bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of crystalline CdSe particles by chemical bath deposition
Authors: Yamamoto Osamu , Sasamoto Tadashi , Inagaki Michio
Published: March 2008

Crystalline CdSe particles were prepared by keeping the precursor solutions at temperatures above 60 °C. It was essential to use sodium sulfite as a stabilizing agent for selenium ions and sodium dicarboxylate as a complexing agent for cadmium in the precursor solution. The principal crystalline phase of the samples obtained at 60 °C was a cubic zincblende-type phase, but those prepared at 80 °C coexisted with a hexagonal wurtzite-type phase. The ratio of cadmium to selenium in the samples decreased with an increase of the concentration of selenourea in the precursor solutions, irrespective of the kind of complex agents and the keeping time of the precursor solutions. The band-gap energy of CdSe with an atomic ratio (Cd/Se) of 1 showed a value of 1.74 eV, but that with the ratio of 2.3 gave a slightly smaller value of 1.42 eV.
High-temperature stability of nanocrystalline structure in a TiAl alloy prepared by mechanical alloying and hot isostatic pressing
Authors: Senkov O. N. , Srisukhumbowornchai N. , Öveçoglu M. L. , Froes F. H.
Published: March 2008

A fully dense nanocrystalline compact of the Ti–47Al–3Cr (at. %) alloy was produced by mechanical alloying and hot isostatic pressing at 725 °C. Microstructure characteristics and grain growth behavior of this compact were studied after annealing for up to 800 h in the temperature range of 725 to 1200 °C, using analytical transmission electron microscopy techniques. The temperature and time dependencies of the grain sizes and the grain size distributions were determined. The grain growth occurred, with a timeand temperature-invariant single-peak grain size distribution (when normalized by the mean grain size), which was consistent with normal grain growth. The experimentally measured grain growth exponent decreased from 10 to 4.6 when the temperature was increased. The grain growth kinetics was described by a single thermally activated rate process limited by a permanent pinning force on the grain boundaries. The microhardness decreased on annealing and followed the Hall–Petch relationship with the parameters Hυo = 5.8 GPa and KH = 1.6 MPa m0.5.
Accelerated sintering and phase transformation of TiO2in microwave radiation
Authors: Xie Zhi-Peng , Fan Xu-Dong , Huang Yong
Published: March 2008

The sintering process and phase transformation of submicrometer powder compacts of TiO2 were investigated using 2.45 GHz microwave radiation. The microwave-sintered samples were densified more rapidly and at much shorter time and lower temperature than that of the conventionally sintered samples. Also, an accelerated phase transformation from anatase to rutile was observed in microwave processing when the dwell time is cut down from 6 h in conventional to 30 min in microwave at 1000 °C. The samples sintered in microwave show a refined microstructure and smaller grain sizes at high density near 98–99% theoretical. In addition, the reasons for rapidly heating behavior and enhanced sintering on TiO2 in microwave are discussed.
The fabrication of near net-shaped spinel bodies by the oxidative transformation of Mg/Al2O3 precursors
Authors: Kumar P. , Sandhage K. H.
Published: March 2008

The feasibility of transforming shaped Mg–Al2O3-bearing precursors into monolithic spinel (MgAl2O4) bodies with a retention of shape and dimensions has been demonstrated.Dense, shaped precursors (disks, bars) were fabricated by the pressureless infiltration of molten Mg into porous Al2O3 preforms. After solidification (and machining, in the case of bar-shaped specimens), the Mg-bearing precursors were oxidized in flowing O2 (g) at 430–700 °C. Postoxidation annealing at 1200 °C resulted in the conversion of MgO and Al2O3 into MgAl2O4. After sintering at 1700 °C, spinel bodies that retained the precursor dimensions (to within 0.65%) were produced. Phase and microstructural analyses at various stages of processing are discussed.
Internal friction and torsional creep behavior of chemically vapor deposited boron nitride
Authors: Pezzotti Giuseppe , Kleebe Hans-Joachim , Ota Ken'ichi , Nishida Toshihiko
Published: March 2008

Dense hexagonal BN processed via chemical vapor deposition (CVD) was tested with respect to damping, shear modulus, and torsional creep rate up to temperatures as high as ≈2300 °C. The microstructural characteristics of the material both before and after creep testing were studied by high-resolution electron microscopy (HREM). The CVD process yields a homogeneous nanosized microstructure with no other secondary phase detectable. Damping experiments revealed no plastic relaxation during testing up to ≈2000 °C, which is consistent with the fact that also no creep deformation could be detected below such a high temperature. Small porosity and an increased amorphization process were noted by HREM inspection after stress exposure at ≈2300 °C. These phenomena may be responsible for both the enhanced damping capacity and the creep rate of the material which, in the range of the present testing conditions, seems to follow the simple viscoelastic behavior of a Maxwell solid.
The crystallization and growth of AlB2 single crystal flakes in aluminum
Authors: Deppisch C. , Liu G. , Hall A. , Xu Y. , Zangvil A. , Shang J. K. , Economy J.
Published: March 2008

An in situ high temperature heat treatment was used to investigate the crystallization and growth behavior of AlB2 flakes in aluminum. Aluminum samples containing 1.8% boron were heated above the liquidus and then rapidly cooled through the Al(L) + AlB12 region to avoid the formation of AlB12 crystals. Subsequently, a homogeneous distribution of high aspect ratio AlB2 flakes crystallized upon holding below the peritectic transition temperature. Growth rate in the (a) and (c) dimensions increased during elevated hold temperatures below the peritectic transition temperature. Surprisingly, faster cooling rates from above the liquidus to room temperature resulted in thinner, wider flakes. Similar to graphite this phenomenon is believed to result from a need to accommodate a changing misfit strain energy between the solidifying aluminum and the growing AlB2 flakes.
Predicting the spreading kinetics of high-temperature liquids on solid surfaces
Authors: Weirauch Douglas A.
Published: March 2008

The rate of movement of liquid drops toward their equilibrium position on smooth, horizontal solid surfaces (spreading kinetics) is considered in this study. A model for nonreactive liquid spreading which was developed for low-temperature liquids is applied to results for a set of high-temperature liquids and room-temperature liquids. These data were generated in a single laboratory following a consistent experimental methodology. The liquid-solid pairs were chosen to result in weak or no interfacial chemical reaction. Furnace atmospheres were chosen to provide data for liquid metals with submonolayer, thin or thick oxide films. Analysis of the high-temperature spreading kinetics for liquids covering a broad range of viscosity, surface tension, and density shows that they can be predicted with a constant shift factor applied to the deGennes expression for nonreactive spreading. The consequences of gravitational and inertial forces, substrate roughness, weak interfacial reactions, and liquid-metal oxide films are discussed.
Prediction of nanoindentation hardness profile from a load-displacement curve
Authors: Xu K. W. , Hou G. L. , Hendrix B. C. , He J. W. , Sun Y. , Zheng S. , Bloyce A. , Bell T.
Published: March 2008

During the nanoindentation process, the load and depth data are continuously recorded. A single load-displacement curve is thus expected to contain material property information from the whole depth range indented. In the present paper, a new method to obtain the hardness-depth curve has been derived for small depths from the load-displacement curve measured at a large depth, based on the assumption that the elastic properties of the indented material can be obtained from the indentation depth. Using this method, hardness values can be computed for various small depths from a single load-displacement curve. From a series of nanoindentation experiments, it has been proven that the method can be used on both homogeneous and surface-modified materials, such as fused silica, single crystal tungsten, and plasma nitrided steel with and without an iron nitride Fe4N compound layer. Testings on a series of Ni–P films coated on 15 MnB steel also gave fairly good results.
Theory of the charged cluster formation in the low pressure synthesis of diamond: Part I. Charge-induced nucleation
Authors: Jang Hyun M. , Hwang Nong M.
Published: March 2008

Based on several experimental observations, Hwang et al. recently proposed “the charged cluster model” [J. Cryst. Growth, 162, 55–68 (1996)] to disentangle the “puzzling thermodynamic paradox” encountered in the gas-activated chemical vapor deposition (CVD) of diamond. Many unusual phenomena observed in the CVD diamond process can be successfully approached by the charged cluster model. However, there are a couple of important subjects still unsolved quantitatively. The first question is connected with the main driving force for this unusual nucleation in the gas phase. The second issue is related to the difference in the thermodynamic stability between graphite and diamond for a nanometer-sized cluster during the growth. In this study, we have theoretically examined the thermodynamic driving forces for the charge-induced nucleation, in general, and have applied this idea to the nucleation of the charged carbon-atom cluster. It was shown that the short-range ion-induced dipole interaction and the ion-solvation electrostatic effect (Born term) were mainly responsible for this unusual nucleation in the gas phase. The theoretical analysis presented in this article is quite generic and, thus, can be applied to any process that involves the charge-induced nucleation.
The adhesion energy between polymer thin films and self-assembled monolayers
Authors: Zhuk Andrew V. , Evans Anthony G. , Hutchinson John W. , Whitesides George M.
Published: March 2008

A superlayer test has been adapted for the measurement of the fracture energy between epoxy thin films and self-assembled monolayers (SAM's) on Au/Ti/Si substrates. The “arrest” mode of analysis has been shown to provide consistent results, particularly when relatively wide lines are used to encourage lateral decohesions. The fracture energy, Γi, of the interface between the monolayer and the epoxy is varied by adjusting the ratio of COOH/CH3 terminal groups. Connections among Γi, the surface energies, and the inelastic deformations occurring in the epoxy are explored upon comparison with interface crack growth simulations.
Quantitative nanoscale mechanical properties of a phase segregated homopolymer surface
Authors: Graham J. F. , Kovar M. , Norton P. R. , Pappalardo P. , Loon J. Van , Warren O. L.
Published: March 2008

Crystallization of poly(ethylene terephthalate) (PET) is accompanied by significant changes in surface topography, easily detected by atomic force microscopy (AFM). Phase imaging by AFM qualitatively indicates contrast in mechanical properties of nanometer scale areas of an annealed PET surface, but cannot provide quantitative data. Using interfacial force microscopy (IFM), we have, for the first time, made quantitative measurements of the elastic moduli of such nm-scale areas on a homopolymer surface. Values of 2.2 GPa, 4.3 GPa, and 11.8 GPa, were found, respectively, for amorphous PET and for phase segregated regions on the surface of an annealed homopolymer PET sample. The method is applicable to any phase segregated surface with nm-sized domains of differing elastic moduli.
Phase relations and superconducting properties of the Y–Ni–B–C system
Authors: Behr G. , Löser W. , Graw G. , Nenkov K. , Krämer U. , Belger A. , Wehner B.
Published: March 2008

The influence of composition and high-temperature heat treatment on phase content and superconducting properties of the Yni2B2C phase was investigated. Phase relations in those parts of the Y–Ni–B–C quaternary phase diagram, which are relevant for the YNi2B2C intermetallic phase formation, were revealed by x-ray diffraction, optical and scanning electron microscopy, and high-temperature differential thermoanalysis. A widespread interval of superconducting transition temperatures TC = 10.4–15.2 K and small transition width <0.3 K were determined from samples of different nominal compositions after high-temperature annealing. The different intrinsic properties are ascribed to composition variations of the YNi2B2C phase and related to structure parameters, residual resistance ratios, and element concentrations determined by the electron probe microanalysis.
Microstructural investigation of low temperature chemical vapor deposited 3C-SiC/Si thin films using single-source precursors
Authors: Lee B-T. , Kim D-K. , Moon C-K. , Kim J. K. , Seo Y. H. , Nahm K. S. , Lee H. J. , Lee K-W. , Yu K-S. , Kim Y. , Jang S. J.
Published: March 2008

Transmission electron microscopy (TEM) was utilized to investigate microstructures of heteroepitaxial SiC/Si films, grown from single-source precursors such as tetramethylsilane [TMS, Si(CH3)4], hexamethyldisilane [HMDS, Si2(CH3)6], and 1,3-disilabutane [1,3-DSB, H3SiCH2SiH2CH3]. In the case of TMS/H2 and HMDS/H2 samples, SiC/Si films grown at relatively high precursor concentration and/or low temperatures showed columnar grains with a high degree of epitaxial relationship with the Si substrate. Higher quality films with larger grains were observed in the case of high temperature and/or low precursor concentration samples, although a high density of interfacial voids was observed. Samples grown from pure 1,3-DSB at a low pressure showed high quality single crystalline films with few interfacial voids. It was suggested that the microstructural behavior of these films closely resembles that of the SiC films formed during the carbonization of Si surfaces by the pyrolysis of hydrocarbons, in which the nucleation rate of the film at the initial stage plays a key role. The improvement achieved during the 1,3-DSB growth is proposed to be due to the low growth pressure and the 1 : 1 ratio of Si and C associated with this precursor.
Microstructure and mechanical properties of NiAl/Al2O3 composites
Authors: Hwang Chii-Shyang , Liu Tien-Jui
Published: March 2008

To improve mechanical properties of NiAl, a method for making NiAl matrix composites containing oxide ceramics is introduced. The method involves oxidation of NiAl powder in air to form a thin and uniform oxide scale, mainly Al2O3, on the NiAl particles. The Al2O3 contents increase with increasing oxidation temperature. The NiAl/Al2O3 composites are then formed by hot-pressing the oxidized NiAl powder under vacuum atmosphere. Al2O3 inhibits the grain growth of NiAl during the hot-pressing. The residual stress and the Ni-rich NiAl composition exist in the hot-pressed NiAl/Al2O3 composites. Strength and toughness data on NiAl/Al2O3 composites indicate that the use of oxidation of NiAl powder is a viable technique for improving these properties over that of monolithic NiAl.
The effect of TiO2 addition on the thermal behavior of sol-gel derived β-spodumene powders
Authors: Wang Moo-Chin
Published: March 2008

The effect of TiO2 addition on the crystallization and phase transformation process in Li2O · Al2O3 · 4SiO2 gels with various TiO2 contents was investigated using differential thermal analysis, x-ray diffraction, and transmission electron microscopy. The activation energy increased from 98.2 to 184.6 kcal/mol as the TiO2 content rose from 2.0 to 8.0 wt. %. The crystallization sequence and phase transformation were similar in LAS gels with various wt.% of TiO2 additions, except in the case of a 2.0 wt.% TiO2 content. During calcination from 800 to 1200 °C, crystallization of the β-spodumene phase progressed with increasing temperature, and a minor crystalline phase, rutile, also appeared.
Small-angle x-ray scattering studies of early-stage colloid formation by thermohydrolytic polymerization of aqueous zirconyl salt solutions
Authors: Hu Michael Z-C. , Zielke Jason T. , Lin J-S. , Byers Charles H.
Published: March 2008

Early-stage processes involving the polymerization of zirconium species in aqueous solutions at elevated temperatures (∼100 °C) as well as colloid formation were studied. Small-angle x-ray scattering (SAXS) data were analyzed via Guinier, “longrods,” and Porod plots to determine particle growth kinetics and morphology. Our SAXS data suggest that zirconium tetramers and octamers polymerize into larger clusters and elongated-rod-(or needle)-shaped primary particles, which have a length of a few nanometers and a radius of gyration of cross section between 4 and 5 Å. Cube-shaped particles are aggregates of the needlelike primary particles. The transition from zirconium tetramer to a colloidal sol particle follows a mass-fractal growth (1 < fractal dimension, D <3)
Preparation and characterization of compounds in the BaBiO3–Ba(Ce1-xGdx)O3-x/2 system
Authors: Mukundan R. , Davies P. K. , Worrell W. L.
Published: March 2008

The structure, nonstoichiometry, and electrical conductivity of compositions in the BaBiO3– Ba(Ce1-xGdx)O3-x/2 system have been investigated in an attempt to prepare new mixed (ionic-electronic) conducting oxides. The substitution of Bi into Ba(Ce1-xGdx)O3-x/2 decreases the concentration of oxygen-ion vacancies, and the effective negative charge of the Gd dopant is compensated by the mixed valence of Bi (3+, 5+). For low Bi contents a decrease in ionic conductivity decreases the overall conductivity; however, higher levels of Bi introduce significant electronic conductivity, and for Ba(Bi0.5Ce0.5)O3, σtotal ≈ 1 S/cm at 800 °C in air. Compositions in the Ba(Bi0.5Ce0.5-xGdx)O3 pseudobinary system undergo a B-cation order-disorder transformation at 1300–1350 °C for x = 0.5 and at ≈1250 °C for x = 0.4; all other compositions retain a disordered B-site arrangement. While these disordered perovskites exhibit oxygen nonstoichiometry under reducing conditions at elevated temperatures, with the extent of reduction decreasing with increasing Gd content, their ordered counterparts remain close to stoichiometry. The electronic conductivities of this pseudobinary could be fitted to a “band-type” model, and, despite the presence of oxygen vacancies for the lower values of x, no significant ionic conductivity was observed.
Determination of domain structure and abundance of epitaxial Pb(Zr, Ti)O3 thin films grown on MgO(001) by rf magnetron sputtering
Authors: Lee Kyeong Seok , Kang Young Min , Baik Sunggi
Published: March 2008

Epitaxial Pb(ZrxTi1−x)O3 (x = 0.0−0.32) ferroelectric thin films of 500 nm thickness were grown on MgO(001) single crystal substrates by in situ rf magnetron sputtering, and evolution of their domain structures is characterized by employing various x-ray diffraction techniques. X-ray θ-2θ scan showed the films were grown highly c-axis oriented with a tetragonal perovskite structure. 90° domain configuration was investigated using the x-ray rocking curve analysis for PZT 100 peaks in two different Φphi; angles. The rocking curve analysis showed that the degree of c-axis orientation and the crystalline quality of the films were improved continuously with increasing Zr concentration. The c-domain abundance as a function of Zr concentration was quantified using the x-ray rocking curves of PZT 001 and 100, taking account of structural factors and Lorentz-polarization factors. High temperature x-ray technique was also employed to quantify the domain structure as a function of temperature during cooling after reheating the samples to 650 °C. During the cooling process, c-domain abundance was found to increase continuously while the crystalline quality of the films was deteriorated below the Curie temperature. The results led us to conclude that the transformation strain of the film at and below the Curie temperature plays a significant role in the final domain structure and abundance of epitaxial PZT thin films.
Nucleation control for hot-working of silicon oxynitride based ceramics
Authors: Ohashi Masayoshi , Iida Yasuo , Hampshire Stuart
Published: March 2008

An attempt was made to develop an engineering ceramic plastically deformable at high temperatures with low flow stress at high strain rates, and without strain hardening. Dense ceramic preforms were fabricated by pressureless sintering Si3N4 + SiO2 mixed powders with an addition of MgAl2O4 at 1500 °C. A transient liquid, which occurs during the reaction sintering of Si2N2O, was utilized for subsequent net-shape forming. The ceramic (6Φ × 6 mm column) was deformed without any cracks and cavities in compression tests at high strain rates (10−2−10−3:s−1) at 1500 °C, but this was not achieved in a test at lower strain rates for a long time, because of the growth of elongated Si2N2O grains during the test. Potassium fluoride (KF) was used as a dopant for retardation of nucleation of Si2N2O during sintering and hot-working. The KF-doped preforms were successfully plastically deformed even in the test for a long time.
Effect of TiO2 addition on the preparation of β-spodumene powders by sol-gel process
Authors: Wang Moo-Chin , Lin Ming-Hong , Liu Hok-Shing
Published: March 2008

This study has shown the possibility of achieving two primary considerations for the advanced fabrication of spodumene with a composition of Li2O · Al2O3 · 4SiO2 · nTiO2 (LAST) glass-ceramics by a sol-gel process, namely, an enormous reduction of sintering temperature from 1600 to 1200 °C together with the appearance of simple phases of β-spodumene/rutile as opposed to products via the conventional melting-crystallization process. Fine glass-ceramic powders with a composition of Li2O · Al2O3 · 4SiO2 (LAS) have been synthesized by the sol-gel process using Si(OC2H5)4, Al(OC2H5)3, LiOCH3, and Ti(OC2H5)4 as the starting materials. The process included well-controlled hydrolysis polycondensation of the raw alkoxides. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction (ED) analysis were utilized to study
the effect of TiO2 addition on the preparation of β-spodumene powders by the sol-gel process. The gelation time of the LAST solution increases as the TiO2 content increases. For the low (<3) or high (>11) pH value, the gelation time was shortened. At pH = 5, regardless of the TiO2 content, the gel has the longest time of gelation. When the dried gels of the LAST system are heated from 800 to 1200 °C, the crystallized samples are composed of the major phase of β-spodumene and a minor phase of rutile (TiO2).
Phase formation and composition of Mn–Zn ferrite powders prepared by hydrothermal method
Authors: Lin Wen-Hao , Jean Shiuh-Ke Jang , Hwang Chii-Shyang
Published: March 2008

Mn–Zn ferrite powders were prepared by hydrothermally aging the coprecipitates of compositional metal ions using ammonium hydroxide as a precipitant. R value (alkalinity) = (moles of added OH−)/[(moles of added Zn2+) × 2 + (moles of added Mn2+) × 2 + (moles of added Fe3+) × 3] was introduced to adjust the amount of added ammonia. The results show that the R value of starting suspension and hydrothermal time have similar and dominant effects on the composition, spinel ratio, and crystallite size of synthesized powders. From the analyses of x-ray diffraction (XRD) and inductively-coupled plasma (ICP), it notes that no α–Fe2O3 peak in the XRD patterns of powders synthesized at R = 2–3, 150 °C × 2 h, may be due to lower degree of crystallinity and less amount of α–Fe2O3 existing in these powders. Both the increase of hydrothermal time and of R value can promote the crystallinity of powders and also cause a significant loss of zinc, hinting that in the hydrothermal process, the loss of zinc may play a crucial role in the crystallinity of hydrothermally synthesized powders.
Thermoelectric properties of PbTe thin films prepared by gas evaporation method
Authors: Ito Masatoshi , Seo Won-Son , Koumoto Kunihito
Published: March 2008

PbTe thin films with fine grains were successfully fabricated by the gas evaporation method. Thermoelectric properties, i.e., Seebeck coefficient and electrical conductivity, both decreased with decreasing grain size. This was attributed to the decrease in carrier mobility exceeding the increase in carrier concentration with decreasing grain size. It was clarified that the effects of grain boundaries and of oxidation on carrier mobility are considerably large.
Formation of TiSi2 on nitrogen ion implanted (001)Si
Authors: Cheng S. L. , Chen L. J. , Tsui B. Y.
Published: March 2008

Formation of TiSi2 on nitrogen ion implanted (001)Si has been investigated. Nitrogen ion implantation was found to suppress the B and As diffusion in silicon. For Ti on 30 keV BF2+−20 keV N2+ and 30 keV As+−20 keV N2+ implanted samples, a continuous low-resistivity TiSi2 layer was found to form in all samples annealed at 700–900 °C. For Ti on 1 ×1015/cm2 N2+ 1- and As+ implanted samples, end-of-range defects were completely eliminated in all samples annealed at 700–900 °C. The results indicated that with appropriate control, N+-implantation can be successfully implemented in forming low-resistivity TiSi2 contacts on shallow junctions in deep submicron devices.
Ion beam enhanced thermal depolymerization of poly(methyl methacrylate)
Authors: Fragalà M. E. , Compagnini G. , Puglisi O.
Published: March 2008

Ion beam enhanced thermal depolymerization of poly(methyl methacrylate) thin films, 1–2 µm thick, has been studied in the temperature range 100–400 °C using a 300 keV He+ beam at very low fluence (5 × 1010−5 × 1011 ions cm−2). A relevant monomer evolution (mass signal m/z = 100) at temperature (150 °C) well below the conventional degradation temperature (360 °C) has been detected during irradiation. The observed phenomenon is discussed in terms of activation energies and diffusion processes within the investigated films. The possibility offered by this phenomenon of performing a microlithography process in only one step is discussed.
Vapor deposition of parylene-F using hydrogen as carrier gas
Authors: Mathur D. , Yang G-R. , Lu T-M.
Published: March 2008

A new method for depositing parylene-F (PA-F) thin films on silicon substrates has been explored. Hydrogen has been used as a carrier gas along with liquid precursors, dibromotetrafluoro-p-xylene and 1,4-bis(trifluoromethyl)benzene, to deposit PA-F. The properties of this film have been compared with the films obtained by the Gorham dimer method and the liquid precursor method using FTIR, XPS, and XRD. The PA-F films deposited by the dimer or liquid precursor acquired some kind of microcrystallinity on annealing. However, the PA-F films deposited in the presence of hydrogen were amorphous on annealing. This property could be potentially exploited for application in microelectronic device fabrication.
Improving the synthesis of alkyl phosphates as sol-gel precursors
Authors: Ali Ashraf Fahim , Mustarelli Piercarlo
Published: March 2008

Alkyl phosphates can be used as sol-gel precursors for phosphate-based glasses and glass-ceramics. An improvement in the synthesis of alkyl phosphates is presented. Following the procedure here described, it is possible to limit the fraction of condensed phosphates to 1–2%. At the same time, a ratio between mono- and di-substituted phosphates near to that given by the reaction stoichiometry may be attained.
Third-order nonlinear optical properties of the Na2S–PbS–GeS2 sulfide glasses and the Na2S–PbO–GeS2 oxysulfide glasses
Authors: Zhou Zhong Hua , Nasu Hiroyuki , Hashimoto Tadanori , Kamiya Kanichi
Published: March 2008

The third-order optical nonlinearity of glasses of the Na2S–PbS–GeS2 and Na2S–PbO–GeS2 systems was measured by third-harmonic generation method. The third-order nonlinearities of glasses of both systems increase with the increasing lead content. The maximum value of the third-order optical nonlinearity was 3.00 × 10-12 esu. The addition of PbO basically has little influence on third-order optical nonlinearity, and the largest nonlinearity is 1.49 × 10-12 esu. The minimum appearing at 15 mol% PbO can be explained by the decrease of number density of lead and sulfur. Chemical durability of oxysulfide glasses is superior to that of a pure sulfide system; thus the addition of PbO is important in this sense.
Structure and misorientation angle distributions of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures
Authors: Fujii Hiroki , Kumakura Hiroaki , Togano Kazumasa
Published: March 2008

We investigated the relationship between the structure and misorientation angle of (001) twist grain boundaries in Bi2Sr2Ca1Cu2Oy/Ag composite tapes processed in different oxygen partial pressures (PO2 = 0.01, 0.21, and 1 atm). Large-angle misoriented twist boundaries (>10°) essentially had no amorphous layers at the interface, and the misorientation angles of these boundaries mostly corresponded to low-energy misorientations. This large-angle misoriented boundary structure was independent of PO2. Small-angle misoriented twist boundaries (<10°), on the other hand, corresponded to high-energy misorientations and sometimes had amorphous layers at the interface. The population of the small-angle boundary with an amorphous layer was very low in the tape processed in PO2 = 1 atm. This suggests that high PO2 during the heat treatment is effective in the improvement of grain coupling, and hence, to increase critical current density.
Formation process of interface states at grain boundaries in sputtered polycrystalline Si films
Authors: Nakano Yoshitaka , Sakata Jiro , Taga Yasunori
Published: March 2008

A systematic investigation has been made on surface defect states of crystallites in the crystallization process of sputtered amorphous silicon films by isothermal annealing. Transmission electron microscopic observations indicate a pronounced vertical columnar structure in the upper part of the films, where the crystallization is delayed. Admittance spectroscopy reveals that two newly generated energy levels with the crystallization are attributed to the crystallites in the lower and upper parts of the films in view of the anisotropic crystallization. These thermally induced changes can be well explained by Si–Si shearing modes at the interfaces of crystallites through the process of crystallization.
Phase selection in a mechanically alloyed Cu2013;In–Ga–Se powder mixture
Authors: Suryanarayana C. , Ivanov E. , Noufi R. , Contreras M. A. , Moore J.J.
Published: March 2008

Formation of a homogeneous nanocrystalline CuIn0.7Ga0.3Se2 alloy was achieved by mechanical alloying of blended elemental Cu, In, Ga, and Se powders in a planetary ball mill. X-ray diffraction and transmission electron microscopy and diffraction techniques were employed to follow the structural evolution during milling. It was observed that, depending upon the milling conditions, either a metastable cubic or a stable tetragonal phase was produced. The grain size of the mechanically alloyed powder was about 10 nm. The mechanically alloyed powder was consolidated to full density by hot isostatic pressing the powder at 750 °C and 100 MPa for 2 h. Irrespective of the nature of the phase in the starting powder, the hot isostatically pressed compact contained the well-recrystallized tetragonal CuIn0.7Ga0.3Se2 phase with a grain size of about 50 nm.
Haasen plot analysis of the Hall–Petch effect in Cu/Nb nanolayer composites
Authors: Tambwe M. F. , Stone D. S. , Griffin A. J. , Kung H. , Cheng Y. , Nastasi M.
Published: March 2008

We investigate the effects of layer thickness (t) on hardness (H) and rate sensitivity of the hardness (∂H/∂ ln ) in 1 μm-thick Cu/Nb nanolayer composites. For t < 10 nm, we find that H correlates with t according to H = H0 = H1t-1/2, suggestive of a Hall–Petch mechanism with layer interfaces replacing grain boundaries as barriers against dislocation motion. The measured levels of ∂H/∂ ln clearly indicate the operation of bulk-like dislocation mechanisms consistent with a Hall–Petch mechanism. However, based on a Haasen-plot activation analysis, it appears that the Hall–Petch coefficient, H1, is strongly rate-dependent, inconsistent with a conventional Hall–Petch mechanism. For specimens with t < 10 nm there is a saturation in hardness, but the rate sensitivity data indicate no clear evidence of a corresponding change in mechanism. Simple models are proposed.
Preparation of polylactic acid composites containing β–Ca(PO3)2 fibers
Authors: Kasuga Toshihiro , Fujikawa Haruhiko , Abe Yoshihiro
Published: March 2008

Novel biomaterials for application to artificial bone with modulus of elasticity close to that of natural bone were prepared using bioresorbable poly-L-lactic acid (PLLA) and high-strength β–Ca(PO3)2 fibers treated with dilute NaOH solution. PLLA dissolved by using methylene chloride was mixed with the fibers. After drying the mixture, it was hot-pressed uniaxially under a pressure of 40 MPa at 180 °C, resulting in fabrication of a PLLA composite containing β–Ca(PO3)2 fibers. Almost no degradation in the bending strength was observed even when a large amount of the fibers (≈50 wt. %) was introduced, and the modulus of elasticity was increased effectively with increasing the fiber content. The PLLA composite with modulus of elasticity of <5 GPa similar to that of natural bone was found to be prepared when the fiber content was over 35 wt. %. The bending test of the composites showed that very high energy is consumed for their fracture and that the fracture proceeds step by step, even beyond the maximum stress.
New approach in the monitoring and characterization of titanium nitride thin films
Authors: Logothetidis S. , Meletis E. I. , Kourouklis G.
Published: March 2008

In situ and ex situ spectroscopic ellipsometry (SE), Raman spectroscopy (RS), x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) have been used to study the stoichiometry and characterize TiNx thin films deposited by magnetron sputtering at various stoichiometries. In situ SE can provide parameters, such as the plasma energy, that can be utilized for monitoring of the film stoichiometry. Besides plasma energy, optical phonon position in RS was also found to be a sensitive probe of TiNx stoichiometry as detected by RS, XPS, and ex situ SE. Under these conditions, AES faces difficulties for reliable film characterization, and the complementary use of other techniques is required for determining the exact film stoichiometry.
High-temperature powder x-ray diffraction of yttria to melting point
Authors: Swamy V. , Dubrovinskaya N. A. , Dubrovinsky L. S.
Published: March 2008

Powder x-ray diffraction data of yttria (Y2O3) were obtained from room temperature to melting point with the thin wire resistance heating technique. A solid-state phase transition was observed at 2512 ± 25 K and melting of the high-uemperature phase at 2705 ± 25 K. Thermal expansion data for α–Y2O3 (C-type) are given for the range 298–2540 K. The unit cell parameter increases nonlinearly, especially just before the solid-state transition. The x-ray diffraction spectrum of the high-temperature phase is consistent with the fluorite-type structure (space group Fm3) with a refined unit cell parameter a = 5.3903(6) Å at 2530 K. The sample recrystallized rapidly above 2540 K, and above 2730 K, all the diffraction lines and spots disappeared from the x-ray diffraction spectrum that suggests complete melting.
Rapid thermal processing of lead zirconate titanate thin films on Pt–GaAs substrates based on a novel 1,1,1-tris(hydroxymethyl)ethane sol-gel route
Authors: Arscott S. , Miles R. E. , Kennedy J. D. , Milne S. J.
Published: March 2008

0.53Ti0.47)O3 have been prepared on platinized GaAs (Pt–GaAs) substrates using a new 1,1,1-tris(hydroxymethyl)ethane (THOME) based sol-gel technique. Rapid thermal processing (RTP) techniques were used to decompose the sol-gel layer to PZT in an effort to avoid problems of GayAs outdiffusion into the PZT. A crystalline PZT film was produced by firing the sol-gel coatings at 600 or 650 ° for a dwell time of 1 s using RTP. A single deposition of the precursor sol resulted in a 0.4 μm thick PZT film. X-ray diffraction measurements revealed that the films possessed a high degree of (111) preferred orientation. Measured average values of remanent polarization (Pr ) and coercive field (Ec) for the film annealed at 650 ° for 1 s were 24 μC/cm2 and 32 kV/cm, respectively, together with a low frequency dielectric constant and loss tangent at 1 kHz of 950 and 0.02. These values are comparable to those obtainable on platinized silicon (Pt–Si) substrates using conventional sol-gel methods, and are an improvement on PZT thin films prepared on platinized GaAs using an earlier sol-gel route based on 1,3-propanediol.
Synthesis of cobalt oxide nanocrystal self-assembled materials
Authors: Yin J. S. , Wang Z. L.
Published: March 2008

Self-assembling of size, shape, and phase-selected nanocrystals into superlattices in a new approach for synthesizing a new generation of advanced materials with functionality. In this paper, high purity and monodispersive tetrahedral of CoO, with edge lengths of 4.4 ± 0.2 nm, have been synthesized and separated from Co nanocrystals using colloidal chemistry and magnetic separation. The tetrahedral CoO nanocrystals behave like a molecular matter, and their assembling forms superlattices with translational symmetry. The phase transformation of the CoO nanocrystals is examined by ex situ annealing in oxygen, and the results showed the formation of Co3O4 with spinel structure.
Two kinds of roles of MgO in the densification and grain growth of alumina under various atmospheres: Sensitive and insensitive roles to the experimental procedures
Authors: Ikegami Takayasu , Eguchi Katsuya
Published: March 2008

Two kinds of high-purity Al2O3 powder were studied with respect to the effects of not only MgO doping but also atmosphere on both densification and grain growth. Controversial results for MgO doping are explained in terms of two roles that MgO can play during these processes: sensitive and insensitive to the experimental procedures. Atmospheres, whether dry or wet, had little influence on densification or grain growth in the early stage. After closed pores appreciably formed, however, both N2 and Ar atmospheres quickly reduced the densification rate.
Preparation and sintering of CaSiO3 from coprecipitated powder using NaOH as precipitant and its apatite formation in simulated body fluid solution
Authors: Siriphannon Punnama , Hayashi Shigeo , Yasumori Atsuo , Okada Kiyoshi
Published: March 2008

CaSiO3 powders were prepared from an ethanol solution dissolving Ca(NO3)2 · 4H2O and Si(OC2H5)4 by the coprecipitation method using various concentrations of NaOH as precipitants. Some Na component remained in the precipitates without washing and strongly affected the characteristics of the resultant powders, but the Na residue was removed by a washing treatment. The precipitate prepared by using 0.33 mol/l of NaOH and twice-washing contained the lowest amount of Na residue. It was calcined at 500 and 900 °C, respectively, to crystallize CaSiO3 phase and ground by a planetary potmill. The ground CaSiO3 powder was sintered to about 89% theoretical density by firing at 1400 °C. By soaking the CaSiO3 sintered bodies in simulated body fluid (SBF) solution for various times, an hydroxylapatite (HAp) layer formed as aggregates of ball-like particles on the surface of the CaSiO3 sintered bodies after soaking for a short period; thereby, the CaSiO3 ceramics is suggested to have very good biocompatibility.
A sol-gel derived 0.9Pb(Mg1/2Nb2/3)O3–0.1PbTiO3 ceramic
Authors: Wan D. M. , Wang J. , Ng S. C. , Gan L. M.
Published: March 2008

Using inorganic chemicals, such as niobium pentachloride, titanium tetrachloride, lead nitrate, and magnesium nitrate, as the starting materials, 0.9PMN–0.1PT has been fabricated via a simple and low cost sol-gel processing route. A colloidal solution was first prepared by adding an aqueous lead nitrate solution into an ethanol solution of niobium and titanium chlorides. Magnesium nitrate was then mixed into the solution when chloride ions were removed by forming precipitates of PbCl2 with the excess lead nitrate. The gelation of the colloidal solution was facilitated in the presence of a small amount of polyethylene glycol (PEG 300) at 70 °C. A fine perovskite 0.9PMN–0.1PT powder was obtained when the resulting gel was dried at 300 °C for 4 h and subsequently calcined. It was observed that the sol-gel derived precursor underwent a pyrochlore phase at 500–600 °C, prior to the formation of a perovskite single phase at a calcination temperature of 850 °C. A sintered density of ˜98% theoretical density was obtained when the fine 0.9PMN–0.1PT powder was sintered at 1250 °C for 2 h and the sintered ceramic shows a maximum dielectric constant of 26,682, together with a room temperature dielectric constant of 19,206 at 1 kHz. The superb dielectric properties are correlated to the microstructural features of the sol-gel derived 0.9PMN–0.1PT, which has been characterized using techniques such as XRD, SEM, and TEM.
Effect of La2O3 substitutions on structure and dielectric properties of Bi2O3–ZnO–Nb2O5-based pyrochlore ceramics
Authors: Wang Hong , Zhang Desheng , Wang Xiaoli , Yao Xi
Published: March 2008

The effect of La2O3 substitutions on structure and dielectric properties of Bi2O3 –ZnO–Nb2O5-based ceramics was investigated. Bi1.5-xLaxZn0.5(Zn0.5Nb1.5)O7 samples were prepared by conventional ceramic processing technology. The crystal structure of the Bi1.5Zn0.5(Zn0.5Nb1.5)O7 sample was characterized as a pure cubic pyrochlore. With a lower amount of La2O3 substitution, the crystal structures were still cubic pyrochlore. Superlattice x-ray diffraction line was identified for some compositions. With the increasing amount of La2O3 substitution, the crystal structure gradually transformed from pure cubic pyrochlore to LaNbO4 phase. The dielectric properties regularly changed with the structure change. The structure-properties relations of the ceramics are discussed.
On the applicability of the x-ray diffraction line profile analysis in extracting grain size and microstrain in nanocrystalline materials
Authors: Jiang H. G. , Rühle M. , Lavernia E. J.
Published: March 2008

Measurements of x-ray diffraction (XRD) profiles have been performed on commercially pure Fe and Al powders, cryomilled Fe–3 wt.% Al powders, cold pressed (CP) pure Fe and Al, hot pressed (HP) and hot isostatically pressed (HIP) Fe–3 wt.% Al. Scherrer equation (SE), integral breadth analysis (IBA), and single-line approximation (SLA) methods have been employed to extract grain size and microstrain. The results demonstrate that, in the case of the cryomilled nanocrystalline Fe–3 wt.% Al powders, all these XRD techniques yielded reasonable, consistent grain size results. However, discrepancies were found in cold pressed (CP-Fe), hot pressed (HP-Fe–3 wt.% Al), and hot isostatically pressed (HIP-Fe–3 wt.% Al) samples. TEM imaging revealed the presence of a certain density of dislocations inside the grains in the HP-Fe–3 wt.% Al and HIP-Fe–3 wt.% Al, which is thought to be partly or fully responsible for the observed discrepancies.
Generation of carbon tripods on copper by chemical vapor deposition
Authors: Normand F. Le , Constant L. , Ehret G. , Speisser C.
Published: March 2008

We report the first observation of large graphitic capped clusters with threefold symmetry (tripods). They were generated under the diamond growth conditions by the chemical vapor deposition process activated by hot filaments on a Cu(111) surface while conditions of very poor diamond nucleation (104–105 cm-2) are fullfilled. They were characterized by direct high resolution imaging and selected area diffraction. Furthermore, a lot of them are connected. The behavior of hydrogen radicals to curl and to close limited-size graphitic planes is emphasized to explain their formation. These tripods appear to be readily stable carbon as they form only after other limited-size graphitic clusters such as graphite lumps or bucky onions. It is thus expected that the chemical vapor deposition process is a quite relevant preparation method to grow in a controlled way new forms of carbon with a narrow size distribution.
Processing and characterization of alumina thin films on chemically vapor deposited diamond substrates for producing adherent metallizations
Authors: Menon E. S. K. , Dutta I.
Published: March 2008

In order to make the surface of chemically vapor deposited diamond (CVDD) substrates amenable to metallization by both thin and thick film approaches currently utilized in electronic packaging, a thin, adherent, insulating aluminum oxide film was grown on diamond at low temperatures (<675 K). The film was produced by reactive thermal evaporation of Al and O in an oxygen atmosphere, followed by low-temperature annealing in oxygen. A Cr intermediate layer was deposited on diamond prior to the deposition of aluminum oxide in order to enhance adhesion between the oxide and diamond. The chemistry, crystal structure, and microstructure of the film were characterized in detail via scanning and transmission electron microscopy, as well as Auger electron spectroscopy. Particular attention was given to the mechanisms of bonding across the CVDD-Cr and Cr-alumina interfaces, as well as the stability of the surface treatment following metallization by fritted pastes requiring firing at elevated temperatures. The Cr was found to be bonded with CVDD by Cr23C6 formation, while the bonding between the Cr and alumina layers was provided by the formation of a compositionally modulated solid solution with Al2O3-rich and Cr2O3-rich regions.
Void nucleation in metal interconnects: Combined effects of interface flaws and crystallographic slip
Authors: Shen Y-L.
Published: March 2008

A micromechanical model of void nucleation in passivated metal interconnection lines is proposed. The model is based on the evolution of stress and strain fields in a two-dimensional model system, obtained from numerical modeling. Interface flaws in the form of debond between the metal and the surrounding dielectric are assumed to exist. A unique pattern of shear stress resolved on the slip systems in the metal line, due to the presence of pre-existing debond, is found. A dislocation slip model is constructed in accordance with the shear mode. The mechanism of crystallographic slip is such that lateral thinning of the metal line at the debond region together with the slip step produced at the edges of debond lead to a net transport of atoms away from the debond area, and a physical void is thus formed. The significance and implications of this proposed micromechanism are discussed.
Forging, textures, and deformation systems in a B2 FeAl alloy
Authors: Zhao P. , Morris D. G. , Munoz M. A. Morris
Published: March 2008

High-temperature forging experiments have been carried out by axial compression testing on a Fe–41Al–2Cr alloy in order to determine the deformation systems operating under such high-speed, high-temperature conditions, and to examine the textures produced by such deformation and during subsequent annealing to recrystallize. Deformation is deduced to take place by the operation of 〈111〉 {110} and 〈111〉{112} slip systems at low temperatures and by 〈100〉{001} and 〈100〉{011} slip systems at high temperatures, with the formation of the expected strong 〈111〉 textures. The examination of the weak 〈100〉 texture component is critical to distinguishing the operating slip system. Both texture and dislocation analyses are consistent with the operation of these deformation systems. Recrystallization takes place extremely quickly at high temperatures (above 800 °C), that is within seconds after deformation and also dynamically during deformation itself. Recrystallization changes the texture such that 〈100〉 textures superimpose on the deformation texture. The flow stress peak observed during forging is found at a very high temperature. Possible origins of the peak are examined in terms of the operating slip systems.