bluuebunny/crossref_metadata_2025 huggingface dataset:
High-temperature phase relationships for YxNd1–xBa2Cu3Oy(0.7 ≤ x ≤ 1.0) superconductors via containerless processing
Authors: Olive J. R. , Hofmeister W. H. , Bayuzick R. J. , Vlasse M.
Published: March 2008

Drop-tube experiments have been performed on YxNd1–xBa2Cu3Oy (0.7 ≤ x ≤ 1.0) to understand the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders 50–100 μm in diameter were processed in pure O2 at furnace temperatures of 1575–1800 °C, every 25 °C. The resulting samples were examined microstructurally by scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was found that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. A decreasing trend in the overall melting temperature with increasing Nd was also identified.
The effect of undercooling and Nd422 phase content on the nucleation of large Nd–Ba–Cu–O grains fabricated by top-seeded melt processing
Authors: Babu N. Hari , Lo W. , Cardwell D. A. , Shi Y.
Published: March 2008

The nucleation and growth of NdBa2Cu3O7–δ (Nd123)–Nd4Ba2Cu2O10 (Nd422) single-grain composites in a controlled 1% O2 in N2 atmosphere were investigated in detail as a function of solidification temperature and Nd422 phase content using a top-seeded melt growth technique. A schematic process phase diagram in the peritectic solidification region of Nd–Ba–Cu–O (NdBCO) was constructed primarily from constant isothermal growth experiments at various temperatures for several compositions and used to fabricate large single-grain material by both isothermal and continuous slow cooling over a limited temperature range. The nucleation at the seed surface and subsequent growth of uniform grains was observed to depend critically on the controlled rate of grain growth and the temperature range over which solidification occurred.
Creep of CdZnTe at high homologous temperatures
Authors: Stevens T. E. , Moosbrugger J. C. , Carlson F. M.
Published: March 2008

The creep behavior of single-crystal Zn-doped CdTe was examined in the small strain regime. Specimens from two different sources, with tensile axes [110] and [112], were deformed at 1073 and 1173 K. Strain rates were of order 10−6 to 10−7 s−1. A laser interferometer was constructed to measure the small sample displacement. Cadmium overpressure was used to inhibit sublimation of test specimens at elevated temperatures. Some tests showed a transition from secondary to tertiary creep at low levels of strain. An activation energy for steady-state creep was calculated as QC = 1.46 eV, and the creep exponent was found to be approximately n = 4.2. These results, coupled with reported activation energies for self-diffusion of Cd in Cd(Zn)Te, indicate a dislocation creep mechanism. Etch pit density was measured before and after deformation and approached a common level regardless of initial etch pit density.
Time evolution of the structural short-range order during the mechanical milling of Fe–Co–Cu nanocrystalline alloys
Authors: Gay-Sanz N. , Prieto C. , Muñoz-Martín A. , de Andrés A. , Vázquez M. , Yu Seong-Cho
Published: March 2008

The local order around Fe, Co, and Cu atoms was investigated by extended x-ray absorption fine structure spectroscopy in Fe–Co–Cu nanocrystalline alloys prepared by mechanical alloying. In order to study the time evolution of the alloying process, Fe30Co20Cu50 samples were studied after several processing times. The analysis of the data shows that, in a first step, a binary Co–Cu alloy is formed, but iron remains separate in the form of nanocrystals with a high defect concentration. Afterwards, in a second step, the final ternary Fe–Co–Cu alloy with the face-centered-cubic structure is obtained.
Effects of porosity on the thermal properties of a 380-aluminum alloy
Authors: Ramírez A. Manzano , Beltrán F. J. Espinoza , Yáñez-Limón J. M. , Vorobiev Yuri V. , González-Hernández J. , Hallen J. M.
Published: March 2008

Effective values of the thermal diffusivity, specific heat, and thermal conductivity of a porous 380-aluminum alloy prepared by melting in a gas-fired furnace, were determined as a function of the volume fraction of porosity. For that, photoacoustic, differential calorimetric, density, and image analyzer measurements were done. Thermal conductivity and specific heat capacity decrease with the increase of porosity, whereas the thermal diffusivity shows less dependence. Among the effective models for analysis of the thermal conductivity of a two-phase system, the Maxwell model best fits the experimental data, implying a homogenous distribution of the pores in the aluminum-alloy matrix.
Effect of phase separation in metal carboxylate gels on perovskite lead magnesium niobate crystallization
Authors: Narendar Yeshwanth , Messing Gary L.
Published: March 2008

Phase separation during the synthesis and decomposition of lead magnesium niobate (PMN)–ethylenediaminetetraacetic acid (EDTA) and PMN–citrate gels strongly affects perovskite Pb(Mg1/3Nb2/3)O3 phase formation. The PMN–EDTA gel was synthesized from a solution containing Pb–EDTA, Mg–EDTA, and peroxo–citrato–niobium complexes at pH 8. Pb–EDTA precipitation was avoided by using Pb:EDTA in the mole ratio >1:2.5 and flash pyrolyzing the PMN–EDTA solution at 225 °C. Consequently, the PMN yield increased from 80 to 98 wt%. The sequential decomposition of Pb–EDTA, Mg–EDTA, and peroxo–citrato–Nb in the PMN–EDTA precursor in 1 vol% O2 leads to phase separation of Pb and PbO and thus lowers the PMN yield to 92 wt%. At PO2 > 2.5 vol% the Pb, Mg, and Nb complexes cothermolyze to form ≥97 % perovskite PMN. The presence of a heterometallic citrato–Pb–Mg–Nb complex in PMN–citrate leads to oxygen partial pressure independent codecomposition of the Pb, Mg, and Nb complexes. Accordingly, PMN yields of ≥96 wt% were obtained from the PMN–citrate precursor for oxygen partial pressures between 1 and 5 vol%.
Effects of cationic dopants on the phase transition temperature of titania prepared by the sol-gel method
Authors: Vargas S. , Arroyo R. , Haro E. , Rodríguez R.
Published: March 2008

The effect of different cations in the anatase–rutile phase transition temperatures for titania prepared by the sol-gel method was studied. The metal dopants were chosen from different periods and groups of the periodic table to see the role played by the electronic configuration, the oxidizing state, the atomic size, etc. on these temperature modifications. Linear relationships between the anatase–rutile phase transition temperatures and the ionic radii for alkali metal, alkaline earth metal, and group 3 and 13 elements were obtained. For elements of the period 4, there was not such a defined tendency; for most of them the modification of the phase transition temperature was too small. The cations used were Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Y3+, La3+, Er3+, Ti4+, Co2+, Ni2+, Cu2+, and Zn2+. In all cases the dopant's concentration was 2 mol% with respect to titanium, and the same anion (nitrate) was used for all salts. A variation of more than 330 °C in the anatase–rutile phase transition temperatures was obtained by using these dopants. The transition temperatures from amorphous to anatase and from anatase to rutile phases were obtained from the x-ray diffractograms.
Atomic force microscopy study of nanoindentation deformation and indentation size effect in MgO crystals
Authors: Sangwal K. , Gorostiza P. , Servat J. , Sanz F.
Published: March 2008

The dependences of various nanoindentation parameters, such as depth of penetration d, indentation diameter a, deformation zone radius R, and height h of hills piled up around indents, on applied load were investigated for the initial (unrecovered) stage of indentation of the (100) cleavage faces of MgO crystals by square pyramidal Si tips for loads up to 10 μN using atomic force microscopy. The experimental data are analyzed using theories of elastic and plastic deformation. The results revealed that (i) a, R, and h linearly increase with d; (ii) the development of indentation size and deformation zone and the formation of hills are two different processes; (iii) the load dependence of nanohardness shows the normal indentation size effect (i.e., the hardness increases with a decrease in load); and (iv) there is an absence of plastic deformation involving the formation of slip lines around the indentations. It is found that Johnson's cavity model of elastic–plastic boundary satisfactorily explains the experimental data. The formation of hills around indentations is also consistent with a new model (i.e., indentation crater model) based on the concept of piling up of material of indentation cavity as hills.
Chemical vapor deposition of barium strontium titanate thin films using direct liquid injection of a single cocktail solution with Ba(methd)2, Sr(methd)2, and Ti(MPD)(tmhd)2
Authors: Lee Jung-Hyun , Rhee Shi-Woo
Published: March 2008

Deposition characteristics of (Ba,Sr)TiO3 (BST) thin films by metalorganic chemical vapor deposition with a mixture solution were investigated. Ba(methd)2 (methd = methoxyethoxytetramethylheptanedionate), Sr(methd)2, and Ti(MPD)2(tmhd)2 (MPD = methylpentanedioxy, tmhd = tetramethylheptanedionate) were dissolved together in methanol solvent. Mass spectrometry showed that Ba(methd)2 was less aggregated than Ba(tmhd)2-tetraglyme adduct (tetraglyme = tetraethylene glycol dimethyl ether) in the gas phase. Similar results were obtained from Sr precursors. Step coverage and electrical properties of the BST films were investigated as a function of deposition temperature from 350 to 600 °C. With the increase of the deposition temperature up to 500 °C, Ti composition in the films was increased, but Ba and Sr remained almost constant, and the step coverage became poor. Also, leakage current density and SiO2 equivalent oxide thickness was reduced as the deposition temperature increased. Poor incorporation of Ti below the deposition temperature of 500 °C was observed.
Formation of patterned microstructures of polycrystalline ceramics from precursor polymers using micromolding in capillaries
Authors: Beh Weng Sing , Xia Younan , Qin Dong
Published: March 2008

Micromolding in capillaries has been used to generate patterned microstructures of ZrO2 or SnO2 from its polymeric precursor. After patterning, the amorphous precursor was converted into the desired polycrystalline ceramic material by calcination in air at 460 °C. The final phase for each ceramic material was determined by powder x-ray diffraction. The shrinkage of the precursor material during pyrolysis was investigated by scanning electron microscopy and atomic force microscopy. These ceramic microstructures could be either supported on solid substrates or released as freestanding fibers and membranes. Their lateral dimensions could be as small as approximately 500 nm.
Role of Ni and Zr doping on the electrical, optical, magnetic, and structural properties of barium zinc tantalate ceramics
Authors: Rong G. , Newman N. , Shaw B. , Cronin D.
Published: March 2008

Properties of Ni- and Zr-doped Ba(Zn1/3Ta2/3)O3 ceramics are reported. The nickel ion has an effective paramagnetic moment of 3.22 ± 0.05. Optical spectra of Ni-doped Ba(Zn1/3Ta2/3)O3 are dominated by discrete internal transitions between Ni2+ 3d orbitals. Absorption from the 3Γ2(F) ground state to 4Γ3(F), 3Γ1(D), 5Γ1(D), 4Γ3(P) excited states occurs at approximately 1.55, 1.75, 2.50, and 2.80 eV, respectively. The ligand field strength of neighboring oxygen ions ranges from about 7300 cm−1 (0.25% Ni) to about 7700 cm−1 (1.0% Ni). A significant increase in the visible continuum background is correlated with increased tan δ. This effect is attributed to point defects in the Ni environment, suggesting that point defects play an important role in microwave loss in practical dielectric material.
Measurement and improvement of the adhesion of copper to polyimide
Authors: Menezes M. , Robertson I. M. , Birnbaum H. K.
Published: March 2008

A contact angle measurement technique has been used to obtain an estimate of the interfacial energy and thermodynamic adhesive strength between copper and polyimide [pyromellitic dyanhydride oxydianalyn (PMDA-ODA) and p-phenylene biphenyltetracarboinide (BPDA-PDA)]. Values of the strength of adhesion from these contact angle measurements are in reasonable agreement with values calculated using the Girifalco–Good–Fowkes nonpolar interfacial adhesion theory. Based on the surface energy it was predicted and experimentally observed that small copper clusters would embed into the polymer matrix if heated under ultrahigh vacuum conditions at temperatures near Tg of the polymer. Controlled embedding of nanometer clusters was utilized to produce a textured interface, where the partially embedded clusters acted as “nanonails” to anchor a metal overlayer to the underlying polyimide substrate. These nanonails greatly increased the bonding between the copper overlayer and the polyimide, as demonstrated by mechanical debonding studies.
Influence of stacking fault energy on microstructural development in equal-channel angular pressing
Authors: Komura Shogo , Horita Zenji , Nemoto Minoru , Langdon Terence G.
Published: March 2008

Equal-channel angular (ECA) pressing is a procedure having the capability of introducing an ultrafine grain size into a material. Experiments were conducted to examine the effect of the low stacking fault energy in pure Cu on microstructural development during ECA pressing at room temperature. The results show that the low 0stacking fault energy and the consequent low rate of recovery lead to a very slow evolution of the microstructure during pressing. Ultimately, a stable grain size of −0.27 μm was established in pure Cu but the microstructure was not fully homogeneous even after pressing to a total strain of ∼10. It is shown by static annealing that the as-pressed grains are stable up to ∼400 K, but at higher temperatures there is grain growth. These results lead to the conclusion that a low stacking fault energy is especially favorable for the introduction of an exceptionally small grain size using the ECA pressing procedure.
Aluminum metallization for flat-panel displays using ion-beam-assisted physical vapor deposition
Authors: Ma Zhenqiang , Was Gary S.
Published: March 2008

Failures in aluminum interconnects in display control devices are often caused by the formation of hillocks during postdeposition annealing. Ion-beam-assisted deposition was used to create a (110) out-of-plane texture in aluminum films to suppress hillocking. X-ray diffraction was used to quantify the (110)/(111) out-of-plane texture ratio, and scanning electron microscopy and atomic force microscopy were used to characterize the surface topology. Results show that no hillocks were observed on (110)-textured aluminum films following annealing for 30 min at 450 °C. Following annealing, the resistivity of the films made by ion-beam-assisted deposition recovered to within a factor of 2 of the physical-vapor-deposition films. Results show that ion-beam-assisted deposition can effectiv09ely modify the aluminum out-of-plane texture in such a way that hillock suppression can be achieved without significant change in resistivity.
Nonstoichiometry and lattice parameter of (Mg0.22Mn0.07Fe0.71)3–δO4 ferrite
Authors: Kang Sun-Ho , Yoo Han-Ill , Park Hyun Min
Published: March 2008

(Mg0.22Mn0.07Fe0.71)3–δO4 ferrites with different oxygen nonstoichiometry (δ) were prepared in the range of −0.006 ≤ δ ≤ 0.0050 by a solid-state electrochemical technique, and their lattice parameter–nonstoichiometry correlation was examined. It was found that the lattice parameter decreases with increasing deviation (|δ|) from the stoichiometric composition (δ = 0). The electrochemical technique is detailed, and the correlation is discussed in light of defect structure of the ferrite.
Czochralski growth and spectroscopic investigations of Yb3+, La3+:Na2SO4(I) and Nd3+:Na2SO4(I)
Authors: Mikhail Patric , Basler Reto , Hulliger Jürg
Published: March 2008

Ln3+-stabilized Na2SO4 (phase I) single crystals were grown by the Czochralski method. Differential thermal analysis revealed the influence of the ionic radius of Ln3+ on the stabilization of Na2SO4(I). Distribution coefficients (∼0.8–1.1) were measured by the inductively coupled plasma optical emission spectroscopy method and x-ray fluorescence spectroscopy. Spectroscopic investigations yielded absorption cross sections of 0.6 × 10−20 cm2 (π-polarized, 928.5 nm) and 1.5 × 10−20 cm2 (π-polarized, 797.3 nm) for Yb3+, La3+:Na2SO4 and Nd3+:Na2SO4, respectively. Crystal growth of Gd3+-stabilized Na2SO4(I) provides an interesting new material for stimulated Raman scattering experiments.
Strain gradient plasticity effect in indentation hardness of polymers
Authors: Chong Arthur C. M. , Lam David C. C.
Published: March 2008

Plasticity in material is typically described as a function of strain, but recent observations from torsion and indentation experiments in metals suggested that plasticity is also dependent on strain gradient. The effects of strain gradient on plastic deformation in thermosetting epoxy and polycarbonate thermoplastic were experimentally investigated by nanoindentation and atomic force microscopy in this study. Both thermosetting and thermoplastic polymers exhibited hardening as a result of imposed strain gradients. Strain gradient plasticity theory developed on the basis of a molecular kinking mechanism has predicted strain gradient hardening in polymers. Comparisons made between indentation data and theoretical predictions correlated well. This suggests that strain gradient plasticity in glassy polymers is determined by molecular kinking mechanisms.
Electrical and mechanical property transitions in carbon-filled poly(vinylpyrrolidone)
Authors: Grunlan Jaime C. , Gerberich William W. , Francis Lorraine F.
Published: March 2008

The effect of carbon black content on the mechanical and electrical properties of carbon-black-filled poly(vinylpyrrolidone) composites was determined. Experimental data show a drop in modulus when the volume of carbon black exceeds 25%, coincident with pore formation documented by scanning electron microscopy. This behavior is consistent with surpassing the critical pigment volume concentration. Electrical conductivity, however, does not show a discontinuous change in behavior at 25 vol% carbon black and continues to increase through a carbon black loading of 35 vol%. A qualitative model of microstructural evolution is presented to explain the observed differences in electrical and mechanical behavior.
Developing a coordination chemistry of intact quantum dots: The preparation of novel nanocomposites of PbS with CdS or CdSe
Authors: Trindade Tito , O'Brien Paul , Zhang Xiao-mei
Published: March 2008

In this communication a new kind of nanocomposite is reported in which a bridging coordination ligand, 2,2′-bipyrimidine, is used to bind quantum dots of CdS or CdSe (4–6 nm) to larger PbS nanoparticles.
Diffusion calculations for the 80-K-to-110-K Bi(Pb)SrCaCuO superconducting phase transformation
Authors: Zhu Wen , Kuo Chu Kun , Nicholson Patrick S.
Published: March 2008

A diffusion model is proposed to fit the measured chemical-transformation rates of the Bi(Pb)CaCuSrO 80-K phase to 110-K phase. Diffusion coefficients and activation energies in PO2 = 0.08 and 0.21 atm are reported. The low diffusion rates and high activation energies suggest cation diffusion controls the transformation.
Thermoelectric properties of sintered polycrystalline ZnIn2S4
Authors: Seo Won-Seon , Otsuka Riki , Okuno Harumi , Ohta Mitsuru , Koumoto Kunihito
Published: March 2008

Ceramic compacts of spinel-type ZnIn2S4 and IIIa-ZnIn2S4 polytype with a layer structure were synthesized by the reaction-sintering of mixed powders of ZnS and In2S3 at 723 K and 1073 K in Ar (containing 1° H2) atmosphere, respectively. The thermoelectric properties were investigated in the temperature range from 473 to 873 K. Thermoelectric figure of merit of the IIIa type was much larger than that of the spinel type, and it was slightly higher than the figure of merit of (ZnO)9In2O3, which is known to show the largest value among the oxide homologous compounds. To improve the thermoelectric properties, a c-plane-oriented sintered body of the IIIa polytype was successfully fabricated by a usual ceramic process. The figure of merit in the direction on the c plane was larger than on the ab plane due to higher electrical conductivity on the c plane and increased with increasing temperature showing the largest value of 1.3 × 10−4 K−1 at 873 K.
Infiltration of C/SiC composites with silica sol-gel solutions: Part I. Infiltration by dipping
Authors: Aparicio Mario , Durán Alicia
Published: March 2008

Oxidation resistance of ceramic matrix composites (CMC) of SiC reinforced with C fibers (C/SiC) can be improved by filling the residual porosity. The aim of this work was to design and analyze a dipping infiltration process under ambient conditions (1 atm pressure and room temperature) with silica sol-gel solutions prepared from tetraethyl orthosilicate. Different substrates and solutions have been studied. Thermal treatments, i.e., curing or sintering between infiltrations, increase the efficiency of the process since the densification of infiltrated silica opens up the remaining porosity. Increasing viscosity and/or concentration of the solution lead to greater weight gains. Weight gains are higher in the initial stages of the process because larger diameter porosity remains unfilled. As the process advances, the average pore size decreases, and only the lower viscosity solution can enter the residual porosity.
Mechanochemically synthesized NbC cermets: Part II. Mechanical properties
Authors: Murphy B. R. , Courtney T. H.
Published: March 2008

The mechanical behavior of mechanochemically synthesized NbC cermets was investigated. Material hardnesses range from a high of 19.6 GPa for as-synthesized cermets containing about 4 vol% of Fe to a low of about 4 GPa for heat-treated cermets containing about 34 vol% Cu. Higher hardness generally correlates with lower fracture toughness (about 2 MPa m1/2 for cermets containing the highest percentage of NbC) and vice versa. Highest fracture toughness (about 7.5 MPa m1/2) is found in NbC–18 vol% Fe cermets heat treated extensively following consolidation. Abnormally low fracture toughnesses are found in high-Cu-content cermets in which Cu segregation takes place during heat treatment. Current models of ceramic toughening can be applied to describe the fracture behavior of NbC–Fe cermets.
Domain and lattice contributions to dielectric and piezoelectric properties of Pb(Zrx, Ti1−x)O3 thin films as a function of composition
Authors: Hiboux S. , Muralt P. , Maeder T.
Published: March 2008

In situ reactively sputter deposited, 300-nm-thick Pb(Zrx, Ti1−x)O3 thin films were investigated as a function of composition, texture, and different electrodes (Pt,RuO2).X-ray diffraction analysis, ferroelectric, dielectric, and piezoelectric measurements were carried out. While for dielectric properties bulklike contributions from lattice as well as from domains are observed, domain wall contributions to piezoelectric properties are very much reduced in the morphotropic phase boundary (MPB) region. Permittivity and d33 do not peak at the same composition; the MPB region is broadened up and generally shifted to the tetragonal side.
Surface modification of aluminum and chromium by ion implantation of nitrogen with a high current density ion implanter and plasma-source ion implantation
Authors: Falkenstein Zoran , Walter Kevin C. , Nastasi Michael A. , Rej Donald J. , Gavrilov Nikolai V.
Published: March 2008

Results of ion implantation of nitrogen into electrodeposited hard chromium and pure aluminum by a high-dose ion-beam source are presented and compared to plasma-source ion implantation. The large-area, high current density ion-beam source can be characterized, with respect to surface modification use, by a uniform emitted dose rate in the range of 1016 to 5 × 1017 N cm−2 min−1 over an area of <100 cm2 and with acceleration energies of 10–50 keV. The implantation range and retained dose (measured using ion-beam analysis), the surface hardness, coefficient of friction, and the change in the wear coefficient (measured by nanohardness indentation and pin-on-disk wear testing) that were obtained with an applied dose rate of ∼1.7 × 1017 N cm−2 min−1 at 25 kV are given, and they are compared to results obtained with plasma-source ion implantation.
Measuring the interface stress: Silver/nickel interfaces
Authors: Josell D. , Bonevich J. E. , Shao I. , Cammarata R. C.
Published: March 2008

Interface stress is a surface thermodynamics quantity associated with the reversible work of elastically straining an internal solid interface. In a multilayered thin film, the combined effect of the interface stress of each interface results in an in-plane biaxial volume stress acting within the layers of the film that is inversely proportional to the bilayer thickness. We calculated the interface stress of an interface between {111} textured Ag and Ni on the basis of direct measurements of the dependence of the in-plane elastic strains on the bilayer thickness. The strains were obtained using transmission x-ray diffraction. Unlike previous studies of this type, we used freestanding films so that there was no need to correct for intrinsic stresses resulting from forces applied by the substrate that can lead to large uncertainties of the calculated interface stress value. Based on the lattice parameters of the bulk, pure elements, an interface stress of −2.02 ± 0.26 N/m was calculated using the x-ray diffraction results from films with bilayer thicknesses greater than 5 nm. This value is somewhat smaller than previous measurements obtained from as-deposited films supported by substrates. For smaller bilayer thicknesses the apparent interface stress becomes smaller in magnitude, possibly due to a loss of layering in the specimens.
Substrate temperature dependence of structure and resistivity of SrRuO3 thin films grown by pulsed laser deposition on (100) SrTiO3
Authors: Zakharov N. D. , Satyalakshmi K. M. , Koren G. , Hesse D.
Published: March 2008

The resistivity of SrRuO3 thin films on (001) SrTiO3 substrates grown at different temperatures by pulsed laser deposition is correlated to the microstructure. Films grown at 775 °C are of an orthorhombic structure, contain very few defects, and exhibit a low resistivity of 150 μΩ cm. Films grown at other temperatures contain a cubic phase and show higher resistivities. The defects present in the films, particularly twins and antiphase boundaries, are analyzed by high-resolution transmission electron microscopy, and their origin, as well as influence on film resistivity, is discussed.
An optimized process for fabrication of SrBi2Ta2O9 thin films using a novel chemical solution deposition technique
Authors: Kim Seung-Hyun , Kim D. J. , Lee K. M. , Park M. , Kingon A. I. , Nemanich R. J. , Im J. , Streiffer S. K.
Published: March 2008

Ferroelectric SrBi2Ta2O9 (SBT) thin films on Pt/ZrO2/SiO2/Si were successfully prepared by using an alkanolamine-modified chemical solution deposition method. It was observed that alkanolamine provided stability to the SBT solution by retarding the hydrolysis and condensation rates. The crystallinity and the microstructure of the SBT thin films improved with increasing annealing temperature and were strongly correlated with the ferroelectric properties of the SBT thin films. The films annealed at 800 °C exhibited low leakage current density, low voltage saturation, high remanent polarization, and good fatigue characteristics at least up to 1010 switching cycles, indicating favorable behavior for memory applications.
A chemical role of refractory metal caps in Co silicidation: Evidence of SiO2 reduction by Ti cap
Authors: Kondoh E. , Conard T. , Brijs B. , Jin S. , Bender H. , de Potter M. , Maex K.
Published: March 2008

An interfacial SiO2 hampers a silicidation reaction between Co and Si. A refractory metal cap is believed to block ambient oxygen diffusing toward the Co/Si interface. However, an interfacial SiO2 can also be present prior to and/or during the annealing. This work reports on our findings of the interaction between SiO2 and Co layers capped with refractory metals. It was found that Ti diffuses through the Co layer and segregates underneath the Co, which leads to the reduction of SiO2 and the formation of free Si. The free Si in-diffuses and reaches the original Ti surface. On the other hand, TiN shows a very inert behavior compared to Ti. The results are discussed in connection with Co silicidation processes.
Resource recovery of waste incineration fly ash: Synthesis of tobermorite as ion exchanger
Authors: Yao Zhidong , Tamura Chikashi , Matsuda Motohide , Miyake Michihiro
Published: March 2008

Tobermorite was synthesized successfully from waste incineration fly ash by hydrothermal treatment in the presence of sodium hydroxide solution. The tobermorite synthesis was examined as a function of reaction temperature, time, and NaOH concentration. The formation of tobermorite was identified in all of the fly ash treated with NaOH at 180 °C, followed by the minor generations of sodalite and cancrinite phases with increasing NaOH concentration and extending reaction time. The NaOH-treated fly ash revealed the uptake behaviors for Cs+ and NH4+, whereas the fly ash untreated with NaOH solution did not show that. The uptake amounts of resulting products were also determined: 0.40 mmol/g for Cs+ and 0.35 mmol/g for NH4+ in the fly ash treated with 2.0 M NaOH at 180 °C for 20 h.
Subsolidus phase equilibria in the La2O3–Ga2O3–CeO2 system
Authors: Hrovat Marko , Samardžzija Zoran , Holc Janez , Bernik Slavko
Published: March 2008

Subsolidus equilibria in air in the La2O3–Ga2O3–CeO2 system were studied with the aim of obtaining information on possible interactions between a LaGaO3-based solid electrolyte and CeO2 during preparation of the anode in solid oxide fuel cells. No ternary compound was found. The tie lines are between La4Ga2O9 and the end of the CeO2 solid solution range with composition La0.5Ce0.5O1.75 and between the LaGaO3 and CeO2 range of solid solutions.
Liquid immersion technique coupled with infrared microscopy for direct observation of internal structure of ceramic powder compact, with alumina as an example
Authors: Uematsu Keizo , Saito Midori
Published: March 2008

Infrared microscopy was applied to observe the internal structure of alumina powder compact, which was made transparent with an immersion liquid. It provided clear images of nonuniformity in the structure for a specimen as thick as 1 mm. Two types of nonuniformity found in this paper are the large pores made from the pores in powder granules and the low-density region forming network structure, which was formed by the presence of a binder. The minimum size of nonuniformity detected in a structure is under 20 μm.
Radiation stability of gadolinium zirconate: A waste form for plutonium disposition
Authors: Wang S. X. , Begg B. D. , Wang L. M. , Ewing R. C. , Weber W. J. , Kutty K. V. Govidan
Published: March 2008

Zirconate and titanate pyrochlores were subjected to 1 MeV of Kr+irradiation. Pyrochlores in the Gd2(ZrxTi1-x)2O7system (x= 0, 0.25, 0.5, 0.75, 1) showed a systematic change in the susceptibility to radiation-induced amorphization with increasing Zr content. Gd2Ti2O7amorphized at relatively low dose (0.2 displacement per atom at room temperature), and the critical temperature for amorphization was 1100 K. With increasing zirconium content, the pyrochlores became increasingly radiation resistant, as demonstrated by the increasing dose and decreasing critical temperature for amorphization. Pyrochlores highly-enriched in Zr (Gd2Zr2O7, Gd2Zr1.8Mg0.2O6.8, Gd1.9Sr0.1Zr1.9Mg0.1O6.85, and Gd1.9Sr0.1Zr1.8Mg0.2O6.75) could not be amorphized, even at temperature as low as 25 K.
A new surface pretreatment approach for enhancing diamond nucleation
Authors: Fan Qi Hua , Fernandes A. , Pereira E. , Grácio J.
Published: March 2008

In this paper we present a new approach of surface pretreatment for enhancing diamond nucleation. The copper substrates were fixed inside a plastic cylinder container with diamond powder diluted in water. This container was coupled to a vibration unit moving up and down at ˜300 cycles/min with a stroke of 15 mm. Finally, samples pretreated for 30 min were deposited with diamond. A high nucleation density comparable to that on substrate abraded with diamond powder was achieved. This method proved to be more effective than our ultrasonic treatment, keeping the advantages of surface preservation. Being simple and straightforward, this “shaking” pretreatment most fits the cases where a thin interlayer has to be used (like diamond coating on steel) and where the samples have a complex shape.
A transmission electron microscopy investigation of sulfide nanocrystals formed by ion implantation
Authors: Meldrum A. , Sonder E. , Zuhr R. A. , Anderson I. M. , Budai J. D. , White C. W. , Boatner L. A. , Henderson D. O.
Published: March 2008

Ion implantation was used to form compound semiconductor nanocrystal precipitates of ZnS, CdS, and PbS in both glass and crystalline matrices. The precipitate microstructures and size distributions were investigated by cross-sectional transmission electron microscopy techniques. Several unusual features were observed, including strongly depth-dependent size variations of the ZnS precipitates and central void features in the CdS nanocrystals. The morphology and crystal structure of the nanocrystal precipitates could be controlled by selection of the host material. The size distribution and microstructural complexity were significantly reduced by implanting a low concentration of ions into a noncrystalline host, and by using multi-energy implants to give a flat concentration profile of the implanted elements.
Semiconductor nanowires from oxides
Authors: Lee S. T. , Zhang Y. F. , Wang N. , Tang Y. H. , Bello I. , Lee C. S. , Chung Y. W.
Published: March 2008

Highly pure, ultralong, and uniform-sized semiconductor nanowires in bulk quantity were synthesized by thermal evaporation or laser ablation of semiconductor powders mixed with oxides. Transmission electron microscopy study shows that decomposition of semiconductor suboxides and defect structures play important roles in enhancing the formation and growth of high-quality nanowires. A new growth mechanism is proposed on the basis of microstructure and different morphologies of the nanowires observed.
Oxidation behavior of platinum–aluminum alloys and the effect of Zr doping
Authors: Dickey E. C. , Pint B. A. , Alexander K. B. , Wright I. G.
Published: March 2008

The isothermal and cyclic oxidation behavior of PtAl and PtAl + Zr was studied followed by postoxidation microstructural and microchemical analyses. Their isothermal oxidation performance at 1200 °C was similar to that of NiAl and NiAl + Zr. In short (1-h) cycles, the cyclic oxidation resistance of undoped PtAl was found to be substantially better than NiAl. However, with longer (100-h) cycles, little improvement in the metal consumption rate was observed relative to NiAl. The addition of Zr to PtAl significantly improved cyclic oxidation performance in both short- and long-cycle tests. Spatially resolved energy dispersive spectroscopy indicated Zr segregation to both the metal–oxide interface and Al2O3 grain boundaries.
Combined effect of grain size and tensile stresses on the ferroelectric properties of sol-gel (Pb,La)TiO3 thin films
Authors: Alguerá M. , Calzada M. L. , Pardo L. , Snoeck E.
Published: March 2008

Transmission electron microscopy has shown that the grain size of sol-gel-prepared lanthanum-modified lead titanate films increases from ∼100 to ∼1 μm when the excess of PbO in the precursor solution is reduced from 20 to 10 mol%. Switchable polarization is higher in the films with a smaller grain size. Profilometry and the temperature dependence of the dielectric permittivity indicate that films are tensile stressed by the substrate. The grain-size effect on polarization switching is explainedby taking into account this tensile stress, which is thought to induce some a-domain orientation and 90° domain wall clamping in the grains attached to the substrate.
Hydrolysis of tetracalcium phosphate in the presence of a poly(alkenoic acid)
Authors: Greish Y. E. , Brown P. W.
Published: March 2008

Ca4(PO4)2O (TetCP) reacts with an acidic polyelectrolyte in the absence of a solvent to form a composite composed of Ca10(PO4)6(OH)2 (hydroxyapatite, or HAp) and the Ca salt of the polyelectrolyte. Mixtures of an acrylic copolymer and TetCP powders were hot-pressed, and the effects of temperature, pressure, and time on HAp formation were studied. Reaction starts when the copolymer is heated to above Tg. Initial carboxyl site neutralization liberates water, continued TetCP hydrolysis, liberates Ca2+ ions, which react with the copolymer forming its Ca salt. When 90% conversion to HAp was achieved, the composite had an average tensile strength of 51 MPa, a Vickers hardness of 145 kg/mm2 and a Tg ˜50 °C.
In situ transmission electron microscopy investigation of threading dislocation motion in passivated thin aluminum films
Authors: Keller-Flaig R-M. , Legros M. , Sigle W. , Gouldstone A. , Hemker K. J. , Suresh S. , Arzt E.
Published: March 2008

In situ transmission electron microscopy (TEM) was performed to study dislocation motion during temperature cycles in aluminum films passivated with a SiO2 layer. The films were cycled from room temperature to 450 °C. Wedge-haped cross-sectional TEM samples were used to retain the constraint of the Si substrate. Besides interactions between dislocations and interfaces, the movement of threading dislocations within the constrained aluminum film was observed. This observation provides an experimental corroboration of the occurrence of threading dislocation motion, which is the basis for rationalizing the high-ield strength of thin films in available models of thin-film plasticity.
Relationship between domain structure and film thickness in epitaxial PbTiO3 films deposited on MgO(001) by reactive sputtering
Authors: Choi Won Kyoung , Choi Si Kyoung , Lee Hyuck Mo
Published: March 2008

The epitaxial PbTiO3 thin films of different thickness were prepared on MgO(001) substrates by the reactive direct-current magnetron sputtering. The volume fraction of c domains, α, which was measured by x-ray diffractometry, increased rapidly from zero with the film thickness, being saturated at about 90% above 100 nm. The films were annealed in a PbO atmosphere at 700 °C for 8 h, and they were used to study the composition change in the Pb/(Pb + Ti) ratio and the relaxation of the residual intrinsic stress. The relationship between change of α and composition was weak. The stress state was calculated through the finite-element method. As for the small thickness, the tensile epitaxial stress overwhelmed compressive intrinsic and thermal stresses, and the domain structure was a-domain oriented. As for the large thickness, the compressive intrinsic stress together with the thermal stress overcame the tensile epitaxial stress, and the population turned into c domain.
Interface structure of AlN/TiN/MgO(001) prepared by molecular beam epitaxy
Authors: Ma X. L. , Sugawara Y. , Shibata N. , Ikuhara Y.
Published: March 2008

Thin AlN films were grown by molecular beam epitaxy on MgO(001) substrate with a thin TiN buffer layer. The as-prepared AlN/TiN/MgO(001) interfaces have been characterized by cross-sectional high-resolution electron microscopy (HREM). It is found that the thin TiN buffer layer is epitaxially grown on the MgO(001) substrate and hexagonal AlN epitaxially on the as-received TiN(001). Based on the growth orientation relationship and HREM images, atomistic structure models for the AlN/TiN interface are proposed, image simulated, and compared with experimental images.
Silicide formation in implanted channels and interfacial reactions of metal contacts under high current density
Authors: Chen K. N. , Lin H. H. , Cheng S. L. , Peng Y. C. , Shen G. H. , Chen L. J. , Chen C. R. , Huang J. S. , Tu K. N.
Published: March 2008

Silicide formation in implanted channels and interfacial reactions of Ni, Co, Ti, and Cu contacts under high current density have been investigated. Silicide lines, forming in the implanted channels, were observed in Ni and Cu/p+–Si samples but not in Ti and Co samples. The silicide line formation is correlated to the high diffusivity of metals in Si. For the Ni/p+–Si sambles, silicode line was found to initiate form the cathode contact. Network structures at the cathode were found in both Co and Ni samples. The depth of silicide formation was found to extend to the junction depth. The relationships between the silicide length and contact size, the applied current, and the method of the applied current are discussed.
Transformation probability of graphite-diamond assisted by nonmetallic catalysts at high pressure and high temperature
Authors: Sun Liling , Wu Qi , Zhang Yafei , Wang Wenkui
Published: March 2008

The tendency of graphite-diamond transformation assisted by nonmetallic catalysts of carbonates, sulfates, or phosphorus under high pressure and high temperature has been investigated by calculating the activation energy and transformation probability of the carbon atoms over a potential barrier. It was found that the activation energy is highly sensitive to the catalyst chosen. The value of activation energy in the systems of graphite-carbonates, graphite-phosphorus, and graphite-sulfate are 130.71 × 103, 206.03 × 103, and 221 × 103 J/mol, respectively. If fd stands for the probability of the transformation from graphite to diamond, the probability sequence of graphite-diamond transformation in different systems was put forward: fd(gr.-carbonate) > fd(gr.-phosphorus). fd(gr.-sulfate).
Local heating associated with crack tip plasticity in Zr–Ti–Ni–Cu–Be bulk amorphous metals
Authors: Flores Katharine M. , Dauskardt Reinhold H.
Published: March 2008

Deformation in metallic glasses is generally considered to arise from flow in localized shear bands, where adiabatic heating is thought to reduce glass viscosity. Evidence has been inferred from the veined fracture surfaces and molten droplets reported for metallic glasses. In this work, the detailed spatially resolved surface temperature increase and subsequent dissipation associated with crack tip plasticity in a Zr–Ti–Ni–Cu–Be bulk metallic glass is characterized for the first time. Maximum temperatures of up to 54.2 K were estimated from a heat conduction model and shown to be in excellent agreement with a nonhardening plasticity model for the heat generated by a propagating crack. Local cooling was also observed and shown to be consistent with thermoelastic effects.
Hydrogen-enhanced dislocation velocities in Ni3Al single crystals
Authors: Jiang C. B. , Patu S. , Lei Q. Z. , Shi C. X.
Published: March 2008

The average dislocation velocity in hydrogenated Ni3Al single crystals was directly measured as a function of resolved shear stress (RSS) at room temperature (293 K) by the etch-pit technique. It was found that the dislocation velocity with hydrogen is about 5–25 times faster than that without hydrogen for the same RSS, and hydrogen decreases activation energy for dislocation motion in Ni3Al single crystals. The reason hydrogen can enhance dislocation velocity in this compound is briefly discussed. These preliminary results quantitatively provide the first evidence of hydrogen-enhancing dislocation mobility in Ni3Al material.
Significant reduction in thermal expansion of a low-carbon steel sheet by depositing a Fe–Ni alloy thin film
Authors: Kim Sang Sub , Park Yong Bum
Published: March 2008

A 3-μm-thick Fe–Ni alloy thin film was deposited on a 0.2-mm-thick low-carbon steel substrate by radio-frequency magnetron sputtering, and the properties of the film were investigated. The film exhibits a columnar growth structure and a fiber texture with the relationship of (110)film//(111)substrate. A thermal cycle test showed good adhesion between the film and the substrate. Most importantly, the Fe–Ni alloy deposition results in a significant reduction in thermal expansion of the whole specimen. These results suggest that a properly deposited Fe–Ni alloy film could be applied to a low-carbon steel sheet to significantly reduce its thermal expansion. Such reduced thermal expansion would enhance the image resolution of a shadow mask made of a low-carbon steel sheet.
Optical and electrical properties of transparent conducting In2O3–ZrO2 films
Authors: Qadri S. B. , Kim H. , Khan H. R. , Piqué A. , Horwitz J. S. , Chrisey D. , Skelton E. F.
Published: March 2008

The optical transparencies and electrical conductivities of thin films of In2O3 mixed with ZrO2 have been investigated. These films were deposited on glass substrates at room temperature using pulsed-laser deposition. Indium–zirconium oxide films with a ZrO2 content up to a 15 wt% were conducting and more than 80% transparent from 450 to 700 nm. As the ZrO2 content increased from 0 to 15 wt%, the electrical resistivities increased from 1.28 × 10−3 to 6.48 × 10−2 Ω cm, the carrier densities were decreased from 2.14 × 1020 to 1.0 × 1018/cm3, and the Hall mobilities decreased from 21 to 5 cm2 V−1 s−1, all monotonically.
Diamond synthesis by high-velocity thermal spray: The laboratory analogue of a meteorite impact
Authors: Goswami R. , Herman H. , Sampath S. , Parise J. B.
Published: March 2008

Nanocrystalline-diamond particles were produced in the form of a coating by depositing Ni-clad graphite powder in a high-velocity thermal spray experiment. Particles were accelerated to impact and formed a thick film (>20 μm) on a steel substrate, with the high-velocity impact generating a shock wave, which propagates through the particle and the underlying deposits. Transmission electron microscopy revealed that this deposit contains cubic diamond nanocrystals having a size range of 5 to 10 nm in graphite. In addition to diamond, it was observed that a portion of the deposit contains “closed-curved graphite.”
Synthesis of crack-free thick diamond wafer by step-down control of deposition temperature
Authors: Lee Jae-Kap , Park Young-Joon , Eun Kwang Yong , Baik Young-Joon , Park Jong-Wan
Published: March 2008

Due to growth tensile stress, which evolves in diamond films during deposition, thick diamond films are easily cracked. In this study we successfully prevented growth cracks by introducing thermal compressive stress with step-down control of deposition temperatures during growth. Three deposition temperature drops of 10 °C each during deposition enabled us to successfully synthesize crack-free four-inch diamond wafers several hundred micrometers in thickness. This method is very simple and may be applicable to coating of films of various materials different from those of substrates.
Nondestructive evaluation of cavitation in an Al–Mg material deformed under creep conditions
Authors: Taleff Eric M. , Leon-Salamanca Teodoro , Ketcham Richard A. , Reyes Reuben , Carlson William D.
Published: March 2008

Cavitation was examined in an Al–Mg solid-solution alloy deformed in tension at 400 °C under conditions providing solute-drag creep, which can produce tensile ductilities from 100% to over 300%. Two nondestructive evaluation techniques were employed to measure the extent of cavitation: ultra-high-resolution x-ray computed tomography and pulse-echo ultrasonic evaluation. Subsequent to nondestructive evaluation, the sample was sectioned for examination by standard metallographic techniques. Metallographic examination confirmed that both nondestructive techniques accurately indicated the extent of cavitation. Ultrasonic testing provided a practical means of distinguishing material with cavities from that without cavities. Ultrahigh- resolution x-ray computed tomography provided an accurate three-dimensional image of internal cavitation.