bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of dielectric and piezoelectric properties on film thickness for highly {100}-oriented lead magnesium niobate–lead titanate (70/30) thin films
Authors: Park Jeong Hwan , Trolier-McKinstry Susan
Published: March 2008

Fiber textured {100}-oriented lead magnesium niobate–lead titanate (PMN–PT) (70/30) films with thicknesses between 0.35 and 2.1 mm were prepared using chemical solution processing. The degree of preferred orientation changed little with increasing thickness. However, the measured dielectric constant, remanent polarization, and piezoelectric coefficients (d31) increased with increasing film thickness. The effective d31 coefficients of highly {100}-oriented PMN–PT films on Pt-coated Si substrates were found to range from −16 to −96 pC/N. Ultraviolet illumination during poling resulted in abnormal aging behaviors and lower overall aging rates for the films. The initial nonlinear aging behavior was attributed to the presence of an internal space-charge field that developed from photoinduced charge carriers. As the space-charge field decays over time, the magnitude of d31 increased until 450–500 min after poling, at which time d31 remained either constant or declined slightly. Thus, the changes in d31 were limited to 1–2%/decade 500–600 min after poling.
Gas flow effects on the structure and composition of SiNx/Si/SiNx films prepared by radio-frequency magnetron sputtering
Authors: Xu Wentao , Li Boquan , Fujimoto Toshiyuki , Kojima Isao
Published: March 2008

The structure and composition of SiNx/Si/SiNx films were investigated by means of x-ray reflectivity, x-ray photoelectron spectroscopy, and atomic force microscopy. The three-layer films were prepared by radio-frequency magnetron sputtering under the condition of constant nitrogen flow and the argon flow. It was found that the deposition rate and surface structure of the silicon nitride films were mainly determined by the nitrogen flow rather than the argon flow. But the composition of the silicon nitride films was controlled by the gas flow ratio (FAr/FN2) used during sputtering.
Dense, bubble-free ceramic deposits from aqueous suspensions by electrophoretic deposition
Authors: Uchikoshi Tetsuo , Ozawa Kiyoshi , Hatton Benjamin D. , Sakka Yoshio
Published: March 2008

The characteristics of electrophoretic deposition (EPD) of positively charged particles onto a cathode were investigated using aqueous alumina and zirconia suspensions. The deposition was performed using several kinds of metal substrates at different current densities. For most substrate materials, a large number of macropores appeared in the deposit, and their size increased with the current density due to gas bubble formation. However, no macropores were formed in the deposit on a palladium substrate, regardless of the current density. The green density and sintering properties of the EPD deposits on a palladium substrate from aqueous suspensions were the same as from slip casting. Bubble-free zirconia/alumina laminate composites were also fabricated by EPD from aqueous suspensions.
Novel photoluminescence from hydrogenated amorphous carbon films prepared by using xylene source
Authors: Xu Jun , Li Wei , Ma Tianfu , Li Zhifeng , Wang Li , Chen Kunji
Published: March 2008

Hydrogenated amorphous carbon thin films were prepared by using organic hydrocarbon source, xylene (C8H10), in a plasma enhanced chemical vapor deposition-(PECVD) system. In contrast to a single broad PL peak from methane (CH4)-based hydrogenated amorphous carbon films, a new PL feature was observed from xylene-based a–C:H films in the blue-green light region. It was found that the aromatic-structures were enhanced in xylene-based a–C:H films deposited at high radio frequency power, which may result in the existence of luminescence centers in the carbon films and induce the appearance of a new PL peak.
Analysis of phase distributions in the Li2O–Nb2O5–TiO2 system by piezoresponse imaging
Authors: Borisevich Albina Y. , Kalinin Sergei V. , Bonnell Dawn A. , Davies Peter K.
Published: March 2008

The M-phase solid solutions Li1+x−yNb1−x−3yTix+4yO3) (0.1 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.175) in the Li2O–Nb2O5–TiO2 system have promising microwave dielectric properties. However, these compounds can contain small quantities of ferroelectric impurities that affect the polarization response of the material. Due to their low concentration and their chemical similarity to the host material, the impurities cannot be detected by x-ray diffraction or local elemental analysis. Scanning surface potential microscopy and piezoresponse imaging were used to analyze phase compositions in this system. Piezoresponse imaging demonstrated the presence of thin (<200–300 nm) ferroelectric layers on the grain boundaries oriented along the c-axis of the M-phase. Differences between the surface potential and the piezoresponse of ferroelectric multicomponent systems are discussed.
A note on a common mistake in the analysis of nanoindentation data
Authors: Chaudhri M. Munawar
Published: March 2008

It is shown that to analyze the load versus displacement data obtained from a nanoindentation experiment on a flat surface, it is incorrect to use the so called “reduced modulus,” which includes the elastic properties of both the indenter and the test solid. It is suggested that, until correct analytical solutions become available, the indenter should always be of a much stiffer material than the test solid and it should be approximated to a rigid indenter in the analysis. Furthermore, when the indenter and the test surface are of comparable elastic moduli, the measured indenter displacement is the distance of mutual approach of the two contacting bodies rather than the penetration of the indenter below the original surface of the test solid.
Synthesis and processing of nanocrystalline Ag–Fe–Ni for low thermal expansion–high conductivity thermal management applications
Authors: Stolk J. , Gross M. , Stolk D. , Manthiram A.
Published: March 2008

Nanocrystalline Ag–Fe–Ni powders were produced by a reduction of the aqueous metal ion solutions with sodium borohydride and then converted to fine-grained silver–Invar alloys that offer attractive thermal, electrical, and mechanical properties. The samples were characterized by x-ray diffraction, scanning electron microscopy, wavelength dispersive x-ray spectrometry, thermomechanical analysis, microhardness measurements, and electrical conductivity measurements; thermal conductivity was estimated using the Wiedemann–Franz law. Sintering of a specimen with a nominal composition of 60 wt% Ag–25.6 wt% Fe–14.4 wt.% Ni led to the formation of a two-phase silver–Invar alloy with a grain size of approximately 2 μm, a hardness of 133 HK200g, coefficient of thermal expansion of 12.44 × 10−6 / °C, and electrical conductivity of 2.13 × 105 (Ω cm) −1.
Carbonization behavior of polyimide film containing iron complex in relation to magnetic properties
Authors: Kaburagi Y. , Toriyama T. , Yoshida A. , Wakabayashi H. , Hishiyama Y. , Inagaki M.
Published: March 2008

A ferromagnetic film composed of carbon matrix and dispersed fine iron particles was prepared by heating a polyimide film containing iron complex at temperatures up to 1000 °C. The particles were formed and distributed homogeneously on the film surfaces by heat treatments at 600 °C and above, and inside the films at 700 °C and above. The particles were α–Fe, γ–Fe (or austenite), and Fe3C with fractions of about 7:2:1 in the films heated at 800 °C and above. The mean crystallite sizes of α–Fe and γ–Fe (or austenite) particles were evaluated to be 19 and 15 nm in the film heated at 800 °C, and 32 and 30 nm at 1000 °C, respectively. The films heated at 600 °C and below were superparamagnetic, while those at 700 °C and above were ferromagnetic, but both components existed in all films. The iron particles promoted the growth of carbon crystallites in the films; i.e., the interlayer spacing was about 0.341–0.343 nm and mean crystallite size 4.0–6.5 nm for the films heated in the range of 700 to 1000 °C. Pores were observed on the surfaces and cross sections of the carbonized films, and they seemed to be loopholes of the clusters. Iron oxides were scarcely formed in the films, even after being kept for a long duration at room temperature in atmosphere.
Microscopic effects of self-radiation damage in 244Cm-doped LuPO4 crystals
Authors: Luo J. S. , Liu G. K.
Published: March 2008

Microscopic effects of self-radiation damage in 244Cm-doped LuPO4 crystals were examined with transmission electron microscopy. These LuPO4 crystals had been doped with 1 wt% 244Cm and exposed to a radiation dose as high as 5 × 1016 α-decay events/mg over 18 years. The microscopic analysis revealed dense arrays of individual defect clusters and numerous bubbles. Whereas, the defect clusters may be interpreted as residuals of alpha-recoil tracks, the bubbles likely resulted from the α-particles generated during the decay events. The bubbles were found to coalesce under electron beam irradiation. Despite the high accumulated dose over the 18 years, the samples exhibited sharp diffraction patterns and periodic lattice spacings. This finding indicated that the samples remained largely crystalline and that the radiation-induced lattice damage was recovered at a rate comparable to that of damage production. This high recoverability is discussed with respect of various annealing processes that may have occurred in the samples.
Preparation of Cu(In,Ga)Se2 thin films at low substrate temperatures
Authors: Nishiwaki S. , Satoh T. , Hashimoto Y. , Negami T. , Wada T.
Published: March 2008

Cu(In,Ga)Se2(CIGS) thin films were prepared at substrate temperatures of 350 to 500 °C. The (In,Ga)2Se2 precursor layers were deposited on Mo coated soda-lime glass and then exposed to Cu and Se fluxes to form CIGS films. The surface composition was probed by a real-time composition monitoring method. The CIGS films were characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, secondary ion mass spectroscopy, and atomic force microscopy. The transient formation of a Cu–Se phase with a high thermal emissivity was observed during the deposition of Cu and Se at a substrate temperature of 350 °C. Faster diffusion of In than Ga from the (In,Ga)2Se3 precursor to the newly formed CIGS layer was observed. A growth model for CIGS films during the deposition of Cu and Se onto (In,Ga)2Se3 precursor is proposed. A solar cell using a CIGS film prepared at about 350 °C showed an efficiency of 12.4%.
Joining characteristics of oxidized SiC particles reinforced Al–Mg matrix composite prepared by reaction infiltration processing
Authors: Shi Zhongliang , Ochiai Shijiro , Hojo Masaki , Lee Jaechul , Gu Mingyuan , Lee Hoin
Published: March 2008

The joining characteristics of oxidized SiC particles with Al–Mg alloy during reaction infiltration processing for fabrication of the composite were studied. From the measurement of weight changes due to the transformation from SiC into SiO2, it became clear that the thickness of SiO2 layer which was formed at the surface of SiC particles increased parabolically with holding time at the given exposing temperatures. The degree of oxidation of the preform made by SiC particles can be controlled by the application of the present oxidation data. The microstructure observed by field emission scanning electron microscopy showed network skeleton via necklike oxidized-joining among the SiC particles and the compressive strength of the perform increased with oxidation temperature. Furthermore, the microstructure of the composite which was fabricated by Al–2 wt% Mg alloy via reaction infiltration processing was examined and the formation of spinel was observed to join the matrix with the particles like a bridge, which is suitable to make the complicate and strong preforms for the near net-shape composites application in electronic packaging.
Modeling of the effects of crystallographic orientation on electromigration-limited reliability of interconnects with bamboo grain structures
Authors: Fayad W. R. , Andleigh V. K. , Thompson C. V.
Published: March 2008

We presented a model for the line-width-dependent grain structure statistics in bamboo interconnects. We then showed, using an electromigration simulation, that grain orientation-dependent interface diffusivities constitute a likely mechanism contributing to the variabilities in lifetimes observed in experiments.
Preparation and characteristics of seeded epitaxial (Sr,Ba)Nb2O6 optical waveguide thin films using sol-gel method
Authors: Koo Junmo , Jang Jae Hyeok , Bae Byeong-Soo
Published: March 2008

Highly c-axis-oriented (Sr,Ba)Nb2O6 (SBN) films were grown on a seeded MgO(100) substrate via sol-gel method. The substrate was preseeded with epitaxial islands of SBN made by breaking up a continuous film into single-crystal islands by pores. Since the number of epitaxial nuclei was increased at the interface between the film and the substrate, the film on a seeded substrate had better highly orientation than that on unseeded substrate. The film having low Sr content exhibited better epitaxial growth because of the distorted unit-cell network and the change of lattice parameters of SBN thin film. For obtaining excellent optical properties, SBN:75 film was prepared on MgO substrate with SBN:25 composition seed layer. Because of low birefringence of refractive indices in the film having high Sr content, the optical scattering loss by the anisotropy of refractive indices was suppressed.
Glass-forming ability of the Ni–Zr and Ni–Ti systems determined by interatomic potentials
Authors: Lai W. S. , Liu B. X.
Published: March 2008

Employing the n-body potentials of the Ni–Zr and Ni–Ti systems, we performed molecular dynamics simulation to study the relative stability of the terminal solid solutions versus the corresponding amorphous states as a function of solute concentrations. The terminal solid solutions transformed into amorphous states spontaneously when the solute concentrations were beyond the maximum allowable values; i.e., the critical solubilities were determined to be 14 at.% Zr in Ni and 25 at.% Ni in Zr for Ni–Zr system and 38 at.% Ti in Ni and 15 at.% Ni in Ti for the Ni–Ti system. The physical implication of the critical concentrations, as well as their correlation with the glass-forming abilities of the Ni–Zr and Ni–Ti systems, is discussed.
Densification and grain growth of Al-doped ZnO
Authors: Han Jiaping , Mantas P. Q. , Senos A. M. R.
Published: March 2008

The densification and grain growth of ZnO doped with Al from 0.08 to 1.2 mol% were investigated during isothermal sintering between 1100 and 1400 °C. The Al dopant significantly inhibited the grain growth of ZnO and increased the grain growth exponent from 3 for pure ZnO to 4–6 for Al-doped ZnO. The grain growth activation energy was also changed from approximately 200 kJ/mol for pure ZnO to approximately 480 kJ/mol for Al-doped ZnO. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy showed that a ZnAl2O4 spinel phase existed as a second phase at the ZnO grain boundaries in Al-doped ZnO specimens. The spinel particles exerted an effective drag (pinning) on the migration of ZnO grain boundaries. The analyses of the Al doping effect on the densification rate provided evidence that the driving force for densification was reduced by the second-phase particles. A mechanism of pore surface drag (pinning) on densification equivalent to the observed drag (pinning) of grain boundaries on grain growth was proposed.
Formation of Nd1+x (Ba1−ySry)2−x Cu3O7±δ solid solutions by crystal pulling
Authors: Yao Xin , Goodilin E. A. , Izumi Teruo , Shiohara Yuh
Published: March 2008

With the addition of Sr into the NdO1.5–BaO–CuOz flux, series single crystals of Nd1+x (Ba1−ySry)2−x Cu3O7±δ solid solutions (Nd1113ss) were successfully grown by crystal pulling. The liquid composition control was of key importance for controlling the crystal composition, which led to a fundamental structure control. The tetragonal Nd1113ss structure was readily obtained, using a Ba-poor liquid, due to a higher Sr liquid solubility, or using a liquid with the Ba/Cu ratio around 0.33. On the other hand, a Ba-rich liquid could effectively suppress the Nd substitution at Ba sites. The higher Sr addition for achieving a stoichiometric Nd1113 compound was thermodynamically prohibited by (i) an inherently low Sr liquid solubility and (ii) the formation of BaSrCu2Oz phase in the flux at the temperature range for crystal growth. The liquid-solid-structure relation was studied.
Field-activated combustion synthesis of Ta–Si intermetallic compounds
Authors: Maglia F. , Anselmi-Tamburini U. , Bertolino N. , Milanese C. , Munir Z. A.
Published: March 2008

The synthesis of silicides of tantalum (TaSi2, Ta5Si3, Ta2Si, and Ta3Si) by field-activated combustion synthesis was investigated. The phases TaSi2, Ta5Si3, and Ta2Si can be synthesized in relatively pure form through field activation. The first compound requires a threshold field of 6 V cm−1 to initiate a combustion wave. The second and third compounds can be synthesized with all field values (0 < E < 20 V cm−1), but require considerable ignition time when E = 0. The stoichiometry Ta3Si does not sustain a combusion front unless E ≥ 20 V cm−1. However, the product is not the desired single phase. Wave velocities in the synthesis of the Si-rich phase, TaSi2, are considerably lower than those of the other two and showed a much weaker dependence on the field. The mechanism of phase formation for TaSi2 and Ta5Si3 was investigated from frozen wave analysis. No intermediate phase forms in the TaSi2 case, while in the case of Ta5Si3, TaSi2 is present as an intermediate phase. Additional investigations on the mechanism of silicide formation included isothermal solid–solid diffusion-couple and solid–liquid experiments.
Misting-free diamond surface created by sheet electron beam irradiation
Authors: Oguri Kazuya , Iwataka Nobuhiro , Tonegawa Akira , Hirose Yoichi , Takayama Kazuo , Nishi Yoshitake
Published: March 2008

We developed a diamond surface that does not mist near the room temperature under a saturated humidity atmosphere, by sheet electron beam irradiation (SEBI) treatment. SEBI treatment decreased the time to clear vision of the diamond surface. Following SEBI treatment for 1.91 s (= 0.72 MGy) to a diamond surface, the time to clear vision was less than 2 s. The effective duration time was a few hours. Based on the results of the size distribution of the drops on the misting-free diamond surface following blowing for 3 s, we proposed an explanation for the short time to clear vision of the diamond surface treated by SEBI.
Nonepitaxial heterogeneous nucleation of α-sialon in the Ca-doped system
Authors: Li Ya-Wen , Wang Pei-Ling , Chen Wei-Wu , Feng Jing-Wei , Cheng Yi-Bing , Yan Dong-Sheng
Published: March 2008

Ca-α-sialon compacts pressureless-sintered to intermediate temperatures, which consisted of both α-sialon and unreacted α–Si3N4 grains, were investigated with transmission electron microscopy for an overall composition Ca1.8Si6.6Al5.4O1.8N14.2. Special attention was paid to identification of the possible crystallographic orientation between a-sialon and the α–Si3N4 particles. In contrast to the frequently occurring heteroepitaxial nucleation of α-sialon in rare-earth-doped samples with low x values, this study showed that most of the newly formed α-sialon grains had no epitaxial orientation relationship with the α–Si3N4 particles, suggesting nonepitaxial heterogeneous nucleation to be a more probable mechanism for the Ca–α-sialon phase with high Ca concentrations.
Preferred orientation of beta-phase and its mechanisms in a fine-grained silicon-nitride-based ceramic
Authors: Xie Rong-Jun , Mitomo Mamoru , Kim Wonjoong , Kim Young-Wook , Zhan Guo-Dong
Published: March 2008

A quantitative texture analysis, including calculations of the orientation distribution function, is applied to investigate the preferred orientation of β–Si3N4 in a fine-grained material containing almost equiaxed grains that has been hot-pressed, annealed, and plane-strain compressed. The results show that (i) plane strain compression can produce relatively strong textures that were dependent on the compressive strain; (ii) the basal plane of hexagonal β–Si3N4 was normal to the hot-pressing direction for the hot-pressed and annealed samples, whereas it was parallel to the stress axis for deformed samples; and (iii) the mechanisms for texture development were preferred grain growth for the annealed sample and grain rotation for the hot-pressed and deformed samples, respectively.
Growth, defects, and properties of GdCa4O(BO3)3and Nd:GdCa4O(BO3)3crystals
Authors: Wang Jiyang , Hu Xiaobo , Yin Xin , Song Renbo , Wei Jingqian , Shao Zongsu , Liu Yaogang , Jiang Minhua , Tian Yulian , Jiang Jianhua , Huang Wanxia
Published: March 2008

Pure and neodymium-doped gadolinium calcium oxoborate crystals of high quality were grown by the Czochralski method. The orientation of crystal was precisely determined, and the samples for measurements were prepared. Through synchrotron x-ray topography and high-resolution x-ray diffractometry, the twin structure was discovered. Some properties such as the figure of merit value, and dielectric, piezoelectric, and elastic constants were measured along with a discussion of the anisotropy of the laser properties.
Low-temperature fabrication of pyroelectric Ba0.8Sr0.2TiO3 thin films by a sol-gel process
Authors: Cheng Jian-Gong , Tang Jun , Guo Shao-Ling , Chu Jun-Hao
Published: March 2008

Ba0.8Sr0.2TiO3 films were fabricated with a 0.05 M solution by a sol-gel process at temperatures between 550 and 650 °C. Analysis by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy revealed that the films annealed at 650 °C showed pure perovskite phase, tetragonal structure, and columnar grains with an average grain size of 150 nm. Electrical measurements performed on the films annealed at 650 °C showed two dielectric peaks in the dielectric constant–temperature curve, a remnant polarization of 1.4 μC/cm2, a coercive field of 18.3 kV/cm, and good insulating property. The measured pyroelectric coefficient for the films annealed at 650 °C was larger than 3.1 × 10−4 C/m2K at the temperatures ranging from 10 to 26 °C and reached the maximum value of 4.1 × 10−4 C/m2K at 16 °C. The excellent pyroelectric property rendered the Ba0.8Sr0.2TiO3 films annealed at 650 °C promising for uncooled infrared detectors and thermal imaging applications.
Surface studies of phase formation in Co–Ge system: Reactive deposition epitaxy versus solid-phase epitaxy
Authors: Goldfarb I. , Briggs G. A. D.
Published: March 2008

Morphological evolution of cobalt germanide epilayers, CoxGey, was investigated in situ by scanning tunneling microscopy and spectroscopy and reflection high-energy electron diffraction, as a function of deposition method and, hence, the phase content of the epilayer. During reactive deposition epitaxy, in which Co atoms were evaporated onto a flat pseudomorphic Ge/Si(001) wetting layer at 773 K, the first phase formed was cobalt digermanide, CoGe2, in the form of elongated pyramidal islands. Each of these three-dimensional islands has locally exerted an additional strain on the Ge wetting layer already strained at the Ge/Si(001) interface, lifting the layer metastability and causing, in turn, the formation of three-dimensional Ge pyramids underneath every CoGe2 island. Solid-phase epitaxy of Co onto the same Ge/Si(001) epilayer resulted in the formation of more Co-rich germanide islands. Coupling of strain from these germanides to the epitaxial Ge/Si(001) strain has also facilitated a two-dimensional-to-three-dimensional transition of the Ge layer, however, with the germanide islands located at the Ge pyramid troughs, rather than crests. The difference in the relative location of germanide and germanium islands in these two cases is explained by accommodation of the large lattice-constant germanides at the more relaxed regions of the Ge pyramid crests and the smaller lattice-constant at the compressed Ge pyramid troughs.
Domain configurations in relaxor ferroelectric single crystals Pb(Mg1/3Nb2/3)O3–PbTiO3
Authors: Xu Guisheng , Luo Haosu , Qi Zhenyi , Xu Haiqing , Yin Zhiwen
Published: March 2008

The 90° macrodomains in tetragonal Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) crystals take the shape of coarse and straight strips under optical microscopes and scanning electron acoustic microscopes. However, 71° or 109° domains in rhombohedral PMNT crystals are relatively poor in contrast and become clearer, coarser and straighter as their composition becomes closer to morphotropic phase boundaries, showing an evolution series of micro-to-macro domain transformation. Moreover, domain configurations are also dependent on the nucleation and growth rate of domains, the crystal defects, and the cooling rate through Curie temperature. The appearance of macrodomains arises from the strengthening of depolarization field and the weakening of random field.
Direct measurement of mechanical properties of (Pb,La)TiO3ferroelectric thin films using nanoindentation techniques
Authors: Algueró M. , Bushby A. J. , Reece M. J.
Published: March 2008

A procedure using nanoindentation with spherical tipped indenters is presented that allows separation of elastic, anelastic, and plastic contributions to the deformation of thin films. The procedure was demonstrated on a range of lanthanum-modified lead titanate (Pb,La)TiO3(PTL) ferroelectric thin films. Indentation stiffness coefficients ranging from 110 to 147 GPa have been obtained depending on the microstructure and orientation of the PTL films. This coefficient was equivalent to (and so, can be directly compared with) Young's modulus of a nontextured, unpoled ceramic when films do not present preferred orientation. The trends of the anelastic contribution with the thickness, structure, microstructure, and stress level at the film/substrate interface of the films were consistent with it being produced by ferroelastic domain wall movement. Pore compaction was a major mechanism of plastic deformation for the PTL films. Grain size also affected plastic deformation, probably as a consequence of its correlation with intergranular porosity. The technique has a high spatial resolution (contact area < 10 μm2for the results presented here), which allowed the mechanical homogeneity of the films to be studied and inhomogeneities to be identified from their mechanical response (elastic, anelastic, and plastic).
Synthesis of open-cell metal foams by templated directed vapor deposition
Authors: Queheillalt Douglas T. , Hass Derek D. , Sypeck David J. , Wadley Haydn N. G.
Published: March 2008

Low-density, open-cell nickel base superalloy foams have been synthesized by a high-rate, electron beam-directed vapor deposition process and their mechanical properties evaluated. The deposition process uses an open-cell polymer foam template upon which is deposited a metal alloy coating. The electron beam evaporated flux was entrained in a rarefied transonic gas jet and propagated along the flow stream lines through the polymer structure. After vapor deposition, the polymer template was removed by low-temperature thermal decomposition. The resultant ultralightweight metal foams consisted of a three-dimensional open cell, reticulated structure possessing hollow triangular ligaments with relative densities of <3%. Their mechanical integrity was increased by either pressureless or transient liquid phase sintering. The mechanical properties of these ultralightweight metal foams were comparable to theoretical predictions for open-cell, reticulated foams.
Synthesis of Nd2Fe14B powders by spray-drying and reduction–diffusion processes
Authors: Dong X. L. , Kim B. K. , Choi C. J. , Park K. S. , Zhang Z. D.
Published: March 2008

The magnetic Nd–Fe–B powders were prepared by a mechanochemical method, including the processes of spray drying, debinding, milling, H2 reduction, Ca reduction, and washing. The liquid solution dissolved with various metal salts was first spray-dried to prepare the precursor powders having uniformly dispersed Nd, Fe, and B components. The precursor powders in turn were subjected to the subsequent processes. The particle size of the resultant Nd–Fe–B powders was about 1 μm. Effects of the process parameters on phases, morphologies, microstructures, compositions, and thermal properties of the powders were investigated.
Phenomenological description of grain growth stagnation for nanocrystalline films and powders
Authors: Dannenberg Rand , Stach Eric , Groza Joanna R.
Published: March 2008

We provide a phenomenological grain growth stagnation force incorporating a near-linear temperature dependence of stagnated grain sizes and irreversible growth. The resulting law captures the observation of the restart of grain growth in the size versus time plateau on temperature increases. This description also reduces to standard laws commonly used for data fitting. The law may be useful for workers who wish to characterize a nanocrystalline film or powder annealing process predictively from a limited number of measurements or may be useful in a designed experiment. Other laws are discussed and compared. Fits to size versus time data from the literature are successfully made.
Finite element modeling of microscale thermal residual stresses in Al interconnects
Authors: Saerens A. , Van Houtte P. , Kalidindi S. R.
Published: March 2008

An elastic-plastic crystalline constitutive model implemented in a finite-element code has been used to predict the microscale thermal residual stresses in Al−1%Si−0.5%Cu interconnects. This fully three-dimensional model accounts for the individual grain orientations in these interconnects, as measured by orientation imaging microscopy. The influence of specific crystal orientations on the residual stress distribution in these interconnects was studied in detail. A sensitivity analysis was performed to identify the parameters that influence strongly the predicted values of the residual stresses and their distributions. For the interconnects studied here, the residual stresses in the metal lines were found to be quite sensitive to the elastic modulus of the passivation material and its geometry. In addition, the volume averages of the predicted stresses were in reasonable agreement with the experimentally determined values from the x-ray technique.
Investigation of optical waveguide formed in Er:Yb:phosphate glass by MeV He+ implantation
Authors: Zhuo Zhuang , Bun Pun Edwin Yue , Wong Sun Fat , Zhou Ying
Published: March 2008

Planar waveguide was fabricated in Er:Yb:phosphate glass by a single energy implantation of 2.5 MeV He+ at a dose of 1.6 × 1016 ions/cm2. The waveguide was characterized by prism coupling method, and the refractive index profile was reconstructed using the inverse Wentzel-Kramers-Brillouin method. The photoluminescence was also measured. The energy loss was simulated, and the results were compared and discussed with respect to the refractive index profile in the waveguide.
Fabrication, characterization, and photoluminescence properties of highly ordered TiO2 nanowire arrays
Authors: Lei Y. , Zhang L. D.
Published: March 2008

Highly ordered TiO2 nanowire arrays were prepared in anodic alumina membranes by a sol-gel method. The nanowires are single-crystalline anatase phase with uniform diameters around 50 nm. At room temperature, photoluminescence (PL) measurements of these TiO2 nanowire arrays showed a visible broad band with three peaks, which were located at about 425, 460, and 530 nm that are attributed to self-trapped excitons, F, and F+ centers, respectively. A model is also presented to explain the PL intensity drop-down of the TiO2 nanowire arrays embedded in the alumina membrane: the blue PL band of the anodic alumina membranes arises from the F+ centers on the pore walls, and the TiO2 nanowires first form in the center area of the pores and then extend to the pore walls.
Precipitation of icosahedral quasicrystalline phase in Hf69.5Al7.5Ni11Cu12 metallic glass
Authors: Li Chunfei , Inoue Akihisa
Published: March 2008

A Hf69.5Al7.5Ni11Cu12 metallic glass was prepared by a single roller melt-spinning method, and the crystallization process was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The metallic glass crystallizes through three exothermic reactions. The low-temperature exothermic reaction corresponded to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature led to the decomposition of the icosahedral quasicrystalline phase to other stable crystalline phases, indicating that the precipitated icosahedral quasicrystalline phase was in a metastable state. The crystallization process of the present alloy was compared with that of other Hf–Al–Ni–Cu alloys, and the reason for the precipitation of the icosahedral quasicrystalline phase was discussed.
Stability of channels at a scalloplike Cu6Sn5 layer in solder interconnections
Authors: Lee Jong-Hyun , Park Jong-Hwan , Lee Yong-Ho , Kim Yong-Seog , Shin Dong Hyuk
Published: March 2008

The thermodynamic stability of the solder channels at a scalloplike Cu6Sn5 layer formed between Sn-containing solders and Cu substrate was evaluated by studying the penetration behavior of the liquid solders into the grain boundaries of a Cu6Sn5 substrate. The orientational relationship between the grains of the Cu6Sn5 layer formed during reflow soldering was also analyzed using the electron backscattered diffraction technique. The results showed that liquid solders penetrate into the grain boundaries at an order of faster speed than the growth rate of the layer, which provided a direct evidence of thermodynamic stability of the channel.
Size effects in powder compaction
Authors: Sevillano J. Gil
Published: March 2008

It is well known that great difficulties are encountered in the cold compaction of ultrafine powders. Such difficulties have been qualitatively attributed to several origins (e.g., increasing relative contribution of oxidized layers to particle resistance as particle size decreases). The main densification stage during compaction is governed by plastic deformation at interparticle contacts under pressure. On account of the strength enhancement of plastic resistance in presence of plastic strain gradients (physically resolved by “geometrically necessary dislocations”) a contribution to the size effect on powder compaction efficiency is here predicted. Some quantitative experimental data available are in good agreement with this explanation.
Twinning domain in 67Pb(Mg1/3Nb2/3)O3–33PbTiO3 ferroelectric complex perovskite crystal grown by the Bridgman method
Authors: Li Donglin , Wang Pingchu , Pan Xiaoming , Luo Haosu , Yin Zhiwen
Published: March 2008

Single crystals of 67Pb(Mg1/3Nb2/3)O3–33PbTiO3 (PMN-PT, PMNT) relaxor-based complex perovskite solid solution grown by Bridgman method have pseudo-cubic symmetry under ambient conditions. Examination by means of polarized light microscopy showed that the microstructure of the crystals was dominated by a large number of coarse twin domains. It was confirmed that the most common composition planes were {110} in addition, {112} planes were also observed. These twins may be associated with the transformation of PMNT complex perovskite from the cubic to tetragonal upon a decrease in temperatures. The morphology of the domain structure may be explained from the theory of martensitic transformation.
Generation of circular and hexagonal microholes in a graphite surface
Authors: Hiura Hidefumi
Published: March 2008

Circular and hexagonal microholes, ranging in size from several nanometers to micrometers, were generated in a graphite surface by electron beam irradiation. The depth of the holes was always 0.34 nm, indicating that only the uppermost layer was modified. The shape of the holes was switched from circular to hexagonal when the size reached about 500 nm. Although the hexagons appeared at random on the surface, they were aligned in one direction, implying that the formation and growth of the holes were determined by the atomic structure of graphite. The results described in this study will be used to modify the surface structure of graphite for many applications.
Enhancement of the 1.31-μm emission properties of Dy3+-doped Ge–Ga–S glasses with the addition of alkali halides
Authors: Shin Yong Beom , Heo Jong , Kim Hyoun Soo
Published: March 2008

Alkali halides such as KBr, KI, CsBr, and CsI were added to Dy3+-doped Ge–Ga–S glasses, and their effects on the 1.31-μm emission property were investigated. The intensities of the 1.31-μm emission (6F11/2 · 6H9/2 → 6H15/2) increased at the expense of the 1.75-μm emission intensity (6H11/2 → 6H15/2) with the alkali halide addition. The lifetimes of the 1.31-μm emission level also increased as much as 35 times from 38 μs for Ge–Ga–S glass to 1320 μs for the glass containing 10 mol% CsBr. These enhancements occurred only when the ratio of MX (M = K, Cs; X = Br, I)/Ga was equal to or larger than unity. Raman spectra of Ge–Ga–S–CsBr glasses indicated the formation of [GaS3/2Br]− complexes, which provide the preferred sites for Dy3+. Due to this new local environment of Dy3+, the multiphonon relaxation rates from the Dy3+:6F11/2 · 6H9/2 level decreased by approximately four orders of magnitude. The enhancement in the 1.31-μm emission properties with alkali halide addition supports the potentials of these glasses as hosts for the Dy3+-doped fiber-optic amplifiers.
Processing- and composition-dependent characteristics of chemical solution deposited Bi4−xLaxTi3O12 thin films
Authors: Wu Di , Li Aidong , Zhu Tao , Li Zhifeng , Liu Zhiguo , Ming Naiben
Published: March 2008

Thin films of lanthanum substituted bismuth titanate, Bi4−xLaxTi3O12 (BLTx), were prepared by chemical solution deposition. Crystallized BLTx films were obtained by rapid thermal annealing at a temperature as low as 650 °C. Structural and electrical characteristics of crystalline BLTx films were studied as functions of La composition. Structure characterization was conducted by x-ray diffraction and Raman spectroscopy. The lowest lattice vibration mode around 116 cm−1 showed softening with increasing lanthanum composition. Surface morphology of BLTx films were recorded by scanning electron microscopy. BLTx films have saturated hysteresis loops with remnant polarization of 9.7, 12.3, and 4.5 μC/cm2, respectively, for x = 0.50, 0.75, and 1.00 films. BLT0.75 films showed fatigue-free behavior over 250 kV/cm, 50 kHz cycling, which could be compared with that of SrBi2Ta2O9 thin films. Fatigue resistance decrease at lower cycling field. The field dependence of fatigue property was discussed briefly in terms of competition between domain pinning and field-assisted unpinning.
Patterning of copper particles on polymeric surface
Authors: Sinha Arvind , Das Swapan Kumar , Rao V. , Ramachandrarao P.
Published: March 2008

In situ synthesis of fine copper particles (>200 nm) has been carried out using borohydride reduction in preorganized gel of poly(vinyl alcohol). The copper ions were chelated by polymer matrix at room temperature thorough physical entrapment along with a weak chemical complexation. The process is akin to biomimetic route and demonstrates a high order of control over nucleation, growth, and morphologies as well as orientation of the end product. The organized arrays of copper sulfate precipitate and copper particles replicate the conformation of organic matrix and form patterned structures similar to one observed in stationary chemical waves.
Metal-organic vapor phase epitaxial growth of high-quality ZnO films on Al2O3(00·1)
Authors: Park W. I. , An S-J. , Yi Gyu-Chul , Jang Hyun M.
Published: March 2008

High-quality ZnO thin films were grown epitaxially at 250–550 °C Al2O3(00·1) substrates using low-pressure metalorganic vapor phase epitaxy. The reactants for the growth were diethylzinc and oxygen. Growth temperature, one of the important experimental parameters for epitaxial layers, was optimized. The films grown at 500 °C exhibited good crystallinity and strong ultraviolet absorption and emission. Photoluminescence spectra of the films showed a dominant excitonic emission with a weak deep level emission. More importantly, a strong stimulated emission peak was observed even at room temperature.
Optimization of the annealing process for the (Ba,Sr)TiO3 thin films grown by low-temperature (420 °C) metalorganic chemical vapor deposition
Authors: Park Jaehoo , Hwang Cheol Seong , Yang Doo Young
Published: March 2008

An optimization study on crystallization annealing of (Ba,Sr)TiO3 (BST) thin films, grown by metalorganic chemical vapor deposition at a wafer temperature of 420 °C, was performed. The as-grown film had an amorphous structure with a dielectric constant of about 20. The annealing parameters, including temperature, atmosphere, time, and sequence, were varied considering the limitations imposed by integration processes for ultralarge-scale integrated dynamic random access memory devices. The dielectric constants of the crystallized films were largely determined by the maximum temperature that the films experienced with minor effects from the annealing atmosphere. However, the leakage current densities were quite dependent on the annealing sequence and atmosphere. It was concluded that the major factors which determine leakage characteristics were concentrations of impurities, especially carbon, oxygen vacancies, and interfacial defects caused by top electrode sputtering.
Delamination of a strong film from a ductile substrate during indentation unloading
Authors: Abdul-Baqi A. , Van der Giessen E.
Published: March 2008

In this work, a finite element method was performed to simulate the spherical indentation of a ductile substrate coated by a strong thin film. Our objective was to study indentation-induced delamination of the film from the substrate. The film was assumed to be linear elastic, the substrate was elastic–perfectly plastic, and the indenter was rigid. The interface was modeled by means of a cohesive surface. The constitutive law of the cohesive surface included a coupled description of normal and tagential failure. Cracking of the coating itself was not included. During loading, it was found that delamination occurs in a tangential mode rather than a normal one and was initiated at two to three times the contact radius. Normal delamination occurred during the unloading stage, where a circular part of the coating, directly under the contact area was lifted off from the substrate. Normal delamination was imprinted on the load versus displacement curve as a hump. There was critical value of the interfacial strength above which delamination was prevented for a given material system and a given indentation depth. The energy consumption by the delamination process was calculated and separated from the part dissipated by the substrate. The effect of residual stress in the film and waviness of the interface on delamination was discussed.
Synthesis of coaxial nanotubes: Titanium oxide sheathed with silicon oxide
Authors: Zhang Ming , Bando Y. , Wada K.
Published: March 2008

The TiO2–SiO22 composite nanotubes with coaxial structure synthesized by sol-gel template method were presented. This process included 2 steps: first, grow SiO22 nanotubes in the pores of anodic alumina with a diameter of 200–250 nm; second, form TiO2 nanotubes within the SiO22 nanotubes. The TiO2 nanotubes with intact SiO22 sheaths were more uniform than those with sheaths partly removed. The existence of Ti–O–Si bonds and the amorphous sheaths is supposed to take an important role in the formation of composite nanotubes.
Entrapment of organosilicon molecules in nonhydrolytic alumina gels and thermal behavior of the resulting composite
Authors: Grader G. S. , Melchior S. A. , De-Hazan Y. , Melamed S. , Shter G. E.
Published: March 2008

This work describes the entrapment of tetrakis(trimethylsilyl)silane (TK) and tetrakis(chlorodimethylsilyl)silane (TKCl) in nonhydrolytic alumina gels, and the materials' thermal behavior. During gelation and drying TK and TKCl are physically entrapped in the gel up to a limit of Si/Al = 0.33. Above this limit, sublimation and decomposition of TK and TKCl occur during heating. A larger fraction of TKCl decomposition products is retained due to their higher reactivity. Below and above Si/Al = 0.33, the gel converts to mullite + α−Al2O3or mullite + amorphous silica, respectively. Conversion to hexagonal mullite indicates atomic scale homogeneity of Si and Al during firing.
Synthesis of dense nanometric MoSi2 through mechanical and field activation
Authors: Orrù R. , Woolman J. , Cao G. , Munir Z. A.
Published: March 2008

The effect of mechanical and field activation on the synthesis of dense nanometric MoSi2 was investigated. Powders of Mo and Si, milled separately or comilled in a planetary ball mill, were reacted in a spark plasma synthesis (SPS) apparatus under different electric current conditions. Milled powders reacted faster and required less current than unmilled powders. Mixtures of powders which were milled separately (to nanometric size) reacted in the SPS to produce micrometric α–MoSi2. Similar results were obtained for samples comilled to produce nanometric reactants which did not contain detectable amounts of the product phase. When products form during milling, they contain both the α and β modifications of MoSi2. The product after the SPS reaction was nanometric MoSi2 with a crystallite size of 140 nm.
Phase formation and reactions in the Bi2O3–ZnO–Nb2O5–Ag pyrochlore system
Authors: Nino Juan C. , Lanagan Michael T. , Randall Clive A.
Published: March 2008

Mixed-phase compositions in the Bi2O3–ZnO–Nb2O5 pyrochlore system have been previously identified as potential low-fire dielectric composites for high-frequency multilayer devices. However, there has been a problem with the ability to co-process this material with silver. It was found that an intermediate BiNbO4 phase that occurs during calcination can interact with silver during co-sintering, forming a deleterious phase. Processing routes to control the presence of remanent BiNbO4 were investigated, such as ZnO stoichiometric adjustment, low partial pressure of oxygen sintering atmosphere, and specific temperature-time dwells.
Mechanical deformation in silicon by micro-indentation
Authors: Bradby J. E. , Williams J. S. , Wong-Leung J. , Swain M. V. , Munroe P.
Published: March 2008

The mechanical deformation of crystalline silicon induced by micro-indentation has been studied. Indentations were made using a variety of loading conditions. The effects on the final deformation microstructure of the load–unload rates and both spherical and pointed (Berkovich) indenters were investigated at maximum loads of up to 250 mN. The mechanically deformed regions were then examined using cross-sectional transmission electron microscopy (XTEM), Raman spectroscopy, and atomic force microscopy. High-pressure phases (Si-XII and Si-III) and amorphous silicon have been identified in the deformation microstructure of both pointed and spherical indentations. Amorphous Si was observed using XTEM in indentations made by the partial load–unload method, which involves a fast pressure release on final unloading. Loading to the same maximum load using the continuous load cycle, with an approximately four times slower final unloading rate, produced a mixture of Si-XII and Si-III. Slip was observed for all loading conditions, regardless of whether the maximum load exceeded that required to induce “pop-in” and occurs on the {111} planes. Phase transformed material was found in the region directly under the indenter which corresponds to the region of greatest hydrostatic pressure for spherical indentation. Slip is thought to be nucleated from the region of high shear stress under the indenter.