bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and interpretation of stress in copper films as a function of thermal history
Authors: Flinn Paul A.
Published: September 2007

Since copper has some advantages relative to aluminum as an interconnection material, it is appropriate to investigate its mechanical properties in order to be prepared in advance for possible problems, such as the cracks and voids that have plagued aluminum interconnect systems. A model previously used to interpret the behavior of aluminum films proves to be, with minor modification, also applicable to copper. Although the thermal expansion of copper is closer to that of silicon and, consequently, the thermally induced strains are smaller, the much larger elastic modulus of copper results in substantially higher stresses. This has implications for the interaction of copper lines with dielectrics.
Formation and growth of an amorphous phase by solid-state reaction between GaAs and Co thin films
Authors: Shiau F-Y. , Chen S-L. , Loomans M. , Chang Y.A.
Published: September 2007

Solid-state amorphization reaction (SSAR) between GaAs and Co thin films was investigated by transmission electron microscopy and Auger electron spectroscopy. Upon annealing of GaAs/Co thin-film couples at 260–300 °C, an amorphous phase was observed to form. Annealing at higher temperatures or for longer times led to the crystallization of the amorphous phase into a supersaturated CoAs solid solution phase with the B31 structure. Amorphization is attributed to the rapid diffusion of Co in the rather open GaAs structure. In order to consider the thermodynamic driving force for amorphization and subsequent crystallization, the phase diagram of CoGa–CoAs was investigated using DTA and metallography. The pseudobinary system was modeled thermodynamically to yield relative stability data for the various phases between GaAs and Co. These data were used to rationalize the amorphization process.
Atomic diffusion mediated by intrinsic point defects in GaAs and AlxGa1−xAs–GaAs superlattices
Authors: Iguchi Hidehiko
Published: September 2007

Point-defect-mediated atomic diffusion in GaAs and AlxGa1−xAs–GaAs superlattices is examined thermodynamically by focusing on activation enthalpy of diffusion. Through a review of available experimental results of impurity diffusion of Si, Zn, and Be, their diffusion phenomena are discussed by taking the characteristics of column-III-site-related point defect, such as Ga vacancy and arsenic-antisite, into consideration. It is suggested that Zn and Be diffusion should be mediated by As-antisite defects. On the other hand, Si diffusion is mediated by either Ga vacancy or As-antisite, depending on the growth method of materials and diffusion conditions. It is argued that As-antisite should be a mediator of diffusion in As-antisite-rich materials and with using As-rich diffusion source under p-type conditions. Cation self-diffusion or interdiffusion is also discussed in the same manner. Impurity-enhanced layer-disordering phenomena are examined by considering the reduction of defect energy of Ga vacancy and As antisite under n-type and p-type conditions, respectively. Beryllium enhanced and suppressed interdiffusion (cation self-diffusion) in MBE-grown AlxGa1−xAs–GaAs superlattices are interpreted in view of point-defect-mediated cation diffusion on the basis of the Fermi-energy dependence of point defect. In order to explain the phenomena, crystal-growth methods and surface-localized point defects which is responsible for Fermi-level stabilization are taken into consideration.
The strength, fracture, and chemical changes of poly-(p-phenylene benzobisthiazole) after exposure to molten and vapor deposited aluminum
Authors: Newman K.E. , Zhang P. , Cuddy L.J. , Allara D.L.
Published: September 2007

The tensile properties, fracture behavior, and surface chemical composition of the rigid-rod heterocyclic aromatic polymer fiber poly-(p-phenylene benzobisthiazole), PBT, have been measured as a function of contact with nominally zero valent aluminum overlayers. The samples were produced by immersion of suitable fiber or film specimens in a molten aluminum-12.7 wt. % silicon alloy or by aluminum-vapor deposition followed by heat treatment. The strength of uncoated PBT fiber was 3.0 GPa. After 5 min immersion in the molten aluminum alloy, strengths drop to 80% and 25% of the uncoated fiber values for 600°and 700 °C immersion, respectively. Fiber strengths after aluminum immersion are from zero to 20% lower than the strength for corresponding uncoated fibers heated at an equivalent temperature in argon. Coated fibers exhibit tensile strengths after heating intermediate to similarly heated uncoated or immersed fibers. For all types of samples, the fiber fracture mode changes from fibrillar at failure strengths >1.9 GPa (independent of the environment) to planar at failure strengths <1.9 GPa. X-ray photoelectron spectroscopy of PBT fiber and film surfaces indicates oxidation of the polymer surface has occurred, most likely during fabrication of the fiber or film. The oxygen content of the surface layer is decreased when the film is immersed in molten aluminum-silicon alloy. The lack of corresponding changes in the relative intensities of the polymer C, S, or N photoemission peaks after this immersion suggests that the surface oxidized layer plays some role in protecting the polymer from degradation by molten aluminum. These results strongly suggest that it is possible to fabricate low-density, high-strength PBT/metal composites by liquid aluminum alloy infiltration if the melt temperature is kept below 680 °C and the contact time with molten aluminum kept below 3 min.
Mg–Ti–spinel formation at the TiN/MgO interface by solid state reaction: Confirmation by high-resolution electron microscopy
Authors: Hultman L. , Hesse D. , Chiou W-A.
Published: September 2007

Mg–Ti–spinel formation along the interface of epitaxial TiN(100) films to MgO(100) substrates has recently been investigated by transmission electron microscopy (TEM) in the diffraction-contrast mode in samples grown at substrate temperatures higher than 800 °C and in such post-annealed at 850 °C. This phenomenon has now been investigated by high resolution electron microscopy of cross-sectional samples, at an acceleration voltage of 300 kV. Emphasis is given to the TiN/spinel and the spinel/MgO interfaces with respect to their structure and morphology. The results obtained confirm the previously drawn conclusions on the atomic mechanism of the solid state reaction during the spinel-forming process: The spinel, which most likely is of the composition Mg2TiO4, forms by counterdiffusion of the cations Ti4+and Mg2+in the rigid oxygen frame provided by the fcc oxygen sublattice of MgO. The latter is completely taken over by the spinel lattice. This “host” character of the MgO substrate lattice for the topotaxial growth of the spinel lattice and the coherency of the solid state reaction with respect to the lattices of all the phases involved are demonstrated. Misfit dislocations at the TiN/MgO, TiN/spinel, and the spinel/MgO interfaces, as well as antiphase boundaries of the cation sublattice of the spinel phase, have also been observed.
A study of silicide formation from LPCVD-tungsten films: Film texture and growth kineticsa
Authors: Zhang S-L. , Buchta R. , Östling M.
Published: September 2007

Tungsten disilicide (WSi2) was formed by annealing tungsten (W) films of 330 nm and 750 nm prepared by low pressure chemical vapor deposition (LPCVD) from tungsten hexafluoride (WF6) on Czochralski 〈100〉-Si substrates. The silicide was found to grow continuously from the WSi2/W interface. The thickness of the formed WSi2 was observed by Rutherford backscattering measurements (RBS) to increase parabolically with the annealing time, with an activation energy of 2.6 eV/atom. The crystal structure of the formed WSi2 and the unreacted W films was analyzed using x-ray diffraction (XRD) technique. The thermal history of the samples was found to play an important role for the film texture of the unreacted W and formed WSi2, indicating that the fast and inexpensive method, XRD, applied as a thickness monitor for kinetics studies of WSi2 growth will undoubtedly introduce large errors. The as-deposited W (on Si) and the unreacted W (on WSi2) were found to be under a tensile stress, as observed by means of the XRD technique.
Ultra-high vacuum chemical vapor deposition and in situ characterization of titanium oxide thin films
Authors: Lu Jiong-Ping , Raj Rishi
Published: September 2007

Chemical vapor deposition (CVD) of titanium oxide films has been performed for the first time under ultra-high vacuum (UHV) conditions. The films were deposited through the pyrolysis reaction of titanium isopropoxide, Ti(OPri)4, and in situ characterized by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A small amount of C incorporation was observed during the initial stages of deposition, through the interaction of precursor molecules with the bare Si substrate. Subsequent deposition produces pure and stoichiometric TiO2 films. Si–O bond formation was detected in the film-substrate interface. Deposition rate was found to increase with the substrate temperature. Ultra-high vacuum chemical vapor deposition (UHV-CVD) is especially useful to study the initial stages of the CVD processes, to prepare ultra-thin films, and to investigate the composition of deposited films without the interference from ambient impurities.
Processing and mechanical behavior of SiC fiber-reinforced Si3N4 composites
Authors: Yang J-M. , Chen Steven T.J. , Jeng S.M. , Thayer R.B. , LeCoustaouec J-F.
Published: September 2007

The interfacial properties and mechanical behavior of the SCS-6/Si3N4 composites fabricated by hot pressing from powder lay-up and tape lay-up techniques were studied. Interfacial shear strength and frictional stress were measured using an indentation test. Fracture toughness and work-of-fracture were measured using a three-point bending test on a chevron-notched specimen. The influence of interfacial shear strength on the toughening mechanisms and crack propagation behavior were investigated. The results indicate that the processing routes and fiber orientation will affect the interfacial properties, which in turn have a significant influence on mechanical properties.
The formation of copper aluminate by solid-state reaction
Authors: Susnitzky David W. , Carter C. Barry
Published: September 2007

Solid-state reactions between bulk samples of copper oxide and alumina have been studied using scanning electron microscopy and electron microprobe analysis. Both CuAl2O4 and CuAlO2 were found to form during reactions in air at 1100 °C between CuO powder and single-crystal alumina substrates. The relative position of the CuAl2O4 and CuAlO2 layers was observed to depend on the crystallographic orientation of the surface of the alumina substrate: CuAl2O4 formed in contact with (0001) alumina substrates while CuAlO2 formed when the alumina substrate surface was (110). Faceted Cu–aluminate/alumina phase boundaries were observed to develop when single-crystal alumina rods were reacted with CuO, although the interfaces invariably tended to be wavy.
Transient kinetics of nucleation and crystallization: Part II. Crystallization
Authors: Shi G. , Seinfeld J.H.
Published: September 2007

Analytical expressions for the time-dependent crystallized volume fraction are derived from new results for the transient rate of nucleation reported in Part I. Conventional formulations that have been used in interpreting crystallization experimental data and for assessing the stability of amorphous phases are shown to be large time limits of the newly derived expressions. An approach for assessing the stability of an amorphous phase is proposed.
A phenomenological model of ion-induced crystallization and amorphization
Authors: Carter G. , Nobes M.J.
Published: September 2007

A simple phenomenological model is developed to explain, qualitatively, the observed temperature and ion flux dependences of either recrystallization or further amorphous growth of amorphous layers in semiconductors when exposed to ion irradiation. The model includes radiation assisted annealing processes and thermally modified amorphous zone production at the amorphous-crystal interface.
Composition and structure of Si–Ge layers produced by ion implantation and laser melting
Authors: Berti M. , Mazzi G. , Calcagnile L. , Drigo A.V. , Merli P.G. , Migliori A.
Published: September 2007

Si samples (001) oriented have been implanted with 101774Ge/cm2 (17.7 at. % maximum Ge concentration) and then pulse annealed with either ruby or excimer (XeCl) lasers in the energy density range from 0.1 to 1.5 J/cm2. Compositional and structural characterization has been performed showing that for both laser wavelengths the final product of the annealing process is a single crystal characterized by a surface layer about 150 nm thick whose composition is Si0.9Ge0.1. While after ruby laser irradiations defects are present even in the fully recrystallized samples, after XeCl irradiations good strained layers in epitaxy to the underlying silicon crystals and free from misfit dislocations are produced. Structural characterization of the regrown films indicates that the governing factor for the recovery of the crystalline quality and for the “building up of strain” is the state of the implantation “end-of-range defect” layer. When this defected layer is not melted, textured columnar grains are formed. Upon melting of the end-of-range defect layer, a single crystal epitaxial layer under compressive strain is formed.
Characterization of thermal plasma CVD diamond coatings and the intermediate SiC phase
Authors: Tsai C. , Gerberich W. , Lu Z.P. , Heberlein J. , Pfender E.
Published: September 2007

Diamond films have been successfully deposited by DC thermal plasma jet CVD at a rate of 40 μm/h under atmospheric and subatmospheric pressures. Transmission electron microscopy (TEM) has been used for the characterization of the diamond films and the intermediate phase. The orientation and the distribution of β-SiC at the interface between the diamond and silicon substrate have been observed using selected-area electron diffraction with the associated dark-field images. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy are used for the characterization of the produced diamond films. Potential applications of selected-area channeling patterns are discussed for investigating the correlations between the growth direction and the crystalline perfection.
Phase equilibria and solidification behavior in the PbF2−AlF3 system
Authors: Moulton Linda V. , Feigelson Robert S.
Published: September 2007

The relationship between phase equilibria in the PbF2−AlF3 system and the solidification behavior of several ternary lead aluminum fluoride compounds was explored. A partial binary phase diagram for the PbF2−AlF3 system was determined from differential thermal analysis, annealing and directional solidification studies. The compounds AlF3, Pb3Al2F12, Pb9Al2F24, and a PbF2 solid solution were identified by x-ray diffraction, energy dispersive and microprobe analysis. The previously reported phases PbAlF5 and PbAl2F8 were not observed. Directional solidification studies showed that it is possible to grow crystals of AlF3, Pb3Al2F12, and the PbF2 solid solution from nonstoichiometric PbF2−AlF3 melts. The compound Pb9Al2F24 was found to decompose on heating by a peritectoid reaction (forming two other solids) and thus could not be solidified directly from a PbF2−AlF3 melt.
Monocrystal elastic constants of orthotropic Y1Ba2Cu3O7: An estimate
Authors: Ledbetter Hassel , Lei Ming
Published: September 2007

For Y1Ba2Cu3O7, using only reported monocrystal measurements and some analysis–theory, we estimated the complete nine-component orthotropic-symmetry elastic-stiffness matrix, the Voigt Cij matrix. Comparison with very-high-frequency tetragonal-symmetry phonon-dispersion results shows good agreement (9% on average), except for C12.
Defect theory applied to YBa2Cu3O7−δ
Authors: Favrot D. , Déchamps M.
Published: September 2007

YBa2Cu3O7−δ superconductor crystals have ferroelastic properties, which makes it possible to interpret their microstructure within the framework of the quasidislocation theory.
Effect of Ca2CuO3 excess on superconducting properties in the Bi–Pb–Sr–Ca–Cu–O system
Authors: Liu H.K. , Dou S.X. , Guo S.J. , Easterling K.E. , Li X.G.
Published: September 2007

The effect of excess Ca2CuO3 on the superconducting properties in the (Bi, Pb)2Sr2Ca2Cu3Oy, (2223) was investigated through the measurements of ac susceptibility, critical current density, and critical field. All the measurements have been performed on the samples that were identified by x-ray diffraction to consist of the mostly high Tc 2223 phase with varying amounts of excess Ca2CuO3. It was found that when the excess Ca2CuO3 is in the range 0.1 M to 0.3 M the loss peak of ac susceptibility appeared at higher temperature than that for an undoped sample, and the Jc showed a maximum at the excess Ca2CuO3 = 0.2 M, indicating that a proper amount of excess Ca2CuO3 enhanced the flux pinning. The upper critical field, Hc2, determined by using a pulse magnetic field showed a maximum at the excess Ca2CuO3 = 0.1 M, and increased linearly with decreasing temperature within the measurement regime.
On the mechanism of grain-boundary migration in metals: A molecular dynamics study
Authors: Rickman J.M. , Phillpot S.R. , Wolf D. , Woodraska D.L. , Yip S.
Published: September 2007

The migration of a (100) θ = 43.6°(Σ29) twist grain boundary is observed during the course of a molecular-dynamics simulation. The atomic-level details of the migration are investigated by determining the time dependence of the planar structure factor, a function of the planar interparticle bond angles, and the location of the center of a mass of planes near the grain boundary. It is found that a migration step consists of local bond rearrangements which, when the simulation cell is made large enough, produce domain-like structures in the migrating plane. Although no overall sliding is observed during migration, a local sliding of the planes near the migrating grain boundary accompanies the migration process. It is suggested that a three-dimensional cloud of thermally produced Frenkel-like point defects near the boundary accompanies, and facilitates, its migration.
The fracture toughness for first matrix cracking of a unidirectionally reinforced carbon/carbon composite material
Authors: Miyajima Tatsuya , Sakai Mototsugu
Published: September 2007

The fracture toughness for first matrix cracking of a uniaxially reinforced C-fiber/C-matrix composite is investigated using a modified controlled surface flaw method. The theoretical models for first matrix cracking of brittle matrix composites including the stress intensity and the potential energy approaches are reviewed in the light of the experimental results. The sharing of the applied load between the reinforcing fibers and the brittle matrix along with extensive crack front debonding enhance the fracture toughness for first matrix cracking.
Co-implantation of Mo+ and S+ in SiO2
Authors: Rai A.K. , Bhattacharya R.S.
Published: September 2007

An amorphous SiO2 substrate was co-implanted with 175 keV Mo+ and 74 keV S+ ions at doses of 4.97 × 1016 and 1.02 × 1017 cm−2, respectively. Energies of the Mo+ and S+ ions were chosen to obtain nearly overlapping depth profiles. Transmission electron microscopy and Rutherford backscattering techniques were used to characterize the ion-implanted materials. The formation of a MoS2 phase was observed in the as-implanted condition. Annealing of the as-implanted material was performed in an oxygen-free atmosphere as well as in air. The MoS2 phase remained stable at 700 °C for 8 h in an oxygen-free atmosphere whereas it starts oxidizing in air at 600 °C for 2 h. Results are discussed in terms of the available data on the oxidation of MoS2 coatings.
Defect/surface interactions in heat-treated ceramic thin films
Authors: Susnitzky David W. , Barry Carter C.
Published: September 2007

The use of transmission electron microscopy to study the interaction of lattice defects with surfaces of heat-treated ceramic materials is discussed. The approach used throughout the work described has been to prepare a thinned sample in a form suitable for imaging in the electron microscope and then to remove all preparation-induced damage by heat-treating the thinned sample. Applications of the technique to the movement and pinning of individual surface steps in alumina and the grooving of antiphase boundaries in silicon carbide are illustrated.
Crystallization kinetics and phase transformation characteristics in seeded monophasic cordierite gel
Authors: Lim Byung C. , Jang Hyun M.
Published: September 2007

Crystallization kinetics and phase transformation characteristics of μ- or α-cordierite seeded gels were compared with those of unseeded monophasic gels. The α-cordierite seeding modified the sequence of phase transformation and lowered the temperature of α-cordierite formation from amorphous gel by ∽150 °C. The μ-seeded transformation was characterized by 3-dimensional isotropic growth with essentially zero activation energy for the nucleation step. Combining the nucleation theory with the transition state theory, we have separately estimated the activation free energy of nucleation and that of growth step in the crystallization of amorphous cordierite gel. The estimated activation free energies showed that the crystallization of unseeded cordierite gel is mainly growth controlled.
Alumina fused cast refractory aging monitored by nickel crystal chemistry
Authors: Galoisy Laurence , Calas Georges , Maquet Michel
Published: September 2007

Aged bricks of AZS and mixed α-β-alumina refractories have been sampled in superstructures of glass making furnaces. α- and β-alumina phases contained in these refractories have been investigated by optical absorption spectroscopy, electron paramagnetic resonance, and electron probe microanalysis. On the side of the brick exposed to the tank atmosphere, β-alumina is the only phase present. The primary corundum grains are transformed into secondary β-alumina under the influence of contaminants from raw materials and oil ashes. The temperature conditions existing in the furnace preclude the formation of β” alumina. The bright blue color of β-alumina originates from the presence of tetrahedral Ni2+ in Al(2) sites, with no evidence for nickel atoms located in the ionic conduction band. By considering the chemical composition of β-alumina, spectroscopic results are consistent with a mutual interaction between divalent and monovalent species during cation diffusion. Indeed, the small divalent cations such as Ni are located in the spinel block and the larger alkali cations play a charge compensation role in the conduction band. As other divalent cations of small ionic radius, nickel hence helps to stabilize β-alumina, which maintains the refractory performance during furnace operation. The spectroscopic evidence of trace amounts of nickel (<100 ppm) in secondary corundum crystals means that this phase formed at the expense of β-alumina inside the high-alumina refractory brick. By considering the diffusion coefficients of Ni2+ in α- and β-alumina, this indicates a fast contamination of the material at an early stage of the furnace history. The formation of a permanent deep layer of primary and secondary corundum has protected the inner part of the refractory brick from further contamination.
Characterization and identification of berlinite crystals by acoustic microscopy
Authors: Gomez Morales J. , Rodriguez R. , Durand J. , Ferdj-Allah H. , Hadjoub Z. , Attal J. , Doghmane A.
Published: September 2007

Berlinite crystals grown in H3PO4, HCl, H3PO4/HCl, H2SO4/HCl, or H3PO4/HCl/H2SO4 solvents are characterized by acoustic microscopy techniques. Surface and subsurface defects can be visualized via acoustical images, whereas elastic parameters of the crystal can be measured on a microscopic scale. They prove to be of great importance in the identification of not only crystal orientations but of preparation methods as well. We show, for example, that a growth in sulfuric and phosphoric mediums improves mechanical behavior of berlinite crystals. Moreover, it seems that anisotropy plays a fundamental role in this characterization technique with an appearance or a disappearance of specific modes.
Properties and behavior of the platinum group metals in the glass resulting from the vitrification of simulated nuclear fuel reprocessing waste
Authors: Krause Ch. , Luckscheiter B.
Published: September 2007

Two types of platinum group metal particles were found in borosilicate nuclear waste glasses: needle-shaped RuO2 particles and spherical PdRhxTey alloys. They form a dense sediment of high electrical conductivity and relatively high viscosity at the bottom of the ceramic melting furnace. The sludge shows a non-Newtonian flow behavior. The viscosity and conductivity of the sludge depend not only on the platinum group metal content but also on the texture and morphology of the RuO2 particles. RuO2 forms long, needle-shaped crystals which are caused by alkalimolybdate salt melts that formed in the calcine layer. The salt melts oxidize the Ru present as small RuO2 particles after calcination to higher oxidation states. Ruthenium (VI) compounds are formed, presumably, which are not stable with respect to RuO2 under the melting conditions. RuO2 precipitates and crystallizes into long, needle-like particles.
Elastic Green's function for a bimaterial composite solid containing a free surface normal to the interface
Authors: Tewary V.K.
Published: September 2007

Elastic plane strain Green's function is calculated for an anisotropic bimaterial composite solid containing a free surface normal to the interface. An exact integral representation is obtained for the Green's function, which is evaluated numerically. The integral is also evaluated analytically, which gives a series representation for the Green's function. The singularities in the stress field associated with the presence of the free surface are identified and discussed. These singularities can be of the type r-δ, ln(r) as well as higher powers of ln(r), where δ is between 0 and 1 and r is the radial distance from the intersection of the free surface and the interface. The stress field may also contain an oscillatory factor of the type exp[ιg ln (r)] where g depends upon the material parameters of the two solids. For illustration, the formalism is applied to a cubic solid containing a Σ-5 grain boundary.
Deformation of an extruded nickel beryllide between room temperature and 820 °C
Authors: Pharr G.M. , Courington S.V. , Wadsworth J. , Nieh T.G.
Published: September 2007

The mechanical properties of nickel beryllide, NiBe, have been investigated in the temperature range 20–820 °C. The room temperature properties were studied using tension, bending, and compression tests, while the elevated temperature properties were characterized in compression only. NiBe exhibits some ductility at room temperature; the strains to failure in tension and compression are 1.3% and 13%, respectively. Fracture is controlled primarily by the cohesive strength of grain boundaries. At high temperatures, NiBe is readily deformable—strains in excess of 30% can be achieved at temperatures as low as 400 °C. Strain hardening rates are high, and the flow stress decreases monotonically with temperature. The high temperature strength of NiBe is as good or better than that of NiAl, but not quite as good as CoAl.
The existence of Ni3MSb phases in ternary nickel-M-antimony systems (where “M” represents aluminum, gallium, or indium)
Authors: Jan C-H. , Chang Y.A.
Published: September 2007

Phases of the nominal composition Ni3MSb (where “M” represents aluminum, gallium, or indium) were found to occur in their respective ternary systems. They were analyzed by x-ray diffraction and were found to exhibit the B81.5′ crystal structure, similar to that of Ni3GaAs. These phases were shown by differential thermal analysis (DTA) to be stable between room temperature and their melting points, which were determined to be >1150 °C, 1066 °C, and 1091 °C for Ni3AlSb, Ni3GaSb, and Ni3InSb, respectively. An analysis of their respective constituent binary systems suggested that these phases were not true ternary compounds, but rather represented specific compositions of extensive solid solutions of constituent binary phases. Speculations were made as to the solution behavior of these phases. The Ni3MSb phases were predicted to form initially in nickel/MSb diffusion couples, in an analogy to what is observed in nickel/GaAs diffusion couples.
Optical properties of HgS and HgS : Co2+ crystals
Authors: Choe Sung-Hyu , Yu Ki-Su , Kim Jae-Eun , Park Hae Yong , Kim Wha-Tek
Published: September 2007

Melt-grown crystals of HgS and HgS : Co2+ were used to measure their optical absorption spectra. The optical energy band gaps of these crystals were 2.030 eV and 1.870 eV at room temperature, respectively. The impurity optical absorption peaks of Co2+ were observed at 4030, 5988, 12285, 12672, and 12905 cm−1. These peaks can be attributed to the electronic transitions between the split energy levels of Co2+ ion located at the Td symmetry site, where the crystal field, Racah, and spin-orbit coupling parameters were given by Dq = 403, B = 427, and Λ = −155 cm−1, respectively.
Microstructure and thermal stability of amorphous materials in the GeS2−La2S3 system
Authors: Kumta Prashant N. , Risbud Subhash H.
Published: September 2007

GeS2 is known to be a good chalcogenide glass former with a transmission cutoff at 11 μm and has been studied for fiber optic application in the mid infrared region. The rare earth sulfides, oxysulfides, and oxides (La–Er) form reasonably good and stable glasses when mixed with chalcogenides such as Ga2S3. In this work, glass formation was studied in the GeS2−La2S3 system. Two compositions containing 60 mol % and 92.5 mol % GeS2, respectively, were analyzed, and the effects of composition on the microstructure and thermal stability of these glasses were investigated. Microstructural studies were conducted on the as-prepared and heat-treated glasses using TEM and SEM/EDXA. Glasses rich in GeS2 exhibited primary (6–88 nm) and secondary (3–13 nm) phase separation at the molecular level. Differential thermal analysis performed on these glasses indicated glass transition temperatures (Tg) of 510 °C and 420 °C for the two compositions studied. The glasses were stable and the (Tg) was observed to decrease with increasing contents of GeS2 in these glasses.
Small-angle neutron scattering characterization of processing/microstructure relationships in the sintering of crystalline and glassy ceramics
Authors: Long G.G. , Krueger S. , Gerhardt R.A. , Page R.A.
Published: September 2007

Small-angle neutron scattering measurements were used to examine the pore microstructure evolution of glassy silica and polycrystalline alpha-alumina as a function of sintering. It was shown that the two major sintering mechanisms, viscous flow and surface and volume diffusion, lead to very different microstructure evolution signatures in terms of the average pore size as a function of density. However, with respect to topology, the evolution of the porosity per unit surface area as a function of density is remarkably similar in the two systems.
Partial agglomeration during Co silicide film formation
Authors: Xiao Z.G. , Rozgonyi G.A. , Canovai C.A. , Osburn C.M.
Published: September 2007

The agglomeration of Co silicide films formed on Si substrates processed with evaporated Co film thicknesses from 9 to 28 nm was investigated by TEM and four-point-probe resistivity measurements. It was found that the upper portion of a reacting Co or Co silicide film can agglomerate independently from the main body of the silicide layer. This phenomenon is designated partial agglomeration in contrast to whole film agglomeration which generally occurs at higher temperatures. Partial agglomeration appears to develop more extensively for thinner films and poses a serious limitation for the application of thin silicide contact layers for advanced VLSI devices. The formation mechanism of partial agglomeration and the reason for its variation with film thickness are explained on the basis of a previously presented [MRS Proc. Vol. 202, p. 101 (1991)] theoretical model of grain boundary grooving and the onset of islanding in silicide films. Kirkendall voids and phase transformation induced volume changes play an important role in the process.
Correlation of Bi and Cu valencies with structural modulation in Bi2Sr2(Ca1−x Yx)Cu2Oy
Authors: Kawano T. , Munakata F. , Yamauchi H. , Tanaka S.
Published: September 2007

The valencies of the Bi and Cu ions in Bi2Sr2(Ca1−x Yx)Cu2Oy were determined separately by a coulometric titration technique. The Cu valency decreased monotonically from 2.16 to 2.04 with increasing Y content over the range from 0 to 1. Superconductivity occurred for Cu valency greater than 2.1. The Bi valency was also found to decrease from +3.12 to +2.99 as the Y content increased. It leveled off at ∼ +3.0 for the Y content larger than 0.8. This change in the Bi valency was correlated with the change in the structural modulation period and with its transformation from an incommensurate to a commensurate state.
Identification of a growth defect in solid C60 by electron diffraction
Authors: Luzzi D.E. , Fischer J.E. , Wang X.Q. , Ricketts-Foot D.A. , McGhie A.R. , Romanow W.J.
Published: September 2007

The origin of an anomalous sawtooth-shaped feature in x-ray powder diffraction of solid C60 is explained via electron diffraction analysis. Films sublimed on holey carbon crystallize with close-packed (111) planes parallel to the surface. Rods of diffuse scattering are found along the 〈111〉 axis normal to the surface but not along other 〈111〉 axes. Powder averaging of these rods, coupled with the x-ray form factor of spherical shells with 3.5 Å radius, accounts for the sawtooth feature. We attribute this phenomenon to planar defects parallel to close-packed layers, which form during the growth of solid C60 by sublimation. A possibly related consequence of the growth mode is the observation of strong macroscopic (111) preferred orientation in films sublimed on a variety of substrates.
New evidence for supported metals in the reaction of KC8 with metal chlorides
Authors: Messaoudi A. , Béguin F.
Published: September 2007

The evolution of the reaction between the binary graphitide KC8 and CoCl2 dissolved in anhydrous tetrahydrofuran (THF) has been investigated by in situ x-ray diffraction (XRD). During the reaction and whatever the host graphite (powder or HOPG), the first stage graphite intercalation compounds K(THF)2.5C24 and K(THF)1.7C24 are first formed and then transformed into higher stages. Finally the matrix is exfoliated and the phases identified are graphite, metallic cobalt, and KCl. Analyses by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) clearly show that the products are mainly located at the edge planes of the graphite, indicating that the electronic exchange occurs at the edge of the graphene layers. It is now clear that graphite-cobalt intercalation compounds cannot be obtained by this method.
Phase separation in gel-derived materials, separation and crystallization of SnO2 within an amorphous SiO2 matrix
Authors: Dal Maschio R. , Dirè S. , Carturan G. , Enzo S. , Battezzati L.
Published: September 2007

On heating a gel of composition 33.5SnO2−66.5SiO2 (wt. %) up to 1050 °C, SnO2 crystallization occurred with different mechanisms according to thermal treatments. Thermal analysis, SAXS (Small Angle X-Ray Scattering), WAXS (Wide Angle X-Ray Scattering), and TEM (Transmission Electron Microscopy) results obtained for samples treated at different temperatures demonstrated that the SnO2 load is divided into two moieties, one composed of isolated SnO2 particles suitable for primary crystallization yielding crystallites with 4.0 nm of average size; the other, being dissolved in SiO2, remains in the amorphous SiO2/SnO2 solid solution up to the highest temperature. The presence of these two phases accounts for SnO2 surface segregation at the expense of the SnO2 concentration of neighboring outer layers and the independence of apparent density on temperature.
Flat interfaces in zinc oxide-based varistor ceramics
Authors: Sung Gun Yong , McKernan Stuart , Carter C. Barry
Published: September 2007

Four types of structurally different, flat interfaces have been observed in ZnO-based varistor ceramics containing metal-oxides additives (Bi, Mn, and Ti) by bright-field and high-resolution imaging in a transmission electron microscope. Orientation relationships have been characterized by selected-area diffraction. The faceting of ZnO grains when in contact with β–Bi2O3 is discussed in relation to the anisotropic growth of the ZnO grains which leads to pronounced faceting parallel to (0001) planes.
Crystallographic changes in (CaxSr1−x)n+1 TinO3n+1 layer perovskites: XPS and XAES investigations
Authors: Myhra S. , Rivière J.C. , Hawkins K. , White T.J.
Published: September 2007

Layered perovskites (Ruddlesden–Popper phases), (CaxSr1−x)n+1 TinO3n+1 with n = 3, ∞ and x ranging from 0 to 1, have been investigated by XPS and XAES. The structural transitions, identified in other studies, have been correlated with changes in the chemical environments of the constituent species. In particular, the tetragonal to orthorhombic transition at x = 0.65 ± 0.1 appears to generate nonequivalent cation environments for the alkaline earth species in (Ca, Sr)O12 coordination. Other binding and kinetic energy shifts can be correlated with changes in and distortions of unit cell volumes.
Fabrication of porous hydroxyapatite ceramics by microwave processing
Authors: Fang Yi , Agrawal Dinesh K. , Roy Della M. , Roy Rustum
Published: September 2007

Porous hydroxyapatite ceramics with porosity up to 73% have been fabricated by microwave processing at 1150 to 1200 °C for 1 to 5 min. Various porosities in these ceramics have been obtained by using starting materials with different morphology, adjusting green density, changing sintering time and temperature, as well as optionally mixing ammonium carbonate in the hydroxyapatite powder during the consolidation process. Porosity, microstructure, and diametral tensile strength of the porous hydroxyapatite ceramics have been studied.
Thermal regrowth of ion-damaged YBa2Cu3O7−δ superconducting thin films
Authors: Wu X.D. , Luo L. , Muenchausen R.E. , Foltyn S.R.
Published: September 2007

Regrowth of ion-damaged YBa2Cu3O7−δ thin films on LaAlO3 was studied using the ion beam channeling technique. The damaged films can be regrown at a temperature as low as 650 °C, and are stable up to 1000 °C. The regrowth process was found to be thermally activated with a single activation energy of 0.46 eV, contrary to two energies found in a previous study on the films on MgO [J. A. Martinez et al., Appl. Phys. Lett. 57, 189 (1990)].
Reduced-pressure MOCVD of highly crystalline BaTiO3 thin films
Authors: Van Buskirk Peter C. , Gardiner Robin , Kirlin Peter S. , Nutt Steven
Published: September 2007

Epitaxial BaTi3 films have been grown on NdGaO3 [100] substrates by reduced pressure MOCVD for the first time. The substrate temperature was 1000 °C and the total pressure was 4 Torr. Electron and x-ray diffraction measurements indicate highly textured, single phase films on the NdGaO3 substrate which are predominantly [100], with [110] also present. TEM and selected area electron diffraction (SAED) indicate two specific orientational relationships between the [110] and the [001] diffraction patterns.
Cohesive properties, electronic structure, and bonding characteristics of RuAl—A comparison to NiAl
Authors: Lin W. , Xu Jian-hua , Freeman A.J.
Published: September 2007

Recent experiments on promising high-temperature aluminide intermetallic compounds discovered that, in contrast to NiAl, RuAl has critical 〈111〉 slip systems that facilitate ductility under compression at room temperature. In order to understand this different mechanical property from a microscopic point of view, the cohesive and electronic properties of NiAl and RuAl have been studied by means of the first principles local density all-electron self-consistent linearized muffin-tin orbital (LMTO) and full-potential linearized augmented plane wave (FLAPW) methods. The ground state cohesive properties calculated by the LMTO method (including equilibrium lattice constant, bulk modulus, and formation energy) are found to be in good agreement with experiment. The analysis of the band structure and density of states shows that the transition metal (Ni or Ru) d-Al p hybridization provides the major contribution to the cohesive energy in both compounds. The anti-phase boundary (APB) energy of RuAl associated with the ½〈111〉 {110} superdislocation (580 mJ/m2) is found to be only 65% that of NiAl. Moreover, the charge density near the Fermi energy reveals that (i) the strong Ni d-Al p hybridization at EF for NiAl causes a directional charge distribution along the 〈111〉 direction which may affect its dislocation dissociation; (ii) for RuAl, a mostly Ru-d electron charge distribution shows only d-d bonding along the 〈100〉 direction between Ru atoms.
The effect of strain rate and temperature on the tensile properties of NiAl
Authors: Noebe R.D. , Cullers C.L. , Bowman R.R.
Published: September 2007

Tensile testing of cast and extruded binary NiAl was performed from 300 to 900 K at strain rates of 1.4 × 10−4 to 1.4 × 10−1 × s−1. The brittle-to-ductile transition temperature (BDTT) was dependent on strain rate, with a three order of magnitude increase in strain rate resulting in approximately a 200 K increase in transition temperature. Regardless of strain rate, at temperatures just above the BDTT the fracture strength increased significantly and the fracture morphology changed from mostly intergranular to predominantly transgranular. It was also determined that the mechanism responsible for the brittle-to-ductile transition in NiAl had an apparent activation energy of approximately 118 kJ/mol. These results support the argument that the mechanism for the brittle-to-ductile transition in NiAl is associated with the onset of a thermally activated deformation process. This process is probably dislocation climb controlled by short circuit diffusion.
Characterization of metal-containing amorphous hydrogenated carbon films
Authors: Wang M. , Schmidt K. , Reichelt K. , Dimigen H. , Hübsch H.
Published: September 2007

Metal-containing amorphous hydrogenated carbon (Me–C: H) films were prepared on silicon substrates. Two kinds of metals (Ti, Ta) were incorporated in the process of reactive rf diode— (13.56 MHz) and DC-magnetron sputtering, respectively. Elastic recoil detection (ERD) and Rutherford backscattering (RBS) of MeV He+ ions were used to determine the hydrogen content and mass density of Me–C: H films. The mechanical properties, i.e., microhardness, Young's modulus, and adhesion, were measured with the help of a nanoindenter and scratch tester. Results show that (1) the mechanical properties of Me–C: H films depend mainly on metal concentrations. At a certain metal concentration, optimal hardness, Young's modulus, and critical load were obtained; (2) the M–C: H films with an optimal metal concentration possess similar hardness, Young's modulus, and higher critical load compared with the corresponding values of diamond-like carbon (a–C: H) films, due to the improvement of the toughness of the films by the incorporation of metals. Therefore, Me–C: H films show high promise of being wear-resistant protective coatings.
Hydrogen binding and diffusion in diamond
Authors: Mehandru S.P. , Anderson Alfred B. , Angus John C.
Published: September 2007

We have investigated the binding and diffusion pathways for atomic hydrogen in diamond using the semiempirical atom superposition and electron delocalization molecular orbital (ASED-MO) theory. The bond-centered site has been found to be more stable than the tetrahedral and hexagonal interstitial sites due to the formation of a low-lying band-gap orbital which takes the promoted electron. A second hydrogen binds even more stably to the nearby antibonding site with additional stabilization of the now doubly occupied band gap orbital. The bond-centered hydrogen is predicted to migrate along the high-density (110) planes in the diamond lattice with an activation barrier of 1.9 eV. A carbon atom vacancy is found to attract interstitial H which bind to dangling orbitals on the surrounding C atoms. These bond strengths decrease as up to a maximum of four H atoms enters the vacancy. A hydrogen atom in a vacancy is found to increase the activation energy for vacancy migration.
Epitaxial growth of C60 thin films on mica
Authors: Krakow W. , Rivera N.M. , Roy R.A. , Ruoff R.S. , Cuomo J.J.
Published: September 2007

Single crystal films of C60 of different thickness values have been deposited on mica substrates by resistance evaporation. Electron diffraction and high resolution microscopy have been used to assess the orientational ordering and the nature of the defects present in these face-centered cubic films which exhibit a 〈111〉 direction normal to the film surface.
Molecular beam epitaxy of dysprosium barium cuprous oxides using molecular oxygen
Authors: Hellman E.S. , Hartford E.H. , Fitzgerald E.A.
Published: September 2007

Epitaxy of cupric oxides, such as the high temperature superconductor YBa2Cu3O7, using “vacuum” techniques requires either activated forms of oxygen, such as atomic oxygen, oxygen plasma, or ozone, or a relatively high pressure of molecular oxygen. In contrast, cuprous oxides (those with formal valence of copper less than +2) can be grown epitaxially in molecular oxygen at pressures below 10−4 Torr. We have explored this regime of epitaxial growth because of the possibility of forming DyBa2Cu3O7 through low temperature ex situ oxidation of DyBa2Cu3O6. We find that the dominant phases growing epitaxially on MgO are CuDyO2, Cu2O, CuBa2O2, DyBa2Cu3O6, and the barium-rich perovskite solid solutions. Sticking coefficients of barium and dysprosium depend on substrate temperature and flux composition for substrate temperatures between 550° and 700 °C. We have obtained superconducting films by annealing Dy-rich, Cu-deficient films in oxygen at 400 °C. The nonstoichiometry (with respect to DyBa2Cu3O6) appears to stabilize “DyBa2Cu3O6,” at low oxygen pressures. We also discuss the use of copper in effusion cells.
Superconducting characteristics and the thermal stability of tungsten-based amorphous thin films
Authors: Kondo Seiichi
Published: September 2007

Superconducting characteristics and the thermal stability of sputtered, tungsten-based, amorphous thin films are investigated. Electronic properties and crystalline structures are analyzed as a function of the metalloid content in the films. It is well known that the superconducting Tc of a bulk crystalline tungsten is 0.01 K, which is one of the lowest transition temperatures among the superconducting metals. We have found that the W film containing 5 to 70 at. % metalloids exhibits a great enhancement in Tc. In the region of 15 to 35 at. % metalloids, the Tc shows the maximum of 5.0 K, and the transition from normal to superconducting state occurs very sharply. SEM observation together with x-ray diffraction analysis indicates that these films are amorphous in structure. The electrical resistivity is about 150 μΩ-cm, and shows little temperature dependence from Tc to 300 K. In addition, the W–Si amorphous superconductor is thermally very stable after annealing at 700 °C, but the W–Ge amorphous alloy crystallizes at 600 °C.