bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of (111)-oriented Pb(Zr,Ti)O3 layers on nanocrystalline RuO2 electrodes using the sol-gel technique
Authors: Norga G. J. , Jin S. , Fè Laura , Wouters D. J. , Bender H. , Maes H. E.
Published: March 2008

The influence of the RuO2 bottom electrode microstructure on the texture and ferroelectric properties of sol-gel PZT in RuO2/PZT/RuO2/Pt capacitors is discussed. For high growth temperatures, RuO2 has a columnar microstructure and a mixed (100)/(110) texture, attributed to epitaxial growth on Pt(111) and TiO2 (110) grains of the preannealed Pt / Ti layer. The mixed orientation of RuO2 resulted in a mixed PZT texture and slanted ferroelectric hysteresis characteristic. As the RuO2 growth temperature was reduced, the microstructure of the RuO2 layer turned to fine-grained equiaxed, with a grain size of approximately 10 nm, and PZT developed a sharp (111) texture (I111/I100 > 100) resulting in a rectangular hysteresis characteristic and a remanent polarization >30 μC/cm2. The emergence of a strong (111) fiber texture in PZT on fine-grained RuO2 shed new light on the orientation selection mechanisms in sol-gel-prepared PZT layers. Possible applications of this phenomenon for high-density ferroelectric memories with a stacked layout are briefly discussed.
Transient creep in fine-grained polycrystalline Al2O3 with Lu3+ ion segregation at the grain boundaries
Authors: Yoshida Hidehiro , Ikuhara Yuichi , Sakuma Taketo
Published: March 2008

The creep deformation in fine-grained polycrystalline Al2O3 is highly suppressed by the addition of 0.1 mol% LuO1.5. The transient creep behavior in Lu-doped Al2O3 was examined at the testing temperature of 1250–1350 °C, and the data were analyzed in terms of the effect of stress and temperature on the extent of transient time and strain. The experimental data on the transient creep in Lu-doped Al2O3 showed good agreement with the prediction from a time function of the transient and the steady-state creep associated with grain boundary sliding as well as an undoped one. The difference in the transient creep between Lu-doped and undoped Al2O3 can also be explained by the retardation of grain boundary diffusion due to the Lu3+ ions segregation in the grain boundaries.
Synthesis of α–SiO2 nanowires using Au nanoparticle catalysts on a silicon substrate
Authors: Liu Z. Q. , Xie S. S. , Sun L. F. , Tang D. S. , Zhou W. Y. , Wang C. Y. , Liu W. , Li Y. B. , Zou X. P. , Wang G.
Published: March 2008

Large-scale SiO2 nanowires were synthesized by using a simple but an effective approach at low temperature. Scanning electron microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy were employed to characterize the samples. The results indicated that SiO2 nanowires with a uniform diameter of about 20 nm and a length up to 10 μm have been synthesized. Photoluminescence measurement showed that the SiO2 nanowires emitted blue light at 2.8 and 3.0 eV. The possible growth process of the SiO2 nanowires is discussed. Using this method, large panels of SiO2 nanowires can be made under conditions that are suitable for device fabrication.
Electron backscatter diffraction analysis of Pb(Mg1/3Nb2/3)O3–35mol%PbTiO3 single crystals grown by seeded polycrystal conversion
Authors: Khan Ajmal , Carpenter Derrick T. , Scotch Adam M. , Chan Helen M. , Harmer Martin P.
Published: March 2008

Electron backscatter diffraction (EBSD) has been applied to characterize Pb(Mg1/3Nb2/3)O3–35 mol%PbTiO3 single crystals grown by the seeded polycrystal conversion method. Macroscopically triangular crystal growth fronts were shown to each be associated with discrete crystals that originated from slightly misoriented segments of an initially cracked single-crystal seed plate. Various types of crystal imperfections, including voids, second-phase regions, and polycrystalline matrix grains trapped within the grown region, were readily identified and distinguished from one another using EBSD. Further, it was shown that trapped matrix grains in the grown region had consistently small misorientations with respect to the grown single crystal and this may be qualitatively explained by a simple boundary energetics argument. The significance of the trapped grains is discussed.
Precipitation of multilayered core–shell TiO2composite nanoparticles onto polymer layers
Authors: Wang Mingtai , Zhang Lide
Published: March 2008

A composite film of titanium dioxide (TiO2) nanoparticles and hydrolyzed styrene–maleic anhydride alternating copolymer (HSMA) was obtained on a substrate when a TiCl4solution was heated at 80 °C with a spin-cast thin HSMA film present in the solution. The composite film was characterized with x-ray photoelectron spectroscopy and transmission electron microscopy. Results revealed that TiO2nanoparticles discretely dispersed on the polymer layer, and they were dominantly rutile phase, of a spherical shape and 18–20 nm in diameter. In contrast, mainly amorphous TiO2powders were obtained from the identical TiCl4solution by drying the solution with the absence of the HSMA film. The TiO2nanoparticles deposited on the polymer layer were regarded to contain polymer chains, and a multilayered core–shell model was suggested for the formation of these composite nanoparticles. It is regarded that the core of a composite particle consisted of an anatase-phase TiO2colloidal nanoparticle, while the shell layer was made of rutile-phase TiO2/polymer multilayers; the composite particles formed by a layer-by-layer self-assembly of TiO2and polymer layers analogous to biomineralization, where the polymer promoted the crystallization of rutile-phase TiO2when TiO2deposited from solution.
Machinable calcium pyrophosphate glass-ceramics
Authors: Kasuga Toshihiro , Terada Miwako , Nogami Masayuki , Niinomi Mitsuo
Published: March 2008

Glass-ceramics containing a large amount of calcium pyrophosphate (β–Ca2P2O7) crystal were prepared via crystallization and sintering; compacts of a calcium phosphate glass powders with a composition of 60CaO · 30P2O5 · 5TiO2 · 5Na2O (in mol%) were heated for 3–6 h at 850 °C in air. The compacts were densified by the viscous flow of the glassy phases during heating. The calcium phosphate glass-ceramics were found to show a bending strength of approximately 100 MPa, and they were easy to machine, as confirmed by a drilling test using a conventional carbide tool. The machinability is thought to arise from the microstructure consisting predominantly of the interlocking and platelike β–Ca2P2O7 precipitated in the glass.
Effects of Ce filling fraction and Fe content on the thermoelectric properties of Co-rich CeyFexCo4−xSb12
Authors: Tang Xinfeng , Chen Lidong , Goto Takashi , Hirai Toshio
Published: March 2008

Single-phase filled skutterudite compounds, CeyFexCo4−xSb12 (x = 0 to 3.0, y = 0 to 0.74), were synthesized by a melting method. The effects of Fe content and Ce filling fraction on the thermoelectric properties of CeyFexCo4−xSb12 were investigated. The lattice thermal conductivity of Ce-saturated CeyFexCo4−xSb12, y being at the maximum corresponding to x, decreased with increasing Fe content (x) and reached its minimum at about x = 1.5. When x was 1.5, lattice thermal conductivity decreased with increasing Ce filling fraction till y = 0.3 and then began to increase after reaching the minimum at y = 0.3. Hole concentration and electrical conductivity of Cey Fe1.5Co2.5Sb12 decreased with increasing Ce filling fraction. The Seebeck coefficient increased with increasing Ce filling fraction. The greatest dimensionless thermoelectric figure of merit T value of 1.1 was obtained at 750 K for the composition of Ce0.28Fe1.52Co2.48Sb12.
In situ microscopic surface characterization studies of polymeric thin films during tensile deformation using atomic force microscopy
Authors: Bobji M. S. , Bhushan Bharat
Published: March 2008

Atomic force microscopy (AFM) has been used to study the cracks developed on thin-film coatings on a polymer substrate subjected to external tension. To conduct in situ tensile tests in AFM, a special stage has been built. A new technique to image the same control area at different strains was developed and used to study the propagation of a crack with increasing strain in magnetic tapes. Metal particulate tapes developed numerous cracks of shorter length, perpendicular to the loading direction. In contrast, metal-evaporated tapes developed cracks that extend edge to edge. The variation of the crack width and the spacing with strain were measured and explained with the help of models based on elasticity.
Crystallization kinetics of amorphous nanostructured Pd40.5Ni40.5P19 alloys
Authors: Ngai H. W. , Leung C. C. , Guo W. H. , Kui H. W.
Published: March 2008

When a homogeneous amorphous Pd40.5Ni40.5P19 alloy was subjected to thermal annealing for 30 min at various temperatures, novel microstructures were observed. At an annealing temperature of 603 K, phase separation of the amorphous phase dominated. At 628 K, a precipitation reaction proceeded first. After its completion, a eutectic growth set in. At 638 K, metastable spinodal decomposition occurred first, followed by a eutectic growth. Finally at 673 K, crystal growth of crystalline spinodal network was fast enough to compete with a eutectic growth.
Effects of strain hardenability and strain-rate sensitivity on the plastic flow and deformation homogeneity during equal channel angular pressing
Authors: Kim Hyoung Seop , Hong Sun Ig , Seo Min Hong
Published: March 2008

The effects of strain hardenability and strain rate sensitivity on the plastic flow and deformation inhomogeneity during equal channel angular pressing were studied using a finite element method analysis. In this study, perfect plastic nonhardening and rate-insensitive materials, and rate-sensitive materials were considered. In case of the nonhardening and rate-insensitive materials, the deformed geometry was predicted to be quite uniform and homogeneous. Deformation inhomogeneity developed, however, in materials with finite work-hardening exponent and strain-rate sensitivity. The corner gap formed in strain-hardening materials whereas the upper and lower channel gaps formed in strain-rate-sensitive materials. The deformation inhomogeneity was strongly dependent on the relative effects of strain-hardening exponent and strain-rate sensitivity. The predictions on the deformation inhomogeneity and the formation of corner and channel gaps were compatible with the experimental data published in the literature.
Thermodynamic stability of tetragonal zirconia nanocrystallites
Authors: Wu Nae-Lih , Wu Ton-Fon , Rusakova Irene A.
Published: March 2008

The thermodynamic stability of tetragonal (t-) ZrO2nanocrystallites below the bulk stability temperature 1200 °C was studied through specially synthesized crystallites that exhibited an extremely slow coarsening rate. The nanocrystallites were mechanically transformed to the monoclinic (m-) structure, and, because the crystallite size was kept below approximately 20 nm, thet-structure was completely recovered solely by thermal treatments between 900 and 1100 °C. These results gave strong evidence to the notion that, for sufficiently small crystallite size, nanocrystallinet-ZrO2is not just kinetically metastable but can be truly thermodynamically more stable than thempolymorph in air below 1200 °C.
Luminescence and decay behaviors of Tb-doped yttrium silicate
Authors: Choi Yoon Young , Sohn Kee-Sun , Park Hee Dong , Choi Se Young
Published: March 2008

The photoluminescence of terbium-activated yttrium silicate with the general formula Y2−XTbxSiO5 was investigated as a function of Tb3+ concentration. Especially, the main attention was focused on the 5D3 fluorescence and its energy transfer behavior. The emission and excitation spectra were measured in terms of Tb3+ concentration. The diffuse reflectance spectrum was also measured in the range from VUV to UV. As a result, yttrium silicate was found to have a broad absorption band extended from the VUV to UV range. The concentration quenching was investigated in terms of luminance and decay time both for 5D3 and 5D4 fluorescence. The energy transfer was also investigated by analyzing the decay curve of 5D3 emission on the basis of the multipolar interaction. The decay curves of 5D3 emission, for which well-known cross-relaxation has been accepted as a main factor, were analyzed by Inokuti and Hirayama's formula on the basis of the direct quenching scheme. Furthermore, the rate equations including a newly proposed quenching scheme were taken into consideration. The rate equations accept the emission quenching as due to the cross-relaxation from 5D3 or 4 to some upper levels such as 7D and the charge-transfer band.
Influence of CaO–SiO2 ratio on the chemistry of intergranular films in liquid-phase sintered alumina and implications for rate of erosive wear
Authors: Brydson Rik , Twigg Peter C. , Loughran Fiona , Riley Frank L.
Published: March 2008

Polycrystalline aluminas sintered with 10 wt% additions of calcium oxide (CaO) and silica (SiO2) in varying molar ratios were fabricated via precipitation, calcination, and hot pressing. Alumina microstructures were analyzed by scanning electron microscopy in terms of their mean grain size, grain size distribution, and grain aspect ratios. High-resolution transmission electron microscopy (HRTEM) showed the presence of an amorphous intergranular glassy phase at two- and three-grain boundaries. The intergranular film width at two-grain boundaries, determined by HRTEM, appeared to vary with the [CaO]:[SiO2] ratio of the additive as did the chemical composition and local chemistry, determined by high-resolution analytical transmission electron microscopy and scanning transmission electron microscopy (using both energy dispersive x-ray and electron energy loss spectroscopy). The factors influencing the erosive wear rate are discussed including the chemistry and associated fracture energy of the intergranular glassy film. Wet erosive wear rates of the densified materials were determined and had a strong dependence on the [CaO]:[SiO2] ratio in the additive.
In situ transmission electron microscopy study of the silicidation process in Co thin films on patterned (001) Si substrates
Authors: Ghica C. , Nistor L. , Bender H. , Steegen A. , Lauwers A. , Maex K. , Landuyt J. Van
Published: March 2008

The results of an in situ transmission electron microscopy study of the formation of Co-silicides on patterned (001) Si substrates are discussed. It is shown that the results of the in situ heating experiments agreed very well with the data based on standard rapid thermal annealing experiments. Fast heating rates resulted in better definition of the silicide lines. Also, better lines were obtained for samples that received already a low-temperature ex situ anneal. A Ti cap layer gave rise to a higher degree of epitaxy in the CoSi2 silicide.
Sol-gel synthesis and the effect of boron addition on the phosphorescent properties of SrAl2O4:Eu2+,Dy3+phosphors
Authors: Chen I-Cherng , Chen Teng-Ming
Published: March 2008

The effects of boron addition on the microstructure and afterglow properties of the long-phosphorescent SrAl2O4:Eu2+,Dy3+(SAED), synthesized via a novel sol-gel route, were systematically investigated. Significant improvement on luminescence intensity and the lengthening of afterglow persistent time in boron-added SAED (BSAED) phases were observed, as compared to those without boron addition and commercial phosphors. Typical bluish-green emissions attributed to the doublet phosphorescence with wavelengths peaking at 412 and 501 nm for BSAED phase and 398 and 486 nm for the pristine SAED phase were observed. Afterglow with wavelengths peaking at 403 and 485 nm was observed for BSAED phase, whereas that with wavelengths peaking at 486.5 nm was found for the pristine SAED phase, as indicated by time-dependent afterglow decay profiles. Results from scanning electron microscopic morphological studies were used to investigate the modification of microstructure of the BSAED phases.
Effects of preparation processes on structure and magnetic properties of Nd2Fe14B/α–Fe-type nanocomposite magnets
Authors: Cui Bao-zhi , Sun X. K. , Xiong L. Y. , Liu Wei , Zhang Zhi-dong , Yang Zhi-qing , Wang Ai-min , Deng Jiang-ning
Published: March 2008

The structure and magnetic properties of Nd8.4Fe86Mo1.1B4.5 nanostructured magnets prepared by mechanical alloying (MA), compared with those by mechanical milling (MM), were studied. The intrinsic coercivity μ0Hc, the reduced remanence Jr/Js, and the maximum magnetic energy product (BH)max for Nd8.4Fe86Mo1.1B4.5 magnets were prepared by MM were notably higher than the values of the corresponding MA-prepared samples. The average grain sizes of both α–Fe and Nd2Fe14B in the MM-prepared samples were measurably smaller than corresponding values of the MA-prepared samples. A more homogeneous distribution of α–Fe grains in the MM-prepared samples than in the MA-prepared samples was obtained.
Microstructural studies of Cu brazing on AlN
Authors: Cai Chaoxian , Lumpp Janet K.
Published: March 2008

The microstructures and phase compositions of Cu–Ag–Ti active-metal brazing alloys have been studied by scanning electron microscopy and energy dispersive x-ray spectroscopy to evaluate alloy wetting on AlN and Cu brazing on AlN. Titanium is segregated from the original alloy, and a Ti-rich layer is formed between the brazing alloy and AlN substrate. The alloy components are able to penetrate into the grain boundary of AlN during wetting or brazing, and the interfacial reaction takes place along the grain and outer boundary of AlN. The bonding of brazing alloys to AlN substrate often induces cracks in the AlN side.
Influence of annealing treatments on microstructure and toughness of liquid-phase-sintered silicon carbide
Authors: Sciti D. , Bellosi A.
Published: March 2008

The possibility of anin situtoughening through the β → α phase transition was evaluated on liquid-phase-sintered SiC (with Al2O3and Y2O3as additives). Dense hot-pressed materials with an equiaxed morphology were annealed at 1850, 1900 and 1950 °C for 1 to 4 h so the effect of time, temperature, composition, and amount of second phase could be investigated. Microstructure features revealed that 1900 °C was the best temperature in producing a high percentage of elongated grains with limited grain coarsening and reduction of second-phase pockets. Mean grain size and aspect ratios increased from 0.5 to 1.5 μm and to 5, respectively, during the first 2 h of treatment at 1900 °C and then maintained a constant value. The amount and composition of second phase influenced the rate of transformation from equiaxed to elongated grain morphology. Toughness increased from 3.3 to 5.5 Mpa · m1/2in 1900 °C annealed samples due to a crack-deflection mechanism.
Synthesis of Zn1–xMgxO and its structural characterization
Authors: Tomar M. S. , Melgarejo R. , Dobal P. S. , Katiyar R. S.
Published: March 2008

Zn1–xMgxO is an important material for optoelectronic devices. We synthesized this material using a solution-based route. We investigated in detail the structural behavior of this material system using x-ray diffraction and Raman spectroscopy. Mg substitution up to x ≈ 0.10 does not change the crystal structure, as revealed by x-ray diffraction and Raman spectroscopic studies. This synthesis route is also suitable to prepare thin films by spin coating with the possibility of p and n doping.
Effects of pressure on the solidification of Al–Mn alloy
Authors: He Duanwei , He M. , Kiminami C. S. , Zhang F. X. , Xu Y. F. , Wang W. K. , Kuo K. H.
Published: March 2008

The solidification of Al–20 wt% Mn alloy was investigated under pressures up to 6 GPa. It was found that the solidification products under pressures below 4 Gpa were about the same, composed mainly of Al and Al6Mn. A new Al–Mn phase with needle like morphology and Al nanocrystallites in size less than 20 nm were obtained in the quenched alloy at 6 GPa. Structure analysis by transmission electron microscopy and x-ray diffraction indicated that the new phase had a C-center othorhombic unit cell with lattice constants of a = 0.7565(4) nm, b = 1.2965(6) nm, and c = 0.7801(6) nm. The composition was determined to be Al77.5Mn22.5 by election probe microanalysis. The phase evolution during solidification under different pressures was discussed. Our experimental results show that the pressure, as a basic thermodynamic variable like temperature, may play an important role on the solidification of the alloy.
Sintering of screen-printed platinum thick films for electrode applications
Authors: Véchembre J. B. , Fox G. R.
Published: March 2008

Pt electrodes with a 6–8-μm thickness were produced on alumina substrates by a double-print Pt screen-printing process that included a sequential heat treatment at 600 °C and 1300 °C. This process improved the final sintered double-print film because the first printed layer acted as a sintering template for the second printed layer. The sintered Pt films have a 95% coverage of the alumina surface, 92% density, 0.73-μm average surface roughness, and 16.10−5 Ω cm resistivity. The sintering behavior of Pt films exhibited three stages of densification: Stage I (T °C < 700 °C), exhibiting neck growth, and Stage II (700 < T °C < 1300 °C), exhibiting grain growth, have activation energies of 64 kJ/mol and 125 kJ/mol, respectively. Stage III exhibits a decrease in shrinkage due to Pt coalescence and island formation. The transition temperature, 700 °C, between Stages I and II corresponds to an anomalous increase in surface roughness and resistivity. The thickness of Pt films was a critical parameter for achieving alumina surface coverage. Uniaxial pressing of dried Pt films increased densification and reduced the surface roughness of double-print Pt films.
Single-domain Yba2Cu3Oy thick films and fabrics prepared by an infiltration and growth process
Authors: Sudhakar Reddy E. , Noudem J. G. , Tarka M. , Schmitz G. J.
Published: March 2008

An infiltration and growth process has been developed to produce single-domain Yba2Cu3Oy(123) as thick films on various substrates or as self-supporting fabrics. Commercially available Y2O3 cloths of square woven or satin woven structure were infiltrated with liquid phases from a suitable source containing barium cuprates and copper oxides and subsequently converted into Y2BaCuO5(211) and −123 phases by a series of distinct peritectic reactions. Depending on the final form of 123, the Y2O3 cloth was either clamped firmly at corners to produce a self-supporting 123 fabric or placed on a suitable substrate to result in a thick film coating of 123. The source material for the liquid phase being in the form of solid blocks was placed at corners of the cloth in the case of free-standing 123 fabrics. In case of the thick film configuration the liquid phase powder was spread on the surface of the Y2O3 cloth. A small c-axis-oriented MgO or Nd(123) seed was used to generate an oriented 123 domain in the infiltrated fabric. The solidification process was optimized to transform the entire Y2O3 fabric into a single-domain 123. The microstructure of the single domain was optimized in terms of 211 size and content for high Jc. A detailed description of the process, the growth mechanism, the resulting microstructures was given, and basic superconducting properties of the new form of 123 are briefly discussed.
Combinatorial synthesis of oxide powders
Authors: Reichenbach H. M. , McGinn P. J.
Published: March 2008

Combinatorial libraries of the mixed oxide system Cu1−xCexO3(0 ≤x≤ 1) have been generated using a modified Pechini powder synthesis process in conjunction with inkjet deposition. Mixed oxide crystalline powders were formed at temperatures below 500 °C. These powders have particle sizes in the range of 20.0 to 85.5 nm, and the powder surface area increases with cerium content. In addition, each of the mixed oxides (0 <x< 1) displayed catalytic activity in the CO oxidation reaction at temperatures between 150 and 350 °C. This novel protocol has also been used to generate a library of oxide powders of the perovskite-like La1−xSrxCoO3?δsystem. The La–Sr–Co–O system from this protocol exhibits lower average surface areas than the Cu–Ce–O system (approximately 11.2 m2/g) due to higher decomposition temperatures but still acts as an active catalyst for the CO oxidation reaction.
Preferential growth mechanism of REBa2Cu3Oy (RE = Y, Nd) crystal on MgO substrate by liquid phase epitaxy
Authors: Nomura Katsumi , Hoshi Saburo , Yao Xin , Kakimoto Kazuomi , Nakamura Yuichi , Izumi Teruo , Shiohara Yuh
Published: March 2008

Growth of the REBa2Cu3Oy (REBCO, RE = Y, Nd) crystals on the MgO substrates by the liquid phase epitaxy (LPE) process was investigated to clarify the growth mechanism. The crystal orientation of in-plane alignment was improved during the LPE process due to the preferential dissolution and growth even from a polycrystalline seed film. The orientation of preferential growth depended on the kind of RE for the REBCO system. The phenomena could be explained by the coarsening model by introducing the difference in the interfacial energies, which were considered not only general lattice matching but the Coulomb force at the interface between the REBCO and the MgO crystals. The preferential growth model was developed, and the calculation results showed a good agreement with the experimental results.
Modification of sol–gel-derived amorphous Al2O3 thin films by F2 excimer laser irradiation at ambient temperature
Authors: Takeda Satoshi , Ikuta Yoshiaki , Hirano Masahiro , Hosono Hideo
Published: March 2008

F2 excimer laser (157 nm) irradiation was applied to modify sol–gel-derived amorphous Al2O3 thin films at ambient temperature. The surface morphology and density of the film were significantly altered by the laser irradiation (power: 2 mW/cm2/pulse). The surface properties of the film were also changed from hydrophilic to hydrophobic. These alterations were not observed when using ArF excimer laser (193 nm) irradiation at the same laser power as that of the F2 laser. It was found that the changes induced by F2 laser irradiation mainly arose from the direct photoexcitation of C = O groups in ethylacetoacetate, which was added as a chelating agent of aluminum-alkoxides. Consequently, photochemical reactions of the Norrish-type occur, resulting in the formation of hydrocarbon or olefin and the elimination of carbon monoxide (CO) or decomposition products. The elimination of CO is considered to cause the marked change in structure and surface properties of the film. Patterning of the gel films was successfully performed by using these findings.
Effect of process variables on the structure, residual stress, and hardness of sputtered nanocrystalline nickel films
Authors: Mitra R. , Hoffman R. A. , Madan A. , Weertman J. R.
Published: March 2008

Nanocrystalline nickel films of about 0.1 μm thickness grown by sputtering with and without substrate bias possessed average grain sizes of 9–25 nm. Variation in substrate bias at room and liquid nitrogen temperature of deposition strongly affected grain structure and size distribution. Qualitative studies of film surfaces showed variation in roughness and porosity level with substrate bias and film thickness (maximum of 8 μm). The films had tensile residual stress, which varied with deposition conditions. The hardness values were much higher than those of coarse-grained nickel but decreased with an increase in the film thickness because of grain growth.
On some discrepancies in the literature about the formation of icosahedral quasi-crystal in Al–Cu–Fe alloys
Authors: Gui Jianian , Wang Jianbo , Wang Renhui , Wang Dahai , Liu Jing , Chen Fangyu
Published: March 2008

To clarify some discrepancies in the literature about the formation of icosahedral quasi-crystal (IQC) in Al–Cu–Fe alloys, microstructures, and constituent phases of Al62.5Cu25Fe12.5 and Al65Cu20Fe15 alloys were studied. Each dendritic arm of the primarily solidified λ–Al13Fe4 phase is a single crystal that possesses no definite orientation relationship with the IQC, formed by peritectic reaction (L + λ + β → IQC) or a solid-state reaction (Cu-rich phases + λ + β →?IQC). This fact disproves an assumption that λ-phase is an approximant of the IQC. Two types of cubic phase, β-phase with CsCl structure containing more Fe and τ3 phase, which is a superstructure and contains less Fe, were observed depending on the composition and thermal history of the samples.
Alternating current conductivity of the interfacial phase in copper oxide–silica gel nanocomposites
Authors: Das D. , Chakravorty D.
Published: March 2008

A nanocomposite structure was induced in gel of composition 60CuO · 40SiO2 (mol%) by first of all precipitating nano-sized copper particles by a reduction treatment and subsequently subjecting these to a controlled oxidation treatment. The particle size was of the order of 6.8 nm. Alternating current (ac) conductivity measurements were carried out on different specimens in the temperature range 300 to 630 K covering a frequency spectrum 0.1 kHz to 2 MHz. The ac conductivity was found to have a variation with frequency given by ωs, ω being the angular frequency and s the frequency exponent. The analysis of the variation of s as a function of temperature led to the conclusion that an overlapping large polaron tunneling mechanism was operative in this system. The effective barrier height for polaron transfer for infinite intersite separation was found to be almost twice in the case of the precursor gel as compared to that for the composite with the interfacial amorphous phase.
Chemical–mechanical polishing of copper and tantalum with silica abrasives
Authors: Li Y. , Hariharaputhiran M. , Babu S. V.
Published: March 2008

Chemical mechanical polishing of copper and tantalum was performed using fumed amorphous silica abrasive particles dispersed in H2O2, Fe(NO3)3, and glycine solutions. Results showed that in DI water silica did not polish Cu but Ta had a relatively high polish rate. Cu polish rate decreased with increasing particle concentration in Fe(NO3)3-based slurries due to the adsorption of Fe3+ on the silica surface. Addition of H2O2 enhanced Cu polish rate but reduced Ta polish rate. The specific surface area of the particles played an important role in the removal of Ta and Cu, presumably due to some chemical bonding between the materials being polished and the silica particles.
Combustion synthesis of mechanically activated powders in the Ti–Si system
Authors: Maglia F. , Anselmi-Tamburini U. , Cocco G. , Monagheddu M. , Bertolino N. , Munir Z. A.
Published: March 2008

The effect of the mechanical activation of the reactants on the self-propagating high-temperature synthesis (SHS) of titanium silicides was investigated. SHS experiments were performed on reactant powders that were milled for different times. Mechanical activation was shown to have a large influence on the combustion characteristics, particularly on wave speed. A much weaker effect was observed on the products phase composition. Single-phase products were obtained only from Ti:Si = 1:2 and Ti:Si = 5:3 starting compositions. Observation of microstructural evolution in quenched reactions of Ti:Si = 1:2 mixtures milled for relatively long times revealed that the combustion reaction was primarily a solid-state process restricted to a surface layer of the large Ti grains. A secondary process involving a solid–liquid interaction between solid Ti and melted Si was dominant in the post front region. The mechanical activation in this case took the role of increasing the contact surface between the reactants. A single reaction coalescence mechanism involving only liquid phases was proposed for the Ti:Si = 5:3 composition. For this composition the apparent activation energy for the overall combustion process was determined (155 kJ mol−1) and was shown to be independent on the degree of mechanical activation of the reactants.
Influence of thermal history on morphology and viscoelastic behavior of ethylene–1-octene copolymers synthesized with metallocene catalysts
Authors: Cerrada M. L. , Benavente R. , Pérez E.
Published: March 2008

The relationships among structure and properties have been established in copolymers of ethylene and 1-octene, synthesized by a particular metallocene catalyst system. The most important factor affecting the structure and properties of these copolymers is, evidently, the comonomer content. However, the cooling treatment from the melt has been found to be also a very significant factor and, although its influence on the thermal properties is rather small, some structural parameters and the viscoelastic behavior are clearly dependent upon thermal history. These parameters include the degree of crystallinity, lattice constants, relaxation processes, stiffness, and microhardness of the samples. Regarding the viscoelastic behavior, the β relaxation is shifted to lower temperatures and its intensity is increased as 1-octene content raises. On the other hand, the α mechanism, associated with motions within the crystalline regions, is also moved to lower temperatures. Such a relaxation is only observed up to a certain 1-octene content in the copolymer.
Rational solvent selection strategies to combat striation formation during spin coating of thin films
Authors: Birnie Dunbar P.
Published: March 2008

Striation defects in spin-coated thin films are a result of unfavorable capillary forces that develop due to the physical processes commonly involved in the spin-coating technique. Solvent evaporation during spinning causes depletion at the surface of the more volatile solution components while simultaneous viscous out-flow occurs providing the main source of solution thickness reduction during any typical spinning run. The composition changes in the surface layer can either stabilize or destabilize the surface with respect to convective motions within the coating solution. Destabilization (and therefore possible striation formation) happens when the surface composition changes so that a larger surface tension will develop. Thus, a careful cross-referencing of solvent volatility with surface tension effects can help establish solution conditions that will prevent this instability from arising. A plot of solvent vapor pressure (Pv) versus solvent surface tension (σ) is introduced and utilized to help discuss the impact of solvent choice when making coatings via spin coating. One important result is that when desiring to deposit a coating having a surface tension of σsolid, then it is favorable to use a fully miscible solvent that has a higher surface tension (i.e., σliquid> σsolid). More complicated solution mixtures were also examined, including dual-solvent systems and water-containing systems.
Growth of melt-textured Nd-123 by hot seeding under reduced oxygen partial pressure
Authors: Kambara M. , Babu N. Hari , Shi Y. H. , Cardwell D. A.
Published: March 2008

The growth of large, melt-textured Nd1+xBa2−xCu3O6+δ (Nd-123) crystals has been achieved by hot seeding and isothermal solidification under a 1% oxygen in nitrogen atmosphere. These crystals, which exhibit a sharp, faceted growth interface, were grown epitaxially from a small Nd-123 single crystal seed placed on the sample surface at elevated temperature. The growth length of the melt-processed crystal was directly proportional to the isothermal holding time (approximately 17 h), as is observed for the growth of YBa2Cu3O7−δ (Y-123). The variation of growth rate with undercooling for this material was linear, however, in contrast to the parabolic dependence observed for Y-123 crystals grown in air. The growth rate of Nd-123 under reduced oxygen was consequently lower than that of Nd-123 and Y-123 grown in air at relatively high values of undercooling. Evaluation of the experimental data against a solidification models suggested that the interface kinetics are responsible, at least in part, for the observed growth features in hot-seeded Nd-123 crystals. This was attributed to the difference in oxygen partial pressure under the respective growth atmospheres, rather than to the species of rare-earth element in the compound.
Effect of hydrogen on true leakage current characteristics of (Pb,La)(Zr,Ti)O3 thin-film capacitors with Pt- or Ir-based top electrodes
Authors: Yoon Soon-Gil , Wicaksana Dwi , Kim Dong-Joo , Kim Seung-Hyun , Kingon A. I.
Published: March 2008

The degradation behavior of polarization and leakage current characteristics of sol-gel-derived (Pb,La)(Zr,Ti)O3 (PLZT) thin films, with Pt, Ir, and IrO2 top electrodes, by annealing under a 4% H2/96% N2 atmosphere were investigated. The leakage current behaviors of Pt/PLZT/Pt and IrO2/PLZT/Pt capacitors annealed at 300 °C for 20 min in 4% H2 were well consistent with the space-charge-influenced injection model proposed. However, IrO2/PLZT/Pt capacitors recovered at 700 °C for 10 min in Ar ambient after hydrogen anneal were not consistent with the proposed model because a conducting phase of IrPb was formed between the top electrode and PLZT during the recovery anneal at 700 °C in Ar ambient and modified the Schottky barrier height. The true leakage current behavior of IrO2/PLZT/Pt capacitors recovered after hydrogen forming are similar to those of Ir/PLZT/Pt capacitors without the hydrogen-forming gas anneal. The P–E loops of Pt/PLZT/Pt and Ir/PLZT/Pt capacitors showed good recovery through recovery anneal after H2 treatment. However, IrO2/PLZT/Pt capacitors depended on the recovery anneal atmosphere (Ar or O2).
Synthesis of Zn2−xMnxSiO4phosphors using a hydrothermal technique
Authors: Yoon Chulsoo , Kang Shinhoo
Published: March 2008

Zn2−xMnxSiO4phosphors were synthesized by a hydrothermal process using ZnO and SiO2. Prismatic Zn4Si2O7(OH)2· H2O particles were formed through heterogeneous nucleation on the surface of the ZnO particles. The Zn2SiO4phase was formed through an isometric phase transition of Zn4Si2O7(OH)2· H2O. Water pressure, as well as the particle size of the raw materials, had a profound effect on the temperature of phase formation. The effect of solution pH on the morphology and growth of the particles was investigated. The photoluminescence of the synthesized Zn2−xMnxSiO4phosphor was also examined. The color coordinate of the Zn2−xMnxSiO4phosphor obtained in this study showed a green color, which was shifted toward short wavelength.
High-Tc superconducting NbN films with low particulate density grown at 25 °C using pulsed laser deposition
Authors: Kaul Anupama B. , Sands Timothy D. , Duzer Theodore Van
Published: March 2008

The growth and characterization of high-Tc NbN films formed on room temperature substrates by pulsed laser deposition is described. The growth was performed at a high laser power density (>5 × 108 W/cm2), where the enhanced reactivity of species in the plume is proposed as the mechanism for increased nitrogen incorporation in films on unheated substrates. The Tcs were 16.2 K on MgO and 13 K on SiNx/Si substrates. In addition to electrical transport measurements, the films were characterized using RBS and x-ray diffraction. The particulate density on films grown at high power density was significantly reduced, which is correlated with the Nb target having a smoother morphology, characteristic of a quenched molten surface layer in the ablated area.
Infrared optical properties of aged porous GaAs
Authors: Zangooie S. , Schubert M. , Tiwald T. E. , Woollam J. A.
Published: March 2008

Aging properties of porous GaAs were investigated nondestructively using variable angle of incidence infrared spectroscopic ellipsometry. In addition to the thickness and volume porosity, properties of the solid part of the porous material are investigated in terms of the long-wavelength dielectric function and chemical composition. The high sensitivity is employed to detect and identify infrared resonant absorptions related to different vibration modes of cubic and amorphous As2O3. Resonances centered at 333.3, 480, 785.8, 838, and 1045.5 cm−1 are from cubic As2O3, whereas resonances centered at 350, 490, and 808.5 cm−1 are from amorphous As2O3.
Deep center luminescence versus surface preparation of ZnSe single crystals
Authors: Garcia J. A. , Muñoz V. , Martinez-Tomas C. , Garitaonandia J. J. S.
Published: March 2008

A close relationship between the photoluminescence emissions labeled Y and S, related to dislocations and extended structural defects, and the preparation of the surface state of ZnSe single crystals before PL (photoluminescence) measurements has been established. The samples were obtained by solid-phase recrystallization under different pressure conditions. An easy method for achieving good quality surfaces with a very significant reduction of such Y and S PL emissions is proposed.
Effects of Cu and Ni additions to eutectic Pb–Sn solders on Au embrittlement of solder interconnections
Authors: Lee Jong-Hyun , Park Jong-Hwan , Lee Yong-Ho , Kim Yong-Seog
Published: March 2008

Effects Cu and Ni additions on Au embrittlement of eutectic Sn–Pb solder interconnections during a solid-state aging treatment were evaluated using a ball shear testing method. The addition resulted in a formation of Au-containing ternary intermetallic compounds, either Au–Sn–Cu or Au–Sn–Ni phase, inside the solder matrix during aging treatment. The fracture energy of the solder interconnection containing 2.9 wt% Cu remained almost the same up to 200 h of aging treatment at 150 °C, demonstrating the possibility of suppressing the Au embrittlement by forming ternary intermetallic phases inside the solder matrix.
Low–power plasma torch method for the production of crystalline spherical ceramic particles
Authors: Chen Chun-Ku , Gleiman Seth , Phillips Jonathan
Published: March 2008

A low-power, atmospheric pressure, microwave plasma torch was used to make spherical alumina particles of controlled size from irregularly shaped precursor powders. Detailed studies of the impact of operating parameters, particularly gas identity (argon or air), gas flow rates, and applied power, showed that particle size changed in a predictable fashion. The most important factor in controlling particle size appears to be precursor particle density in the aerosol stream that enters the plasma hot zone. This and other facts suggest that particle collision rate is primarily responsible for determining ultimate particle size, although atomic addition also plays a role. Reproducible volume average particle sizes ranging from 97 to 1150 μm3 were formed from precursor particles of order 14 μm3. Moreover, for the first time we report the creation of an atmospheric pressure low-power air plasma (<1 kW).
Mechanochemistry of the titanium–silicon system: Compositional effects
Authors: Doppiu S. , Monagheddu M. , Cocco G. , Maglia F. , Anselmi-Tamburini U. , Munir Z. A.
Published: March 2008

The mechanochemical behavior of the Ti–Si system was investigated across the whole composition range at a constant milling intensity. At low Si content the mechanical alloying process leads progressively to an amorphous structure. In the central range of the equilibrium diagram, crystalline intermetallic compounds form with a combustion-like behavior. A nanostructured composite of TiSi2 gradually evolves above the Ti25Si75 stoichiometry. Transformation behaviors relate to the thermodynamic and thermochemical properties of the tested mixtures as well as with their mechanical features and structural refinement, which change drastically within the explored composition range.
Effect of host compositions on the afterglow properties of phosphorescent strontium aluminate phosphors derived from the sol-gel method
Authors: Chen I-Cherng , Chen Teng-Ming
Published: March 2008

The effect of compositions of host precursors on the afterglow and phosphorescent decay properties of Eu2+- and Dy3+-coactivated strontium aluminates (SAED) synthesized by a sol-gel process has been investigated. A variety of strontium aluminates such as Sr3Al2O6, SrAl2O4, and SrAl12O19 have been identified in the samples prepared from starting precursors with Al/Sr ratios ranging from 1 to 12, respectively. The initial afterglow intensity (I0) for SAED phases was found to vary with Al/Sr ratio of the sol-gel precursor, with a maximal I0 appearing in the sample with Al/Sr of 2 in which SrAl2O4 dominated. The afterglow decay rate was found to be fastest for sample with Al/Sr ratio of 1:1 in which Sr3Al2O6 phase dominated. Moreover, the afterglow decay rates for those with Al/Sr ratio of 2:1 to 12:1, in which SrAl2O4 and SrAl12O19 dominated, were found to be slow and similar.
Growth, structure, and mechanical properties of transition metal carbide superlattices
Authors: Högberg H. , Birch J. , Odén M. , Malm J-O. , Hultman L. , Jansson U.
Published: March 2008

Superlattices of TiC/VC have been deposited on MgO(001) substrates by simultaneous direct current metal magnetron sputtering and C60 evaporation in the temperature range 200–800 °C. Thin superlattices (approximately 1000 Å) deposited at 400 °C exhibited an epitaxial growth with abrupt interfaces while films deposited at 200 °C showed a partial loss of epitaxy. At 800 °C roughening by surface diffusion started to degrade the superlattices and introduced a columnar microstructure. A loss of epitaxy was observed for thicker (>7000 Å) superlattice films deposited at 400 °C. The results suggest that this observation is due to difficulties in depositing epitaxial VC.
Textural properties of SiO2 · CaO · P2O5 glasses prepared by the sol-gel method
Authors: Balas F. , Arcos D. , Pérez-Pariente J. , Vallet-Regí M.
Published: March 2008

Five glasses in the system SiO2 · CaO · P2O5 have been synthesised via sol-gel method. The textural properties of the calcined glasses have been studied using mercury intrusion and N2 adsorption porosimetries. The glasses with higher SiO2 content showed lower pore volume, smaller diameters in the meso- and macropore regions, and higher surface areas. The pore morphology in the mesopore range was influenced by the SiO2 content, where there was a transition from ink bottle to cylinder shaped pores.
Damping behavior of in situ Al–(graphite, Al4C3) composites produced by reciprocating extrusion
Authors: Chu Hsu-Shen , Liu Kuo-Shung , Yeh Jien-Wei
Published: March 2008

The effect of graphite particles on the damping behavior of 6061 Al–graphite composites was investigated with an aim to develop a high damping, stiffness, and hardness material. The composites were processed by mixing 6061 alloy powder with graphite particles, hot pressed as a billet and consolidated by reciprocating extrusion 10 times. The results showed that the graphite particles were greatly refined and niformly distributed in the matrix. The graphite in situ reacted with the Al matrix to orm fine dispersed Al4C3 particles during both reciprocating extrusion and subsequent olution treatment. The Al4C3 phase could result in a pronounced dispersion trengthening effect. The damping capacity of the composite increased with increasing raphite content. The composite showed a peak in damping capacity during aging reatment. The 6061 Al–20% (graphite, Al4C3) composite solution-treated for 24 h and eak-aged displayed an excellent combination of damping capacity, stiffness, and ardness. The composite retained high damping while maintaining a high modulus ecause of the coexistence of graphite and Al4C3. The operative damping mechanisms, ncluding intrinsic damping of graphite particle, interface damping, dislocation amping, and grain boundary damping, are discussed with consideration of material icrostructure.