to the extracted effective dielectric constant. With an out-of-plane dielectric constant of 2.6, the in-plane dielectric constant of FPI-136M is estimated to be 3.0. This technique is applicable to other dieletrics.
New Methodologies for Characterization of Low Dielectric Constant Thin Films
Authors: Todd Ryan E. , Cho Taiheui , Malik Irfan , Zhao Jie-Hua , Lee J.K. , Ho Paul S. 
Published: April 2011

AbstractNew methodologies are being developed in our laboratory that allow measurements of the Young's modulus (E) and thermal expansion coefficient (TEC) for materials that cannot be prepared as free standing films. The first employs a bending beam measurement of stress versus temperature. We measure the thermal stress of a given film on two substrates, Si and GaAs. The use of two substrates allows the determination of both E and TEC. A TEOS film is used to demonstrate the technique. Another technique is a variation of the stress-strain measurement of E. The brittle material of interest is coated onto a polymer substrate, and the composite film is elongated to obtain the stress-strain curve of the composite film. Subtraction of the polymer substrate contribution to this curve yields the stress-strain behavior of the brittle film and allows calculation of E.The in-plane dielectric constants of potential interlayer dielectrics (ILD) are determined from the interline capacitance between metal lines passivated with the material. We have developed a finite difference simulation to account for the fringe capacitance, and it allows the extraction of the in-plane dielectric constant from the measured capacitance. The method was used to measure the anisotropies in two polymer ILDs. A flexible chain polymer showed the same anisotropy in both a blanket film and on patterned lines, but a rigid rod-like polymer was found to be much less anisotropic on the patterned lines relative to the blanket film. This result indicates that the molecular orientation of the film is different on the patterned lines.
Diagnostics, Mechanisms of Deposition, and Process Control of Thin Fluoropolymeric Films in RF Discharges
Authors: d'Agostino R. 
Published: April 2011

AbstractPlasma deposited fluoropolymer films are shown to have composition, chemical structures and properties variable continuously in a very broad range. Films obtained under high fragmentation and structure retention conditions are discussed and compared. The mechanism of deposition is shown to explain etching-deposition competition. Finally, actinometric spectroscopy is discussed briefly as a semi-quantitative diagnostics tool enabling the control of the chemistry of the process under high fragmentation conditions‥
Novel Approaches to Linear Polyimides
Authors: Marasco J. P. , Garapon J. , Sillion B. 
Published: April 2011

AbstractPolyamic amides or polyamic esters are alternative polyimides precursors exhibiting a better storage-stability than classical polyamic acids. Two original synthetic routes to these polymers were investigated through either diisoimides and diimidazolides in order to enhance stability and to obtain pure para catenation.
Thermal Stability of a-C:F,H Films Deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition
Authors: Theil Jeremy A. , Mertz Francoise , Yairi Micah , Seaward Karen , Ray Gary , Kooi Gerrit 
Published: April 2011

AbstractAmorphous carbon films grown with fluorohydrocarbons can be grown to have dielectric constant values around 2.0. The behavior of these films when subjected to thermal excursion is studied. We have investigated material deposited in an ECR plasma, and find that the F:H ratio of the gas mixture is a good guide to material properties. Films deposited at 5°C were placed in a vacuum chamber at 400°C as long as 60 minutes. The film thickness, dielectric constant, and infrared absorption spectrum change with the F:H ratio of the incoming gas and thermal cycling. It was found that the dielectric constant and loss tangent decrease upon heating and that there is an apparent increase in C=C groups. As expected, as the F:H ratio increases, the dielectric constant and thermal stability decrease. Good thermal stability is shown for F:H ratios of 1.5, which result in films with a dielectric constant of ∼2.4 after heating.
Low K Sog Etchback and Teos Oxide Capping
Authors: Huang K.G. , Cheung D. , Nguyen D. , Forester L. 
Published: April 2011

AbstractSOG etchback was studied using Applied Materials' 200mm MxP+ etch chamber on Allied Signal's SOG (spin-on-glass) T11 and low κ SOP (spin-on-polymer) 418 together with liner films of PE-oxide and oxynitride for IMD (inter-metal dielectric) planarization. Excellent chamber performance and wide process window were demonstrated. Etch selectivities between various SOG and liner films are tunable in a wide range allowing optimization of IMD planarization.
In-Situ Transmission Electron Microscopy of the Solid-Phase Epitaxial Growth of GaAs: Sample Preparation and Artifact Characterization
Authors: Belay K. B. , Ridgway M. C. , Llewellyn D. J. 
Published: April 2011

AbstractIn-situ transmission electron microscopy (TEM) has been used to characterize the solidphase epitaxial growth of amorphized GaAs at a temperature of 260°C. To maximize heat transfer from the heated holder to the sample and minimize electron-irradiation induced artifacts, non-conventional methodologies were utilized for the preparation of cross-sectional samples. GaAs (3xI) mm rectangular slabs were cut then glued face-to-face to a size of (6x3) mm stack by maintaining the TEM region at the center. This stack was subsequently polished to a thickness of ~ 200 ýtm. A 3 mm disc was then cut from it using a Gatan ultrasonic cutter. The disc was polished and dimpled on both sides to a thickness of ~15 mimT.h is was ion-beam milled at liquid nitrogen temperature to an electron-transparent layer. From a comparison of in-situ and ex-situ measurements of the recrystallization rate, the actual sample temperature during in-situ characterization was estimated to deviate by ≤ 20°C from that of the heated holder. The influence of electron-irradiated was found to be negligible by comparing the recrystallization rate and microstructure of irradiated and unirradiated regions of comparable thickness. Similarly, the influence of “thin-foil effect” was found to be negligible by comparing the recrystallization rate and microstructure of thick and thin regions, the former determined after the removal of the sample from the microscope and further ion-beam milling of tens of microns of material. In conclusion, the potential influence of artifacts during in-situ TEM can be eliminated by the appropriate choice of sample preparation procedures.
Phase Separation: From the Initial Nucleation Stage to the Final Ostwald Ripening Regime
Authors: Sagui Celeste , O'Gorman Dean Stinson , Grant Martin 
Published: April 2011

ABSTRACTIn this work we have re-examined the classical problem of nucleation and growth. A new model considers the correlations among droplets and naturally incorporates the crossover from the early-stage, nucleation dominated regime to the scaling, late-stage, coarsening regime within a single framework.
Time Dependent Nucleation in a Bulk Metallic Glass Forming Alloy
Authors: Croat T. K , Kelton K. F. 
Published: April 2011

ABSTRACTThe effect of composition on the time-dependent nucleation rates in Zr65Al7.5Ni10CU17.5 glasses is investigated to better understand nucleation processes in partitioning systems. Asquenched glasses were annealed to produce a homogeneous dispersion of nanocrystals within the amorphous matrix. The nucleation rates were estimated from the number of crystallites produced as function of annealing time, using scanning and transmission electron microscopy. Experimental results for single and multiple-step annealing treatments are presented. The nucleation results are discussed briefly within the time-dependent model of the classical theory of nucleation.
Computer Simulations of the Chessboard-Like Microstructure Formation in Decomposing Alloys
Authors: Bouar Y. Le , Khachaturyan A. G. 
Published: April 2011

ABSTRACTThe mechanism of formation of a chessboard-like structure observed during coherent decomposition in alloys with several orientation variants of the precipitate phase is considered. It is based on the accommodation of coherency strain achieved by spatial rearrangement of orientation variants of the precipitate phase in an optimal pattern. The computational model of precipitation of the ordered tetragonal phase, based on the continuum stochastic field kinetic equations for the composition and lro parameters profiles, is formulated. Its numerical solution describes the spatial and temporal evolution of the microstructure, from nucleation to coarsening. It is shown that the chessboard-like microstructure is produced by strain-driven, self-assembling of orientation variants of the precipitate phase, faceted by the planes normal to the elastically soft directions. Coarsening of such microstructures occurs by consequent disappearance of entire rows of “tiles” in the pattern.
Approximations for Vibrational Thermodynamics of Disordered Alloys: Effective Supercells and the Quasiharmonic Method
Authors: De Fontaine Didier , Althoff Jeffrey , Morgan Dane , Asta Mark , Foiles Stephen , Quong Andrew , Johnson Duane 
Published: April 2011

ABSTRACTRecent work has suggested that vibrational effects can play a significant role in determining alloy phase equilibria. In order to better understand these effects and the methods used in their calculation, we investigate the vibrational properties of disordered Ni3A1 using the Embedded-Atom Method. We examine the effectiveness of the Special Quasirandom Structure (SQS) approximation, and find that an SQS-8 can accurately represent the vibrational thermodynamics of the disordered state. By the use of Monte Carlo (MC) techniques, we also find that the quasiharmonic approximation becomes less accurate as we approach the melting temperature, but that the accuracy may be extended to higher temperatures by resorting to the MC equation of state giving the specific volume as a function of temperature.
Competition Between SRO and LRO in CuAu3
Authors: Kompatscher M. , Lang H. , Püschl W. , Pfeiler W. 
Published: April 2011

ABSTRACTOrdering in CuAu3 was investigated by residual resistivity and X-ray scattering. L12 longrange ordering (LRO) in this alloy is quite sluggish, therefore for low quenching temperatures and sufficiently short annealing times only effects of short-range order (SRO) are observed. With increasing quenching temperature and/or increasing annealing time evolution of LRO was observed by both residual resistometry and X-ray scattering. From the resistivity measurements information can be gained on the boundaries of the order-disorder two-phase field. An analysis of SRO-relaxation yields an ordering activation energy of 2.1±0.1 eV.
Reentrance and Multistriped Phases in the Blume-Emery-Griffiths Model with Biased Diffusion
Authors: Seshaaiyar Geetha , McKay Susan R. 
Published: April 2011

ABSTRACTWe report new multistriped phases at high densities in a three-state model (Si = 0, ± 1) driven by an external field E and influenced by repulsive nearest neighbor interactions. The dynamics are dictated by local Metropolis rates with the ratio of particle-particle to particle-hole exchange given by γ. In the noninteracting limit, this model shows an ordered, low-current phase above a density-dependent critical field. In this phase the two types of charges are segregated from each other and from the vacancies, forming stripes transverse to the field direction. Addition of a repulsive bilinear interaction J favors mixing of the charges. This interaction competes directly with the charge-segregated ordering and the system undergoes a nonequilibrium transition to one of four other types of striped phases, some with checkerboard ordering. We have calculated the staggered charge density and used the amplitude of its longest wavelength Fourier component along the field direction as an order parameter to characterize this new type of striped ordering. The phase diagram in the parameter space of E, J, γ, and density shows both first and second order transitions, with second order transitions most prevalent in the high-E/J, high density regions. Our study also shows a reentrant phase diagram with only second order transitions for high γ and a tricritical topology at low γ. For field strengths close to zero, the system orders in a checkerboard fashion above a J-dependent density. Results were obtained using Monte Carlo simulations on a 30×30 square lattice with periodic boundary conditions and charge conservation.
Transitory Metastable Phases in Refractory Metals-Based Systems Solidified by Drop-Tube Processing: A First-Principles Approach
Authors: Pasturel A. , Vinet B. 
Published: April 2011

ABSTRACTRefractory metals and alloys are deeply undercooled in an ultrahigh vacuum drop-tube facility. During rapid solidification, some brightness traces give evidences of two successive phase transformations. First-principles calculations of the structural stability in these systems are developed to appreciate the possibilities of obtaining metastable phases.