bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanostructured red-emitting MgGa2O4:Eu3+ phosphors
Authors: Tsai Bin-Siang , Chang Yen-Hwei , Chen Yu-Chung
Published: May 2005

Nano-grained phosphors of Eu3+-doped MgGa2O4 crystallites were prepared by sol-gel technique. The characterization and optical properties of luminescent MgGa2O4:Eu3+ powders have been investigated. The dried sol-gel powders were calcined in air at different temperature from 600 to 1000 °C for 5 h. The x-ray diffraction profiles showed that the MgGa2O4:Eu3+ powders began to crystallize around 600 °C and formed stable MgGa2O4 phase in the temperature range of 600–900 °C. The transmission electron microscopy morphology observations revealed that the fired powders exhibit small grain size less than 20 nm. In the PL studies, under ultraviolet (394 nm) excitation, the calcined powders emitted bright red luminescence (615 nm, 5D0→7F2), and the powders fired at 900 °C were found to have the maximum photoluminescence intensity. The quenching concentration of Eu3+ in MgGa2O4 crystallites was also indicated to be about 5∼6 mol%.
Solid-state recycling for machined chips of iron by hot extrusion and annealing
Authors: Chino Yasumasa , Iwasaki Hajime , Mabuchi Mamoru
Published: May 2005

Solid-state recycling for machined chips of pure iron by hot extrusion at 823 K and annealing at 1073–1273 K was carried out. The as-extruded solid recycled specimen without annealing was fractured prior to yielding at room temperature. However, high ductility was recovered by annealing at 1073–1273 K. This is because the oxides at the interface of the machined chips dispersed in grain by annealing. The annealed solid recycled specimens showed higher yield stress than the annealed virgin extruded specimens. Grain refinement for the solid recycled specimens was enhanced by the high dislocation density in the machined chips, resulting in higher strength in the recycled specimens. Thus, the solid-state recycling is a low energy upgrade recycle process.
Coating of TiO2 nanolayer on spherical Ni particles using a novel sol-gel route
Authors: Lee Jae-Young , Hong Seong-Hyeon , Lee Jong-Heun , Lee Yong Kyun , Choi Jae-Young
Published: May 2005

A nano-thin TiO2 layer was uniformly coated on spherical Ni particles for applications in multilayer ceramic capacitors via a controlled hydrolysis process using TiCl4, (C2H5)2NH (diethylamine, DEA), and C4H9OH as Ti-source, gradual (OH)- former, and solvent, respectively. At the constant [DEA]/[TiCl4] =10.6, the Ti-hydroxide could be coated uniformly using the dilute source solution ([TiCl4] ≤ 0.2 M) while the Ti-hydroxide powder in a separated form was frequently observed at [TiCl4] ≥ 0.4 M. A uniform coating was attained at the slower precipitation, and the kinetics of precipitation was controlled by tuning the trace amount of water in the solution. The TiO2-coating not only prevented Ni oxidation but also retarded the sintering between the Ni particles to a large extent.
Critical factors that determine face-centered cubic to body-centered cubic phase transformation in sputter-deposited austenitic stainless steel films
Authors: Zhang X. , Misra A. , Schulze R.K. , Wetteland C.J. , Wang H. , Nastasi M.
Published: May 2005

Bulk austenitic stainless steels (SS) have a face-centered cubic (fcc) structure. However, sputter deposited films synthesized using austenitic stainless steel targets usually exhibit body-centered cubic (bcc) structure or a mixture of fcc and bcc phases. This paper presents studies on the effect of processing parameters on the phase stability of 304 and 330 SS thin films. The 304 SS thin films with in-plane, biaxial residual stresses in the range of approximately 1 GPa (tensile) to approximately 300 MPa (compressive) exhibited only bcc structure. The retention of bcc 304 SS after high-temperature annealing followed by slow furnace cooling indicates depletion of Ni in as-sputtered 304 SS films. The 330 SS films sputtered at room temperature possess pure fcc phase. The Ni content and the substrate temperature during deposition are crucial factors in determining the phase stability in sputter deposited austenitic SS films.
Alloys that form conductive and passivating oxides for proton exchange membrane fuel cell bipolar plates
Authors: Aukland Neil , Boudina Abdellah , Eddy David S. , Mantese Joseph V. , Thompson Margarita P. , Wang Simon S.
Published: May 2005

During the operation of proton exchange membrane (PEM) fuel cells, a high-resistance oxide is often formed on the cathode surface of base metal bipolar plates. Over time, this corrosion mechanism leads to a drop in fuel cell efficiency and potentially to complete failure. To address this problem, we have developed alloys capable of forming oxides that are both conductive and chemically stable under PEM fuel cell operating conditions. Five alloys of titanium with tantalum or niobium were investigated. The oxides were formed on the alloys by cyclic voltammetry in solutions mimicking the cathode- and anode-side environment of a PEM fuel cell. The oxides of all tested alloys had lower surface resistance than the oxide of pure titanium. We also investigated the chemical durability of Ti–Nb and Ti–Ta alloys in more concentrated solutions beyond those typically found in PEM fuel cells. The oxide films formed on Ti–Nb and Ti–Ta alloys remained conductive and chemically stable in these concentrated solutions. The stability of the oxide films was evaluated; Ti alloys having 3% Ta and Nb were identified as potential candidates for bipolar plate materials.
Fracture mode transitions in brittle coatings on compliant substrates as a function of thickness
Authors: Chai Herzl , Lawn Brian R.
Published: May 2005

The fundamentally changing nature of fracture in brittle coatings on compliant substrates with diminishing coating thickness is examined. Attention is focused on cracking induced by concentrated loading with a spherical indenter at the top surface. It is shown that the fracture mode undergoes transitions, from top-surface ring cracking around the contact (“thick-coating” region) to bottom-surface radial cracking at the lower ceramic surface (“intermediate” region) and, finally, back to surface ring cracking (“thin-coating” region). These transitions reflect a progressively changing stress field in the layer structures and highlight the differences in failure mechanism that may be anticipated at the large- and small-scale levels. Simple fracture relations are derived for each mode, expressing critical loads in terms of coating thickness relative to contact or sphere radius, coating strength and coating/substrate modulus mismatch. Data from finite element simulations and contact experiments on model ceramic/polymer bilayer systems are used to validate the basic elements of the analytical relations and to quantify deviations. Implications of the transitional behavior in relation to the strength of brittle coating/film systems are discussed.
Grain refinement at the nanoscale via mechanical twinning and dislocation interaction in a nickel-based alloy
Authors: Tao N.R. , Wu X.L. , Sui M.L. , Lu J. , Lu K.
Published: May 2005

A nanostructured surface layer was formed on an Inconel 600 plate by subjecting it to surface mechanical attrition treatment at room temperature. Transmission electron microscopy and high-resolution transmission electron microscopy of the treated surface layer were carried out to reveal the underlying grain refinement mechanism. Experimental observations showed that the strain-induced nanocrystallization in the current sample occurred via formation of mechanical microtwins and subsequent interaction of the microtwins with dislocations in the surface layer. The development of high-density dislocation arrays inside the twin-matrix lamellae provides precursors for grain boundaries that subdivide the nanometer-thick lamellae into equiaxed, nanometer-sized grains with random orientations.
Predicted pyrochlore to fluorite disorder temperature for A2Zr2O7compositions
Authors: Rushton M.J.D. , Grimes Robin W. , Stanek C.R. , Owens Scott
Published: May 2005

In a previous publication the order–disorder pyrochlore to fluorite transformation temperatures for a series of A2Hf2O7pyrochlores were predicted [C.R. Stanek and R.W. Grimes: Prediction of rare-earth A2Hf2O7pyrochlore phases.J. Am. Ceram. Soc.2002,85,p. 2139]. This was facilitated by establishing a relationship between these temperatures and the energy required to introduce a specific defect structure into the perfect pyrochlore lattice. Here an equivalent relationship for A2Zr2O7pyrochlores was generated, and from this the disorder temperatures for a number of compositions including Eu2Zr2O7were predicted.
Microwave-assisted synthesis of one-dimensional nanostructures
Authors: Lu Qingyi , Gao Feng , Komarneni Sridhar
Published: May 2005

A microwave-assisted solvothermal method was used for the synthesis of selenium nanorods. The obtained selenium nanorods have axis ratios higher than 100 with their diameters in the range of 30–150 nm. This method is quite simple, rapid, adjustable, and general. Besides the effects of the experimental parameters on the synthesis of the selenium nanorods, the generality of this method has also been investigated, by which other one-dimensional nanostructures, metal lead and semiconductor cadmium sulfide nanorods, were also successfully synthesized.
A new scheme for computational modeling of conical indentation in plastically graded materials
Authors: Cao Yan Ping , Lu Jian
Published: May 2005

In this paper, a new scheme has been proposed for the computational modeling of conical indentation in plastically graded materials. Based on the new scheme and the work of Dao et al. [Acta Mater.49, 3899 (2001)], and taking the example of conical indentation with an indenter whose tip apex angle is θ = 70.3°, an analytical expression to predict the loading P - h curve for the indentation of plastically graded materials has been presented. A reverse algorithm has further been established to determine the plastic properties of a plastically graded surface. The existence, uniqueness, and stability of the solution to the inverse problem have been systematically investigated. The current work can be applied to the evaluation or optimization of various plastically graded surfaces.
Effect of drop impact energy on contact resistance of anisotropic conductive adhesive film joints
Authors: Islam Rashed Adnan , Chan Y.C. , Ralph B.
Published: May 2005

The contact resistances investigated in this study of anisotropic conductive adhesive film joints using Au/Ni bumps and flexible substrates are found to be increased by the drop impact energy and also by the combined effect of heat/humidity and the impact energy. The samples humidified at 85 °C/85% RH for 384 h, on which impact energy of 50 J was induced, exhibit the most severe results. The contact resistance increases by 700%, which had been about 0.062 Ω in the as-bonded condition. The samples without humidification showed a sluggish and gentle increase in contact resistance with induced drop impact energy. The contact resistance was found to be increased by 400% after absorbing 90 J energy. Scanning electron microscopy images show particle deformation due to abrasion and friction between the contacting surfaces resulting from the sudden impact. Joints are also observed with no connections, which signify open circuits. Almost 25% of circuits were found open in the samples (after 384 h in a humid environment), which have suffered severe mechanical shock. Breaking of the conductive layer of the particle and exposing the underlying polymeric portion was also observed.
Magnetic field–induced biomimetic synthesis of superparamagnetic poly (vinyl alcohol)–maghemite composite
Authors: Sinha Arvind , Chakraborty Jui , Joy P.A. , Ramachandrarao P.
Published: May 2005

Poly (vinyl alcohol)–mediated synthesis of monodisperse, self-assembled, superparamagnetic maghemite particles was carried out through a magnetic field–induced biomimetic route. Modifying the kinetics of precipitation, the magnetic field promoted the nucleation of the maghemite phase over magnetite and also induced a self-assembly–assisted shape anisotropy during the precipitation of the particles in the polymer matrix.
Mechanical properties of nanostructured amorphous metal multilayer thin films
Authors: Vella J.B. , Mann A.B. , Kung H. , Chien C.L. , Weihs T.P. , Cammarata R.C.
Published: May 2005

The hardness of amorphous metal multilayered films was investigated by nanoindenation. Bilayer material systems of amorphous CuNb, FeB, and FeTi were produced by dc sputtering on 〈112￣0〉 sapphire substrates to a total thickness of 1 μm. The bilayer periods (Λ) ranged from 2 to 50 nm. The films’ noncrystallinity was verified by x-ray diffraction (XRD) and electron diffraction. The layer structure was verified by transmission electron microscopy and grazing angle XRD. The hardness and elastic modulus properties of the films, measured by nanoindentation, were shown to be statistically equivalent to the rule mixtures predictions. The hardness behavior is in contrast with the behavior of crystalline multilayered films, which generally display significant enhancements as the bilayer period is decreased below 10 nm. The lack of a significant hardness variation in the amorphous films strongly suggests that dislocation-mediated mechanisms do not govern inhomogeneous flow in amorphous metals.
Field-effect transistors made from macroscopic single crystals of tetracene and related semiconductors on polymer dielectrics
Authors: Katz Howard E. , Kloc Christian , Sundar Vikram , Zaumseil Jana , Briseno Alejandro L. , Bao Zhenan
Published: May 2005

We report properties of devices made by the adhesion of semiconductor crystals, including several tetracene specimens, to polymer gate dielectrics along with measurements of tetracene crystals on conventional Si/SiO2 dielectric surfaces. For the best tetracene, pentacene, and alpha-6T devices, mobilities exceeding 0.1 cm2/V were measured, correlating well with expectations based on the literature, and in the case of tetracene and alpha-6T, exceeding the thin film mobility value. The devices were prepared in the open laboratory using simpler crystal handling techniques than had been thought necessary.
Doped polyaniline polymer fuses: Electrically programmable read-only-memory elements
Authors: Marsman Albert W. , Hart Cees M. , Gelinck Gerwin H. , Geuns Tom C.T. , de Leeuw Dagobert M.
Published: May 2005

We demonstrate polymeric electrically programmable read-only-memory elements based on camphorsulfonic-acid–doped polyaniline lines. Their working mechanism relies on irreversible reduction of the electrical conductivity by Joule heating like electrical safety fuses. The heating power is supplied electrically. The critical power required to “blow up” the fuse is strongly reduced by notches. The influence of the notch design can be predicted reasonably well using a simple thermal model. The critical power becomes less than 1 mW for fuses with notches narrower than 2 μm. This power can be delivered by organic transistors already at modest voltages, opening the way of integration of these memory elements in all-polymer circuits.
Self-organization of phthalocyanines on Al2O3 (1120) in aligned and ordered films
Authors: Barrena E. , Ossó J.O. , Schreiber F. , Garriga M. , Alonso M.I. , Dosch H.
Published: May 2005

We studied the self-organization process of F16CuPc films (20–30 ML) on stepped Al2O3 (1120) substrates. X-ray diffraction measurements revealed a highly ordered layered structure with the molecules in a nearly upright configuration. The morphology, investigated by atomic force microscopy, consisted of long (several microns) and narrow (20–100 nm) needlelike terraces unidirectionally aligned along one of the main crystallographic directions of the Al2O3 (1120) surface. High resolution atomic force microscopy images revealed in-plane molecular order with the molecular stacking direction parallel to the needlelike terraces. Such anisotropic morphology is the result of a self-organization process of F16CuPc in elongated crystallites driven to a preferential orientation by the interaction with the substrate. Spectroscopic ellipsometry showed that these films exhibit anisotropic optical properties correlated with the molecular arrangement.
Switchable window based on electrochromic polymers
Authors: Xu Chunye , Liu Lu , Legenski Susan E. , Ning Dai , Taya Minoru
Published: May 2005

A large contrast ratio (>ΔΤ = 60%) and rapid switching (0.3–1 s) electrochromic (EC) polymer device that consists of a laminated two-layer structure between two electrodes was prepared. The new design consists of an indium tin oxide (ITO) glass electrode, a cathodic EC polymer film, a solid electrolyte, and a counterelectrode that replaces the anodic EC polymer and ITO electrode. Four EC polymers including two new EC polymers, Poly[3-methyl-3′-propyl-3,4-dihydro-2H-thieno(3,4-b)(1,4)dioxepine] (PProDOT-MePro) and Poly[3,3-diethyl-3,4-dihydro-2H,7H-(1,4)dioxepino(2,3-c)pyrrole] (PProDOP-Et2), were synthesized as cathodic EC polymers. A carbon-based counterelectrode was prepared for comparison with an Au-based counterelectrode. Several kinds of polymer gel electrolytes were prepared for comparison. The devices (windows) were increased in area from 0.028 × 0.04 in.2, 1 × 1 in.2 to 3 × 3 in.2 Three main components, the EC polymer film, the gel electrolyte, and the counterelectrode, were studied and their optical properties, conductivities, and repeatabilities were compared. The effects of window size on the contrast ratio, switching speed, power usage, and repeatability were studied.
Huge values of room-temperature dielectric constants in pellets of poly(3-methylthiophene)
Authors: Moraes S. , Walmsley L. , Pereira E.C. , Correa A.A.
Published: May 2005

Room temperature data of impedance and phase angle in pellets of electrochemically synthesized ClO4− doped poly(3-methylthiophene) (P3MT) were analyzed assuming the sample being represented by a parallel resistor-capacitor (RC) circuit or by a series RC circuit. The last assumption proved to be the correct one, and to confirm it we use the sample as the RC component of a resistor-capacitor-inductor series resonator. We discuss the possibility of this RC series behavior to be due to a charge-density wave characteristic also evidenced from the huge values of the low-frequency dielectric constant of the system.
Hybrid interfaces of conjugate polymers: Band edge alignment studied by ultraviolet photoelectron spectroscopy
Authors: Salaneck W.R. , Fahlman M.
Published: May 2005

The control of hybrid interfaces in polymer-based electronic devices may be enabling in many applications. The engineering of hybrid interface involves (requires) an understanding of the electronic structure of materials—one organic and one inorganic—that form the two halves of hybrid interfaces, as well as the electronic and chemical consequences of the coupling of the two. Although much literature exists describing the interfaces between vapor-deposited organic molecules and model molecules for polymers on the surfaces of clean metals in ultrahigh vacuum, few studies have been reported on spin-coated, semiconducting polymer films on realistic substrates. Spin coating in an inert atmosphere (or even air) is a central part of the process of the fabrication of polymer-based light-emitting devices and other modern polymer-based electronic components. Here, work on the electronic structure of semiconducting (conjugated) polymer films spin-coated onto selected inorganic substrates, carried out using ultraviolet photoelectron spectroscopy, is reviewed and summarized to generate a generalized picture of the hybrid interfaces formed under realistic device fabrication conditions.
From polymer transistors toward printed electronics
Authors: Clemens W. , Fix W. , Ficker J. , Knobloch A. , Ullmann A.
Published: May 2005

Printed organic circuits have the potential to revolutionize the spread of electronic applications. This will be enabled by inexpensive and fast fabrication with printing techniques using soluble organic materials. Two main challenges have to be mastered on the way towards printed electronics. First, the development of stable transistors and an adapted chip design for organic materials, and second, the development of a reliable fabrication process. We present our results on high performance polymer transistors, mainly based on poly-3alkylthiophene (P3AT) as semiconducting material. Fast circuits up to 200 kHz and stable circuits with operation lifetimes of more than 1000 h under ambient conditions without any encapsulation are shown. We also report on a fully printed, all organic ring oscillator.
Application of nucleation theory to the rate dependence of incipient plasticity during nanoindentation
Authors: Schuh Christopher A. , Lund Alan C.
Published: May 2005

We propose a nucleation theory-based analysis for incipient plasticity during nanoindentation and predict the statistical distribution of rate-dependent pop-in events for many nominally identical indentations on the same surface. In the framework of stress-assisted, thermally activated defect nucleation, we quantitatively rationalize new nanoindentation measurements on 4H SiC and extract the activation volume of the nucleation events that mark the onset of plastic flow. We also illustrate how this statistical approach can differentiate between unique nucleation events for different indenter tip geometries.
Microstructural refinement and deformation twinning during severe plastic deformation of 316L stainless steel at high temperatures
Authors: Yapici G.G. , Karaman I. , Luo Z.P. , Maier H.J. , Chumlyakov Y.I.
Published: May 2005

The present work focuses on the severe plastic deformation and deformation twinning of 316L austenitic stainless steel deformed at high temperatures (700 and 800 °C) using equal channel angular extrusion (ECAE). Very high tensile and compressive strength levels were obtained after ECAE without sacrificing toughness with relation to microstructural refinement and deformation twinning. The occurrence of deformation twinning at such high temperatures was attributed to the effect of high stress levels on the partial dislocation separation, i.e., effective stacking fault energy. High stress levels were ascribed to the combined effect of dynamic strain aging, high strain levels (∈ ∼ 1.16) and relatively high strain rate (2 s−1). At 800 °C, dynamic recovery and recrystallization took place locally leading to grains with fewer dislocation density and recrystallized grains, which in turn led to lower room temperature flow strengths than those from the samples processed at 700 °C but higher strain hardening rates. Apparent tension-compression asymmetry in the 700 °C sample was found to be the consequence of the directional internal stresses.
Synthesis, crystal structure, and anisotropic thermal expansion of Dy4.67(SiO4)3O
Authors: Misture S.T. , Harvey S.P. , Francy R.T. , DeCarr Y. Gao S. , Bancheri S.C.
Published: May 2005

A new phase in the Dy–Si–O system, Dy4.67(SiO4)3O, was prepared in powderform using the mixed oxide method. Dy4.67(SiO4)3O was first observed at 1300 °C, and phase purity was achieved after 96 h at 1600 °C. The crystal structure was determined using single crystal diffraction using synchrotron radiation, and powder x-ray diffraction data was refined using the Rietveld method. The structure was found to be apatite-type, hexagonal, with space groupP63/manda=b= 0.93883(2) nm,c= 0.67820(1) nm,Z= 2. High-temperature x-ray powder diffraction was used to characterize the anisotropic thermal expansion over the temperature range of 24–1450 °C, providing the axial and cell volume expansion.
Spalling of intermetallic compounds during the reaction between lead-free solders and electroless Ni-P metallization
Authors: Sohn Y.C. , Yu Jin , Kang S.K. , Shih D.Y. , Lee T.Y.
Published: May 2005

Intermetallic compound (IMC) spalling from electroless Ni-P film was investigated with lead-free solders in terms of solder-deposition methods (electroplating, solder paste, and thin foil), P content in the Ni-P film (4.6, 9, and 13 wt% P), and solder thickness (120 versus .200 μm). The reaction of Ni-P with Sn3.5Ag paste easily led to IMC spalling after 2-min reflow at 250 °C while IMCs adhered to the Ni-P layer after 10-min reflow with electroplated Sn or Sn3.5Ag. It has been shown that not only the solder composition but also the deposition method is important for IMC spalling from the Ni-P layer. The spalling increased with P content as well as with solder volume. Ni3Sn4intermetallics formed as a needle-shaped morphology at an early stage and changed into a chunk-shape. Needle-shaped compounds exhibited a higher propensity for spalling than chunk-shaped compounds because many channels among the needle-shaped IMCs facilitated Sn penetration. A reaction between the penetrated Sn and the Ni3P layer formed a Ni3SnP layer and Ni3Sn4IMCs spalled off the Ni3SnP surface. Dewetting of solder from the Ni3SnP layer, however, did not occur even after spalling of most IMCs.
Determination of the elastic modulus of microscale ceramic particles via nanoindentation
Authors: Leggoe J.W.
Published: May 2005

Nanoindentation of the reinforcement in a particulate reinforced metal matrix composite (PR MMC) enables direct investigation of reinforcement properties within the finished material. Mismatch between the elastic moduli of the reinforcement and matrix creates a “secondary indentation” effect, whereby the stiffer reinforcement particles themselves “indent” the more compliant matrix. A finite-element investigation was undertaken to quantify the additional penetration arising under secondary indentation for spherical and cylindrical particles. Modification of Sneddon’s equation for a flat punch by a scalar particle shape factor provided an accurate estimate of the additional penetration. The modified equation was combined with the analysis of Field and Swain to extract the particle elastic modulus from results obtained using a spherical indenter under a multiple partial-unloading indentation regime. The resulting methodology was used to determine the elastic moduli of silicon carbide particles and MicralTM microspheres in two aluminum-matrix PR MMCs.
Synthesis of platinum/multi-wall carbon nanotube catalysts
Authors: Mu Pan , Haolin Tang , Shichun Mu , Runzhang Yuan
Published: May 2005

The purpose of this research is to investigate the feasibility of the synthesis of platinum/multi-wall carbon nanotube (Pt/MWNT) catalysts and such catalysts' application in fuel cells. The as-received MWNTs were purified and decorated by pretreatment. Infrared-spectrum indicates the carboxylic (-COOH) and carbonyl (-C=O) groups were introduced on the surface of the MWNTs after pretreatment. These functional groups will act as anchor sites for the Pt deposition. Then the Pt particles in nano scale were deposited on the surface of MWNTs by reduction of a solution of hexachloroplatinic acid. Transmission electron microscopy examination reveals that Pt particles are attached to the surface of MWNTs. If as-received MWNTs are not pretreated in the proper way, the Pt particle aggregates are mostly found on the open end of MWNTs. Occasionally Pt penetrated inside the tube of MWNTs. The relationship between the Pt particle morphology and the conditions of pretreatment and reduction reaction is discussed. After heat treatment, Pt particles recrystallized to form the Pt/MWNT catalysts. The Pt/MWNT catalysts were applied to a single cell and the test result shows a promising future of these catalysts with low Pt loading when applied in proton exchange membrane fuel cells (PEMFCs).
Failure behavior upon shear test of 5Sn–95Pb solder bump after high temperature reliability test
Authors: Liu Yeh-Hsiu , Chuang Chiang-Ming , Lin Kwang-Lung
Published: May 2005

The shear strength, intermetallic compound formation, and failure mechanism of high-lead solder (5Sn–95Pb) bump on flip chip under bump metallurgy, Al/Ni(V)/Cu, were investigated after thermal cycling, multiple reflow, and high-temperature aging. Two kinds of intermetallic compound, Cu3Sn and AlxNiy, were found at the interface. The Cu3Sn was formed between the solder and Ni(V) layer while AlxNiy was formed between Ni(V) and Al layer. The formation of the Cu3Sn compound will not affect the shear strength, 27–30 g, of the solder bump even after a high temperature long time aging test. However, the shear strength after the 30th reflow drops to less than 25 g, ascribed to the formation of a brittle compound, AlxNiy. The failure modes of the solder bump upon shear test were also discussed.
Formation of U-type hexaferrites
Authors: Lisjak Darja , Makovec Darko , Drofenik Miha
Published: May 2005

The formation of U-type hexaferrites with the composition Ba4B2Fe36O60 (B = Co, Ni, Zn) was studied. Samples were characterized by means of x-ray diffraction, electron microscopy (with energy-dispersive spectroscopy), and thermogravimetric and thermomagnetic analyses. U-hexaferrites are formed from the intermediate phases M-hexaferrite (BaFe12O19) and Y-hexaferrite (Ba2B2Fe12O22), which at the same time represent units in the U-hexaferrites’ crystal structure. The preparation of monophase U-hexaferrites was made possible by combining high-energy milling or chemical coprecipitation with a calcination at 1250–1300 °C. Structural defects, such as stacking faults, were observed in monophase samples with a high-resolution transmission electron microscope. The observed defects can be regarded as seeds for the formation of other hexaferrite phases after prolonged calcination times or higher calcination temperatures.
Ultrafine WC-10Co cemented carbides fabricated by electric-discharge compaction
Authors: Wu X.Y. , Zhang W. , Wang W. , Yang F. , Min J.Y. , Wang B.Q. , Guo J.D.
Published: May 2005

This research investigates the microstructure and mechanical properties of ultrafine WC-10Co cemented carbides fabricated by an electric-discharge compaction (EDC) process, from powder synthesized by a spray-conversion process (SCP). Due to a short holding time during EDC, a grain size as small as 120 nm can be achieved. We also found that dispersion of pores in WC-Co cemented carbides may contribute to fracture toughness, besides the bridging ligament mechanism.
Inter- and intragranular nanostructure and possible spinodal decomposition in low-resistivity bulk MgB2 with varying critical fields
Authors: Song Xueyan , Braccini Valeria , Larbalestier David C.
Published: May 2005

Three electromagnetically well-characterized bulk samples with nominal resistivities at 40 K [ρ(40 K)], varying from 1 to 18 μΩcm, were investigated by conventional and high-resolution transmission electron microscopy. Clean, coherent, or semi-coherent grain boundaries and dirty-grain boundaries wetted by amorphous phases were found in all three samples, even though the starting sample A had the very low resistivity of 1 μΩcm at 40 K, characteristic of clean-limit samples. Taking into account its porosity and wetted-grain boundary area, the true resistivity value is about 0.5 μΩcm. Additional samples B and C, prepared by exposing sample A to Mg vapor, showed enhanced ρ(40 K) values of 14 and 18 μΩcm, without noticeable change in either inter- or intra-granular microstructure. Intragranular nanoprecipitates with characteristics of a spinodal of MgB7, with a size of 1–5 nm, were observed in a few areas of samples A and B at high local density; however at too low an overall density to explain the increased resistivities and upper critical fields.
Rapid constructing magnetic phase diagrams by magneto-optical imaging of composition spread films
Authors: Turchinskaya M.J. , Bendersky L.A , Shapiro A.J. , Chang K.S. , Takeuchi I. , Roytburd A.L.
Published: May 2005

In this paper we present a new method of the rapid construction of magnetic phase diagrams in a temperature-composition space, using magneto-optic imaging with an indicator film technique (MOIF). The method is applied for mapping the diagram for the La1–xCaxMnO3 colossal magneto-resistive oxide, using the spread films deposited on a SrTiO3 substrate. The constructed magnetic diagram is in a good agreement with data on uniform films and bulk crystals of this system. The MOIF study of transitions under cooling and heating has revealed the formation of a non-magnetic phase in the area of temperatures from 5 K to 57 K and compositions from x = 0 to x = 0.5.
High-performance bulk Ti-Cu-Ni-Sn-Ta nanocomposites based on a dendrite-eutectic microstructure
Authors: Dai Q.L. , Sun B.B. , Sui M.L. , He G. , Li Y. , Eckert J. , Luo W.K. , Ma E.
Published: May 2005

Using a Ti–Cu–Ni–Sn–Ta alloy as an example, we demonstrate a strategy for the in situ formation of nanocomposite microstructures that can lead to simultaneous high strength and ductility. Our approach employs copper mold casting for the production of bulk alloys from the melt, and the solidification microstructure is designed to be composed of micrometer-sized ductile dendrites uniformly distributed inside a matrix of nanoscale eutectic reaction products. The nanostructured matrix is achieved at a relatively deep eutectic, which facilitates the formation of an ultrafine eutectic microstructure over a range of cooling rates. The multi-component recipe stabilizes a ductile solid solution as the toughening phase and helps to reduce the eutectic spacing down to nanoscale. The multi-phase microstructure (including phase distributions, morphologies, and interfaces) has been examined in detail using transmission electron microscopy (TEM) and high-resolution TEM. The metastable eutectic reaction and the nanoscale spacing achieved are explained using thermodynamic and solidification modeling. The benefits expected from the microstructure design are illustrated using the high strength and large plasticity observed in mechanical property tests. Our nanocomposite design strategy is expected to be applicable to many alloy systems and constitutes another example of tailoring the microstructure on nanoscale for extraordinary properties.
Relationship of glass formation ability and eutectics in ternary Ni–Zr–B system
Authors: Sun W.S. , Zhang H.F. , Ding B.Z. , Hu Z.Q.
Published: May 2005

Five Ni–Zr–B ternary eutectic alloys were synthesized by means of melt spinning and were found “amorphous” by standard surface x-ray diffraction. The thermal stability was determined by differential scanning calorimetry. Glass-formation ability (GFA) was characterized by reduced glass transition temperature among the five “amorphous” alloys. The existence of intermetallic compounds which are structurally complex and have bigger lattice parameters is proved to enhance the higher GFA. The effective suppression of nucleation and growth of intermetallic compounds plays a very important role for the glass formation.
Better control over the onset of microcrystallinity in fast-growing silicon network
Authors: Mukhopadhyay Sumita , Das Debajyoti , Ray Swati
Published: May 2005

In view of obtaining a Si:H network at the onset of microcrystallinity at a high deposition rate, we have adopted an intelligent approach to find out a tricky plasma condition in radio frequency (rf) plasma-enhanced chemical vapordeposition that provides a better control on growth introducing retarded microcrystallization. The deposition parameter includes a combination of high electrical power applied to the (SiH4+H2)-plasma and high gas pressure in thereaction chamber. High rf power increases the number density of film-forming precursors as well as atomic H density in the plasma, which helps to increase thefilm deposition rate and to promote microcrystallinity, respectively. In addition,high pressure helps not only to increase the film-growth rate by producing a dense plasma but also retards the microcrystallization process by increasing significantlythe gas phase collision frequency and consequently reducing the effective reactivityof atomic H on the surface of a fast-growing Si:H network. A combination of high-power and high-pressure plasma conditions provides a reasonably wide rangeof H2 dilution to work with and better control in producing a Si:H network at theonset of microcrystallinity, while increasing the film-growth rate.
Parameter determination of an analytical model for phase transformation kinetics: Application to crystallization of amorphous Mg–Ni alloys
Authors: Liu F. , Sommer F. , Mittemeijer E.J.
Published: May 2005

This study used an analytical model for phase-transformation kinetics. We used different combinations of various nucleation mechanisms [mixed nucleation (site saturation plus continuous nucleation), Avrami nucleation, and site saturation plus Avrami nucleation] and growth mechanisms (volume diffusion-controlled growth and interface-controlled growth) for a single transformation. Our work incorporated the effect of impingement of the growing particles. These factors have been applied to the same experimental results to find out the prevailing mechanisms. We made a detailed analysis for the determination of the parameters of the analytical phase-transformation model, in order to determine the most reasonable nucleation and growth modes, and the values for the activation energies of nucleation and growth. We used the model to study the crystallization kinetics of Mg82Ni18 and Mg88.7Ni11.3, as measured by means of both isothermal and isochronal differential scanning calorimetry.
Nanoscale flow deformation of silicate glass ultrathin films for development of nano-patterned glass surfaces
Authors: Akiba Shusaku , Hara Wakana , Sato Shuhei , Matsuda Akifumi , Sasaki Atsushi , Yoshimoto Mamoru
Published: May 2005

The nanoscale behavior of high-temperature flow deformation for silicate-based oxide glass ultrathin films was characterized with focus on forming a nano-patterned glass surface. The oxide glass thin films were deposited at room temperature by pulsed laser deposition onto the ultrasmooth sapphire substrates with 0.2-nm-high atomic steps. It was found from atomic force microscopy (AFM) measurements that the silicate ultrathin films (about 3 nm thick) started to deform at a temperature 50 °C lower than the glass transition point of the bulk glass. The glass thin films annealed at high temperatures exhibited the nano-stepped surface structure reflecting the sapphire substrate surface. By scanning the AFM tip on the as-deposited glass film in a contact mode and then thermal annealing the film, we could pattern the nano-stepped glass surface at a nanoscale.
Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique
Authors: Voronin G.A. , Zerda T.W. , Gubicza J. , Ungár T. , Dub S.N.
Published: May 2005

A high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness.
Room-temperature growth of ultrasmooth AlN epitaxial thin films on sapphire with NiO buffer layer
Authors: Sasaki Atsushi , Liu Jin , Hara Wakana , Akiba Shusaku , Saito Keisuke , Yodo Tokuo , Yoshimoto Mamoru
Published: May 2005

Room-temperature epitaxy of AlN thin films on sapphire (0001) substrates was achieved by pulsed laser deposition using an epitaxial NiO ultrathin buffer layer (approximately 6 nm thick). Four-circle x-ray diffraction analysis indicates a double heteroepitaxial structure of AlN (0001)/NiO(111)/sapphire (0001) with the epitaxial relationship of AlN [10-10] ‖ NiO [11-2] ‖ sapphire [11-20]. The surface morphology of room-temperature grown AlN thin films was found to be atomically smooth and nanostepped, reflecting the surface of the ultrasmooth sapphire substrate with 0.2-nm-high steps.
Rapid coating of Ti6Al4V at room temperature with a calcium phosphate solution similar to 10× simulated body fluid
Authors: Tas A. Cuneyt , Bhaduri Sarit B.
Published: May 2005

In this paper, we report the utilization of high ionic strength (>1100 mM) calcium phosphate solutions in depositing 20–65-μm-thick, bonelike apatitic calcium phosphate on Ti6Al4V within 2–6 h, at room temperature. The super-strength solution used here multiplied the concentrations of calcium and phosphate ions in human plasma or simulated body fluid (SBF) by a factor of ten. The interesting features of the technique are given in the following. First, the solutions did not contain any buffering agents, such as Tris or Hepes. Second, during the process, homogeneous formation of calcium phosphate nano-clusters took place. However, their presence did not adversely affect the coating process. Third, other than simple surface treatments to begin with, no other additional intermediate steps were necessary. The only step needed after the preparation of the solution from reagents is the addition of proper amounts of NaHCO3 to raise the pH to 6.5 prior to the coating procedure. Fourth, there is no CO2 bubbling required, and hence, this is a robust process. Fifth, such a procedure led to a significant enhancement of coating rate enabling the formation in as little as 2–6 h. Coating proceeded with a linear rate. Sixth, the adhesion strength (12 ± 2 MPa) of the present coatings was comparable to coatings produced by soaking in 1.5× SBF solutions over a prolonged period of time, typically two to three weeks. Finally, the carbonate content (8 wt%) and Ca/P molar ratio (1.57) qualify the coating as bonelike.
Double peritectic behavior of Ag–Zn intermetallics in Sn–Zn–Ag solder alloys
Authors: Song Jenn-Ming , Lin Kwang-Lung
Published: May 2005

In the Sn–9Zn–xAg (x ranges from 0.5 to 3.0%) solder system, the Ag–Zn intermetallics start crystallizing as β–AgZn at about 300 °C. Subsequently, the solder experiences two peritectic transformations upon solidification. This results in the multiphase structural feature. The complicated crystallization process can be briefly described as L(liquid) → L + AgZn → L + AgZn + Ag5Zn8 → AgZn + Ag5Zn8 + AgZn3.
Structures and magnetic properties of Nd–Fe–B bulk nanocomposite magnets produced by the spark plasma sintering method
Authors: Saito Tetsuji , Takeuchi Tomonari , Kageyama Hiroyuki
Published: May 2005

We studied the effects of the sintering temperature and applied pressure on Nd–Fe–B bulk nanocomposite magnets produced by the spark plasma sintering (SPS) method. Amorphous Nd4Fe77.5B18.5 melt-spun ribbons were successfully consolidated into bulk form by the SPS method. When sintered at 873 K under applied pressures between 30 and 70 MPa, the bulk materials consisted of nanocomposite materials with a soft magnetic Fe3B phase and hard magnetic Nd2Fe14B phase. The density and magnetic properties of the bulk materials sintered at 873 K were strongly dependent on the applied pressure during sintering. Bulk Nd4Fe77.5B18.5 nanocomposite magnets sintered at 873 K under an applied pressure of 70 MPa showed a high remanence of 9.3 kG with a high coercivity of 2.5 kOe.
Combined empirical–analytical method for determining contact radius and indenter displacement during Hertzian indentation on coating/substrate systems
Authors: Hsueh Chun-Hway , Miranda Pedro
Published: May 2005

An analytical model was developed in a previous work to relate the normalized indenter displacement to both the coating-to-substrate Young's modulus ratio and the coating-thickness-to-contact-radius ratio for Hertzian indentation on coating/substrate systems. However, application of this model is contingent upon the determination of the contact radius during indentation. Using the data from finite element analyses, an empirical equation is proposed in this paper to determine the normalized contact radius. Combining this empirical equation with the previous analytical equation, both the contact radius and the indenter displacement for Hertzian indentation on coating/substrate systems are predicted. The predictions obtained by this combined empirical–analytical method are shown to agree with the finite element results in general although the indenter displacement is over-estimated when the coating is stiffer than the substrate. Finally, the potential applications of this method to determine the elastic properties of coatings from the indentation data are envisaged.
Soft magnetic properties of bulk nanocrystalline Fe–Co–B–Si–Nb–Cu alloy with high saturated magnetization of 1.35 T
Authors: Shen Baolong , Inoue Akihisa
Published: May 2005

Bulk nanocrystalline body-centered cubic- (bcc) (Fe,Co) alloy with high saturated magnetization and good soft magnetic properties was synthesized by the simple process of casting and annealing for the glass-type Fe62.8Co10B13.5Si10Nb3Cu0.7 alloy. It crystallizes through two exothermic reactions. The cylindrical glassy rod with the diameter of 1.5 mm was produced by copper mold casting. The subsequent annealing at the temperature higher than that of the first exothermic peak causes the formation of bcc-(Fe,Co) nanocrystalline with particle sizes between 10 and 15 nm. The bcc-(Fe,Co) alloy rods exhibit good soft magnetic properties of 1.35 T for saturation magnetization and 5 A/m for coercive force.
Microstructure of Ti5Si3–TiC–Ti3SiC2 and Ti5Si3–TiC nanocomposites in situ synthesized by spark plasma sintering
Authors: Wang Lianjun , Jiang Wan , Chen Lidong , Bai Guangzhao
Published: May 2005

Nanostructured Ti5Si3–TiC–Ti3SiC2 and Ti5Si3–TiC composites were in situfabricated through the spark plasma sintering (SPS) technique using Ti and SiC powders as reactants. It was found that the composites could be prepared in arelatively short time (6 min at 1260 °C) above 98% theoretical density. The phase constituents and microstructures of the samples were analyzed by x-ray diffractionand observed by scanning electron microscopy. Transmission electron microscopywas used for detailed microstructural analysis. The results showed that the reaction products mainly consisted of Ti5Si3 and TiC phases or Ti5Si3, TiC and Ti3SiC2phases, depending on the molar ratio of reactants (Ti to SiC). The composites exhibited fine microstructure; TiC grain size was less than 200 nm. Fracturetoughness at room temperature was also measured by indentation tests.
Contribution of substrate to converse piezoelectric response of constrained thin films
Authors: Chen Lang , Li J-H. , Slutsker J. , Ouyang J. , Roytburd A.L.
Published: May 2005

The converse piezoelectric response of a thin film constrained by a substrate is analyzed in different geometries under various boundary conditions. We considerthe effects of elastic deformation of the substrate on the total displacement of thefilm surface induced by the electric field. The change of film thickness and the bending curvature of a film/substrate couple are calculated. For a thin film island clamped on a large thick substrate, the theoretical estimation of the piezoresponse, including a local bending in the vicinity of the island/substrate interface, is in agreement with the finite element calculation.