bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a submicrometer-grained microstructure in aluminum 6061 using equal channel angular extrusion
Authors: Ferrasse Stephane , Segal Vladimir M. , Hartwig K. Theodore , Goforth Ramon E.
Published: March 2008

Submicrometer-grained (SMG) microstructures are produced in an Al–Mg–Si alloy (6061) by subjecting peak-aged and overaged billets of the alloy to intense plastic strain by a process known as equal channel angular extrusion. Two types of refined structure are distinguished by optical and transmission electron microscopy. One structure is created through intense deformation (four extrusion passes through a 90° die, ε = 4.62) by dynamic rotational recrystallization and is a well-formed grain (fragmented) structure with a mean fragment or grain size of 0.2–0.4 μm. The other structure is produced by post-extrusion annealing through static migration recrystallization, resulting in a grain size of 5–15 μm. Intense deformation of peak-aged material to a true strain ε of 4.62 (four passes) produces a strong, ductile, uniform, fine, and high angle grain boundary microstructure with increased stability against static recrystallization as compared to the overaged material.
Optical properties of potassium acid phthalate
Authors: Comoretto Davide , Rossi Laura , Borghesi Alessandro
Published: March 2008

Potassium acid phthalate (KAP) crystals are promising as substrates for the growth of highly oriented films of conjugated polymers with exceedingly high and fast nonlinear optical response. We report the KAP optical properties (real and imaginary parts of the refractive index ñ = n + ik) in the near infrared and visible range deduced by ellipsometric measurements and direct inversion of transmittance and near-normal incidence absolute reflectance measurements. In the infrared region n was also deduced by the interference fringes.
Synthesis and properties of an aluminum nitride/polyimide nanocomposite prepared by a nonaqueous suspension process
Authors: Chen Xiaohe , Gonsalves Kenneth E.
Published: March 2008

A nanocomposite of a chemically synthesized nanostructured aluminum nitride (AlN) and a polyimide has been studied. Using a nonaqueous polar solvent,N-methylpyrrolidinone (NMP), as the suspension media, the degree of particle agglomeration of AlN was reduced dramatically from micron to nanoscale size. Upon the addition of poly(amic acid) to the AlN/NMP suspension, a further deagglomeration of the particles was observed. The surface physicochemical interactions have been investigated by characteristic model reactions using FTIR spectroscopy. A mechanistic interpretation for the deagglomeration and stabilization behavior is discussed. The formation of the AlN/PI nanocomposite was achieved by the rapid solidification of the precursor suspension followed by compression molding. Such an approach for nanocomposites exhibits better homogeneity with ultrafine fillers and allows a tailorable composition and property at the nanoscale level. Finally, AlN/PI nanocomposites with an increased ceramic loading, up to 65% by volume, were attained and their thermal and mechanical properties, along with the compositional effects, have been investigated.
Phase formation in molybdenum disilicide powders during in-flight induction plasma treatment
Authors: Fan Xiaobao , Ishigaki Takamasa , Sato Yoichiro
Published: March 2008

In-flight modification of MoSi2 powders has been carried out by using an Ar–H2 induction plasma. Reactor pressure, powder feed rate, and plate power level were taken as the experimental parameters to alter the thermal history of the injected powder particles. Metastable hexagonal structure of β–MoSi2 is the major phase observed in the Ar–H2 induction plasma-treated molybdenum disilicide powders, while the stable phase of tetragonal structure of α–MoSi2 usually retains no less than 30 wt. %. Depending on the experimental condition and the deviation from stoichiometry in raw materials, low silicides, Mo5Si3 and Mo3Si, and free Si were observed,
Phase-formation kinetics of xerogel and electrical properties of sol-gel-derived BaxSr1−xTiO3 thin films
Authors: Jang Soo-Ik , Choi Byung-Cheul , Jang Hyun M.
Published: March 2008

Chemically homogeneous BaxSr1−xTiO3 (BST with x = 0.6) multicomponent sol was synthesized using barium oxide, strontium chloride, and Ti-alkoxide (titanium isopropoxide) as starting materials. Acetylacetone (AcAc) was introduced as a chelating agent to reduce a rapid hydrolysis rate of Ti-alkoxide. Analysis of Fourier transform infrared spectroscopy (FTIR) spectra indicated that the stabilization of BST sols was achieved by the chelation of Ti-alkoxide with the enolic form of AcAc. The effective activation energy associated with the formation of perovskite phase from the xerogel was estimated by the differential thermal analysis (DTA) experiment using various heating rates. It is approximately 400 kJ/mol with the Avrami exponent (reaction order) of n = 1, suggesting that the growth of perovskite BST is diffusion-controlled. The calculated half-life time suggests that the minimum temperature for the crystallization which is practically accessible to a real processing is approximately 600 °C. The BST thin film fabricated on the “Pt(150 nm)/Ti(100 nm)/SiO2(100 nm)/Si” substrate exhibited the relative dielectric permittivity of 310 and can be represented by an equivalent circuit consisting of a resistive component originated from the bulk perovskite grain and a parallel RC component resulting from the presence of the grain boundary.
Hot filament assisted diamond growth at low temperatures with oxygen addition
Authors: Tolt Z. Li , Heatherly L. , Clausing R. E. , Feigerle C. S.
Published: March 2008

Addition of a small amount of oxygen to the CH4 and H2 feed gas permits hot filament assisted chemical vapor deposition (HFCVD) of diamond at significantly lower filament and substrate temperatures. The former can be reduced to as low as 1400 °C and the latter to 450 °C. The amount of oxygen required is much lower than what has been used in most studies of the oxygen effect. For each CH4%, there is a narrow window in the O/C ratio, where diamond can be deposited at low temperature. This window shifts to higher O/C ratios as the CH4% increases and expands with increases in filament temperature. The effect of changing substrate and filament temperatures on growth rate and film quality are often not consistent with previous experiences with HFCVD of diamond. Increasing the filament temperature does not always improve the growth rate and film quality, and the non-diamond carbon content in the film is dramatically reduced at lower substrate temperatures. Optimum conditions were found that gave reasonable growth rates (∼0.5 μm/h) with high film quality at filament temperatures below 1750 °C and substrate temperatures below 600 °C. With these reductions in operating temperatures, power consumption can be significantly reduced and the filament lifetime extended indefinitely.
Nitrogen plasma source ion implantation for corrosion protection of aluminum 6061-T4
Authors: Booske J. H. , Zhang L. , Wang W. , Mente K. , Zjaba N. , Baum C. , Shohet J. L.
Published: March 2008

It is established that nitridation of aluminum (Al) 6061-T4 by plasma source ion implantation (PSII) can dramatically enhance the pitting corrosion resistance of this alloy in marine environments (i.e., chlorine-ion-bearing aqueous solutions or humid atmospheres). Corrosion tests and microstructure analyses establish that the mechanism for successful passivation against chloride-induced pitting corrosion involves the formation of a multilayered microstructure, including the presence of a continuous layer of aluminum-nitride (AlN). Important process variables are the implantation voltage and the nitrogen dose (or total implantation time), as these two variables establish the implanted nitrogen concentration. Too high or too low an implanted nitrogen concentration will not yield the continuous AlN layer required for good corrosion resistance. PSII is attractive for this application as it provides for uniform, conformal implantation of irregularly shaped objects without masking, beam rastering, or object rotation.
Excess Li ions in a small graphite cluster
Authors: Nakadaira M. , Saito R. , Kimura T. , Dresselhaus G. , Dresselhaus M. S.
Published: March 2008

We calculate the optimized geometry and the corresponding electronic structure of Li ions doped in a small graphite cluster with dangling bonds or hydrogen terminations at the edge surrounding the cluster. The calculations imply both covalent and ionic bonds of Li ions to carbon atoms, which may be relevant to explaining the broad signal of the 7Li NMR Knight shift spectra. Li intercalation, in particular, is possible even at the hydrogen-terminated edges. Because of the finite size effect of the cluster, the ionicity of intercalated Li ions has a large distribution of values, ranging from positive values close to that in graphite intercalation compounds to even slightly negative values, depending on the bonding geometry. We propose that the cluster edge surface plays a special role in accommodating excess Li ions in the disordered graphite system.
Surface and bulk characterization of Rh/ZrO2 prepared by absorption of Rh4(CO)12 clusters on ZrO2 powder
Authors: Depero L. E. , Bertoncello R. , Boni T. , Levrangi P. , Sora I. Natali , Tempesti E. , Parmigiani F.
Published: March 2008

Rh nanoparticles supported on ZrO2 powder were prepared by adsorbing Rh4(CO)12 clusters from hexane solution under Ar atmosphere. Four samples with Rh content ranging from 0.25 Rh wt.% up to 4.10 Rh wt.% were studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), and time of flight secondary ion mass spectroscopy (ToF-SIMS). TEM measurements show, for all the samples, Rh particles with a size of about 50 Å. The 4.10 Rh wt.% sample also shows some agglomerates of Rh nanoparticles and only for this sample Rh metallic phase was detected by XRD. The profile analysis of the XRD lines indicates an average size of the Rh crystallites of about 60 Å. XPS studies show only a single spectral component for the Zr3d5/2 core line at 182.2 eV. Instead, at least, two components at 307.2 eV and 308.5 eV are detected for the Rh3d5/2 core line. These results suggest that Zr is present only as oxidized state, whereas nonoxidized and oxidized Rh are both observed. A nonoxidized Rh state is also suggested by the XPS valence band electron removal spectrum which exhibits a significant emission within the ZrO2 band gap assigned to Rh 4d bands. A further support to this finding arises from scanning Auger maps of OKVV and RH where nonoxidized Rh is observed. Finally scanning Auger maps using the OKVV and the Zr emissions show surface regions where only the Zr Auger lines are detected, whereas on pure ZrO2 powder this effect is not observed. Since it is possible to rule out from the XPS Zr3d core line spectra, the presence of metallic zirconium hydrogen spillover mechanisms is invoked to explain this result.
Vapor-deposited CaWO4 phosphor
Authors: Carcia P. F. , Reilly M. , Torardi C. C. , Crawford M. K. , Miao C. R. , Jones B. D.
Published: March 2008

In this paper we describe the preparation, microstructure, and x-ray excited luminescence of vapor-deposited CaWO4 films up to about 50 μm thick, comparing them to particulate CaWO4 phosphor screens, used in medical diagnostic imaging. Films that we e-beam evaporated on substrates heated at or above 500 °C were polycrystalline with the scheelite structure, while on unheated substrates, films were initially amorphous but became crystalline after annealing them in air above about 750 °C. Crystalline CaWO4 films irradiated with x-rays produced light emission peaked at 430 nm. The emission intensity depended on film thickness and grain size and was comparable to particulate CaWO4 phosphor screens. Because the vapor-deposited films also exhibited superior resolution, they are promising for diagnostic x-ray imaging.
Phase formation and thermodynamics of unstable Cu–Cr alloys
Authors: Michaelsen C. , Gente C. , Bormann R.
Published: March 2008

The quantitative description of highly nonequilibrium processes for the preparation of metastable and unstable phases requires the determination of the thermodynamic functions of the system under investigation. However, in systems such as Cu–Cr which are immiscible in the equilibrium states, the determination of the thermodynamic functions over the entire concentration range is often difficult if not impossible because reliable experimental data are not available for the metastable or unstable regime. The present paper demonstrates that such data can be obtained by a combination of thin film deposition techniques and differential scanning calorimetry. It is concluded that the phase formation in such thin films can be described in terms of the thermodynamics of the system, even when the heats of mixing are highly positive. The results indicate that models of the regular solution type still provide a reasonable description of the thermodynamic functions of such alloys.
Stoichiometric icosahedral phase in the Zn–Mg–Y system
Authors: Tsai A. P. , Niikura A. , Inoue A. , Masumoto T.
Published: March 2008

Stoichiometric composition and formation process of the icosahedral phase in the Zn–Mg–Y system have been studied. The icosahedral phase exhibit a stoichiometric composition in the vicinity of Zn60Mg30Y10. During cooling, (Zn, Mg)5Y phase primarily crystallizes from the melt at ∼960 K and then undergoes a peritectic reaction with the residual Mg-enriched melt (∼820 K) to form the icosahedral phase. The melt with a constant composition close to Mg7Zn3 is in equilibrium with the (Zn, Mg)5Y phase above the peritectic temperature in a wide compositional range.
A study of micropyretic reactions in the Mo–Si–Al ternary system
Authors: Fu Ming
Published: March 2008

Micropyretic synthesis technique employs self-sustaining exothermic (combustion) reactions for the preparation of various ceramic, intermetallic, and composite materials. In the present work, the combustion reactions of Mo and Si with Al additions have been systematically studied. The atomic mixtures of the reactant powders are chosen to be Mo + (2 − x)Si + xAl with x = 0−0.4. In comparison with the Mo + 2Si reaction which leads to the formation of MoSi2, the substitution of Al for Si decreases the sample ignition temperature, but increases the intensity of the combustion reactions. In addition, the substitution of Al for Si results in the formation of a ternary intermetallic phase, called molybdenum alumino-silicide Mo(Si, Al)2, in the synthesized product. When the content of Al in the reactant mixtures reaches 0.4, nearly single phase Mo(Si, Al)2 is obtained and no MoSi2 is detected in the reaction product. These influences are analyzed by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA). The effect of Al additions on the reaction mechanism is also discussed.
High energy ball-milled Ti2RuFe electrocatalyst for hydrogen evolution in the chlorate industry
Authors: Blouin Marco , Guay Daniel , Huot Jacques , Schulz Robert
Published: March 2008

The high energy mechanical alloying of a Ti–Ru–Fe powder mixture (atomic ratio 2 : 1: 1) has been performed by extensive ball-milling in a steel crucible. The structural evolution of the resulting materials has been studied by x-ray powder diffraction analysis. The identification of the various phases present in the materials, as well as the crystallite size and strain, has been performed by Rietveld refinement analysis. In the first stage of the material transformation, Ru or Fe atoms dissolved into Ti to yield to the formation ofβ–Ti. Upon further ball-milling, almost all the original constituents of the powder mixture have disappeared and a new simple cubic Ti2RuFe phase is formed, with a crystallite size as small as 8 nm. The electrochemical properties of these materials have been tested in a typical chlorate electrolyte by cold-pressing the powders into disk electrodes. At 20 h of ball-milling, where the phase concentration of Ti2RuFe reaches 96%, a reduction of the activation overpotential at 250 mA cm−2of nearly 250 mV is observed when compared to that of a pure iron electrode.
Impact of boundary nucleation on product grain size distribution
Authors: Tong W. S. , Rickman J. M. , Barmak K.
Published: March 2008

We examine quantitatively the impact of boundary nucleation on the size distribution of product grains in a computer simulation of a two-dimensional phase transformation. This is accomplished by determining the probability distribution of product grain areas under different nucleation conditions. Specifically, a comparison of the moments of normalized area distributions of product grains arising from site-biased nuclei with the corresponding moments of the area distribution of Voronoi grains reveals those spatial features of the collection of catalytic sites which most affect product microstructure. The impact of other relevant length scales, including the square root of the inverse nucleation site density, the lattice parameter, and the system size, on microstructure is also discussed.
Material characterization in support of the development of an anode substrate for solid oxide fuel cells
Authors: Simwonis D. , Naoumidis A. , Dias F. J. , Linke J. , Moropoulou A.
Published: March 2008

A new design for solid oxide fuel cells (SOFC's) was developed aiming at the reduction of the total electrical resistance of the cell. The thickness of the electrolyte was decreased, while the anode took on the role of the substrate. The pore structure with respect to gas permeability of this component has to be optimized for the proper operation of this design. Anode substrates, consisting of a cermet (yttrium-stabilized ZrO2 and metallic Ni) and produced by two different processes, coat mix and tape casting, were characterized with respect to pore structure (shape and mean radius), porosity (total, open and permeable), pore size distribution and air permeability. The following methods were used: (i) optical and electron scanning microscopy in combination with image analysis, (ii) mercury porosity, and (iii) air permeability. Correlations between air permeability and porosity and also the percentage of permeable pores in anodes show the superiority of coat mix samples to tape-cast ones. It has been observed that the coat mix process can produce anode substrates with interconnecting porosity, while tape casting, as used in this study, needs some modifications in order to be appropriate for this purpose.
Thermodynamic coupling effect and catalyst effect for the artificial diamond growth
Authors: Wang Ji-Tao , Huang Zhong-Qiang , Wan Yong-Zhong , Zhang David Wei , Jia Hong-Yong
Published: March 2008

The activated chemical vapor deposition (CVD) diamond process became one of the worldwide interesting projects in the 1980s. The basic question is why diamond can grow under activated low pressure conditions. The driving force of the transformation from graphite to diamond under low pressure is coming from a coupled reaction of the association of superequilibrium atomic hydrogen. The thermodynamic coupling effect in the activated CVD process is different from the catalyst effect in the high pressure, catalyst-assisted process for the artificial diamond growth.
A new microwave dielectric ceramics based on the solid solution system between Ba(Ni1/3Nb2/3)O3and Ba(Zn1/3Nb2/3)O3
Authors: Cho Seo-Yong , Youn Hyuk-Joon , Hong Kug-Sun , Kim In-Tae , Kim Yoon-Ho
Published: March 2008

Microwave dielectric properties of the solid solution between Ba(Ni1/3Nb2/3)O3and Ba(Zn1/3Nb2/3)O3were investigated. Samples were prepared by the conventional mixed oxide method as well as the Pechini method. Sintered samples were analyzed using x-ray diffraction and scanning electron microscopy, and their microwave dielectric properties were measured by the post resonator method. The sample prepared by the Pechini method revealed excellent dielectric properties, i.e., permittivity of 35.6, quality factor of 5700 at 10 GHz, and very small temperature coefficient of resonant frequency. Order-disorder behavior of this solid solution system was found to depend on processing parameters. Variation in microwave dielectric properties was discussed in terms of the order-disorder behavior, chemical composition, mixture rule, etc.
The effect of excess bismuth on the ferroelectric properties of SrBi2Ta2O9 thin films
Authors: Chen Tze-Chiun , Li Tingkai , Zhang Xubai , Desu Seshu B.
Published: March 2008

The effect of excess bismuth on the ferroelectric properties of SrBi2Ta2O9 (SBT) thin films having a perovskite-like layered structure was investigated for excess bismuth contents ranging from 0% to 100%. For the first time, a limited solid solution of SBT and Bi2O3 was shown to exist when the amount of excess Bi was less than 50%. The formation of a solid solution enhanced the grain size and a-b plane orientation of the films, resulting in substantial improvement in the ferroelectric hysteresis properties of the films. On the other hand, when the amount of excess Bi exceeded 50%, Bi2O3 appeared as a second phase which led to high leakage current and poor ferroelectric hysteresis curves. 30–50% excess Bi content was found to be the optimum composition with respect to grain size, crystallographic orientation, and single phase formation. Within this range, SBT films exhibit low leakage current density (˜10−9 A/cm2) and maximum remanent polarization (2Pr ˜12 µC/cm2).
Preparation of Pb(Zr0.52Ti0.48)O3 thin films on Pt/RuO2 double electrode by a new sol-gel route
Authors: Kim Seung-Hyun , Choi Yong-Soo , Kim Chang-Eun , Oh Young-Jei
Published: March 2008

Pb(Zr0.52Ti0.48)O3 (PZT) thin film on Pt/RuO2 double electrode was successfully prepared by using a new alkoxide-alkanolamine, sol-gel method. It was observed that the use of Pt/RuO2 double electrode reduced leakage current, resulting in a marked improvement in the leakage characteristics and more reliable capacitors. Typical P-E hysteresis behavior was observed even at low applied voltage of 5 V, manifesting greatly improved remanence and coercivity. Fatigue and breakdown characteristics, measured at 5 V, showed stable behavior, and no degradation in polarization was observed up to 1011 cycles.
Mechanism of 1:1 nonstoichiometric short-range ordering in La-doped Pb(Mg1/3Nb2/3)O3 relaxor ferroelectrics
Authors: Lee Kyu-Mann , Jang Hyun M. , Park Woo-Jin
Published: March 2008

The mechanism of the 1:1 nonstoichiometric short-range ordering in donor-doped Pb(B′1/3B″1/3)O3-type relaxor perovskites was examined using the La2O3-doped Pb(Mg1/3Nb2/3)O3 (PMN) system as a typical example. Based on the dielectric analysis and the transmission electron microscopy (TEM) observation, the observed increase in the degree of diffuse phase transition (DPT) in the presence of La2O3 was interpreted as the enhancement of the 1:1 nonstoichiometric short-range ordering accompanied with the growth of the negatively charged nanodomains. The mechanism of the defect process responsible for the 1:1 nonstoichiometric short-range ordering was elucidated by analyzing the electrical conductivity of the La-doped PMN system as a function of the partial pressure of oxygen. It was shown that the substitution of La3+ ions for Pb2+ ions in the A-site sublattice of perovskite PMN produced the positively charged sites with a concomitant generation of electrons for the electronic compensation. This expedites the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.
Enhanced diffuse phase transition and defect mechanism of Na-doped Pb(Mg1/3Nb2/3)O3 relaxor ferroelectrics
Authors: Lee Kyu-Mann , Jang Hyun M.
Published: March 2008

The diffuse phase transition (DPT) characteristics and the associated defect mechanism of Na-doped Pb(Mg1/3Nb2/3)O3 (PMN) relaxor perovskite were studied. The enhanced DPT and the decrease in the intensity of the superlattice reflection were observed in the presence of Na2O. These contradictory observations were interpreted in terms of the inhibition of the growth of the 1 : 1 nonstoichiometric short-range ordered domains and the increase in the microcompositional fluctuation of the B-site cations caused by the formation of negatively charged Na′Mg sites. The mechanism of the associated defect process was then elucidated by analyzing the electrical conductivity as a function of the oxygen partial pressure. It was shown that the substitution of Na+ ions for Mg2+ ions in the B-site sublattice of perovskite PMN produced the negatively charged sites with a concomitant generation of oxygen vacancies () for the ionic compensation. This expedites the enhancement of the compositional inhomogeneities of the B-site cations and suppresses the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.
Influence of substrate annealing on the epitaxial growth of BaTiO3 thin films by metal-organic chemical vapor deposition
Authors: Hwang Cheol Seong , Vaudin Mark D. , Stauf Gregory T.
Published: March 2008

BaTiO3 thin films were deposited by metal-organic chemical vapor deposition at 840 °C on two differently treated (100) MgO single crystal substrates. One MgO substrate was only mechanically polished and the other substrate was polished and then annealed at 1100 °C for 4 h in oxygen. Observation by transmission electron microscopy showed that the BaTiO3 thin film deposited on the unannealed substrate was fine-grained and that the whole film was epitaxial (100) in nature. In contrast, the film deposited on the annealed substrate consisted of large, (100)-oriented, epitaxial grains within which were distributed (110)-oriented grains with random in-plane orientations. These differences in BaTiO3 films deposited on differently treated substrates are discussed with reference to the surface structure of the MgO substrate and nucleation kinetics of BaTiO3 thin films on MgO.
Morphological investigations on mesostructured metal oxides
Authors: Weidenhof V. , Gropper F. , Müller U. , Marosi L. , Cox G. , Houbertz R. , Hartmann U.
Published: March 2008

The synthesis and characterization of mesostructured zirconia and titanium oxides are presented. The samples were investigated by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). XRD and TEM revealed only lamellar structures for both materials, whereas AFM could detect locally restricted initial stages of cubic or hexagonal phases in a globally lamellar Ti oxide.
A high-resolution electron microscopy study of blue-light emitting β–SiC nanoparticles in C+-implanted silicon
Authors: Gao Y. H. , Zhang Z. , Liao L. S. , Bao X. M.
Published: March 2008

A high-resolution electron microscopy study of β–SiC nanoparticles formed by C+-implantation of single crystal silicon with subsequent annealing has been carried out. The as-implanted sample had a trilayered structure, in which the surface layer, A, and the bottom layer, C, were crystalline but damaged, and the middle layer, B, was amorphous. After annealing this structure, β–SiC particles were formed throughout the trilayered structure but with different forms: a few epitaxial β–SiC nanoparticles in layers A and C, and more random nanoparticles in layer B. The β–SiC nanoparticles, in the size range 2–8 nm, should be responsible for the blue-emitting effect of the silicon-based porous β–SiC.
Influence of substitutional nitrogen in synthetic saw-grade diamond on crystal strength
Authors: Jackson W. E. , Webb Steven W.
Published: March 2008

The amount and defect type of substitutional nitrogen in synthetic diamond strongly influences crystal strength. There is an optimum amount of nitrogen that yields the highest compressive fracture strength for crystals derived from common growth conditions. It is postulated that the role of nitrogen is to charge-balance vacancies created during growth. If too little nitrogen exists in the diamond, vacancies are not charge-balanced and may serve as crack initiation and/or propagation sites. Excess nitrogen above that required to charge-balance vacancies may weaken the lattice by adding local strain to the crystal. IR microscopy indicates that most of the substitutional nitrogen in synthetic diamond is increased in the vicinity of the intersections of growth sectors on the crystal surface. Most surface IR-visible nitrogen is biased toward the (111)–(100) intersection. The bias in incorporation of substitutional nitrogen at external growth sector intersections (i.e., edges and corners) of an industrial high-grade saw diamond crystal influences the progression of fatigue by microfracture during cutting of hard stone.
Preparation of semiconductive SrTiO3 thin films by metal-organic chemical vapor deposition and their electrical properties
Authors: Nagano Daisuk , Funakubo Hiroshi , Sakurai Osamu , Shinozaki Kazuo , Mizutani Nobuyasu
Published: March 2008

Insulating epitaxially grown SrTiO3 thin films were prepared on (100)MgO substrates by metal-organic chemical vapor deposition (MOCVD). Semiconductive SrTiO3 thin films were obtained by the rapid cooling after reheating in reduction atmosphere. The microstructure, crystal structure, and electrical properties of these films were investigated. The electrical properties varied by the composition of films and heat-treatment conditions, i.e., the heating temperature, the oxygen partial pressure, and the cooling rate after the annealing. Change of the resistivity of the film was attributed to that of the carrier concentration. Mobility of films was unchanged, and the value was almost the same order of that of bulks. The lowest resistivity of 0.1 Ω·cm was obtained when a sample of Ti/Sr = 1.0 was heated at 1200 °C under 10−15 Pa of PO2 and then rapidly cooled. This value is similar to that of bulks (100 –10−1 Ω · cm).
Polyimide degradation induced by irradiation with N+ ions
Authors: Švorčík V. , Miček I. , Rybka V. , Hnatowicz V. , Černý F.
Published: March 2008

The samples of Upilex R polyimide (PI) were irradiated with 90 keV N+ ions to the fluences from 5 × 1014 to 2 × 1017 cm−2, and sheet resistance (Rs) and thermoelectric power (TEP) were measured in dependence on the ion fluence and the sample temperature. The Rs achieves its minimum for the ion fluence of 1 × 1017 cm−2, and from the measured temperature dependence of Rs it may be concluded that the ion beam modified PI exhibits semiconductor properties with charge transport governed by the variable range hopping mechanism. The measured TEP of the PI samples irradiated to the fluences above 1 × 1016 cm−2 is low (the order of μV/K). Such properties are typical for metals, and the conclusion is that the charge transport in the irradiated PI samples is contributed by the mechanisms which are characteristic for both semiconductors and metals. The role of conjugated double bonds was examined by measuring absorption UV-VIS spectra. The number of the conjugated double bonds correlates with observed Rs, and the width of the forbidden band, determined from UV-VIS spectra, is a decreasing function of the ion fluence.
Refinement of Nd-422 Phase Trapped in a Nd1+δBa2−δCu3O7−y Superconducting Matrix
Authors: Frangi F. , Yoo S. I. , Sakai N. , Murakami M.
Published: March 2008

The possibility of controlling Nd-422 phase dimension and morphology, both in the partially melted state and in the final superconducting matrix, was investigated. Nd–Ba–Cu–O samples were prepared by the melt powder melt growth (MPMG) technique. Precursor materials containing Nd as either Nd2O3 or Nd-422, formed during precursor quenching, were used. The role of Pt in Nd-422 refining was analyzed. The effect on Nd-422 nucleation and growth, of stoichiometries with increasing Nd-422 molar excesses (0%, 10%, 20%, and 40%) combined with different heating processes, up to the partially melted state, were examined. Uniformly distributed needle-like particles (1 μm diameter and 10–15 μm length) were obtained at 1120 °C and resulted in a further refined distribution trapped in completely processed samples.
Modeling of Peritectic YBa2Cu3O7−x Growth Using Transparent Organic Analogues
Authors: Terborg R. , Schmitz G. J.
Published: March 2008

Transparent organic analogues were directionally solidified to investigate, via in situ observation the peritectic reaction occurring in the YBa2Cu3O7−x (YBCO)-superconductor system. Nucleation and growth of peritectic and properitectic phases were examined with respect to similarities with the solidification of the YBCO superconductor. The selected organic system, salicylic acid-acetamide, turned out to match the requirements concerning crystal shape, small nucleation rate of the peritectic phase on the properitectic phase, existence of stoichiometric phases with no solubility limits, and undercooling ability of the peritectic phase. Several features of YBCO growth which were previously deduced only from metallographic cross sections could be verified by direct observation. The organic analogue system will also be used in the future to improve numerical simulations.
Low Energy Ion Impact-enhanced Growth of Cubic Boron Nitride in a Supersonic Nitrogen/argon Plasma Flow
Authors: Berns D. H. , Cappelli M. A.
Published: March 2008

This paper describes the growth and analysis of cubic boron nitride films in a low-density, supersonic nitrogen/argon plasma flow into which boron trichloride gas was injected. Both hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN) were synthesized using this apparatus. Phase selectivity is obtained by applying a relatively low negative bias voltage to the substrate. All of the films described in this paper were grown on {100} silicon wafers at substrate temperatures varying from 400–700 °C. Boron nitride films with greater than 90% cubic phase were successfully synthesized with this method. The films were analyzed using infrared spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. The volumetric percentages of the hexagonal and cubic phases were determined from model fits to the infrared transmission spectra of the films. X-ray photoelectron spectroscopy provided qualitative evidence for the presence and/or lack of sp2 bonding through the identification of a π-plasmon feature in the spectra. Infrared reflectance spectra are used to provide insight into the growth mechanisms leading to c-BN formation and have revealed features which are not present in the transmission spectra, specifically the 1305 cm−1 LO mode of c-BN and the 1610 cm−1 LO mode of h-BN. The mean ion energies involved with this bias-enhanced chemical vapor deposition (CVD) process are much lower than the ion energies in traditional physical vapor deposition (PVD) processes; however, the ion fluxes (currents) used in this CVD process are at least an order of magnitude higher, resulting in a total momentum transfer to the deposited atoms through ion bombardment that is at least equal to or greater than that reported for many ion-enhanced PVD processes.
Quantitative Analysis of Electromigration Damage in Al-based Conductor Lines
Authors: Kraft O. , Sanchez J. E. , Bauer M. , Arzt E.
Published: March 2008

Electromigration damage in Al-based interconnects with three compositions (pure Al, Al–1%Si–0.5%Cu, and Al–2%Cu) was studied quantitatively. Using scanning electron microscopy, the spacings between more than 1000 voids and hillocks were measured. The distribution of the spacings was found to be a function of the composition, the applied current density, and the linewidth. The measurements confirm the existence of a threshold product of current density and diffusion length. In particular, a dependence of this threshold product on the Cu content was found. The results of the analysis show that there are clear correlations between the details of the microscopic damage processes and the lifetime of the conductor lines.
Characterization of Low-cycle Fatigue Damage in Inconel 718 by Laser Light Scanning
Authors: Chou K. J. C. , Earthman J.C.
Published: March 2008

A technique for in situ laser light scanning (LLS) was developed to monitor surface damage on nickel-base superalloy specimens under low-cycle fatigue conditions. This technique characterizes the surface state with a parameter called the defect frequency which minimizes memory requirements and data processing time since it does not involve image processing. As a result, the present technique is capable of scanning speeds that are substantially greater than those achieved with image processing methods. Cylindrical Inconel 718 specimens were tested using an automated servo-hydraulic machine at ambient temperature under fully reversed strain control conditions for constant strain amplitudes ranging from 0.3% to 1%. The fatigue damage was monitored by scanning a laser beam along the gauge section of the specimens during periodic interruptions of the cyclic loading. Acetate replicas of the gauge section surface were also made on some of the specimens to characterize the damage using SEM and image analysis techniques. Comparisons of the results demonstrate the capabilities of the present light-scanning technique for characterizing fatigue damage on the surface of the Inconel 718 specimens. In particular, a rapid rise in the mean defect frequency is shown to correspond to an initial increase in microcrack density that saturates at approximately 20% of the fatigue life. This transient behavior is followed by a plateau in defect frequency which corresponds to crack propagation and interlinkage until failure occurs. The number of cycles to microcrack density saturation as indicated by the defect frequency is found to be linearly related to the number of cycles to failure. Accordingly, the present system provides a characterization of microcrack damage that may be used to predict the low-cycle fatigue life of Inconel 718 specimens long before failure occurs.
Contact Area Evolution During an Indentation Process
Authors: Li Kangjie , Wu T. W. , Li J. C. M.
Published: March 2008

The evolution of the contact area during an indentation process has been xamined by an ac technique and also by finite element analysis on five mechanically different materials. Constant contact area regimes were observed during the initial unloading stage and the duration of that regime depends strongly on material properties. The consistency of the results obtained by the two approaches not only proves the validity and advantage of the ac indentation technique but also confirms the applicability of contact stiffness equation. The influence of a hardness impression on unloading characteristics has also been clearly demonstrated by numerically simulating a reloading process.
Formation of Single-crystal CoSi2 Buffer Layers on Si(100) Substrates by High Dose Co Ion Implantation for the Deposition of YBa2Cu3O7−x Thin Films
Authors: Li Yijie , Seidel P. , Machalett F. , Linzen S. , Schmidl F.
Published: March 2008

High quality single-crystal CoSi2 layers have been successfully formed on Si(100) using low energy high dose Co ion implantation followed by subsequent annealing method as a buffer layer for the deposition of YBa2Cu3O7−x (YBCO) thin films. Rutherford backscattering spectrometry with channeling (RBS-C) measurements showed that CoSi2 layers after annealing at temperatures between 850 and 950 °C had a minimum yield Xmin of about 3%. X-ray diffraction (XRD) spectra revealed that CoSi2 layers had the same orientation as the Si(100) substrates. Phi scan XRD spectra proved that CoSi2 layers epitaxially grew in the cube-on-cube epitaxial growth mode with respect to the Si(100) substrates. YBCO films and CeO2/YSZ buffer layers were deposited on CoSi2/Si(100) substrates via laser ablation and electron beam evaporation, respectively. θ-2θ, ω, and φ scan XRD spectra illustrated that YBCO films and CeO2/YSZ buffer layers had the epitaxial structure both in a-b plane and along the c-axis. YBCO films grown on this multilayered structure demonstrated excellent superconducting properties with the zero resistance transition temperature Tc0 of 87–90 K. The transition width (ΔTc) was about 1 K. Orientation and epitaxial crystalline quality of YBCO films and CeO2/YSZ buffer layers were confirmed by XRD and RBS-C characterization. All films consisted of c-axis oriented grains. RBS-C spectra indicated a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 8%, and interdiffusion between the YBCO film and buffer layers or between the YBCO film and the substrate was limited. This multilayer system shows the possibility for the application of YBa2Cu3O7−x thin films on technical Si substrates in the field of hybrid superconductor-semiconductor technology.
Secondary Phase Formation and Microstructural Development in the Interaction Between SrBi2Ta2O9 Films and Pt/Ti/SiO2/Si Substrates
Authors: Lu Chung-Hsin , Fang Buh-Kuan
Published: March 2008

The phase formation and microstructural development of SrBi2Ta2O9 thin films prepared via spin-coating using metalorganic solution on Pt/Ti/SiO2/Si substrates have been investigated in this study. The spun-on films started to crystallize from above 550 °C and were well crystallized at 800 °C. At higher than 850 °C a secondary phase having a pyrochlore structure was formed in the films. The analysis of EDS and SIMS confirmed that the interaction between the films and the titanium species which diffused outward from the titanium layer on substrates was the origin for the occurrence of the pyrochlore phase. In addition, varying the thickness of the coated films and platinum layers had remarkable influence on the formation amount of the pyrochlore phase.
Pb()O3-type Perovskites: Part I. Pair-correlation Theory of Order-disorder Phase Transition
Authors: Jang Hyun M. , Kim Su-Chan
Published: March 2008

The limitation of the long-range order parameter and the necessity of the short-range order parameter for the thermodynamic description of Pb()O3-type perovskites are discussed. Based on the discussion, a statistical thermodynamic model that takes into account the configuration of the neighboring B-site ions (B′ and B″ cations) was developed. A pair-correlation approximation was used in the calculation of the configurational entropy and the long-range coulombic interaction energy between the nearest B-site ions. The theoretical calculations using Pb(Sc1/2Ta1/2)O3 (PST) and Pb(Sc1/2Nb1/2)O3 (PSN) systems indicate that the short-range order parameter persists over a wide range of temperatures examined (0–1800 K) and that there possibly occur consecutive long-range order-disorder transitions in the configuration of B-site cations. The possibility of the existence of short-range ordering above the long-range order-disorder transition temperature was also examined using the annealed PSN specimen as a typical example of Pb()O3-type perovskites.
Characterization of the Induced Plastic Zone in a Single Crystal TiN(001) Film by Nanoindentation and Transmission Electron Microscopy
Authors: Odén Magnus , Ljungcrantz Henrik , Hultman Lars
Published: March 2008

The slip system of TiN at room temperature has been determined to be {110} 〈110〉 by Burgers vector analysis using transmission electron microscopy and slip trace analysis of indents made on a TiN(001) film deposited on a MgO(001) substrate. Both small indents (0.4 mN maximum load) and large indents (40 mN maximum load) were used to study the dislocation structure in TiN. The nucleation of dislocations was investigated using small indents. Further development of the plastic zone was studied using large indents and microhardness indents (1.6 N). The critical resolved shear stress evaluated at the load when pop-in occurs was estimated to be 3.7 GPa, assuming a Hertzian elastic contact. Indents made with a 0.4 mN maximum load show a complex dislocation pattern with loops and straight segments that belong to the same slip system. Dislocations of mixed screw and edge type are dominant. The cascade of dislocations generated during pop-in is likely to nucleate from loops. For larger indents, the plastic zone extends more than three times the diameter of the imprint. The straight dislocations outside the large imprint are arranged in arrays along the 〈100〉 and 〈110〉 directions. A scanning force microscopy study of the surface outside a microhardness indent revealed a raised surface along 〈110〉 and formation of troughs along 〈100〉.
Structural Characterization of Fe3O4–NiO Superlattices Using High-reSolution Transmission Electron Microscopy
Authors: Rečnik A. , Carroll D. L. , Shaw K. A. , Lind D. M. , Rühle M.
Published: March 2008

Superlattices of Fe3O4–NiO layers have been studied by high-resolution transmission electron microscopy (HRTEM). These superlattices are grown by oxygen-plasma-assisted molecular-beam epitaxy (MBE) on (001) oriented MgO substrates, and exhibit a high degree of ordering at the interfaces between the interlayers. The lack of misfit dislocations at the Fe3O4–NiO interfaces suggeststhat lattice strain is largely accommodated by changes in the lattice spacing. By quantitative HRTEM analysis of Fe3O4–NiO interfaces, possible atomic models are discussed, having implications in magnetic ordering and spin exchange mechanisms for such interlayer systems.
Effects of (100)-textured LaNiO3 Electrode on the Deposition and Characteristics of PbTiO3 Thin Films Prepared by rf Magnetron Sputtering
Authors: Wu Chii-Ming , Hong Tian-Jue , Wu Tai-Bor
Published: March 2008

Highly (100)-oriented thin films of PbTiO3 were prepared on (100)-textured LNO/Pt/Ti/SiO2/Si substrates by rf magnetron sputtering at temperatures ≥480 °C, while randomly oriented PbTiO3 films were obtained on Pt/Ti/SiO2/Si substrates. The textured LNO layer can help to control the orientation of PbTiO3 thin films, and reduce their surface roughness quite significantly. The dielectric constant (εT) of PbTiO3 films deposited on LNO was lower than that of films on Pt and the dielectric loss (tan δ) increased when a higher deposition temperature or longer time was used. The highly (100)-textured PbTiO3 films also showed different ferroelectric hysteresis characteristics, i.e., a higher coercive field and a lower remanent polarization, from that of randomly oriented films deposited on Pt.
Structure Development Studies of SrBi2(Ta1−xNbx)2O9 Thin Films
Authors: Chen Tze-Chiun , Li Tingkai , Zhang Xubai , Desu Seshu B.
Published: March 2008

In this research, two tasks were pursued: (1) determination of the onset temperature of ferroelectric hysteresis properties of SrBi2Ta2O9 thin films by structure development study, and (2) low temperature processing for thin film fabrication. For task (1), a nondestructive optical method using spectroscopic ellipsometry was utilized for characterizing the structure development of SrBi2Ta2O9 thin films. The optical constants and film thickness were measured as a function of annealing temperature by spectroscopic ellipsometry. By observing the changes in refractive indices and film thickness, the temperatures of phase transformation and grain growth were determined. Consistent results were obtained from x-ray diffraction measurements. By comparing the results of the structure development study and ferroelectric hysteresis properties investigation, the onset temperature of the hysteresis curve of SrBi2Ta2O9 with 50% excess Bi was determined to be about 700 °C. The critical factor for the compound to exhibit a well-defined hysteresis curve was found to be the grain size. For task (2), the effects of excess Bi content and Nb/Ta ratio of SrBi2(Ta1−xNbx)2O9 on the ferroelectric hysteresisproperties were studied. It was found that the onset temperature for obtaining well-defined hysteresis properties can be reduced by adding excess Bi or increasing Nb/Ta ratio. By choosing SrBi2Nb2O9 with 50% excess Bi, the onset temperature of the hysteresis curve was reduced to about 650 °C.