bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of polyparaphenylene (PPP)-based carbons
Authors: Matthews M. J. , Dresselhaus M. S. , Endo M. , Sasabe Y. , Takahashi T. , Takeuchi K.
Published: March 2008

Polyparaphenylene (PPP)-based carbons heat-treated at temperatures (THT) from 600 °C up to 3000 °C have been characterized both structurally and in terms of their physical properties. Special attention is given to PPP heat-treated at 700 °C (denoted by PPP-700), since samples heat-treated to this temperature were observed to have exceptionally high lithium affinities when electrochemically doped with Li. At low THT below 700 °C, it is found that the local structure of PPP-based samples can be characterized mostly in terms of a disordered polymer. As a result of heat treatment to high temperature, PPP-based carbon shows graphitization behavior with regard to x-ray diffraction d002 (graphite c-axis d-spacing) development and to the increase of the Raman IG/ID intensity ratio (where IG and ID are the integrated intensities of the 1580 cm−1 and 1360 cm−1 Raman modes, respectively), as is found in so-called graphitizing carbons. However, development of the c-axis crystallite size (Lc) is restricted to very small values, in the range of so-called nongraphitizing carbons, while the a-axis crystallite size (La) attains values up to roughly 120 Å for heat treatments near 3000 °C. These structural properties of PPP-based carbons are consistent with the observed electrical characteristics and their dependence on THT. Low temperature magnetic susceptibility measurements were analyzed, along with Raman spectra, allowing for the characterization of disorder in terms of localized spin states for several heat-treated PPP samples. By interpreting the results of these various characterization techniques, we are able to present an insightful perspective on the nature of PPP-based carbons and the role of PPP-700 as an effective lithium host material for secondary battery applications.
Controlled double-jet precipitation of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates
Authors: Her Yie-Shein , Matijević Egon , Chon Min Che
Published: March 2008

The synthesis of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates at a low temperature of 85 °C by the controlled double-jet precipitation (CDJP) technique is described. The stoichiometry of the powders can be precisely controlled by adjusting the compositions of the starting reactant solutions. Barium titanate with 20% Zr substitution, sintered at 1275 °C, satisfied the requirements for the Y5V multilayer capacitors application. The grain sizes are uniform and small, ranging from 1 to 3 μm. Solids with an extremely sharp change in the dielectric constant as a function of temperature, which are suitable for thermal IR detectors application, can be obtained when both Sr and Zr are incorporated as dopants.
The selective area deposition of diamond films
Authors: Roberts P. G. , Milne D. K. , John P. , Jubber M. G. , Wilson J. I. B.
Published: March 2008

Diamond films were selectively nucleated and grown on single crystal (100) silicon by microwave plasma assisted chemical vapor deposition with submicron spatial resolution. A thermal silicon dioxide layer on the wafers was patterned by standard photolithography. Nucleation was performed by applying a dc bias of −250 to −350 V in a hydrogen-methane plasma. Lifting off the oxide layer by HF etching prior to growth delineated the nucleation pattern which was replicated by the diamond film after growth. The growth of polycrystalline diamond was performed in a hydrogen-carbon monoxide-methane mixture selected to facilitate (100) texturing. Individual faceted crystallites were grown on a square matrix of sites, with a pitch of 3 μm, by controlling the nucleation densities within the windows exposing the prenucleated silicon. However, the orientation of the crystallites was randomly aligned with respect to the (100) silicon lattice within the micron scale windows employed in this study.
The structural changes of polycrystalline film C60/C70: Ni caused by Ni diffusion
Authors: Czerwosz E. , Byszewski P. , Diduszko R. , Wronka H. , Dluźewski P. , Mizera E.
Published: March 2008

C60/C70: Ni films with 1.5 wt. % Ni concentration obtained by vacuum deposition under different thermal conditions have been investigated. The structural changes of the layers were investigated by transmission electron microscopy, electron and x-ray diffraction, and Raman spectroscopy. The polycrystalline structure was detected for the layers grown at approximately 450 K on the substrate. At elevated temperature and maintained temperature gradient on the substrate during the process, the changes of the layer's structure and the formation of Ni microcrystals were observed. The Ni microcrystals (5–10 nm in the diameter) and the elongated shapes dimensioned 10 × 150 nm were perceived.
Micromechanical and tribological characterization of doped single-crystal silicon and polysilicon films for microelectromechanical systems devices
Authors: Bhushan Bharat , Li Xiaodong
Published: March 2008

Microelectromechanical systems (MEMS) devices are made of doped single-crystal silicon, LPCVD polysilicon films, and other ceramic films. Very little is understood about tribology and mechanical characterization of these materials on micro- to nanoscales. Micromechanical and tribological characterization of p-type (lightly boron-doped) single-crystal silicon (referred to as “undoped”), p+-type (boron doped) single-crystal silicon, polysilicon bulk, and n+-type (phosphorous doped) LPCVD polysilicon films have been carried out. Hardness, elastic modulus, and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Friction and wear properties were measured using an accelerated ball-on-flat tribometer. It is found that the undoped silicon and polysilicon bulk as well as n+-type polysilicon film exhibit higher hardness and elastic modulus than the p+-type silicon. The polysilicon bulk and n+-type polysilicon film exhibit the lowest friction and highest resistance to scratch and wear followed by the undoped silicon and with the poorest behavior of the p+-type silicon. During scratching, the p+-type silicon deforms like a ductile metal.
Fractal morphologies from decomposition of Fe−Ni−Invar alloys
Authors: Li Q. , Wiedenmann A. , Wollenberger H.
Published: March 2008

Small angle neutron scattering investigations performed on Fe1−x–Nix alloys with 0.26 ≤ x ≤ 0.45 revealed a thermodynamically driven decomposition below 800 °C. The miscibility gap extends at least from 30 at.% Ni to 45 at.% Ni. The diffusioncontrolled decomposition produces fractal morphologies during the early stages of the process. During annealing the structure of the precipitated phase densifies continuously from mass fractals with small dimensionality (1 ≤ dm ≤ 3) to surface fractals with 2 ≤ ds ≤ 3. The results are compared with recent simulations of aggregation and growth as well as with a new analysis of spinodal decomposition, both predicting fractal morphologies.
Structural properties of molecular beam epitaxy grown Ni/Pt superlattices
Authors: Staiger W. , Michel A. , Pierron-Bohnes V. , Hermann N. , Cadeville M. C.
Published: March 2008

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.
Residual surface stress by localized contact-creep
Authors: Widjaja Sujanto , Jakus Karl , Atri Revti , Ritter John E. , Bhattacharya Sandeepan
Published: March 2008

When a ceramic material creeps under a localized stress and then cools under load, a portion of the creep flow stress is retained as a residual compressive stress due to elastic rebound being constrained by the creep zone. Localized contact-creep was used to generate residual compressive surface stress in soda-lime glass and two sintered aluminas. The Vickers indentation technique was used to measure the residual stress within the contact-creep area. Alumina with a higher elastic modulus than glass retained higher residual compressive surface stress. The results were in reasonable agreement with the predicted stress distribution given by finite element analysis.
Change of the weak-field properties of Pb(ZrTi)O3 piezoceramics with compressive uniaxial stresses and its links to the effect of dopants on the stability of the polarizations in the materials
Authors: Zhang Q. M. , Zhao Jianzhong , Uchino K. , Zheng Jiehui
Published: March 2008

The properties of several Pb(ZrTi)O3 (PZT) piezoceramics under compressive uniaxial stresses were characterized. It was observed that uniaxial stresses have a marked effect on the soft PZT materials, including reducing the piezoelectric coefficients and depoling the samples at relatively low stress levels. The effect of the uniaxial stresses on the properties of hard PZT's is more complicated because the domain structure of the materials can be changed substantially without depoling the samples. Therefore, under a compressive stress along the poling direction, the piezoelectric and electromechanical coupling factor can be increased markedly due to both the increased non-180° domain boundary motions and the deaging effect. In addition, the experimental results support the notion that the difference between a hard PZT and a soft PZT lies in the types of defects introduced by dopants. Immobile defects create frustrations in the lattice and result in a soft behavior, and mobile defects stabilize the polarization and produce a hard behavior.
Computer simulations of interactions between ultrafine alumina particles produced by an arc discharge
Authors: Teng M. H. , Marks L. D. , Johnson D. L.
Published: March 2008

We wrote two computer programs, 3D and BUMP, to interpret transmission electron microscope (TEM) micrographs made during a study of the initial stage sintering of ultrafine alumina particles (UFP's, 20–50 nm in diameter). The first simulated the 3D geometric relationships of particles, from which we concluded that surface diffusion was the predominant sintering mechanism because no shrinkage occurred. BUMP simulated random contact of two particles and showed that the particle chains that formed before sintering were not formed purely by chance. Instead the particles experienced a rearrangement process (rotation and sliding) which reduced the total surface energy.
The structural characterization of amorphous thin films and coatings in their as-deposited state using x-rays at shallow angles of incidence
Authors: Rigden J. S. , Newport R. J. , Bushnell-Wye G.
Published: March 2008

We demonstrate the method of x-ray diffraction at shallow angles of incidence, using the intrinsically highly collimated x-ray beam generated by a synchrotron source, to study the atomic-scale structure of amorphous thin films and coatings in their as-deposited (i.e., on-substrate) state. As the incident angle is decreased, scattering from the film/coating can be isolated as contributions from the substrate are reduced. Systems studied include chemical vapor deposition (CVD) diamond films deposited onto both silicon and steel substrates, where evidence of an interfacial region between the film and silicon wafer has been observed, but we focus on a range of amorphous films/coatings (mixed TiO2 : SiO2 sol-gel spun films, hydrogenated carbon films and “glassy” carbon coatings, silicon: germanium semiconducting films and alumina coatings). The data are used both to comment upon the systems studied and to elucidate the potential, and the limitations, of the experimental method.
Deformation-induced planar defects in Al–Cu–Fe quasicrystals
Authors: Shield J. E. , Kramer M. J.
Published: March 2008

Planar defects were observed in a hot isostatically pressed Al–Cu–Fe alloy. The defects were determined to be perpendicular to the fivefold direction. They were also found to be regions where the quasiperiodicity in the five-fold direction was disrupted, resulting in a periodicity along this direction of 1.06 nm. The defects were stable up to approximately 750 °C. The defects were determined to be formed by the applied shear forces associated with the consolidation process. The displacement vector of the defects was determined to be in a twofold direction perpendicular to the periodic direction.
Lowering the formation temperature of the C54-TiSi2 phase using a metallic interfacial layer
Authors: Cabral C. , Clevenger L. A. , Harper J. M. E. , d'Heurle F. M. , Roy R. A. , Saenger K. L. , Miles G. L. , Mann R. W.
Published: March 2008

We demonstrate that the formation temperature of the C54 TiSi2 phase from the bilayer reaction of Ti on Si is lowered by approximately 100 °C by placing an interfacial layer of Mo or W between Ti and Si. Upon annealing above 500 °C, the C49 TiSi2 phase forms first, as in the reaction of Ti directly on Si. However, the temperature range over which the C49 phase is stable is decreased by approximately 100 °C, allowing C54 TiSi2 formation below 700 °C. Patterned submicron lines (0.25−1.0 μm wide) fabricated without the Mo layer contain only the C49 TiSi2 phase after annealing to 700 °C for 30 s. With a Mo layer less than 3 nm thick between Ti and Si, however, a mixture of C49 and C54 TiSi2 was formed, resulting in a lower resistivity. The enhanced formation of the C54 TiSi2 is attributed to an increased density of nucleation sites for the C49-C54 phase transformation, arising from a finer grained precursor C49 phase.
Rietveld analysis of the cubic crystal structure of Na-stabilized zirconia
Authors: Fagherazzi G. , Canton P. , Benedetti A. , Pinna F. , Mariotto G. , Zanghellini E.
Published: March 2008

Using x-ray Rietveld analysis the fcc (fluorite-type) structure of a Na-containing nanocrystalline zirconia powder (9.5 nm estimated crystallite size) obtained by precipitation and calcination has been confirmed. The result shows that conventional x-ray diffraction techniques can distinguish the cubic crystallographic form of ZrO2from the tetragonal one in nanosized powders. These conclusions are supported by independent Raman scattering experiments.
Composition of SiCN crystals consisting of a predominantly carbon-nitride network
Authors: Bhusari D. M. , Chen C. K. , Chen K. H. , Chuang T. J. , Chen L. C. , Lin M. C.
Published: March 2008

We report here on the synthesis of large crystals of Si-containing carbon nitride, consisting of a predominantly C–N network, by microwave CVD. The Si content in this material varies from crystal to crystal and also with the deposition conditions and has been observed to be as low as less than 5 at.% in some crystals, wherein the Si atoms are believed to substitute for some of the C sites only. This is the first time that such large and well-faceted crystals consisting almost entirely of carbon-nitride network have been synthesized. Moreover, there is no obvious deposition of amorphous CN material.
Chemical synthesis of a new tin dioxide based (SnO2 : Co, Al, Nb) varistor
Authors: Santhosh P. N. , Potdar H. S. , Date S. K.
Published: March 2008

A new varistor composition based on SnO2 doped with Co, Al, and Nb has been successfully synthesized by a chemical route. It exhibits excellent nonlinear current-voltage (I-V) characteristics with α ≈ 72 and E1mA ≈ 1820 V/mm.
Analysis of SCS-6 silicon carbide fibers by Fourier transform infrared spectroscopy
Authors: Krishnamurthy S.
Published: March 2008

Fourier transform infrared (FTIR) spectroscopy analysis of SCS-6 silicon carbide fibers was performed to detect the presence of oxygen in the form of SiO2. The results showed infrared peaks corresponding to SiC fundamental lattice absorption as well as reflection. No absorption peak due to SiO2 was observed. These results are in agreement with previously reported data indicating low levels of oxygen in this fiber.
Chemical analysis in YBa2Cu3O7−x melt-textured samples
Authors: Gotor F. J. , Ayache J. , Pellerin N. , Odier P.
Published: March 2008

A melt-textured process that involves the peritectic reaction Y2BaCuO5 + liquid → YBa2Cu3O7−x is the best method to develop bulk YBa2Cu3O7−x superconductors with improved transport and magnetic properties. Up to this point, information regarding cationic stoichiometry in textured samples is rather lacking in the literature. In this work, wavelength dispersive analysis (WDS) at a microscopic level and energy dispersive x-ray analysis (EDX) at a nanoscopic level were used to characterize the chemical composition of YBa2Cu3O7−x textured samples. The melt-textured process generally modifies the sample stoichiometry. Thus, a textured sample composition cannot be directly obtained even from an accurate knowledge of the starting composition. We have shown that WDS can be used to determine the overall composition and therefore the Y2BaCuO5 content in these samples. It is also a powerful method to control chemical homogeneity and to investigate chemical modifications occurring during processing, especially those resulting from interaction between melt and substrate. The exact nature of YBa2Cu3O7−x nucleation and crystallization still presents many unsolved questions. Nanoanalysis allowed us to study Y2BaCuO5 dissolution in the peritectic liquid, and we have confirmed that it takes place exclusively by removing yttrium from Y2BaCuO5 particles. We have also shown the existence of an yttrium-rich liquid phase, i.e., with a higher yttrium concentration that can be deduced from the equilibrium phase diagram. A liquid phase having a composition close to that of YBa2Cu3O7−x can be inferred from this work. This suggests that YBa2Cu3O7−x nucleation and crystallization take place homogeneously from this liquid.
The stability of Si1−xGex strained layers on small-area trench-isolated silicon
Authors: Schonenberg K. , Chan Siu-Wai , Harame D. , Gilbert M. , Stanis C. , Gignac L.
Published: March 2008

The combined effects of isolation stress, active area size, and SiGe misfit strain on dislocation generation in an advanced SiGe heterojunction bipolar transistor (HBT) process were studied. Eight-inch wafers were patterned with polysilicon-filled deep, and oxide-filled shallow trench isolation similar to that used in IBM's analog SiGe HBT technology. Half of the wafers were subjected to an additional stress-producing oxidation prior to SiGe growth. Si1−xGex films containing 0, 5.5, 9, and 13 at.% Ge were grown epitaxially by ultrahigh vacuum chemical vapor deposition (UHV CVD). The films were of constant thickness with an intrinsic Si cap. Some samples received an additional relaxation anneal following deposition. After the growth and anneal cycles, the dislocation density was determined by transmission electron microscopy (TEM). On nonstressed samples, no dislocations were observed in the device areas, even at Ge concentrations which are not stable to misfit dislocation generation in blanket form. This small area effect has been observed on patterned substrates that do not have functional device isolation. On the stressed-isolation wafers, the compressive stress from the oxidation of the trench sidewalls was found to intensify stress in the SiGe films, and to lower the critical strain at which misfit dislocations appeared. In large active areas on these wafers, two distinct dislocation regions were observed. Defects at the edge resembled those caused by isolation stress, while the defects in the center were more typical of the misfit dislocations associated with lattice-mismatch epitaxial films. It is clear that isolation stress must be minimized when fabricating integrated circuits using SiGe epitaxial films. It is also evident that SiGe films grown on nonstressed isolation exhibit the same increase in critical thickness with decreasing lateral dimension that has been observed on much simpler patterned substrates.
An analysis for geometrical effects on the cooling performance of (Bi, Sb)2Te3/Bi2(Te, Se)3-based thin film thermoelectric modules
Authors: Kim Il-Ho , Lee Dong-Hi
Published: March 2008

Geometrical effects on the cooling performance of the thin film thermoelectric (TFTE) modules were investigated by varying the film thickness and the number of p/n couples of the (Bi, Sb)2Te3/Bi2(Te, Se)3-based system which were fabricated by the flash evaporation technique. Maximum temperature difference (δTmax, maximum cooling) and optimum input current (Iopt) increased with film thickness for a fixed number of couples. For the case of given thickness, however, Iopt decreased with the number of couples, maintaining almost constant δTmax. The measured values for the cooling characteristics were compared with the results obtained through computer simulation work by the finite difference method (FDM). The thinner the film and the larger the number of p/n couples of the modules, the larger was the deviation between the experimental and the simulated values.
Comments on the effects of solution precursor characteristics and thermal processing conditions on the crystallization behavior of sol-gel derived lead zirconate titanate thin films
Authors: Schwartz R. W. , Voigt J. A. , Tuttle B. A. , Payne D. A. , Reichert T. L. , DaSalla R. S.
Published: March 2008

Lead zirconate titanate (PZT 40/60) thin films were fabricated on electroded silicon wafers using chemical solution deposition. Two different chelating agents, acetic acid and acetylacetone, were used in the synthesis of the precursor solutions. The microstructure of the acetylacetone-derived film was characterized by nucleation at the platinum electrode and a columnar growth morphology (˜100−200 nm lateral grain size). In contrast, the acetic acid-derived film was characterized by both columnar grains nucleated at the electrode, and larger (˜1 μm) grains nucleated at the surface of the film. Using Fourier transform infrared (FTIR) diffuse reflectance spectroscopy, we also noted that the pyrolysis behavior of the films was dependent on the chelating agent employed. The acetylacetone-derived films, which displayed only one nucleation event, were also characterized by a higher pyrolysis temperature than the acetic acid-derived films. Previously, microstructural differences of this nature were attributed to variations in “precursor structure.” In this paper, we discuss an alternative mechanism for the observed microstructural variations in films prepared from different solution precursors. In the model proposed, we discuss how changes in film pyrolysis temperature result in a change in film crystallization temperature, and hence, a change in the effective driving force for crystallization. We show how the change in crystallization driving force is expected to impact the thin film microstructure due to the accompanying variations that occur in the barrier heights for interface (lower electrode) and surface nucleation. A standard approach to nucleation in glasses is used as the basis of the proposed model. Finally, we also discuss how the model can be used to understand the observed effects of heating rate and thickness on the microstructure of solution-derived thin films.
Measurement of solid state diffusion coefficients by a temperature-programmed method
Authors: Kapoor Rajat , Oyama S. T.
Published: March 2008

This paper presents a method for determining diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentration. The method involves measuring the flux of the diffusive species out of the solid under the influence of a temperature program. A general model is developed, based on nonisothermal Fickian diffusion, which is applicable to solid particles with slab or spherical geometry. The solution is presented both as an analytical expression and as correlation charts of experimentally observable quantities. These charts are contour diagrams of the temperatures of peak diffusion rate with ln(E/R) and ln(D0/h2) as the axes, whereEandD0are the activation energy and pre-exponential terms of the diffusivity expressionD=D0exp(−E/RT), where R is the gas constant, andhthe size of the particles. This paper deals exclusively with the case of oxygen diffusion in the vanadium oxide system. In this case, vanadium oxide was reduced in a reactive ammonia stream at conditions in which the surface reaction was fast compared to the diffusive transport process. Using this method the diffusion parameters were found to beD0= 1.9 × 10−5cm2s−1andE= 101 kJ/mol. The method was checked by varying the crystallite size of the vanadium oxide sample in the range 2h= 0.14−0.29 μm.
Linear free energy relationships in solid state diffusion processes
Authors: Kapoor Rajat , Oyama S. T.
Published: March 2008

This paper presents a new form of linear free energy (LFE) relationship for diffusive mass transport in oxides and other binary compounds. The relationship applies to a family of related compounds. For a given substance,i, solid-state diffusivity is related to the equilibrium constantKior the free energy of transformation,, via a transfer coefficient γ, through the expression lnDi= γ lnKi+ constant. The system investigated here is the series of suboxide intermediates of vanadium pentoxide formed during temperature-programmed synthesis of vanadium nitride. The value of γ for this series is 0.27. The diffusivity values are determined by fitting a mathematical model to the experimental data. Diffusivity data are presented graphically in contour diagrams which correlate pre-exponential values, activation energies, particle sizes, and heating rates used in the temperature-programmed syntheses. An Evans–Polanyi linear relation,, relating activation energy,Ei, to enthalpy change of transformation,, via a transfer coefficient α = 0.53, is also shown to exist for the above system. The discrepancy between α and γ is resolved by using the Horiuti concept of the stoichiometric number of the rate-determining step.
Phase structure and thermal evolution in coatings and powders obtained by the sol-gel process: Part I. ZrO2−11.3 mol% Y2O3
Authors: Rivas P. C. , Caracoche M. C. , Martínez J. A. , Rodríguez A. M. , Caruso R. , Pellegri N. , de Sanctis O.
Published: March 2008

Yttria-stabilized cubic zirconia powders and coatings produced by the sol-gel method have been investigated by Perturbed Angular Correlation Spectroscopy (PAC). Results indicate that the metastable cubic phase is retained during heating and cooling cycles. The hyperfine interaction that describes this cubic phase, once crystallized, exhibits two components in a constant ratio of 4 : 1. The components represent different vacancy configurations. For the fast movement of oxygen vacancies starting at 750 °C, which is reflected by the damping of the hyperfine pattern, an activation energy of 0.96 eV was determined.
Interactions between lead oxide and ceramic substrates for thick film technology
Authors: Bersani Massimo , Morten Bruno , Prudenziati Maria , Gualtieri Alessandro
Published: March 2008

This paper deals with the mechanisms and kinetics of interactions between screen printed and fired PbO layers and ceramic substrates: alumina and beryllia. The interaction with alumina occurs via two main processes: (i) a reaction between PbO and Al2O3 grains, which induces the formation of a crystalline phase, Pb2Al2O5; and (ii) an interdiffusion process involving Pb and the intergranular amorphous phase in the ceramic substrate. This latter process results in a compositional change of the intergranular phase at considerable depths inside the ceramic substrate, as well as in the formation of a high lead glass layer on the substrate surface. Since PbO is not completely reacted, the Pb penetration in the ceramic is diffusion limited (penetration depth , where td is the reaction time) with an activation energy of 1.20 ± 0.05 eV. The ceramic microstructure significantly affects the interaction processes.
Ordering and microwave dielectric properties of Ba(Ni1/3Nb2/3)O3 ceramics
Authors: Kim In-Tae , Kim Yoon-Ho , Chung Su Jin
Published: March 2008

Ordering and microwave dielectric properties of Ba(Ni1/3Nb2/3)O3 have been investigated using x-ray diffraction, transmission electron microscopy, energy-dispersive spectroscopy, and a network analyzer. Samples sintered at 1400 °C for 2 h were disordered and showed the presence of Nb-rich liquid phase at grain boundary junctions. Degree of ordering increased with following annealing at 1300 °C. Growth of the ordered region during the annealing process was discussed in terms of nucleation and growth. A long-range order parameter was calculated using structure factor. Measurements of microwave dielectric properties showed that permittivity and temperature coefficient of resonant frequency decreased with ordering, and quality factor increased with ordering. The correlation between microwave dielectric properties and ordering was discussed in terms of covalency of bonding, inhomogeneous charge distribution, and defects concentration.
Preparation of epitaxial La1−xSrxMnO3 films on SrTiO3(001) by dipping-pyrolysis process
Authors: Manabe T. , Yamaguchi I. , Kondo W. , Mizuta S. , Kumagai T.
Published: March 2008

La1−xSrxMnO3 (LSMO) (x = 0−0.3) films were prepared on SrTiO3(001) substrates by the dipping-pyrolysis process using metal naphthenates as starting materials. Epitaxially grown LSMO films were obtained by heat treatment at 800–1200 °C; the fluctuation of alignment of these films, evaluated by reciprocal-space mapping of asymmetric x-ray diffraction, was markedly small, as comparable to that of the substrates. The LSMO films with x = 0.1−0.3 showed metallic conduction behavior at 25–300 K, and the resistivity was as low as that of LSMO single crystals, e.g., 4.5 × 10−4 Ω · cm at 150 K for the film with x = 0.3.
Waveguide refractometry as a probe of thin film optical uniformity
Authors: Potter B. G. , Dimos D. , Sinclair M. B.
Published: March 2008

Optical inhomogeneities through the thickness of a sol-gel-derived, spin-coated Pb(Zr,Ti)O3 (PZT) thin film have been evaluated using prism-coupled waveguide refractometry. Unusual waveguide coupling angle behavior has been treated using a multilayer model to describe the optical characteristics of the film. Waveguide refractometry measurements, performed after incremental reductions in film thickness, were used to develop a consistent model for optical inhomogeneity through the film thickness. Specifically, a thin film layer model, consisting of alternating layers of high and low refractive index material, was found to accurately predict irregularities in transverse-electric (TE) mode coupling angles exhibited by the film. This layer structure has a spatial periodicity that is consistent with the positions of the upper film surface at intermediate firings during film synthesis. The correlation emphasizes the impact of the multistep thin-film deposition approach on the optical characteristics of the resulting thin film.
Very high pressure sintering of cBN fine particles coated with TiN–TiB2 layer formed by disproportionation reaction in molten salts
Authors: Yoshida Haruo , Kume Shoichi
Published: March 2008

Sintering of a fine cubic boron nitride (cBN) particle with a grain size of less than 2 μm was successfully carried out under 5.5 GPa pressure at 1720 K for 30 min. TiN–TiB2-coated cBN particles were used as the starting powder without adding any other binding materials. The coating was carried out by dipping the cBN particles in molten salts. The obtained cBN sintered compact shows a smooth microstructure with a well-controlled grain boundary; TiN–TiB2 is distributed over the cBN-grain boundary in the shape of a net mesh similar to tiled floors. The Vickers microhardness of the obtained compact was found to be higher than that of commercially available typical cBN-cutting tools.
Sol-gel derived Ba(Mg1/3Ta2/3)O3 thin films: Preparation and structure
Authors: Zhou Ji , Su Qing-Xin , Moulding K. M. , Barber D. J.
Published: March 2008

Ba(Mg1/3Ta2/3)O3 thin films were prepared by a sol-gel process involving the reaction of barium isopropoxide, tantalum ethoxide, and magnesium acetate in 2-methoxyethanol and subsequently hydrolysis, spin-coating, and heat treatment. Transmission electron microscopy, x-ray diffraction, and Raman spectroscopy were used for the characterization of the thin films. It was shown that the thin films tend to crystallize with small grains sized below 100 nm. Crystalline phase with cubic (disordered) perovskite structure was formed in the samples annealed at a very low temperature (below 500 °C), and well-crystallized thin films were obtained at 700 °C. Although disordered perovskite is dominant in the thin films annealed below 1000 °C, a low volume fraction of 1 : 2 ordering domains was found in the samples and grows with an increase of annealing temperature.
Phase transformation in Sr1−xBaxNb2O6 ceramics
Authors: Wang Xiaoli
Published: March 2008

The phase transformation in Sr1−xBaxNb2O6 (0.25 ≤ x ≤ 0.8) ceramics was investigated. There is an intermediate transitive phase before forming the tungsten bronze phase at higher temperatures. The phase transformation from the intermediate type into tungsten bronze type is sluggish, affected principally by temperature. In the compositions rich in Ba (x > 0.672), Ba ions prefer to occupy the A2 sites rather than the A1 sites of the tungsten bronze structure. The percentages of vacancies in the A1 sites and A2 sites are no longer the same. With the increase of Ba, the vacancies in the A1 sites increase, whereas the vacancies in the A2 sites decrease.
Growth of TlBa2Ca2Cu3O9−y superconducting films with local biaxial alignment extending up to 5 mm on Ag substrates using a spray-pyrolysis technique
Authors: Paranthaman M. , List F. A. , Goyal A. , Specht E. D. , Vallet C. E. , Kroeger D. M. , Christen D. K.
Published: March 2008

We report on the superconducting properties of TlBa2Ca2Cu3O9−y (Tl-1223) thick films grown on smooth and rough Ag substrates. Thallium-free precursor films of the type Ba2Ca2Cu3Ag0.37O7 were deposited on Ag substrates using a spray-pyrolysis technique followed by post-thallination in a two-zone furnace. X-ray diffraction (XRD) results showed the presence of c-axis aligned Tl-1223 films and some degree of local in-plane texture (often referred to as a colony microstructure). The microstructure of the Ag surface dictates the growth behavior of Tl-1223 films. The transport critical-current densities (Jc) for Tl-1223 films grown on smooth and rough Ag substrates were ∼ 65,000 A/cm2 and ˜ 37,000 A/cm2, respectively, at 77 K and zero field. The films grown on smooth Ag substrates were strongly linked and had good in-field properties with a Jc value of ∼104 A/cm2 at 77 K and 0.5 T.
Vacancy structures on the GaN(0001) surface
Authors: Packard William E. , Dow John D. , Doverspike Kathleen , Kaplan Ray , Nicolaides Ruth
Published: March 2008

Scanning tunneling microscopy images are reported for the wurtzite GaN(0001) surface. Terraces are observed, with three kinds of defect structures that are assigned to ordered N-vacancies: (i) striations perpendicular to the step edges, (ii) row defects spaced about 16 Å that intersect the steps at an angle of 30°, and (iii) “oval” defects that result from intersections of lines of vacancies (oriented at 60° with respect to step edges) with the row defects.
Enhanced nucleation density of chemical vapor deposition diamonds by using interlayer
Authors: Lee J. J. , Yang W. S. , Je Jung Ho
Published: March 2008

Effects of interlayers on diamond nucleation were investigated for the Si substrates. Interlayers were deposited on the diamond-abraded Si substrates by rf sputtering prior to diamond growth using microwave plasma chemical vapor deposition (CVD). Compared with 1 × 108/cm2 for the just abraded substrate, the nucleation density was greatly enhanced to 1 ∼ 2 × 109/cm2 by 50 nm thick interlayer, irrespective of the kind of interlayer material used in this study (Si, Mo, Ti, Pt, Ag, TiN, or SiO2). As the thickness of the Si interlayer increased from 20 to 500 nm, the nucleation density reached a maximum value, 3 × 109/cm2 at 100 nm. However, the growth rate was monotonically reduced from ∼300 nm/h to ∼100 nm/h. For the 700 nm thick Si interlayer, no diamond growth was observed. These results indicate that there is an optimum interlayer thickness around 100 nm for the higher nucleation density. The role of the interlayer in enhancing the nucleation density is believed to protect the nucleation sites generated by the diamond abrasion, otherwise they could be considerably etched away by atomic hydrogen during the initial diamond deposition.
Influence of elemental B addition on the heat-treated cast structures of Ti–47Al–2Cr–(2–4)Nb alloys
Authors: Jung J. Y. , Park J. K.
Published: March 2008

The influence of elemental B addition on the heat-treated cast structure of Ti–47Al–2Cr–(2–4)Nb alloys has been investigated using x-ray diffractometry, optical microscopy, scanning and transmission electron microscopy, and tensile testing. The phase sequence is β → β + α → α → α + γ → α + β + γ → β + γ. The addition of (0–2 at. %) B does not change the phase sequence. It, however, tends to stabilize α phase by shifting the (α + β + γ) three-phase region toward a higher (Cr + Nb) content. The B addition does not significantly alter the equilibrium composition within (α + γ) two-phase field. The B addition markedly accelerates the lamellar formation kinetics and enhances the thickening rate of γ plates, despite the fact that it increases both the misfit between α and γ plates and the α/γ interfacial energy. The acceleration of lamellar formation kinetics is thus believed to be primarily due to the enhancement of chemical diffusivity as a result of B addition. The B addition induces a significant refinement of heat-treated cast structure. This is primarily due to the role of boride to disperse the interdendritic γ regions to a fine network and to refine the dendrite cell size. Further refinement arises from the boride's role to act as the nucleation site for γ grains and from the intrinsic B effect to enhance the chemical diffusivity and the γ thickening rate. The addition of a small amount of B enhances both the strength and tensile ductility of near gamma structure. The strengthening arises from grain size refinement and from the boride dispersion. The calculation of fracture strain suggests that an enhancement of ductility for small B addition (up to ∼0.2 at. %) is mostly due to its effect to refine the γ grains.
Role of matrix microstructure in the ultrasonic characterization of fiber-reinforced metal matrix composites
Authors: Krishnamurthy S. , Matikas T. E. , Karpur P.
Published: March 2008

This work deals with the application of ultrasonic nondestructive evaluation for characterizing fiber-reinforced metal matrix composites. The method involved the use of a recently developed technique in which the fiber reinforcement acts as a reflector to incident ultrasonic shear waves. Single fiber and multifiber, single ply composites consisting of SiC fibers in several titanium alloy matrices were investigated. The ultrasonic images obtained were correlated with the results of metallographic characterization of the composites. The results showed that the ultrasonic response of the metal matrix composites is significantly influenced by the microstructure of the matrix through which the incident wave traverses. The general effects of matrix on ultrasonic wave propagation are reviewed, and the ultrasonic signals obtained from various SiC fiber-reinforced titanium alloy composites are discussed in terms of the scattering effects of matrix microstructure.
High pressure compaction of nanosize ceramic powders
Authors: Gallas M. R. , Rosa A. R. , Costa T. H. , Jornada J. A. H. da
Published: March 2008

High-density ceramic materials from nanosize ceramic powders were produced by high pressure under nearly hydrostatic environment up to 5.6 GPa, on a special configuration in a toroidal-type apparatus, at room temperature. Attempts to use a common solid pressure transmitting medium, as NaCl, resulted in cracked samples. Lead and indium, which have an extremely low shear strength, proved to be the suitable choices as a pressure-transmitting medium to compact these ceramic materials, in order to obtain high-density samples. Transparent amorphous SiO2-gel and translucent γ−Al2O3 samples, in bulk, with volumes about 40 mm3, hard and crack-free were obtained. Densities over 90% of full density for the γ−Al2O3 samples and over 80% for the compacted SiO2-gel samples were obtained. In addition, from the density-pressure curve, the yield strength (σ) for γ−Al2O3 was estimated, for the first time, as 2.6 GPa. Vickers microhardness values were in the range of 5.7 GPa for the γ−Al2O3 samples, and 4.0 GPa for the SiO2-gel samples, under loads of 50 g. An important and practical application of these results is the possibility of producing bulk γ−Al2O3, a new alumina material, which was not possible to prepare before due to the conversion to a phase during the normal sintering process. Additionally, specially for SiO2-gel, a very important application of this study is the possibility of incorporation of organic substances in an inorganic matrix, using high pressure at room temperature.
Effect of heat treatment on formation of sol-gel (Pb, La)TiO3 films for optical application
Authors: Koo Junmo , Kim Sung-Uk , Yoon Dae Sung , No Kwangsoo , Bae Byeong-Soo
Published: March 2008

Lead lanthanum titanate [(Pb, La)TiO3] sol-gel films have been prepared to investigate the effect of heat treatment on the fabrication of uniform and crack-free thick films by applying different heating schedules. The surface morphology as well as the optical properties such as refractive index, optical transmission, and optical propagation loss of the films was examined, depending on the film thickness. Because the slower and longer heating is enough to remove the organic and nitrate residues and diminish the thermal shock while heating the films, slower and longer heating can produce the uniform and crack-free thick films having higher refractive index as well as lower optical propagation loss. Also, the drying and heating of the films on a hot plate in every coating resulted in the fabrication of thick films having above 8000 Å without any defects and microcracks. This film presented the highest refractive index as well as the lowest optical propagation loss which grows exponentially with increasing the film thickness due to the scattering of defects in the film.
Role of antimony sulfide buffer layers in the growth of ferroelectric antimony sulfo-iodide thin films
Authors: Solayappan N. , Raina K. K. , Pandey R. K. , Varshney U.
Published: March 2008

The growth and properties of ferroelectric antimony sulfo-iodide (SbSI) films on platinized silicon (Pt/Ta/SiO2/Si) for various applications are reported here. Films were grown with and without antimony sulfide (Sb2S3) buffer layers using the physical vapor transport technique (PVT). The Sb2S3 buffer layers significantly improve the crystalline orientation and microstructure of the SbSI films. It is possible to control the crystalline orientation of the SbSI films to a large degree by annealing the buffer layers under optimized conditions of temperature and time. The films are chemically homogeneous, uniform in thickness, and ferroelectric in nature. The PVT method is effective for the growth of device quality ferroelectric SbSI films with preferred orientation along the c-axis either perpendicular or parallel to the substrate surface. The former configuration is particularly suited for the fabrication of uncooled focal plane arrays, whereas the films with c-axis orientation parallel to the substrate are useful for the development of infrared imagers based on the pyro-optic effect. The peak dielectric constant of c-axis oriented films (perpendicular to the substrate) is determined to be 590 at the Curie point of 19 °C. This is the highest value of the dielectric constant ever reported for SbSI films.
Investigation of the interface reactions of Ti thin films with AlN substrate
Authors: He Xiangjun , Yang Si-Ze , Tao Kun , Fan Yudian
Published: March 2008

Pure bulk AlN substrates were prepared by hot-pressing to eliminate the influence of an aid-sintering substance on the interface reactions. AlN thin films were deposited on Si(111) substrates to decrease the influence of charging on the analysis of metal/AlN interfaces with x-ray photoelectron spectroscopy (XPS). Thin films of titanium were deposited on bulk AlN substrates by e-gun evaporation and ion beam assisted deposition (IBAD) and deposited on AlN films in situ by e-gun evaporation. Solid-state reaction products and reaction mechanism of the Ti/AlN system annealed at various temperatures and under IBAD were investigated by XPS, transmission electron microscopy (TEM), x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS). Ti reacted with AlN to form a laminated structure in the temperature range of 600 °C to 800 °C. The TiAl3 phase was formed adjacent to the AlN substrate, TiN, and Ti4N3−x as well as Ti2N were formed above the TiAl3 layer at the interface. Argon ion bombardment during Ti evaporation promoted the interface reactions. No reaction products were detected for the sample as-deposited by evaporation. However, XPS depth profile of the Ti/AlN/Si sample showed that Ti–N binding existed at the interface between the AlN thin films and the Ti thin films.
In situ measurements of texture and phase development in (Bi, Pb)2Sr2Ca2Cu3O10–Ag tapes
Authors: Thurston T. R. , Haldar P. , Wang Y. L. , Suenaga M. , Jisrawi N. M. , Wildgruber U.
Published: March 2008

Hard x-rays from a synchrotron source were utilized in diffraction experiments performed at elevated temperatures (up to ˜ 870 °C) on (Bi, Pb)2Sr2Ca2Cu3O10 (Bi-2223) tapes completely encased in silver. The general behavior of the phase and texture development under typical processing conditions was determined, and the effects that several variations in processing conditions had on the phase and texture development were examined. These results and their implications for improving processing conditions are discussed.
The Fracture Toughness of Polysilicon Microdevices: A First Report
Authors: Ballarini R. , Mullen R. L. , Yin Y. , Kahn H. , Stemmer S. , Heuer A. H.
Published: March 2008

Polysilicon microfracture specimens were fabricated using surface micromachining techniques identical to those used to fabricate microelectromechanical systems (MEMS) devices. The nominal critical J-integral (the critical energy release rate) for crack initiation, Jc, was determined in specimens whose characteristic dimensions were of the same order of magnitude as the grain size of the polysilicon. Jc values ranged from 16 to 62 N/m, approximately a factor of four larger than Jc values reported for single crystal silicon.