bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of Sr0.7Bi2+xTa2O9 Thin Films on SiO2/Si at Low Temperature by Pulsed Laser Deposition and Fatigue-Tolerant C-V Characteristics with Large Memory Window
Authors: Okuyama Masanori , Matsumuro Yoshinori , Sugiyama Hideki , Noda Minoru
Published: April 2011

Preferentially (105)-oriented Sr0.7Bi2.8Ta2O9(SBTO) thin films on SiO2/n-Si(100) have been prepared by pulsed laser deposition at temperatures as low as 350°C, which is the lowest process temperature for growing SBTO ferroelectric thin films. Dielectric properties of the SBTO films have been improved by increasing the Sr/Bi atomic ratio from 0.7/2.8 to 0.7/2.0. Memory windows of as large as 3.6V and 4.V in the MFIS capacitor have been obtained at Sr/Bi ratios of 0.7/2.0 and 1.0/2.0 respectively and are the largest values reported in the MF(I)S diode structures. Little C-V degradation is observed up to with the 1010 cycles for the process temperature of 400°C, especially for Sr/Bi of 0.7/2.0, with the memory window remaining at more than 3.2V. Memory retention time was about 3×103 sec at which the difference in capacitance between “ON” and “OFF” states reduces to half of its initial value. Optimum hold bias voltage exists in the retention test. Improvement in memory characteristics is strongly related to the insulating properties of the ferroelectric and dielectric thin films rather than the value of dielectric constant.
Controlling the Chemical Order in PMN-Type Relaxors
Authors: Davies P. K. , Akbas M. A.
Published: April 2011

Investigations of pure and chemically substituted tantalate and niobate members of the Pb(Mg1/3 Nb2/3)O3 (PMN) family of perovskite relaxors demonstrate that the degree of cation ordering and size of the chemically ordered domains can be extensively modified by thermal treatment. These observations and refinements of the cation occupancies in well ordered samples conflict with the predictions of the widely accepted “space charge model”, and instead support a “random site” model for the 1:1 B-site ordering. In this model one of the positions in the ordered structure is occupied by Ta (or Nb) and the other contains a random distribution of Mg and the remaining Ta cations. The stability of the order and magnitude of the domain growth can be enhanced by relatively small concentrations of selected solid solution additives (e.g. Zr in Pb(Mg1/3Ta2/3)O3 (PMT); Th or Sc in PMN). Correlations between the stability of the 1:1 order and the size of the solid solution additive can be used to understand the different responses of the cation order in PMN and PMT to thermal treatment. Results are also presented for the dielectric response of fully ordered relaxors in the (l–x) Pb(Mg1/3Ta2/3)O3 – (x) Pb(Sc1/2 Ta1/2)O3 system. While large domain samples of PMT-rich compositions exhibit a relaxor response, a crossover to normal ferroelectric behavior is observed for x = 0.5. The change in the dielectric response can be rationalized in terms of the effect of the chemistry of the random site sub-lattice on the correlation length of the ferroelectric coupling.
Thermally Induced Imprint of PZT and SBT Thin Films
Authors: Kim Dong-Joo , Kim Seung-Hyun , Maria Jon-Paul , Kingon Angus I.
Published: April 2011

The imprint characteristics of chemical solution deposited Pb(Zr,Ti)O3 (PZT) and SrBi2Ta2O9(SBT) thin films have been investigated. The imprint properties were evaluated by polarization-electric field hysteresis measurements. Imprint was measured at the elevated temperatures to accelerate imprint rate. Several parametric variables such as voltage and DC bias were also used to investigate possible imprint mechanisms. To quantify imprint, two different standards for evaluation of ferroelectric capacitors were compared: voltage shift and asymmetric polarization shift. Two types of PZT thin films with the same Zr/Ti composition were prepared to investigate the influence of loop shape on the rate of imprint. In addition, the imprint behavior of SBT was also investigated. It is shown that the imprint rate is strongly dependent upon the method of evaluation as well as the loop shape.
Electrochemical Potential Gradients in Pb(Zr,Ti)O3 Thin Films
Authors: Brazier M. , Mansour S. , McElfresh M.
Published: April 2011

Thin film PbZr0.55Ti0.45O3 (PZT) capacitors were observed to develop a dc voltage offset when driven with an ac applied electric field. This voltage offset displayed a strong dependence on the ambient oxygen partial pressure, PO2, of the atmosphere above the film, in addition to applied electric field and temperature dependencies. A scenario is proposed wherein a chemical potential gradient is established in the film, the magnitude of which is determined by the ambient PO2. The subsequent redistribution of oxygen vacancies is thought to create the observed voltage offset. This hypothesis was supported by the observation of similar voltage offsets in compositionally graded PZT films. This effect shows promise for novel low-temperature oxygen sensing applications.
Crystal Structures of SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 Ferroelectric Materials
Authors: Shimakawai Y. , Nakagawa Y. , Kubo Y. , Kamiyama T. , Asano H.
Published: April 2011

Structural and ferroelectric properties of stoichiometric SrBi2Ta2O9 and Sr-deficient-and-Bi-excess Sr0.8Bi2.2Ta2O9 bulk ceramics materials are studied. The ferroelectric Curie temperatures for SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 are 300 and 400°C, respectively. Structure analysis by neutron powder diffraction reveals that Bi2O2 layer and TaO6 octahedra are considerably distorted and that atomic displacement along the a-axis causes ferroelectric spontaneous polarization. In Sro8Bi22Ta2O9, both Bi-substitution and cation-vacancies exist at the Sr-site. The calculated polarization of Sr0.8Bi2.2Ta2O9 is higher than that of the stoichiometric sample, which is consistent with observations of remanent polarization in thin-film capacitors. The Bi-substitution and the cation-vacancies at the Sr site enhance structural distortion in the TaO6 octahedron and lead to the higher Curie temperature and the higher ferroelectric spontaneous polarization.
Self-Poling of Thin BaTiO3 Films by Contact Potential Difference
Authors: Lubomirsky Igor , Chang David T. , Stafsudd Oscar M.
Published: April 2011

The substrate dependence of the ferroelectric properties of sol-gel derived BaTiO3 thin films was investigated. Thin (0.35 µm) films were deposited on Si substrates of various orientations and doping. Films deposited on p+ Si (1020 cm−3 B, 2% Ge) (110) were self-poled. The poling direction is self-restoring even after being reversed by an external bias or heated above the Curie temperature. The pyroelectric coefficient was not zero above the Curie point, which indicated that the films were permanently subjected to an electric field, which originates from the contact potential between the film and the substrate. Thisconclusion was confirmed by surface photo voltage spectroscopy. The possibility of a paraelectric to ferroelectric transition driven by an electric field due to the contact potential difference must be taken into account for dynamic random access memory (DRAM) applications.
Thick PLZT Films Grown by Sol-gel for Optical Device Applications
Authors: Linnik M. , Wilson O. , Christou A.
Published: April 2011

The preparation and characterization of thick PLZT films for spatial phase modulator applications are reported. Films were fabricated on LSCO/LAO substrates by a sol-gel technique using multiple heat-treatment parameters. The crystal quality of PLZT 9/65/35 films was investigated by X-ray diffraction and scanning electron microscopy.
Optical Phase and Amplitude Modulation in (9/65/35) Pb-La-Zr-Ti-O Thin Films
Authors: Young D. , Li H. , Choopun S. , Wang L. , Salamanca-Riba L. , Ramesh R. , Christou A.
Published: April 2011

Electro-Optic Pb0.91gLa0.09Zr0.65Ti0.35O3 (PLZT) thin films are studied for transverse optical modulator applications. PLZT thin films were grown by pulsed laser ablation on MgO and GaAs substrates. Structural characterization by x-ray diffraction, transmission electron microscopy, Rutherford backscattering, and sputter Auger electron profiling indicate polycrystalline, phase pure PLZT with evidence of interdiffusion and approximately 20nm RMS surface roughness.

Single PLZT thin films, grown on MgO substrates with a SrTiO3 (STO) buffer layer, were fabricated into simple modulator structures for electro-optical characterization.

Measurements were performed in normal transmission mode. Application of an oscillating electric field across the PLZT layer produced optical amplitude and phase modulation.

The application of an oscillating electric field of frequency f across the PLZT has been observed to produce f and 2f frequency modulation in both the phase and amplitude of the output light. Theoretical considerations show that this can be attributed to the quadratic nature of the electro-optic effect in PLZT.
Thin Liquid Films: Instabilities of Driven Coating Flows on a Rough Surface
Authors: Kondic L. , Bertozzi A.
Published: April 2011

The flow of a thin layer of fluid on a solid surface is of considerable technological importance; many industrial applications, ranging from spin coating of microchips to the design of photographic film, are susceptible to often undesirable instabilities. We use a recently developed numerical scheme to analyze the problem of flow down an inclined plane, and concentrate on the case of completely wetting fluid characterized by a small precursor film height, b. In particular, we explore the role of imperfections of the solid surface, exploring the influence of the length scale of the surface roughness on the film stability and eventual pattern formation (fingers and rivulets). It is found that perturbations characterized by very short length scale do not influence considerably the film stability, in contrast to the perturbations specified by longer length scales. Further, we find that the role of imperfections becomes more pronounced at smaller precursor film thicknesses, b. We also analyze the effect of a time dependent body force on the film stability.
Diffusion in Two Dimensions in The Presence of Sinks
Authors: Lavine J. P.
Published: April 2011

The diffusion of electrons in two dimensions is investigated when the model space has one or more sinks. A random walk approach is used to follow each electron until it is trapped at a sink. The times to capture are combined to form the survival time distribution. This is found to decay exponentially with time for the cases considered here. The characteristic time for the decay depends directly on the model space area and inversely on the number of traps or sinks and the trap radius. Power laws with non-integers are found for all three parameter dependences.
Confined Anomalous Dynamics: A Fractional Diffusion Approach
Authors: Metzler Ralf , Klafter Joseph
Published: April 2011

We study different boundary value problems for fractional diffusion equations which describe a non-Brownian particle. Absorbing and reflecting walls of a box, and the escape problem through a fluctuating bottleneck with coloured noise are considered.
Diffusion and Reactive Properties in Disordered Porous Media and in Confining Geometries
Authors: Levitz Pierre
Published: April 2011

Disordered porous networks are important examples of confining geometries. A challenging problem is to couple the morphology and the topology of such disordered systems with the diffusion and the reactive properties of embedded fluids (gases or liquid) inside the porous medium. Looking at the properties of the self-diffusion propagator, we first discuss how the geometric confinement influences the molecular diffusion and how the coupling between interfacial geometry and transport evolves in space and time. In the long time regime, two specific situations are presented. First, we focus on transport properties inside a membrane-like disordered matrix, the sponge phase (symmetric or asymmetric). Second, we discuss some basic properties of the Knudsen diffusion. The particular coupling with the pore network geometry allows to analyse this transport process in term of the continuous time random walk formalism (C.T.R.W.). An interesting consequence for some specific disordered porous media or “low dimension” geometries is a transition from a Gaussian diffusion to a Levy walk. Finally, excitation and relaxation kinetics are discussed. More specifically, NMR relaxation of water inside a Vycor glass is investigated and a comparison with recent experimental results is presented.
Molecular Configurations and Solvation Forces in Confined Alkane Films
Authors: Wang Jee-Ching , Fichthorn Kristen A.
Published: April 2011

We review the results of two studies [1,2] aimed at clarifying the surface forces of con fined fluids. In the first study [1], molecular-dynamics simulations are used to study the influence of chain branching on the molecular configurations of alkane films physically adsorbed on a solid surface. The symmetric n-decane molecules exhibit strong layering, while t-butyl-hexane films have a novel pillared-layered structure, in which a few randomly distributed molecules orient themselves with the t-butyl end near the surface and the alkyl tail perpendicular to the surface. These molecules are surrounded by parallel, layered molecules. In the second study [2], we outline the development of a new NP‖AT ensemble method, with advantages for simulating confined fluids. For confined Lennard-Jones particles simulated with the new method, clear oscillatory solvation-force profiles and step-like dependencies of the number of confined molecules on surface separation were observed. As the parallel pressure increases, the oscillations in solvation forces are enhanced and tend to become repulsive.
Low Dielectric Constant Fluorocarbon Films
Authors: Lau K. K. S. , Gleason K. K.
Published: April 2011

Introduction

Chemical vapor deposition (CVD) continues to generate immutable interest as a method of producing thin fluorocarbon films. This impetus stems from both the process advantages of CVD and the extensive market potential for the resultant films. Fluorocarbon films find extremely diverse applications because of their unique electrical, chemical and surface properties. They are currently being evaluated, among other applications, as dielectric interconnects in microelectronic circuits1–3 and as passivation coatings in clinical devices.
Temperature Stability Of Plasma Polymerized Antiadhesive Coatings
Authors: Michaeli W. , Dahlmann R. , Fonteiner I.
Published: April 2011

By means of microwave-assisted plasma polymerization it is possible to deposit polymer coatings on different surfaces such as plastics or metals. The surface tension can be influenced in a wide range. However, many applications require a high thermal stability of such low surface tension layers. Therefore, the influence of variations of the process parameters on temperature stability of such layers is examined. The produced layers were studied regarding their chemical and physical characteristics under temperature influence by means of contact angle measurements, xray photoelectron spectroscopy (XPS), thermo gravimetric analysis (TGA) combined with Fouriertransformed infrared spectroscopy (FTIR). Fluorine containing monomers offer good perspectives. Up to temperatures of approx. 200°C the antiadhesivity of these coatings is adjustable to values close to those of poly(tetrafluoroethylene) (PTFE).
Recent Measurements of Experiment Sensitivity to G-Jitter and Their Significance to ISS Facility Development
Authors: Herring R. A. , Tryggvason B.
Published: April 2011

Recent experimental measurements of various microgravity experiments have been taken on the Mir and Space Shuttle under different conditions of microgravity using the Microgravity-vibration Isolation Mount (MIM). The results to date show a clear difference when the experimental measurements are taken from g-levels offered by the Mir and the Space Shuttle (non isolated) to g-levels offered by MIM (isolated) which have been reduced by two orders of magnitude. Concern for the International Space Station (ISS) experimental facilities arises when the quality of microgravity on the Mir and Space Shuttle (non isolated), which is believed to be not good enough, has been measured to be better than the ISS Requirement established by NASA for isolated racks, which will be significantly better than those racks not isolated.
High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells
Authors: Freundlich A. , Newman F. , Aguilar L. , Vilela M. F. , Monier C.
Published: April 2011

Realization of high quality GaAs photovoltaic materials and devices by Metal-organic Molecular Beam Epitaxy (MOMBE) with growth rates in excess of 3 microns/ hours is demonstrated. Despite high growth rates, the optimization of III/V flux-ratio and growth temperatures leads to a two dimensional layer by layer growth mode characterized by a (2×4) RHEED diagrams and strong intensity oscillations. The not intentionally doped layers exhibit low background impurity concentrations and good luminescence properties. Both n(Si) and p(Be) doping studies in the range of concentrations necessary for photovoltaic device generation are reported. Preliminary GaAs (p/n) tunnel diodes and solar cells fabricated at growth rates in excess of 31µm/h exhibit performances comparable to state of the art and stress the potential of the high growth rate MOMBE as a reduced toxicity alternative for the production of Space 111-V solar cells.
Electronic Structure, Charge Transfer and Bonding in Intermetallics Using EELS and Density Functional Theory
Authors: Humphreys C. J. , Botton G. A. , Pankhurst D. A. , Keast V. J. , Temmerman W. M.
Published: April 2011

Electron energy loss spectroscopy and density functional theory have been used to show that there is a covalent component to the bonding in NiAl, CoAl and FeAl, between the transition metal atom and Al. There is no charge transfer and no ionic component to the bonding in NiAl and probably not in CoAl and FeAI. The bonding in non-stoichiometric NiAl is studied. Preliminary results are given for a Σ3 boundary in NiAl.
High-Temperature Phase Transformation in Cr Added TiAl Base Alloy
Authors: Abe E. , Niinobe K. , Nobuki M. , Nakamura M. , Tsujimoto T.
Published: April 2011

We have investigated a microstructure evolution of a Ti-48Al-3.5Cr (in at.%) alloy at high-temperatures (>1473K). In the alloy annealed at 1673K for 1.8ks, followed by air-cooling, a characteristic microstructure with a feathery fashion was uniformly formed. From a cooling-rate-controlling study, it was found that formation of the feathery structure is accomplished during continuous cooling from 1673K to 1573K, within the α+γ two-phase region. Transmission electron microscopy revealed that the feathery structure is composed of lamellar colonies (5–10µm) which are crystallographicaly tilted slightly (a few degree) with their neighbors. A surprising fact is that lamellae in each colony are mostly the γphase with few α2 phase less than 5% in volume. This suggests that the feathery structure is a metastable product and has not resulted from the α → α+γ transformation above 1573K. Instead, the feathery structure formation should be attributed to the non-equilibrium α → γtransformation which occurs at high-temperatures with a small degree of supercooling. We discuss this interesting phase transformation in terms of the α→γ massive transformation, based on the continuous-coolingtransformation (CCT) diagram constructed for the present alloy.
Iron Aluminide Composites
Authors: Schneibel J. H.
Published: April 2011

Iron aluminides with the B2 structure are highly oxidation and corrosion resistant. They arethermodynamically compatible with a wide range of ceramics such as TiC, WC, TiB2, and ZrB2. Inaddition, liquid iron aluminides wet these ceramics very well. Therefore, FeAI/ceramic compositesmay be produced by techniques such as liquid phase sintering of powder mixtures, or pressureless meltinfiltration of ceramic powders with liquid FeAl. These techniques, the resulting microstructures, andtheir advantages as well as limitations are described. Iron aluminide composites can be very strong.Room temperature flexure strengths as high as 1.8 GPa have been observed for FeAl/WC. Substantialgains in strength at elevated temperatures (1073 K) have also been demonstrated. Above 40 vol.% WCthe room temperature flexure strength becomes flaw-limited. This is thought to be due to processingflaws and limited interfacial strength. The fracture toughness of FeAl/WC is unexpectedly high andfollows a rule of mixtures. Interestingly, sufficiently thin (<1 μm) FeAl ligaments between adjacentWC particles fracture not by cleavage, but in a ductile manner. For these thin ligaments the dislocationpile-ups formed during deformation are not long enough to nucleate cleavage fracture, and theirfracture mode is therefore ductile. For several reasons, this brittle-to-ductile size transition does notimprove the fracture toughness of the composites significantly. However, since no cleavage cracks arenucleated in sufficiently thin FeAl ligaments, slow crack growth due to ambient water vapor does notoccur. Therefore, as compared to monolithic iron aluminides, environmental embrittlement is dramaticallyreduced in iron aluminide composites.
Production and Characterization of Nanostructured Ti-Based Intermetallics
Authors: Calderónt H. A. , Garibay-Febles V. , Cabrera A. , Umemoto M. , Cabañas-Morenol J. G. , Tsuchiya K.
Published: April 2011

Mechanical alloying and plasma assisted sintering are used to produce nanocrystalline Ti-Al alloys. Microstructural characterization and measurement of mechanical properties are reported. The alloys investigated include AITi+X and Al3Ti+X where X represents either Cr, Mn or Fe. Mechanical alloyed powders have a microstructure, which consist of an amorphous matrix containing small crystalline domains. Sintered specimens have a crystalline microstructure with nano-sized grains. Alloys based on AlTi-X are composed mainly of the phases α 2 (DO19) and γ (Ll0) distributed homogeneously in the form of nanograins (100–300 nm) resembling a globular structure. Al3Ti-X alloys show a cubic ordered phase (L12) with grain sizes ranging from 16 to 40 nm. Vickers hardness measurements of sintered alloys show a considerable increase with respect to as-cast alloys. Compression tests show a high mechanical strength of these alloys, although in the case of A13Ti-X, no ductility is found.
Characteristics of Ordinary ½⟨110] Slip in Single Crystals of γ-TiAl
Authors: Jiao S. , Bird N. , Hirsch P. B. , Taylor G.
Published: April 2011

A study of the occurrence of ordinary slip in single crystals of Ti 54.5 at% Al with various orientations at different temperatures shows that the critical resolved shear stress is approximately the same for ¼⟨110] slip on {111} and {110} planes near the peak of the yield stress anomaly. However the shapes of the glide loops are quite different, suggesting that the order of relative mobilities of screw and edge dislocations is reversed in the two cases. The reason for this and its possible effect on the mechanism responsible for the yield stress anomaly of ½⟨110] {111} slip are discussed. Experiments on the thermal reversibility of the yield stress when either ordinary- or super- dislocation slip systems are operating at both temperatures have shown that the yield stress is reversible for the latter but not reversible in the former case.
Burner Rig Hot Corrosion of a Single Crystal Ni-48Al-Ti-Hf-Ga Alloy
Authors: Nesbitt J. A. , Darolia R. , Cuy M. D.
Published: April 2011

The hot corrosion resistance of a single crystal Ni-48Al-1Ti-0.5Hf-0.2Ga‡ alloy was examined in a Mach 0.3 burner rig at 900C for 300 hours. The combustion chamber was doped with 2 ppmw synthetic sea salt. The hot corrosion attack produced a random mound morphology on the surface. Microstructurally, the hot corrosion attack appeared to initiate with oxide-filled pits which were often broad and shallow. At an intermediate stage, the pits increased in size to incorporate unoxidized Ni islands in the corrosion product. The rampant attack stage, which was observed only at sharp sample corners, was characterized by rapid inward growth of alumina in finger-like protrusions incorporating significant amounts of Al-depleted Ni islands. Aluminum consumption in the oxide fingers resulted in the growth of a γ' layer ahead of the advancing oxide fingers.
Clustered, Terraced And Mixed Surface Phases Of The Al70Pd21Mn9 Quasicrystal
Authors: Ledieu J. , Munz A. W. , Parker T. M. , McGrath R. , Diehl R. D. , Delaney D. W. , Lograsso T. A.
Published: April 2011

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to the bulk. For surfaces annealed to 1050 K for less than 2 hours, STM images indicate that cluster and terrace phases coexist, and a third phase having aligned arrays of clusters is identified which appears to be intermediate between the cluster and terrace phases.
Symmetry Changes At The Surface Of Al70Pd20Mn10
Authors: Bolliger B. , Erbudak M. , Hensch A. , Kortan A.R. , Vvedensky D.D.
Published: April 2011

Sputtering with Ar+ ions induces structural phase transitions at the pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10. Sputtering at different temperatures changes the surface composition, thereby stabilizing different structures. At room temperature, the structure changes to body-centered cubic but, at elevated temperatures, it displays decagonal symmetry. In both cases, annealing the sample restores both the bulk composition and the icosahedral symmetry of the original surface.
Plastic Deformation of Approximants: Dislocations vs. Phason Lines
Authors: Klein H. , Feuerbacher M. , Schall P. , Urban K.
Published: April 2011

Deformation experiments were performed on single crystals of the ξ-AIPdMn approximant in bending geometry at high temperature. Two different mechanisms of plastic deformation are shown to exist in this phase: one based on dislocations and another novel mechanism based on the motion of phason lines. Burgers vector and line directions of dislocations were determined. Phason lines are shown to build a periodic lattice. The interaction of a dislocation with the phason line lattice results in dislocations on another length scale. This meta-dislocation in the periodic phason line lattice has a Burgers vector of magnitude 165 Å. The relative importance of phason lines and dislocations for the plastic deformation is discussed as a function of the orientation of the sample with respect to the bending geometry.
Crystal Growth Of A Decagonal AI-Co-Ni Quasicrystal
Authors: Guo J.Q. , Sato T. J. , Kimura T. , Hirano T. , Tsai A. P.
Published: April 2011

We have grown a decagonal single quasicrystal with a size of centimeter order in an A172Co16Ni12 alloy by floating zone method at a growth rate of 0.5 mm/h. The single decagonal quasicrystal has been inspected by Laue X-ray as well as neutron diffraction, revealing a very high quasicrystalline quality. By quenching the liquid during growth, a flat solid-liquid interface has been directly observed. There exists solute redistribution at the growing solid-liquid interface. At steady state growth Al is enriched and Co, Ni are depleted in front of solid-liquid interface. Solute partition ratios of Al, Co and Ni were determined to be about 0.91, 1.57 and 1.08, respectively.
Porous Structure And High Electrical Resistivity Of AIPdRe Icosahedral Phase
Authors: Kirihara K. , Kimura K.
Published: April 2011

Mechanism of the structure formation of the I-phases, which is required for complete understanding of the origin of their high electrical resistivity and preparation of the high quality samples, is proposed. During annealing within 30 minutes, atomic difiusion of Al and Pd atoms from Al3Pd phase to Al07Re0.3 phase occurs and porosity is formed in the Al3Pd phase. It is supposed that the porosity formation results from Kirkendall effect.
Thermal Expansion And Grüneisen Parameters Of Quasicrystals
Authors: Edagawa K. , Kajiyama K. , Takeuchi S.
Published: April 2011

To investigate anharmonic phonon properties, thermal expansion measurements have been performed for icosahedral (i-) Al-Pd-Mn and decagonal (d-) Al-Cu-Co quasicrystals by X-ray diffractometry in the temperature range between 100 and 800K. The linear thermal expansion coefficient α(T) of i-Al-Pd-Mn is 1.1 × 10−5K−1 at 300K, which is about a half of that of pure Al phase. The measured α(T) of d-Al-Cu-Co coincides almost completely with that of i-Al-Pd- Mn and no appreciable anisotropy was detected between the tenfold periodic direction and a quasiperiodic direction perpendicular to it. The Grfneisen parameter γ(T), has been evaluated from the measured α(T) using the data of lattice specific heat and elastic moduli previously reported. The γ(T) values for the two phases are comparable to those for conventional metallic crystals and almost constant over the temperature range studied.
The Dodecagonal Quasicrystalline Telluride (Ta, V)1.6Te And Its Crystalline Approximant (TaV)97Te60
Authors: Reich C. , Conrad M. , Krumeich F. , Harbrecht B.
Published: April 2011

The dodecagonal (dd) quasicrystalline tantalum telluride dd Ta1.6Te and the crystalline approximant Ta97Te60have been modified by partly replacing tantalum by vanadium. The impact of the substitution on the structures has been studied by X-ray and electron diffraction and by high-resolution transmission electron microscopy. The layered-type approximant structure of Ta83V14Te60was determined by single crystal X-ray means. The partitioning of vanadium on 21 out of 29 crystallographically inequivalent metal sites is referred to, but not controlled by the Dirichlet domain volume available at the sites. A HRTEM projection of dd (Ta, V)1.6Te onto the dodecagonal plane is analysed with respect to the arrangement of (Ta, V)151Te74clusters on the vertices of an irregular aperiodic square-triangle tiling, the edge length of which corresponds to the distance between the centres of two such clusters. The clusters comprise about 1 nm thick corrugated lamellae which are periodically stacked by weak Te-Te interactions.
Effect of Network Elasticity on Nematic Liquid Crystal/Cross-Linked Polymer Phase Diagram
Authors: Nwabunma D. , Kyu T. , Pogue R.T. , Bunning T.J.
Published: April 2011

The influence of elasticity on the phase behavior of a mixture of nematic liquid crystal (LC) and in-situ cross-linked polymer has been investigated. Unlike the phase diagram of the LC/pre-cured polymer, the experimental diagram of LC/cross-linked polymer phase supported by theoretical calculation showed no critical point. Instead, the binodal curve exhibits an upward asymptotic behavior as the LC volume fraction approaches unity due to domination arising from network elasticity, particularly at high LC volume fraction. An examination of the effect of cross-links segment length and network functionality on the phase diagram of LC/cross-linked polymer showed that the segment length between cross-links exerts a greater influence.
Oriented Polymer/Metal Nanocomposites: A New Method for the Production of Polarization Dependent Color Filters
Authors: Dirix Yvo , Bastiaansen Cees , Caseri Walter , Smith Paul
Published: April 2011

Uniaxially oriented composites of high-density polyethylene and silver nanoparticles were prepared using solution-casting, melt-extrusion and solid-state drawing techniques. The absorption spectrum in the visible wavelength range of the drawn nanocomposites was observed to strongly depend on the polarization direction of the incident light. For instance, the nanocomposites appear bright yellow or red when the vibration direction of linearly polarized light is perpendicular or parallel, respectively, to the drawing axis. The optical anisotropy of the drawn nanocomposites originates from uniaxially oriented, pearl-necklace type of arrays of nanoparticles of high aspect ratios. The absorption spectrum of the nanocomposites can be shifted to higher wavelengths using appropriate annealing procedures. The annealing results in an increased size of the primary silver particles, due to Ostwald ripening, and consequently a range of polarization-dependent colors can be generated in the drawn nanocomposites. It is suggested that the drawn nanocomposite films can be used in liquid crystal displays (LCD's) were they serve a dual purpose in combining polarization filter and color filter. The new display configuration transmits colored light in both the on- and off-state of the device, this in contrast to a conventional color LCD which only transmits colored light in the off-state. As a consequence, an enhanced brightness and light (energy) efficiency of the new display set-up is envisioned.
The Dynamic Properties of 5Cb Filled with Aerosil Particles Investigated by Pcs
Authors: Aliev F.M. , Kreuzer M. , Panarin Yu.P.
Published: April 2011

Nematic liquid crystal filled with Aerosil particles, a prospective composite material for optoelectronic application, has been investigated by static light scattering and Photon Correlation Spectroscopy (PCS). The Aerosil particles in filled nematic liquid crystals (FN) form a network structure with LC domains about 2500 Å in size with a random distribution of the director orientation of each domain.

We found that the properties of 5CB are considerably affected by the network. The N-I phase transition in filled 5CB was found to be smeared out and depressed. PCS experiments show that two new relaxation processes appear in filled 5CB in addition to the director fluctuation process in bulk. The slow relaxation process, with a broad spectrum of relaxation times, is somewhat similar to the slow decay, which is observed in confined nematic liquid crystal.

The middle frequency process was assigned to the director fluctuations in the surface layer formed at the particle-LC interface. The decay function describing this relaxation process is a stretched exponential (β ≍ 0.7). The temperature dependence of the relaxation times of the middle frequency obeys the Vogel-Rilcher law. Such a temperature dependence, accompanied by a broad spectrum of relaxation times suggests that the dynamics of the director fluctuations near the Aerosil particle-LC interface is glass-like.
A Study On High Coercivity And Lio Ordered Phase In Copt And Fept Thin Films
Authors: Ristau R. A. , Barmak K. , Lewis L. H. , Coffey K. R. , Howard J. K.
Published: April 2011

This study relates the microstructure of equiatomic binary alloys of CoPt and FePt with their room-temperature hysteretic magnetic properties, particularly their high coercivity. A transformation from an atomically disordered, face-centered-cubic structure to the Li0ordered structure occurred during post-deposition annealing and was characterized using digital analysis of dark-field transmission electron microscopy (TEM) images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from a superconducting quantum interference device (SQUID) magnetometer. Although the relationship most commonly described in the literature is that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.
Magnetic Anisotropy in La0.7(Sr,Ca)0.3MnO3 Epitaxial Thin Films And Crystals
Authors: Steenbeck K. , Hiergeist R. , Revcolevschi A. , Pinsard-Gaudart L.
Published: April 2011

The biaxial and uniaxial magnetic anisotropies of epitaxial { 100} oriented La0.7(Sr,Ca)0.3MnO3 films on different substrates and of a sphere-shaped single crystal were measured by torque magnetometry at temperatures ranging from T = 20K to room temperature. In the films the biaxial anisotropy with easy axes <110= dominates and is described by a cubic crystal anisotropy constant ranging up to K1 ≈−104J/m3. The uniaxial anisotropy was |Ku| ≤ 103 J/m3 and is explained by anisotropic stress. In the single crystal the main anisotropy is uniaxial with a hard axis parallel to [ 111], and with an anisotropy constant KR up to 104J/m3. KR was measured in different planes and explained by the rhombohedral lattice distortion. The biaxial anisotropy in the crystal (K1 = −103 J/m3 at T = lOOK) was smaller than in the films. Differences between film and single crystalline behaviour are discussed in terms of crystal structure and lattice constriction.
Impact of Low-Temperature Anneals of Electroplated Copper Films on Copper CMP Removal Rates
Authors: Smekalin Konstantin , Jiang Qing-Tang
Published: April 2011

CMP removal rate (RR) of electrodeposited Cu film was found to increase by 35% over time after plating. The RR increase was attributed to Cu film hardness reduction of 43% and grain growth from the initial 0.1urn at as-deposit to lum at the final stage at room temperature. The removal rate increase will translate to variations in manufacturing environment and are therefore unacceptable. It was found that annealing at ∼100C for 5 minutes in inert gas will stabilize Cu films and provide consistent CMP removal rate.
Modified Preston Equation- Revisited
Authors: Ramarajan S , Babu S.V.
Published: April 2011

The effect of pressure and velocity on the polish rates of copper was determined in DI water and in the presence of ferric nitrate, H202/glycine, and NH4OH with alumina particles as the abrasives. The polish rate shows a stronger dependence on velocity than that predicted by the Preston equation in the case of ferric nitrate, a highly reactive chemical. The velocity dependence is weaker for the other two less reactive chemicals, and is the same as that predicted by Preston equation for DI water. Our earlier empirical model, R = KPV + BV + Rc, where K, B, and Rc are constants, describes all the polish rate data satisfactorily.
Development of a Robust KIO3 Tungsten CMP Process
Authors: Liu Albert H. , Solis Randy , Givens John
Published: April 2011

A production worthy, Tungsten Chemical Mechanical Polish (CMP) process using a commercially available K103 slurry was developed, characterized, and tested for sub-0.35μm multilevel interconnect fabrication. The effects of pre-tungsten CMP process on tungsten polish are reported in detail. A head-to-head comparison of the optimized KIO3 process with the standard Fe(NO3)3 process is described. Critical CMP tool parameters (process and hardware) were flexed using statistically valid experimental designs. The advantages and disadvantages of a post tungsten polish, oxide buff, are discussed. Across-wafer non-uniformity, specifically the enhanced polish rate of tungsten at the wafer edge, was significantly reduced with the optimized process parameters and hardware setup. Also, an automated endpoint system was utilized and a set of robust endpoint algorithms were developed to minimize the amount of oxide loss during tungsten CMP processing. Finally, the positive effects of the optimized KIO3 tungsten CMP process on interconnect integration and die yield are reported.
Growth of Thin SiO2 bY “SPIKE” Rapid Thermal Oxidation
Authors: Fiory A. T.
Published: April 2011

Wafers prepared with HF and RCA cleaning were oxidized at atmospheric pressure O2 with an incandescent-lamp processor using temperature ramping at rates up to 150°C/s for heating and 80°C/s for cooling. The minimum oxidation time obtained by the “spike” method of turning off lamp power prior to reaching a desired peak temperature is effectively 2s. Film thickness for spike oxidation ranges from about 1.6 nm for peak temperature of 1000°C to about 2.2 nm for peak temperature of 1100°C. Activation energies of 2.5 eV are determined for 1.5 – 4 nm films. Films grown for varied times and temperatures to produce equal oxide thickness, as measured by ellipsometry, show nearly equivalent physical properties in measurements by corona-charge and Kelvin probe surface photovoltage techniques.
Fowler-Nordheim Tunneling Current Oscillation Study of Interface Roughness
Authors: Lai L. , Irene E.A.
Published: April 2011

A decrease in the amplitude of Fowler-Nordheim current oscillations (FN-CO) due to interface roughness is observed for thin film (∼40Å) metal-oxide-semiconductor (MOS) devices, only when the interface has high spatial complexity. Previous studies have shown no measurable changes in FN-CO's resulting from the oxidation of purposely roughened Si surfaces. The present research continues with an FN-CO study using Si surfaces with roughness of higher spatial complexity than the previous studies. The spatial complexity of the purposely roughened Si surfaces was compared using the fractal dimension (DF). Atomic force microscopy (AFM) was used to measure the interface topography, and fractal dimension (DF) was used to describe the surface complexity while root-mean-square (RMS) roughness was used for obtaining vertical information of the roughness. It was found that the oscillation amplitude decrease substantially with an increase of DF but with no dependence on RMS.
Enhanced Reliability of Thin Silicon Dioxide Grown on Nitrogen-Implanted Silicon
Authors: Kurinec S. K. , Jackson M. A. , Capasso K. C. , Zhuang K. , Braunstein G.
Published: April 2011

Thin oxides (3-20 nm) have been grown on nitrogen-implanted silicon by regular thermal oxidation and by rapid thermal oxidation in dry oxygen. The implant dose ranged from 1×1013 to 1×1015 cm−2. Significant oxidation retardation has been observed for nitrogen doses above 1×1014 cm−2. Al-gate MOS capacitors were fabricated to characterize the thin oxides for dielectric breakdown strength and leakage. Gate oxides, grown by our standard baseline process, exhibited a decrease in their dielectric strength from ∼10 MV/cm for thickness > 18 nm to 3-4 MV/cm for < 8 nm thickness. The nitrided oxides maintained their integrity at ∼10 MV/cm as thickness decreased, unless a critical dose was exceeded, which resulted in poor performance. These electrical measurements indicate that a nitrogen implant, prior to gate oxide growth, is beneficial to oxide integrity.

The structure of the SiO2/Si interface has been probed using X-ray photoelectron spectroscopy (XPS) and analyzing Si 2p core level spectra. The XPS analyses on as grown samples of nitrided and un-nitrided oxides of similar thickness (3 nm) do not show any significant suboxide peaks corresponding to Si1+, Si2+ or Si3+ states at the interface. However, on exposing the surface to argon ion sputtering at 3.5 kV for 30 seconds, prior to XPS analysis, the presence of suboxides at the SiO2/Si interface is detected. The SiO suboxide (Si2+) density in oxides grown on nitrogen-implanted silicon is much less than that in the oxides grown on unimplanted silicon. This is a direct evidence of sputter damage resistance of nitrided thin oxides. The beam-induced damage in the oxide is also found to be less in nitrided oxides. The suppression of suboxide formation at the interface due to the presence of nitrogen appears to be responsible for the enhanced reliability of nitrided oxides.
Self-control Phenomenon for Crystallinity and Morphology Observed at Epitaxial Growth of BaTiO3 by Alternating Deposition Method
Authors: Shimoyama K. , Kanda T. , Iida M. , Maeda T. , Yamabe K.
Published: April 2011

We directly observed self-control crystallization of epitaxial BaTiO3 films during alternate depositions of BaO and TiO2. When TiO2 (or BaO) was supplied excessively, surface crystallinity and smoothness degraded due to three-dimensional (3D) growth. However, when the following BaO (or TiO2) was supplied onto the rough TiO2 (or BaO) surface, the surface smoothness was recovered drastically. It was found that a single phase BaTiO3 film grew by repeating the alternate deposition cycle of excessive supply of both BaO and TiO2. The mechanism of this phenomenon was discussed.
Study of Thermal Stability of Cvd Ta205/Si Interface
Authors: Mao A. Y. , Son K. A. , White J. M. , Kwong D. L. , Roberts D. A. , Vrtis R. N.
Published: April 2011

The effects of vacuum and inert gas annealing of ultra-thin (20Å) CVD Ta2O5 films deposited on Si substrates, with and without oxynitride interface layer, on the Ta2O5/Si interface stability were examined extensively by means of in-situ X-ray Photoelectron Spectroscopy (XPS), ex-situ Time-of-Flight Secondary Ion mass Spectrometry (ToF-SIMS), and Temperature Programmed Reaction (TPR). When annealed to 680 °C for up to 50 min, changes in ∼ 20Å Ta2O5 films formed on Si(100) are negligible, but annealing to 820 °C for 10 min in vacuum, Ar or N2 produces major chemical restructuring. SiO is formed at the Ta2O5 - Si(100) interfaces and becomes incorporated into the tantalum oxide. A reduced form of Ta, attributed to TaSix, forms at the buried interface. Extending the annealing time to 20 min produces no further changes. SiO desorbs during annealing at 1000 °C. Nitriding Si prior to forming the Ta2O5 film deposition inhibits these processes.
Characterisation of Process Variables for Ultraviolet Assisted Injection Liquid Source Chemical Vapour Deposition (Uvils-Cvd) of Tantalum Pentoxide Films
Authors: Beechinor J.T. , Mooney M.B. , Kelly P.V. , Crean G.M. , Zhang J.-Y. , Boyd I.W. , Paillous M. , Jimenez C. , Stnateur J.-P.
Published: April 2011

The characterisation of the physical and chemical properties of tantalum pentoxide (Ta2O5) films, deposited on silicon using a newly developed low temperature deposition technique - ultraviolet assisted injection liquid source chemical vapour deposition (UVILSCVD), is reported. The effect of deposition parameters including substrate temperature, oxidising agent (N2O) flow, precursor carrier gas (Ar) flow, number of drops of precursor injected and precursor solution concentration is discussed. Spectroscopic ellipsometry (SE) was used to determine the refractive index and thickness of the Ta2O5films. The film thickness was observed to increase with temperature, number of injected drops and precursor solution percentage, while the refractive index was found to be most sensitive to temperature. SIMS measurements showed good agreement with extracted thickness values. Fourier transform infrared spectroscopy was used to identify and monitor Ta2O5(pentoxide), TaO2and TaO (suboxide) formation via curve fitting analysis of spectral features. Results showed increased suboxide formation as a function of increasing pressure and as a function of decreasing N2O flow, precursor solution concentration and number of drops injected. The summation of the areas under peaks characteristic of the tantalum-oxygen bonding correlated well with the thicknesses determined by spectroscopic ellipsometry. The FTIR spectra revealed a dramatic increase in the proportion of suboxide in the absence of the oxidising gas.