bluuebunny/crossref_metadata_2025 huggingface dataset:
The electrical properties of La2CuO4/ZnO heterocontacts at different relative humidities
Authors: Traversa Enrico , Bearzotti Andrea , Miyayama Masaru , Yanagida Hiroaki
Published: September 2007

The humidity-sensing electrical properties of heterocontacts betweenp-type La2CuO4andn-type ZnO semiconductors, and of the single oxides, as a comparison, were studied. The heterocontacts was prepared by mechanically pressing sintered disks of the two oxides. The electrical characterization of the heterocontacts was carried out using dc and ac measurements at various relative humidity (RH) values, in order to evaluate the sensing mechanisms and the electrical properties of thesep-njunctions. Their humidity sensitivity was explained in terms of the variation of the barrier height at thep-njunctions, due to the saturation of the original interface states by physisorbed water, which leads to the release of trapped electrons, resulting in an increase in the forward current. The higher the number of interface states, the higher the RH-sensitivity of the heterocontacts. Electrochemical impedance spectroscopy (EIS) measurements showed, at 90% RH, a distribution of capacitances with different relaxation times, which may be caused by the electrolysis of water molecules atp-njunction sites. For their use as humidity sensors, they showed a response of 4 orders of magnitude in the whole RH range tested, and a fast response time. The response of the heterocontacts was bias-dependent, tunable by externally applied electric field. They also have stand-by capability and a self-cleaning mechanism, which allow them to be described as intelligent materials.
Loss spectra of pure and La-doped MgTiO3 microwave ceramics
Authors: Ferreira V.M. , Baptista J.L. , Petzelt J. , Komandin G.A. , Voitsekhovskii V.V.
Published: September 2007

Pure and La-doped magnesium titanate (MgTiO3) microwave ceramics were sintered and structurally and dielectrically characterized. Doping provides small inclusions of a second phase found to correspond to the La2Ti2O7 compound. It increases the microwave dielectric loss appreciably and gives rise to three absorption peaks in the submillimeter range assigned to polar phonons of the La2Ti2O7 structure. This assignment was confirmed by a direct reflectivity measurement on La2Ti2O7 ceramics. From the temperature dependence of submillimeter losses in the pure sample, one can estimate that from 1000 down to at least 8 GHz about half of the room temperature losses are intrinsic, i.e., due to two-phonon absorption processes.
Chemistry, microstructure, and electrical properties at interfaces between thin films of platinum and alpha (6H) silicon carbide (0001)
Authors: Porter L.M. , Davis R.F. , Bow J.S. , Kim M.J. , Carpenter R.W.
Published: September 2007

Thin films (4-1000 Å) of Pt were deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type α (6H)-SiC(0001) substrates and examined in terms of chemistry, microstructure, and electrical properties. The as-deposited contacts were polycrystalline and showed excellent rectifying behavior with low ideality factors (n < 1.1) and leakage currents of 5 × 10−8 A/cm2 at −10 V. The Schottky barrier height increased from 1.06 eV before annealing to 1.26 eV after successive 20 min anneals at 450, 550, 650, and 750 °C. In addition, the leakage currents decreased to 2 × 10−8 A/cm2 at −10 V. Interfacial reactions were not observed at annealing temperatures below 750 °C; above this temperature, Pt2Si and C precipitates were identified in the reaction zone.
Electrical and photoconductive properties of boron-doped potycrystalline diamond films
Authors: Zhang Wenjun , Hu Bo , Xie Erqin , Zhang Yafei , Han Li , Song Zhizhong , Chen Guanghua
Published: September 2007

The current-voltage (I-V) characteristics and time-dependence photoconductivity of the undoped and B-doped diamond films (DF's) before and after annealing were investigated. The boron and hydrogen concentration in diamond films were measured by means of nuclear reaction analysis (NRA) and the elastic-recoil detection (ERD) technique, respectively. The results show that induced boron atoms and hydrogen atoms affect the electrical and photocoaductive properties of diamond films. During the annealing process, B concentration kept even, but H content decreased. For undoped diamond films, the escaping of H atoms has great effects on the electrical characteristics, but for B-doped samples, this effect decreases with the increase of B concentration.
A comparison of C54-TiSi2 formation in blanket and submicron gate structures using in situ x-ray diffraction during rapid thermal annealing
Authors: Clevenger L.A. , Roy R.A. , Cabral C. , Saenger K.L. , Brauer S. , Morales G. , Ludwig K.F. , Gifford G. , Bucchignano J. , Jordan-Sweet J. , DeHaven P. , Stephenson G.B.
Published: September 2007

We demonstrate the use of a synchrotron radiation source for in situ x-ray diffraction analysis during rapid thermal annealing (RTA) of 0.35 μm Salicide (self-aligned silicide) and 0.4 μm Polycide (silicided polysilicon) TiSi2 Complementary Metal Oxide Semiconductor (CMOS) gate structures. It is shown that the transformation from the C49 to C54 phase of TiSi2 occurs at higher temperatures in submicron gate structures than in unpatterned blanket films. In addition, the C54 that forms in submicron structures is (040) oriented, while the C54 that forms in unpatterned Salicide films is randomly oriented. Although the preferred oreintation of the initial C49 phase was different in the Salicide and Polycide gate structures, the final orientation of the C54 phase formed was the same. An incomplete conversion of C49 into C54-TiSi2 during the RTA of Polycide gate structures was observed and is attributed to the retarding effects of phosphorus on the transition.
Structural properties of unconventional lead cuprate glass
Authors: Hazra S. , Ghosh A.
Published: September 2007

Glass formation and structural properties of the unconventional lead cuprate glasses of compositions (CuO)x (PbO)100−x (mol %), are reported for the first time. X-ray diffraction and electron microscopic studies show that the glass formation occurs for x = 15-50 mol%. The compositional dependence of the density, molar volume, and glass transition temperature suggests that all glass compositions in this domain have the same topology and network connectivity. The glass structure is built up of [PbO4] tetrahedral units. On heat treatment above glass transition temperatures, the glasses crystallize to CuO and PbO. Electron Spin Resonance (ESR) spectra of the glass compositions consist of broad resonance lines.
Diffusion of water in silica glass
Authors: Doremus Robert H.
Published: September 2007

The diffusion of water into silica glass is modeled to result from the diffusion of molecular water into the glass and its reaction with the silicon-oxygen network to form SiOH groups. Equations for this diffusion-reaction mechanism are presented and compared with experimental diffusion profiles. At temperatures above about 500 °C the reaction goes to equilibrium, but at lower temperatures it does not, leading to a time dependence of the concentration of surface-reacted OH groups and of their apparent diffusion coefficient. At higher temperatures, the OH groups are nearly immobile, but diffuse far enough to sample neighboring OH groups, leading to a bimolecular reverse reaction. At lower temperatures only OH pairs react, giving a first-order reaction. When water tagged with O18 diffuses into silica, the O18 exchanges with O16 in the silicon-oxygen network of the glass. This process is also controlled by the rate of diffusion of molecular water into the glass, and the rate of O18-O16 exchange. This diffusion-reaction mechanism gives a unified description of the diffusion of water in silica glass from 160 °C to 1200 °C at least.
The Debye temperature of nanocrystalline β–Sn measured by x-ray diffraction
Authors: Hong L.B. , Ahn C.C. , Fultz B.
Published: September 2007

A nanocrystalline β–Sn film of 7 nm average grain size was prepared by inert gas condensation followed by ballistic consolidation, and was investigated by x-ray diffractometry at temperatures of 77 and 293 K. Although Sn normally undergoes a βα phase transformation at 286 K, this transformation was suppressed in the nanocrystalline film. Compared with large-grained β-Sn, a larger Debye–Waller factor and a lower Debye temperature were measured for nanocrystalline β-Sn; ΘD = 133 K for nanocrystalline material while ΘD = 161 K for large-grained material. The lower Debye temperature of the nanocrystalline β-Sn indicates that its vibrational entropy is increased by 0.6 kB/atom with respect to large-grained material.
SiC–Al–Si composites by rapid pressureless infiltration in air
Authors: Yang X.F. , Xi X.M.
Published: September 2007

A rapid, pressureless infiltration technique for fabricating SiC-reinforced Al-Si composites is described. The infiltration can be performed by simply dipping a ceramic preform into a molten alloy in an open air environment. This method makes it possible to produce composites that contain a high volume fraction (80%) of a variety of ceramic reinforcements, including particulates and fibers. This technique has potential for low-cost and versatile production of SiC-Al-Si composites for many industrial applications, such as automobile components and electronic packaging.
Fabrication and characterization of highly textured (Bi,Pb)2Sr2Ca2Cu3Ox superconducting ceramics using high magnetic field and cold isostatic pressing
Authors: Lo Wai , Stevens R. , Doyle R. , Campbell A.M. , Liang W.Y.
Published: September 2007

High textured (Bi,Pb)2Sr2Ca2Cu3Ox ceramics have been fabricated by aligning deflocculated flakes of (Bi,Pb)2Sr2Ca2Cu3Ox suspended in an organic medium by means of a high de magnetic field (6 T) at room temperature followed by cold isostatic pressing. The proportion of the (Bi,Pb)2Sr2Ca2Cu3Ox phase in the precursor powder was carefully controlled, and the characteristics of the powder, such as size distribution and morphology, were determined. A high degree of grain alignment was found in the specimens after the magnetic alignment, although the bulk density of the materials was low. Cold isostatic pressing substantially increased the density of the magnetically prealigned specimens which also resulted in a slight decrease in the degree of grain alignment. This minor realignment was found to be due to the various kinds of processing defects that appeared in the specimens during compaction due to the grinding and cracking of the grains and their interlocking. The microstructural and superconducting properties of the sintered ceramic have been studied using texture goniometry, high resolution scanning electron microscopy, transmission electron microscopy, ac magnetic susceptometry, and critical current measurements.
The influence of the reactant size on the micropyretic synthesis of NiAl intermetallic compounds
Authors: Li H.P. , Sekhar J.A.
Published: September 2007

The effect of the nickel (Ni) and aluminum (Al) reactant particle size on the micropyretic synthesis of NiAl is studied in this article. A change in the low melting component (Al particle) size is noted to have a limited influence on the micropyretic synthesis conditions. However, a change in the high melting component (Ni particle) size not only influences the combustion temperature and propagation velocity, but also affects the final porosity and grain size of the synthesized products. The combustion mode is also noted to change from stable to unstable when the Ni particle size is increased. It is noted that a diffusion-type control mechanism is dominant for the rapid reaction sequence in the NiAl system. An atomistic mechanism of the Ni-Al micropyretic reaction is also proposed in this article. Following this model, analytical expressions are developed to relatc the variation of the Ni size to the NiAl formation rate with the imposed processing conditions during the micropyretic synthesis. The mechanism of the final grain formation and the grain size changes with changes in the processing variables is also discussed.
Silicon carbide fiber-reinforced alumina extrusion
Authors: Blackburn S. , Böhm H.
Published: September 2007

Silicon carbide fiber-reinforced alumina bodies have been produced by ram extrusion. The Al2O3 powder and SiC fiber were milled together to give a dry dispersion of up to 30 vol % fiber which was subsequently mixed to a paste by high shear kneading using hydroxypropylmethylcellulose solutions as the binder phase. Extruded bodies with green densities ranging between 56 and 63% full theoretical density were achieved. The paste flow behavior was characterized using physically based equations which show that for any given moisture content the pressure drop and the constituent paste parameters are all systematically reduced as the fiber loading is increased. This observation can be explained almost completely by combining packing theory with the paste rheology data. Fiber interactions within the paste and the die system appear not to greatly influence the rheological character of the material. It is shown statistically that the fibers are homogeneously dispersed throughout the paste mass after extrusion. Image analysis has been used to aid in macrodefect analysis, and it is shown that the optimum concentration of fiber was 20 vol % with a quantity of binder sufficient to give an initial yield stress of 2 MPa.
Measurement of surface topography and area-specific nanohardness in the scanning force microscope
Authors: Scholl D. , Everson M.P. , Jaklevic R.C.
Published: September 2007

A Scanning Force Microscope (SFM) is employed to indent and image surfaces with sub-micron resolution. The SFM image shows the area and depth of each indentation as well as its location with respect to nearby topographic surface features. The image also reveals the surface roughness, which can set a lower limit on useful nanoindentation size. A cross section of a nitrided steel surface is measured to illustrate the method. The use of the SFM with separate tip-cantilever structures for indenting and imaging has significant advantages over other nanohardness methods for the study of samples with lateral inhomogeneities.
Analysis of pore structure of activated carbon fibers using high resolution transmission electron microscopy and image processing
Authors: Oshida K. , Kogiso K. , Matsubayashi K. , Takeuchi K. , Kobayashi S. , Endo M. , Dresselhaus M.S. , Dresselhaus G.
Published: September 2007

Activated carbon fibers (ACF's), already used widely as absorbent materials, are now expected to be useful as new electrical and electronic materials, for their very large specific surface areas (SSA). Chemical adsorption as well as x-ray diffraction have been mainly used for characterizing the ACF structure. While TEM observations reveal the texture of ACF's, such observations have not yet yielded quantitative information about the microstructure. To promote the quantitative interpretation of the TEM images, computer image analysis is used in this work to clarify the pore structure of ACF's. The microstructures of three samples, which are all isotropic pitch-based ACF's but with different SSA values, have been investigated. Operations such as noise reduction, low frequency cut-off filtering, and binary image formation are used to clarify the pore images of the ACF's. The distribution of the ACF porosity size is clearly shown by a frequency analysis of the two-dimensional fast Fourier transform (FFT). The results suggest that TEM images include contributions from many different pore sizes. Pores in different size ranges are extracted by the inverse FFT (IFFT) operation by selecting the specific frequency range, and by-this analysis the pore structure is shown to have fractal characteristics.
Synthesis of titanium boride (TiB)2 nanocrystallites by solution-phase processing
Authors: Bates Susan E. , Buhro William E. , Frey Claire A. , Sastry Shankar M.L. , Kelton K.F.
Published: September 2007

Nanocrystalline TiB2 is prepared by reaction of NaBH4 and TiCl4. The initial solution-phase reaction affords an amorphous precursor powder from which 5-100 nm TiB2 crystallites are obtained upon annealing at 900-1100 °C. Crystallite sizes depend on the annealing temperature and other processing parameters. Crystallite morphology is size dependent; crystallites smaller than 12-15 nm are cuboidal, whereas crystallites larger than 12-15 nm are hexagonal platelets. The procedure affords gram quantities of the smallest available TiB2 nanocrystallites.
Generation of amorphous ceramic capacitor coatings on titanium using a continuous sol-gel process
Authors: Dixon Brian G. , Walsh Myles A. , Phillips Peter G. , Scott Morris R.
Published: September 2007

Thin amorphous films of ceramic capacitor materials were successfully deposited using sol-gel chemistry onto titanium wire using a continuous, computer-controlled process. By repeatedly depositing and calcining very thin layers of material, smooth and even coats can be produced. Surface analyses revealed the layered nature of these thin coats, as well as the amorphous nature of the ceramic. The electrical properties of the better coatings, all composed of niobrium, bismuth, and zinc oxides, were then evaluated.
YBa2Cu3O7−δ on MgO films grown by pulsed organometallic beam epitaxy and a grain boundary junction application
Authors: Dean K.A. , Buchholz D.B. , Marks L.D. , Chang R.P.H. , Vuchic B.V. , Merkle K.L. , Studebaker D.B. , Marks T.J.
Published: September 2007

MgO films and YBa2Cu3O7−δ/MgO multilayer films were developed with the pulsed organometallic beam epitaxy (POMBE) growth technique, and grain boundary junctions were fabricated from the films to demonstrate the utility of the multilayers. High-quality MgO films were grown on LaAlO3 substrates by POMBE using a Mg(dpm)2 precursor. MgO crystallinity, as assessed by x-ray diffraction rocking curves, improved with the use of CuOx or YBa2Cu3O7−δ buffer layers. YBa2Cu3O7−δ films grown on the MgO layer by POMBE exhibited a Tc0 of 83 K and a Jc (12 K) exceeding 106 A/cm2 for applied magnetic fields up to 3 × 104 G. Grain boundary junctions were formed by growing YBa2Cu3O7−δ on MgO films that had been pretreated with a simple sputtering technique. This sputtering induces a controlled, 45°grain boundary in subsequently deposited YBa2Cu3O7−δ films. The resulting boundary showed weak-link current-voltage behavior and an IcRn product of 52 μV at 10 K, demonstrating that sputter-induced grain boundary junctions are compatible with multilayer technology.
Excimer laser-induced doping of crystalline silicon carbide films
Authors: Krishnan S. , D'Couto G.C. , Chaudhry M.I. , Babu S.V.
Published: September 2007

0.25 μm thick, single crystal, n-type, silicon carbide (β-SiC) films thermally grown on p-type Si(100) were doped with boron by using KrF excimer laser radiation and a spin-on dopant with a boron concentration of 1020/cm3. The threshold fluence for the doping to occur was approximately 0.08 J/cm2. Similarly, p-SiC/n-SiC diodes were fabricated by laser-induced doping of single-crystal β-SiC (n-type, 6 μm thick) films on n-type Si(100). The diodes obtained at 0.25 J/cm2 showed good rectifying characteristics. The threshold fluence for surface modification and/or ablation was approximately 0.3 J/cm2, indicating that doping and diode formation have to be accomplished within the fluence window of 0.08 J/cm2-0.3 J/cm2 for these films.
Changes in surface area and composition during grinding of silicon in environments of various quality
Authors: Tkáčová Klára , Števulová Nadežda , Bastl Zdeněk , Stopka Pavel , Bálintová Magdaléna
Published: September 2007

Changes in particle size, surface properties, and composition brought about by planetary grinding of silicon in air and various permittivity liquids were investigated. Using a variety of spectroscopic techniques (ESR, IRS, and XPS), a mechanically induced surface oxidation was proved. While at grinding in air and organic liquids a part of the centers originating from dangling orbitals on SiIIIare preserved, the properties of water-ground silicon are fully governed by the oxide surface shell. The most effective particle size reduction and surface protection can be reached by grinding in nonpolar liquids.
Observation and analysis of extended dislocations in an Al–Pd–Mn icosahedral quasicrystal by transmission electron microscopy
Authors: Feng Jianglin , Wang Renhui , Dai Mingxing
Published: September 2007

Extended dislocations including partial dislocations and a stacking fault in Al70Pd20Mn10 icosahedral quasicrystal have been observed and identified for the first time. The diffraction contrast and defocus convergent-beam electron diffraction experiments show that the dissociation of the extended dislocations is of the form 1/2<1 −2 0 0 −2 1> → 1/4<1 −3 1 −1 −1 1>+ 1/4<1 −1 −1 1 −xs3 1> with a stacking fault between these two partial dislocations. For the partial dislocations, the Burgers vector components in physical space b¶part are along different fivefold axes with a magnitude of 0.17 nm, which is about one seventh of that in complementary space. For the perfect dislocation, the Burgers vector component in physical subspace b¶perf is along a twofold axis with a magnitude of 0.183 nm, which is about an eleventh of that in complementary space.
“Square” hysteresis loops in phase-switching Nb-doped lead zirconate stannate titanate thin films
Authors: Gaskey C.J. , Udayakumar K.R. , Chen H.D. , Cross I.E.
Published: September 2007

Niobium-doped lead zirconate stannate titanate thin films have been prepared by a modified sol-gel spin on technique, utilizing the hydrolysis-resistant precursor lead acetylacetonate. Films of compositions in the antiferroelectric tetragonal and antiferroelectric orthorhombic phases were prepared and phase-switched with the application of appropriate electric fields. A distinctly “square” hysteresis response was observed in a low titanium, low tin, orthorhombic composition, with a maximum polarization, Pmax, of 40 μC/cm2 and switching field values of Ef = 175 kV/cm and Ea = 75 kV/cm, while varying degrees of squareness, along with lower polarizations and switching fields, were observed in the higher tin, tetragonal compositions. Electric field-induced strains of up to 0.33% have been measured in the orthorhombic composition, with tunable electromechanical coefficients. Film properties showed only slight variation with electrode size over a range of diameters from 0.8 mm to 6.35 mm; large area electrodes are vital for practical actuator and sensor devices. With a capacitance density of 30–35 μF/cm2, films of the orthorhombic composition are promising as power plane decoupling capacitors in multichip modules.
Calibration of the Raman effect in α–Al2O3 ceramic for residual stress measurements
Authors: Gallas M.R. , Chu Y.C. , Piermarini G.J.
Published: September 2007

The pressure shifts of the 418 and 379 cm−1 Raman lines of polycrystalline α-Al2O3 ceramic were measured at room temperature to 3190 MPa. A diamond anvil high pressure cell was used in conjunction with a microRaman spectrometer system. Pressures were measured by the ruby fluorescence method. Distilled water was used as the pressure transmitting medium. The pressure dependence of the wave number for the hydrostatic range (to 1585 MPa) was found to be 0.00220 ± 0.00007 cm−1 MPa−1 for the 418 cm−1 Raman line and 0.0011 ± 0.0001 cm−1 MPa−1 for the 379 cm−1 line. Both shifts are based on a linear least squares fit to the data within a 95% confidence interval. Measurements that included the nonhydrostatic regime (to 3190 MPa) gave similar shifts, but with almost twice the uncertainty. Absolute residual stresses in alumina ceramics are in the 200 to 600 MPa range with higher values, 1790 MPa, reported for single-crystal alumina. For the 418 cm−1 Raman line, these values correspond to shifts of 0.4, 1.4, and 3.9 cm−1, respectively. The sensitivity of the microRaman technique is sufficient to detect and measure residual stresses of this magnitude.
The mechanism and kinetics of the niobium-carbon reaction under self-propagating high-temperature synthesis-like conditions
Authors: He Cheng , Stangle Gregory C.
Published: September 2007

The mechanism and kinetics of the chemical reaction between Nb(s) and C(s) under self-propagating high-temperature synthesis (SHS)-like (or combustion synthesis-like) conditions have been studied. Experiments were designed and conducted in order to produce a transport-resistance-free reaction between Nb and C under time-temperature conditions that are characteristic of the combustion synthesis process. To do so, a reaction couple, consisting of carbon and either a thin niobium foil or a fine niobium wire, was used. The effects of the temperature history and the formation of a liquid phase on the reaction were studied. In addition, theoretical experiments of the reaction were also conducted. The results showed that at high temperatures, layered niobium carbide phases formed in a direction that was parallel to the original carbon-niobium interface. As might be expected, local melting played a very significant role in the reactions. The mechanism and kinetics of these reactions provide a fundamental understanding of the manner and rate by which a powder-based Nb/C SHS process takes place, and, by extension, to a large, general class of solid-solid material synthesis processes that are based on the SHS (or combustion synthesis) process.
Effect of composition on phase formation and morphology in Ti–Si1−xGex solid phase reactions
Authors: Aldrich D.B. , Chen Y.L. , Sayers D.E. , Nemanich R.J. , Ashburn S.P. , Öztürk M.C.
Published: September 2007

The effects of Si1−xGex alloy composition on the Ti-Si1−xGex solid phase reaction have been examined. Specifically, effects on the titanium gcrmanosilicide phase formation sequence. C54 Ti(Si1−yGey)2 nucleation temperature, and C54 Ti(Si1−yGey)2 morphology were examined. It was determined that the Ti-Si1−xGex reaction follows a “Ti-Si-like” reaction path for Si-rich Si1−xGex alloys and follows a “Ti-Ge-like” reaction path for Ge-rich Si1−xGex alloys. The coexistence of multiple titanium germanosilicide phases was observed during Ti-Si1−xGex reactions for Si1−xGex alloys in an intermediate composition range. The morphology and stability of the resulting C54 germanosilicides were directly correlated to the Ti-Si1−xGex reaction path. Smooth continuous C54 titanium germanosilicide was formed for samples with Si1−xGex compositions in the “Ti-Si-like” regime. Discontinuous islanded C54 germanosilicides were formed for samples with Si1−xGex compositions in the mixed phase and “Ti-Ge-like” regimes. Using rapid thermal annealing techniques, it was found that the C54 titanium germanosilicides were stable to higher temperatures. This indicated that the morphological degradation occurs after C54 phase formation. The C54 Ti(Si1−xGex)2 formation temperature was examined as a function of alloy composition and was found to decrease by ≍ 70 °C as the composition approached x ≍ 0.5. An optimum Si1−xGex alloy composition range of 0 ⋚ x ⋚ 0.36 was determined for the formation of stable-continuous-low-resistivity-C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy. The results were described in terms of the relevant nucleation processes.
Effects of deposition temperature on the electrical properties of electron cyclotron resonance plasma-enhanced chemical vapor deposition Ta2O5 film and the formation of interfacial SiO2
Authors: Kim Il , Kim Jong-Seok , Cho Bok-Won , Ahn Sung-Duck , Chun John S. , Lee Won-Jong
Published: September 2007

High-quality Ta2O5 thin films for high-density memory devices were prepared at low temperatures by electron cyclotron resonance plasma-enhanced chemical vapor depostion (ECR-PECVD) without postannealing treatment. The effects of deposition temperature on the microstructure, composition, and electrical properties of the dielectric films were studied. The increase in deposition temperature from 145 °C to 205 °C improved the stoichiometry of the Ta2O5 thin films. As a consequence, EBD increased from 3.3 MV/cm to 4.4 MV/cm, and ∊Ta2O5, increased from 14 to 25. Interfacial SiO2 layer was observed by cross-sectional TEM, and its effects on the electrical properties of the overall dielectric film were also studied. The incubation period in which interfacial SiO2 grows was discussed with regard to reactivity between oxygen and Si substrate.
Further analysis of the size effect in indentation hardness tests of some metals
Authors: Atkinson M.
Published: September 2007

The variation of apparent hardness observed in previously reported Vickers indentation tests of metals is reexamined. Common deseriptions of the effect are shown to be inaccurate: the variation of apparent hardness is monotonic but not simple. The effect is consistent with varying size of a previously postulated “plastic hinge” at the perimeter of the indent. This complexity confers uncertainty on the estimation of characteristic macrohardness from small scale tests. Association of the indentation size effect with friction and with strain hardening is confirmed.
Equilibrium phase diagrams in the system CuO–PbO–Ag
Authors: Liu H.K. , Dou S.X. , Ionescu M. , Shao Z.B. , Liu K.R. , Liu L.Q.
Published: September 2007

Silver has played a critical role for the fabrication of metal/high temperature superconductor composites. Phase equilibrium and microstructure in the ternary PbO-CuO-Ag system have been investigated using differential thermal analysis (DTA), thermogravimetry (TG), scanning electron microscope (SEM), and x-ray diffraction (XRD) techniques. Composition versus temperature diagrams have been established for these systems in air. In the ternary CuO-PbO-Ag system, there is a eutectic reaction CuO + PbO + Ag = L at 750 °C and a composition of 12.04 mol % Ag, 16.35 mol % CuO, and 72.62 mol % PbO. Two immiscible regions near the two binary tie lines PbO-Ag and CuO-Ag were detected. No binary or ternary compound was detected in these systems. SEM and EDS results confirm the presence of two liquid phases and the eutectic point
In situ reduction kinetics of NiCl2 in SiO2 gel matrix
Authors: Basumallick A. , Biswas K. , Das G.C. , Mukherjee S.
Published: September 2007

Silica gcls containing NiCl2 and dextrose have been reduced by heat-treating the gels under N2 atmosphere at 800 °C, 850 °C, 900 °C, and 950 °C, respectively. The influence of the volume ratio of ethyl alcohol to tetraethylorthosilicate and the amount of dextrose on the in situ reduction kinetics of NiCl2 in gel matrix have been investigated. The kinetic data on in situ reduction have been analyzed by a reduced time method which indicates that mixed mechanisms are operative. The predominant mechanism of reduction of NiCl2 in SiO2 gel matrix is of nucleation and growth type. The activation energies over different temperatures and fraction converted have been computed by the integration method.
Lattice distortion effects on electrical switching in epitaxial thin film NdNiO3
Authors: DeNatale J.F. , Kobrin P.H.
Published: September 2007

Crystalline thin films of NdNiO3 have been epitaxially grown on the (100) face of single-crystal LaAlO3 substrates. These films exhibit the characteristic reversible change in electrical conductivity with temperature previously observed in bulk polycrystalline material. The temperature of the electrical transition in the epitaxial thin films was lower than reported for the bulk polycrystalline ceramics. This effect is attributed to lattice strains associated with the film processing and interfacial lattice matching constraints.
Patterning of dielectric oxide thin layers by microcontact printing of self-assembled monolayers
Authors: Jeon N.L. , Clem P.G. , Nuzzo R.G. , Payne D.A.
Published: September 2007

This communication describes a technique used to pattern oxide thin layers using microcontact printing (μCP) and sol-gel deposition. The technique involves μCP of self-assembled monolayers (SAM's) of alkylsiloxane on various substrates (SiO2/Si, sapphire, ITO, and glass), followed by deposition of oxide thin layers from sol-gel precursors. Delamination of oxide layers from SAM-derivatized regions allows selective deposition of crystalline dielectric oxide layers on underivatized regions. To demonstrate the viability of this technique for integrated microelectronics and optics applications, patterned (Pb,La)TiO3 (PLT) and LiNbO3 layers were deposited on sapphire, silicon, and indium tin oxide (ITO) substrates. Use of lattice-matched substrates allows lithography-free deposition of patterned heteroepitaxial oxide layers. Strip waveguides of heteroepitaxial LiNbO3 with 4 μm lateral dimensions were fabricated on sapphire. Dielectric measurements for patterned PLT thin layers on ITO are also reported.
Thin film deposition and interface characterization of YBCO on LiNbO3 substrates
Authors: Wu N.J. , Li X.Y. , Li J. , Lin H. , Fredricksen H. , Xie K. , Mesarwi A. , Ignaticv A. , Shih H.D.
Published: September 2007

High transition temperature superconducting YBa2Cu3O7−x (YBCO) thin films have been epitaxially grown on YZ-cut LiNbO3 (LNO) substrates by the pulsed laser deposition technique. The interface between YBCO and LNO has been systematically investigated by scanning electron microscopy, atomic force microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Off-stoichiometry LiNbOx phases are found to segregate on the substrate surface because of lithium and oxygen vacancies formed during the high temperature YBCO growth. These submicrometer particles are observed along the Z-axis on the X-Z plane of LNO with height of ∼30 nm above the LNO surface. This rough growth surface results in YBa2Cu3O7−x thin films grown on the LNO surface that have reduced Jc and Tc, possibly limiting the use of YBCO/LNO heterostructures for surface acoustic wave (SAW) devices.
Morphology of twinned diamond particles
Authors: Wang Long , Angus John C. , Aue David
Published: September 2007

Morphology of twinned diamond particles grown by chemical vapor deposition was characterized by atomic force microscopy in both contact and tapping modes. Quantitative angle measurements using a surface normal algorithm were performed on untwinned crystals, penetration twins, re-entrant corners, and fivefold dimples. Tip-sample interaction is discussed. The morphology of the penetration twins and some of the re-entrant corners can be explained by low order Σ3 twins and flat crystallographic surfaces. Abnormally shallow re-entrants with large vicinal faces are attributed to rapid nucleation of new layers at a point along the re-entrant intersection.
Microstructural evolution of diamond/Si(100) interfaces with pretreatments in chemical vapor deposition
Authors: Chen C.J. , Chang L. , Lin T.S. , Chen F.R.
Published: September 2007

Diamond was deposited on Si(100) substrates by the microwave plasma-assisted chemical vapor deposition method in three steps: carburization, biasing, and growth. High-resolution transmission electron microscopy in cross-sectional view has been used to observe the evolution of microstructures around the interfacial region between diamond and Si in each processing step. The chemistry near the interface was characterized with elemental mapping using an energy-filtered imaging technique with electron energy loss spectroscopy. An amorphous carbon layer, β-SiC and diamond particles, and graphite plates have been observed in the carburization stage. β-SiC can form in epitaxial orientation with Si in the following stage of biasing. Graphite and amorphous carbon were not observed after the bias was applied. Diamond grains were aligned in a strongly textured condition in the growth stage. It has been found that diamond, SiC, and Si all have (111) planes in parallel. The relation of the evolution of microstructure with the processing conditions is also discussed.
Structural properties and thermal stability of Fe/Al2O3 multilayers
Authors: Lenoble O. , Bobo J.F. , Fischer H. , Bauer Ph. , Ravet M.F. , Piecuch M.
Published: September 2007

Iron/alumina multilayers have been deposited on sapphire wafers using RF magnetron sputtering. To study the interdiffusion, the multilayers were annealed in a tubular furnace under a 10−7 mbar vacuum, and the samples examined by using a combination of classical diffractometry (θ/2θ) and Grazing Incidence Scattering (GIS) for the phase determination, and Small Angle X-ray Scattering (SAXS) for the superstructure of the multilayers. In all cases, in the as-deposited state the alumina is amorphous and the iron is crystalline in the bcc phase. Thermal anneals at temperatures between 573 and 873 K give evidence for segregation to the interfaces. At higher temperatures, interdiffusion occurs, leading to the formation of different phases. The Fe-Al2O3 interdiffusion coefficient has been evaluated in the temperature range from 873 to 1273 K.
Memory effect of ZrO2 matrix on surface Co3O4–CoO transition
Authors: Zeng H.C. , Lin J. , Tan K.L.
Published: September 2007

Cobalt oxide system Co3O4-CoO has been studied on the ZrO2 matrix surfaces with FTIR and XPS. The tetragonal and monoclinic ZrO2 matrix materials have been synthesized from the Zr-n-propoxide-acetylacetone-water-isopropanol system. The study shows that the ZrO2 matrix is able to retain the relative Co3O4:CoO population at elevated temperatures. The thermodynamically stable oxide population (Co3O4:CoO) at room temperature for ZrO2-supported Co3O4-CoO is about 50:50 (Co2+ :Co3+ = 2:1), which is markedly different from the 100:0 case (Co2+ :Co3+ = 1:2) for an unsupported Co3O4-CoO surface oxide system. The relative Co3O4 :CoO ratio in the surface region of the ZrO2 is temperature dependent but matrix-polymorph independent. The composition of an oxide solid solution formed by the Co3O4-CoO and matrices of ZrO2 is determined to have a cobalt molar percentage of 4.5%. Diffusion thermodynamic quantities are investigated, and the measured diffusion activation energy for a cobalt ion in the ZrO2 matrices is 0.21 eV. The mechanism of the ZrO2 memory effect on surface Co3O4-CoO transition will also be addressed.
Self-propagating high-temperature synthesis of TiC and NbC by mechanical alloying
Authors: Liu Z.G. , Ye L.L. , Guo J.T. , Li G.S. , Hu Z.Q.
Published: September 2007

Titanium and niobium carbides have been synthesized through self-propagating high-temperature reaction by mechanically alloying the elemental powder mixtures. It is found that this reaction is very similar to the conventional self-propagating high-temperature synthesis (SHS) process, but the ignition of the reaction is identified to be the mechanical collisions instead of heating the materials. Analysis of the products reveals that the final products of the Ti-C system are in good agreement with the equilibrium phase diagram, showing less relation with the alloying process. The decrease of the C content shortens the milling time prior to the SHS reaction of TiC by promoting the intimate mixing of the components, but lowers the heat release of the reaction and makes the propagation of the reaction more slowly. The SHS reaction during the mechanical alloying of the Nb-C system shows little difference, but the decrease of the C content can hardly influence the milling time prior to the reaction. By lowering the heat release of the SHS reaction of NbC, it lowers the reaction propagating rate. Mechanical alloying Nb50C50and Nb55C45results in the formation of NbC, while mechanical alloying Nb60C40results in NbC + Nb instead of NbC + Nb2C according to the phase diagram. It was attributed to the fact that the rapid SHS reaction favors the formation of NbC, but hinders the occurrence of Nb2C phase through slow diffusion between NbC and the residual Nb. The measurement of the lattice parameters of TiC and NbC for different composition affirms the observed results. The particle sizes of obtained TiC and NbC are very fine at around or even less than 1 μm.
A phase transformation study in the BaO · Al2O3 · 2SiO2 (BAS)–Si3N4 system
Authors: Bandyopadhyay A. , Aswath P.B.
Published: September 2007

A phase transformation study was carried out with barium aluminosilicate (BAS) forming powders (BaCO3, Al2O3, and SiO2) in a BAS-Si3N4 system. Powders were heat-treated in air at 1 atm pressure at different temperatures from 600 to 1150 °C at an interval of 50 °C to study the phase transformations during the formation of BAS. The phase transformations of α to β-Si3N4 is studied by heat-treating the powders at 1600 °C for different sintering times in a nitrogen environment at 1 atm pressure. Formation of different phases was identified by using powder x-ray diffraction. Formation of different forms of barium silicates occurs as an intermediate step between 650 and 950 °C and hexagonal BAS forms between 900 and 950 °C. The hexagonal form of BAS always forms first and persists as a metastable phase in the composites with no evidence of the monoclinic phase. An attempt made to fully transform hexagonal BAS to monoclinic BAS by using LiF as a mineralizer proved to be successful. The hexagonal form of BAS forms first when heat-treated at 1000 °C and is fully transformed to monoclinic BAS when heat-treated at 1100 °C.
Dielectric and piezoelectric properties of the thermally annealed Pb(Zn,Mg)1/3Nb2/3O3–PbTiO3 system across the rhombohedral/tetragonal morphotropic phase boundary
Authors: Jang Hyun M. , Lee Kyu-Mann
Published: September 2007

Effects of thermal annealing on the dielectric/piezoelectric properties of Pb(Zn,Mg)1/3Nb2/3O3-PbTiO3 ceramics (PZMN-PT with Zn/Mg = 6/4) were examined across the rhombohedral/tetragonal morphotropic phase boundary (MPB). Examination of the lattice parameters and the rhombohedral angle indicated that the MPB is in the vicinity of 24 mol% PbTiO3. Both the relative dielectric permittivity (∊r) and the piezoelectric constant (d33)/electromechanical coupling constant (kp) were increased by thermal annealing (800–900 °C) after sintering at 1150 °C for 1 h. The observed improvements in the dielectric and piezoelectric properties were attributed to the elimination of PbO-rich amorphous intergranular layers (about 1 nm thickness) induced by thermal annealing. Both the dielectric analysis using the series mixing model and the microscopic examination by transmission electron microscopy supported this conclusion.
Comparison of Chloroform–Methanol-Extracted and Solvent-Free Triglyceride Determinations in Four Fish Species
Authors: Bennett Pamela M. , Weber Lynn P. , Janz David M.
Published: September 2007

Lipids, including triglycerides, are important variables in fish bioenergetics and can be used to estimate overall fish condition. Triglycerides are the major energy storage form in fish and therefore are a more ecologically and physiologically relevant measure of bioenergetics than total lipids. Chloroform–methanol-extracted total body lipids (Bligh and Dyer) and total body triglycerides determined in chloroform–methanol extracts and unextracted whole-body fractions were measured in four fish species: northern pike Esox lucius, burbot Lota lota, slimy sculpin Cottus cognatus, and spottail shiners Notropis hudsonius. Determinations of total body lipids were consistently greater than those of total body triglycerides when measured in the same solvent-extracted fraction, although both measures followed similar trends. In an effort to eliminate the need for extraction with organic solvents, we compared the performance of an enzyme-based triglyceride assay in both the solvent-extracted fraction and a whole-body unextracted homogenate for each fish. The chloroform–methanol-extracted triglyceride values were consistently lower than triglycerides measured in the unextracted whole-body homogenate. In addition, comparison of triglyceride measurements revealed limitations to the solvent extraction and subsequent triglyceride determinations in lean fish. Thus, in addition to being simple, rapid, and not requiring organic solvents, determination of triglycerides in an unextracted whole-fish homogenate may be a useful alternative to chloroform–methanol-based methods of lipid extraction and subsequent triglyceride measurement.
Peritonite bacteriana espontânea: impacto das mudanças da microbiologia
Authors: Almeida Paulo Roberto Lerias de , Camargo Nutianne Schneider , Arenz Maximilhano , Tovo Cristiane Valle , Galperim Bruno , Behar Paulo
Published: September 2007

RACIONAL: A peritonite bacteriana espontânea é uma complicação grave nos pacientes cirróticos com ascite, sendo as alterações das características microbiológicas relatadas nos últimos anos de impacto na escolha do tratamento antibiótico. OBJETIVO: Avaliar as mudanças na epidemiologia e na resistência antibiótica de bactérias causadoras de peritonite bacteriana espontânea em um período de 7 anos. MÉTODOS: Foram avaliados retrospectivamente todos os casos de pacientes cirróticos com peritonite bacteriana espontânea cuja cultura do líquido de ascite foi positiva, sendo estudados dois períodos: 1997-1998 e 2002-2003. Foram verificados os microorganismos mais freqüentes e a sensibilidade in vitro aos antibióticos. RESULTADOS: No primeiro período (1997-1998) houve 33 casos, sendo 3 (9%) com infecção polimicrobiana. As bactérias mais freqüentes foram: E. coli em 13 (36,11%), estafilococos coagulase-negativos em 6 (16,66%), K. pneumoniae em 5 (13,88%), S. aureus em 4 (11,11%) e S. faecalis em 3 (8,33%). Em 2002-2003, houve 43 casos, sendo 2 (5%) com infecção polimicrobiana. As bactérias mais freqüentes foram: estafilococos coagulase-negativos em 16 (35,55%) S. aureus em 8 (17,77%), E. coli em 7 (15,55%) e K. pneumoniae em 3 (6,66%). Nenhum paciente realizava profilaxia para peritonite bacteriana espontânea. A prevalência de S. aureus meticilino-resistentes aumentou, no decorrer desse período, de 25% para 75%, tendo a resistência desse patógeno às quinolonas e a sulfametoxazol-trimetoprim evoluído de 25% para 50%; somente a vancomicina demonstrou atividade absoluta no decorrer do referido período. Da mesma forma, a prevalência de E. coli resistente às cefalosporinas de terceira geração e às quinolonas aumentou de 0% para 16%. CONCLUSÃO: Houve modificação da população bacteriana causadora de peritonite bacteriana espontânea, com freqüência aumentada de microorganismos gram-positivos, bem como houve aumento da resistência aos antibióticos tradicionalmente utilizados. O estudo sugere a provável iminente inclusão de droga eficaz contra gram-positivos no tratamento empírico da peritonite bacteriana espontânea.
Double-checked preoperative localization of brain lesions
Authors: Fernandes Yvens B. , Borges Guilherme , Ramina Ricardo , Carelli Edmur F.
Published: September 2007

We describe two simple methods that can be used together or alone to localize brain convexity lesions. These methods are based on computerized tomography or magnetic resonance imaging to calculate the position of a given lesion under the skin and help neurosurgeons to plan their surgical approaches. Using spatial fixed points traced on the radiological scans and transposing them to the skin scalp allows the lesion to be projected or drawn on the calvaria.