bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric properties of tetragonal lead barium niobate (Pb1−xBaxNb2O6) crystals near the morphotropic phase boundary
Authors: Lee Myeongkyu , Feigelson Robert S.
Published: March 2008

Tungsten bronze ferroelectrics with a morphotropic phase boundary (MPB) have become increasingly important for a variety of applications because of their enhanced and unique properties near the MPB. Lead barium niobate (Pb1−xBaxNb2O6) crystals, which have a morphotropic phase boundary between the orthorhombic (1 − x > ∼0.63) and tetragonal (1 − x, <, 0.63) phases, were grown in sealed Pt crucibles by the vertical Bridgman method for tetragonal compositions near the MPB, and their ferroelectric properties were investigated. The ferroelectric domain structures in as-grown crystals were revealed either by etching in hydrofluoric acid or by polishing with colloidal silica, the latter providing clearer features. Domain size on the surface perpendicular to the polar axis was 10–50 μm. Crystals could be poled by slowly cooling from above the Curie temperatures (300–400 °C) under a dc field of 5 V/mm. The spontaneous polarization Ps of tetragonal Pb1−xBaxNb2O6 was found to be in the range of 0.40–0.70 μC/mm2 at room temperature depending on composition and increased as the composition approached morphotropic phase boundary (1 − x = ∼0.63), as expected.
High efficiency photoresist-free lithography of UO3 patterns from amorphous films of uranyl complexes
Authors: Gao M. , Hill Ross H.
Published: March 2008

The solid state photochemistry of uranyl carboxylate complexes is presented with the purpose of developing methods for optical lithography of uranium oxide films. These complexes of the general formula, UO2(OOCR)2 (R = i-C3H7, C5H11, CH2C6H5, CH2OC2H5, C2H4OC2H5), were all photosensitive as thin amorphous films. The primary photochemical reaction for each of these complexes was the extrusion of a CO2 from the ligand and the production of radicals which initiated a chain reaction. The nature of this chain reaction was dependent upon the identity of the organic substituents, R. In some cases the chain reaction required a photochemical step while others were entirely thermal in nature. Of importance are the potentially high quantum yields which can be associated with thermal chain reactions. Some of the systems presented here exhibit quantum yields in excess of 1. This process was shown to be compatible with optical lithography by the patterning of the uranium oxide product on silicon surfaces.
Carbon Nanotube Based Molecular Electronic Devices
Authors: Menon Madhu , Srivastava Deepak
Published: March 2008

Complex three-point junctions of single-walled carbon nanotubes are proposed as building blocks of nanoscale electronic devices. Both T- and Y-junctions, made up of tubes with differing diameters and chiralities, are studied as prototypes. All the proposed complex junctions have been found to be local minima of the total energy on relaxation with a generalized tight-binding molecular dynamics scheme.
Do Carbon Nanotubes Spin When Bundled?
Authors: Kwon Young-Kyun , Tománek David , Lee Young Hee , Lee Kee Hag , Saito Susumu
Published: March 2008

Using ab initio and parametrized techniques, we determine the equilibrium structure of an ordered “bundle” of (10,10) carbon nanotubes. Because of small intertube interaction and lattice frustration, we predict a very soft libration mode to occur at v ≈ 12 cm−1. This mode is predicted to disappear above the orientational melting temperature which marks the onset of free tube rotations about their axis. We discuss the effect of the weak intertube coupling and orientational disorder on the electronic structure near the Fermi level.
Scanning Tunneling Microscopy and Spectroscopy Studies of Single Wall Carbon Nanotubes
Authors: Odom Teri Wang , Huang Jin-Lin , Kim Philip , Ouyang Min , Lieber Charles M.
Published: March 2008

Scanning tunneling microscopy and spectroscopy have been used to characterize the atomic structure and tunneling density of states of individual single wall carbon nanotubes (SWNT's) and ropes containing many SWNT's. Analysis of atomically resolved SWNT images shows that the nanotubes consist of a wide range of diameters and helicities with no one structure clearly dominant. Tunneling spectroscopy measurements made simultaneously on atomically resolved SWNT's exhibit semiconducting and metallic behavior that depend predictably on helicity and diameter. In addition the band gaps of the semiconducting tubes were also found to depend inversely on diameter. These results are compared to theoretical predictions, and the implications of these studies as well as important future directions are discussed.
Raman Scattering Study of Coalesced Single Walled Carbon Nanotubes
Authors: Fang S. L. , Rao A. M. , Eklund P. C. , Nikolaev P. , Rinzler A. G. , Smalley R. E.
Published: March 2008

High temperature heat treatment of single wall carbon nanotube bundles in flowing H2 was used to produce a significant fraction (∼40%) of diameter-doubled, or coalesced tubes with a mean diameter corresponding to that of ∼(20, 20) tubes. At three laser excitation wavelengths (514.5, 647, and 1064 nm), a reduction in the Raman scattering intensity of the strong radial and tangential modes was observed in the H2-treated sample, consistent with the reduced fraction of tubes in the sample after coalescence. However, using 488 nm excitation, little or no change is observed in the Raman spectrum after the H2 treatment, suggesting that this excitation wavelength couples only to chiral symmetry tubes. Using the 647 nm excitation, the effect of H2 treatment on the tangential band is quite unique, and a significant change in the shape of the tangential band was observed. Our lineshape analysis, and other results reported in this issue, suggest that this unique change of shape is due to lost scattering intensity from metallic tubes partially compensated by tangential mode scattering from the coalesced tubes. The normally prominent radial breathing mode band, which would be expected at ∼90 cm−1 for ∼(20, 20) tubes was not observed, indicating that these larger diameter tubes do not exhibit strong resonant scattering, at least at any of the wavelengths used in this study.
Optical Properties of MS2 (M = Mo, W) Inorganic Fullerenelike and Nanotube Material Optical Absorption and Resonance Raman Measurements
Authors: Frey G. L. , Tenne R. , Matthews M. J. , Dresselhaus M. S. , Dresselhaus G.
Published: March 2008

The optical properties of inorganic fullerene-like and nanotube MS2 (M = Mo, W) material are studied through absorption and resonance Raman, and compared to those of the corresponding bulk material. The absorption measurements show that the semiconductivity is preserved. Nevertheless, the positions of the excitons are altered in comparison to the bulk. The Raman spectra of the nanoparticles show a close correspondence to that of the bulk. However, the first-order peaks are broadened and, under resonance conditions, new peaks are observed. The new peaks are assigned to disorder-induced zone edge phonons.
Structure and Oxidation Patterns of Carbon Nanotubes
Authors: Yao N. , Lordi V. , Ma S. X. C. , Dujardin E. , Krishnan A. , Treacy M. M. J. , Ebbesen T. W.
Published: March 2008

We discuss the oxidation of carbon nanotubes and how it is affected by structure and geometry. While graphite is known to oxidize primarily at defects to create etch pits, nanotubes have additional structural features such as high curvature, helicity, and contain five and seven membered rings which modify the initiation and propagation of oxidation. Oxidation does not necessarily start at the tip of the tubes, and there are pronounced differential oxidation rates between layers which depend on the helicity of the individual shells.
Tailoring Carbon Nanoclusters to Desired Morphologies
Authors: Jiao Jun , Seraphin Supapan
Published: March 2008

The preparation and structural characterization of carbon nanoclusters of different morphologies produced by three different methods and under a variety of conditions is reported. In a comparative manner, the growth phenomena and structural properties of carbon nanoclusters are investigated as synthesized by (a) the high temperature (˜3000 °C) and high carbon-content process of the conventional arc-discharge, (b) the high temperature but low carbon-content process of the modified arc-discharge, and finally (c) the relatively low temperature (˜500 °C) process of Ni catalytic disproportionation of carbon monoxide.
Processing of Carbon Nanotube Reinforced Aluminum Composite
Authors: Kuzumaki T. , Miyazawa K. , Ichinose H. , Ito K.
Published: March 2008

Carbon nanotube reinforced aluminum (Al) composites were produced by hot-press and hot-extrusion methods. The interfacial structure between the carbon nanotube and Al was examined using a transmission electron microscope (TEM), and the mechanical properties were measured by a tensile test. TEM observations have shown that the nanotubes in the composites are not damaged during the composite preparation and that no reaction products at the nanotube/Al interface are visible after annealing for 24 h at 983 K. The strength of the composites is only slightly affected by the annealing time at 873 K, while that of the pure Al produced in a similar powder metallurgy process significantly decreases with time. These studies are considered to yield experimental information valuable for producing high performance composites.
Screen-printed Cu3BiS3-polyacrylic Acid Composite Coatings
Authors: Hu H. , Gomez-Daza O. , Nair P. K.
Published: March 2008

A technique for preparing electrically conductive coatings of Cu3BiS3 powder in polyacrylic acid matrix is presented. Bi2S3 powder obtained by chemical precipitation was introduced into a freshly prepared CuS chemical deposition bath. After the initial nucleation period, CuS started to deposit on the Bi2S3 surface. The as-obtained CuS–Bi2S3 powder was mixed with polyacrylic acid aqueous solution, and the resulting mixture was used as a paste to form a screen-printed composite coating. Up to 200 °C the film behaves like a simple CuS film; the sheet resistance is around 100 and the crystallized phase in the composite is CuS (Covellite). When the temperature is equal or higher than 250 °C, atomic diffusion at the CuS–Bi2S3 interface is promoted, leading to the formation of the ternary compound Cu3BiS3 (Wittichenite) in the composite film. The formation of the compound depends on the temperature, relative abundance of the Bi2S3 and CuS components in the CuS–Bi2S3 pigment, as well as on the annealing atmosphere.
Role of Yttria-stabilized Zirconia Produced by Ion-beam-assisted Deposition on the Properties of RuO2 on SiO2/Si
Authors: Jia Q. X. , Arendt P. , Groves J. R. , Fan Y. , Roper J. M. , Foltyn S. R.
Published: March 2008

Highly conductive biaxially textured RuO2 thin films were deposited on technically important SiO2/Si substrates by pulsed laser deposition, where yttria-stabilized zirconia (YSZ) produced by ion-beam-assisted-deposition (IBAD) was used as a template to enhance the biaxial texture of RuO2 on SiO2/Si. The biaxially oriented RuO2 had a room-temperature resistivity of 37 μΔ-cm and residual resistivity ratio above 2. We then deposited Ba0.5Sr0.5TiO3 thin films on RuO2/IBAD-YSZ/SiO2/Si. The Ba0.5Sr0.5TiO3 had a pure (111) orientation normal to the substrate surface and a dielectric constant above 360 at 100 kHz.
Shape Forming Simultaneous with Jc Enhancement in REBa2Cu3O7 Superconductors
Authors: Reddy E. Sudhakar , Rajasekharan T.
Published: March 2008

An infiltration and growth (IG) process which enables the fabrication of three-dimensional (3D) components of REBa2Cu3O7 (RE = Y, Gd, Sm, Nd, etc.) (RE-123) superconductors with a highly textured microstructure is described. The advantages of the process in comparison with conventional melt processing are discussed. The process has been demonstrated to yield highly favorable microstructures in the case Y-123 processed in air, as well as in the case of Gd-123 processed in reduced oxygen partial pressure.
Systematic Study of Graphite Encapsulated Nickel Nanocrystal Synthesis with Formation Mechanism Implications
Authors: Host Jonathon J. , Dravid Vinayak P. , Teng Mao-Hua
Published: March 2008

By systematically varying the carbon content, chamber pressure, arc current, and blowing gas velocity in a tungsten-arc encapsulation setup, the effects of each of these variables on the encapsulation of nickel in graphite layers were observed. The data from these optimally designed experiments revealed that the properties of the arc translate into changes in the encapsulated product. Specifically, a larger, hotter arc results in more encapsulation in the final sample. These findings, along with evidence of graphite layers which have formed on precrystallized particles, indicate that the graphite layers may form by two sequential formation steps. The first step is the simple phase segregation of carbon from a cooling liquid particle, resulting in surface graphite. The second step is the growth of carbon on a crystallized nickel particle, regardless of the temperature at which this occurs. The proposed formation mechanism has significant implications for both a scientific understanding of the encapsulation phenomena, and possible commercial applications.
Correlation Between Anatase-to-rutile Transformation and Grain Growth in Nanocrystalline Titania Powders
Authors: Ding Xing-Zhao , Liu Xiang-Huai
Published: March 2008

During the heat treatment of an anatase nanocrystalline powder at a high temperature, the two processes of anatase-to-rutile (A → R) transformation and grain growth would occur simultaneously and affect each other. With decrease of the original anatase grain size, the A → R transformation temperature range became extended on both sides, which may be partially attributed to the prevention effect of grain growth on this transformation. On the other hand, the grain growth process could be significantly enhanced by the A → R transformation, which can be ascribed to the higher atomic mobility because of the bond breakage during the transformation.
Microstructure and Properties of Nanosemicrystalline Si3N4 Ceramics with Doped Sintering Additives: Part I. Microstructural Characterization of Nanosemicrystalline Si3N4 Powders
Authors: Ryu K. H. , Yang J-M.
Published: March 2008

The characteristics of nanosized silicon nitride powders with doped Y2O3 and Al2O3 fabricated by a plasma-reacted chemical process were investigated. The chemical compositions of the powders were analyzed by wet chemical analysis. The morphology and the size distribution were determined by transmission electron microscopy (TEM). TEM with energy dispersive spectroscopy (EDS) was used to verify the existence of sintering additives in each individual particle. The crystal structure of the powders was identified by the selected area diffraction pattern (SADP). X-ray diffraction (XRD) technique was used for phase analysis and the measurement of degree of crystallinity. The characteristics of chemical bonding was analyzed by using Fourier transform infrared spectroscopy (FTIR).
Microstructure and Properties of Nanosemicrystalline Si3N4 Ceramics with Doped Sintering Additives: Part II. Phase Transformation and Microstructural Control
Authors: Ryu K. H. , Yang J-M.
Published: March 2008

The low temperature pressureless sintering of a nanosized Si3N4 powder with doped sintering additives was investigated. The microstructural evolution during sintering at different temperatures was analyzed using x-ray diffraction and scanning electron microscopy. The effect of using nanosized Si3N4 powder as a catalyst to accelerate the α→β–Si3N4 transformation of a commercial Si3N4 powder with larger particle sizes was also investigated. Finally, two stage sintering was used to study the feasibility of controlling the microstructure and the mechanical properties of the nanosized silicon nitride.
High-temperature Creep Resistance in Rare-earth-doped, Fine-grained Al2O3
Authors: Yoshida H. , Ikuhara Y. , Sakuma T.
Published: March 2008

High-temperature creep in undoped Al2O3 and La2O3- or Y2O3- or Lu2O3-doped Al2O3 with a grain size of about 1 µm is examined in uniaxial compression testing at temperatures between 1150 and 1350 °C. The high-temperature creep resistance in Al2O3 is highly improved by the rare-earth oxide doping in the level of 0.045 mol %, and the creep rate is suppressed in the order La2O3 <Y2O3 <Lu2O3. Rare-earth ions in each doped Al2O3 are found to segregate in Al2O3 grain boundaries without forming amorphous phase or second-phase particles. The activation energy for creep in undoped Al2O3 is estimated to be 410 kJ/mol, while it is about 800 kJ/mol in the three rare-earth oxide-doped Al2O3. The grain boundary diffusivity must be highly reduced by the segregation of the dopant cation in Al2O3 grain boundaries.
Micro-Raman Spectroscopic Characterization of Nanosized TiO2 Powders Prepared by Vapor Hydrolysis
Authors: Zhang Yun-Hong , Chan Chak K. , Porter John F. , Guo Wei
Published: March 2008

Micro-Raman analysis was used to study the structure of TiO2 powders produced at low (260 °C) and high (600–900 °C) temperatures by vapor hydrolysis of titanium tetraisopropoxide (TTIP). Spatial inhomogeneity was discovered after the amorphous TiO2 powders produced at low temperature were calcined at 700, 800, and 900 °C for 3 h. The TiO2 powders produced at high temperatures (from 600 to 900 °C) were found to be spatially homogeneous and predominately anatase in structure. Small amounts of rutile and brookite are found for powders produced at 700, 800, and 900 °C after calcination at 600 °C for 3 h. The rutile and brookite impurities are believed to be concentrated on the surface of anatase based on a comparison of results of Raman and x-ray diffraction studies.
Screen Printed La2/3Sr1/3MnO3 Thick Films on Alumina Substrates
Authors: Durand L. , Balcells Ll. , Calleja A. , Fontcuberta J. , Obradors X.
Published: March 2008

We report here on the preparation of La2/3Sr1/3MnO3 magnetoresistive thick films on polycrystalline Al2O3 substates by using the screen printing technique. It is shown that films can be obtained using high temperature sintering. While there is a reacted layer, this improves adhesion and is not too troublesome if the films are made thick enough. It is shown that PbO–B2O3 –SiO2 glass additives allow sintering at lower temperatures and can be used to improve the mechanical stress of the films. However, it is found that glass concentrations large enough to significantly improve the film adherence result in a weak low field magnetoresistance probably because grains are coated with high resistivity material. Strategies to overcome these difficulties are discussed.
Indentation Response of Molybdenum Disilicide
Authors: Newman A. , Jewett T. , Sampath S. , Berndt C. , Herman H.
Published: March 2008

The influence of microstructure on the indentation cracking behavior of molybdenum disilicide (MoSi2) has been examined. The indentation response of samples produced by various methods has been measured to examine the elastic/plastic nature, hardness, and fracture toughness. Fracture toughness comparisons were made by measuring indentation crack lengths, observing the elastic/plastic indentation response, and quantifying the differences in the indentation cracking behavior. Further information was gained by monitoring the acoustic activity during indentation for selected specimens. It has been observed that the fine grain size and the dispersion of the silica phase promote microcracking and crack deflection.
Hard protective overlayers on viscoelastic-plastic substrates
Authors: Gerberich W. W. , Strojny A. , Yoder K. , Cheng L-S.
Published: March 2008

A simple superposition solution for a point-loaded elastic plate on a soft substrate is proposed. The solution considers a “drumhead” being elastically bent into a compliant substrate that is viscoelastic-plastic. With simplifying assumptions it is found that the drumhead and substrate support loads proportional to δ1/2 and δ3/2, respectively, where δ is the vertical point displacement. At fixed displacement, relaxation proceeds at high loads, but if sufficiently unloaded, recovery or increased load results with time. Qualitative verification of the time-dependent drumhead solution is shown by relaxation and recovery data on polycarbonate covered by polysiloxane, composite or diamondlike carbon (DLC) coatings, and films.
Energy considerations regarding yield points during indentation
Authors: Bahr D. F. , Wilson D. E. , Crowson D. A.
Published: March 2008

Two experiments that probe the nature of the rapid transition from elastic to plastic deformation are described. The load, and therefore stress, at which this yield point occurs is shown to be relatively independent of temperature in an iron alloy. When stresses lower than those required to generate a yield point during loading are applied for times between seconds and minutes, yielding occurs while the sample is under an applied stress. The time to generate a yield point increases as the applied stress is decreased. The possibilities of dislocation glide loop nucleation, double kink nucleation, and dislocation breakaway from pinning points are examined. Only glide loop nucleation appears to match the experimental observations. Criteria based on the stress-volume requirements of glide loop nucleation and the stress field underneath an indenter are presented which qualitatively describe the experimental data.
Using the P-δ2 analysis to deconvolute the nanoindentation response of hard-coated systems
Authors: McGurk M. R. , Page T. F.
Published: March 2008

The continuously recording indentation responses of a number of coated systems, mainly thin (<10 μm) hard nitride coatings on stainless steels and a powder metallurgy tool steel, have been explored using nanoindentation with indenter displacements increasing progressively to values greater than the coating thickness. The resultant load-displacement data have been analyzed not only to produce conventional load-displacement (P-δ) plots but also to examine the relationship between P and δ2. Recent models have proposed that there should be a linear P-δ2 relationship for homogeneous systems and that such plots have the potential to reveal the load/displacement regimes in which either the coating or the substrate, or both, are dominant in controlling the overall behavior of the coated system. By utilizing point-to-point differentiation of the P-δ2 relationship, this paper extends this approach to confirm not only that these different regimes of behavior may be readily experimentally identified in this way, but also that further details, such as the propagation of cracks, may be recognized. Our analysis also provides a valuable experimental link to models describing the near-surface deformation behavior of coated systems.
A critical examination of the fundamental relations used in the analysis of nanoindentation data
Authors: Hay Jack C. , Bolshakov A. , Pharr G. M.
Published: March 2008

Methods for analyzing nanoindentation load-displacement data to determine hardness and elastic modulus are based on analytical solutions for the indentation of an elastic half-space by rigid axisymmetric indenters. Careful examination of Sneddon's solution for indentation by a rigid cone reveals several largely ignored features that have important implications for nanoindentation property measurement. Finite element and analytical results are presented that show corrections to Sneddon's equations are needed if accurate results are to be obtained. Without the corrections, the equations underestimate the load and contact stiffness in a manner that leads to errors in the measured hardness and modulus, with the magnitudes of the errors depending on the angle of the indenter and Poisson's ratio of the half-space. First order corrections are derived, and general implications for the interpretation of nanoindentation data are discussed.
Substrate composition effects on the interfacial fracture of tantalum nitride films
Authors: Moody N. R. , Strojny A. , Medlin D. L. , Talin A. , Gerberich W. W.
Published: March 2008

In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of −6.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I componentof the fracture energies was essentially equal on both substrate materials at a value near 3.1 J/m2. These energies are on the order of the energies for metallic bonding.
Nanoindentation of particulate coatings
Authors: Adams M. J. , Akram A. , Briscoe B. J. , Lawrence C J. , Parsonage D.
Published: March 2008

A knowledge of the formation and rupture mechanisms for agglomerates is essential when seeking to model equipment designed to produce and process such materials. In the work described here, nanoindentation of “two-dimensional” agglomerate films, basically particulate coatings, was carried out to establish a means of identifying the generic breakage mechanisms for agglomerates. Selected applied load and penetration depth data in the range (0.02 mN and 700 nm, respectively) are provided as a function of the loading time during continuous loading for a model system composed rather of monodispersed colloidal silica particles (20–24 nm diameter) bound with a poly(methyl methacrylate) at 5 vol%. It is argued that these data enable the sequence of binder bridge failures to be observed, thus giving an indication of the breakage mechanism of the agglomerate and also the strength of the individual junctions. These data are also incorporated into a mechanical model that describes the rupture and deformation behavior of these planar agglomerate systems.
Measuring the critical thickness of thin metalorganic precursor films
Authors: Roeder Ryan K. , Slamovich Elliott B.
Published: March 2008

Successful application of sol-gel, metalorganic decomposition, or hydrothermal routes to ceramic thin films depends on the mechanical integrity of the precursor film. Above a critical thickness, a precursor film will crack or decohere from the substrate during drying. The cracking and thickness of thin metalorganic precursor films were simultaneously observed during drying using a standard optical microscope. Isochromatic color fringes produced by interference of reflected white light were used to monitor film thickness. The critical film thickness was determined by the color fringe corresponding to the thickness at which propagating cracks terminated. As a demonstration of the technique, the critical thickness of titanium di(isopropoxide) bis(ethyl acetoacetate) films was measured, showing increased critical thickness with the addition of small amounts of an elastomeric polymer.
Epitaxial cerium oxide buffer layers and YBa2Cu3O7−δ thin films for microwave device applications
Authors: Jacobsen Sissel N. , Madsen Lynnette D. , Helmersson Ulf
Published: March 2008

CeO2 films with thicknesses ranging from 8.8 to 199 nm were grown on Al2O3 (1102) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO2 (001) planes parallel to the Al2O3 (1102) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10–90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (111)-facets. High-quality YBa2Cu3O7−δ (YBCO) thin films were deposited directly onto the CeO2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO2 layer. Postdeposition ex situ annealing was carried out on two CeO2 films and evaluated by AFM. Upon annealing samples at 930 °C, a relatively smooth morphology without facets was obtained. Annealing films at 800 °C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.
X-ray diffraction study of texture in melt-processed Gd-123 as a function of 211 concentration
Authors: Reddy E. Sudhakar , Singh A. K. , Rajasekharan T.
Published: March 2008

The texture in the melt-processed GdBCO superconductor is studied as a function of Gd2BaCuO5 additions, using a texture goniometer. A systematic variation observed in the background intensity is connected to the microstructural variations and the powder x-ray diffraction spectra.
Cross-sectional observation on the indentation of [001] silicon
Authors: Wu Y. Q. , Shi G. Y. , Xu Y. B.
Published: March 2008

A transmission electron microscope (TEM) micrograph of cross-sectionally viewed Vickers indentation made on the surface of (001) silicon at ambient temperature was obtained. The picture clearly reveals a triangle area, pointing downward and having nondiffraction-contrast, left after unloading, which further confirms the amorphized range induced by indentation in silicon. Analysis of the picture directly manifests a significant recovery of indentation depth. Surface shape and range of the amorphous silicon region do not coincide with that of the indenter and the corresponding distribution pattern of hydrostatic stress beneath indentation predicted by elastoplastic theory, respectively. It seems that the amorphization could not be attributed to the result of hydrostatic stress alone.
Effect of doping level during rapid thermal processing of multilayer structures
Authors: Abramson A. R. , Nieva P. , Tada H. , Zavracky P. , Miaoulis I. N. , Wong P. Y.
Published: March 2008

A numerical model has been developed to examine the temperature history of a multilayer wafer undergoing rapid thermal processing (RTP) for various doping densities. Partial transparency and thin film interference effects are considered. Doping levels from ∼1015 to ∼1018 cm−3 are examined. Numerical temperature predictions of the lightly doped wafer are compared with experimental measurements. Heating rates for the lightly doped wafer fluctuate due to partial transparency effects and reach a maximum of ∼50 °C/s. The heavily doped wafer sees a maximum heating rate of ∼100 °C/s. Because the wafers are opaque above 700 °C regardless of their level of doping, all wafers reach steady state at ∼845 °C.
Synthesis of bulk polycrystalline indium nitride at subatmospheric pressures
Authors: Dyck Jeffrey S. , Kash Kathleen , Hayman Cliff C. , Argoitia Alberto , Grossner Michael T. , Angus John C. , Zhou Wei-Lie
Published: March 2008

Polycrystalline, wurtzitic indium nitride was synthesized by saturating indium with nitrogen from microwave plasma sources. The structure was confirmed by x-ray diffraction, electron diffraction, and elemental analysis. Two types of growth were observed: (i) dendritic crystals on the original melt surface, and (ii) hexagonal platelets adjacent to the In metal source on the upper edge of the crucible. The method does not involve a foreign substrate to initiate growth and is a potential alternative to the high-pressure techniques normally associated with bulk growth of indium nitride. The lattice parameters were a = 3.5366 ± 0.0005 Å and c = 5.7009 ± 0.0005 Å, with c/a = 1.612 ± 0.0005.
X-ray diffraction and microstructural studies in 2 : 17 type Sm–Co magnetic alloys containing Fe, Cu, and Zr
Authors: Gopalan R. , Sastry T. S. R. K. , Singh A. K. , Chandrasekaran V.
Published: March 2008

X-ray diffraction and microstructural studies were carried out on 2 : 17 type Sm–Co alloys containing Fe, Cu, and Zr (13–14 at.% Sm, 57–60 at.% Co, 20–22 at.% Fe, 4 at.% Cu, and 3 at.% Zr) in as-cast and heat-treated conditions. Microstructural studies revealed that the as-cast alloys contain three phases. It was observed that the samples subjected to sintering at 1463 K for 45 min followed by a solution treatment at 1448 K for 1 h resulted in nearly a single-phase, rhombohedral crystal structure (Th2Zn17-type). Subsequent isothermal aging at 1123 K and ramp-cooling to 673 K resulted in a mixture of Sm2Co17- and SmCo5-type phases with the former as major phase. It was also found that samples (Sm > 13 at.%) sintered at temperatures >1463 K showed incipient melting and multiphase formation.
Kinetics and mechanism of low-temperature internal oxidation of Ag–2 and 4 at.% Mg alloys
Authors: Rikel M. O. , Goldacker W.
Published: March 2008

Gravimetry and x-ray diffraction were used to study the kinetics and mechanism of internal oxidation in air at 300–600 °C of Ag–2 and 4 at.% Mg alloys. All the features typical of the non-Wagnerian behavior in more dilute alloys (the slower initial and faster intermediate kinetics, oxygen release from the samples at the late stages, and stabilization of highly hyperstoichiometric oxides with O/Mg up to 1.74 ± 0.02) are also observed in these more concentrated alloys. A linear correlation between the lattice parameter of oxidized alloys, magnesium content, and amount of excess oxygen is found and used for analyzing the published data on the lattice parameters in other oxidized Ag–Mg alloys. Such analysis suggests that, at early stages of low-temperature oxidation, O/Mg ratios could be higher than 4 ± 0.8, which is interpreted as evidence that O–Mg interaction at these stages is the trapping of mobile O atoms by immobile Mg atoms, so that oxidation of Ag–Mg alloys can be considered as formation and subsequent decomposition of Ag–Mg–O solid solutions, and it is the decomposition stage that significantly affects the oxidation kinetics. Possible impact of these findings on optimization of alloy-sheath composition and microstructure in Bi2223/AgMg superconducting tapes is discussed.
Mutually reactive elements in a glass host matrix: Ag and S ion implantation in silica
Authors: Bertoncello R. , Gross S. , Trivillin F. , Cattaruzza E. , Mattei G. , Caccavale F. , Mazzoldi P. , Battaglin G. , Daolio S.
Published: March 2008

Ag, S, Ag + S, and S + Ag single and double ion implantations in silica glass were performed at room temperature. The implantation energies were chosen in order to get a projected range of 40 nm. The fluences were 2 × 1016 S+ cm−2 and 5 × 1016 Ag+ cm−2. Silver interacts weakly with the host silica matrix and forms essentially metallic clusters; this weak interaction between Ag and SiO2 induces formation of silver silicate rather than silver oxide. Double ion implantations of silver and sulfur lead to chemical interaction between the two species that is critically influenced by the implantation sequence. In particular, in the Ag + S sample silver and sulfur atoms react to form crystalline core (Ag)–shell (Ag2S) nanoclusters.
Preparation of Ti-less aliovalent substituted isomorphs of KTiOPO4
Authors: Chani Valery I. , Shimamura Kiyoshi , Endo Shinji , Fukuda Tsuguo
Published: March 2008

KTiOPO4 (KTP) phase formation in stoichiometric mixtures corresponding to chemical formulas of {A1} [B5+1/2C3+1/2]O(D5+)O4 (A = K+; B = Nb5+ and Ta5+; C = Al3+, Cr3+, Ga3+, Fe3+, and In3+; and D + P5+ and As5+), and {A+} [B5+2/3C2+1/3]O(D5+)O4 (C = Mg2+ and Zn2+) prepared by solid-state reaction technique is reported. It was found that the mixtures containing Nb5+, Ga3+, Fe3+, and As5+ form the longest series of members of the KTP structural family. KTP phase formation was detected by x-ray powder diffraction analysis. Comparison of the lattice parameters measured with those known for the nonsubstituted crystals of the KTP family was carried out. The data obtained were used for the discussion of variations of KTP structural stability on composition.
Preparation and ferroelectric properties of mixed composition layered lead zirconate titanate thin films for nonvolatile memory applications
Authors: Kim Seung-Hyun , Kim Dong-Joo , Streiffer S. K. , Kingon A. I.
Published: March 2008

Mixed composition layered lead zirconate titanate (PZT) films sZr/Ti ratio = 30/70 + 65/35d with stoichiometric lead containing PZT thin layer at the film/electrode interface were successfully fabricated by a modified chemical solution deposition method. These modified PZT thin films are highly (111) textured, and have square-shaped P-E hysteresis loops with large remanent polarization and low coercive field, as well as low saturation voltage. In addition, these films show good fatigue and imprint behavior with Pt electrodes; the retained polarization of the modified film was above 50% after fatigue testing to 109 cycles, and the thermally induced voltage shifts (ΔV) were 0.51 V after heating at 150 °C for 4410 s, two times lower than for films without a stoichiometric thin layer.
Dielectric properties of Ln(Mg1/2Ti1/2)O3 as substrates for high-Tc superconductor thin films
Authors: Cho Seo-Yong , Kim Chang-Hun , Kim Dong-Wan , Hong Kug Sun , Kim Jong-Hee
Published: March 2008

Ln(Mg1/2Ti1/2)O3 (Ln = Dy, La, Nd, Pr, Sm, Y) compositions have been prepared, and their pertinent properties for use as thin film substrates for YBa2Cu3Ox (YBCO) were measured. X-ray diffraction shows that Ln(Mg1/2Ti1/2)O3 compositions have noncubic symmetry and the GdFeO3-type structure. Dielectric constant measurements revealed values between 22 and 27, which are larger than those of the LnAlO3 family. Quality factor (=1/ tan δ) of the ceramic specimens measured at room temperature was larger than 3000 at 10 GHz. Among the compounds, La(Mg1/2Ti1/2)O3 exhibited the highest dielectric constant and the lowest dielectric loss. Chemical reaction was observed between Ln(Mg1/2Ti1/2)O3 (Ln = Dy, Sm, Y) and YBCO after annealing a 1 : 1 mixture at 950 °C. Considering dielectric and physical properties, La(Mg1/2Ti1/2)O3 and Sm(Mg1/2Ti1/2)O3 were determined to be suitable substrates for YBCO thin film used in microwave applications.
Deposition, structure, and hardness of polycrystalline transition-metal nitride superlattice films
Authors: Chu X. , Wong M. S. , Sproul W. D. , Barnett S. A.
Published: March 2008

Polycrystalline TiN/VN, NbN/VN, and TiN/NbN superlattices with periods Λ between 2 and 160 nm were deposited onto steel substrates using an opposed-cathode reactive magnetron sputtering system. The nitrogen partial pressure and the substrate bias values were optimized in order to obtain dense stoichiometric films, which yielded the highest Vickers hardnesses HV. HV for TiN/VN and TiN/NbN superlattices reached maximum values of ≈5000 kgf/mm2 at Λ ≈ 5–10 nm, compared with ≈2000 kgf/mm2 for homogeneous TiN, NbN, and VN films. In contrast, HV ≈ 2000 kgf/mm2 was obtained for VN/NbN superlattices independent of Λ. Model calculations in which the hardness enhancement was proportional to the difference in layer shear moduli gave good agreement with the data. The lack of hardness enhancement in VN/NbN indicates that any other hardening mechanisms, such as coherency strains and dislocation blocking by interfacial misfit dislocations, were not important.
Reactivity in the chromium oxide-calcium fluoride system: An empirical approach
Authors: Vos Frans , Delaey Luc , Bonte Marc De , Froyen Ludo
Published: March 2008

The reaction mechanisms observed when sintering loose Cr2O3–CaF2 powder mixtures were analyzed, and the influence of the sintering parameters on the reaction behavior is presented. Using x-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and differential thermal analysis (DTA) measurements, CaCrO4 was shown to be the reaction product when sintering in air. The reaction occurs in two steps: CaF2 transforms to CaO at the Cr2O3–CaF2 interface, followed by a CaO–Cr2O3 interaction, which creates the reaction product. Scanning electron microscopy (SEM) and x-ray fluorescence (XRF) analysis showed an increasing loss of CaF2 with increasing sintering temperature and heating rate, while an opposite evolution of the amount of reaction product was observed.
Substrate temperature: A critical parameter for the growth of microcrystalline silicon-carbon alloy thin films at low power
Authors: Dasgupta Arup , Saha S. C. , Ray Swati , Carius R.
Published: March 2008

P-type microcrystalline silicon-carbon alloy thin films have been prepared at low power by employing radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) technique; judicious choice of deposition parameters is necessary. Substrate temperature has been observed to be the most critical parameter, while high hydrogen dilution is necessary but not a sufficient condition for obtaining crystallinity in silicon-carbon alloy thin films. Best microcrystallinity at moderate power density (78 mW/cm2) has been obtained at a fairly low substrate temperature (180 °C). The highest conductivity of 5.7 Scm−1 of a boron-doped microcrystalline sample could be achieved. Incorporation of carbon in these films has been confirmed from x-ray photoelectron spectroscopic (XPS) studies. Carbon is, however, incorporated only in the amorphous phase while the crystallites are of silicon only as observed from Raman spectra.
Isothermal sections in the Cr–Ga–N system in the 650–1000 °C temperature range
Authors: Farber L. , Barsoum M. W.
Published: March 2008

Isothermal sections at 670, 740, and 800 °C in the Cr–Ga–N ternary system were investigated. Details of the Cr–Ga and Cr–N binary phase diagrams were confirmed, and the equilibrium diagrams were constructed. At all temperatures, Cr3GaN was in equilibrium with all the condensed phases, except GaN. In the 670–800 °C temperature range, Cr2GaN appears to be kinetically stable in contact with GaN. This led to the construction of behavior diagrams that are valid only as long as GaN is present in the initial mixture. Above ∼910 °C, Cr2GaN decomposes to form Cr3GaN, CrN, and Ga(1). At 1000 °C, Cr3GaN is in equilibrium with all the condensed phases, and CrN is in equilibrium with Ga.
A dense transparent ink-jet receptive film that provides instantaneous print drying
Authors: Yoldas Bulent E.
Published: March 2008

Ink-jet printing is an important image transfer technology. In this technology, the electronic capabilities are often constrained by shortcomings of materials functions. One of the constraints for fast reproduction of high-resolution photographic quality color images is the print dry time. This presents a challenge in the film technology where large quantities of solvent must be rapidly removed without transporting colorants outside the targeted areas. In this work, this is achieved by chemical immobilization of water by organic polymers incorporated into the film matrix. In this dense film, immobilization of large volumes of water becomes possible by a transient local swelling of the matrix—as much as 600–700%. This mechanism of water immobilization not only creates a virtually dry state instantaneously, but also leads to a tighter containment of colorants within the targeted areas, resulting in a significant improvement in edge acuity and image resolution. In addition, the film is printer and ink nonspecific and produces a high gloss on photographic paper.
Preparation of nonaggregated Y2O3 : Eu phosphor particles by spray pyrolysis method
Authors: Kang Yun Chan , Park Seung Bin , Lenggoro I. Wuled , Okuyama Kikuo
Published: March 2008

Y2O3 : Eu phosphor particles were directly prepared by a spray pyrolysis method. Photoluminescence, morphology, and crystallinity of the as-prepared particles were investigated. The as-prepared particles above 600 °C had good crystallinity, and the crystallinity increased with increasing reactor temperatures. The particles had spherical morphology and were nonaggregated. The mean size of the particles increased from 0.34 to 1.2 µm when the solution concentration was increased from 0.03 to 1 M. The as-prepared particles had good red emission without annealing at high temperatures when excited with uv light. The main emission peak was 612 nm. The brightness of the as-prepared particles increased with increasing temperatures because of good activation and crystallization at high temperatures.
Crystal defects of mordenite structures
Authors: Song S. G.
Published: March 2008

Crystal defects in mordenite materials were observed and characterized by high-resolution electron microscopy (HREM). These defects are identified as line, planar, and 3D defects, which may result in pore blockage of the mordenite channel structure and be detrimental to their chemical properties for catalytic applications. The planar defects are the most severe ones affecting the structural properties of mordenite because of their density and scale. The main emphasis of this investigation is focused on the crystallographic aspects of these defects.
Synthesis and optical characterization of stable and highly luminescent poly-(9-vinylcarbazole)-aluminum-tris-(8-hydroxyquinoline) blends
Authors: Allegrini M. , Arena A. , Girlanda R. , Pace C. , Patanè S. , Saitta G.
Published: March 2008

An electrochemical method used to obtain aluminum(III)-8 hydroxyquinoline (Alq3) blended into poly(N-vinylcarbazole) (PVK) matrix is described. The PVK-Alq3 blends show an intense green photoluminescence whose intensity increases by adding a small percentage of a substituted coumarin to the PVK-Alq3 solution. The material can easily be spin-coated to obtain homogeneous luminescent thin films suitable for optoelectronic applications. Spectrophotometry in the uv-vis-ir range, photoluminescence, and lifetime measurements are used to characterize the PVK-Alq3 films.
c-axis lithium niobate thin film growth on silicon using solid-source metalorganic chemical vapor deposition
Authors: Lee S. Y. , Feigelson R. S.
Published: March 2008

Textured c-axis oriented LiNbO3 films have been grown for waveguiding applications on silicon substrates by the solid-source metalorganic chemical vapor deposition (MOCVD) method using tetramethylheptanedionate sources. Thermally grown SiO2 layers were used as cladding layers to provide optical confinement in the LiNbO3 films. The texture direction could be varied from the [006] to the [012] direction by either increasing the growth temperature and/or decreasing the growth rate. Under optimal growth conditions, 100% [006] texturing could be achieved without the aid of an electric field or by using a SiNx buffer layer. The crystallinity and surface rms roughness of c-axis oriented films were found to be strongly dependent on the growth rate. Rocking curve full-width half-maximum (FWHM) values of (006) peaks could be decreased to less than 2° by increasing the growth rate. The surface roughness also decreased with growth rate, and rms values as low as 1.5 nm were achieved. On the other hand, too high a growth rate leads to increased roughness due to gas phase nucleation. The optical losses were closely correlated with surface roughness, and the best films had optical losses near 4.5 dB/cm at a wavelength of 632.8 nm.