bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Mapping of Subsurface Cracks in Alumina Using FIB
Authors: Inkson B.J. , Wu H.Z. , Steer T. , Möbus G.
Published: April 2011

A new method has been developed to map cracks in 3D using focused ion beam (FIB) microscopy. Using the FIB, many parallel 2D slices are cut in the specimen. Imaging each 2D slice down several directions enables the 3D co-ordinates of features in the slice to be determined. Computer alignment and reconstruction of the 2D slices generates a 3D data set of the analysed zone. The 3D mapping method has been applied to the analysis of the cracks around an indentation site in a Al2O3-5vol.%SiC nanocomposite. This reveals the 3D location and morphology of radial and deep lateral cracks at the indent periphery, surface localised crack clusters, and a crack deficient zone close to the indent centre.
Physical Origin of a Size Effect in Nanoindentation
Authors: Bushby A.J. , Downes J.R. , Jayaweera N.B. , Kidd P. , Kelly A. , Dunstan D.J.
Published: April 2011

We have reported results of nanoindentation using spherical indenters to observe the full indentation stress-strain curve. We observe the onset of plasticity in semiconductor strained-layer superlattices. These structures have alternating layers with strains of opposite sign. The yield pressure is reduced by the presence of the coherency strain. By varying the thicknesses and strains, we have been able to show that both sets of layers, compressive and tensile, reduce the yield pressure. This requires that a yield criterion must be satisfied over a volume, large enough to include layers of both sign. In these studies, we observe a large and reproducible size effect in the yield pressure. That is, with smaller radius indenters the mean pressure acting over the contact area at the deviation from purely elastic behaviour increases, by up to a factor of two for a 2μm radius indenter tip. Here we show how the requirement for meeting a yield criterion over a finite volume naturally leads to the size effect. Essentially, with smaller radius indenters, the peak stresses must be greater in order to satisfy the yield criterion over a finite volume. By integrating the strain energy over a suitable volume we show that there is a critical volume of ≍ 0.5μm radius over which yield is initiated for all indenter radii in the range 1-35μm. This is an important result for the understanding of nanoindentation and other systems in which stresses are highly inhomogeneous on a small scale.
Grain Boundary Modification During Neutron Irradiation at Intermediate Temperatures
Authors: Bruemmer S. M. , Edwards D. J. , Gertsman V. Y. , Simonen E. P.
Published: April 2011

Grain boundary compositions and near-boundary microstructures have been measured in complex Fe-Cr-Ni alloys after neutron irradiation at intermediate temperatures where nanometer-scale damage promotes structural integrity problems in nuclear reactor systems. Radiation-induced segregation (RIS) and dislocation loop microstructures have been determined as a function of irradiation dose up to 13 dpa and at temperatures near 280°C. The most significant effect on RIS was the grain boundary structure (low-energy special boundaries versus high-energy random boundaries) and composition (enrichment of Cr and Mo) before irradiation. Grain boundary character distribution did not change with irradiation and only high-energy boundaries exhibited significant radiation-induced changes. The initial grain boundary composition in mill-annealed stainless steels was difficult to remove during subsequent irradiation and retarded the development of Cr- and Mo-depleted regions.
Radiation-Induced Segregation in 316 and 304 Stainless Steels Irradiated at Low Dose Rate
Authors: Allen T. R. , Cole J. I. , Ohta J. , Dohi K. , Kusanagi H. , Kenik E. A. , Ridge Oak
Published: April 2011

As part of the shutdown of the EBR-II reactor, structural materials were retrieved to analyze the effects of long-term irradiation on mechanical properties and microstructure. In this work, the effect of low dose rate irradiation (10−7 to 10−8 dpa/s) on grain boundary composition in 316 and 304 stainless steels was analyzed. Samples were taken from surveillance specimens and subassemblies irradiated in the reflector region of EBR-II at temperatures from 371-390°C to maximum doses of 30 dpa. The effects of dose, dose rate, and bulk composition on radiation- induced segregation are analyzed. In 316 stainless steel, changes in grain boundary chromium and nickel concentrations occur faster than changes in iron and molybdenum concentrations. In 304 stainless steel, decreasing the dose rate increases the amount of grain boundary segregation. For a dose of 20 dpa, chromium depletion and nickel enrichment are greater in 304 stainless steel than in 316 stainless steel, the difference most likely due to dose rate. In both 304 and 316 stainless steels, the presence of a grain boundary precipitate significantly changes the composition of the adjacent grain boundary.
Concurrent Annealing Of Vacancy-Type And Interstitial-Type Damage In Neutron Irradiated Stainless Steel
Authors: Simonen E. P. , Edwards D. J. , Bruemmer S. M.
Published: April 2011

Analysis of the effect of annealing on change in void and loop size distributions provided insights that complement microstructural characterization using transmission electron microscopy (TEM). The predictions of concurrent vacancy-type and interstitial-type damage annealing are applied to measurements in neutron-irradiated austenitic stainless steels. Irradiation at 330°C produces void and loop microstructures for which the measured annealing response is in accord with predictions. Irradiation at 275° produces only Frank loop microstructure for which the annealing response cannot be predicted from measured microstructures. The model predictions are based on an assumed vacancy source not detected using TEM. The measured loop microstructure is typically reported to be interstitial in character but this analysis suggests that a significant component of the loop population is vacancy-type damage based on defect inventory and kinetic arguments.
Microstructure Evolution in Charged Particle Irradiated 316 SS Modified to Reduce Radiation Damage
Authors: Gan J. , Simonen E. P. , Edwards D. J. , Bruemmer S. M. , Sencer B. H. , Fournier L. , Was G. S.
Published: April 2011

The objective of this work is to investigate the addition of misfit elements in both size and mass on the evolution of irradiated microstructure in 316 SS. Alloys were modified by the addition of Pt and Hf to suppress the radiation damage. Pt and Hf were added as a lattice perturbation to catalyze defect recombination within the early stage of cascade formation and defect migration. Irradiations were conducted with 5 MeV Ni-ions at 500 °C to doses up to 50 dpa or with 3.2 MeV protons at 400 °C. Microstructures were characterized using transmission electron microscopy. While no beneficial effect was seen for Pt addition, Hf appears to effectively alter the microstructural response to irradiation.
Nature of the Fine-Scale Defects and Radiation Hardening in Stainless Steels Neutron-Irradiated at 550K
Authors: Edwards D. J. , Simonen E. P. , Bruemmer S. M.
Published: April 2011

Our understanding of radiation effects in stainless steels irradiated at temperatures below annealing stage V (<573K) remains unclear. The microstructure under these conditions has been loosely described in terms of Frank loops and “black spot” damage, the latter of which is typically considered to be 4-5 nm or less in size. To further clarify the nature of these defects, 6 stainless steels heats neutron irradiated at 550K from 0.6 to 13.3 dpa have been characterized by TEM. The microstructure is comprised of a very high density of small Frank loops present in sizes as small as 1 nm and perhaps lower, which could be of both vacancy and interstitial-type. The density of the visible loops is already established at the lowest dose available, however, the microstructure continues to evolve as the dose increases. The size distributions of the Frank loops change from a narrow symmetric distribution to a much broader size distribution with a bimodal distribution beginning to form at the higher doses.
Heavy Ion Irradiation of Brannerite-type Ceramics
Authors: Lian Jie , Wang Lumin , Lumpkin Gregory R. , Ewing Rodney C.
Published: April 2011

Brannerite, UTi2O6, occurs in polyphase Ti-based, crystalline ceramics that are under development for plutonium immobilization. In order to investigate radiation effects caused by α- decay events of Pu, several brannerite compositions were synthesized: UTi2O6, ThTi2O6, CeTi2O6 and a more complex material, which is composed of Ca-containing brannerite and pyrochlore. An 1 MeV Kr+ irradiation was performed over a temperature range of 25 K to 1020 K with in-situ TEM. The ion irradiation-induced crystalline-to-amorphous transformation was observed in all brannerite samples. At room temperature, the critical amorphization dose, Dc, resulting from Kr+ ion irradiation increases in the order: Dc (CeTi2O6) < Dc (ThTi2O6) < Dc (Ca- containing brannerite) < Dc (UTi2O6) < Dc (Ca-containing pyrochlore). The critical amorphization dose for stoichoimetric brannerite increases at elevated temperature due to the effect of thermal annealing. The critical amorphization temperatures of the different brannerite compositions are: 970 K, UTi2O6; 990 K, ThTi2O6; 1020 K, CeTi2O6. The effects of structure and chemical composition on radiation resistance of brannerite-type and pyrochlore-type ceramics are discussed.
Kinetic Monte Carlo simulations of cascades in Fe alloys
Authors: Domain C. , Becquart C.S. , van Duysen J.C.
Published: April 2011

The Pressurized Water Reactor vessel steels are embrittled by neutron irradiation. Among the solute atoms, copper play an important role in the embrittlement and different Cu-rich defects have been experimentally observed to form. We have investigated by Kinetic Monte Carlo (KMC) on rigid lattices the evolution of the primary damage. Since the point defects created by the displacement cascades have very different kinetics, their evolution is tracked in two steps. In a first step, we have studied their recombination in the cascade region and the formation of interstitial clusters using “object diffusion”. The parameters of this model are based on MD simulations, or on first principles calculations. In a second part, we have investigated the subsequent evolution of the primary damage with a model based on a vacancy jump mechanism. These simulations which rely on an adapted EAM potential show the formation of copper rich defects. Some of the potential's predictions that played a key role in the model were checked by ab initio calculations. The defects obtained from these simulations, subsequent to the primary damage created by displacement cascades, exhibit similarities with the ones observed by atom probe. The influence of temperature and Cu content on the final damage was investigated.
MD Refinement of Topologically Simulated Irradiation Cascades in Silica
Authors: Yuan Xianglong , Pulim Vinay , Hobbs Linn W.
Published: April 2011

Refinement of several topologically generated displacement cascades in silica has been conducted using molecular dynamics (MD) simulation. Several metastable amorphous silicas with substantially different medium-range order (as characterized by ring topologies) were obtained. However, their total correlation functions were found scarcely distinguishable. Major structural reconstruction was observed when the refinement took place above a glass transition temperature, below which the cascades largely retained their original topological ring structures. Attempts are made to correlate topological ring distributions with the first sharp diffraction peak, which may in turn provide some insight into the medium range structures of irradiated silicas.
The Influence of PKA Direction on Displacement Cascade Evolution
Authors: Stoller Roger E.
Published: April 2011

An extensive database of atomic displacement cascades in iron has been developed using molecular dynamic simulations. More than 300 cascades have been completed at 100K at energies between 100 eV and 100 keV, with fewer simulations at 600 and 900K. A systematic evaluation of the database has revealed an unexpected influence of PKA direction in low energy simulations. For primary knockon (PKA) directions that lie in the close-packed {110} planes, the cascade tends to be constrained to develop in only two dimensions. This planar “channeling” leads to much higher point defect survival than when a random high-index PKA direction is used to initiate the cascade. For example, the average number of stable Frenkel pair produced in 300 eV cascades is about 2.1 for cascades initiated with a [135] PKA, and 3.2 for [114] cascades. Some influence of this PKA direction effect was observed for energies up to 2 keV. The interstitial clustering behavior also appears to be affected in cascades with high defect survival.
An Analysis of the Structure of Irradiation induced Cu-enriched Clusters in Low and High Nickel Welds
Authors: Hyde Jonathan M. , English Colin A.
Published: April 2011

Two high copper irradiated welds, one containing very low Ni and the other containing very high Ni, have been examined using 3-D atom probe (3DAP) microscopy, small angle neutron scattering (SANS) and field emission gun-scanning transmission electron microscopy (FEG- STEM).

Irradiation induced clusters were observed in both welds. They were found to be significantly smaller and exist at a higher number density in the high Ni weld. A new algorithm was developed to precisely identify the shape, composition and size of clusters observed in the atom probe data. Representative irradiation induced clusters from each weld were then examined in greater detail. They were shown to be ramified and have a significant Fe content (∼60at.%). Cu was found to be more strongly associated with the core of the clusters than Mn or Ni. In the low Ni weld, there was evidence for P at the interfaces between the clusters and matrix. Cluster composition estimates from FEG-STEM analyses were consistent with those observed by 3DAP microanalysis. For each weld, the mean radius of gyration of the clusters was found to be almost identical to the radius of gyration determined directly from SANS analyses of these materials. Finally, the number density of features was estimated from the SANS data by using the compositional information from the 3DAP observations. Consistency with the number density calculated directly from the 3DAP data was obtained provided that it is assumed that the clusters exhibit some magnetic properties.
Atomistic Simulation of Vacancy and Self-Interstitial Diffusion in Fe-Cu Alloys
Authors: Marian Jaime , Wirth Brian D. , Perlado J. Manuel , Odette G. R. , de la Rubia T. Diaz
Published: April 2011

Neutron hardening and embrittlement of pressure vessel steels is due to a high density of nanometer scale features, including Cu-rich precipitates which form as a result of radiation enhanced diffusion. High-energy displacement cascades generate large numbers of both isolated point defects and clusters of vacancies and interstitials. The subsequent clustering, diffusion and ultimate annihilation of primary damage is inherently coupled with solute transport and hence, the overall chemical and microstructural evolutions under irradiation. In this work, we present atomistic simulation results, based on many-body interatomic potentials, of the migration of vacancies, solute and self-interstitial atoms (SIA) in pure Fe and binary Fe-0.9 and 1.0 at.% Cu alloys. Cu diffusion occurs by a vacancy mechanism and the calculated Cu diffusivity is in good agreement with experimental data. Strain field interactions between the oversized substitutional Cu solute atoms and SIA and SIA clusters are predominantly repulsive and result in both a decreased activation energy and diffusion pre-factor for SIA and small (N <5) SIA cluster migration, which occurs by three-dimensional motion. The Cu appears to enhance the re- orientation of the SIA clusters to different <111> directions, as well as the transition from <110> to mobile <111> configurations. The migration behavior of larger SIA clusters, which undergo only one-dimensional diffusion during molecular dynamics timescales, is largely unaffected by the Fe-Cu alloy, although SIA clusters are effectively repelled by coherent Cu precipitates.
Synthesis of III-Nx-V1-x Thin Films by N Ion Implantation
Authors: Yu K. M. , Walukiewicz W. , Shan W. , Wu J. , Beeman J. W. , Ager J. W. , Haller E. E. , Ridgway M. C.
Published: April 2011

Dilute III-Nx-V1-x alloys were successfully synthesized by nitrogen implantation in GaAs and InP. The fundamental band gap energy for the ion beam synthesized III-Nx-V1-x alloys was found to decrease with increasing N implantation dose in a manner similar to that commonly observed in epitaxially grown GaNxAs1-x and InNxP1-x thin films. The fraction of N occupying anion sites (“active” N) in the GaNxAs1-x layers formed by N implantation was thermally unstable and decreased with increasing annealing temperature. In contrast, thermally stable InNxP1-x alloys with N mole fraction as high as 0.012 were synthesized by N implantation in InP. Moreover, the N activation efficiency in InP was at least a factor of two higher than in GaAs under similar processing conditions. The low N activation efficiency (<20%) in GaAs can be improved by co-implanting Ga and N in GaAs.
A Damage Model for Disordered Structures in Ion Irradiated Silicon
Authors: Cheng Ju-Yin , Gibson J. Murray
Published: April 2011

Medium-range order has been observed in ion-implanted amorphous silicon, suggesting a paracrystalline structure for this material. The origin of a paracrystalline structure may be due to an energy spike phenomenon. To evaluate the influence of energy spikes on a particular process, we have attempted to calculate the characteristic energy in a spike. However, the observed depth dependence of amorphous structures in as-implanted silicon is puzzling. To explain this, we simulated the depth distribution of cascade events in a particular energy range. We found a great increase of point defect concentration and cascade events as the depth increases. This result could explain the experimental depth dependence.
Impact of Boron and Gallium on Defects Production in Silicon
Authors: Khan Aurangzeb , Dharmarasu Nethaji , Yamaguchi Masafumi , Araki Kenji , Vu Tuong K. , Saga Tatsuo , Abe Takao , Annzawa Osamu , Imaizumi M. , Matsuda Sumio
Published: April 2011

We report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm-3, together with the impact of oxygen on radiation –induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si.
Grain Boundary Dynamics: A Novel Tool for Microstructure Control
Authors: Gottstein G. , Molodov D.A. , Shvindlerman L. S. , Winning M.
Published: April 2011

The reaction of grain boundaries to a wide spectrum of forces is reviewed. Curvature, volume energy and mechanical forces are considered. The boundary mobility is strongly dependent on misorientation, which is attributed to both grain boundary structure and segregation. In magnetically anisotropic materials grain boundaries can be moved by magnetic forces. For the first time a directionality of boundary mobility isreported. Flat boundaries can also be moved by mechanical forces, which sheds new light on microstructure evolution during elevated temperature deformation. Curvature driven and mechanically moved boundaries can behave differently. A sharp transition between the small and large angle boundary regime is observed. It is shown that grain boundary triple junctions have a finite mobility and thus, may have a serious impact on grain growth in fine grained materials. The various dependencies can be utilized to influence grain boundary motionand thus, microstructure evolution during recrystallization and grain growth.
A phase field model of the premelting of grain boundaries in pure materials
Authors: Lobkovsky Alexander E. , Warren James A.
Published: April 2011

We present a phase field model of solidification which includes the effects of the crystalline orientation in the solid phase. This model describes grain boundaries as well as solid-liquid boundaries within a unified framework. With an appropriate choice of coupling of the phase field variable to the gradient of the crystalline orientation variable in the free energy, we find that high angle boundaries undergo a premelting transition. As the melting temperature is approached from below, low angle grain boundaries remain narrow. The width of the liquid layer at high angle grain boundaries diverges logarithmically.
Phase Field Methods and Dislocationss
Authors: Rodney D. , Finel A.
Published: April 2011

We present a general formalism for incorporating dislocations in Phas Field methods. This formalism is based on the elastic equiva;ence betweem a dislocation loop and a platelet inclusion of specific stress-free strain related to the loop Burgers vector and normal. Dislocations are thus treated as platelet inclusions and may be coupled dynamically to any other field such as a concentration field. The method is illustrated through the simulation of a Frank-Read source and of the shrinkage of a loop in presence of a concentration field.
Dislocation patterning: tochastic approach to mesoscale modeling
Authors: Häahner Peter
Published: April 2011

Plastic deformation by dislocation glide is known to be associated with the spontaneous formation of mesoscopic patterns of various types, e.g. cellular dislocation structures during unidirectional deformation and quasi-periodic persistent slip band structures during cyclic deformation. hile it is recognized that dislocation patterning represents a dissipative far-from-equilibrium process, theoretical modelling of those phenomena is complicated by the long-range nature of dislocation interactions inducing collective dislocation behaviour on a mesoscopic scale. n this paper the problem is addressed using a stochastic approach with random uctuations acting on the evolution of the dislocation ensemble. he intensity of the uctuations is determined self-consistently from dynamic dislocation interactions and, hence, re ects correlated dislocation motion. t is shown that those uctuations may induce dislocation patterns by stabilizing non-uniform dislocation distributions. icrostructure-based models are presented for unidirectional and cyclic plastic deformation. n the rst case fractal dislocations distributions corresponding to hierarchically organized dislocation cell structures are obtained, while in the latter case a decomposition into dislocation-rich walls or veins and depleted channels is found, which are associated with the formation of persistent slip bands and matrix structures. he good agreement with experimental observations in single-crystalline f.c.c. metals points at the importance of collective dislocation e ects in the self-organization of those structures.
A microstructure evolution model including dislocation plasticity
Authors: Cleri Fabrizio , D'Agostino Gregorio
Published: April 2011

We present a stochastic microstructure evolution model applicable to grain growth and its recent extensions, in particular relative to dislocation plasticity. The model is implemented by means of numerical simulations based on the velocity Monte Carlo algorithm. It describes the evolution of a two-dimensional microstructure by tracking the motion of triple junctions, i.e. the vertices where three grain boundaries meet. Grain boundaries can be modeled as straight or curved segments; the misorientation dependence of both grain-boundary energies and mobilities can be included, as well as grain rotation. We show simple examples of normal, abnormal and oriented grain growth. The model is already capable of dealing with a two-phase (liquid-solid) system, to simulate both grain growth and grain dissolution in the liquid. Finally, we report preliminary results of a recent extension of the model to include mechanical deformation from dislocation plasticity.
Forces between Dislocations due to Dislocation Core Fields
Authors: Henager Charles H. , Hoagland Richard G.
Published: April 2011

Atomistic dislocation models were used to determine the properties of dislocation core fields in Al using an EAM potential. Equilibrium atom configurations were compared with initial configurations displaced according to the Volterra field to determine core displacement fields for edge, screw, and mixed (60° and 30°) geometries. The core field was approximated by a line force defect field lying parallel to the dislocation line direction. Best-fit parameters for the core fields were obtained in terms of the anisotropic elastic solution for a line force defect, from which the line force strengths and the origin of the line forces were determined. The line force stress fields were then used to compute the forces between dislocations for several dislocation configurations. The Volterra field dominates beyond 50b but core field forces modify the equilibrium angle of edge dislocation dipoles and determine the force between otherwise noninteracting edge and screw dislocations at distances out to 50b compared to the Volterra-only forces.
Genesis of Defects in Massively Transformed L10-ordered τ-MnAl Alloys
Authors: Yanar Cagatay , Radmilovic Velimir , Soffa William. A. , Wiezorek Jorg M. K.
Published: April 2011

Defects produced in massively transformed L10-ordered τ-MnAl have been characterized by detailed TEM studies. The defect population in massive τ-MnAl comprises arrays of overlapping stacking faults, {111}-conjugated microtwins, thermal antiphase boundaries and dislocations. The genesis of these defects has been attributed to atomic attachment faulting on {111}- and {020}-type facets of the essentially incoherent growth interface between the parent and product phases. The features of the defect genesis in τ-MnAl are discussed with respect to the role of atomic level processes at solid-state transformation interfaces in general and growth interfaces in massively transforming materials systems in particular.
Influence of Fe on the Morphology of Spinel in the System MgO-Al2O3-Fe2O3.
Authors: Kharissova O.V. , Ortiz U. , Hinojosa M.
Published: April 2011

The investigation of the morphology of crystalline solids surfaces is of practical and general interest because many processes such as the growth of epitaxial films, catalytic reactions and others, are intimately connected with surface conditions. In this work we study the surface morphology and structure of the spinel as produced in the system MgO- Al2O3-Fe2O3 at 1400°C for 15 h in a conventional furnace and in a microwave oven for 30 min. The spinel was analyzed by X-ray diffraction, scanning electron microscopy (SEM), X-ray spectrometry (EDX), and atomic force microscopy (AFM). The AFM images were recorded in the contact mode. Images scanned at different magnifications show steps and flat terraces. Experimental observations were made on the nature and distribution of the observed polygonal morphology.
Oxygen Exchange on a Highly Oriented Thin Film Electrode
Authors: Yang Y. L. , Chen C. L. , Luo G. P. , Chu C. W. , Jacobson A. J.
Published: April 2011

The cathodic kinetic processes on a highly oriented LSCO thin film electrode supported on YSZ(100) surface were studied with a 3-probe ac impedance method under varying bias potential and annealing temperatures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the YSZ electrolyte, the ionic transfer at the LSCO/YSZ interface, and the oxygen exchange on the LSCO electrode surface. The changes of the three features with respect to the annealing history and bias potential were measured. The impedance data were analyzed using an equivalent circuit model: (RelCel)(RinterfaceQinterface)(RsurfCsurf).
Microstructure of Sputter Deposited TiO2/SiO2 Multilayer Optical Coatings
Authors: Sutter E. , Sutter P. , Moore J.J.
Published: April 2011

The microstructure of TiO2/SiO2 multilayer optical filters has been investigated in detail by cross-sectional transmission electron microscopy and related to their optical properties and stability. The amorphous TiO2 layers in the as-deposited multilayers are found to consist of nanocolumns and intercolumnar regions with non-stoichiometric or lower density material. In humid ambients this microstructure absorbs moisture which causes a shift in the absorption edge of the filters. Upon annealing the TiO2layers are found to recrystallize into the low-temperature anatase modification which leads to significantly improved stability of the optical properties of the filters.
Characterization of Oxide Layers of Bulk Si1-xGex
Authors: Suzukake W. , Nemoto S. , Iida T. , Takanashi Y. , Sakuragi S.
Published: April 2011

Bulk crystals of Si0.4Ge0.6, grown using the vertical Bridgman method, were oxidized at 800 °C for 1 h using oxygen in dry oxidation and a stream of de-ionized water in wet oxidation. Single-like and polycrystalline Si0.4Ge0.6samples were used. The oxidized samples were analyzed using x-ray photoelectron spectroscopy to determine the chemical states of the Si and Ge in the oxide. In the sample oxidized using a dry ambient, the oxide layer consisted mainly of SiO2, and GeO2 formed the subsurface area only. This can be accounted for by the differences in the formation of the free energies of the SiO2 and GeO2. In wet oxidation, the oxide layer had a mixed structure consisting of SiO2 and GeO2. To understand the oxide formation mechanisms in the wet oxidation process, an introduction of a chemical bond manipulation explained the formation of the mixed structure.
Electronic Structure and Bonding at the Al-terminated Al(111)/α-Al2O3(0001) Interface: A First Principles Study
Authors: Siegel Donald J. , Hector Louis G. , Adams James B.
Published: April 2011

We have performed ab initio calculations to determine the bonding character of the Al-terminated Al(111)/α-Al2O3(0001) interface. By using an optimized model in which all atomic coordinates were relaxed to their minimum energy positions, we have determined that Al-O bonds constitute the primary interfacial bonding interaction. Our electron localization, Mayer bond order, and Mul- liken population analyses reveal that these bonds are very similar to the cation-anion bonds found in the bulk oxide, and are therefore mainly ionic, with a smaller amount of covalent character. However, there is also evidence of metal-cation bonding across the interface, a result which could be significant to understanding bonding at interfaces with other corundum-like oxides.
Calculations of Perovskite Surface Relaxation
Authors: Heifets E. , Kotominc E.A. , Eglitisc R.I. , Cohen R.E.
Published: April 2011

The (100) and (110) surface relaxations are calculated for SrTiO3 and BaTiO3 perovskite thin films by means of a semi-empirical shell model (SM) for different surface terminations. Our SM results for the (100) surface structure are in good agreement with our present ab initio Hartree-Fock calculations with electron correlation corrections, previous ab initio pseudopotential calculationsand LEED experiments. The surface energy for the Ba-, Sr-, TiO- terminated (110) surfaces is found much larger than that for the (100) one. In contrast, the surface energy for the asymmetric O-termination, where outermost O atoms are strongly on-plane displaced, is the lowest for all (110) terminations and thus the most stable.
Exudation of Silicate Liquid from Polycrystalline Alumina
Authors: Ravishankar N. , Farrer Jeffrey K. , Carter C. Barry
Published: April 2011

The presence of a liquid film at grain boundaries affects the mechanical properties of the material. One of the ways to eliminate the liquid film is to exude it from the grain boundaries to the free surface of the material. The present paper presents results on the exudation of a liquid silicate from grain boundaries in polycrystalline alumina. The results are compared to exudation behavior from bicrystals of alumina. This approach is very useful in understanding the mechanism of the exudation process.
Scaled PLZT Thin Film Capacitors with Excellent Endurance and Retention Performance
Authors: Chu Fan , Fox Glen , Davenport Tom
Published: April 2011

The requirements for future ferroelectric non-volatile memories (FRAM) include lower operating voltages, higher densities and tighter design rules. In order to achieve these requirements the key component of the FRAM device, viz., the PbZrxTi1划xO3 (PZT) thin film capacitor must be scaled dimensionally to obtain reduced film thickness and capacitor area. This paper presents the ferroelectric performance of RF magnetron sputtered PLZT thin films with thickness scaled down to 1000Å. The switching performance of the thickness scaled PLZT thin films meets the requirements of 1.8V FRAM device. Though PLZT ceramic thin films, of which the fatigue is often a concern, are utilized as non-volatile component, excellent fatigue performance was observed. The scaled PLZT thin film capacitors are fatigue free up to 1011 fatigue cycles (E=200kV/cm). The scaled 1000Å PLZT thin films also showed good imprint performance. The opposite-state charge after 10 years baking at 150°C was still above the sensing level. The thickness scaled PZT thin films, showing dramatically improved ferroelectric performance, can be applied to the manufacturing of low voltage FRAM products.
Fatigue in PZT Thin Films
Authors: Shur V. , Nikolaeva E. , Shishkin E. , Baturin I. , Bolten D. , Lohse O. , Waser R.
Published: April 2011

We have used the new approach to fatigue phenomenon for analysis of the switching current and C-V characteristic evolution during cycling in PZT thin films. It was shown that in accordance with theoretical predictions the rejuvenation stage precedes the fatigue one. We have demonstrated that fatigue behavior corresponds to the spreading of the internal bias field distribution function during ac switching.
Electrical Characteristics of Chemical Solution Deposited Nd3+ Doped PZT (53/47) Thin Films in Planar Electrode Configuration
Authors: Majumder S.B. , Perez B. , Roy B. , Martinez A. , Katiyar R.S.
Published: April 2011

Electrical characteristics of ferroelectric thin films in planar electrode configuration are important to characterize these materials for their applications in micro electro mechanical (MEM) and tunable microwave devices. In the present work we have prepared polycrystalline Pb1划3x/2Ndx(Zr0.53Ti0.47)O3 (x = 0.0 to 10.0 at %) thin films on platinized silicon substrate by chemical solution deposition (CSD) technique. The films were characterized in terms of their dielectric and ferroelectric properties by depositing planar interdigital finger electrodes on the surface of the films by electron beam lithography. The capacitance and loss tangent of undoped and 4 at % Nd doped PZT films measured at 100 kHz were found to be 138 pF, 0.033 and 95 pF, 0.019 respectively. Saturated hysteresis loops were obtained in undoped PZT film by applying 100 V across 10 μm electrode separation. Nd doped PZT films on the other hand, electrically shorted at comparatively lower voltage. The electrical characteristics of these films are correlated with their phase formation behavior and microstructural features.
High Frequency Thin Film Acoustic Ferroelectric Resonators
Authors: Kirby Paul , Su Qing-Xin , Komuro Eiju , Imura Masaaki , Zhang Qi , Whatmore Roger
Published: April 2011

Both ZnO and PZT Thin Film Bulk Acoustic Resonator filters were fabricated, tested and modeled in this study. The development of an accurate Mason model allows the effect of particular parasitic components on the microwave s-parameters in the region of the series and parallel resonances to be identified. The parasitic components that limit the performance of our ZnO and PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filters are analysed. From an analysis of PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator measurements values for the longitudinal acoustic velocity and electromechanical coupling coefficient can be derived. Measured PbZr0.3Ti0.7O3 Thin Film Bulk Acoustic Resonator filter responses confirm that the larger electromechanical coupling coefficients in this material compared to ZnO give wider filter band-widths.
Improvement of Retention Property of YMnO3/Y2O3/Si MFIS Capacitor
Authors: Daisuke Ito Norifumi Fujimura , Kakuno Kousuke , Ito Taichiro
Published: April 2011

We have been proposing YMnO3 with low remanent polarization and permittivity as a ferroelectric gate transistor, and reported that c-oriented YMnO3 films were obtained on (111)Si with (111) oriented Y2O3 buffer layer. The ferroelectricity was confirmed by pulsed C-V measurement. However, the retention property was not satisfied because of its poor crystallinity. To improve the crystallinity of YMnO3 films, deposition conditions of Pulsed Laser Deposition (PLD) were optimized. The laser power, oxygen pressure and introducing Ozone gas are effective for maintaining the stoichiometry during the deposition. Improvement of the crystallinity of the YMnO3 film makes the retention property better. We also demonstrate the use of epitaxially grown Y2O3 buffer layer to improve the crystallinity of the YMnO3 films.
Direct Comparison of Structural and Electrical Properties of Epitaxial (001)-, (116)-, and (103)-Oriented SrBi2Ta2O9 Thin Films on SrTiO3 and Silicon Substrates
Authors: Lee H. N. , Pignolet A. , Senz S. , Harnagea C. , Hesse D.
Published: April 2011

Anisotropies of the properties of the bismuth-layered perovskite SrBi2Ta2O9 (SBT) have been investigated using epitaxial thin films grown by pulsed laser deposition both on conducting Nb-doped SrTiO3 (STO) single crystal substrates and on Si(100) substrates. It has been found that the three-dimensional epitaxy relationship SBT(001)∥STO(001); SBT [110] ∥STO[100] can be applied to all SBT thin films on STO substrates of (001), (011), and (111) orientations. An about 1.7 times larger remanent polarization was obtained in (103)-oriented SBT films than in that of (116) orientation, while the (001)-oriented SBT films revealed no ferroelectricity along their c-axis. Non-c-axis-oriented SBT films with a well-defined (116) orientation were also grown on silicon substrates for the first time. They were deposited on Si(100) covered with a conducting SrRuO3 (110) bottom electrode on a YSZ(100) buffer layer.
Nanometer Scale Domain Measurement of Ferroelectric Thin Films Using Scanning Nonlinear Dielectric Microscopy
Authors: Odagawa Hiroyuki , Matsuura Kaori , Cho Yasuo
Published: April 2011

A very high-resolution scanning nonlinear dielectric microscope with nanometer resolution was developed for the observation of ferroelectric polarization. We demonstrate that the resolution of the microscope is of a sub-nanometer order by measurement of domains in PZT and SBT thin films. The experimental result shows that nano-sized 180° c-c ferroelectric domain with the width of 1.5 nm for PZT thin film are observed. The result also shows that the resolution of the microscope is less than 0.5 nm for the PZT thin film.
Lattice Vibrational Properties of SrBi2Ta2O9
Authors: Liu Ran , Han Pengdi
Published: April 2011

SrBi2Ta2O9 is one of the layered perovskite ferroelectrics with excellent fatigue resistance and thus has gained great interest of semiconductor industries recently in non-volatile ferroelectric random access memory (FERAM) applications. The understanding of the lattice vibrational properties of this material can provide crucial information on its structure and dielectric behavior. In this work, we carried out Raman spectroscopy study of thin film, powder and single crystal SrBi2Ta2O9. At temperatures above the Curie temperature, all 12 Raman modes expected from the tetragonal (I4/mmm) structure have been observed and assigned to the 4 A1g, 6 Eg and 2 B1g modes based the polarized Raman spectra from the single crystal samples. At lower temperature, the Raman spectra have revealed all 22 A1 modes, but only 3 out of the 20 A2 modes and 5 out of the 42 B1/B2 modes were observed in the ferroelectric phase (A21am). The soft mode was found to be of A1 symmetry and appearing only when light polarization lay in the ab-plane.
Strain-Induced Elevation of the Spontaneous Polarization in BaTiO3 Thin Films
Authors: Tian W. , Haeni J. H. , Schlom D. G. , Pan X. Q.
Published: April 2011

A manmade ferroelectric-paraelectric heterostructure, a BaTiO3 / SrTiO3 superlattice, was studied to explore the effect of strain on ferroelectricity. An atomically abrupt BaTiO3 / SrTiO3 superlattice was grown on a (001) SrTiO3 substrate by reactive molecular beam epitaxy. Both BaTiO3 and SrTiO3 layers were grown with their individual thicknesses less than the critical thickness for the formation of interfacial misfit dislocations, leaving the entire superlattice fully coherent with the substrate. This resulted in a uniformly and highly strained BaTiO3 layer to study the effect of strain on ferroelectricity. Quantitative high-resolution transmission electron microscopy was employed to examine the atomic positions of cations and anions in the strained BaTiO3 layers. It was found that the relative static displacement of cations (Ti4+, Ba2+) to anions (O2−) is larger than that of bulk BaTiO3. Our observation thus illustrates the strain-induced elevation of spontaneous polarization in BaTiO3 thin films.
Orientation Selection in Sol-Gel Derived PZT Thin Films
Authors: Norga G. J. , Fé Laura
Published: April 2011

Motivated by the growing impact of PZT film orientation on ferroelectric film properties as film thickness is scaled down, we present basic studies on orientation selection in sol-gel derived PZT films, using pre-annealed Pt/Ti electrode layers as a model electrode system. FTIR was used to study, on a real temperature scale, chemical reactions in the films during the initial thermal steps prior to crystallization. We found that the chemical structure of the pyrolyzed film has a much larger impact on orientation selection than has previously been realized. In addition to pyrolysis conditions, the ambient used for the crystallization step was found to play a crucial role in orientation selection. As film thickness decreases, excessive oxygen incorporation in the films is seen to result in the loss of the preferential (111) texture when crystallization is performed in air. By performing crystallizations in N2, 40 nm thick PZT films with a strongly preferential (111) orientation could be obtained.
Electrophoretic Deposition of Barium Strontium Titanate Functionally Graded Thick Film Composites for Electronically Scanning Antennas
Authors: Gersten Bonnie , Synowczynski Jennifer
Published: April 2011

The composition 40 wt% Ba0.55Sr0.45TiO3 (BST) – 60 wt% MgO bulk material was recently found to be a promising candidate as a low loss, tunable material for electronically scanning antennas (ESA). However, due to the high permittivity of the BST-MgO composite impedance mismatch within the antenna could be a source of loss. Electrophoretic deposition (EPD) could be used as a processing tool to develop functionally graded structures tailored to reduce the impedance mismatch without a reduction in the tunability. In addition, EPD could be used in thin or thick films to decrease the required biasing fields. In this study, EPD was used as a method for deposit thick films of BST functionally graded composites. The concentration of the suspension, solvent type, mixed solvent concentrations, bias field, time, particle size of powders and distance between electrodes were studied to control the deposition yield and thickness. SEM or calipers were used to measure deposit thickness. The relative weight ratio of BST to MgO in the suspension was compared to the final structure as measured by EDS.
Connection between Near Millimeter Range Dielectric Loss and High Frequency Acoustic Attenuation
Authors: Garin Boris M. , Ivanov Sergey N. , Khazanov Efim N. , Nikitin Ivan P.
Published: April 2011

A series of crystalline isomorphic solid solutions of Yttrium-Lutetium Aluminum Garnets (Y1−cLuc)3Al5O12 (c = 0 – 1) has been studied. The measurements of dielectric loss (DL) tangent tgδ has been performed at electromagnetic wavelengths 1 – 0.6 mm and temperature T = 300 K. The results obtained has been compared with longitudinal acoustic waves (AW) attenuation data for frequencies f = 1 – 9.4 GHz, T = 4.2 – 300 K and with theory. The correlation between the DL and the AW attenuation is observed. The dependencies of DL (at T = 300 K) and AW attenuation (at T > 77 K) on concentration c are qualitatively identical in the whole interval c = 0 – 1. From comparison with theory it follows that the observed DL is due to the two-phonon intrinsic lattice loss. It is caused by the lattice anharmonicity as well as the AW attenuation at not too low temperatures. Also the prediction for concentration dependence of DL at very low temperatures is discussed that follows from comparison with the results of “heat pulse” propagation experiments for the same samples at T = 2 K and theory.
Tunability in Ba1–xSrxTiO3-based Ferroelectrics
Authors: Potrepka Daniel M. , Tidrow Steven C. , Tauber Arthur
Published: April 2011

Ferroelectrics are presently of interest for phase shifters, filters, and true time delay devices. Voltage tunable paraelectrics have the potential to lower device cost and reduce power consumption compared with presently available devices. In order to improve device performance to acceptable levels, materials must have high tunability, low dielectric constant, low loss tangent, and low leakage current. Using existing predictive techniques, compositions of Ba0.6Sr0.4TiO3-based ferroelectrics with charge-compensated substitutions for Ti4+ were synthesized. Results of capacitance measurements are used to obtain dielectric constant and tunability in the paraelectric (T > TC) regime. The relevance to device requirements is discussed. Results for substituted samples are compared to those for (unsubstituted) Ba0.6Sr0.4TiO3. Discussion of the impact of the results on predictive techniques for tunability is addressed.
Resonating Microelectromechanical Structures for Metrology
Authors: Allen A. M. , Johnson G. C.
Published: April 2011

A method for determining geometric process errors in MEMS devices from the resonant fre- quencies of simple structures is presented. The ability to accurately determine the as-built ge- ometry of MEMS devices is important given the magnitude of the geometric uncertainty relative to the dimensions of these devices. As MEMS become smaller, the need for reliable metrology becomes even more important. The method presented here provides a way to determine the etch offset (the difference between the design width of a planar feature and the as-built width), the average angle of the side-walls and the compliance of the support of the structure. An important feature of the approach presented is that by using frequency ratios for various structural modes, neither the elastic modulus nor the mass density of the film need be known.