bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for making substrate-independent hardness measurements of soft metallic films on hard substrates by nanoindentation
Authors: Tsui Ting Y. , Ross C. A. , Pharr G. M.
Published: March 2008

A new method for making substrate-independent hardness measurements by nanoindentation techniques that applies to soft metallic films on very hard substrates is presented. The primary issue to be addressed is substrate-induced enhancement of indentation pileup and the ways it influences the indentation contact area. On the basis of experimental observations of soft aluminum films deposited on silicon, glass, and sapphire substrates, an empirical relationship was derived that relates the amount of pileup to the contact depth. From this relationship and the associated experimental observations, a method was developed that allows the intrinsic hardness of the film to be estimated, even when the indenter penetrates through the film into the substrate. The method should prove useful for very thin films (<100 nm) in which it is not possible to make measurements at penetration depths small enough to avoid subtrate effects.
Controllable synthesis of palladium nanoparticles via a simple sonoelectrochemical method
Authors: Qiu Xiao-Feng , Xu Jin-Zhong , Zhu Jian-Ming , Zhu Jun-Jie , Xu Shu , Chen Hong-Yuan
Published: March 2008

A simple pulse sonoelectrochemical technique was used to synthesize highly dispersed spherical palladium particles and a dendritic Pd superstructure in the presence of cethyltrimethylammonium bromide (CTAB) at room temperature. The shape and size of spherical nanocrystalline Pd can be controlled by varying current density, the interval between two continuous ultrasonic pulses, ultrasonic intensity, and the concentration of CTAB. The possible growth mechanism of dendritic-structured Pd is discussed.
Role of Pb excess in the crystallization of lead zirconate titanate films derived via sol-gel processing
Authors: Jacobs Randolph N. , Salamanca-Riba L.
Published: March 2008

Sol-gel spin coating of lead-titanate films differs from most processing routes, such as metalorganic chemical vapor deposition and pulsed laser deposition, in that crystallization cannot occur without a postdeposition annealing step. This work focuses on the annealing of sol-gel-derived PbZrTiO3 films on LaAlO3 substrates in attempts to identify the precise conditions necessary to grow films of quality similar to that obtained through other techniques. In particular, the effects of Pb excess (in precursor solutions), annealing times, and temperature were investigated through transmission electron microscopy and four-circle x-ray diffraction. The significance of this work is in the direct observation of the correlation between Pb excess and film crystallization. It is shown that the effects of Pb excess on the completeness of film crystallization become more dramatic at lower annealing temperatures, even while epitaxial quality is maintained.
Determination of reactive wetting properties of Sn, Sn–Cu, Sn–Ag, and Sn–Pb alloys using a wetting balance technique
Authors: Chang Hsiu-yu , Chen Sinn-wen , Wong David Shan-hill , Hsu Hsiu-Feng
Published: March 2008

Wetting properties of lead-free solders, Sn–0.7 wt.% Cu and Sn–3.5 wt.% Ag, pure Sn, and conventional Sn–40 w.t% Pb on Ni, Cu, and Ag substrates at 250 and 240 °C were determined by using a wetting balance technique. Wetting times and wetting forces were determined directly from the wetting curves, and surface tensions of molten solders were calculated from the wetting force measurements. A statistic tool, analysis of variance (ANOVA), was used to analyze the experimental results. By using the wetting time as an indication, it was found that Sn–Pb exhibited the best wetting followed by Sn–Ag, Sn–Cu, and Sn, in that order. A very significant but frequently ignored issue is that most solders react with substrates, and the molten solders are not in contact with the original substrates but rather with intermetallic compounds. On the basis of theoretical analysis and experimental observations, it was concluded that the withdrawing forces and the surface tensions of the molten solders determined by the present technique are not significantly affected by the interfacial reactions if the interfacial reactions are not too excessive. However, wetting times are strong functions of both solders and substrates and the interfacial reactions between them.
Thermal stability of sputtered copper films containing dilute insoluble tungsten: Thermal annealing study
Authors: Lin C. H. , Chu J. P. , Mahalingam T. , Lin T. N. , Wang S. F.
Published: March 2008

This paper describes studies on the thermal annealing behavior of Cu films with 2.3 at.% W deposited on Si substrates. The magnetron cosputtered Cu films with insoluble W were vacuum annealed at temperatures ranging from 200 to 800 °C. Twins were observed in focused ion beam and transmission electron microscopy images of as-deposited and 400 °C annealed pure Cu film, and these twins were attributed to the intrinsic low stacking fault energy. Twins in pure Cu film may provide an additional diffusion path during annealing for copper silicide formation. The beneficial effect of W on the thermal stability of Cu film was supported by the following observations: (i) x-ray diffraction studies show that Cu4Si was formed at 530 °C in Cu–W film, whereas pure Cu film exhibited Cu4Si growth at 400 °C; (ii) shallow diffusion profiles for Cu into Si in Cu–W film through secondary ion mass spectroscopy analyses, and the high activation energy needed for the copper silicide formation from the differential scanning calorimetry study; (iii) addition of W in Cu film increases the stacking fault energy and results in a low twin density.
Modeling of effects of adhesive interlayers on contact-induced radial cracking in brittle coatings on substrates
Authors: Hsueh Chun-Hway , Kim Jong Ho , Kim Do Kyung
Published: March 2008

The effects of soft adhesive interlayers on contact-induced radial cracking in brittle coatings on supporting substrates were investigated recently. A semiempirical equation for the critical load to initiate radial cracking was derived, which used three fitting parameters obtained by comparison with the finite element results. An analytical model is derived in the present study to illustrate the effects of adhesive interlayers. This is achieved by adopting the analogy between the coating/substrate system and a plate on an elastic foundation. In the presence of an adhesive interlayer, the interlayer/substrate bilayer is treated as the effective elastic foundation. The effective modulus of foundation for the bilayer is derived, and the solution for coating/interlayer/substrate systems can be obtained from the existing solution for coating/substrate systems by replacing the modulus of foundation. Specific results are calculated for critical loads to initiate radial cracks in silicon coatings bonded by adhesive interlayers of different materials and thicknesses to glass substrates. The present analytical solution provides an alternative other than the existing semiempirical equation in predicting the effects of adhesive interlayers.
Mechanical properties of Fe-based bulk glassy alloys in Fe–B–Si–Nb and Fe–Ga–P–C–B–Si systems
Authors: Inoue A. , Shen B. L. , Yavari A. R. , Greer A. L.
Published: March 2008

Mechanical properties of cast Fe-based bulk glassy alloy rods with compositions of (Fe0.75B0.15Si0.1)96Nb4 and Fe77Ga3P9.5C4B4Si2.5 were examined by compression and Vickers hardness tests. The Young's modulus (E), yield strength (σy), fracture strength (σf), elastic strain (εe), fracture strain (εf), and Vickers hardness (Hv) were 175 GPa, 3165 MPa, 3250 MPa, 1.8%, 2.2%, and 1060, respectively, for the former alloy and 182 GPa, 2980 MPa, 3160 MPa, 1.9%, 2.2%, and 870, respectively, for the latter alloy. The εf /E and Hv/3E were 0.019–0.017 and 0.020–0.016, respectively, for the alloys, in agreement with the previous data for a number of bulk glassy alloys. The agreement suggests that these Fe-based bulk glassy alloys have an elastic–plastic deformation mode. The syntheses of high-strength Fe-based bulk glassy alloys with distinct compressive plastic strain and elastic–plastic deformation mode are encouraging for future development of Fe-based bulk glassy alloys as structural and soft magnetic materials.
Nanoscale continuous In2O3 coating on phosphor particles for improved low-voltage cathodoluminescent properties
Authors: Kim Jin Young , You Yong Chan , Kang Jong Hyuk , Jeon Duk Young , Yu Il
Published: March 2008

A nanoscale continuous coating of In2O3 on phosphors for low-voltage display applications is proposed in which the electrical conductivity of phosphor screen plays a major role. The effect of In2O3 coating by the sol-gel method on the cathodoluminescence (CL) of ZnGa2O4:Mn phosphors improves the intensity of low-voltage CL noticeably compared with that of In2O3 mixing. It is understood that electrically conductive channels are formed by a much smaller amount of In2O3 addition than that of In2O3 mixing. Especially, based on transmission electron microscopy analysis, the formation of uniform nanoscale continuous In2O3 layers on the phosphor surface was confirmed. Also, the structural and CL characterizations presented in this paper clearly demonstrate that the nanoscale encapsulation of In2O3 layers on phosphors served as protective layers retarding the CL degradation introduced by the low-energy electron irradiation, which is critically important for the development of low-voltage display applications.
Sputter-deposition and characterization of paramelaconite
Authors: Blobaum K. J. , Van Heerden D. , Wagner A. J. , Fairbrother D. H. , Weihs T. P.
Published: March 2008

While processing techniques for deposition of CuOx/Al multilayer foils were being developed, a method for synthesizing paramelaconite (Cu4O3) was serendipitously discovered. These paramelaconite films were successfully synthesized by sputter-deposition from a CuO target. Milligram quantities of uncontaminated material were produced enabling new studies of the morphology, stoichiometry, and thermodynamics of this unique copper oxide. At moderate temperatures, equiaxed paramelaconite grains deposited with a strong out-of-plane texture; at lower temperatures the paramelaconite grains showed no texture but were columnar in geometry. X-ray photoelectron spectroscopy showed that the as-deposited Cu4O3had a nonstoichiometric Cu:O ratio of 1.7:1; the ratio of Cu+to Cu2+was 1.8:1. On heating, this phase decomposed into CuO and Cu2O at temperatures ranging from 400 to 530 °C. Using differential scanning calorimetry, the heat of formation and Gibbs free energy for Cu4O3were estimated to be −453 and −279 kJ/mol, respectively. On the basis of these calculations and our observations, we confirmed that Cu4O3is a metastable phase.
Electrodeposition of diamondlike carbon films on nickel substrates
Authors: Chen Alex Minhua , Pingsuthiwong Charoendee , Golden Teresa Diane
Published: March 2008

Diamondlike carbon (DLC) films were electrodeposited on nickel substrates from a solution of acetylene in liquid ammonia at low temperature and low potential using a three-electrode cell. Raman spectra showed a shoulder D peak at 1365 cm−1and a broad G peak at 1558 cm−1for the films, indicating ansp3andsp2carbon mixture. The presence of a 1230 cm−1peak also indicated some four-fold-coordinated bonds of microcrystalline diamond. Fitting of the peaks in the Raman spectra specified the electrodeposited films were hydrogenated amorphous alloys, a-C:H. X-ray photoelectron spectra also pointed to the films containing a mixture ofsp3andsp2carbon. Fourier transform infrared spectra of the electrodeposited films had C-H stretching vibrations, which is consistent with hydrogenated DLC films.
Microstructure characterization of oxide coatings deposited by pulsed excimer laser ablation
Authors: Jilavi M.H. , Kriven W.M. , Chung H. , Mazumder J.
Published: March 2008

This work addresses the issues of coating of oxide fibers or laminates with debondable oxide interphases. It fabricates a model system for an alumina matrix reinforced with alumina fibers, wherein an enstatite interphase is transformation weakened, resulting in interphase debonding. A suitable multilayer coating sequence was chosen to act as a chemical bridge between the alumina fiber and matrix. The pulsed excimer laser ablation method (KrF excimer laser of λ = 248 nm) was used to deposit several oxide materials individually onto silicon wafers. Titania (TiO2or T), aluminum titanate (Al2O3· TiO2,Al2TiO5or AT), and enstatite (MgO · SiO2, MgSiO3or EN) layers were deposited from sintered target materials. X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy investigations indicated that as-deposited coatings were amorphous or partially crystallized into nanosize grains, and their thicknesses were uniformly distributed over the Si-substrate, growing in columnar texture (although not as pronounced for enstatite). Transmission electron microscopy/energy dispersive spectroscopy analysis confirmed that the chemical composition of the coating materials was the same as that of the target materials and that the coatings were completely crystallized into nano- or submicrometer grain size after annealing at 1200 °C for 1 h. With these data, sapphire monofilaments were sequentially coated with five layers of Al2TiO5, TiO2, MgSiO3, TiO2, and Al2TiO5. This construction provided a chemical bridge between the alumina monofilament and the enstatite debondable interphase.
Mechanism and an empirical model of the fixed abrasivepolishing process on a web-format tool
Authors: Venigalla Rajasekhar , Economikos Laertis , Babu S. V.
Published: March 2008

Several chemical–mechanical planarization characterization test wafers were polished to understand the polishing mechanism of the fixed abrasive process. Oxide thickness removal in the “active” (up) and the “recessed” (down) regions of the wafer was monitored for different times of polish. It was found that there was no significant removal in the recessed areas until the step height was reduced to about 100 Å, and the polish rate in the active area decreased rapidly once this critical step height had been attained. At this critical step height, the polish rate of the down areas started to increase and approached that of the up area, with both eventually reaching the negligibly low removal rate of the blanket wafer. The drop in the polish rate of the up area, after planarity had been attained, was fitted to an exponential model.
High-density aligned carbon nanotubes with uniform diameters
Authors: Cao P. J. , Gu Y. S. , Liu H. W. , Shen F. , Wang Y. G. , Zhang Q. F. , Wu J. L. , Gao H. J.
Published: March 2008

A new method was found to synthesize large-area (7 × 15 mm2), high-density (higher than 109 cm−2), aligned carbon nanotubes (CNTs) with uniform diameters on a silica wafer. Ferrocene/melamine mixtures were pyrolyzed through a three-step process in an Ar atmosphere in a single-stage furnace. The structure and composition of the CNTs were investigated by scanning electron microscopy, transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS). It was found that these nanotubes have uniform outer diameters of about 22 nm and varying lengths from 10 to 40 μm. High-resolution TEM images showed that CNT is composed of graphite-like layers arranged in a stacked-cup-like structure. XPS results showed that the layer covering the tops of the aligned CNTs consists of carbon and iron. The EELS spectrum showed that these tubes are pure carbon.
Tailoring of the self-organized structure of sulfonated polyaniline from a fibrillar network to a colloidal aggregate
Authors: Jana Tushar , Nandi Arun K.
Published: March 2008

Self-organized structures of the sodium salt of sulfonated polyaniline (prepared from the leucoemeraldine base of polyaniline) in the presence of a mixture of cationic and nonionic surfactants were studied. It was used in the latex form, which has been prepared using a conventional method with sodium dodecyl sulfate. The cationic surfactant used was didodecyl dimethyl ammonium bromide, and the nonionic surfactant used was Triton-X-100. The supramolecular organization was made in aqueous medium by varying the concentrations of the components. A three-dimensional fibrillar network and colloidal aggregate were produced due to the supramolecular organization. The thermal study indicated reversible first-order phase transition in the former cases fulfilling the criteria of thermoreversible gels. A probable explanation of the different morphology from the variation of charge density on the vesicle surface has been offered. The conductivity of fibrillar network is two orders higher than that of the colloidal aggregate.
Photoinduced formation of colloidal Au by a near-infrared femtosecond laser
Authors: Zhao Chongjun , Qu Shiliang , Qiu Jianrong , Zhu Congshan
Published: March 2008

A Au colloid was prepared in a 5 mM HAuCl4solution through irradiation with a focused infrared femtosecond laser at 800 nm. The Au colloid was characterized by absorption spectra, transmission electron microscopy, and x-ray diffraction analysis. The appearance of absorption peak around 526 nm in the absorption spectra and the wine-red color of sample solution HAuCl4under focused laser irradiation verified the formation of Au colloid. The solution color changed in the order of yellow → orange → wine-red due to the local formation of Au nanoparticles near the focus. The pulse energy, focus position of laser beam, and solvent composite play important roles in formation, grain size, and stability of the Au colloid. A mechanism for the precipitate of Au nanoparticles was proposed, and a multiphoton process of femtosecond laser was involved.
Anisotropic thermal expansion in yttrium silicate
Authors: Fukuda Koichiro , Matsubara Hiroyuki
Published: March 2008

In this study, crystals of Y2SiO5 were examined by high-temperature powder x-ray diffractometry to determine the changes in unit-cell dimensions with temperatures up to 1273 K for the X1 phase (the low-temperature phase, space group P121/c1) and 1473 K for the X2 phase (the high-temperature phase, space group I12/a1). The lattice deformations of both phases induced by thermal expansion were investigated by matrix algebra analysis to determine the directions and magnitudes of the principal distortions (λi, i = 1, 2, and 3). For the X1 phase, λ1 and λ2 invariably showed a positive thermal expansion. On the other hand, λ3 showed a negative thermal expansion below 1173 K; the maximum contraction of 0.10(4)% occurred at 685 K. The λ2 axis invariably coincides with the crystallographic b axis. The directions of λ1 and λ3, defined by the acute angle λ3 ^ c changed between 53(3)° (T = 394 K) and 45(1)° (T = 788 K). For the X2 phase, all of the principal distortions steadily increased with increasing temperature. The angle λ3 ^ c steadily decreased from 71(2)° to 62.1(1)° with increasing temperature. The mean linear thermal expansion coefficients were, when compared at the same temperatures, necessarily higher for the X1 phase than for the X2 phase. The lattice change of X1–RE2SiO5 (RE = Y and Yb–La), which was induced by the substitution of rare-earth (RE) ions, showed a striking resemblance with the lattice deformation of X1-Y2SiO5, which was caused by the thermal expansion. Because the lattice change of the former must be caused by the isotropic expansion of the RE sites, the anisotropic thermal expansion of the latter would be essentially attributable to the isotropic thermal expansion of the YO9 and YO7 polyhedron.
Suppression of pyrochlore phase formation in Sr0.7Bi2.4Ta2O9 thin films using nanoseed layer
Authors: Jung Se-Yeon , Hwang Seung-Joon , Sung Yun-Mo
Published: March 2008

A Sr0.7Bi2.4Ta2O9 (SBT) seed layer approximately 40 nm thick was formed on Pt/Ti/SiO2/Si substrates, and SBT thin films with the same chemical composition were deposited on the substrates with and without seed layer using sol-gel and spin coating methods. The influence of seed layer on the phase formation characteristics of SBT thin films was investigated using x-ray diffraction and scanning electron microscopy analyses. Formation of pyrochlore as well as Aurivillius phase was observed in both the unseeded and seeded SBT films heated at 740 °C. However, it was revealed that Aurivillius phase formation was enhanced in seeded SBT thin films and pyrochlore phase formation was highly suppressed. In this study, two possible mechanisms for the suppression of pyrochlore phase formation were proposed from the perspectives of activation energy difference between Aurivillius and pyrochlore phase formation, and Bi-ion diffusion to pyrochlore phase.
Enhanced hydrogen sorption capacities and kinetics of Mg2Ni alloys by ball-milling with carbon and Pd coating
Authors: Janot R. , Aymard L. , Rougier A. , Nazri G. A. , Tarascon J. M.
Published: March 2008

Solid-state hydrogen storage alloys are becoming a practical method to transport and utilize hydrogen as fuel for various technologies. In this paper, the kinetics and capacity of hydrogen desorption from Mg-based alloys have markedly been enhanced by tuning the surface composition of alloy particles. Mg2Ni–Ct, x composites (where t refers to the pregrinding time and x to the Brunauer–Emmet–Teller specific surface area) were prepared by ball-milling the alloy in the presence of preground graphite, and Pd-coated Mg2Ni alloy powders were obtained by controlled chemical deposition of Pd on the alloy surface. We have found that the optimization of the pregrinding step of carbon is a determinant factor in enhancing the hydrogen desorption capacity of the Mg2Ni–10 wt.% C10,320 composites to 2.6 wt.% at 150 °C, the maximum performance so far reported on desorption for Mg-based alloys. Such value can even be raised to 2.8 wt.% by applying Pd deposition on the composite.
Effect of oxygen partial pressure during pulsed laser deposition on the orientation of CeO2 thin films grown on (100) silicon
Authors: Choi Woong , Sands Tim
Published: March 2008

The effect of oxygen partial pressure on the preferred orientation of CeO2 thin films was investigated by depositing CeO2 thin films and Pb(Zr, Ti)O3/CeO2 multilayers on Si (100) substrates by pulsed laser deposition. CeO2 thin films exhibited random polycrystalline grain structures at high oxygen partial pressure (≥40 mtorr), a result that is contrary to previous reports. The relationship of the preferred orientations observed between Pb(Zr, Ti)O3 films and the CeO2 layer underneath confirmed that random polycrystalline CeO2 was obtained at high oxygen partial pressure. It was suggested that x-ray diffraction data in previous reports might have been misinterpreted.
Effect of lanthanum on the piezoelectric properties of lead zirconate titanate–lead zinc niobate ceramics
Authors: Lee Seung-Ho , Yoon Chang-Bun , Seo Seung-Beom , Kim Hyoun-Ee
Published: March 2008

The effect of lanthanum (La) addition on the piezoelectric properties of lead zirconate titanate–lead zinc niobate (PZT–PZN) was investigated. When small amounts of La were added to the 0.82PZT–0.18PZN, the phase of the specimen changed from rhombohedral to tetragonal and the grain size was steadily reduced. To retain the morphotropic phase boundary (MPB) condition of the specimens with La contents of up to 4 mol%, the Zr/Ti ratio in the PZT was increased to 54/46. When more than 5 mol% La was added, pyrochlore phases were formed, and the piezoelectric properties were reduced. Therefore, the optimum piezoelectric properties (d33 = 545 pC/N, kp = 0.64, and s33 = 0.39% at 2 kV/mm) were observed in the specimen having MPB composition and with an La content of 4 mol%.
Oxide reduction and sintering of Fe–Cr alloy honeycombs
Authors: Nadler Jason H. , Sanders Thomas H. , Speyer Robert F.
Published: March 2008

H2 reduction and densification of extruded Fe2O3–Cr2O3 mixtures with honeycomb geometry (0.3-mm wall thickness) were studied using dilatometry, x-ray diffraction, and scanning electron microscopy. Reduction of pure Fe2O3 heated at 5 °C/min was completed by approximately 525 °C. Two separate sintering steps ensued, well separated in temperature from reduction, one associated with elimination of pores between Fe agglomerates (750–900 °C), and the other associated with sintering of these agglomerates (995–1275 °C). With increasing Cr2O3 content, sintering was increasingly delayed until initiation of Cr2O3 reduction above 1000 °C. The α → γ iron phase transformations were consistent with the Fe–Cr phase diagram, but the γ → α transformations at higher temperatures deviated from the phase diagram because of the influence of impurities (Si, Ca) in the solid solution. Pure Cr2O3 honeycomb formed an approximately 35-μm-thick porous Cr coating that imposed a diffusion barrier to further reduction. The high vapor pressure of chromium prohibited compositions in excess of 25 wt.% Cr2O3 from full reduction and densification.
Interfacial evolution between Cu and Pb–free Sn–Zn–Ag–Al solders upon aging at 150 °C
Authors: Cheng Shou Chang , Lin Kwang Lung
Published: March 2008

The interfacial intermetallic formation at 150 °C between Cu and various solders, including Sn–9Zn, Sn–8.55Zn–1Ag, and Sn–8.55Zn–1Ag–XAl was investigated. The Al contents X of the quaternary solder alloys investigated were 0.01–0.45 wt.%. The compositions and the growth kinetics of intermetallic compounds (IMCs) were investigated. The IMC consisted of three layers for Sn–9Zn/Cu, Sn–Zn–Ag/Cu, and Sn–Zn–Ag–XAl/Cu specimens after aging for 100–600 h. These three layers included the Cu3(Zn, Sn) phase adjacent to the solder, the Cu6(Sn, Zn)5 phase in the middle, and the Cu–rich phase near to Cu. For long–term aging time over 1000 h, the Cu6(Sn, Zn)5 phase grew, while the Cu3(Zn, Sn) phase diminished. Al segregation formed in the IMC for all of the Sn–Zn–Ag–XAl/Cu specimens after aging.Cracks formed, when aged for 1000 h, at the solder/IMC interface or within the IMC layer for the following solders: Sn–9Zn, Sn–8.55Zn–1Ag, Sn–8.55Zn–1Ag–0.1Al, Sn–8.55Zn–1Ag–0.25Al, and Sn–8.55Zn–1Ag–0.45Al. The crack was not detected up to 3000 h for the Sn–8.55Zn–1Ag–0.01Al/Cu couple, of which the IMC growth rate was the slowest among all solders.
Fabrication of transparent Sc2O3 ceramics with powders thermally pyrolyzed from sulfate
Authors: Li Ji-Guang , Ikegami Takayasu , Mori Toshiyuki
Published: March 2008

Scandia (Sc2O3) is a ceramic material that shows interesting thermal and optical properties, but is difficult to grow as single crystals. As an alternative, in this work we fabricated polycrystalline Sc2O3 transparent ceramics via vacuum sintering, using powders thermally pyrolyzed at 1200 °C from a scandium sulfate salt, Sc2(SO4)3 · 7.8H2O, that we prepared. Characterization of the powders was achieved by differential thermal analysis/thermogravimetry, x-ray diffractometry, Brunauer–Emmett–Teller analysis, and field-emission scanning electron microscopy. Sintering behaviors of the Sc2O3 powders were studied in air via dilatometry. The sulfate salt transforms to oxide at temperatures ≥1000 °C, and the best pyrolysis temperature for transparent ceramics fabrication is 1200 °C, at which the resultant Sc2O3 powder is good in dispersion, ultrafine in particle size (∼80 nm), and almost free from residual sulfur. Transparent ceramics were fabricated from this powder via vacuum sintering at 1625 °C or above. The ceramics sintered at 1700 °C for 4 h exhibit an in-line transmittance of approximately 56–58% in the visible light region at a sample thickness of 1.0 mm.
Effects of rare-earth oxide and alumina additives on thermal conductivity of liquid-phase-sintered silicon carbide
Authors: Zhou You , Hirao Kiyoshi , Yamauchi Yukihiko , Kanzaki Shuzo
Published: March 2008

SiC ceramics were prepared from a β–SiC powder doped with two different sintering additives—a mixture of La2O3and Y2O3and a mixture of Al2O3and Y2O3—by hot pressing and annealing. Their microstructures, phase compositions, lattice oxygen contents, and thermal conductivities were evaluated. The SiC doped with rare-earth oxides attained thermal conductivities in excess of 200 W/(m K); however, the SiC doped with additives containing alumina had thermal conductivities lower than 71 W/(m K). The high thermal conductivity of the rare-earth-oxide-doped SiC was attributed to the low oxygen content in SiC lattice, high SiC–SiC contiguity, and lack of β– to α–SiC polytypic transformation. The low thermal conductivity of the alumina-doped SiC was attributed to the point defects resulting from the dissolution of Al2O3into SiC lattice and the occurrence of polytypic transformation.
Modified embedded-atom method calculation for the Ni–W system
Authors: Shim Jae-Hyeok , Park Sung Il , Cho Young Whan , Lee Byeong-Joo
Published: March 2008

A semi-empirical interatomic potential of the Ni–W system was developed using a modified embedded-atom method (MEAM) formalism including second-nearest-neighbor interactions. The cross potential was determined by fitting physical properties of tetragonal Ni4W available in the literature. The MEAM potential was used to predict phase stabilities, lattice constants, and bulk moduli of nonequilibrium and equilibrium phases in the Ni–W system. The results were in good agreement with experimental information or first-principles calculation.
Microstructure and optical properties of AlOx thin films grown on ZnO-deposited glass
Authors: Lin Su-Shia , Huang Jow-Lay
Published: March 2008

AlOx thin films were grown on ZnO-deposited glass substrates under different conditions using magnetron sputtering. The influence of processing parameters (mainly direct-current power and oxidizing atmosphere) on the structure and optical properties were investigated. The AlOx films for all samples in this study showed the coexistence of amorphous and polycrystalline structures. The kinetics of crystal growth could influence the dominant crystal orientation. Fast-growing planes were not the most thermodynamically stable, but were kinetically controlled under the film growth condition. Oxidizing the sample in O2 atmosphere made the AlOx film grow in random directions. The excess oxygen was chemisorbed at the interface between AlOx and ZnO. Therefore, the neighboring oxygen–oxygen distance of AlOx and that of ZnO on their closest-packed planes seriously mismatched. At high power, the particles arrived at the substrate with high kinetic energy and high rate, which led to low density due to porous structure. The transmission decreased with an increase of the pores and surface roughness of AlOxfilm on ZnO-deposited glass. However, the diffusion of oxygen into the grains improved transmission when the sample was oxidized in O2 atmosphere.
Role of water during AlN-hydrolysis-assisted solidification in ceramic suspensions studied by proton nuclear magnetic resonance T2 relaxation
Authors: Novak S. , Lahajnar G. , Sepe A. , Kosmač T.
Published: March 2008

Using proton nuclear magnetic resonance (1H-NMR), we have studied the thermally activated hydrolysis of aluminum nitride admixed into Al2O3 aqueous suspensions. We paid special attention to the formation of aluminum hydroxide and its role in binding the host ceramic particles into a stiff solid matrix. The water–proton NMR spin-spin relaxation time (T2) was continuously measured as a function of the time of the AlN hydrolysis in the host Al2O3 ceramic suspension. T2 was found to correlate with an increasing fraction of bound water at the surface of the formed hydrogel and so provided us with information about the gel-surface growth during the hydrolysis process. These results are in good agreement with the observed time- and composition-related increases in high-frequency impedance for the analyzed suspensions.
Determination of the stress-dependent stiffness of plasma-sprayed thermal barrier coatings using depth-sensitive indentation
Authors: Malzbender J. , Steinbrech R. W.
Published: March 2008

The elastic response of atmospheric plasma-sprayed coatings was investigated using Vickers and spherical indenter geometries. In both cases a strong dependency of the stiffness on the applied load (indentation depth) was observed. The stiffness of the coatings decreased with increasing load for a Vickers indenter, whereas it increased for a spherical indenter. This contrary behavior was related to the relative crack density in the deformed volume and to the stress dependence of the stiffness due to crack closure. The effect of annealing on the stiffness was quantified for both tip geometries. The heat treatment yielded additional information on the relationship between the indentation data and the microstructural defects. From the results it was concluded that the stiffness measured using a sharp indenter and small load reflected the elastic behavior of single spraying splats. With the relatively large spherical indenter, the average global stiffness of the thermal barrier coating was measured even at small loads. From the data obtained using the spherical indenter, a compressive stress–strain curve was suggested. Furthermore, values of the apparent crack density and yield strength were determined from the indentation tests.
Effects of substrate bias on nanocrystal-(Ti, Al)Nx/amorphous-SiNy composite films
Authors: Yau Bao-Shun , Huang Jow-Lay , Kan Ming-Chi
Published: March 2008

Nanocrystal-(Ti, Al)Nx/amorphous-SiNy composite films were prepared in a codeposition process under different substrate bias voltages. The effects of substrate bias voltage on the deposition rate, composition, microstructure, and mechanical properties of nanocomposite films were investigated. Results indicated that the films with bias voltages caused resputtering due to the bombardment of high-energy ions on film surface. The resputtering effect had substantial influence on deposition rate, surface morphology, and composition of films. The films with (220) preferred orientation were also observed as the applied substrate bias voltages exceeded 50 V. As the substrate bias voltage increased, the nanocrystallite size increased, lattice strain raised, and the hardness decreased.
Ultrafine-grained microstructure in a Cu–Zn alloy produced by electropulsing treatment
Authors: Zhou Yizhou , Zhang Wei , Wang Baoquan , Guo Jingdong
Published: March 2008

High-current-density electropulsing was applied to a coarse-grained Cu–Zn alloy with two phases of α-phase and β′-phase. It was found that with an electropulsing treatment, ultrafine-grained (UFG) microstructure could be formed in the α-phase, but could not be formed in the β-phase. The results indicated that the formation of UFG microstructure was dependent on solid-state phase transformation. The main reason for the formation of UFG microstructure by electropulsing treatment resulted from the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system, but not from the high heating and cooling rate during electropulsing treatment. The bulk UFG samples prepared by electropulsing treatment were free of porosity and contamination and had no large microstrain. It was reasonable to anticipate that a new method might be developed to produce ideal bulk UFG samples directly from the conventional coarse-grained materials by application of electropulsing.
Fabrication and compressive strength of macrochannelled tetragonal zirconia polycrystals with calcium phosphate coating layer
Authors: Koh Young-Hag , Kim Hae-Won , Kim Hyoun-Ee , Halloran John W.
Published: March 2008

Macrochannelled tetragonal zirconia polycrystals (TZP) coated with a calcium phosphate layer were fabricated using a coextrusion process to produce strong and bioactive porous bioceramics. The initial feedrod, composed of three materials [TZP (shell), calcium phosphate (intermediate layer), and carbon black (core)], was coextruded through a 750-μm orifice at 120 °C, producing a continuous and flexible filament. Each sheet, which was composed of a unidirectional array of filaments, was stacked and then warm-pressed at 140 °C with 10 MPa. After binder burnout, the green billet was sintered between 1350 and 1600 °C for 1 h in air, leaving uniform macrochannels clad on the inside with bioactive calcium phosphate on a strong TZP body. The compressive strength of the specimen was much higher than that of calcium phosphate with a similar structure.
Bulk processing of high-performance nanocrystalline intermetallics
Authors: Shang C. H. , Cammarata R. C. , Van Heerden C. , Weihs T. P. , Chien C. L.
Published: March 2008

We present an inexpensive, bulk-processing technique for the mass fabrication of a high-performance, nanocrystalline intermetallic with no internal flaws: the recrystallization of plastically deformed ingots through controlled heat treatments. We demonstrate that FeCo alloys with average grain sizes of 100 nm can be produced using this method. The nanocrystalline materials have tensile yield strengths as high as 2.2 GPa and have plastic tensile ductilities over 1.3%. Such superior properties at room temperature are currently unattainable when nanocrystalline materials are prepared by other methods.
Pressure-dependent flow behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass
Authors: Lu Jun , Ravichandran Guruswami
Published: March 2008

An experimental study of the inelastic deformation of bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10Be22.5 under multiaxial compression using a confining sleeve technique is presented. In contrast to the catastrophic shear failure (brittle) in uniaxial compression, the metallic glass exhibited large inelastic deformation of more than 10% under confinement, demonstrating the nature of ductile deformation under constrained conditions in spite of the long-range disordered characteristic of the material. It was found that the metallic glass followed a pressure (p) dependent Tresca criterion τ = τ0 + βp, and the coefficient of the pressure dependence β was 0.17. Multiple parallel shear bands oriented at 45° to the loading direction were observed on the surfaces of the deformed specimens and were responsible for the overall inelastic deformation.
Identification of Nd163 phase in melt-textured NdBa2Cu3O7−δbulk samples
Authors: Gombos Marcello , Gomis Vicente , Carrillo Anna Esther , Vecchione Antonio , Pace Sandro , Obradors Xavier
Published: March 2008

In this work, we report on the observation of Nd1Ba6Cu3O10,5(Nd163) phase of the NdBaCuO system in melt-textured Nd123 bulk samples grown from a mixture of Nd123 and Nd210 phase powders. The observation was performed with polarized light optical microscopy and scanning electron microscopy–energy dispersive x-ray analyses. Images of the identified phase crystals show an aspect quite different from Nd422 crystals. Unexpectedly, Nd163 was individuated, even in “pure” Nd123 samples. Moreover, after long exposure to air, Nd163 disappeared completely in samples synthesized from powders containing Nd210. Thermogravimetry analyses of powders show that the stability of this phase in air is limited to temperatures higher than 900 °C, so Nd163 is unstable and highly reactive at room temperature. Moreover, an explanation of the observation of Nd163 in Nd210 free samples, based on the spontaneous formation of Nd163 phase in a Nd123 melt, is proposed.
Semi-inverse method for predicting stress–strain relationship from cone indentations
Authors: DiCarlo A. , Yang H. T. Y. , Chandrasekar S.
Published: March 2008

A method for determining the stress–strain relationship of a material from hardness values H obtained from cone indentation tests with various apical angles is presented. The materials studied were assumed to exhibit power-law hardening. As a result, the properties of importance are the Young's modulus E, yield strength Y, and the work-hardening exponent n. Previous work [W.C. Oliver and G.M. Pharr, J. Mater. Res. 7, 1564 (1992)] showed that E can be determined from initial force–displacement data collected while unloading the indenter from the material. Consequently, the properties that need to be determined are Y and n. Dimensional analysis was used to generalize H/E so that it was a function of Y/E and n [Y-T. Cheng and C-M. Cheng, J. Appl. Phys. 84, 1284 (1999); Philos. Mag. Lett. 77, 39 (1998)]. A parametric study of Y/E and n was conducted using the finite element method to model material behavior. Regression analysis was used to correlate the H/E findings from the simulations to Y/E and n. With the a priori knowledge of E, this correlation was used to estimate Y and n.
Synthesis of Ni-based bulk metallic glass matrix composites containing ductile brass phase by warm extrusion of gas atomized powders
Authors: Lee M. H. , Bae D. H. , Kim D. H. , Sordelet D. J.
Published: March 2008

To prevent catastrophic failure by propagating highly localized shear bands and to overcome the limited dimension of metallic glass, centimeter-scale Ni59Zr20Ti16Si2Sn3 bulk metallic glass matrix composites were fabricated by warm extrusion of a mixture of gas-atomized fully amorphous powders and ductile brass powders. After consolidation, the composite retained the fully amorphous matrix found in the gas-atomized powder combined with the brass second phase. The glass-transition and crystallization temperatures of the extruded material were the same as those of the starting powders. The confined ductile brass phase enabled the bulk metallic glass matrix composites to deform plastically under uniaxial compression at room temperature. The combination of strength and ductility in the inherently brittle Ni-based monolithic materials could be obtained by introducing a ductile phase in the bulk metallic glass matrix. However, control of the volume fraction and distribution of the ductile brass phase was important for the proper combination of the strength and plasticity.
Effect of oxygen on the thermomechanical behavior of passivated Cu thin films
Authors: Shu Jonathan B. , Clyburn Susan B. , Mates Thomas E. , Baker Shefford P.
Published: March 2008

The thermomechanical behavior of Cu thin films, 600–1125 nm thick and encapsulated between SiNx barrier and SiNx or AlNx passivation layers on silicon substrates, was studied during thermal cycling between room temperature and 400 or 500 °C using the substrate curvature method. Films were prepared with varying oxygen contents, and the distribution of oxygen through the thickness of selected films was studied before and after thermal cycling using secondary ion mass spectrometry. Large variations in the thermomechanical behavior with oxygen content were found and correlated with segregation of oxygen to the film/barrier and film/passivation interfaces. These variations are thought to be due to recovery of stored misfit dislocation energy, which is, in turn, controlled by oxygen in the film. Effects of oxygen on film deformation through variations in interfacial adhesion and diffusion-induced dislocation glide are considered.
Determination of hardness from nanoscratch experiments: Corrections for interfacial shear stress and elastic recovery
Authors: Tayebi Noureddine , Conry Thomas F. , Polycarpou Andreas A.
Published: March 2008

A frequent application of the nanoscratch technique is to estimate hardness of ultrathin films when substrate effects are encountered with the nanoindentation technique. A model based on the work of Goddard and Wilman, which assumes a rigid-plastic behavior of the deformed surfaces, is commonly used for the determination of hardness from scratch tests, yet it overestimates the hardness of materials by as much as a factor of three at very shallow indentation depths on the order of 1–10 nm. The Goddard and Wilman model was extended in this paper to include the effects of the component of the shear stress tangential to the meridianal plane and the elastic recovery of the plastically deformed surfaces assuming elastic-perfectly-plastic material behavior. The proposed model was subsequently verified by performing nanoscratch experiments on fused quartz, which is homogeneous and isotropic with no known surface layers and with known hardness. The hardness was calculated using both the model based on the work of Goddard and Wilman and the extended model. The hardness calculated using the extended model was in very close agreement with the accepted value of bulk hardness of fused quartz over the range of scratch depths tested, showing the importance of the effects of elastic recovery and interfacial shear stress. The model was further verified for the case of a pure aluminum sample and the native thin film coating of alumina that forms on the surface upon air exposure.
Influence of the electrokinetic behaviors of abrasive ceria particles and the deposited plasma-enhanced tetraethylorthosilicate and chemically vapor deposited Si3N4 films in an aqueous medium on chemical mechanical planarization for shallow trench isolation
Authors: Kim Sang-Kyun , Lee Sangkyu , Paik Ungyu , Katoh Takeo , Park Jea-Gun
Published: March 2008

The effects of the electrokinetic behavior of abrasive ceria particles suspended in an aqueous medium and the deposited plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) Si3N4 films on chemical mechanical planarization (CMP) for shallow trench isolation were investigated. The colloidal characteristics of ceria slurries, such as their stability and surface potential, in acidic, neutral, and alkaline suspensions were examined to determine the correlation between the colloidal properties of ceria slurry and CMP performance. The surface potentials of the ceria particles and the PETEOS and CVD Si3N4 films in an aqueous suspending medium were dependent on the pH of the suspending medium. The differences in surface charges of ceria particles and the PETEOS and CVD Si3N4 films have a profound effect on the removal rate and oxide-to-nitride selectivity of CMP performance.
Effect of geometrical parameters on the field-emission properties of single-walled carbon nanotube ropes
Authors: Zhao Z. G. , Tong Y. , Liu C. , Cheng H. M.
Published: March 2008

Aligned single-walled carbon nanotube (SWNT) ropes show excellent field-emission performance due to their high aspect ratio and sound alignment. In this study, the effect of geometrical parameters, such as cathode-anode distance and the height of SWNT ropes on the field-emission properties of SWNT ropes was investigated. It was found that the cathode-anode distance influences the emission properties, such as the turn-on fieldFtoand threshold fieldFthr, of SWNT ropes, and the turn-on and threshold fields are marginally decreased at relatively larger gaps between the SWNT emitter tip and the anode plane. It was also found that the emission properties of SWNT ropes are improved by increasing the rope length, at least in the present experimental range. A possible two-step field amplification model was proposed to explain this length effect of SWNT ropes. The estimated results show that the local field at the tip of SWNT ropes, which causes a certain emission-current density, seems not to change with the cathode-anode distance, and the effective emission area of the SWNT rope is much smaller than the apparent cross-sectional area of the SWNT rope. The results obtained suggest that it is possible to optimize the performance of SWNT rope-based cold cathode by adjusting geometrical parameters of SWNT rope emitters.
Formation, properties, thermal characteristics, and crystallization of hard magnetic Pr–Al–Fe–Cu bulk metallic glasses
Authors: Li Zheng , Yang Hai , Pan Ming Xiang , Zhao De Qian , Wang Wan Lu , Wang Wei Hua
Published: March 2008

The Pr55–xAl12+xFe33–yCuy(0 ≤x≤ 5, 0 ≤y≤ 8) bulk metallic glasses (BMGs) 5 mm in diameter and 100 mm in length were prepared by copper mold suction casting. Hysteresis loops of the Pr55–xAl12+xFe33–yCuyBMGs and the corresponding Pr55Al12Fe30Cu3crystallized alloy were measured, and the results showed that the Pr55–xAl12+xFe33–yCuyBMGs are hard magnetic, while the completely crystallized Pr55Al12Fe30Cu3alloy is paramagnetic at room temperature. The thermal behavior and crystallization of the Pr55Al12Fe30Cu3BMG were studied by differential scanning calorimetry, and the results indicated that the Pr-based BMG has obvious glass transition and a wide supercooled liquid region up to 75 K. The crystallization activation energy for the Pr55Al12Fe30Cu3BMG is much smaller than that of Zr–Ti–Cu–Ni–Be BMG.