bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Attachment of Organic Functional Groups to Single-walled Carbon Nanotube Material
Authors: Chen Y. , Haddon R. C. , Fang S. , Rao A. M. , Eklund P. C. , Lee W. H. , Dickey E. C. , Grulke E. A. , Pendergrass J. C. , Chavan A. , Haley B. E. , Smalley R. E.
Published: March 2008

We have subjected single-walled carbon nanotube materials (SWNTM's) to a variety of organic functionalization reactions. These reactions include radioactive photolabeling studies using diradical and nitrene sources, and treatment with dichlorocarbene and Birch reduction conditions. All of the reactions provide evidence for chemical attachment to the SWNTM's, but because of the impure nature of the staring materials, we are unable to ascertain the site of reaction. In the case of dichlorocarbene we are able to show the presence of chlorine in the SWNT bundles, but as a result of the large amount of amorphous carbon that is attached to the tube walls, we cannot distinguish between attachment of dichlorocarbene to the walls of the SWNT's and reaction with the amorphous carbon.
Segregation of Vanadium at the WC/Co Interface in VC-doped WC-Co
Authors: Jaroenworaluck A. , Yamamoto T. , Ikuhara Y. , Sakuma T. , Taniuchi T. , Okada K. , Tanase T.
Published: March 2008

Morphology of carbide grain in WC–12 wt.% Co–0.5 wt.% VC was examined by HREM and EDS with a special interest in the segregation of V at the WC/Co interfaces. A small addition of VC in WC-Co is effective to suppress the grain growth of carbide grains. HREM observation revealed that the WC/Co interfaces are faceted and consist of mainly two kinds of habit planes, (1010) and (0001), respectively. EDS analyses clearly showed the segregation of doped V along the interfaces. In addition, the concentration of segregated V is higher at the (0001) type habit plane than (1010) one. The retardation of the grain growth of carbide grains in the VC-doped WC-Co is closely related to the formation of the faceted WC/Co interface.
Cathodoluminescence, Photoluminescence, and Optical Absorbance Spectroscopy of Aluminum Gallium Nitride (AlxGa1−xN) Films
Authors: Robins Lawrence H. , Lowney Jeremiah R. , Wickenden Dennis K.
Published: March 2008

Aluminum gallium nitride (AlxGa1−xN) films, grown by metalorganic chemical vapor deposition on sapphire, were characterized by low-temperature cathodoluminescence (CL) and photoluminescence (PL), and room-temperature optical absorbance. The aluminum fractions are estimated to range from x = 0 to x = 0.444. Most films were silicon-doped. The absorption spectra have a Urbach (exponential) form below the bandgap. The width of the Urbach edge, EU, increases with Al fraction, x, as EU = (0.045 +1 0.104x) eV. The luminescence (CL or PL) spectra show a relatively narrow band-edge peak and a broad deep-level peak. The full-widths at half-maximum of the band-edge CL peaks (measured at T = 15 K) are remarkably similar to the Urbach absorption widths, EU (measured at T = 300 K). PL spectra were obtained from the top surfaces and the film-substrate interfaces of several films. The interface PL spectra of some films show an extra peak 0.15 eV to 0.45 eV below the bandgap, which is ascribed to structural defects or impurity phases localized near the interface. The energy of the band-edge luminescence peak shifts with excitation mode (CL, top-surface PL, or interface PL). This effect is attributed to the variation of the excitation depth, between the top surface and film-substrate interface, with excitation mode, together with the depth variation of film properties such as residual stress or aluminum fraction.
The Effects of Chloromethane on Diamond Nucleation and Growth in a Hot-filament Chemical Vapor Deposition Reactor
Authors: Wu Jih-Jen , Hong Franklin Chau-Nan
Published: March 2008

The effects of chloromethane on diamond nucleation and growth were studied by employing laser reflective interferometry. Chloromethane enhances the film-growth rate only slightly compared to methane. However, chloromethane greatly enhances the nucleation density and shortens the film-forming stage, more significantly at a lower temperature. Thus, chloromethane facilitates the low temperature growth mainly through the enhancement of nucleation. Nucleation density is strongly dependent on the compositions of H atoms and carbon species prior to diamond growth. The residual diamond seeds by diamond-grit scratching are suggested to be the major nucleation sites. Chloromethane can enhance diamond nucleation by protecting the residual seeds from being etched by H atoms.
The Effect of Ternary Addition on Structure and Stability of NbCr2 Laves Phases
Authors: Takasugi T. , Yoshida M.
Published: March 2008

The alloying effect on microstructure and stability of the NbCr2 Laves phases is investigated using x-ray diffraction (XRD) and transmission electron microscopy (TEM). In as-cast condition, the binary alloy as well as the ternary alloy containing V consisted of the C15 phase while the ternary alloys containing Mo, Ti, and W consisted of both the C14 (or C36) and the C15 phases, accompanied by a number of stacking faults and microtwins in their constituent phases. By a prolonged heat treatment at 1673 K, the retained C14 (or C36) phase is completely transformed to the C15 phase. However, their kinetics is slower in the sequence of the ternary alloys containing Mo > Ti > W. The alloying effect on the stability of the C15 (or the C14) phase and the associated transformation process is discussed on the basis of phase stability and kinetics.
Disintegration and Powder Formation of Nb75M25 (M = Al, Si, Ga, Ge, and Sn) Due to Hydrogenation in an Arc-melting Chamber
Authors: Li Xingguo , Chiba Akihiko , Takahashi Seiki , Ohsaki Katsuhisa
Published: March 2008

Nb75M25 (M = Al, Si, Ga, Ge, and Sn) alloy ingots were prepared by the conventional arc-melting method and then were directly reacted with high purity hydrogen of 0.1 MPa in an arc-;melting chamber without exposing the ingots to air. As the clean surface of the arc-;melted ingots is preserved, the ingots rapidly absorb a large amount of hydrogen without any activation treatments and disintegrate violently into fine particles. The disintegration of ingots depends on the M element. The collected particles are investigated by x-ray diffraction, electron microscopy, chemical analysis, and thermal analysis. The particles are hydrides of Nb75M25 after hydrogenation and have a sharp-edged polygonal appearance. After dehydriding, fine Nb3M powders with A15 crystalline structure are obtained except for Nb75Si25. In comparison with the atomized Nb3M powders, the Nb3M powders prepared by the present study have a smaller average particle size and lower impurity contents.
Preparation of β–SiC Nanorods with and Without Amorphous SiO2 Wrapping Layers
Authors: Meng G. W. , Zhang L. D. , Mo C. M. , Zhang S. Y. , Qin Y. , Feng S. P. , Li H. J.
Published: March 2008

Preparation of β–SiC nanorods with and without amorphous SiO2 wrapping layers was achieved by carbothermal reduction of sol-gel derived silica xerogels containing carbon nanoparticles. The β–SiC nanorods with amorphous SiO2 wrapping layers were obtained by carboreduction at 1650 °C for 1.5 h, and at the end of 1.5 h the temperature was steeply raised to 1800 °C and held for 30 min; they are typically up to 20 µm in length. The diameters of the center thinner β–SiC nanorods within the amorphous SiO2 wrapping layers are in the range 10–30 nm, while the outer diameters of the corresponding amorphous SiO2 wrapping layers are between 20 and 70 nm. The β–SiC nanorods without amorphous SiO2 wrapping layers were produced by carbothermal reduction only at 1650 °C for 2.5 h, and their diameters are in agreement with those of the center thinner β–SiC nanorods wrapped in amorphous SiO2 layers. Large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are both favorable to the formation of much thinner β–SiC nanorods. The formation of the outer amorphous SiO2 wrapping layer is from the combination reaction of decomposed SiO vapor and O2.
Influence of Bi-site Substitution on the Ferroelectricity of the Aurivillius Compound Bi2SrNb2O9
Authors: Durán-Martín- P. , Castro A. , Millán P. , Jiménez B.
Published: March 2008

Ceramics based on the composition Bi2SrNb2O9 with isomorphic substitutions of cations in the Bi2O22+ and the perovskite layers, Bi2−xTexSr1−xNa(K)xNb2O9, have been prepared by solid state reaction. The ferroelectricity of this Aurivillius type structure has been studied. Dielectric measurements as a function of the temperature show a low temperature maximum in the dielectric constant that would correspond to a ferro-;paraelectric phase transition. The temperature of this maximum increases when the radius of the ion that substitutes Sr for decreases. A second maximum in the dielectric constant is found at higher temperature possibly corresponding to a relaxor ferroelectric. Measurements of remanent polarization as a function of the temperature seem to confirm the relaxor behavior, because the polarization disappears at temperatures between the two maxima of the dielectric constant. Saturated hysteresis loops are obtained for all the substituted samples at temperatures above 300 °C. Ferroelectric parameters such as the polarization, coercive field, and coupling factors of the BSN family compounds were obtained for the first time. The ac electric conductivity shows anomalies at temperatures close to those where the remanent polarization disappears. Activation energies calculated from measurements of dc electric conductivity, impedance arcs, and dielectric modulus data may be associated with thermally activated oxygen vacancies.
Diagnostics and Modeling of Nanopowder Synthesis in Low Pressure Flames
Authors: Glumac N. G. , Chen Y-J. , Skandan G.
Published: March 2008

Laser-induced fluorescence, thermophoretic sampling, laser light scattering, and emission spectroscopy have been used to probe low pressure hydrogen/oxygen flames in which 3–50 nm, loosely agglomerated oxide nanopowders have been synthesized at high production rates by the pyrolysis of precursor vapors, followed by condensation in the gas phase. These measurements have enabled the identification of pyrolysis, condensations, and particle growth regions in the flame. Flame simulations using a one-dimensional stagnation flow model, with complex chemistry, demonstrate that the chemical and thermal flame structure can be accurately predicted for flames without a precursor. Furthermore, some flame structure changes induced by the addition of a precursor can be simulated by addition of analogous species to the chemical mechanism.
Phase Formation and Thermodynamic Analysis of Self-propagating High-temperature Synthesis Al–Zr–N System Composites
Authors: Chen Kexin , Ge Changchun , Li Jiangtao
Published: March 2008

The self-propagating high temperature synthesis (SHS) of Al–Zr–N system composite ceramics was investigated in this paper. The melting point of Al was low (Tm = 660 °C), while that of Zr was high (Tm =1855 °C). Therefore, Al will melt and coalesce during reaction, which inhibit diffusion of nitrogen from outside the metal compact to interior due to collapse of the pore openings, while Zr will not melt under the combustion temperature which is lower than its melting point. It will not affect the permeation of nitrogen under the conditions. Accordingly, the ratio of Al and Zr in the initial mixed powders will affect the permeation of nitrogen from outside the sample to the interior, which results in different phase formation of the products. In this study, the relationship between the combustion parameters and the phase formation of the products will be experimentally determined through XRD analysis, and then thermodynamically analyzed.
Texture Evolution in Si/SiC Layered Structures Deposited on Si(001) by Chemical Vapor Deposition
Authors: Björketun L-O. , Hultman L. , Kordina O. , Sundgren J-E.
Published: March 2008

Texture evolution in Si/SiC multilayers deposited by atmospheric pressure chemical vapor deposition on carbonized Si(001) substrates was investigated using x-ray diffraction and transmission electron microscopy. SiC layers were epitaxial and (001)-oriented. Si layers deposited on the SiC exhibited a columnar structure with predominantly (110) orientation which could be related to the nucleation. Orientational relationships were Si[111] ║ SiC[110] and Si[112] ║ SiC[110]. Also, a low density of (112)-oriented columns was present. Extensive twinning on the vertical {111} planes within the Si columns led to domains of hexagonal stacking up to 10 nm in size with the presence of 2H-Si and 4H-Si. Subsequent SiC layer growth on the (110)-oriented Si layer resulted in a (110)-oriented SiC layer if the Si layer was carbonized prior to growth.
Investigation of CF3I as an Environmentally Benign Dielectric Etchant
Authors: Levy R. A. , Zaitsev V. B. , Aryusook K. , Ravindranath C. , Sigal V. , Misra A. , Kesari S. , Rufin D. , Sees J. , Hall L.
Published: March 2008

In this study, trifluoroiodomethane (CF3I), a non-global-warming gas, has been investigated as a substitute for typical PFC's currently used in wafer patterning and CVD chamber cleaning processes. Dielectric films consisting of plasma enhanced chemically vapor deposited silicon dioxide and silicon nitride were comparatively etched in CF3I and C2F6/O2 plasma environments. The etch rate of these films was ascertained as a function of applied rf power, etchant gas flow rate, reaction chamber pressure, and CF3I: O2 ratio. Destruction efficiencies of CF3I at different processing parameters were evaluated. Depending on the flow rate, rf power, and chamber pressure, utilization efficiency of CF3I varied from as low as 10% to as high as 68%. CF4, C2F6, COF2, and CO2 were the predominant by-products found in the exhaust stream; however, their concentrations were very low compared to the traditional process employing C2F6/O2 mixtures.
X-ray Absorption Fine Structure Study on Coordination State of Implanted Gold Ions in Silica Glass
Authors: Fukumi Kohei , Kageyama Hiroyuki , Kadono Kohei , Chayahara Akiyoshi , Kamijo Nagao , Makihara Masaki , Fujii Kanenaga , Hayakawa Junji , Satou Mamoru
Published: March 2008

Coordination state of gold atoms implanted in silica glass to an energy of 1.5 MeV and a dose of 1 × 1017 ions/cm2 has been studied by x-ray absorption fine structure spectroscopy. It was found that most of the gold atoms form gold clusters in which the nearest neighboring Au–Au interatomic distance is shorter by 0.05 °A than that in bulk gold. The contraction of Au–Au interatomic distance of gold clusters in silica glass is less than that reported in the previous studies on gold clusters within the other substrates. Gold atoms are coordinated by about four gold atoms in average. In addition, it was found that Au–O bonds are formed at the gold clusters/silica glass interface. It was deduced that the formation of Au–O bond at the gold clusters/silica glass interface depresses the contraction of Au–Au interatomic distance.
Indentation plastic displacement field: Part II. The case of hard films on soft substrates
Authors: Tsui T. Y. , Vlassak Joost , Nix William D.
Published: March 2008

The plastic displacements around Knoop indentations made in hard titanium/aluminum multilayered films on soft aluminum alloy substrates have been studied. Indentations were cross-sectioned and imaged using focused-ion-beam (FIB) milling and high-resolution scanning electron microscopy (SEM), respectively. The FIB milling method has the advantage of removing material in a localized region without producing mechanical damage to the specimen. The micrographs of the cross-sectioned indentations indicate that most of the plastic deformation around the indentation is dominated by the soft aluminum substrate. There is a very small change in the multilayered film thickness around the indentation—less than 10%. The plastic deformation of the thin film resembles a membrane being deflected by a localized pressure gradient across the membrane. Stress-induced voids are also observed in the multilayered film, especially in the area around the indentation apex. The density and the size of the voids increase with indentation depth. Indentation sink-in effects are observed in all of the indentations inspected. Based on the experimental results, the amount of sink-in of the hard film–soft substrate composite is larger than the bulk substrate and film alone. This is confirmed by the finite element analyses conducted in this work.
Nanoindentation of a 10 nm thick thin film
Authors: Sawa Takeshi , Akiyama Yasushi , Shimamoto Atsushi , Tanaka Kohichi
Published: March 2008

In a nanometer order nanoindentation test, roundness or truncation of the indenter tip cannot be avoided. In this paper, we have analyzed the indentation problem of a rounded triangular indentation into a layered elastic half-space by a finite element analysis and then established a method to estimate the intrinsic elastic modulus of the film from the nanoindentation data. The method was applied to analyze the nanoindentation data of a less-than-10 nm penetration depth on a 10 nm thick diamondlike carbon film deposited on a 50 nm thick magnetic layer.
Accurate determination of the mechanical properties of thin aluminum films deposited on sapphire flats using nanoindentations
Authors: Lim Y. Y. , Chaudhri M. M. , Enomoto Y.
Published: March 2008

Nanoindentations using a Berkovich diamond indenter have been made on 1, 2, and 5 μm thick 99.99% purity polycrystalline aluminum films thermally evaporated in vacuum on to 2 mm thick R-cut polished sapphire flats. The projected contact areas of the residual indentations were estimated from the unloading load-displacement curves, and some of the indentations were imaged with an atomic force microscope (AFM). It was found that a large majority of indents showed material pileup, and the projected areas of these indents, as measured with the AFM, were up to 50% greater than those calculated from the unloading curves. This discrepancy between the calculated and directly measured indentation areas has a strong influence on the derived values of Young's modulus and hardness of the aluminum films. Using a new analytical model, Young's modulus of the aluminum films has been determined to be in the range of 50–70 GPa, independent of the relative indentation depth. The composite nanohardness of the 1 and 2 μm thick films was found to have a load-independent value of 1 GPa, whereas the composite nanohardness of the 5 μm film decreased from 1 to 0.7 Gpa with increasing indenter penetration. Finally, it has been suggested that in order to improve the accuracy with which the mechanical properties of thin films or bulk specimens can be determined by nanoindentation techniques, the projected contact areas should be measured by direct methods, such as atomic force microscopy.
Ultra-micro-indentation of silicon and compound semiconductors with spherical indenters
Authors: Williams J. S. , Chen Y. , Wong-Leung J. , Kerr A. , Swain M. V.
Published: March 2008

Details of microindentation of silicon, such as the semiconductor-to-metal transformation, which takes place on loading, have been examined using spherical indenters. Various forms of silicon are studied, including heavily boron-doped wafers and silicon damaged and amorphized by ion implantation as well as material containing dislocations. Results indicate that only silicon, which contains high concentrations of point defects or is amorphous, exhibits mechanical properties that differ significantly from undoped, defect-free crystal. Amorphous silicon exhibits plastic flow under low indentation pressures and does not appear to undergo phase transformation on loading and unloading. Indentation of compound semiconductors is also studied and the load/unload behavior at room temperature is quite different from that of silicon. Both gallium arsenide and indium phosphide, for example, undergo slip-induced plasticity above a critical load.
The effect of target crystallography on the growth of Pb(Mg1/3Nb2/3)O3 thin films using pulsed laser deposition
Authors: Corbett M. H. , Catalan G. , Bowman R. M. , Gregg J. M.
Published: March 2008

Pulsed laser deposition has been used to make two sets of lead magnesium niobate thin films grown on single-crystal h100j MgO substrates. One set was fabricated using a perovskite-rich target while the other used a pyrochlore-rich target. It was found that the growth conditions required to produce almost 100% perovskite Pb(Mg1/3Nb2/3)O3 (PMN) films were largely independent of target crystallography. Films were characterized crystallographically using x-ray diffraction and plan view transmission electron microscopy, chemically using energy dispersive x-ray analysis, and electrically by fabricating a planar thin film capacitor structure and monitoring capacitance as a function of temperature. All characterization techniques indicated that perovskite PMN thin films had been successfully fabricated.
Evidence for continuous areas of crystalline β–C3N4 in sputter-deposited thin films
Authors: Chowdhury A. K. M. S. , Cameron D. C. , Hashmi M. S. J. , Gregg J. M.
Published: March 2008

Carbon nitride films have been deposited using Penning-type opposed target dc reactive sputtering. These films show large (>10 μm2) continuous areas of nanocrystalline material in an amorphous matrix. Electron diffraction shows the nanocrystalline areas to have crystallography consistent with the β–C3N4 phase. Film chemistry analysis using Rutherford backscattering and Raman spectroscopy indicates that only carbon, nitrogen, and trace levels of hydrogen are present. Given this film chemistry and the fit of diffraction data to that predicted for the β–C3N4 structure, it seems likely that the sputtering parameters used have, indeed, produced continuous regions of the elusive β–C3N4 phase.
Lower crystallization temperature of sol-gel PbTiO3 on Ti/Pt-coated substrates
Authors: Avila R. E. , Velilla T. P. , Retuert P. J.
Published: March 2008

PbTiO3 (PT) thin films have been deposited by sol-gel on Pt/Si, SiO2/Si, Pt/Ti/SiO2/Si, and Ti/Pt/Ti/SiO2/Si and annealed for 45 min in the 400–670 °C range. Analysis by x-ray diffraction (XRD) and spectroscopic ellipsometry shows that the Ti overlayer promotes early crystallization in the tetragonal perovskite phase, reducing the presence of a second phase, tentatively identified as pyrochlore, starting by 450 %C. The refractive index and extinction coefficient (n, k) of the PT film increase rapidly with the sintering temperature in the range of 450–570 °C and saturate by 570 °C to values of n varying from 2.4 to 2.9, and k from 0.03 to 0.3, over the 1.65–2.95 eV range. Most of the increase of n is related to thin film densification.
A new method to study cyclic deformation of thin films in tension and compression
Authors: Hommel M. , Kraft O. , Arzt E.
Published: March 2008

In this paper, a new method to study cyclic plastic deformation in thin metal films is presented. Cu films were deposited onto compliant substrates allowing the film to be subjected to tensile and compressive stresses on loading and unloading of the film/substrate composite. The film stress was measured in situ by x-ray diffraction. First results lend to characteristic stress-strain hysteresis curves, indicative of fatigue processes in small dimensions.
Effect of surface kinetics on the step coverage during chemical vapor deposition
Authors: Hwang Gyeong Soon , Moon Sang Heup , Nam Suk Woo , Shin Chee Burm
Published: March 2008

Profile evolution simulations during chemical vapor deposition based on a 2D continuum model reveal that the type of surface kinetics plays an important role in determining step coverage of films deposited in high aspect ratio trenches and vias. Linear surface kinetics, resulting from an adsorption rate limited process, is found to cause difficulty in bringing about conformal step coverage in deep narrow trenches without reducing the growth rate considerably. Under such condition, void-free filling cannot be achieved while maintaining a growth rate acceptable to integrated circuit (IC) manufacturing. The numerical study also suggests that the high tendency of the precursor for chemical equilibrium on a surface, resulting in nonlinear kinetics by a surface reaction limited process, is crucial to achieve a uniform step coverage as typically observed in SiO2 deposition from tetraethylorthosilicate (TEOS).
Microstructure and 1000–1400 K mechanical properties of cryomilled NiAl–0.7Zr
Authors: Whittenberger J. D. , Garg A. , Hebsur Mohan G.
Published: March 2008

An attempt has been made to improve the intermediate temperature strength of cryomilled NiAl by utilizing third element solid solution or precipitation strengthening mechanisms. To this end an NiAl–0.7 (at.%) Zr alloy was cryomilled, densified by hot extrusion, and tested between 1000 and 1400 K. Although over 3 wt% nitrogen was introduced via cryomilling, mechanical testing revealed that the cryomilled NiAl–0.7Zr was significantly weaker than the base alloy between 1000 and 1200 K. Chemical and microstructural analyses revealed that, in addition to ∼ 16 vol% AlN, all the Zr had been converted into ZrN. A thermodynamic analysis of cryomilling indicated that the formation of ZrN could have been anticipated since it is a more stable nitride than AlN. While Zr was an unsatisfactory addition in NiAl, thermodynamics also suggest several alloying elements that might lead to good intermediate temperature strength after cryomilling.
Possible evidence for the stabilization of β–carbon nitride by high-energy ball milling
Authors: Fahmy Y. , Shen T. D. , Tucker D. A. , Spontak R. L. , Koch C. C.
Published: March 2008

The possibility of stabilizing the theoretically predicted β–C3N4phase by high-energy ball milling is investigated. Charges of graphitic carbon were milled with and without minor alloying additions under different atmospheric media, namely gas and/or liquid phases of nitrogen, air, or ammonia. Milling was performed at either of two energy levels for periods of up to 48 h. The β–C3N4phase was found to exist as small crystallites in a matrix of primarily amorphous carbon at volume fractions estimated between 5 and 10 at.%. High-resolution electron diffraction and x-ray diffraction indicate that the crystalline nature of the C3N4phase corresponds with a hexagonal lattice witha= 6.46 Å andc/a= 0.374, which are within 2% of the theoretically calculated lattice parameter values. Analysis of electron energy-loss spectroscopy (EELS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectra verify the presence of chemically bonded carbon and nitrogen with chemical states reflecting combinedsp2andsp3hybridization. Chemical analysis confirms nitrogen enrichment at levels consistent with the C3N4stoichiometry and the estimated degree of stabilization. The possible mechanism(s) responsible for the stabilization of the β–C3N4phase are briefly discussed.
Mechanism of in-plane texture development by ion-beam-assisted deposition
Authors: Ji H. , Was G. S.
Published: March 2008

The objective of this work was to determine the mechanism of in-plane texture development in films made by ion-beam-assisted deposition (IBAD). Both in-plane texture and surface roughness were studied as functions of film thickness. A phenomenological growth model based on the preferential growth of aligned grains due to channeling was proposed, linking the surface roughness evolution and texture development. Good correlation was found between the measured roughness and the model prediction, as well as between the roughness evolution and the in-plane texture development. A critical thickness was introduced at which in-plane texture is completed. Both surface roughness and texture results gave a critical film thickness of 114–250 nm for an ion energy of 1000 eV and anRratio of 0.4. This range of critical film thickness was far beyond the nucleation stage, providing evidence that the development of in-plane texture in IBAD Nb films was growth-controlled.
Grain boundary grooving by surface diffusion in SrTiO3 bicrystal
Authors: Jin Minxian , Shimada Eriko , Ikuma Yasuro
Published: March 2008

High-purity SrTiO3 bicrystal sample (the angle between two [001] directions is 24°) was used in the present experiment to develop a thermal grain boundary groove along the bicrystal grain boundary at different temperatures (1150–1400 °C) and times (15–6720 min) in air. An atomic force microscope (AFM) was used to observe the surface morphological change in the annealed bicrystal sample in order to measure the width W and depth h of the developed grain boundary groove. It was found that the log W–log t (at 1150–1400 °C) and the log h°log t (at 1400 °C) relationships are approximately linear, having slopes of approximately 1/4. Using Mullins' formulas, the surface diffusion coefficients of SrTiO3 at different temperatures were calculated. Finally, the surface diffusion coefficient determined in the present experiment appears to correspond to the titanium atom, which has the lowest diffusivity in SrTiO3.
Formation and phase transition of VO2 precipitates embedded in sapphire
Authors: Gea Laurence A. , Budai J. D. , Boatner L. A.
Published: March 2008

Crystallographically coherent precipitates of vanadium dioxide (VO2) have been formed in the near-surface region of single crystals of sapphire (Al2O3) using a combination of ion implantation and thermal treatments. As in the case of either bulk VO2 single crystals or thin films of VO2, the thermally induced semiconductor-to-metal phase transition of the embedded VO2 precipitates is accompanied by a large hysteretic change in the infrared optical transmission. The VO2 precipitate transition temperature (Tc = 72 to 85 °C) is higher than that of bulk VO2 (Tc = 68 °C) and is sensitive to the implantation conditions. The present results show that the damage resulting from the coimplantation of vanadium and oxygen into an Al2O3 host lattice dictates the final microstructure of the VO2 precipitates and, consequently, affects the transition temperature, as well as the optical quality of the VO2/Al2O3 surface-nanocomposite precipitate system.
Oxygen and phosphorus coordination around iron in crystalline ferric ferrous pyrophosphate and iron-phosphate glasses with UO2 or Na2O
Authors: Booth C. H. , Allen P. G. , Bucher J. J. , Edelstein N. M. , Shuh D. K. , Marasinghe G. K. , Karabulut M. , Ray C. S. , Day D. E.
Published: March 2008

Fe K-edge x-ray absorption fine-structure (XAFS) measurements were performed on glass samples of (Fe3O4)0.3(P2O5)0.7 with various amounts of Na2O or UO2. Near-edge and extended XAFS regions are studied and comparisons are made to several reference compounds. We find that iron in the base glass is ∼25% divalent and that the Fe2+ coordination is predominantly octahedral, while Fe3+ sites are roughly split between tetrahedral and octahedral coordinations. Also, we measure roughly one Fe–O–P link per iron. Substitution of Na2O or UO2 up to 15 mol% primarily affects the first Fe–O shell. The results are compared to data from the related material Fe3(P2O7)2.
New insights on the crystalline forms in binary systems of n-alkanes: Characterization of the solid ordered phases in the phase diagram tricosane + pentacosane
Authors: Rajabalee F. , Métivaud V. , Mondieig D. , Haget Y. , Cuevas-Diarte M. A.
Published: March 2008

X-ray diffraction analyses of the pure components n-tricosane and n-pentacosane and of their binary mixed samples have enabled us to characterize the crystalline phases observed at “low temperature.” Contrary to what was announced in literature on the structural behavior of mixed samples in odd-odd binary systems with Δn = 2, the three domains are not all orthorhombic. This work has enabled us to show that two of the domains are, in fact, monoclinic (Aa, Z = 4), and the other one is orthorhombic (Pca21, Z = 4). The conclusions drawn in this work can easily be transposed to other binary systems of n-alkanes.
Optical and electrical properties of Ge10+xSe40Te50−x thin film
Authors: Fayek S. A. , El-Ocker M. , Hassanien A. S.
Published: March 2008

Thin films with thickness 100 nm of Ge10+xSe40Te50−x (x ranging from 0.0 to 16.65 at.%) were formed by vacuum deposition at 1.33 × 10−4 Pa. The change in electrical resistivity of the films has been measured using the coplanar method. The measurements have been carried out in a temperature range between 400 and 142 K. The values of the electrical activation energies lie in the range of 0.18–0.38 eV. The optical absorption behavior of these ternary thin films was studied from the reflection and transmission. The optical band gap was found to be in the range of 0.90–1.11 eV and arose from indirect transitions. On the other hand, the width of the band tail Ee was found in the range 0.19–0.32 eV and exhibits opposite behavior. This behavior is believed to be associated with a defected bond of Te–Te and a cohesive energy (CE).
Electronic paramagnetic resonance study of Cu2+ ions in copper ion-exchanged layers of lithium niobate crystals
Authors: Caccavale F. , Sada C. , Segato F. , Bogomolova L. D. , Jachkin V. A. , Krasil'nikova N. A.
Published: March 2008

Copper-doped LiNbO3 layers prepared by an Cu–Li ion-exchange process are characterized by electronic paramagnetic resonance. It is found that the majority of Cu2+ ions are coupled by strong exchange interactions which is characteristic of short distances between paramagnetic ions. Such ions are accumulated in a thin layer near the crystal surface and can enter in new crystalline phases formed as a result of the Cu–Li ion exchange. A small amount of Cu2+ ions is incorporated into weakly distorted LiNbO3 crystal lattice inside the diffusion layer.
Production and characterization of titanium and iron oxide nano-sized thin films
Authors: Comini E. , Sberveglieri G. , Ferroni M. , Guidi V. , Frigeri C. , Boscarino D.
Published: March 2008

We present a simple and reproducible method to obtain TiO2and Fe2O3mixed-oxide thin films by reactive radio-frequency sputtering. The influence of iron concentration on the structural properties of the layers has been studied. Structural characterization, carried out by electron microscopy analysis, allowed one to correlate the inhibition of the grain growth of titania to the presence of iron oxide and to its segregation at grain boundaries. This behavior should be ascribed to a superficial-tension phenomenon. As a possible application of these thin films, we have investigated the gas-sensing properties toward CO, with particular focus on the role of Fe. The layers were capable to sense CO down to the level requested for environmental monitoring.
Interfacial embrittlement by bismuth segregation in copper/tin–bismuth Pb-free solder interconnect
Authors: Liu P. L. , Shang J. K.
Published: March 2008

Microchemistry and mechanical properties of a copper/tin–bismuth Pb-free solder interconnect were examined in the as-reflowed and aged conditions by in situ Auger fracture and interface fracture mechanics techniques. In the as-reflowed condition, the solder–copper interface was highly resistant to fracture, and the fracture mechanism was ductile with the crack path following the interface between the solder alloy and the copper–tin intermetallic phase. Upon thermal aging, bismuth segregation was found to occur on the copper–intermetallic interface. Auger depth profiling indicated that the segregation was confined to about one monolayer from the interface. The segregation was shown to embrittle the interface, resulting in an approximately 5-fold decrease in the interfacial fracture resistance.
Metal–oxide films with magnetically-modulated nanoporous architectures
Authors: Grimes Craig A. , Singh R. Suresh , Dickey Elizabeth C. , Varghese Oomman K.
Published: March 2008

A magnetically-driven method for controlling nanodimensional porosity in sol-gel-derived metal–oxide films, including TiO2, Al2O3, and SnO2, coated onto ferromagnetic amorphous substrates, such as the magnetically-soft Metglas1 alloys, is described. On the basis of the porous structures observed dependence on external magnetic field, a model is suggested to explain the phenomena. Under well-defined conditions it appears that the sol particles coming out of solution, and undergoing Brownian motion, follow the magnetic field lines oriented perpendicularly to the substrate surface associated with the magnetic domain walls of the substrate; hence the porosity developed during solvent evaporation correlates with the magnetic domain size.
Structures and microwave dielectric properties of Ba6−3x(Nd,Biy)8+2xTi18O54 (x = 2/3) solid solution
Authors: Wu Yong Jun , Chen Xiang Ming
Published: March 2008

The effects of Bi substitution for Nd in Ba6−3xNd8+2xTi18O54 (x = 2/3) solid solution upon the microstructures and microwave dielectric properties were investigated. The solid solubility limit of Bi in Ba6−3xNd8+2xTi18O54 (x = 2/3) solid solution was about 15 mol%, the same as that for x = 0.5, and densification of the present solid solutions could be performed well at lower temperatures. However, the variation tendency of microwave dielectric properties with composition in the present ceramics quite differed from that for x = 0.5: (1) The temperature coefficient of resonant frequency in the present ceramics showed a continuous variation from positive to negative and did not indicate extreme value at the solid solubility limit. (2) Near-zero temperature coefficient of resonant frequency combined with high-ε and high-Qf values could be obtained in the present ceramics, while that for x = 0.5 had a lower limit of +15 ppm/°C. (3) The dielectric constant also showed a continuous increase for the present compositions, while that in x = 0.5 had an extreme at solid solubility limit. Ceramics with composition of Ba6−3x(Nd0.85,Bi0.15)8+2xTi18O54 (x = 2/3) showed excellent dielectric properties of ε = 99.1, Qf = 5290 GHz, and τf = −5.5 ppm/°C.
Epitaxial growth of PbZr0.5Ti0.5O3 thin films on SrRuO3/SrTiO3 substrates using chemical solution deposition: Microstructural and ferroelectric properties
Authors: Kim J. H. , Kim Youngman , Chien A. T. , Lange F. F.
Published: March 2008

Epitaxial PbZr0.5Ti0.5O3 (PZT) thin films were grown on top of a SrRuO3 epitaxial electrode layer on a (100) SrTiO3 substrate by the chemical solution deposition method at various temperatures. The microstructure of the PZT thin films was investigated by x-ray diffraction and transmission electron microscopy, and the ferroelectric properties were measured using the Ag/PZT/SRO capacitor structure. In the PZT thin film annealed at low temperature (450 °C/1h), both the perovskite PZT phase at the film/substrate interface and the fluorite PZT phase in the upper region of the film were obtained. It exhibited nonferroelectric properties. The PZT thin film annealed at temperature as low as 525 °C had only a perovskite tetragonal phase and the epitaxial orientational relationship of (001)[010]PZT∥(001)[010]SRO∥(001)[010]STOwith the substrate, and shows a ferroelectric property. The remnant (Pr) and saturation polarization (Ps) density of the sample annealed at 600 °C/1h were measured to be Pr ˜ 51.4 μC/cm2 and Ps ˜ 62.1 μC/cm2 at 5 V, respectively. The net switched polarization dropped only to 98% of its initial value after 7 × 108 fatigue cycles.
Molecular dynamics analysis of adhesion strength of interfaces between thin films
Authors: Iwasaki T. , Miura H.
Published: March 2008

We have developed a molecular-dynamics technique for determining the adhesion strength of the interfaces between different materials. This technique evaluates the adhesion strength by calculating the adhesive fracture energy defined as the difference between the total potential energy of the material-connected state and that of the material-separated state. The extended Tersoff-type potential is applied to calculate the adhesive fracture energy of metal/dielectric interfaces as well as metal/metal interfaces. We used the technique to determine the adhesion strength of the interfaces between ULSI-interconnect materials (Al and Cu) and diffusion-barrier materials (TiN and W). It was also applied to determine the adhesion strength of interfaces between the interconnect materials and a dielectric material (SiO2). Because the adhesion strength determined by this technique agrees well with that measured by scratch testing, this technique is considered to be effective for determining the adhesion strength.
Crystallization kinetics of yttrium aluminum garnet (Y3Al5O12)
Authors: Johnson Bradley R. , Kriven Waltraud M.
Published: March 2008

The kinetics and pathways for crystallization of solid, amorphous, yttrium aluminum garnet (YAG) were studied using isothermal differential thermal analysis, x-ray diffraction, and transmission electron microscopy. The activation energy for crystallization was 437 KJ/mol and the measured Avrami exponent was 2.74, which corresponded to three-dimensional crystal growth with a constant number of nuclei. Time–temperature–transformation (T–T–T) curves were developed from the data to predict crystallization rates as a function of temperature. The crystallization pathway for YAG in this system is compared to others reported in the literature.
L12- and L10-like cation-ordered structures in ZrO2–Y2O3 ceramics
Authors: Rao J. C. , Zhou Y. , Li D. X.
Published: March 2008

Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases, with L12- and L10- like cation-ordered structures, respectively, have been found in ZrO2–Y2O3 ceramics in both the sintered and annealed states. High-resolution electron microscopy, energy-dispersive x-ray spectroscopy and computer simulation have been used to reveal the presence of the phases. The formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases was initiated during the sintering procedure and developed with the increase in annealing temperature and time. Segregation of yttrium, which was prevalent in different regions even within one grain, induced the formation of Y0.25Zr0.75O2−x and Y0.5Zr0.5O2−y phases.
Packing and solidification in ceramic injection moulding
Authors: Krug S. , Evans J. R. G. , Maat J. H. H. ter
Published: March 2008

The occupation of volume in large ceramic injection mouldings solidified under different pressures using two moulding techniques is considered. Large (60 × 45 × 25 mm) alumina injection mouldings were prepared in cavities fitted with conventional (metallic) and insulated [poly(ether ether ketone)] sprues. These provide quite distinct solidification histories which, in turn, influence the physical properties of the moulding and the extent and type of defects it contains. In the former case, the gate solidified after 26 s whereas, in the latter, the hold pressure could be applied for over 240 s. In insulated sprue moulding, the advance of the solid liquid boundary during packing and solidification was traced by fractography. Pressure was varied from 5 to 120 MPa. The interdependencies of moulding mass, apparent density, local density, polymer crystallinity, and microstructure were accounted for as a function of pressure and pressure transmission method. Changes in polymer crystallinity due to different cooling rates at different positions in the mouldings were insufficient to account for observed density differences. Systematic changes in the mass as a function of hold pressure were related to macroporosity in conventional mouldings and to microporosity in insulated sprue mouldings.
Evaluation of Recovery Goals for Endangered White Sturgeon in the Kootenai River, Idaho
Authors: Paragamian Vaughn L. , Hansen Michael J.
Published: March 2008

Our objective was to evaluate recovery goals for endangered white sturgeon Acipencer transmontanus in the Kootenai River, Idaho. We used demographic statistics for white sturgeon in the Kootenai River in a stochastic density-dependent population model to estimate recruitment rates needed for population recovery. We simulated future abundance of white sturgeon in the Kootenai River over a 25-year period and a range of hypothetical recruitment rates to estimate the level of recruitment that would lead to population recovery (7,000 fish, the number present before the population suffered recruitment failure). We compared simulations of future abundance at enhanced levels of recruitment with those based on the present status of the population and with the recruitment criterion in the Kootenai River White Sturgeon Recovery Plan. We found that the population would decline to only 57 individuals after 25 years and only 6 individuals after 50 years if recruitment failure continued. The population would reach the target carrying capacity of 7,000 individuals within 25 years only when each adult produced 0.4 age-1 recruits, a recruitment rate equivalent to reaching the target level of recruitment in the recovery plan every year. In contrast, the population would grow to only 1,200 individuals if the target level of recruitment in the recovery plan was produced in only 3 of every 10 years, as specified in the recovery plan. We suggest that recovery goals for white sturgeon in the Kootenai River can be modified as follows: (1) a population goal of 7,000 subadults and adults; (2) population recovery within 25 years; and (3) a minimum recruitment rate of at least 20 age-1 juveniles detected from each year-class in each of 10 years by use of a standardized monitoring protocol.
Measuring the Performance of Two Stationary Interrogation Systems for Detecting Downstream and Upstream Movement of PIT-Tagged Salmonids
Authors: Connolly Patrick J. , Jezorek Ian G. , Martens Kyle D. , Prentice Earl F.
Published: March 2008

We tested the performance of two stationary interrogation systems designed for detecting the movement of fish with passive integrated transponder (PIT) tags. These systems allowed us to determine the direction of fish movement with high detection efficiency and high precision in a dynamic stream environment. We describe an indirect method for deriving an estimate for detection efficiency and the associated variance that does not rely on a known number of fish passing the system. By using six antennas arranged in a longitudinal series of three arrays, we attained detection efficiencies for downstream- and upstream-moving fish exceeding 96% during high-flow periods and approached 100% during low-flow periods for the two interrogation systems we tested. Because these systems did not rely on structural components, such as bridges or culverts, they were readily adaptable to remote, natural stream sites. Because of built-in redundancy, these systems were able to perform even with a loss of one or more antennas owing to dislodgement or electrical failure. However, the reduction in redundancy resulted in decreased efficiency and precision and the potential loss of ability to determine the direction of fish movement. What we learned about these systems should be applicable to a wide variety of other antenna configurations and to other types of PIT tags and transceivers.