bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric domains in coarse-grained lead zirconate titanate ceramics characterized by scanning force microscopy
Authors: Muñoz-Saldaña J. , Hoffmann M. J. , Schneider G. A.
Published: March 2008

Ferroelectric domain configurations in silver- and lanthanum-doped lead zirconate titanate (PZT) ceramics were characterized by scanning force microscopy using contact as well as piezoelectric response force [i.e., piezoelectric force microscopy (PFM)] modes. Coarse crystallites of hard and soft PZT ceramics (12 μm in Ag-PZT and 30 μm in La-PZT average grain size, respectively) with surface oriented in the {001} planes were chosen to characterize the domain configuration. Results show the conventional right-angled domain structures, which correspond to the {110} twin-related 90° and 180° domains of homogeneous width from 50 to 150 nm. The ability of PFM to image the orientation of pure in-plane arrays of domains (containing 90°-aa- and 180°-aa-types of domain boundaries) is highlighted, and a more detailed notation for in-plane domains is proposed. In addition to such periodical domain arrays, other ordered domains were found, having a misfit of 26° with respect to the{110} domain walls and the {100} surface. This array of domain walls could not be predicted with a geometrical analysis of the intersection of domain walls at the surface according to the conventional spatial array of {110} crystallographic planes. It could be explained only with {210} planes being the domain walls. The reason for this unconventional domain configuration is explained with the clamped conditions of the investigated crystallites in the polycrystalline material.
Sonochemical method for the synthesis of antimony sulfide microcrystallites with controllable morphology
Authors: Zhang J. H. , Chen Z. , Wang Z. L. , Ming N. B.
Published: March 2008

Spindlelike, rodlike, starlike, and spherical antimony sulfide (Sb2S3) microcrystallites have successfully been synthesized via a sonochemical method at room temperature. The x-ray diffraction pattern analysis based on the Rietveld method demonstrates that ultrasound can convert the structure of Sb2S3 from amorphous phase to crystalline phase. The crystallinity and morphology of Sb2S3 particles can be modified by using different solvents or solutions. It is found that the spindlelike and starlike particles result from the aggregation of nanoparticles while the rodlike particles arise from epitaxial growth. Due to the quantum confinement effect of charge carriers in small microcrystalline volumes, the characteristic peaks in the optical absorption spectrum of the synthesized 0.001 M Sb2S3 (<100 nm) colloidal solutions are blue-shifted by about 500 nm as compared to the bulk band gaps of Sb2S3.
Preparation of BaTiO3/SrTiO3 composite dielectric ceramics with a flat temperature dependence of permittivity
Authors: Takeuchi Tomonari , Kageyama Hiroyuki
Published: March 2008

Composite dielectric ceramics of BaTiO3/SrTiO3 were prepared using the spark plasma sintering (SPS) method. Relatively dense (>92% of the theoretical x-ray density) composite ceramics were obtained for a relatively short sintering time (∼3 min). Such a short sintering time was advantageous in suppressing the formation of a complete solid solution (Ba, Sr)TiO3. Fixed-frequency (100 kHz), room-temperature permittivity measurements of the BaTiO3/SrTiO3 = 9/1 composites showed a flat temperature dependence within the range 30–110 °C. X-ray diffractometry measurements showed that the current SPS-BaTiO3/SrTiO3 composites consisted of BaTiO3 and small amounts of (Ba1−xSrx)TiO3 with various x values having different phase transition temperatures. Such multicomponent microstructures would be responsible for the flat temperature dependence of permittivity.
Mechanism of combustion and phase formation in the BaO2–TiO2–organic compound system
Authors: Lee J. H. , Nersisyan H. H. , Simkins M. L. , Won C. W.
Published: March 2008

The high-temperature combustion mechanism of the BaO2–TiO2–organic compound system [urea, CO(NH2)2; hexamethylenetetramine, C6H12N4] was investigated by the microthermocouple technique. The adiabatic combustion temperatures (Tad) and equilibrium compositions of the final products were calculated by the computer program THERMO. The distribution of the temperature T(x), rate of heat generation Φ(x), and degree of conversion η(x) in the combustion wave were determined. The relative sizes of the combustion zones, the leading stage of the reaction, the kinetic law of components interaction, and parameters (activation energy, pre-exponential factor, braking parameter) were then calculated. Through this method, the optimal conditions for tetragonal BaTiO3 powder synthesis with spherical form and particles size of 2–5 μm were found.
High-temperature oxidation of Al–Cu–Fe–Be quasicrystalline powders
Authors: Fleury E. , Kim J. S. , Kim D. H. , Kim W. T.
Published: March 2008

The oxidation behavior in air of gas atomized Al–Cu–Fe–Be powders was investigated during isothermal exposures at 750, 800, and 830 °C. Oxidation data obtained at 750 °C for Al–Cu–Fe and Al–Cu–Fe–Cr powders are also presented and used as references. Thermogravimetric analyses showed that Be significantly improved the oxidation resistance of the icosahedral phase at 750 °C. At this temperature the i-phase in Al–Cu–Fe–Be powders was found to be stable even after oxidation for 300 h, while oxidation at and beyond 800 °C led to the formation of a cubic β′-phase. Auger analyses suggested that, in addition to its role on the stability of the icosahedral phase, the presence of Be in the oxide layer provided efficient protection against air oxidation at high temperature.
Self-propagating high-temperature synthesis microalloying of MoSi2 with Nb and V
Authors: Maglia F. , Milanese C. , Anselmi-Tamburini U. , Munir Z. A.
Published: March 2008

Microalloying of MoSi2 to form Mo(1−x)MexSi2 (Me = Nb or V) was investigated by the self-propagating high-temperature synthesis method. With alloying element contents up to 5 at.%, a homogeneous C11b solid solution was obtained. For higher contents of alloying elements, the product contained both the C11b and the hexagonal C40 phases. The relative amount of the C40 phase increases with an increase in the content of alloying metals in the starting mixture. The alloying element content in the hexagonal C40 Mo(1−x)MexSi2 phase was nearly constant at a level of about 12 at.% for all starting compositions. In contrast, the content of the alloying elements in the tetragonal phase is considerably lower (around 4 at.%) and increases slightly as the Me content in the starting mixture is increased.
Low-temperature metalorganic chemical vapor deposition of Al2O3 for advanced complementary metal-oxide semiconductor gate dielectric applications
Authors: Skordas Spyridon , Papadatos Filippos , Nuesca Guillermo , Sullivan John J. , Eisenbraun Eric T. , Kaloyeros Alain E.
Published: March 2008

A low-temperature metalorganic chemical vapor deposition process was developed and optimized, using a design of experiments approach, for the growth of ultrathin aluminum oxide (Al2O3) as a potential gate dielectric in emerging semiconductor device applications. The process used the aluminum β-diketonate metalorganic precursor [aluminum(III) 2,4-pentanedionate] and water as, respectively, the metal and oxygen source reactants to grow Al2O3 films over a temperature range from 250 to 450 °C. The resulting films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction measurements, Rutherford backscattering spectrometry, nuclear-reaction analysis for hydrogen profiling, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The as-deposited Al2O3 phase was amorphous and dense and exhibited carbon and hydrogen incorporation of, respectively, 1 and 10 at.%. Postannealing at 600 °C led to a reduction in hydrogen concentration to 1 at.%, while maintaining an amorphous Al2O3 matrix.
Low crystallization temperature and unusual switching properties of ferroelectric Nb-doped Bi4Ti3O12 thin films prepared by rapid thermal annealing
Authors: Kim Jong Kuk , Kim Sang Su , Kim Jinheung
Published: March 2008

Nb-doped Bi4Ti3O12 (Nb-BIT) ferroelectric thin films were prepared in the presence of a nonionic surfactant (pluronic P123) added as an additive to the sol solution and by rapid thermal annealing (RTA). The film annealed at the relatively low temperature of 600 °C was well crystallized and showed good ferroelectricity. The switching charge of capacitors with polarization reversal rapidly increased with a large amplitude and low frequency of the applied pulse, and gradually decreased with a small amplitude and high frequency. The remanent polarization (2Pr) after subjecting the Nb-BIT capacitors to 108 read/write cycles was 46 μC/cm2, which is remarkably higher than 20 μC/cm2 observed in the initial state. These phenomena seem to appear by the presence of space charges trapped after heat treatment by the RTA process.
Effect of organic modifiers on the thermo-optic characteristics of inorganic–organic hybrid material films
Authors: Kang Eun-Seok , Park Jang-Ung , Bae Byeong-Soo
Published: March 2008

The thermo-optic coefficient (dn/dT) of inorganic–organic hybrid material films prepared by the sol-gel process of organoalkylsilanes is measured using a prism coupler equipped with a hot stage. The effect of the organic modifier on the variation of dn/dT in inorganic–organic hybrid material films has been investigated. The value of dn/dT becomes more negative with increasing molecular weight of the organic modifier or with an increase in the proportion of modifier in the sample. On the other hand, dn/dT increases with an increase in the degree of organic photopolymerization. From these results, it can be seen that the value of dn/dT in these films can be varied between −0.83 × 10−4/°C to −2.43 × 10−4/°C by changing the organic modifier concentration and type.
Formation of Mg–Mg2Cu nanostructured eutectic in Mg-based metal matrix composite
Authors: Ma N. G. , Deng C. J. , Yu P. , Kwok W. Y. , Aravind M. , Ng D. H. L. , Chan S. L. I.
Published: March 2008

We report the fabrication and characterization of a Mg-based metal matrix composite reinforced by MgO ceramic and Mg–Mg2Cu eutectic. The composite was fabricated by sintering and quenching of a Mg–20 wt.% CuO sample. We performed differential scanning calorimetry (DSC) on the sample and found that the reaction between Mg and CuO took place at about 420 °C. When the sample was sintered to 550 °C and cooled down, the two-phase Mg–Mg2 Cu eutectic formed. The final composite product contained MgO particles and Mg–Mg2Cu eutectic, which were embedded in the Mg matrix. Based on the results from DSC and scanning and transmission electron microscopies, a model is proposed to describe the competitive growth of Mg and the eutectic during solidification. We also found that the microstructure of the Mg–Mg2 Cu eutectic strongly depended on the rate of cooling. The lamellar thickness of the eutectic could be reduced to 120 nm by oil-quenching the sintered sample.
High-temperature MgO–C–Al refractories–metal reactions in high-aluminum-content alloy steels
Authors: Lee Jyh-Wei , Duh Jenq-Gong
Published: March 2008

MgO–C–Al refractories were used in this study to evaluate high-temperature refractory–metal reactions with molten Fe–Mn–Al alloys. Dynamic reaction tests at 1570 °C and static reaction tests at 1500 °C and 1600 °C, respectively, were used. MgAl2O4 and Al4C3 phases were observed in the refractory bulk, and a large amount of protective MgAl2O4 phase formed due to the decomposition of Al4C3 phases on the refractory–metal reaction interface of the MgO–C–Al brick to retard the high-temperature attack of Fe–Mn–Al alloy melts. The oxygen partial pressure was substantially reduced by the oxidation of graphite in the MgO–C–Al brick during high-temperature test. This resulted in the nitridation of aluminum in molten Fe–Mn–Al alloy. White aluminum nitride (AlN) with the shape of whisker-like powder was formed and adhered to the surface of the MgO–C–Al brick. Aluminum was depleted from the Fe–Mn–Al alloy by nitridation or the oxidation reaction by CO gas. The alloy would also be carburized due to the absorption of CO gas or the reaction between aluminum and CO gas, which was produced by the oxidation of graphite in the MgO–C–Al refractory after static reaction test. It is argued that the MgO–C–Al refractory is not suitable to be used in the melting of Fe–Mn–Al alloys with high aluminum contents.
Comments on “Mechanical relaxation time scales in a Zr-Ti-Ni-Cu-Be bulk metallic glass” by Daewoong Suh and Reinhold H. Dauskardt [J. Mater. Res. 17, 1254 (2002)]
Authors: Schröter K.
Published: March 2008

The stress relaxation results below the glass-transition temperatureTgare a continuation of the viscoelastic relaxation aboveTg. This means that the dynamic glass transition and not a secondary relaxation is the reason for the observed effects.
Temperature dependence of positron annihilation in a Zr–Ti–Ni–Cu–Be bulk metallic glass
Authors: Suh Daewoong , Dauskardt Reinhold H. , Asoka-Kumar P. , Sterne Philip A. , Howell Richard H.
Published: March 2008

A strong temperature dependence of positron annihilation with low-momentum electrons is reported for a Zr-based bulk metallic glass in the temperature range 50–300 K. The observed behavior was rationalized in terms of shallow versus deep positron traps. An interpretation of the data was presented based on the idea that there were two different types of open-volume regions: Bernal interstitial sites and thermally unstable larger holes. Bernal interstitial sites, intrinsic to the glass structure, were found to be insensitive to annealing. Alternatively, the larger holes were removed by annealing. The strong correlation between these larger holes and diffusion and viscous flow processes suggests that they may act as diffusion and flow defects.
Imaging of piezoelectric activity in laser-ablated c-axis-oriented LiNbO3/ZnO thin film multilayer on glass using atomic force microscopy
Authors: Sharma Parmanand , Sreenivas K. , Belova L. M. , Rao K. V.
Published: March 2008

A LiNbO3/ZnO multilayer with a preferred c-axis orientation normal to the plane of the substrate was grown on glass and SiO2/Si substrates by laser ablation. The piezoelectric activity in as-deposited films was demonstrated using a novel approach to the atomic force microscope. In the presence of an in-plane, low-frequency (0.1–5 Hz) alternating current electric field, we monitored and imaged the induced piezoelectric response normal to the film plane between two electrodes.
Preparation of ZnO by a nearby vaporizing chemical vapor deposition method
Authors: Nishino Junichi , Nosaka Yoshio
Published: March 2008

Zinc oxide (ZnO) films were prepared by a nearby vaporizing chemical vapor deposition method using bis(2,4-pentanedionato)zinc as a source material. The deposition rate increased exponentially from 0.58 to 147 nm min−1with increasing substrate temperature (Ts). The highest preferred orientation to thecaxis was obtained under the conditions that the distance between substrate and source surface was 5.0 mm, and theTswas 300 °C. When we used a sapphire (0001) substrate, an epitaxial ZnO film could be deposited on this condition.
Synthesis of vapor-grown carbon fibers from camphor without catalyst and their characterization
Authors: Pradhan Debabrata , Sharon Maheshwar , Mukhopadhyay Indrajit
Published: March 2008

Vapor-grown carbon fibers and carbon micro-beads were produced in the absence of catalysts from a natural precursor, camphor, by a thermal chemical vapor deposition process, at different temperatures in an argon medium. Scanning and transmission electron microscopy, Raman spectra, and electrical conductivity studies were used to characterize these fibers. It was observed that cylindrical fibers (diameter ∼3 μm) were obtained at 1033 K and rippled fibers (diameter ∼5 μm) were formed at 1273 K while carbon beads (diameter ∼0.5–1 μm) were formed at 1173 K. It is proposed that agglomeration of carbon beads predominate at pyrolysis temperature greater than 1173 K, resulting into rippled type fibers.
Growth of thick Yba2Cu3O7−δ films carrying a critical current of over 230 A/cm on single LaMnO3-buffered ion-beam assisted deposition MgO substrates
Authors: Paranthaman M. , Aytug T. , Christen D. K. , Arendt P. N. , Foltyn S. R. , Groves J. R. , Stan L. , DePaula R. F. , Wang H. , Holesinger T. G.
Published: March 2008

A single LaMnO3 buffer layer was developed for the growth of superconducting thick YBa2Cu3O7−δ (YBCO) films on polycrystalline Ni-alloy substrates where a biaxially textured MgO layer, produced by ion-beam assisted deposition (IBAD), was used as a template. Using pulsed laser deposition, a 1.65-μm-thick YBCO film with a critical current density of 1.4 × 106 A/cm2 in self field at 75 K was achieved on sputtered LaMnO3-buffered IBAD MgO substrates. This corresponds to a critical current (Ic) of 231 A/cm-width. This result demonstrates the possibility of using both LaMnO3 buffer and IBAD MgO template for producing high current density YBCO-coated conductors.
Linear strain hardening in elastoplastic indentation contact
Authors: Sakai M. , Akatsu T. , Numata S. , Matsuda K.
Published: March 2008

Finite-element analyses for elastoplastic cone indentations were conducted in which the effect of linear strain hardening on indentation behavior was intensively examined in relation to the influences of the frictional coefficient (μ) at the indenter/material contact interface and of the inclined face angle (β) of the cone indenter. A novel procedure of “graphical superposition” was proposed to determine the representative yield stress YR. It was confirmed that the concept of YR applied to elastic-perfectlyplastic solids is sufficient enough for describing the indentation behavior of strainhardening elastoplastic solids. The representative plastic strain of εR (plastic) ≈ 0.22 tan β, at which YR is prescribed, is applicable to the strain-hardening elastoplastic solids, affording a quantitative relationship of YR = Y + ε;R (plastic) × EP in terms of the strain-hardening modulus EP. The true hardness H as a measure for plasticity is estimated from the Meyer hardness HM and then successfully related to the yield stress Y as H = C(β,μ) × Y for elastic-perfectly-plastic solids and as H = C(β,μ) × YR for strain-hardening solids, by the use of a β- and μ-dependent constraint factor C(β,μ) ranging from 2.6 to 3.2.
Effect of supersaturation of Cu on reaction and intermetallic compound formation between Sn–Cu solder and thin film metallization
Authors: Ha J. S. , Oh T. S. , Tu K. N.
Published: March 2008

Interfacial reactions and intermetallic compound formation of the eutectic Sn–0.7Cu and hypereutectic Sn–3Cu on thin film metallization of Al/Ni/Cu, Al/Cu, and Al/Ni were investigated. While the Ni layer of Al/Ni/Cu was almost consumed by Sn–0.7Cu after one reflow at 240 °C, most of it was preserved with Sn–3Cu even after ten reflows. Since the Cu content in Sn–0.7Cu is below the solubility limit of Cu in Sn at 240 °C, the Cu layer of Al/Ni/Cu was dissolved completely into Sn–0.7Cu, and the Ni was exposed to the molten solder to form intermetallics. As Cu content in Sn–3Cu is more than the solubility limit, intermetallics formed between the solder and the Cu layer, but not the Ni layer, of Al/Ni/Cu. The supersaturation of Cu in Sn–3Cu was found to be beneficial in reducing the interfacial intermetallic compound formation and in improving the interfacial stability.
Fabrication of large-size Fe-based glassy cores with good soft magnetic properties by spark plasma sintering
Authors: Shen Baolong , Inoue Akihisa
Published: March 2008

Glassy Fe65Co10Ga5P12C4B4 alloy powders with a large supercooled liquid region of 50 K before crystallization were synthesized in the particle size range below 125 μm by Ar gas atomization. With the aim of developing a large-size Fe-based glassy core with good soft magnetic properties, the consolidation method of spark plasma sintering was applied to the Fe65Co10Ga5P12C4B4 glassy powders. The existence of the supercooled liquid region enabled us to form a large-size glassy alloy disc 20 mm in diameter and 5 mm in thickness with a high relative density of 99.7% at the glass-transition temperature of 723 K and under the external applied pressure of 300 MPa. The resulting glassy core of 18 mm in outer diameter, 10 mm in inner diameter, and 4 mm in thickness exhibits good soft magnetic properties: 1.20 T for saturation magnetization, 6 A/m for coercive force, and 8900 for maximum permeability. The good soft magnetic properties of the Fe-based bulk glassy core are attributed to the combination of the high relative density and the maintenance of the single glassy structure.
Viscous Poisson's coefficient determined by discontinuous hot forging
Authors: Zuo Ruzhong , Aulbach Emil , Rödel Jürgen
Published: March 2008

A high-resolution laser-assisted loading dilatometer was applied for the precise measurement of radial and axial strain rates under different uniaxial loads, using alumina as a model material. As a continuous application of an external load can lead to an anisotropic microstructure, a discontinuous hot forging technique was utilized to determine the viscous Poisson's coefficient. In these studies, samples were presintered to different densities and only then were hot-forging tests performed. The result provides an isotropic viscous Poisson's coefficient, which increases smoothly between 0.21 and 0.42 within the accessible density range. Combined with the uniaxial viscosity measured before using the same technique, the hydrostatic sintering stress, bulk viscosity, and shear viscosity as a function of density are now available for solid-state sintering. A comparison of the experimentally obtained results with several theoretical models is included.
Strength and interface-constrained plasticity in thin metal films
Authors: Shen Y-L.
Published: March 2008

This study seeks to provide a mechanistic rationale for the substrate confinement effect on the strength and plasticity of thin metal films. Atomistic simulations of tensile loading of the freestanding and substrate-bonded films were carried out. Particular attention was devoted to correlating the overall mechanical response and the defect mechanisms on the atomic scale. The existence of an interface with the underlying substrate was observed to constrain significantly the dislocation motion in the film. The extent of film strengthening due to the substrate was dictated by the capability of atoms to slide along the interface.
Prediction of metastable phase formation in an immiscible Cu–Cr system from interatomic potential and ab initio calculation
Authors: Gong H. R. , Kong L. T. , Liu B. X.
Published: March 2008

Ab initio calculation was performed to predict the structures, lattice constants, and cohesive energies of metastable Cu75Cr25 and Cu50Cr50 phases. An n-body Cu–Cr potential was derived through fitting to some ab initio calculated results and was capable of reproducing some intrinsic properties of the Cu–Cr system. Based on the derived potential, molecular dynamics simulations predicted that for a Cu100−xCrx alloy, the face-centered-cubic structure is more stable than the body-centered-cubic (bcc) one when 0 ≤ x ≤ 25, while the bcc structure becomes energetically favored when 25 < x ≤ 100. Interestingly, the predictions match well with the experimental observations.
Tellurium nanowire arrays synthesized by electrochemical and electrophoretic deposition
Authors: Zhao A. W. , Ye C. H. , Meng G. W. , Zhang L. D. , Ajayan P. M.
Published: March 2008

This article describes both electrochemical deposition and electrophoretic deposition of high-density tellurium (Te) nanowire arrays with wire diameters of 60 nm and lengths of 15–20 μm in the nanochannels of anodic aluminum oxide (AAO) templates. The Te nanowires synthesized via electrochemical deposition (ECD) are generally single crystalline in nature with the wire longitudinal axis along the [001] direction, whereas those synthesized via electrophoretic deposition (EPD) show polycrystalline structures with numerous tiny Te crystallites packed randomly in the wires. The single-crystalline Te nanowires produced by the ECD route are believed to form under a near chemical equilibrium condition; however, the imposed transport and the rapid packing of Te nanocrystallites in the nanochannels of AAO template in external fields lead to polycrystalline Te nanowires in the EPD process. This comparative study of the Te nanowire formation in the nanochannels of AAO template will facilitate the tailoring of the growth of other inorganic nanowires of high quality.
Electron spin resonance and x-ray photoelectron spectroscopic studies on an electrochemically deposited film of mixed manganese/vanadium oxides
Authors: Nakayama Masaharu , Nishio Masanori , Ogura Kotaro
Published: March 2008

A thin film of mixed manganese and vanadium oxides was formed on a platinum electrode by electro-oxidation of Mn2+ precursors in aqueous solution with VO3−. X-ray analysis revealed that the film consists of an amorphous phase including trivalent and tetravalent Mn ions. The infrared spectrum exhibited the bands attributable to V2O5, suggesting that protonation and dehydration of VO3− occur to form the polymeric structure. The mixed oxide film showed no electron spin resonance signal in an as-deposited state. After the film-coated electrode was immersed into water and then dehydrated, however, a characteristic signal (g = 2.022) of Mn2+ in the solid phase appeared, accompanying a decrease in the vanadium content. This suggests that Mn3+ ions not in the oxide network, but pairing with unreacted VO3−, are disproportionated to MnO and MnO2 by the reaction with water, while the VO3− is diffused to keep the charge valance of the film.
P-doped μc-Si:H films at a very low thickness and high deposition rate: Suitable for application in solar cells
Authors: Das Debajyoti , Jana Madhusudan
Published: March 2008

Using Ar-induced promotion of microcrystallization to the Si:H network, P-doped μc-Si:H films were prepared at a deposition rate of 50 Å/min. However, a large fraction of an amorphous component was identified, and a definite structural inhomogeneity was evident in the Si:H matrix. Efficient defect elimination, structural reorientation, and grain growth were performed, and an improved microcrystalline network with enhanced dopability was attained by introducing H2 to the Ar-assisted SiH4 plasma and by using their individual advantages to facilitate the microcrystallization process. A high conductivity of approximately 2 × 101 S cm−1 and a homogeneous distribution of micrograins of average diameter approximately 80 Å, contributing to a crystalline volume fraction of 67% in the matrix, were obtained. A significant achievement was to maintain microcrystallinity at a very low thickness of the bulk layer. The n-type μc-Si:H film of dark conductivity approximately 100 S cm−1 was realized at a thickness of approximately 350 Å with a deposition rate of 24 Å/min. Using this material at the tunnel junction as well as at the bottom layer of a double-junction a-Si solar cell, a conversion efficiency of 11.7% was attained without compromising the other parameters.
Chemical bonding characteristics and dielectric properties of Nd2(Ba1−xSrx)ZnO5 solid solutions
Authors: Kan Akinori , Ogawa Hirotaka , Mori Kenkichi , Ohsato Hitoshi , Andou Yoshinori
Published: March 2008

The relationship between the microwave dielectric property and crystal structure of Nd2(Ba1−xSrx)ZnO5 solid solutions was investigated using bond valence theorem and first principle method (DV-Xα method). The evaluation of the covalence characteristics of cation–oxygen bonds revealed that as the x value increased, the covalence characteristics of the M–O (M = Ba and Sr) bonds in the MO10 polyhedron decreased while those of the Zn–O(2) bonds in the ZnO4 tetrahedron increased. From the DV-Xα method, it was found that the 3d electrons of the Zn2+ ion are closely related to the strong covalence characteristics of the Zn–O(2) bonds. The dielectric constants were approximately constant over the whole composition; this result is considered to relate to the decrease in the covalence characteristic of the M–O bonds. The quality factors increased from 4915 to 25,836 GHz, and the grain growth of the solid solutions are considered to improve the Q × f values.
Mechanism of solid-state reaction for fabrication of new glassy V45Zr22Ni22Cu11alloy powders and subsequent consolidation
Authors: El-Eskandarany M. Sherif , Ishihara Satoru , Inoue A.
Published: March 2008

A single glassy phase of V45Zr22Ni22Cu11alloy powders was synthesized by milling the elemental alloying powders in an argon atmosphere using a low-energy ball-milling technique. During the early and intermediate stages of milling, the atoms of Zr, Ni, and Cu migrated and diffused into the V (base material) lattice to form a body-centered-cubic (bcc) solid-solution, which transformed into a glassy phase with the same composition upon annealing at 850 K for 300 s in an argon atmosphere differential scanning calorimeter (thermally-enhanced glass formation reaction). As the milling time increased, the powders were subjected to continuous defects and lattice imperfections that led to a gradual change in the free energy so that solid-solution phase was transformed (mechanically enhanced glass formation reaction) to another metastable phase (glassy). Toward the end of the milling processing time, the bcc solid-solution transformed completely into a single glassy phase with the same composition. The glass-transition temperature, the crystallization temperature, and the enthalpy change of crystallization of the fabricated glassy powders were 741 K, 884 K, and −2.18 kJ/mol, respectively. This fabricated glassy alloy showed a wide supercooled liquid region (143 K) of metallic glassy alloy. The glassy powders were compacted in an argon gas atmosphere at 864 K with a pressure of 780 MPa using a hot-pressing technique. The consolidated sample was fully dense (above 99.2°) and maintained its chemically homogeneous glassy structure. The Vickers microhardness of the consolidated glassy V45Zr22Ni22Cu11alloy was measured and found to be in the range between 6.89 GPa to 7.02 GPa.
Morphology and electronic properties of carbon nanotubes grown with Fe catalyst
Authors: Kowalska E. , Radomska J. , Byszewski P. , Kowalczyk P. , Antonova K. , Diduszko R. , Lange H. , Dłuzewski P.
Published: March 2008

We describe the synthesis and characterization of aligned carbon nanotubes deposited on quartz substrates by pyrolysis of a xylene–ferrocene mixture at 700 °C at atmospheric pressure. For microscopic characterization of the pyrolyzed products, scanning and transmission electron microscopies and scanning tunneling microcopy were used, and properties of bulk samples were characterized by Raman spectroscopy and x-ray powder diffraction methods. The nanotubes have topological defects and many contain metal particles. Scanning tunneling spectroscopy proved that the nanotubes had a metallic electrical conductivity with resonant states near the Fermi energy. The states are ascribed to the dangling bonds originating from the defects.
Thermal diffusivity of (Ca1–xSrx)3Co4O9 thin films using transient grating configuration
Authors: Takata Yoshiaki , Adachi Yutaka , Haneda Hajime , Wada Yoshiki , Mitsuhashi Takefumi , Itaka Kenji , Koinuma Hideomi
Published: March 2008

The past impossibility to create optical diffraction fringe image out of transparent TiO2(100) substrate was overcome by pumping light pulse of 266-nm wavelength. Thermal diffusivities (D) of TiO2(100) substrate and (Ca1–xSrx)3Co4O9 (0 ≤ x ≤ 0.125) thin films can successfully be determined with a newly proposed transient grating configuration method arising from a generic nanoscale measurement technique. The D values obtained at room temperature were 0.04 cm2/s for the former and 0.07–0.12 cm2/s for the latter, respectively.
Spectrosopic and paramagnetic properties of molybdenum oxyhydroxide films electrochemically formed from the Keggin-type (PMo12O40)3− complex
Authors: Nakayama Masaharu , Ii Takahiro , Ogura Kotaro
Published: March 2008

Molybdenum-containing films electrochemically deposited from an aqueous solution of 12-molybdphosphate (PMo12O40)3− (denoted as PMo12) have been characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and electron spin resonance (ESR) techniques. XPS and FTIR data indicate that electrolysis of PMo12 leads to the formation of Mo–O–Mo linkage by condensation of the polyanions accompanied by decomposition of the phosphate moiety. The ESR spectrum of the deposited film exhibits an asymmetric signal with g ∼1.92, indicative of pentavalent molybdenum (d1). The feature of this signal is close to that for a MoV ion in the amorphous MoO3 phase, but not in the PMo12 framework. It is therefore suggested that the deposited film no longer has the Keggin structure PMo12, but consists of a continuous structure containing molybdenum oxide.
Spectral fingerprinting of structural defects in plasma-treated carbon nanotubes
Authors: Chakrapani Nirupama , Curran Seamus , Wei Bingqing , Ajayan Pulickel M. , Carrillo Alvaro , Kane Ravi S.
Published: March 2008

Controlled introduction of defects into aligned multiwalled carbon nanotubes (MWCNTs) was achieved by time-dependent plasma etching. The subsequent morphological changes in MWCNTs have been fingerprinted using Raman and x-ray photoelectron spectroscopy, by which induction of defects by functionalization was confirmed. We found that the introduction of defects along the nanotube body affects all Raman vibrational modes. A systematic analysis of the relationship between D, D′, D*, and G modes leads us to believe that no one peak can be used as an accurate standard for estimation of defects in nanotubes.
Synthesis of carbon nitride nanocrystals on Co/Ni-covered substrate by nitrogen-atom-beam-assisted pulsed laser ablation
Authors: Xu Ning , Lin Hao , Li Li , Pan Weijian , Sun Jian , Wu Jiada , Ying Zhifeng , Wang Peinan , Du Yuancheng , Li Fuming
Published: March 2008

Carbon nitride nanocrystals were synthesized on Co/Ni-covered Si(100) wafers using a nitrogen-atom-beam-assisted pulsed laser ablation deposition method. Transmission electron miscroscopy, x-ray diffraction, and Raman spectroscopy showed that as-deposited films were constructed primarily from nanometer-sized β-C3N4 and CNx crystallites. The co-catalyzation by the cobalt and nickel in the synthesis process is considered to play an important role in the formation of nanocrystalline β-C3N4. The reasons for the formation of carbon nitride nanocrystals were analyzed.
Fabrication of tapered, conical-shaped titania nanotubes
Authors: Mor G.K. , Varghese Oomman K. , Paulose Maggie , Mukherjee Niloy , Grimes Craig A.
Published: March 2008

Using anodic oxidation with a time-dependent linearly varying anodization voltage, we have made films of tapered, conical-shaped titania nanotubes. The tapered, conical-shaped nanotubes were obtained by anodizing titanium foil in a 0.5% hydrofluoric acid electrolyte, with the anodization voltage linearly increased from 10-23 V at rates varying from 2.0-0.43 V/min. The linearly increasing anodization voltage results in a linearly increasing nanotube diameter, with the outcome being an array of conical-shaped nanotubes approximately 500 nm in length. Evidence provided by scanning electron-microscope images of the titanium substrate during the initial stages of the anodization process enabled us to propose a mechanism of nanotube formation.
Synthesis and dielectric properties of tungsten-based complex perovskites
Authors: Khalyavin D.D. , Han Jiaping , Senos A.M.R , Mantas P.Q.
Published: March 2008

Ba2MeWO6 (Me=Mg, Ni, Zn) double perovskites were prepared by the conventional solid-state reaction in a wide temperature range. Single-phase ceramics were obtained only at low temperatures approximately 1200°C, whereas a small amount of second phases existed in the samples sintered at higher temperatures. All the compounds are characterized by the cubic perovskite structure (space group Fm3m) with a complete NaCl type ordering between B-site ions. Anomalous temperature variation of the dielectric loss tangent found in the Ba2NiWO6 perovskite is supposed to be connected with a dielectric relaxation due to electronic hopping within thermally activated Ni3+-6W(6-1/6)+/W5+-6Ni(2+1/6)+ clusters. Dielectric measurements showed that the other two perovskites—Ba2ZnWO6 and Ba2MgWO6—exhibit a positive value of the temperature coefficient of permittivity. Such temperature variation is assumed to be caused by a considerable influence of the second polar mode involving B-site ion vibrations on the low-frequency dielectric properties.
Effect of water/water vapor on microstructure and phase stability of (Y0.25Bi0.75)2O3solid electrolytes
Authors: Huang Chaur-Chi , Fung Kuan-Zong
Published: March 2008

Highly conductive cubic (Y0.25Bi0.75)2O3tends to transform to rhombohedral (Y0.25Bi0.75)2O3when annealed at 600°C for more than 200 h. Although the rhombohedral phase of (Y0.25Bi0.75)2O3was known to be the stable phase at temperatures ≤600°C, it was found that the annealed (Y0.25Bi0.75)2O3was not thermodynamically stable in the water-containing environment. From x-ray diffraction and transmission electron microscopy analysis, it was observed that the annealed (Y0.25Bi0.75)2O3easily decomposed into monoclinic α-Bi2O3and yttrium hydroxide at a temperature as low as 50°C. The monoclinic α-Bi2O3further reacted with CO2and formed Bi2O2CO3. Consequently, the annealed (Y0.25Bi0.75)2O3degraded and became flaky powder. Scanning electron microscopy micrographs of water-reacted (Y0.25Bi0.75)2O3also showed surface swelling and peeling. Such surface deterioration was caused by a large volume increase during the water reaction. Similar reaction was also observed when the annealed (Y0.25Bi0.75)2O3was exposed in the humidified air at 300°C. As the temperature was raised to 500°C, little reaction was observed between water vapor and (Y0.25Bi0.75)2O3. The better stability of (Y0.25Bi0.75)2O3at elevated temperature was observed.
Transmission electron microscopic studies on an initial stage in the conversion process from α-tricalcium phosphate to hydroxyapatite
Authors: Tamai Masato , Isshiki Toshiyuki , Nishio Koji , Nakamura Mitsuhiro , Nakahira Atsushi , Endoh Hisamitsu
Published: March 2008

The microstructural changes in the initial stage of a conversion process of α-tricalcium phosphate [α-Ca3(PO4)2] (α-TCP) to hydroxyapatite [Ca10(PO4)6(OH)2] (HAp) by the hydrolysis method were investigated by transmission electron microscopy (TEM). To investigate the microstructural changes that take place during the conversion process, we prepared two types of α-TCP specimens for TEM: α-TCP powder and sintered α-TCP thin film. According to our results, the microstructural changes can be summarized as follows. At first, the surface of the α-TCP was covered with an amorphous calcium phosphate layer, resulting from hydration or the dissolution of α-TCP. Subsequently, the nucleation of HAp occurred on the amorphous layer, and then dendritic structures appeared on the layer. Thereafter, the dendritic structures would grow into needlelike fine HAp crystals.
Molecular orientation of methylene blue intercalated in layer-charge-controlled montmorillonites
Authors: Kaneko Yoshiro , Iyi Nobuo , Bujdák Juraj , Sasai Ryo , Fujita Takektoshi
Published: March 2008

The effect of the layer-charge density of clay on the orientation and aggregation of a cationic dye, methylene blue (MB), in MB/clay films was investigated using a series of layer-charge-controlled montmorillonites as host materials. Polarized ultraviolet-visible spectroscopy and x-ray diffraction were used for the characterization of the arrangement and orientation of dye cations in host interlayer spaces. It was revealed that high charge densities of layers induced the formation of relatively ordered and homogeneous phases with dye dimers. The reduction of the charge led to the formation of disordered, mixed phases with large amounts of monomers (isolated dye cations). Dimers and monomers were slightly tilted against the plane of the clay surface, and their angles were not affected by the layer charge.
Carbon-coated titania nanostructured particles: Continuous, one-step flame-synthesis
Authors: Kammler Hendrik K. , Pratsinis Sotiris E.
Published: March 2008

Concurrent synthesis of titania-carbon nanoparticles (up to 52 wt.% in C) was studied in a diffusion flame aerosol reactor by combustion of titanium tetraisopropoxide and acetylene. These graphitically layered carbon-coated titania particles were characterized by high-resolution transmission electron microscopy (HRTEM), with elemental mapping of C and Ti, x-ray diffraction (XRD), and nitrogen adsorption [Brunauer-Emmett-Teller (BET)]. The specific surface area of the powder was controlled by the acetylene flow rate from 29 to 62 m2/g as the rutile content decreased from 68 to 17 wt.%. Light blue titania suboxides formed at low acetylene flow rates. The average XRD crystal size of TiO2 decreased steadily with increasing carbon content of the composite powders, while the average BET primary particle size calculated from nitrogen adsorption decreased first and then approached a constant value. The latter is attributed to the formation of individual carbon particles next to carbon-coated titania particles as observed by HRTEM and electron spectroscopic imaging.
Diffusion and isotope effect in bulk-metallic glass-forming Pd–Cu–Ni–P alloys from the glass to the equilibrium melt
Authors: Zöllmer Volker , Raätzke Klaus , Faupel Franz
Published: March 2008

We report on radiotracer diffusion measurements in metallic bulk-glass-forming Pd-Cu-Ni-P alloys. The Pd-Cu-Ni-P system, with its high stability against crystallization, allows diffusion measurements from the glassy state to the equilibrium melt for the first time. Serial sectioning was performed by grinding and ion-beam sputtering. The time and temperature as well as mass dependence, expressed in terms of the isotope effect E, of codiffusion were investigated. In the glassy state as well as in the deeply supercooled state below the critical temperature Tc, where the mode-coupling theory predicts a freezing-in of liquidlike motion, the measured very small isotope effects indicated a highly collective hopping mechanism. Below Tc, the temperature dependence showed Arrhenius-type behavior. Above Tc, the onset of liquidlike motion was evidenced by a gradual drop of the effective activation energy, resulting from the decay of hopping barriers, and by the validity of the Stokes-Einstein equation, which was found to break down below Tc. This strongly supports the mode-coupling scenario. Isotope effect measurements, which have never been carried out near Tc in any material, showed atomic transport up to the equilibrium melt to be far away from the hydrodynamic regime of uncorrelated binary collisions. The latter appears to be a prerequisite of excellent glass-forming abilities.
Effects of surface treatment on the adhesion of copper to a hybrid polymer material
Authors: Ge J. , Turunen M.P.K. , Kusevic M. , Kivilahti J.K.
Published: March 2008

The effects of various surface pretreatments on the adhesion of electroless and sputter-deposited copper metallizations to a hybrid polymer material were investigated. Without pretreatment, the adhesion between copper and the polymer was virtually zero. The adhesion of electroless copper to the polymer was poor regardless of the pretreatment used. However, the wet-chemical pretreatment of the polymer surface markedly increased the adhesion of sputtered copper to the polymer. It preferentially removed the inorganic part of the polymer and formed micropores on the surface. The plasma and reactive ion etching pretreatments, in turn, selectively etched away the organic part of the polymer and noticeably increased the hydrophilicity. Although this resulted in even higher increase in the surface free energy than was achieved with the chemical treatment, the granular surfaces became mechanically brittle. With the help of x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and contact-angle measurements and with the recently developed pull test, the physicochemical changes of the wet-chemically pretreated polymer surfaces were demonstrated to have significant effects on the adhesion.
Influence of sulfur incorporation on field-emission properties of microcrystalline diamond thin films
Authors: Gupta S. , Weiner B.R. , Morell G.
Published: March 2008

Results are reported on the electron field emission properties of microcrystalline diamond thin films grown on molybdenum substrates by the sulfur (S)-assisted hot-filament chemical vapor deposition technique using methane (CH4), hydrogen sulfide (H2S), and hydrogen (H2) gas mixtures. Electron field-emission measurements revealed that the S-incorporated microcrystalline diamond thin films have substantially lower turn-on fields and steep rising currents as compared to those grown without sulfur. The field-emission properties for the S-incorporated films were also investigated systematically as a function of substrate temperature (TS). Lowest turn-on field achieved was observed at around 12.5 V/μm for the samples grown at TS of 700°C with 500 ppm H2S. To establish the property-structure correlation, we analyzed the films with multiple characterizations include scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy (RS), and x-ray photoelectron spectroscopy (XPS) techniques. It was found that sulfur addition causes significant microstructural changes in microcrystalline diamond thin films. S-assisted films show smoother, coarse-grained surfaces (non-faceted) than those grown without it (well-faceted) and a relatively higher content of non-diamond carbon (primarily sp2-bonded C). RS and investigations on the morphology by SEM and AFM indicated the increase of sp2 C content with increasing TS followed by a morphological transition at 700°C in the films. XPS investigations also showed the incorporation of S in the films up to a few atomic layers. It is believed that the electron-emission properties are governed by the sulfur incorporation during the chemical vapor deposition process. Although most of the S is expected to be electrically inactive, under the high doping conditions hereby used, it is shown rather indirectly through multiple characterizations that there may be some amount of S in donor states. Therefore the results are discussed in terms of the dual role of S whereby it induces the structural defects in the form of enhanced sp2 C content at the expense of diamond quality and a possibility of availability of conduction electrons. In fact the latter finding is supported through room temperature electrical conductivity measurements.
Structural characterization of the C60[C(COOC2H5)2] whiskers prepared by the liquid–liquid interfacial precipitation method
Authors: Miyazawa Kun'ichi , Mashino Tadahiko , Suga Tadatomo
Published: March 2008

Fine whiskers of a C60 derivative, i.e., C60 monosubstituted by ethyl ester of malonic acid, C60[C(COOC2H5)2], were fabricated for the first time using a system of toluene with concentrated C60[C(COOC2H5)2] and isopropyl alcohol. The center-to-center distance of C60[C(COOC2H5)2] molecules along the close-packed direction of the C60[C(COOC2H5)2] whiskers was in the same range as that of the C60 nanowhiskers prepared by the same method. The C60[C(COOC2H5)2] whiskers were assumed to take body-centered tetragonal or hexagonal close-packed crystal structures. The C60[C(COOC2H5)2] whiskers showed a high density of stacking faults. The C60[C(COOC2H5)2] whiskers with the growth direction different from the C60 whiskers were observed.