bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of silicon microwire
Authors: Petrovic J. J. , Hoover R. C. , Field R. D. , Han K.
Published: March 2008

Silicon microwires have been synthesized by the Taylor microwire process. In this process, silicon is melted inside a glass tube by a local heating source and fine microwire is then drawn out by mechanical pulling. The silicon microwire is encapsulated in a silica glass coating. Flexible 10–25-μm diameter polycrystalline silicon microwires were synthesized by this method in continuous lengths up to 460 mm.
Enthalpies of formation of lanthanide oxyapatite phases
Authors: Risbud A. S. , Helean K. B. , Wilding M. C. , Lu P. , Navrotsky A.
Published: March 2008

A family of lanthanide silicates adopts an oxyapatitelike structure with structural formula Ln9.33 0.67(SiO4)6O2 (Ln = La, Sm, Nd, Gd,   = vacancy). The enthalpies of solution, ΔHS, for these materials and their corresponding binary oxides were determined by high-temperature oxide melt solution calorimetry using molten 2PbO B2O3 at 1078 K. These data were used to complete thermodynamic cycles to calculate enthalpies of formation from the oxides, ΔH0 f-oxides (kJ/mol): La9.33 0.67(SiO4)6O2 = 776.3 ± 17.9, Nd9.33 0.67(SiO4)6O2 = 760.4 ± 31.9, Sm9.33 0.67(SiO4)6O2 = 590.3 ± 18.6, and Gd9.33 0.67(SiO4)6O2 = 446.9 ± 21.9. Reference data were used to calculate the standard enthalpies of formation from the elements, ΔH0 f (kJ/mol): La9.33 0.67(SiO4)6O2 = 14611.0 ± 19.4, Nd9.33 0.67(SiO4)6O2 = 14661.5 ± 32.2, Sm9.33 0.67(SiO4)6O2 = -14561.7 ±; 20.8, and Gd9.33 0.67(SiO4)6O2 = -14402.7 ± 28.2. The formation enthalpies become more endothermic as the ionic radius of the lanthanide ion decreases.
Formation of quasi-one-dimensional carbon chains in cubic nanocrystals by photon-breaking of C–S bonds in polythiophene
Authors: Ren Z. M. , Lu Y. F. , Choy H. W. , Chong T. C. , Ng S. C. , Miao P.
Published: March 2008

A solid polythiophene pellet was ablated by a KrF excimer laser beam to deposit thin films on silicon substrates. The laser-ablated plasma was studied by optical emission spectroscopy to identify the photon-breaking of C–S bonds in the ablated heterocycles. Raman and x-ray photoelectron spectroscopy measurements of the deposited thin films also supported the selective photon-induced bond breaking. After eliminating sulfur in the molecular structures, the thin films appeared to be composed of cubic nanocrystals with a uniform size of 240 nm. X-ray diffraction measurement determined the cubic crystal structures with a lattice constant of α =3.38 Å and suggested a quasi-onedimensional carbon chain structure along the body diagonal of the cube.
Preparation and characterization of CuInS2 nanorods and nanotubes from an elemental solvothermal reaction
Authors: Jiang Yang , Wu Yue , Yuan Shengwen , Xie Bo , Zhang Shuyuan , Qian Yitai
Published: March 2008

A simple and convenient solvothermal reaction has been developed to produce CuInS2 nanorods and nanotubes from the elements in ethylenediamine at 280 °C. The products were characterized by x-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. Analysis shows that the coordinating ability of ethylenediamine and the existence of liquid In may play important roles in the growth of one-dimension nanocrystallites and the electron-transfer reaction. In addition, spherical CuInS2 micrometer particles were obtained at 350 °C.
Electrical and microstructural characteristics of ZnO–Bi2O3-based varistors doped with rare-earth oxides
Authors: Hung Nguyen The , Quang Nguyen Dinh , Bernik Slavko
Published: March 2008

ZnO-based varistor samples with a relatively high Sb2O3 to Bi2O3 ratio of 5 were fired at 1200 °C and found to have a high threshold voltage (VT) of 280 V/mm and a low energy-absorption capacity of 50 J/cm3. The introduction of rare-earth oxides (REO) increased the energy-absorption capacity of Pr6O11- and Nd2O3-doped samples to 110 J/cm3 while their threshold voltage (VT) remained slightly above 300 V/mm. Doping with Pr6O11 and Nd2O3 altered the formation of the spinel phase and significantly changed its particle size and distribution which, as a result, had a positive effect on the energy-absorption capacity of the REO-doped samples. Doping with small amounts of Pr6O11 and Nd2O3 appears to be promising for the preparation of ZnO-based varistors with a high breakdown voltage and a high energy absorption capacity.
Calorimetric determination of the enthalpy of formation of InN and comparison with AlN and GaN
Authors: Ranade M. R. , Tessier F. , Navrotsky A. , Marchand R.
Published: March 2008

The standard enthalpy of formation of InN at 298 K has been determined using high-temperature oxidative drop solution calorimetry in a molten sodium molybdate solvent at 975 K. Calorimetric measurements were performed on six InN samples with varying nitrogen contents. The samples were characterized using x-ray diffraction, chemical analysis, electron microprobe analysis, and Brunauer–Emmett–Teller surface area measurement. The variation of the enthalpy of drop solution (kJ/g) with nitrogen content is approximately linear. The data, when extrapolated to stoichiometric InN, yield a standard enthalpy of formation from the elements of ?28.6 ± 9.2 kJ/mol. The relatively large error results from the deviation of individual points from the straight line rather than uncertainties in each set of data for a given sample. This new directly measured enthalpy of formation is in good agreement with the old combustion calorimetric result by Hahn and Juza (1940). However, this calorimetric enthalpy of formation is significantly different from the enthalpy of formation values derived from the temperature dependence of the apparent decomposition pressure of nitrogen over InN. A literature survey of the enthalpies of formation of III–N nitride compounds is presented.
Structural and dielectric characterization of Ba4Nd2Ti4+xTa6−xO30−x/2 nonstoichiometric ceramics
Authors: Chen X. M. , Zheng X. H. , Wang J.
Published: March 2008

Ba4Nd2Ti4Ta6O30 dielectric ceramics with high-Ε and low dielectric loss were modified to improve the temperature coefficient of dielectric constant. Through partial substitution of Ti4+ for Ta5+, a significantly reduced temperature coefficient of dielectric constant (tΕ = –664p pm/°C) combined with a dielectric constant above 110 and a low dielectric loss (tanδ–0.0005 to 0.0006 at 1 MHz) resulted in the nonstoichiometric dielectric ceramics with nominal compositions Ba4Nd2Ti4+xTa6-xO30?x/2 (x = 0.8–1.2).
Excellent buffer layer for growing high-quality Y–Ba–Cu–O thin films
Authors: Tang W. H. , Gao J. , Liu C. X. , Mai Z. H.
Published: March 2008

Eu2CuO4 (ECO) has been used as a buffer layer for growing of Yba2Cu3O7–δ (YBCO) thin films on SrTiO3(100) and Y-stabilized ZrO2(100) substrates. The epitaxy, crystallinity, and surface of YBCO thin films have been significantly improved by using ECO buffer layer as investigated by x-ray diffraction, rocking curves, scanning electron microscope, surface step profiler, and x-ray small-angle reflection. The best value of the full width at half-maximum of the YBCO(005) peak can be greatly reduced down to less than 0.1°. The scanning-electron-microscope photos indicate a very smooth surface for the YBCO thin films. The average roughness is less than 5 nm over a wide scanning region of 2000 mm. The results of x-ray small-angle reflection indicate a very clear and flat interface between YBCO and ECO layers. Meanwhile, the resistivity of ECO is about 20 times higher than that of PrBa2Cu3Oy at the boiling point of liquid nitrogen. Our results suggest that ECO should be a good barrier candidate for fabricating high-Tc superconductor junctions.
Nucleation and growth of YBa2Cu3Ox on SrTiO3 and CeO2 by a BaF2 postdeposition reaction process
Authors: Wu L. , Zhu Y. , Solovyov V. F. , Wiesmann H. J. , Moodenbaugh A. R. , Sabatini R. L. , Suenaga M.
Published: March 2008

The nucleation and growth of the c-axis-aligned Yba2Cu3Ox on SrTiO3 and CeO2, from precursor films, were studied by examining quenched and fully processed specimens using transmission electron microscopy techniques. The precursor films, a stoichiometric mixture of fine-grained Y, Cu, and BaF2, were deposited using physical vapor deposition methods. An Y-Ba oxy-fluoride formed from the precursor contributed to the nucleation of Yba2Cu3Ox, while a liquid layer between the unreacted precursor and the Yba2Cu3Ox layer played an important role in the growth of Yba2Cu3Ox. However, the process of nucleation of Yba2Cu3Ox on SrTiO3 and CeO2 were significantly different.
Piezoelectric actuation of crack growth along polymer–metal interfaces in adhesive bonds
Authors: Du Tianbao , Liu Ming , Seghi Steve , Hsia K. J. , Economy J. Economy , Shang J. K.
Published: March 2008

A new experimental technique for determining mechanical properties of polymer–metal interfaces was developed by replacing the conventional mechanical testing machine with a piezoelectric actuator. The actuator was made from a thin ferroelectric ceramic beam attached to a bilayer polymer-metal composite specimen. The trilayer specimen was loaded by applying ac electric fields on the piezoelectric actuator to drive crack growth along the polymer-metal interface. Subcritical crack growth was observed along the epoxy/aluminum interface, and the growth rate was found to depend on the magnitude of the applied electric field. The fracture mechanics driving force for the crack growth was computed from the finite element analysis as a function of crack length, applied field, material properties, and specimen geometry. Kinetics of the crack growth was correlated with the piezoelectric driving force.
Study of the activation process of Mg-based hydrogen storage materials modified by graphite and other carbonaceous compounds
Authors: Bouaricha S. , Dodelet J-P. , Guay D. , Huot J. , Schulz R.
Published: March 2008

A nanocomposite (Mg–V)nano made of 90 wt% Mg and 10 wt% V was prepared by high-energy ball-milling during 40 h. The activation characteristics of (Mg–V)nano are rather poor, the hydrogen content [H] reaching 4 wt% after more than 100 h (t4wt%) following the initial exposure of the material to H2. Adding 9 wt% graphite to (Mg–V)nano and resuming the milling operation for 30 min leads to the formation of (Mg–V)nano /G, which exhibits a t4wt% value of only 10 min. The addition of more than 9 wt% graphite to (Mg–V)nano does not lead to any significant reduction of the t4wt% value. However, extending the milling period with graphite over 30 min leads to a steady increase in t4wt% and, thus, to a deterioration of the activation characteristics. Comparison of the behavior of graphite with other C-based compounds revealed that perylene (C20H12) and pentacene (C22H14), which are made of linked benzene rings, and thus have a 2D structure similar to that of the graphene sheet, are as effective as graphite in improving the activation characteristics of (Mg–V)nano. A structural investigation of (Mg–V)nano /G as a function of the milling time through both C 1s core-level x-ray photoelectron spectroscopy and C K edge x-ray absorption near-edge spectroscopy has shown that the integrity of graphite is progressively lost as the milling period is extended over 30 min. On the basis of these results, it is hypothesized that the adsorption of graphene layer on freshly created Mg surfaces and the formation of highly reactive C species during milling prevents the re-formation of the surface oxide layer responsible for the poor activation characteristics of untreated (Mg–V)nano
Effect of oxygen on the reactions in the Si/Ta/Cu metallization system
Authors: Laurila Tomi , Zeng Kejun , Kivilahti Jorma K. , Molarius Jyriki , Suni Ilkka
Published: March 2008

The effect of oxygen on the reaction mechanisms in the Si/Ta/Cu metallization system was studied experimentally and by utilizing the thermodynamically assessed Ta–O binary system. It was presented that an interfacial tantalum oxide was formed between Cu and Ta and that it established an additional barrier layer for Cu diffusion. The formation of additional barrier layer was supported by the following observations: (i) No detectable amount of Cu was found from the Ta layer with the combined transmission electron microscopy and energy dispersive spectroscopy at temperatures as high as 650 °C. (ii) Secondary ion mass spectrometry measurements indicated that significant amount of oxygen was incorporated into the films already after the sputtering stage. (iii) 181Ta16O molecular ion signals were detected from the Ta/Cu interface, indicating that the additional layer was in fact some form of tantalum oxide. The diffusion of Cu through the Ta layer could not proceed until the interfacial oxide had been dissolved by the Ta matrix. Since the oxygen solubility in Ta matrix is high in the temperature range of interest, the interfacial oxide dissolution was kinetically controlled. It is to be noted that the threshold temperature range of the dissolution reaction was found to coincide with that of the β–Ta to the bcc-Ta transition, which was anticipated to enhance the kinetics of the dissolution.
Microstructure of La1–xCaxMnO3 studied by transmission electron microscopy
Authors: Chen Q. , Tao J. , Zuo J. J. , Spence J. J. H.
Published: March 2008

Microstructures of La1-xCaxMnO3 compounds (x = ⅓ and 0.5) prepared with and without intermediate grinding were studied using transmission electron microscopy. A high density of antiphase boundaries (APBs) with displacement vector 1/2 〈111〉, indexed in orthorhombic unit cell, has been observed in bulk samples with no or minimum intermediate grinding. The nature of this APB is analyzed and found to bedue to the symmetry breaking introduced by the tilting of MnO6 octahedra relative to the ideal perovskite structure. Samples prepared using two intermediate grinds do not show these defects indicating that the microstructure can be controlled through synthesis routes. The effect of domain boundaries on the colossal magnetoresistance effect is discussed.
Phase formation and crystal growth of Sr–Bi–Ta–O thin films grown by metalorganic chemical vapor deposition
Authors: Bachhofer H. , von Philipsborn H. , Hartner W. , Dehm C. , Jobst B. , Kiendl A. , Schroeder H. , Waser R.
Published: March 2008

The crystallization process of SrxBiyTa2O5+x+3y/2 thin films grown by metalorganic chemical vapor deposition was investigated. Phase formation and crystal growth is greatly affected by the film composition and crystallization temperature. Phase diagrams for varying Sr or Bi contents were determined as a function of the crystallization temperature. The higher the Sr or Bi content in the film, the lower the phase transition temperature from the amorphous to the fluorite-type phase and from the fluorite-type to the Bi-layered Aurivillius phase. Low Sr and Bi contents support pyrochlore-type phase formation as a second phase. During annealing, excess Bi is not lost due to evaporation, but due to migration to the bottom electrode. Contrary to the fluorite-type phase, the Aurivillius phase is not able to incorporate the excess of Bi atoms. Decreasing grain size and pyrochlore-type phase formation entail decreasing remanent polarization.
Numerical study on the measurement of thin film mechanical properties by means of nanoindentation
Authors: Chen Xi , Vlassak Joost J.
Published: March 2008

Nanoindentation is a technique commonly used for measuring thin film mechanical properties such as hardness and stiffness. In this study, we used the finite element method to investigate the effect of substrate and pileup on hardness and stiffness measurements of thin film systems. We define a substrate effect factor and construct a map that may be useful in the interpretation of indentation measurements when it is not possible to make indentations shallow enough to avoid the influence of the substrate on the measurements. A new technique for measuring mechanical properties of thin films by nanoindentation is suggested at the end of this article.
Oxygen transport during annealing of Pb(Zr,Ti)O3 thin films in O2 gas and its effect on their conductivity
Authors: Ayguavives F. , Agius B. , EaKim B. , Vickridge I.
Published: March 2008

Lead zirconate titanate (PZT) thin films were deposited in a reactive argon/oxygen gas mixture by radio-frequency-magnetron sputtering. The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using oxygen 18 as a tracer, to study the oxygen diffusion in the thin films. Electrical properties and crystallization were optimized with a 90-nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550 °C) show very low leakage current densities (J = 2 × 10−8 A/cm2 at 1 V). In this article we show that a strong correlation exists between the oxygen composition in the PZT film and the leakage current density.
Structural and electrical properties of strontium barium niobate thin films crystallized by conventional furnace and rapid-thermal annealing process
Authors: Mendes R. G. , Araújo E. B. , Eiras J. A.
Published: March 2008

Strontium barium niobate (SBN) thin films were crystallized by conventional electric furnace annealing and by rapid-thermal annealing (RTA) at different temperatures. The average grain size of films was 70 nm and thickness around 500 nm. Using x-ray diffraction, we identified the presence of polycrystalline SBN phase for films annealed from 500 to 700 °C in both cases. Phases such as SrNb2O6 and BaNb2O6 were predominantly crystallized in films annealed at 500 °C, disappearing at higher temperatures. Dielectric and ferroelectric parameters obtained from films crystallized by conventional furnace and RTA presented essentially the same values.
Electron microscopy of high-temperature and high-pressure as-grown diamond crystals
Authors: Yin Long-Wei , Li Mu-Sen , Cui Jian-Jun , Xu Bin , Gong Jian-Hong , Hao Zhao-Yin , Zhang Jiong-Fa
Published: March 2008

Electron microscopy was used to investigate microstructures of diamond single crystals prepared at high temperature and high pressure (HPHT) from the Fe–Ni–C system. Analysis through selected-area electron diffraction pattern suggests that the crystal structure of the HPHT-grown diamond is cubic; polycrystalline diamonds are contained in the diamond. Etch pits on the (111) surface of the diamond by scanning electron microscopy revealed the dislocation motion under the action of applied stress. An array of parallel dislocation lines taken with reflection of [110] was observed directly by transmission electron microscopy (TEM). Fringe distortions and concentric dislocation loops were examined by rotation moiré images, which arose from two overlapping (111) close-packed planes rotated with respect to each other at a 5° angle. The parallel dislocation lines, distorted fringes, and concentric dislocation loops might have derived from the micro-inclusions. The parallel layers with growth cellular interface by TEM provided direct evidence that the diamond grew from solution of carbon in the molten catalyst at HPHT and the growth interface diamond was not stable.
Explanation of the effects of gravity on crystallization of ZrF2–BaF2–LaF3–AlF3–NaF glass
Authors: Tucker Dennis S. , Ethridge Edwin C.
Published: March 2008

The effects of gravity on crystallization of ZrF2–BaF2–LaF3–AlF3–NaF glasses have been studied by utilizing NASA's KC135 aircraft and a sounding rocket. Fibers were heated to the crystallization temperature in unit and reduced gravity. The fibers processed in unit gravity exhibited crystallization, while fibers processed in reduced gravity showed no signs of crystallization. An explanation based on shear thinning of liquids is presented to explain these results.
Ion energy dependence of film properties for diamond-like carbon prepared with plasma-assisted deposition
Authors: Zexian Cao
Published: March 2008

Hydrogen-free diamondlike carbon films were prepared on Si(100) with electron cyclotron wave-resonance plasma, which serves to sputter the graphite target and to simultaneously bombard the growing surface. Direct penetration of postionized carbon atoms (up to 140 eV) in addition to the momentum transfer from Ar plasma facilities the formation of the Ta–C structure. Surface morphology, mechanical, and optical properties of the deposits were examined with respect to the ion energy. Atomic force microscope images revealed island morphology in deposits with a typical root-mean-square roughness of 20 nm. A maximum content of about 70% for the fourfold-bonded structure was estimated from the Raman profiles, giving rise to a micro hardness of 60 ± 5 GPa.
Single-crystal growth of the Al–Cu–Fe icosahedral quasicrystal from the ternary melt
Authors: Guo J. Q. , Tsai A. P.
Published: March 2008

An Al–Cu–Fe partial phase diagram involving the icosahedral quasicrystal has been constructed along an Al62.5Cu37.5−xFex (x = 2.5 to 25 at.%) isopleth. The icosahedral quasicrystal forms at 850 °C via a peritectic reaction between a liquid and (Al,Cu) 13Fe4 phase and coexists with a liquid phase at temperature below the peritectic reaction. The icosahedral quasicrystal crystallizes as a primary phase in the temperature range of 760 to 850 °C from alloys surrounded by composition points of Al–Cu–Fe: 62.5–33–4.5, 62.5–34.5–3, 57.5–39.5–3 and 57.5–38.0–4.5 at.%. On the basis of the phase diagram, single grains of the Al–Cu–Fe icosahedral quasicrystal with a maximum size of 5 mm were successfully grown from Al–Cu–Fe melts.
Microstructures of La1−xAx(A = Ca or Sr)MnO3−δthin films by liquid-delivery metalorganic chemical vapor deposition
Authors: Xin Y. , Han K. , Mateeva N. , Garmestani H. , Kalu P. N. , Dahmen K-H.
Published: March 2008

The microstructure of La1–xAx(A = Ca or Sr)MnO3–δthin films grown by liquid-delivery metalorganic chemical vapor deposition on (001) MgO and (110)pseudo-cubicLaAlO3were studied by transmission electron microscopy. The La1–xCaxMnO3–δthin film on large lattice mismatched MgO exhibited very defective microstructures and consisted of two typical regions. The first region was close to the film–substrate interface and had an epitaxial relationship to the substrate with many differently oriented domains nucleated on the substrate surface. The second region consisted of columnar grains with some degree of texture. In contrast, the smaller lattice-mismatched La1–xSrxMnO3–δ/(110)pseudo-cubicLaAlO3film had good crystalline quality with highly oriented columnar grains but exhibited complicated dislocation structures. Apart from the misfit dislocations formed at the film–substrate interface, two types of anomalous dislocations with limited contribution to relieving misfit stresses were also observed. One type of dislocation had extra planes in the film and some climbed into the substrate. These dislocations were considered to form from dislocation loops during nucleation of the film. The other type of dislocations had extra planes parallel to the film–substrate interface and glided into the substrate side resulting in a 2° tilt of the film with respect to the substrate. The complicated dislocation configurations present in the sample were related to the complex strain field in the film. The relative strains along the interface measured in the film were heterogeneous. The variations of the strains in the film were related to the local Curie temperature changes and second-order phase transitions of the film.
Simplified method for analyzing nanoindentation data and evaluating performance of nanoindentation instruments
Authors: Sawa Takeshi , Tanaka Kohichi
Published: March 2008

Nanoindentation is a simple and effective means for evaluating the mechanical properties of thin films. In such circumstances, nanoindentation testers have been developed and commercialized by some companies. In this study, we tested the standard four specimens using six different types of testers and established a method to evaluate the nanoindentation data. The method requires only two correction factors; one is the frame compliance, Cf, of the testers, and the other is the error of the detection of the original surface which includes both the truncation of the indenter apex and the damage of the surface caused by the preloading of the indenter. The latter correction is conducted by adding a correction length, ΔhC, to the measured penetration depth, h. It was found that the values ΔhC increase with decrease in the hardness of material and are very sensitive to the performance of the testers.
Low-resistance films of polyimides with impregnated copper sulfide
Authors: Rowe R. V. A. , Kunita M. H. , Porto M. F. , Muniz E. C. , Rubira A. F. , Nery R. C. , Radovanovic E. , Taylor L. T. , Nazem N.
Published: March 2008

Surface modification of polyimides has been used to obtain better interaction with an inorganic material. Copper sulfide incorporation onto the surface of commercial Kapton® polyimide showed that treatment with base was necessary for adherence of the copper sulfide to the polymeric matrix. The optimized conditions for composite preparation, obtained by response surface methodology, was pH 1.4 at 80 °C for 3.67 h. Using these conditions, we obtained electrical resistance as low as 1.0 ohm for CuS\Kapton® composites. These optimized conditions were used to prepare other low-resistance polyimide composites. The resulting composites were analyzed by photoelectron spectroscopy. The presence of S(2p) and Cu(2p) peaks demonstrated the incorporation of copper sulfide onto the polyimide surface. Scanning electron microphotographs and the images from atomic force microscopy showed a homogeneous CuS distribution in all composites.
Aligned carbon nanotube growth under oxidative ambient
Authors: Cao Anyuan , Zhang Xianfeng , Xu Cailu , Liang Ji , Wu Dehai , Wei Bingqing
Published: March 2008

Carbon nanotubes (CNTs) are always produced under a reductive ambient with hydrogen present using the chemical vapor deposition method. Oxidative media, such as carbon dioxide and oxygen, could damage the tubular structures by opening the nanotube ends or etching the tube walls. Here we report the synthesis of aligned defective, but clean, CNTs in the presence of water vapor. The tube walls were found broken as well as the tube ends. CNTs with a large amount of exposed broken sites on their tube walls have potential applications in many areas such as energy storage.
Single-layer submicron-thick BaTiO3 coatings from poly(vinylpyrrolidone)-containing sols: Gel-to-ceramic film conversion, densification, and dielectric properties
Authors: Kozuka Hiromitsu , Higuchi Atsushi
Published: March 2008

BaTiO3-coating films were prepared from a solution containing poly(vinylpyrrolidone) (PVP) of molar composition Ba(CH3COO)2:Ti(OC2H5)4:PVP:CH3COOH:H2O: C2H5OH = 1:1:0.5:27:4:5, via nonrepetitive, single-step dip-coating. The gel films were found to be converted into BaTiO3 films via evaporation of the solvent and CH3COOH below 210 °C, decomposition of PVP at 210–360 °C, decomposition of CH3COO− below 440 °C, and crystallization at 500–610 °C. The decomposition of PVP was accompanied by the progress of the condensation reaction, which resulted in significant reduction in film thickness. When the gel films were heated isothermally at 700 °C, crack-free BaTiO3 films as thick as 0.9 μm were obtained. When the gel films were heated isothermally at 360 °C and then at 700 °C, the film became denser. Higher dielectric constants around 290 were found for the film that underwent the isothermal heat treatment at 360 °C. A slower rate of PVP decomposition was thought to be the key for the film densification.
Relation between tolerance factor and Tc in Aurivillius compounds
Authors: Suárez Donají Y. , Reaney Ian M. , Lee William E.
Published: March 2008

The structures and microstructures of a range of Aurivillius phases were investigated by transmission electron microscopy. Systematic rows of superlattice reflections arising from tilting of octahedra around the c axis were identified, and their intensities at room temperature were shown to diminish as the tolerance factor (t) of the perovskite blocks increased. For compounds with t's approaching 1, no superlattice reflections were observed. the paraelectric-to-ferroelectric phase transition temperature (Tc) was monitored through permittivity measurements as a function of temperature, and Tc was also shown to decrease as t increased. Consequently, the onset of octahedral tilting and Tc appeared to be strongly related Aurivillius phases. Planar defects arising from the structural phase transitions and from stacking irregularities were also discussed.
Halide removal from BaM (BaFe12O19) and SrM (SrFe12O19) ferrite fibers via a steaming process
Authors: Pullar R. C. , Taylor M. D. , Bhattacharya A. K.
Published: March 2008

Aligned fibers of barium and strontium M hexaferrite (BaFe12O19 and SrFe12O19) were manufactured from an aqueous inorganic sol-gel-based spinning process, but halides have been found to be retained up to 1000 °C, inhibiting the formation of the hexagonal ferrite phases. Therefore an investigation was carried out into the removal of the halides at lower temperatures through steaming between 500 and 900 °C/3 h, and the subsequent effects upon microstructure and magnetic properties. The fibers were prefired to 400 °C to remove all organic components, and in all cases the steaming process resulted in loss of alignment of the fibers. It was found that the M phase began to form at only 600 °C, becoming single-phase SrM or virtually pure phase BaM at 700 °C, confirming that halides had indeed delayed M phase formation. Both materials had a grain size below 100 nm, but other unusual surface features not seen before on ferrite fibers were observed. The fibers steamed at 700 °C had Ms and Hc values comparable to random M ferrite fibers fired to 1000 °C in air, while steaming over a temperature range from 400 to 800 °C/3 h gave products with improved magnetic properties, with SrM fibers having an Ms of 81.4 emu g–1 and Hc of 457 kA m−1.
Direct laser writing of self-developed waveguides in benzyldimethylketal-doped sol-gel hybrid glass
Authors: Bae Byeong-Soo , Park Oun-Ho , Charters Robbie , Luther-Davies Barry , Atkins Graham R.
Published: March 2008

Exposure of benzyldimethylketal (BDK)-doped sol-gel hybrid glass films to ultraviolet light produces a refractive index increase up to 43 × 10−3 and an increase in thickness due to photolocking of the BDK into the sol-gel hybrid glass matrix. Thus, single mode ridge waveguides at λ = 1550 nm can be fabricated by direct laser exposure without using photomask and development processes. The slower laser writing speed gives greater refractive index change producing more circular guided mode profiles.
Alternative technique for analyzing instrumented indentation data
Authors: Oliver W. C.
Published: March 2008

A new analysis technique for calculating the hardness, modulus, and contact area from indentation data obtained using pyramidal or conical indenters was formulated and compared with another commonly used technique. Experimental data using a Berkovich indenter to indent fused silica and tungsten were examined. In addition, finite element modeling results were used to examine the effectiveness of the analytical techniques when a wide range of materials properties was considered. The new technique relies on the slope of the loading curve rather than the indenter displacement as an input. It is shown that the new technique is far less affected by the deviation of the geometry of the indenter from its intended shape. This effect removes the necessity to have detailed descriptions of the precise tip geometry in some cases. The new technique does not reduce errors associated with pile up of material near the indenter.
Defect formation due to the crystallization of deep amorphous volumes formed in silicon by mega electron volt (MeV) ion implantation
Authors: Liu A. C. Y. , McCallum J. C. , Wong-Leung J.
Published: March 2008

Solid-phase epitaxy was examined in deep amorphous volumes formed in silicon wafers by multi-energy self-implantation through a mask. Crystallization was effected at elevated temperatures with the amorphous volume being transformed at both lateral and vertical interfaces. Sample topology was mapped using an atomic force microscope. Details of the process were clarified with both plan-view and cross-sectional transmission electron microscopy analyses. Crystallization of the amorphous volumes resulted in the incorporation of a surprisingly large number of dislocations. These arose from a variety of sources. Some of the secondary structures were identified to occur uniquely from the crystallization of volumes in this particular geometry.
Effect of material properties on integration damage in organosilicate glass films
Authors: Ryan E. Todd , Martin Jeremy , Junker Kurt , Wetzel Jeff , Gidley David W. , Sun Jianing
Published: March 2008

Most organosilicate glass (OSG), low dielectric constant (low-κ) films contain Si–R groups, where R is an organic moiety such as −CH3. The organic component is susceptible to the chemically reactive plasmas used to deposit cap layers, etch patterns, and ash photoresist. This study compares a spin-on, mesoporous OSG film with a completely connected pore structure to both its nonmesoporous counterpart and to another low-density OSG film deposited by plasma-enhanced chemical vapor deposition. The results show that the film with connected pores was much more susceptible to integration damage than were the nonmesoporous OSG films.
Properties of YBa2Cu3O7−δ multilayer films from the fluoride-based sol-gel process
Authors: Siegal M. P. , Dawley J. T. , Overmyer D. L.
Published: March 2008

The inability to rapidly grow thick or multilayer epitaxial films for either electronic or electrical power applications limits the utility of fluoride-based processes for YBa2Cu3O7−δ (YBCO). This problem is due to the use of water vapor in the growth process, necessary for the dissociation of metallofluorides. Flowing wet gas at low temperatures is corrosive to cuprates and responsible for destroying underlying YBCO layers in attempts to grow secondary layers. This is avoided simply by increasing the temperature where vapor is introduced into the growth ambient. Resulting two-layer films of YBCO have properties similar to those of high critical current density single-layer films.
High-temperature thermoelectric properties of n-type BayNixCo4−xSb12
Authors: Tang X. F. , Zhang L. M. , Yuan R. Z. , Chen L. D. , Goto T. , Hirai T. , Dyck J. S. , Chen W. , Uher C.
Published: March 2008

Effects of Ba filling fraction and Ni content on the thermoelectric properties of n-type BayNixCo4−xSb12 (x = 0−0.1, y = 0−0.4) were investigated at temperature range of 300 to 900 K. Thermal conductivity decreased with increasing Ba filling fraction and temperature. When y was fixed at 0.3, thermal conductivity decreased with increasing Ni content and reached a minimum value at about x = 0.05. Lattice thermal conductivity decreased with increasing Ni content, monotonously (y ≤ 0.1). Electron concentration and electrical conductivity increased with increasing Ba filling fraction and Ni content. Seebeck coefficient increased with increasing temperature and decreased with increasing Ba filling fraction and Ni content. The maximum ZT value of 1.25 was obtained at about 900 K for n-type Ba0.3Ni0.05Co3.95Sb12.
Nondestructive measurement of striation defect spacing using laser diffraction
Authors: Haas Dylan E. , Birnie Dunbar P.
Published: March 2008

A simple method is presented for measuring the characteristic spacing between striation defects that sometimes develop when coatings are deposited by the spin-coating process. Striation defects, because of their substantial regularity of thickness variation, are able to diffract laser light. By measuring the diffraction angle, it is possible to determine a characteristic spacing that corresponds to the most dominant spatial frequency for the striation defects that have formed. This diffraction technique is compared with other methods for determining the average striation spacing. This noncontact characterization technique may also be applicable to other regularly or quasi-regularly spaced defect structures that appear in coatings or other materials. The limits and accuracy of this technique are discussed in detail.
Solvothermal route to Bi3Se4 nanorods at low temperature
Authors: Liu Yuan-fang , Zeng Jing-hui , Zhang Wei-xin , Yu Wei-chao , Qian Yi-tai , Cao Jin-bo , Zhang Wan-qun
Published: March 2008

Nanorods Bi3Se4 were synthesized directly through the reaction between BiCl3 and elemental selenium in an autoclave with hydrazine hydrate as solvent at 165 °C for 10 h. X-ray powder diffraction patterns, x-ray photoelectron spectra, and transmission electron microscope images show that the products are well-crystallized hexagonal Bi3Se4 nanorods. The solvent hydrazine hydrate played an important role in formation and growth of Bi3Se4 nanorods. The possible reaction mechanism was proposed.
Adhesion of polymer–inorganic interfaces by nanoindentation
Authors: Li Min , Carter C. Barry , Hillmyer Marc A. , Gerberich William W.
Published: March 2008

Nanoindentation combined with atomic force microscopy was applied to measure the fracture toughness of polystyrene/glass interfaces. Film delamination occurs when the inelastic penetration depth approximately equals or exceeds the film thickness. The delamination size was accurately measured using atomic force microscopy. Using multilayer indentation and annular-plate analyses, the interfacial fracture toughness was then assessed. The values obtained from the two analyses are in good agreement with the fracture toughness of the interface being approximately 350 mJ/m2. By appropriate fracture surface characterization, it was shown that fracture occurs along the polystyrene/glass interface. Crack arrest marks were observed, and their possible cause discussed. On the basis of the morphology of the fracture surface, the fracture toughness was also evaluated using a process zone analysis. The result agrees well with those obtained from the other two analyses.
Structural characterization of laser-treated Cr3C2–NiCr coatings
Authors: Serra P. , Miguel J. M. , Morenza J. L. , Guilemany J. M.
Published: March 2008

The interconnected porosity of the Cr3C2–NiCr coatings obtained by high-velocity oxy fuel spraying is detrimental in corrosion and wear resistance applications. Laser treatments allow sealing of their surfaces through melting and resolidification of a thin superficial layer. A Nd:YAG laser beam was used to irradiate Cr3C2–NiCr coatings either in the continuous wave mode or at different repetition rates in the pulsed one. Results indicated that high peak and low mean laser irradiances are not good, since samples presented deep grooves and an extensive crack network. At low peak and higher mean laser irradiances the surface was molten, and only a few shallow cracks were observed. The interconnected porosity was completely eliminated in a layer up to 80 μm thick, formed by large Cr7C3 grains imbedded in a NiCr matrix.
Raman scattering of cubic boron nitride films deposited from the low-pressure gas phase
Authors: Zhang W. J. , Matsumoto S.
Published: March 2008

By introduction of the chemical effects of fluorine, thick cubic boron nitride (cBN) films with high phase purity and low residual stress were synthesized on silicon substrates by dc-bias-assisted dc jet chemical vapor deposition in an Ar–N2–BF3–H2 system. In this paper, the characterization of the films by scanning electron microscopy, glancing-angle x-ray diffraction, infrared spectroscopy, and Raman spectroscopy was done. Among these techniques, Raman spectroscopy was intensively studied, and a method was established to evaluate the crystallinity and residual stress of the cBN films from the line width and peak shift of Raman charactersitic peaks. The influences of the experimental parameters, i.e., bias voltage, substrate temperature, and deposition time, on the film quality were systematically studied. An experimental window for the deposition of cBN films was described. The cBN films deposited under optimized conditions showed the similar line width of both Raman TO and LO modes and thus a crystallinity comparable to that of 4–8-μm cBN single crystals synthesized by high-ressure and high-temperature methods.
Microstructure and misfit relaxation in SrTiO3/SrRuO3 bilayer films on LaAlO3(100) substrates
Authors: Wu J. S. , Jia C. L. , Urban K. , Hao J. H. , Xi X. X.
Published: March 2008

We studied the microstructure of SrTiO3/SrRuO3 bilayer films on (001) LaAlO3 substrates by high-resolution transmission electron microscopy. At the SrRuO3/LaAlO3 interface a defect configuration of stacking faults and nanotwins bounding either Frank partial dislocations or Shockley partial dislocations and complex interaction between these planar defects were found to be the dominant means of misfit accommodation. The misfit in the SrTiO3/SrRuO3 system, however, is mainly accommodated by elastic strain. Most of the observed defects in the SrTiO3 layer can be related to the [111] planar defects in the SrRuO3 layer propagating and reaching the SrTiO3/SrRuO3 interface. Furthermore, a [110] planar defect can also be introduced in the SrTiO3 layer due to the structure change of the SrTiO3/SrRuO3 interface.
Structure and the nonlinearity of lithium triborate studied by Raman and infrared reflectivity spectroscopy
Authors: Xia H. R. , Li L. X. , Yu H. , Dong S. M. , Wang J. Y. , Lu Q. M. , Ma C. Q. , Wang X. N.
Published: March 2008

Raman and infrared measurements of the LiB3O5 (LBO) crystals were completed. The experimental results shown here are more and stronger Raman lines and infrared absorption peaks, which implies that the external vibrations of the trigonal (BO3)3− and tetrahedral (BO4)5− ions, especially the former, in the six-membered boron–oxygen rings at the low wave number are strong and the internal vibrations of the (BO4)5− ions above 200 cm−1 are stronger than those of the (BO3)3− ions if compared with the Raman spectra of BaB2O4 crystals. These are caused due to the slope and distortions of the B3O7 rings and their BO3 and BO4 units in LBO, which change the structural rigidity of the crystals, intensify the long-range electrostatic force and short-range molecular force, and shorten the ultraviolet absorption edge.
Bulk- or interface-limited electrical conductions in IrO2/(Ba,Sr)TiO3/IrO2 thin film capacitors
Authors: Hwang Cheol Seong
Published: March 2008

The electrical conduction behavior of sputter-grown (Ba,Sr)TiO3 thin films having IrO2 electrodes were studied under the assumption of a fully accumulated film having a negative space charge density of 1 × 1019 cm−3 at 25 °C. The negative space charge decreased the actual field strength in the film and resulted in a decreasing leakage current with increasing film thickness at a given applied field. The current conduction in a very low field, roughly less than 150 KV/cm, showed a linear current density–voltage (J–V) behavior at 25 °C. From that field to about 420 KV/cm, the bulk-limited Poole–Frenkel mechanism controlled the overall conduction property at room temperature. Under high field strength, from 420 KV/cm to 1 MV/cm, the interface-limited thermionic field emission mechanism was dominant. The dielectric constant obtained from Poole–Frenkel fitting was approximately 300 ± 50 at 25 °C, which was in qualitative agreement with the value obtained from low-frequency capacitance measurements. The detailed mechanisms of the linear and nonlinear field-dependent emission conductions were discussed with reference to the direction of band bending, not to the carrier concentration.
Combustion synthesis method for synthesis of aluminum nitride powder using aluminum containers
Authors: Lin Chun-Nan , Chung Shyan-Lung
Published: March 2008

A combustion synthesis method was developed for synthesis of AlN powder. Al powder and small amounts of NH4Cl were thoroughly mixed and placed in low-melting-point containers made of a thin, perforated aluminum sheet. The combustion reaction was ignited by heating the top surface of the powder stack, and the aluminum container was converted completely to AlN during the combustion reaction. High product yields were obtained under N2 pressures of 0.2–0.5 MPa. The product was composed of a dense outer portion and a loose inner portion. Effects of several process parameters on the product yield were investigated and discussed.
Fretting wear rate of sulphur deficient MoSx coatings based on dissipated energy
Authors: Zhang Xiaoling , Lauwerens W. , Stals L. , He Jiawen , Celis J-P.
Published: March 2008

The fretting wear of sulphur-deficient MoSx coatings with different crystallographic orientations has been investigated in ambient air of controlled relative humidity. The coefficient of friction and the wear rate of MoSx coatings sliding against corundum depend not only on fretting parameters like contact stress, fretting frequency, and relative humidity, but also strongly on the crystallographic orientation of the coatings. For randomly oriented MoSx coatings, the coefficient of friction and the wear rate increased significantly with increasing relative humidity. In contrast, basal-oriented MoSx coatings were less sensitive to relative humidity. The coefficient of friction of both types of MoSx coatings decreased on sliding against corundum with increasing contact stress and decreasing fretting frequency. A correlation between dissipated energy and wear volume is proposed. This approach allows detection in a simple way of differences in fretting wear resistance between random- and basal-oriented MoSx coatings tested in ambient air of different relative humidity.
Microstructure studies of potassium hexatitanate whiskers
Authors: Li G. L. , Liu M. , Wang G. H.
Published: March 2008

Microstructures of potassium hexatitanate (K2Ti6O13) whiskers prepared by calcination of KF and TiO2 mixture were studied through high-resolution electron microscopy. The rod axis of a K2Ti6O13 whisker is along the [010] direction. These whiskers normally have a lamellar structure in their longitudinal direction, and adjacent lamellae usually have the same crystallographic orientation. Each lamella might be further divided into several fine layers with a width on the nanometer scale in the same crystallographic orientation. The whisker can be split in the longitudinal direction along either the boundary between two lamellae or the weak binding crystal plane, such as (100) and (201) planes. The mechanisms for the formation of lamella and layer structures and for the splitting of whiskers are discussed.
Effect of ion implant dose on the mechanical properties of polyethersulfone films
Authors: Palacio Manuel Luis B. , Wang Yongquiang , Gerberich William W.
Published: March 2008

Films of poly(ether sulfone) have been implanted with 50-keV As+ in the dose range of 1015 to 1017 ions/cm2. Nanoindentation tests were then conducted on these films using a conical diamond tip with a 90° included angle, applying loads from 10 μN to 2 mN. The modulus and hardness were evaluated from the load–displacement data using the elastic unloading [J. Mater. Res. 7, 1564 (1992)] and the elastic–plastic unloading [J. Mater. Res. 13, 421 (1998)] models. The latter approach gave more reliable values for the mechanical properties since it is not as sensitive to creep-in effects. The implanted film showed as much as a twofold increase in hardness compared to the unimplanted polymer. However, the films with the highest dose did not exhibit the maximum values for the mechanical properties. Hardness and modulus values increased with increasing implantation dose up to 1 × 1017 ions/cm2 but dropped at higher doses, presumably due to a combination of sputtering of material and surface roughening. The dose dependence of the mechanical properties is observed to have the same trend as are reported for the electrical properties.