bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray photoelectron spectroscopy studies of bond structure between polyvinyl alcohol and a titanate cross-coupling agent
Authors: Gülgün Mehmet A. , Popoola Oludele O. , Kriven Waltraud M.
Published: September 2007

Chemical interactions between polyvinyl alcohol (PVA) and triethanol amine titanate chelate were studied using x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The titanate chelate cross coupled the PVA solution and produced a viscous gel. The gel had a three-dimensional network structure containing -CPVA-O-Ti-O-CPVA- organic complexes. A new C(ls) signature at 285.7 eV and an O(ls) signature at 531.25 eV were associated with the formation of these complexes. The water of the PVA solution was physically retained in the gelled structure and was readily available for chemical reactions. The removal of this entrapped water was irreversible and led to a collapsed film of Ti-cross-linked PVA.
YBa2Cu3O7−x single-crystal growth by the pulling method with crystal rotation effect control
Authors: Namikawa Y. , Egami M. , Yamada Y. , Shiohara Y.
Published: September 2007

YBa2Cu3C7−x (Y123) single crystals have been grown by the modified pulling method (Solute Rich Liquid Crystal Pulling method, SRL-CP). For further superconductor device application, it is important to establish a technique that enables us to produce larger Y123 single crystals consistently. We have investigated the relationship among the crystal size, the crystal rotation rate, the flow pattern in the melt, and the temperature at the crystal growth interface experimentally. Increase of the crystal diameter and/or the crystal rotation rate increased the strength of the forced convection in the melt, and as a result, the temperature at the crystal growth interface increased. This resulted in a reduction of the crystal growth rate. On the other hand, the forced convection should be kept high enough to prevent floating particles attaching to the growing crystal. Therefore, in order to grow a larger single crystal, it was necessary to control the crystal rotation rate according to the change of the crystal diameter with time. We succeeded in crystal pulling along the c-axis of a relatively large Y123 single crystal which was 17 mm × 17 mm and 8 mm in length.
Oxygen diffusion through dielectrics: A critical parameter in high critical temperature superconductors multilayer technology
Authors: Tidrow S.C. , Wilber W.D. , Tauber A. , Schauer S.N. , Eckart D.W. , Finnegan R.D. , Pfeffer R.L.
Published: September 2007

We have studied the relative diffusion rates of oxygen through dielectric/buffer layers used in high critical temperature superconducting multilayer structures. Epitaxial bilayer films of dielectric (CeO2, LaGaO3, NdGaO3, LaAlO3, MgO, SrTiO3, LaLiTi2O6, or LaNaTi2O6) on YBa2Cu3O7−δ (YBCO) have been deposited onto (001) oriented single-crystal MgO substrates using pulsed laser deposition. These bilayers have been investigated for oxygen diffusion over the temperature range 350 to 650 °C by postdeposition annealing the films for 20 min in 0.5 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile the relative concentration of 18O to 16O in each bilayer. Compared to YBCO, the dielectrics MgO, SrTiO3, LaLiTi2O6, and LaNaTi2O6 are relatively slow diffusers, while CeO2, LaGaO3, NdGaO3, and LaAlO3 are relatively fast diffusers.
The cracking resistance of nanoscale layers and films
Authors: Leung D.K. , He M.Y. , Evans A.G.
Published: September 2007

Thin film cracking has been studied for a nanometer brittle/ductile layered system consisting of Si and Cu. Single Si films and Cu/Si/Cu trilayers were fabricated by physical vapor deposition. The films were deposited onto a ductile substrate consisting of stainless steel with a thin polyimide interlayer. Straining of the substrate induced cracking of the Si. Cracking strains ≥1% were observed, particularly in layers ≤100 nm thick. The critical cracking strain was found to depend upon the Si layer thickness, as well as the thickness and elastic/plastic properties of the adjacent ductile layers. Si cracking was suppressed by the presence of adjacent Cu layers. The measured strains were compared with lower-bound critical strains for tunnel and channel cracking. Comparisons indicated that these mechanisms control the critical strain found in trilayers, because trilayer fabrication introduces edge flaws larger than the Si layer thickness. Conversely, for Si films, the measured critical strains exceed the channel cracking strain, because the flaws in these films are relatively small.
Synthetic diamond crystal strength enhancement through annealing at 50 kbar and 1500 °C
Authors: Webb Steven W. , Jackson W.E.
Published: September 2007

High-pressure, high temperature (HPHT) annealing of synthetic type I diamond crystals at 1200–1700 °C and 50–60 kbar was found to induce aggregate-nitrogen dissociation and metal coalescence as well as heal diamond lattice dislocations. For crystals with low levels of metal inclusions, HPHT annealing was observed to increase the average compressive fracture strength of the crystals by apparently strengthening the strongest crystals of the population. Crystals with high metal-content, or otherwise of low quality, are weakened by anncaling. Strengthening is believed to occur by locally stabilizing the diamond lattice by healing lattice dislocations as well as dispersing nitrogen within the lattice. A general model is presented that ties together these results with those of other researchers.
Sputtered WSix for micromechanical structures
Authors: Ger Muh-Ling , Brown Richard B.
Published: September 2007

Tungsten silicide (WSix) thin tilms have been investigated for use as integrated circuit interconnect and self-aligned MESFET (metal-semiconductor field-effect transistor) gates because of their low resistivity and thermal and chemical stability. These same characteristics make them interesting materials for prospective use in micromechanical structures. However, little information on residual stresses, elastic moduli, or other micromechanical properties has been available for refractory metal silicide thin films. This paper presents the morphology and stress characteristics of cosputtered WSix thin films, including crystal structure variations and orientation-dependent stresses, as a function of the deposition pressure. The compositions of WSix thin films were analyzed by Rutherford backscattering spectrometry (RBS). The biaxial elastic modulus and thermal coefficient of expansion were found for the sputtered films. Stress-measurement methods and annealing are discussed. Released diaphragms of different sizes and shapes, having controlled residual stress, have been fabricated.
Fabrication of near-net-shape Al2O3-fiber-reinforced Ni3Al composites by combustion synthesis
Authors: Williams William C. , Stangle Gregory C.
Published: September 2007

In this paper, a one-step, combustion synthesis-based process for fabricating Al2O3 fiber-reinforced Ni3Al is described. The process uses relatively low temperatures and pressures, and can be used to prepare relatively large, dense, near-net-shape articles that possess either simple or relatively complicated shapes. This process can be used to incorporate continuous, aligned fibers into the Ni3Al matrix material in such a way that the fibers are not damaged either mechanically (due to relatively small loads applied during the process) or chemically (due to the very short time at which the sample remains at elevated tempertures during the process). (Chopped fibers, as well as equiaxed particles or whiskers, could also be similarly incorporated using this process.) This combustion synthesis process is a relatively simple one-requiring only relatively low temperatures and pressures, as well as relatively low-cost starting materials-which suggests that its scale-up beyond the laboratory scale would be particularly straightforward.
Sintering-viscosity relation for mixed-alkali glass powder compacts
Authors: Kim Ki-Dong
Published: September 2007

The sintering of glass powder compacts was studied by dilatometer in the (25 -x) Na2O–xK2O–75SiO2glass system. The dilatometrically determined sintering temperature (Tsin) at constant heating rate decreases and the shrinkage at isothermal sintering increases when Na2O is replaced by K2O up to the mole fraction of K2O/(Na2O + K2O) = 0.5. This is due to the decrease in viscosity and means that sintering can be possibly accelereted by introduction of mixed alkali oxides in this system. According to calculation using the VFT-equation, the viscosity value atTsinis almost independent of glass composition. From these results it may be supposed that the dilatometrically determined sintering begin temperature (Tsin) can be a characteristic point for the sintering of glass.
Magnetic alignment in 2212 Bi-based superconducting system: II. Bi2Sr2Ca1−xDyxCu2O8−yx = 0.2 glass recrystallized in 0.6 T magnetic field
Authors: Stassen S. , Cloots R. , Rulmont A. , Ausloos M.
Published: September 2007

Starting from a glassy precursor, Bi2Sr2Ca1−xDyxCu2O8−y (for x = 0.2) was recrystallized under a 0.6 T magnetic field. After splat quenching, the samples were heated and sintered at different temperatures T1, then slowly cooled. X-ray diffraction data, sometimes showing 00l peak splitting and electron scanning microscopy pictures, were collected. The results showed that the magnetic field could orient the grains and led to a magnetically textured growth process. Secondary phases formed in the system during this process were identified by EDX analysis. The optimum T1 for texturing was found to be between 930 °C and 950 °C.
Heat conduction in silicon thin films: Effect of microstructure
Authors: Wei Lanhua , Vaudin Mark , Hwang Cheol Song , White Grady , Xu Jason , Steckl Andrew J.
Published: September 2007

A study was made of the thermal properties of low pressure chemical vapor deposition (LPCVD) silicon thin films with amorphous and polycrystalline microstructures, produced by varying the substrate temperature. Thermal diffusivity measurements were conducted using a thermal wave technique. The thermal diffusivity of the polycrystalline films was found to be about three times that of the amorphous films, but about one eighth that of bulk silicon single crystals. There was also an indication that the diffusivity increased with deposition temperature above the transition temperature from the amorphous to the polycrystalline state. The relationships between the thermal properties and microstructural features, such as grain size and grain boundary, are discussed.
On the new structural phases in Al65Cu20Cr15 quasicrystalline alloy
Authors: Khare Varsha , Lalla N.P. , Tiwari R.S. , Srivastava O.N.
Published: September 2007

The quasicrystalline (qc) alloy Al65Cu20Cr15, unlike its Ru- and Fe-bearing counterparts like Al65Cu20Ru15 and Al65Cu20Fe15, is a metastable phase. This qc alloy has been shown to possess several structural variants and curious structural characteristics. We have investigated the qc alloy Al65Cu20Cr15 with special reference to the possible occurrence of new structural variants. TEM exploration of the as-quenched qc alloy has indeed revealed the existence of several new phases. These are (i) body-centered cubic (bcc) (a = 12.60 Å, disordered) and simple cubic (s.c.) (a = 12.60 Å, ordered), which are the 1/1 approximants of the primitive icosahedral phase (i phase); (ii) a twice order-induced modulated cubic phase (bcc, a = 25.20 Å) which has been shown to correspond to 1/1 approximant of the ordered i phase [i.e., face-centered icosahedral (FCI)]; and (iii) real crystalline bcc (a = 8.90 Å) and face-centered cubic (fcc) (a = 17.98 Å) phases possessing a specific orientation relationship with the icosahedral matrix phase. Tentative structural models showing the interrelationships between the bcc/fcc phases have been outlined.
Crack progression and interface debonding in brittle/ductile nanoscale multilayers
Authors: Leung D.K. , Zhang N.T. , McMeeking R.M. , Evans A.G.
Published: September 2007

Crack initiation and progression have been studied in nanoscale brittle/ductile multilayers of Cu and Si. Variations in the interface debond energy on the cracking behavior have been examined by using thin interlayers comprising either Cr (strong interface) or Au (weak interface). For strongly bonded Cr interfaces, it has been found that cracks forming in the Si invariably extend through the Cu layers, despite the ductile rupture characteristics of the Cu. This behavior occurs even when the Cu layers comprise more than 70% of the multilayer volume. It also contrasts with the crack arrest capabilities exhibited by relatively thick ductile layers (∼10-100 μm). The disparity in behavior is attributed to the relatively large cracking strain required for the thin brittle layers. Weak Au interfaces result in debonding which, in turn, can suppress the propagation of cracks into adjacent layers. However, when the interface includes strongly bonded sections, the debond arrests, and often kinks into the attached Si. In this case, cracking still progresses sequentially through the Si layers. Careful control of the interface debond energy is needed to fully suppress crack progression in nanoscale multilayers.
Influence of surface roughness on the wetting angle
Authors: Zhou X.B. , De Hosson J.Th.M.
Published: September 2007

A this paper the influence of surface roughness on contact angles in the system of liquid Al wetting solid surfaces of Al2O3 has been studied. It was observed that contact angles of liquid Al vary significantly on different rough surfaces of Al2O3. A model is proposed to correlate contact angles with conventional roughness measurements and wavelengths by assuming a cosine profile of rough grooves with a Gaussian distribution of amplitudes. In comparison with the experimental results, the model provides a good estimate for describing the influence of surface roughness on contact angles of liquid Al on Al2O3.
Synthesis of nanophase silicon, carbon, and silicon carbide powders using a plasma expansion process
Authors: Rao N. , Micheel B. , Hansen D. , Fandrey C. , Bench M. , Girshiek S. , Heberlein J. , McMurry P.
Published: September 2007

Nanophase powders of Si, C, and SiC with narrow size distributions are synthesized by dissociating reactants in a dc are plasma and quenching the hot gases in a subsonic nozzle expansion. The plasma is characterized by calorimetric energy balances and the powders by on-line aerosol measurcment techniques and conventional materials analysis. The measured nozzle quench rate is about 5 × 106 K/s. The generated particles have number mean diameters of about 10 nm or less, with Si forming relatively dense, coalesced particles, while SiC forms highly aggregated particles. Our data suggest that SiC particle formation is initiated by the nucleation of small silicon particles.
Microwave dielectric properties of (Zr0.8Sn0.2)TiO4 ceramics with pentavalent additives
Authors: Yoon Ki Hyun , Kim Young Sol , Kim Eung Soo
Published: September 2007

The microwave dielectric properties of (Zr0.8Sn0.2)TiO4 were investigated as a function of the amount of additives such as Nb2O5 Ta2O5 and Sb2O5 in the temperature range of 20 °C to 80 °C at 7 GHz. As the amount of additives increased up to 1.0 mol %, the unloaded Q increased due to the decrease of oxygen vacancies in the (Zr0.8Sn0.2)TiO4 lattice and then decreased with further addition of additives because the electron concentration was increased. The temperature coefficient of the resonant frequency turned more negative with increasing additives. Although the Nb+5, Ta+5, and Sb+5 ions have a similar ionic size and the same valence electronics, each resulted in different microwave dielectric properties.
Metal incorporation in sputter-deposited MoS2 films studied by extended x-ray absorption fine structure
Authors: Lince Jeffrey R. , Hilton Michael R. , Bommannavar Arun S.
Published: September 2007

Solid lubricant films produced by cosputtering metals with MoS2 and by forming metal/MoS2 multilayers are being planned for use in the next generation of solid lubricated devices on spacecraft, including gimbal and sensor bearings, actuators, and sliding electrical contacts. The films exhibit increased densities and wear lives compared to films without additives, but the mechanism of density enhancement is not well understood. The extended x-ray absorption fine structure (EXAFS) technique is ideal for elucidating the structure of these poorly crystalline films. We analyzed MoS2 films cosputtered with 0, 2, and 10% Ni, as well as Ni/MoS2 and Au(Pd)/MoS2 multilayer films. The results obtained at the Mo-K absorption edge showed that the metal-containing films comprised predominantly the same nanocrystalline phases present in similar films without added metals: pure MoS2 and a MoS2−xOx phase. MoS2−xOx is isostructural with MoS2, with O atoms substituting for S atoms in the MoS2 crystal lattice. For all Ni-containing films, EXAFS data obtained at the Ni-K absorption edge showed that the Ni had not chemically reacted with the MoS2−xOx and MoS2, but formed a disordered NiOx phase. However, Ni-cosputtered films showed decreasing Mo-Mo bond lengths in the MoS2−xOx phase with increasing Ni content, probably due to preferential oxidation of Ni compared to MoS2. EXAFS of these Ni-cosputtcred films showed only a small decrease in short-range order with Ni content, while x-ray diffraction showed a concurrent large decrease in long-range order. The results indicate that film densification in Ni-cosputtered films is caused by NiOx formation at the edges of nucleating MoS2−xOx/MoS2 crystallites, limiting the crystallite size attainable within the films.
Amine-reactive surface chemistry of zinc phosphate glasses
Authors: Hersh L.S. , Onyiriuka E.C. , Hertl W.
Published: September 2007

Surface chemical studies on zinc phosphate glasses were carried out with an ammonia probe using FTIR and XPS. Low softening point zinc phosphate glasses can be co-extruded with high softening point polymers to form polymer filled blends. NH3 reacts with P-OH groups (Br⊘nsted acid sites) to form bound NH4+ and with the zinc ions (Lewis acid sites) to form coordinately bound NH3. Bulk nitridation reactions, forming various P-N bonds to >100 nm, occur concurrently. The glass surfaces were depleted in Zn compared to the batch compositions. Exposure to ambient water vapor removed Lewis acid bound ammonia; aqueous washing removed both types. Di- and tri-methyl amines also reacted with surface Br⊘nsted and Lewis acid sites. These amine reactions have the potential for binding polymer chains to the glass surface.
Atomic force microscopy of slip lines in FeAl
Authors: Schneibel J.H. , Martínez L.
Published: September 2007

Fe–40 at. % Al–0.1 at. % B specimens were polished flat, strained at room temperature, and examined in an atomic force microscope. The angles of height contours perpendicular to the slip lines were interpreted as shear strains and were statistically evaluated. The frequency distributions of these shear strains correlated well with the macroscopic strains. The maximum shear strains found were not much larger than the macroscopic strains. In particular, no steep slip steps corresponding to large local shears were found.
In situ imaging of μN load indents into GaAs
Authors: Lilleodden E.T. , Bonin W. , Nelson J. , Wyrobek J.T. , Gerberich W.W.
Published: September 2007

Nanomechanical devices constitute an important and growing field, as they allow for new understanding of the mechanical properties at interfaces and surfaces. As an example, a newly developed nanoindentation device has been used to accomplish μN load indents into GaAs. First, it is shown that a plastic zone can be measured and is comparable to theory. Also, it is shown that the rate of indentation affects both the depth and upset zone of low load indents, implying a strain-rate sensitivity effect at room temperature. This is reinforced by observation of what appears to be a glide-based relaxation process.
In situ single-liquid-source metal-organic chemical vapor deposition of (La0.8Ca0.2)MnO3 giant magnetoresistive films
Authors: Li Y.Q. , Zhang J. , Pombrik S. , DiMascio S. , Stevens W. , Yan Y.F. , Ong N.P.
Published: September 2007

A large magnetoresistance change (ΔR/RH) of −550% has been observed at 270 K in (La0.8Ca0.2)MnO3 thin films. The films were prepared in situ on LaAlO3 substrates by single-liquid-source metal-organic chemical vapor deposition. M(thd)n (M = La, Ca, and Mn, and n = 2, 3) were dissolved together in an organic solution and used as precursors for the deposition of (La0.8Ca0.2)MnO3 thin films. Deposition was conducted at an oxygen partial pressure of 1.2 Torr and a substrate temperature ranging from 600 °C to 700 °C. The mechanism for the large magnetoresistance change in this manganese oxide is briefly discussed.
Dielectric properties and structure of hydroxyapatite ceramics sintered by different conditions
Authors: Prieto Valdes J.J. , Victorero Rodriguez A. , Guevara Carrio J.
Published: September 2007

Several conditions for hydroxyapatite ceramic preparation were used: sintering at 1150 °C in air or under H2O vapor flow, quenched in water at room temperature after sintering, or slow cooling inside the furnace. Depending on specific combinations of these preparation conditions, in the resulting ceramics significant differences are observed in the phase composition and dielectric properties, ranging from capacitive to a semiconducting response. Comparison between the experimental x-ray diffraction patterns and those calculated by the Rietveld method show that during sintering in air, approximately 40% of hydroxyapatite is transformed to tricalcium phosphate. The XRD analysis shows that this transformation could be possible using the following process: Ca10(PO4)6(OH)2= 2Ca3(PO4)2+ Ca2P2O7+ 2CaO + H2O.
Industrial ecology—The need to rethink the materials cycle: Some problems, solutions, and opportunities in the materials field
Authors: Szekely Julian , Trapaga Gerardo
Published: September 2007

The main thrust of this paper is to define the concept of industrial ecology and to discuss how its principles may be utilized to reconsider the materials cycle. Simply put, ecological principles imply that we minimize waste during manufacture and ensure that the products are recycled at the end of their useful life. Such a rethought materials cycle has to stress waste minimization and, at the same time, track energy flows and cost considerations simultaneously with the movement of the materials streams. In this paper, special attention is paid to recycling issues in metals production, municipal waste, and also to recycling issues pertaining to electronic materials. Comments are made on the driving forces and the barriers to industrial ecology, including economics, regulation, management and education, and on the international aspects of industrial ecology.
Mechanical properties of biodegradable soy-protein plastics
Authors: Schilling C.H. , Babcock T. , Wang S. , Jane J.
Published: September 2007

Experiments were performed to evaluate the room-temperature mechanical properties of soy-protein that were compression-molded with varying concentrations of glycerin plasticizer. Specimens exhibited stiff and brittle behavior with good tensile strength reliability based on Weibull statistics analysis. Raising the glycerin concentration from 0 to 20% progressively increased the tensile strain-to-failure from 1.1 to 1.8% and reduced the tensile strength from 42.1 to 23.6 MPa. the tangent modulus from 4.56 to 1.79 GPa, and the Rockwell hardness from R118.4 to R75.7. Ultrasonic measurements indicated that raising the glycerin concentration from 0 to 20% increased Poisson's ratio from 0.348 to 0.409 and reduced Young's modulus from 7.01 to 5.4 GPa and the shear modulus from 2.5 to 1.8 GPa. Significant increases in the tensile strength and the strength reliability resulted from eliminating Griffith's flaws by sieving the press powder before compression molding. Rockwell hardness rapidly decreased upon immersing these plastics in water at 25 °C, an effect which was pronounced for the glycerin-containing specimens.
Texture and transport in spray pyrolyzed TlBa2Ca2Cu3O9 thick films
Authors: Tkaczyk J.E. , Sutliff J.A. , DeLuca J.A. , Bednarczyk P.J. , Briant C.L. , Wang Z.L. , Goyal A. , Kroeger D.M. , Lowndes D.H. , Specht E.D.
Published: September 2007

The electron backscattering pattern technique has been applied to the microstructural investigation of Tl(1223) thick films formed by vapor-phase thallination of Ag-containing Ba–Ca–Cu–oxide precursors. For samples grown on polycrystalline YSZ, considerable biaxial alignment is found in localized, multigrain regions as wide a 100 μm or more. However, on scales above 1 mm the overall texture remains only uniaxial with the c-axes (i.e., [001]) aligned perpendicular to the plane of the substrate. On single-crystal KTaO3 an epitaxial relationship is evident which persists to the surface of a 3 μm thick film. Modest variations in the processing protocol yield films containing grains oriented with the c-axis in the plane, resulting in the degradation of transport properties. The data suggest a growth mode in which sparse nucleation occurs at the substrate followed by rapid lateral crystallization.
Copper-alumina materials made by infiltration in boehmite
Authors: Pierre V. , Pierre D. , Pierre A.C.
Published: September 2007

New materials were made by infiltration of sol-gel boehmite thin films with copper acetate. The structure and phase transformation of these materials during heat treatment were studied. It was found that infiltration in the boehmite state did not end up in the same material as direct infiltration in the θ-alumina derived from boehmite, even after both types of materials were heat-treated at 900 °C. Infiltration in boehmite makes it possible to synthesize sandwich structures comprised of alternate layers of CuO and of γ-alumina.
Impedance spectroscopy of grain boundaries in nanophase ZnO
Authors: Lee J. , Hwang J.-H. , Mashek J.J. , Mason T.O. , Miller A.E. , Siegel R.W.
Published: September 2007

Sintered compacts of nanophase ZnO (∼60 nm average grain size, presintered at 600 °C) were made from powders (∼13 nm) prepared by the gas-condensation technique. Impedance spectra were taken as a function of temperature over the range 450–600 °C and as a function of oxygen partial pressure over the range 10−3−1 atm (550 and 600 °C only). The activation energy was determined to be 55 kJ/mole (0.57 eV) and was independent of oxygen partial pressure. The oxygen partial pressure exponent was −1/6. Impedance spectra exhibited nonlinearI-Vbehavior, with a threshold of approximately 6 V. These results indicate that grain boundaries are governing the electrical properties of the compact. Ramifications for oxygen sensing and for grain boundary defect characterization are discussed.
Interfacial reactions and adhesion strength of metal/ceramic composites
Authors: Wang Hsin-Fu , Gerberich William W. , Angelo Jim E.
Published: September 2007

The interfacial fracture energy of Ti/Al2O3 composites was measured with and without a diffusion barrier at different bonding temperatures by using four-point bending tests. It was found that the interfacial fracture energy increases with increasing bonding temperature up to 950 °C. When the bonding temperature was further raised to 1000 °C, the interfacial fracture energy drops. The decrease of the interfacial fracture energy is due to the formation of the continuous intermetallic compound, Ti3Al, at the interface between Ti and Al2O3. By using a diffusion barrier, the interfacial fracture energy decreases from 25.4 to near O J/m2 and 32.9 to 8.7 J/m2 for applied bonding temperatures of 800 and 900 °C, respectively. This is because the diffusion barrier reduced the diffusion of Al across the interface and into the Ti, thereby preventing a strong chemical bond at the interface. For the composite bonded at 900 °C, the crack propagation was found to occur at the interface between the Ti and Al2O3. The interfacial failure was found to be in the Ti3Al reaction layer for the composite processed at 1000 °C. With a diffusion barrier, the crack propagation path follows several interfaces. Evaluation of the processing temperature on the mechanical properties of the Ti was also obtained by using a nanoindentation technique.
Improving wettability of polycarbonate and adhesion with aluminum by Ar+ ion irradiation
Authors: Koh Seok-Keun , Song Seok-Kyun , Choi Won-Kook , Jung Hyung-Jin , Han Sung-Nam
Published: September 2007

Improving wettability of the polycarbonate (PC) surface to triple distilled water has been carried out by Ar+ ion irradiation with blowing oxygen gas. The amount of Ar+ was changed from 1014 to 5 × 1016 ions/cm2 at 1 keV energy by a Kaufman-type ion source. Contact angle of the water to PC has been reduced from 78°to 50°with Ar+ irradiation, and to 12°with Ar+ irradiation in various vacuum pressures adjusted by oxygen gas flow rate (0-4 sccm). Strong O-H stretching vibration peaks at about 3370 cm−1 on FT-IR spectra of the polymer appeared after the surface treatments, and the wetting angle of the treated PC was returned to its value (78°) when the PC was exposed in air environment. The minimum contact angles were maintained with the same value when the irradiated polymers were kept in dilute HCl solution. The improved wettability and surface chemical reaction by Ar+ ion irradiation with oxygen was explained by the formation of a hydrophilic functional group. Enhanced adhesion between aluminum and PC was confirmed by the scotch tape test, and was discussed with relation between the hydrophilic group on the polymer surface and the deposited metal.
Structure of Au ultrafine particles in silica glass by x-ray absorption fine structure spectroscopy
Authors: Fukumi Kohei , Kageyama Hiroyuki , Kadono Kohei , Chayahara Akiyoshi , Kamijo Nagao , Makihara Masaki , Fujii Kanenaga , Hayakawa Junji , Satou Mamoru
Published: September 2007

The structure of ultrafine gold particles embedded in silica glass by ion implantation has been studied by x-ray absorption fine structure spectroscopy. It is found that the Au–Au interatomic distance in the particles is very similar to that in bulk gold within 0.01 Å. Mean-square relative displacement in the particles is 1.2–1.3 times larger than that in bulk gold.
Magnetic torque of oriented bulk Bi2212 by the shock-loading method
Authors: Kawamata S. , Okuda K. , Kikuchi M. , Hikosaka H. , Syono Y.
Published: September 2007

The magnetic torque of oriented bulk specimen of Bi2Sr2CaCu2O8+δ by the shock-loading method was measured under magnetic fields up to 8 kOe in the temperature range from 4.2 to 100 K. The torque amplitude of the shocked specimen was much larger than that of the as-grown bulk specimen measured as a reference. The angular dependence of the torque was reproduced by assuming the Gauss-type distribution for the crystalline orientation. It became clear that the magnetic torque of the shocked specimen showed the high degree of crystalline orientation in which the c-axis is perpendicular to the pellet disk plane and that the flux pinning perpendicular to the pellet disk plane was enhanced by shock-loading.
Microstructure and high-temperature deformation of the C15 NbCr2-based Laves intermetallics in Nb–Cr–V alloy system
Authors: Takasugi T. , Yoshida M. , Hanada S.
Published: September 2007

The microstructure and the high-temperature deformation behavior of the C15 NbCr2 intermetallics alloyed with V, which consist of both the C15 monophase and the duplex structure with the bcc solid solution, are observed by some microscopic techniques and compression tests. The alloys consisting of the C15 monophase microstructure show moderately higher 0.2% yield stress than the unalloyed NbCr2, and the same BDTT as that in the unalloyed NbCr2, indicating a moderate improvement of the high temperature deformability. This result is attributed to the larger atomic free volumes between the atomic stacking layers along the {111} planes than those of the unalloyed NbCr2. The alloys consisting of the duplex microstructure show lower 0.2% yield stress and considerably decreased BDTT than the unalloyed NbCr2. The considerable deformation improvement in this group of alloys is attributed to the existence of the ductile bcc solid solution.
Processing of high-strain-rate superplastic Si3N4w/Al–Mg–Si composites
Authors: Mabuchi Mamoru , Higashi Kenji
Published: September 2007

Effects of reduction, reinforcements, and dynamic precipitation on grain refinement by hot extrusion have been investigated in a Si3N4w/Al-Mg-Si (6061) composite by tensile tests and microstructural investigation. The grain refinement was attributed to an interaction of recrystallization and dynamic precipitation, which was enhanced by reinforcements. Not only fine-grained microstructure, but also relaxing stress concentrations which are caused at matrix/reinforcement interfaces during superplastic flow are required to attain large elongations. Partial melting resulting from segregation plays an important role in relaxing the stress concentrations. DSC investigations revealed that the degree of segregation was increased by hot extrusion.
Autostoichiometric vapor deposition: Part I. Theory
Authors: Xu Ren
Published: September 2007

The possibility of an autostoichiometric vapor deposition is explored. Heterometal-organic complexes such as double alkoxides are potential candidate precursors for such deposition. Two reaction schemes, the hydrolysis-assisted pyrolysis and the hydrolysis-polycondensation of double alkoxides, are identified to be autostoichiometric reactions. A simple low-pressure apparatus is suggested for autostoichiometric vapor deposition. Mass-flow analysis allows for the identification of a nonstoichiometry factor K which can be used as a quantitative measure of the precursor's autostoichiometric capability.
Infrared optical properties of pulsed laser deposited carbon films with the bonding and properties of diamond
Authors: Davanloo F. , You J.H. , Collins C.B.
Published: September 2007

Composed of packed nanophase nodules in which the carbon atoms are linked with the tetrahedral bonding of diamond, laser plasma films are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 1011 W cm−2. The high energy of condensation provides both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress. Coatings of 2–5 μm thicknesses have extended lifetimes of important optical materials against the erosive wear from high-speed particles and droplets by factors of tens to thousands. In this work, the optical properties of these films at infrared (IR) wavelengths were studied. Transmission spectra of several freestanding films on silicon frames were measured. Using a model considering rough surface scattering and free carrier absorption, satisfactory fits to these transmission spectra were obtained and from them the optical parameters were extracted. The characterization studies performed in this work indicated a great potential for the laser-deposited nanophase diamond films in optical applications.
Zirconia-mullite ceramics made from composite particles coated with amorphous phase: Part II. Effects of boria additions to the amorphous phase
Authors: Shyu Jiin-Jyh , Chen Yuan-Chieh
Published: September 2007

Mullite and zirconia-mullite ceramics have been prepared by coating alumina/zirconia particles with an amorphous silica layer. The effect of composition change of the amorphous silica layer by adding B2O3 was investigated. For the zirconia-free compositions, the addition of B2O3 remarkably accelerates the kinetics of the crystallization of the amorphous coating layer, the viscous sintering, and the mullitization. For the zirconia-containing ceramics, the addition of B2O3 enhanced the viscous sintering kinetics and delayed the decomposition of the transient zircon phase and the subsequent t- to m ZrO2 transition, thus resulting in a higher ratio of t- to m-ZrO2. The B2O3-containing zirconia-mullite composites exhibit the same level of fracture toughness (Kic) as the B2O3-free zirconia-mullite composites.
Optical and electrical conductivity investigations of Fe3+-(acrylonitrile-butadiene-styrene) terpolymer complex systems
Authors: Bakr N.A. , Abdel-hamid M.I.
Published: September 2007

Infrared (IR) and UV-spectra have been obtained for pure and Fe3+ doped acrylonitrile-butadiene-styrene (ABS) terpolymer. IR study revealed the appearance of a new band at about 380 cm−1, and a change of the shape and the intensity of the band at 1450–1500 cm−1 and 2240 cm−1 indicates the structural change on blending due to the τ-complexes and the complexes of the functional groups with Fe3+ forming an ion-coordination polymer. The UV spectrum confirms this result. The optical energy for pure and Fe3+-doped ABS is found to be 3.75 eV and 3.55 eV, respectively. The dc and ac electrical conductivities have been investigated. The apparent conductivity of high Fe3+-doped ABS at the ambient temperature is about six orders of magnitude greater than that of the undoped film. The activation energy drastically decreases as the wt. % of FeCl3 increases. The enhanced conductivity in the complex film may be attributed to the capacity of the dopant to give additional charge carriers. Transport of charge carriers will occur by hopping of charge carriers between close neighbors across the intervening dielectric, probably via a thermally activated process.
Second harmonic characteristics of Disperse Red 1 doped polysulfones
Authors: Lor Sze Keung , Hiraoka Hiroyuki , Yu Ping , Cheng Lap-Tak , Wong George K.L.
Published: September 2007

Polysulfones, such as poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylid-ene-1,4-phenylene), poly(phenylene ether sulfone), poly(phenylene sulfone), and aliphatic polysulfone, poly(bicycloheptene sulfone), were employed as a host resin. N-ethyl-N-hydroxyethyl-4-(4'-nitrophenylazo)phenylamine (Disperse Red 1) acted as a guest molecule and was dispersed in those hosts with a concentration of 5 wt. % to 10 wt.%. Their second harmonic generation properties were characterized and compared. Xijk values obtained varied from 11 pm/V to 21 pm/V. The merits of polysulfones as a host material are good optical clarity, easy film forming, and fairly high glass transition Tg temperature (140 °C to 190 °C). Chemically, compared to polyimides they have good resistance to moisture, i.e., less vulnerable to hydrolysis. It is a good candidate for electro-optical materials.
Synthesis of alumina/nickel composite by electrodeposition of nickel
Authors: Hirata Yoshihiro , Hatano Hirohisa , Kyoda Hideharu , Hamasaki Keiji
Published: September 2007

Ni2+ ions in aqueous solutions were electrochemically deposited within pores of alumina compacts attached to carbon or Pt electrode at room temperature. The deposition behavior of Ni metal in the pores of alumina compacts was expressed by an empirical power law equation of W = ktn, where W is the weight of Ni deposited, k the deposition rate constant, t the deposition time, and n the experimental constant (0.52-0.56). The shape of Ni deposited was dependent on the geometry of positive electrode.
Poisson's ratio of porous and microcracked solids: Theory and application to oxide superconductors
Authors: Dunn Martin L. , Ledbetter Hassel
Published: September 2007

We present a theoretical study of the effective Poisson's ratio of elastic solids weakened by porosity and microcracks. Explicit expressions of the effective Poisson's ratio are obtained using the Mori-Tanaka mean-field approach as applied to macroscopically isotropic solids containing randomly distributed and randomly oriented spheroidal pores. We focus on the influence of pore shape and concentration and devote special attention to the limiting cases of spherical, penny-shape, and needle-shape pores. A key result of this study is that the effective Poisson's ratio depends only on pore concentration, pore shape, and Poisson's ratio of the bulk solid. In other words, it is independent of any other elastic constants of the bulk solid. Also, theratioof the shear and bulk moduli behaves similarly. Unlike other elastic constants which monotonically decrease with pore concentration, Poisson's ratio may increase, decrease, or remain unchanged as a function of pore concentration, depending on the pore shape and Poisson's ratio of the bulk solid. We discuss ramifications of these findings with regard to the elastic constants of oxide superconductors, especially the bismuth cuprates, which show unusually low Poisson's ratios. We also discuss these low Poisson's ratios, including the possibility of negative Poisson's ratios.
Effect of hydrolysis catalyst on the Ti deficiency and crystallite size of sol-gel-TiO2 crystalline phases
Authors: Morales Bokhimi A. , Novaro O. , López T. , Sánchez E. , Gómez R.
Published: September 2007

We prepared sol-gel titania by using different hydrolysis catalysts, and characterized it by x-ray powder diffraction. The structure of the crystalline phases—brookite, anatase, and rutile—in the samples annealed between 70 and 900 °C was refined by using the Rietveld technique. From the refinement we obtained the structure parameters, the concentration of each phase, and their average crystallite size. These quantities and their evolution with temperature depended on the hydrolysis catalyst. Anatase and rutile were deficient in Ti, suggesting that their crystalline structure contained hydrogen atoms, forming OH− ions inside. In anatase this deficiency depended on its crystallite size, but it was constant in rutile. When anatase was annealed, it dehydroxylized, producing either crystallitc growing up or its conversion into rutile. From the analysis we also found the conditions for obtaining single-phase samples that could be used as precursors for making up titania single-phase thin films.
Effect of ion fluence on the surface morphology of single crystal magnesium oxide implanted with xenon
Authors: Jiang Wenbiao , Norton M. Grant , Poker David B.
Published: September 2007

The surface morphology (001)-oriented single-crystal magnesium oxide (MgO) implanted with xenon ions has been examined using atomic force microscopy. It was found that at the lowest fluence used in this study (1.0 × 1014/cm2), a slight roughening of the (001) surface occurred. The magnitude of this roughening remained fairly constant with increases in fluence in the range 1.0 × 1014/cm2 to 3.0 × 1016/cm2. Implantation at fluences of ≥ 1.0 × 1017/cm2 caused significant surface roughening with the concomitant formation of micron-sized blisters. The appearance of some of these blisters resembles the rosette pattern that is also observed when the cleaved surfaces of MgO crystals are etched following indentation using a spherical indenter. This observation suggests that these blisters are formed by the growth of xenon inclusions, during implantation, by a dislocation loop punching mechanism.
Photooxidative self-cleaning transparent titanium dioxide films on glass
Authors: Paz Y. , Luo Z. , Rabenberg L. , Heller A.
Published: September 2007

In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant deposits was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm2) or 254 nm (0.8 mW/cm2) irradiation. Approximately 3 × 10−4 stearic acid molecules were stripped per 365 nm photon in either front- or back-illuminated soda lime glass, and 6 × 10−4 molecules when the films were coated on fused quartz. For thin TiO2 films on fused quartz, the rate of photooxidation, normalized by the number of photons absorbed per unit area, was independent of the wavelength. In contrast, for films on soda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoactivity on glass at the deeply penetrating wavelength (365 nm), as well as the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-contacting zone of the TiO2 layer.
Extraordinary adhesion of a simple niobium metal-bonding structure
Authors: Chen H.S. , Bacon D.D. , Law H.H. , Kammlott G.W. , Wu T.C.
Published: September 2007

Extraordinary adhesion of a Nb-based/Au-Sn metallization structure on a SiO2/Si substrate has been observed by a tensile pull test. The metallization bond fails mostly via fracture through either the Si substrate or epoxy adhesive. The intrinsic adhesion pull strength of the metallization scheme is concluded to be greater than 10 kpsi, and the adhesion exceeds the Si-Si cohesive strength. The Nb-Si and Nb-O bonds at the interface are thermodynamically stable.
An atomistic study of brittle fracture: Toward explicit failure criteria from atomistic modeling
Authors: Gumbsch Peter
Published: September 2007

Atomistic techniques are used to study brittle fracture under opening mode and mixed mode loading conditions. The influence of the discreteness of the lattice and of the lattice-trapping effect on crack propagation is studied using an embedded atom potential for nickel to describe the crack tip. The recently developed FEAt (Finite Element-Atomistic) coupling scheme provides the atomistic core region with realistic boundary conditions. Several crystallographically distinct crack-tip configurations are studied and commonly reveal that brittle cracks under general mixed mode loading situations follow an energy criterion (G-criterion) rather than an opening-stress criterion (Kl-criterion). However, if there are two competing failure modes, they seem to unload each other, which leads to an increase in lattice trapping. Blunted crack tips are studied in the last part of the paper and are compared to the atomically sharp cracks. Depending on the shape of the blunted crack tip, the observed failure modes differ significantly and can drastically disagree with what one would anticipate from a continuum mechanical analysis.
Interstitial diffusion along twist grain boundaries in Cu
Authors: Nomura Miki , Adams James B.
Published: September 2007

Interstitial diffusion along twist grain boundaries was studied using the Embedded Atom Method (EAM). Six (100) twist grain boundaries (8.79°–43.6°) in copper were investigated. Interstitial formation energies were found to be much lower (0.26-0.78 eV) than in the bulk, and migration energies were found to be comparable (0.01 eV-0.24 eV) to the bulk values (0.09 eV). The vacancy mechanism is favored for low angle boundaries, and the interstitial mechanism is favored for high angle boundaries. The trends in formation energy versus twist angle were partly explained in terms of the volume expansion of the grain boundary. The total diffusion rate due to both mechanisms was calculated, and agreed reasonably well with experimental data for Cu in polycrystalline Cu. The calculated diffusion rate for specific twist boundaries also agreed well with experimental measurements for Zn/Al.
Elastic properties of sodium borovanadate glasses
Authors: Muthupari S. , Lakshmi Raghavan S. , Rao K.J.
Published: September 2007

The elastic properties of sodium borovanadate glasses have been studied over a wide range of composition using ultrasonic measurements. It is found that variation of different elastic moduli is very similar in any given series of composition. The bulk and shear moduli show a monotonic variation with the covalent bond energy densities calculated from the proposed structural model for these glasses. The bulk moduli also vary as a negative power function of the mean atomic volume. The Debye temperature varies linearly with the glass transition temperature. The implications of the observed behavior have been discussed.