bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of hydrogen desorption from palladium and ruthenium-palladium foils
Authors: Cabrera A.L. , Morales Erie , Armor J.N.
Published: September 2007

The absorption of hydrogen and carbon monoxide at room temperature by palladium and 5% ruthenium-palladium foils was studied using thermal desorption spectroscopy. It was found that hydrogen readily diffused in the palladium and desorbed as one broad peak at about 650 K. Plots of the In (rate) versus inverse absolute temperature indicate that the desorption order isn= 1.25 and the activation energy is about 8.5 Kcal/mol. Carbon monoxide is adsorbed, as two different states, on the surface of the foil and complete coverage is quickly reached below 100 L. Hydrogen also diffuses in 5% ruthenium-palladium foil but to a lesser degree. Two hydrogen desorption peaks are observed in the Ru-Pd alloy. The desorption traces can be fitted with two peaks and the desorption orders aren= 2 for the first peak andn= 1.25 for the second peak. Activation energies of 10.7 and 5.6 Kcal/mol are obtained for the first and second hydrogen peaks, respectively. The first hydrogen desorption peak is regarded as hydrogen desorbing from the surface sites while the second peak is regarded as hydrogen diffusing from below the surface. Activation energies for bulk diffusion were obtained from hydrogen uptake measurements using a sensitive microbalance. These energies corresponded to 4.4 Kcal/mol for Pd foil and 4.9 Kcal/mol for the Ru-Pd alloy. Discussion about the relation between these results with prior studies of hydrogen adsorption on Pd single crystal is included. The appearance of a fractional order for hydrogen desorption is also discussed.
Study of the resputtering effect during rf-sputter deposition of YBCO films
Authors: Xu Jun-Hao , Moon B.M. , Rao K.V.
Published: September 2007

We propose an angular redistribution model to understand the negative ions resputtering effect in sputter depositing YBa2Cu3O7−x (YBCO) films. On the basis of this model, the negative oxygen ions resputtering effect has been greatly minimized by introducing a Cu mask between the substrate and the target to block energetic oxygen particles from directly bombarding the growing film. Thus, YBCO films with almost exact stoichiometric composition and zero resistance critical temperatures as high as 90 K are obtained under oxygen partial pressure as low as 3 mTorr in a temperature regime well beyond that proposed by R.H. Hammond and R. Bormann. Preliminary results of a modified masking and shiclding technique to eliminate the resputtering effect and fabricate large area (>1 in. × 1 in.) YBCO superconducting films with high uniformity are also presented.
High temperature deformation behavior of titanium samples with superplastic layer
Authors: Zelin M.G. , Li Q. , Valiev R.Z. , Lukač P. , Mukherjee A.K.
Published: September 2007

The progress of high temperature deformation in samples of two commercial titanium alloys with superplastic (SP) structure, non-SP structure, and with an SP layer sandwiched between the non-SP regions has been studied on the scale of the entire deformed volume and on the scale of grain groups. The results of mechanical behavior showed that samples with SP layer exhibit higher stress level than those with completely SP structure and higher strain rate sensitivity than those with completely non-SP structure. Samples with SP layer demonstrate a more pronounced deccrease in strain rate sensitivity with the increase of strain than samples with completely SP structure. Deformation in the SP layer proceeds as grain shear in a layer-by-layer manner. The deformation of SP layer through the operation of cooperative grain boundary sliding, i.e., sliding of grain groups as an entity along certain grain boundary surfaces, provides the main contribution to the total strain.
Optical and structural properties of semi-insulating polycrystalline silicon thin films
Authors: Compagnini G. , Lombardo S. , Reitano R. , Campisano S.U.
Published: September 2007

Optical properties of semi-insulating polycrystalline silicon (SIPOS) thin films containing 30 at. % oxygen atoms are investigated in the near ultraviolet, visible and infrared region to improve knowledge on the structure and chemical bonding of these mixtures. An effective medium approximation model is used for a microscopic investigation of the oxide species involved as a function of the annealing temperature (600–1200 °C). The results are compared with other optical spectroscopies (infrared and Raman) and with transmission electron microscopy to give a selected picture of the pure and oxide components.
Polarization switching mechanisms and electromechanical properties of La-modified lead zirconate titanate ceramics
Authors: Li Jie-Fang , Dai Xunhu , Chow Albert , Viehland Dwight
Published: September 2007

The electromechanical properties of (Pb1−xLax)(ZryTi1−y)O3 [PLZT x/y/(1 - y)] have been investigated in the compositional range 0 < x < 0.10 for y = 0.65 (rhombohedral PLZT) and 0 < x < 0.18 for y = 0.40 (tetragonal PLZT). Both field-induced strains (∊-E) associated with polarization switching and piezoelectric responses (d33) were studied. Transmission electron microscopy (TEM) and dielectric investigations were also performed. Room temperature TEM investigations revealed common trends in the domain structure with increasing La content for both PLZT x/65/35 and x/40/60, including a micron-sized domain structure, a subdomain tweed-like structure, and a nanopolar domain state. Changes in the field-induced strains and piezoelectric properties were then related to these microstructural trends. The dominant electromechanical coupling mechanism in the micron-sized domain state was found to be piezoelectricity. However, an electrostrictive coupling became apparent with the appearance of the subdomain tweed-like structures, and became stronger in the nanopolar domain state. It is believed that polarization switching can-occur through 70°or 110°domains, the subdomain tweed-like structure, or nanopolar domains depending on La content.
Combustion synthesis and characterization of BaTiO3
Authors: Zhong Zhimin , Gallagher Patrick K.
Published: September 2007

An important, somewhat novel procedure for the bulk synthesis of finely divided crystalline BaTiO3 powder has been studied and is applicable to the synthesis of other compounds in the BaO-TiO2 system as well. An aqueous solution of Ba(NO3)2, TiO(NO3)2, and alanine is spray dried. A combustion reaction occurs when heating the product to 300 °C. The reaction converts the spray-dried mixture to BaTiO3. This BaTiO3 powder and its sinterability have been characterized by thermal analysis, XRD, SEM, dielectric, and particle size measurements. The powder resulting from the thermal runaway reaction is finely divided and sinters more readily than the conventionally prepared high purity BaTiO3.
A micromechanistic model of microstructure development during the combustion synthesis process
Authors: Zhang Yangsheng , Stangle Gregory C.
Published: September 2007

The influence of the key nucleation and grain growth parameters on (i) the evolution of the microstructure of the product phase (on a microscopic level) and (ii) the combustion synthesis process (on a macroscopic level) were investigated for the combustion synthesis process in the Nb-C system. This work is an integral part of the continuing effort1–3 to develop a more complete theoretical model for combustion synthesis processes in general. In particular, the nucleation and growth of the NbC(s) product phase from the supersaturated liquid Nb/C mixture that appears briefly during the combustion synthesis process was treated in a greater detail by using a decidedly more sophisticated treatment of the nucleation and growth process (as developed in the field of rapid solidification and welding). It was shown that the microstructure of the NbC(s) product phase, including the evolution of the grain size and the size distribution, and the development of the grain's morphology, as well as the combustion wave velocity, are significantly influenced by the total number density of the nucleation sites, nmax, that are present in the system. The grain size distribution was shown to possess a monosize distribution, since during the combustion synthesis process the rate of increase of the degree of local undercooling was very high so that the nucleation process took place (locally) during a very brief period of time. This work provides a sound basis for developing a better control of the microstructure, and for a better understanding and interpretation of the results of related experimental studies.
Microstructure of TiN films and interfaces formed by ion-beam-enhanced deposition and simple physical vapor deposition
Authors: Cheng Z.Y. , Zhu Jing , Liu X.H. , Wang Xi , Yang G.Q.
Published: September 2007

The microstructure and composition of TiN films, formed by ion beam enhanced deposition (IBED) with different energy (40 keV and 90 keV) xenon ion bombardment and by simple physical vapor deposition (hereafter S-PVD) without any ion beam enhancement, and the interfaces between TiN films and Si substrates have been studied by cross-sectional view analytical electron microscopy in this work. Both the IBED TiN films prepared by Xe+ bombardment with either 40 keV or 90 keV energy ions and the S-PVD TiN film consist of nanocrystals. The TEM observations in the S-PVD case reveal an amorphous layer and a mixed layer of TiN grains and amorphous material at the TiN/Si interface. The thicknesses of the amorphous layer and the mixed layer are about 210 nm and at least 40 nm, respectively. Upon 40 keV Xe+ bombardment, an amorphous Si transition layer of about 50 nm thickness is found at the TiN/Si interface, and the TiN grains close to the TiN/Si interface are of weak preferred orientation. Upon 90 keV Xe+ bombardment, amorphous TiN and Si layers are found with a total thickness of 80 nm at the TiN/Si interface, and the TiN grains near the TiN/Si interface are of preferred orientation [111]TiN ‖ [001]Si. The energy of xenon ion bombardment has a strong effect on the microstructural characteristics of TiN films and the interfaces between the TiN films and the Si substrates, as well as the size and the preferred orientation of TiN grains.
Elimination of an isolated pore: Effect of grain size
Authors: Shih Wan Y. , Shih Wei-Heng , Aksay Ilhan A.
Published: September 2007

The effect of grain size on the elimination of an isolated pore was investigated both by the Monte Carlo simulations and by a scaling analysis. The Monte Carlo statistical mechanics model for sintering was constructed by mapping microstructures onto domains of vectors of different orientations as grains and domains of vacancies as pores. The most distinctive feature of the simulations is that we allow the vacancies to move. By incorporating the outer surfaces of the sample in the simulations, sintering takes place via vacancy diffusion from the pores to the outer sample surfaces. The simulations were performed in two dimensions. The results showed that the model is capable of displaying various sintering phenomena such as evaporation and condensation, rounding of a sharp corner, pore coalescence, thermal etching, neck formation, grain growth, and growth of large pores. For the elimination of an isolated pore, the most salient result is that the scaling law of the pore elimination time tp with respect to the pore diameter dp changes as pore size changes from larger than the grains to smaller than the grains. For example, in sample-size-fixed simulations, tp ∼ d3p for dp < G and tp ∼ d2p for dp > G with the crossover pore diameter dc increasing linearly with G where G is the average grain diameter. For sample-size-scaled simulations, tp ∼ d4p for dp < G and tp ∼ d3p for dp > G. That tp has different scaling laws in different grain-size regimes is a result of grain boundaries serving as diffusion channels in a fine-grain microstructure such as those considered in the simulations. A scaling analysis is provided to explain the scaling relationships among tp, dp, and G obtained in the simulations. The scaling analysis also shows that these scaling relationships are independent of the dimensionality. Thus, the results of the two-dimensional simulations should also apply in three dimensions.
Pulsed-laser deposition of polytetrafluoroethylene
Authors: Jiang Wenbiao , Norton M. Grant , Tsung Lancy , Thomas Dickinson J.
Published: September 2007

Thin films of polytetrafluoroethylene have been deposited on amorphous substrates by the pulsed-laser deposition technique. By transmission electron microscopy, the polymer films were shown to consist of both amorphous and crystalline components. The data for the crystalline component are consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film substrate interface plane. The fraction of crystalline material in the films was found to be related to the substrate temperature during deposition with the maximum amount of crystalline material occurring when the substrate temperature was close to the melting temperature of the polymer.
Low temperature synthesis of thin films of carbon nitride
Authors: Ghanashyam Krishna M. , Gunasekhar K.R. , Mohan S.
Published: September 2007

Thin films of carbon nitride have been prepared using triode ion plating. It has been observed that the compound formation occurs at ambient substrate temperature itself. Though the films are completely amorphous at temperatures below 900 °C. they are hard and transparent down to a wavelength of 200 nm. It has also been observed that the film transmission can be modulated using nitrogen ion flux and partial pressure. The IR transmission spectra clearly show the C-N stretch band around 2200 cm−1. Onset of crystallization, as evidenced from electron diffraction, occurs around 900 °C substrate temperature.
Study of diamond growth from a variety of input gases
Authors: Menningen K.L. , Erickson C.J. , Childs M.A. , Anderson L.W. , Lawler J.E.
Published: September 2007

The gas phase densities of CH3 and CH and the hydrogen dissociation fraction are measured in a hot filament diamond deposition system for each of several different hydrocarbon input gases. The crystal growth rate and the appearance of the diamond grown from the different input gases are also examined. A comparison of the measurements indicates that the nature of the input hydrocarbon is relatively unimportant because fast gas phase reactions completely scramble the identities of the input carbon atoms. The addition of oxygen greatly alters the gas phase densities and other experimental factors such as the filament surface condition. Small concentrations of atomic impurities in the gas phase are also detected using high sensitivity absorption spectroscopy.
Analysis of the diffusion controlled growth of cobalt silicides in bulk and thin film couples
Authors: Barge T. , Gas P. , d'Heurle F.M.
Published: September 2007

The solid state reaction between Co and Si has been studied in bulk diffusion couples between 850 and 1100 °C. At the scale of the observations made, the three phases Co2Si, CoSi, and CoSi2 are found to grow simultaneously, according to diffusion controlled kinetics. The results are analyzed in term of the Nernst-Einstein equation that directly relates diffusion fluxes to the free energy changes driving the formation. The growth rates obtained for CoSi2 at high temperatures, in the present bulk samples, are compared with those determined by others in thin films, at much lower temperatures. The comparison requires that attention should be paid to two factors. The first one is that the laws of growth are slightly different for a phase growing simultaneously with two other ones (bulk) and one phase growing alone (thin films). The second factor is the grain size of the various samples, which varies with the temperature of reaction. Once this is done, excellent agreement is obtained between the two sets of measurements. Moreover it is shown that knowing the grain size, it is possible to calculate quite accurately the growth rate from the respective isotope diffusion coefficients both for lattice and grain boundaries of Co and Si in CoSi2.
The decagonal quasicrystal formed from an Al–Pd–Mn icosahedral quasicrystal
Authors: Sun W. , Hiraga K.
Published: September 2007

We present a detailed investigation on the decagonal quasicrystal (D-phase) formed from an Al-Pd-Mn icosahedral quasicrystal (I-phase) through a solid-state phase transformation, including its formation, compositional and crystallographical relationships with the matrix I-phase, growth mode, and structural characteristics. The as-melt-spun Al70Pd20Mn10 alloy contains only I-phase. By annealing at 800 °C, the D-phase is found to grow cpitaxially from the I-phase to establish a D/I two-phase equilibrium with distinctly different composition between them. The D-phase exhibits a stepped growth interface, which consists of a facet plane, formed by sharing the tenfold plane with a fivefold plane of the matrix I-phase, and some ledges across it. The growth of the D-phase into the I-phase proceeds through lateral movement of the ledges along the tenfold plane. High-resolution electron microscopy reveals that the structure of the D-phase is constructed by an aperiodic arrangement of decagonal atom clusters with definite linkages and long-range quasiperiodic correlation.
Combustion synthesis of MoSi2−TiC composites
Authors: Subrahmanyam J. , Mohan Rao R. , Sundarasarma G.
Published: September 2007

Stability of the binary phases in the quaternary system Mo–Ti–Si–C was examined for the combustion synthesis or Self-propagating High-temperature Synthesis (SHS) of MoSi2−TiC composites. Thermochemical calculations were carried out to obtain the adiabatic temperatures and the amounts of molten phases at the adiabatic temperature for the SHS of these composites. MoSi2−20 wt. % TiC and MoSi2−40 wt. % TiC composites were prepared by thermal explosion and SHS modes of combustion from elemental powders. The phase formation was confirmed by x-ray diffraction, and the morphologies were observed under SEM. No general correlation was obtained between the phase formation or product morphology on the one hand, and the adiabatic temperature or the amount of molten phase formed at the adiabatic temperature, on the other. MoSi2−40 wt. % TiC composites obtained by SHS mode of combustion show a highly homogeneous distribution of the two phases with negligible amounts of ternary phases.
Oxygen incorporation in aluminum nitride via extended defects: Part I. Refinement of the structural model for the planar inversion domain boundary
Authors: Westwood Alistair D. , Youngman Robert A. , McCartney Martha R. , Cormack Alastair N. , Notis Michael R.
Published: September 2007

The model proposed by Harris et al. [J. Mater. Res. 5, 1763–1773 (1990)], describing planar inversion domain boundaries in aluminum nitride, consists of a basal plane of aluminum atoms octahedrally coordinated with respect to oxygen, and with a translation of R = 1/3〈1011〉. This thin sandwich is inserted onto the basal plane of the wurtzite structure of aluminum nitride. This model does not take into consideration any interfacial relaxation phenomena, and is arguably electrically unstable. Therefore, this paper presents a refinement of the model of Harris et al., by incorporating the structural relaxations arising from modifications in local chemistry. The interfacial structure was investigated through the use of conventional transmission electron microscopy, convergent electron diffraction, high resolution transmission electron microscopy, analytical electron microscopy, and atomistic computer simulations. The refined planar inversion domain boundary model is closely based on the original model of Harris et al.; however, the local chemistry is changed, with every fourth oxygen being replaced by a nitrogen. Atomistic computer simulation of these defects, using a classical Born model of ionic solids, verified the stability of these defects as arising from the adjustment in the local chemistry. The resulting structural relaxations take the form of a 0.3 mrad twist parallel to the interface, a contraction of the basal planes adjacent to the planar inversion domain boundary, and an expansion of the c-axis component of the displacement vector; the new displacement vector across the interface is R = 1.3〈1010〉 + ∊〈0001〉, where ∊meas = 0.387 and ∊calc = 0.394.
The deposition of α–Fe2O3 by aerosol chemical vapor deposition
Authors: Martínez A. , Peña J. , Labeau M. , González-Calbet J.M. , Vallet-Regí M.
Published: September 2007

α-Fe2O3 thin films have been deposited on Si(111) substrates at high temperatures (600–800 °C) by the spray pyrolysis method. Four different iron(III) β-diketonates have been used as precursors in order to obtain polycrystalline films of good adherence, which have been characterized by x-ray diffraction, scanning electron microscopy, and magnetic measurements.
Devitrification inhibitors in borosilicate glass and binary borosilicate glass composite
Authors: Jean Jau-Ho , Gupta Tapan K.
Published: September 2007

Cristobalite is known to precipitate out of borosilicate glass (Corning 7740) and a binary glass mixture of borosilicate glass and high silica glass when these glasses are heated to elevated temperatures. To prevent cristobalite from forming in these glass systems, a devitrification inhibitor needs to be found. Among oxides selected for testing, both Al2O3 and Ga2O3 are found to prevent cristobalite from forming in these glass systems.
Hg–Ba–Ca–Cu–O system phase diagram and the formation of HgBa2Can−1CunO2n+2+δ superconducting phases
Authors: Che G.C. , Du Y.K. , Dong C. , Wu F. , Zhao Z.X.
Published: September 2007

The Hg-Ba-Ca-Cu-O system phase diagram and the formation of HgBa2Can-1CunO2n+2+δ superconducting phases have been investigated by XRD (x-ray diffraction). The isothermal sections of the HgO-BaO-CuO system at 800 °C and the BaO-CaO-CuO system at 870 °C are presented. HgBa2Can-1CunO2n+2+δ superconducting phases are formed through the reactions of HgO with intermediate products Ba2CuO3 + BaCuO2 + CaO, BaCuO2 + CaO2, and BaCuO2 + Ca2CuO3 for n = 1, 2, and 3 phases, respectively.
Anomalous low-temperature Raman scattering in a–Si1−xHx
Authors: Bhusari D.M. , Kumbhar Alka , Kshirsagar S.T.
Published: September 2007

We have reported here on low-temperature Raman scattering measurements on thin films of hydrogenated amorphous silicon (α-Si:H) alloys having different H contents. The Stoke's intensity, 77KITO, scattered at 77 K by the TO-phonon is found to be several times greater than its corresponding magnitude (300KITO) at 300 K. The ratio (77KITO/300KITO) is observed to vary exponentially with an increase in H concentration of the film. After eliminating various possible contributions to the scattering cross section, and therefore to the scattered intensity, this anomalous light scattering at 77 K is attributed to the possibility of polarizability modulation, which is believed to be caused due to a possible reduction in light-induced migration of H in α-Si:H and to the charge-carrier-induced enhancement of electron phonon coupling at 77 K.
Tunability of the dielectric constant of Ba0.1Sr0.9TiO3 ceramics in the paraelectric state
Authors: Outzourhit Abdelkader , Trefny John U. , Kito Tomoko , Yarar Baki
Published: September 2007

Ba1−xSrxTiO3 (x = 0.9) ferroelectric ceramics were prepared successfully using a new wet technique and their structure and dielectric properties compared with those synthesized by the solid-state reaction method. The voltage dependence of the dielectric constant in the paraelectric phase was examined. It was found that the dielectric constants of these materials, prepared by both methods, exhibit large changes with applied voltage in the paraelectric phase. Tunability (the percentage change of the dielectric constant from its zero-bias value in the presence of a de-biasing electric field) was observed to exceed 30% at only 1.7 kV/cm at 77 K in the samples prepared by the solid-state reaction method. The tunability was found to decrease dramatically as the operating temperatures increased above the Curie point. These observations are interpreted in light of an existing phenomenological theory. The dependence of the dielectric constant in the paraelectric state upon a de-biasing electric field is also demonstrated as a potential method for the characterization of dielectric nonuniformities in ferroelectric ceramics.
Growth and oxidation of boron-doped diamond films
Authors: Farabaugh E.N. , Robins L. , Feldman A. , Johnson Curtis E.
Published: September 2007

Boron-doped diamond films have been grown by the hot filament chemical vapor deposition process. The feed gas was a mixture of argon, bubbled through a solution of B2O3 in ethanol, and hydrogen. The highest growth rate was 0.7 μm/h. The boron concentration in the films depended on the concentration of B2O3 in the ethanol. The highest boron doping level, as measured by secondary ion mass spectroscopy, was 6300 atomic ppm. Raman spectroscopy and x-ray diffraction both confirmed the presence of crystalline diamond in the films. The frequency of the diamond Raman line decreased with increasing boron concentration. This shift may arise from an interaction of the charged carriers (holes) produced by the boron doping and the Raman-active optic phonon. The oxidation rates of doped and undoped films were measured by thermogravimetric analysis at 700 °C in flowing high purity oxygen. Films with a boron concentration of 6300 ppm oxidized at one-tenth the rate of undoped diamond. A layer of B2O3, detected on the surface of an oxidized B-doped film, is believed to act as a protective barrier that decreases the oxidation rate.
Fabrication of carbon-carbon composites by forced flow-thermal gradient chemical vapor infiltration
Authors: Vaidyaraman Sundar , Jack Lackey W. , Freeman Garth B. , Agrawal Pradeep K. , Langman Matthew D.
Published: September 2007

Carbon fiber-carbon matrix composites were fabricated using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. The preforms for the infiltration were prepared by stacking 40 layers of carbon cloth in a graphite holder. The preforms were infiltrated with carbon using propylene or methane as a reactant, with hydrogen as a diluent. Composites with porosities as low as 7% have been processed within 8-12 h. The highest deposition rate obtained in the present study was ∼3 μm/h, which is more than an order of magnitude faster than the typical value of 0.1-0.25 μm/h for the isothermal infiltration process.
A study on the mechanism of amorphous phase formation by interdiffusion in Ni/Zr multilayers
Authors: Chang Sang-Gweon , Lee Jai-Young , Kim Geun-Hong , Chun Chang-Hwan
Published: September 2007

The mechanism of the solid-state amorphization has been investigated by means of the microstructural studies on the evolution of Ni/Zr diffusion couples, prepared at different sputtering pressures, during short heating times at high temperature. In the sample deposited at 8 mTorr compared to that at 3 mTorr, the possibility of the supersaturation sequence prior to amorphization is observed, and the amorphous phase grows extremely fast with diffuse interface. A high-resolution TEM image shows that the amorphous phase preferentially penetrates along the Zr grain boundary into the Zr layer and selectively grows from the grain boundary into the region of Zr grain with many defects. From the results, the importance of interstitial diffusion has been discussed, and a modified mechanism has been suggested.
Preparation of acicular particles of α-alumina
Authors: Iga Takeo , Murase Yoshio
Published: September 2007

Aluminum ammonium sulfate (AA) solution (0.1 mol/l) and ammonium hydrogen carbonate (AHC) solution (1.2 mol/l) were allowed to react at room temperature. The precipitates formed were kept with the mother liquor in a closed vessel and aged at 100 °C. Acicular-shaped crystalline particles of Al(NH4)CO3(OH)2, (AACH), were obtained after the elongated aging period. Acicular α-alumina particles were obtained through the thermal decomposition at 1300 °C out of the AACH particles which were previously treated with a small amount of tetraethoxysilane (about 1.6 wt. % of SiO2).
Molecular dynamics simulations of grain boundary diffusion in Al using embedded atom method potentials
Authors: Liu Chun-Li , Plimpton S.J.
Published: September 2007

Molecular dynamics (MD) simulations of diffusion in a Σ5(310) [001] Al tilt grain boundary were performed using for the first time three different potentials based on the embedded atom method (EAM). The EAM potentials that produce more accurate melting temperatures also yield activation energies in better agreement with experimental data. Compared to pair potentials, the EAM potentials also give more accurate results.
Nonuniform distribution of second phase particles in melt-textured Y–Ba–Cu–O oxide with metal oxide (CeO2, SnO2, and ZrO2) addition
Authors: Kim Chan-Joong , Kim Ki-Baik , Hong Gye-Won , Lee Ho-Yong
Published: September 2007

Segregation of second-phase particles within Y1Ba2Cu3O7−y domain was investigated in melt-textured Y-Ba-Cu-O with metal oxide (CeO2, SnO2, and ZrO2) addition. It is found that coarse particles (Y2Ba1Cu1O5) are trapped with a special pattern in the interior of Y1Ba2Cu3O7−y domain, while fine BaCeO3 and BaSnO3 particles are present within the remnant liquid-phase region. During the growth of Y1Ba2Cu3O7−y domain, fine particles appear to be pushed out of the advancing Y1Ba2Cu3O7−y /liquid interface toward the liquid phase. The particle segregation that occurred during peritectic growth of the Y1Ba2Cu3O7−y domain was explained in terms of the Uhlmann-Chalmers-Jackson theory based on the particle interaction at solid/liquid interface.
Gas-phase particle size distributions and lead loss during spray pyrolysis of (Bi,Pb)–Sr–Ca–Cu–O
Authors: Gurav Abhijit S. , Kodas Toivo T. , Joutsensaari Jorma , Kauppincn Esko I. , Zilliacus Riitta
Published: September 2007

Gas-phase particle size distributions and lead loss were measured during formation of (Bi,Pb)-Sr-Ca-Cu-O and pure PbO particles by spray pyrolysis at different temperatures. A differential mobility analyzer (DMA) in conjunction with a condensation particle counter (CPC) was used to monitor the gas-phase particle size distributions, and a Berner-type low-pressure impactor was used to obtain mass size distributions and size-classified samples for chemical analysis. For (Bi,Pb)-Sr-Ca-Cu-O, as the processing temperature was raised from 200 to 700 °C, the number average particle size decreased due to metal nitrate decomposition, intraparticle reactions forming mixed-metal oxides and particle densification. The geometric number mean particle diameter was 0.12 μm at 200 °C and reduced to 0.08 and 0.07 μm, respectively, at 700 and 900 °C. When the reactor temperature was raised from 700 and 800 °C to 900 °C, a large number (∼107 no./cm3) of new ultrafine particles were formed from PbO vapor released from the particles and the reactor walls. Particles made at temperatures up to 700 °C maintained their initial stoichiometry over the whole range of particle sizes monitorcd; however, those made at 800 °C and above were heavily depleted in lead in the size range 0.5–5.0 μm. The evaporative losses of lead oxide from (Bi,Pb)-Sr-Ca-Cu-O particles were compared with the losses from PbO particles to gain insight into the pathways involved in lead loss and the role of intraparticle processes in controlling it.
A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite: Part IV. The basal plane resistivity
Authors: Andersson O.E. , Sundqvist B. , McRae E. , Lelaurain M. , Marêché J.F.
Published: September 2007

Using an inductive technique, we have measured the in-plane resistivity ρa of stages 2, 4, 5, and 8 SbCl5-GIC's versus temperature T and pressure p in the ranges 130–300 K and 0–0.85 GPa. The room temperature values of ρa range from 4.0 μΩcm for the stages 5 sample to 7.7 μΩcm for the stage 8 sample. At all pressures, ρa shows a metallic temperature dependence ρa ∼ Tα, with 1 ≤ a ≤ 2, but in contrast to the c-axis resistivity ρc, it depends only very weakly on pressure and/or intercalate structural order. We show that the behavior observed is consistent with a band conduction model.
Hydrogen desorption properties and electrode performances of Ti–Zr–Ni–V–Mn alloy
Authors: Yang H.W. , Lee W.S. , Wang Y.Y. , Wan C.C. , Cheng T.W. , Liang K.H.
Published: September 2007

The measurements of the desorption pressure-composition-temperature (P-C-T) of the TixZr1−xNiyV2−y(0 ≤x≤ 1,0 ≤y≤ 2) alloy have been investigated by means of a 32factorial design method. The response surface function of hydrogen desorption between 0.01 and 10 atm was calculated by Yates' algorithm. Alloy withx= 0.35,y= 0.60 (i.e., Ti0.35Zr0.65Ni0.6V1.4) was found to possess maximum hydrogen desorption capacity. When examined by EDAX and SEM, this alloy shows three distinguishable phases and exhibits C14 structure. The effect of substitution of Mn and Ni for V was also studied. Alloy such as Ti0.35Zr0.65Ni1.2V0.4Mn0.4has nearly a pure C14 structure with 89% hydrogen desorption ability. This alloy has 255 mAh/g, 231 mAh/g, and 210 mAh/g capacities at 25 mA/g, 50 mA/g, and 100 mA/g discharge rates, respectively. This indicates that the substitution of Mn and Ni for V not only can improve its hydrogen desorption ability, but also make the alloy structure more uniform and more suitable to be an electrode material.
Nickel-coated carbon fiber-reinforced tin-lead alloy composites
Authors: Ho C.T.
Published: September 2007

Nickel is deposited over pristine, surface-treated, and brominated P-100 carbon fibers using cementation and electroplating techniques. The fibers are brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment is performed by etching fibers electrochemically in a dilute sodium electrolyte for 3 min or by immersing fibers in nitric acid for 72 h. Electroplated-coated fibers show better tensile properties than cementation-coated fibers. Tin-lead alloy composites reinforced by nickel-coated fibers (which are pristine, anodically oxidized, and brominated) are fabricated by squeeze casting. The composites containing coated carbon fibers with bromination or surface treatment have higher tensile and shear strength than the ones containing coated pristine carbon fibers. In addition, the composite containing coated carbon fibers with brominalion shows the best performance in the tensile properties.
Phase partitioning and epitaxy of Zr(Al)O2 thin films on cubic zirconia substrates
Authors: Narwankar P.K. , Speck J.S. , Lange F.F.
Published: September 2007

Thin films of ZrO2-Al2O3 were grown on cubic-Zr(Y)O2 substrates by a liquid precursor route. Phase formation and epitaxy of these films was studied as a function of heat-treatment temperature and time. The following sequence of phases was observed in these thin films: Precursor → t-(Zr,Al)O2 → t-(Zr,Al)O2 + γ-(Al,Zr)2O3 → m-ZrO2 + α-Al2O3 Observations strongly suggest that the epitaxial process initiated before the metastable, single phase t-(Zr, Al)O2 partitioned to t-(Zr, Al)O2 + γ-(Al, Zr)2O3. Observations at 1400 °C show that, after the γ to α transformation, α-Al2O3, grains develop an elongated, prismatic morphology and an epitaxial relation with the underlying and surrounding m-ZrO2. The phase that is chemically and structurally similar to the substrate, in this case t-(Zr,Al)O2, or m-ZrO2, forms an epitaxial layer between the substrate and isolated, prismatic grains of heteroepitaxial α-Al2O3.
Microstructures and interdiffusions of Pt/Ti electrodes with respect to annealing in the oxygen ambient
Authors: Park Kyu Ho , Kim Cha Yeon , Jeong Young Woo , Kwon Hyun Ja , Kim Kwang Young , Lee Jeong Soo , Kim Sung Tae
Published: September 2007

The microstructural variation and the interdiffusion of Pt (80 nm)/Ti (70 nm)/SiO2/Si during annealing in O2 were investigated using Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. While the as-deposited and 400 °C annealed samples showed well-defined layer structures without any significant interfacial reaction, the degree of oxidation remarkably increased with increasing temperature above 500 °C. The PtTi alloy phase with Pmma structure (AuCd type) was observed from the 500 °C annealed sample. Drastic interdiffusion occurring above 600 °C changed the Pt/Ti bilayer into a very entangled structure. Some TiO2 phases were exposed to the ambient between Pt hillocks. In addition, a small amount of Pt-silicide was found near the TiOx/SiO2 interface.
Chemical analyses of stains formed on Co–Nb–Zr metal-in-gap heads sliding against oxide and metal particle magnetic tapes
Authors: Gupta B.K. , Bhushan Bharat , Zhou Ying , Winograd N. , Krishnan K.
Published: September 2007

The playback efficiency of metal-in-gap (MIG) inductive read-write heads in magnetic recording devices is strongly influenced by wear of the air-bearing surface, metal core recession, and staining. In this study, stains were formed by sliding Co–Nb–Zr MIG tape heads against Co–γFe2O3 (oxide) and metal particle (MP) tapes in an accelerated mode. Optical and SEM imaging indicated that staining on a head run against the Co–γFe2O3 tape is thick and patchy, whereas on a head run against the MP tape, staining is in the form of a uniform film. Thickness variations of stains on the metal core formed by Co-γFe2O3 and MP tapes, measured using atomic force microscopy (AFM), were about 30–150 nm and 20 nm, respectively. Constituents of stains were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning Auger electron spectroscopy (AES), and micro-Fourier transform infrared (micro-FTIR) and micro-Raman spectroscopies. Stains formed on the head run against the Co-γFe2O3 tape consist of organic species with trace amounts of iron and oxygen (inorganic) constituents. On the other hand, stains formed on the head run against the MP tape consist of inorganic constituents of oxidized magnetic particles from the tape. In addition to organic species and iron from tapes, stains formed by either tape also exhibit wear debris from the metal core, ferrite core, and glass region of the head itself. In the case of heads run against both tapes, most of the staining was found to be on the metal core.
Tribology and mechanical properties of excimer laser-processed Ti–Si3N4 surfaces
Authors: Jervis T.R. , Hirvonen J-P. , Nastasi M. , Kung H.
Published: September 2007

Titanium films were mixed, using excimer laser radiation, into the surface of bulk Si3N4 materials. The tribological and mechanical properties of these surfaces were then evaluated using pin-on-disk and nanoindenter techniques, respectively. Reduced friction and a change in the wear mechanism that resulted in a more benign failure mode were observed. These results are interpreted as resulting from the establishment of a transfer film, changes in the compliance of the surface which reduces instantaneous stresses in the surface, and toughening of the surface, all results of the laser process.
Formation of metastable π phase in mechanically alloyed tellurium-rich Ag–Te alloys
Authors: Chitralekha J. , Raviprasad K. , Gopal E.S.R. , Chattopadhyay K.
Published: September 2007

This paper reports on the formation of metastable π phase on mechanical alloying of elemental Ag and Te powders in the composition range of 50 to 75 at. % Te. Contrary to the reported results in vapor-deposited thin films, no amorphous phase could be detected during mechanical alloying. The extent to which the π phase forms on milling is restricted, compared to rapid solidification. Formation of the metastable π phase coincides with the achievement of nanometric grain size and is preceded by the formation of intermetallic compound Ag2Te. An approximate estimation of the free energies of the competing phases has been attempted to provide insight into the phase selection process. It is suggested that tellurium diffusion through the nanoscale grain boundaries plays an important role in the formation of the metastable π phase.
The study on charge-density distribution in TiAl by quantitative electron crystallography method
Authors: Miao Yu , Zhu Jing , Lin X.W. , Jiang W.J.
Published: September 2007

Structure factors of μ-TiAl equiaxed grain in TiAl duplex intermetallic compound before and after V-alloying were measured by the quantitative electron crystallography method. Then the structure factors were transferred into charge-density distributions of real space. Comparing the charge-density distributions in γ-TiAl with those in V-alloyed γ-TiAl, it was found that V-alloying with the optimum amount decreases the electronic charge density in the Ti-Ti interatomic bond, and increases the electronic charge density in the Al-Al interatomic bond and Ti-Al interatomic bond. Thus, the anisotropy of charge-density distribution in γ-TiAl equiaxed grain is reduced.
Activation energy for Pt2Si and PtSi formation measured over a wide range of ramp rates
Authors: Colgan E.G.
Published: September 2007

The activation energies, Ea's, for Pt2Si and PtSi formation were determined using in situ resistance measurements with ramp rates ranging from 0.4 °C/m to 100 °C/s. Measurements were performed using both conventional furnace and rapid thermal annealing (RTA). Pt films were evaporated on undoped polycrystalline Si and single-crystal Si on sapphire substrates. The Ea's determined from Kissinger plots were 1.63 ± 0.05 and 1.61 ± 0.06 eV for Pt2Si formation and 1.83 ± 0.06 and 1.83 ± 0.07 eV for PtSi formation with polycrystalline Si and silicon on sapphire substrates, respectively. These are the first reported measurements of Ea's for Pt2Si and PtSi formation over such a wide range of heating rates (greater than four orders of magnitude) and at such high heating rates. The phase formation sequence remained the same for the range of heating rates examined.
A simplified analytical model of diamond growth in direct current arcjet reactors
Authors: Dandy David S. , Coltrin Michael E.
Published: September 2007

A simplified model of a direct current arcjet-assisted diamond chemical vapor deposition reactor is presented. The model is based upon detailed theoretical analysis of the transport and chemical processes occurring during diamond deposition, and is formulated to yield closed-form solutions for diamond growth rate, defect density, and heat flux to the substrate. In a direct current arcjet reactor there is a natural division of the physical system into four characteristic domains: plasma torch, free stream, boundary layer, and surface, leading to the development of simplified thermodynamic, transport, and chemical kinetic models for each of the four regions. The models for these four regions are linked to form a single unified model. For a relatively wide range of reactor operating conditions, this simplified model yields results that are in good quantitative agreement with stagnation flow models containing detailed multicomponent transport and chemical kinetics. However, in contrast to the detailed reactor models, the model presented here executes in near real-time on a computer of modest size, and can therefore be readily incorporated into process control models or global dynamic loop simulations.
Smooth diamond films grown by hot filament chemical vapor deposition on positively biased silicon substrates
Authors: Popovici Galina , Chao C.H. , Prelas M.A. , Charlson E.J. , Meese J.M.
Published: September 2007

Diamond films have been grown by hot filament chemical vapor deposition (CVD) on mirror-polished positively biased Si substrates. Very smooth films a few micrometers thick were obtained in only 30 min. SEM, x-ray diffraction patterns, and Raman were used to characterize the films. Not only diamond but other carbon phases, were also detected. The initial structure showed a high density of defects and large stresses. Structural changes in time were found to occur with films apparently undergoing a phase transformation.
The relationship between indentation and uniaxial creep in amorphous selenium
Authors: Poisl W.H. , Oliver W.C. , Fabes B.D.
Published: September 2007

Ultralow load indentation techniques can be used to obtain time-dependent mechanical properties, termed indentation creep, of materials. However, the comparison of indentation creep data to that obtained during conventional creep testing is difficult, mainly due to the determination of the strain rate experienced by the material during indentation. Using the power-law creep equation and the equation for Newtonian viscosity as a function of stress and strain rate, a relationship between indentation strain rate, , and the effective strain rate occurring during the indentation creep process is obtained. Indentation creep measurements on amorphous selenium in the Newtonian viscous flow regime above the glass transition temperature were obtained. The data were then used to determine that the coefficient relating indentation strain rate to the effective strain rate is equal to 0.09, or .
Single-crystal growth and characterization of the Pb0.5Sr2.5Y1−xCaxCu2Oy system
Authors: Jin H. , Wang N.L. , Chong Y. , Deng M. , Cao L.Z. , Chen Z.J. , Zhou G.E. , Mao Z.W.
Published: September 2007

Two kinds of methods such as spontaneous nucleation from flux-free stoichiometric melt and CuO flux method have been used for the growth of Pb0.5Sr2.5Y1−xCaxCu2Oy single crystals. The morphologies, phases, and compositions occurring in the crystals grown from the two kinds of methods were compared systematically. Optimum conditions for the growth of larger 1212 phase single crystals are x =0.15, 0.25, and 0.35. The lattice parameters of the crystals with the 1212 phase were found to be increasing upon Ca doping. The resistivity behavior of the PbSrYCaCuO single crystals with the 1212 phase both in the state of as-grown and after extended annealings under various oxygen partial pressure was also discussed briefly.
Optimization of Y2BaCuO5 phase morphology for the growth of large bulk YBCO grains
Authors: Frangi F. , Higuchi T. , Deguchi M. , Murakami M.
Published: September 2007

YBCO samples were prepared using different types of precursor powders: quenched, or YBa2Cu3O7−x and Y2BaCuO5 commercial powders, with and without Pt addition. Two stoichiomctrics, corresponding to 0 and 40% molar excess of the Y2BaCuO5 phase, were adopted. The behavior of the Y2BaCuO5 phase through thermal treatments, typical of melt processes, was observed by quenching the samples at various stages. YBa2Cu3O7−x grain growth kinetics was enhanced and liquid phase losses were limited by optimizing the morphology of the Y2BaCuO5 phase in the partially melted state, with the simultaneous presence of round particles ≤1 μm and needle-like particles with very high aspect ratio. The optimized processing conditions were adopted, together with a seeding technique, to grow YBCO samples. At 77 K, a magnetic levitation force of 2.5 kg was measured for a sample with 18 mm diameter, and magnetization critical current densities over 104 A/cm2 were reached at 1 T.
Growth of ternary Si1−x-yGexCy thin films from a single-source precursor, Ge(SiMe3)4
Authors: Chiu Hsin-Tien , Shie Ching-Shing , Chuang Shiow-Huey
Published: September 2007

Ge(SiMe3)4 was used as a single-source precursor to deposit thin films of alloys of germanium, silicon, and carbon, Si1−x-yGexCy, by low-pressure chemical vapor deposition on silicon substrates at temperatures 873-973 K. X-ray diffraction studies indicated that the films grown above 898 K were cubic phase (a = 0.441–0.442 nm). Infrared spectra of the films showed a major absorption near 783 cm−1. X-ray photoelectron spectra of a typical thin film showed binding energies of Ge3d, Si2p, and C1s electrons at 30.0, 100.6, and 283.2 eV, respectively. As determined by wavelength dispersive spectroscopy, x was 0.07–0.15 and y was 0.43–0.50, indicating that the films contained 7–15% Ge, 38–43% Si, and 43–50% C. At 973 K, the C/(Si + Ge) ratio was 1. Based on these data, the films deposited above 898 K have a structure of β-SiC with Ge atoms replacing some Si atoms in the lattice.