bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchrotron x-ray microbeam diffraction from abalone shell
Authors: DiMasi E. , Sarikaya M.
Published: May 2005

Microstructured biomaterials such as mollusk shells receive much attention at present, due to the promise that advanced materials can be designed and synthesized with biomimetic techniques that take advantage of self-assembly and aqueous, ambient processing conditions. A satisfactory understanding of this process requires characterization of the microstructure not only in the mature biomaterial, but at the growth fronts where the control over crystal morphology and orientation is enacted. In this paper, we present synchrotron microbeam x-ray diffraction (XRD) and electron microscopy observations near the nacre–prismatic interface of red abalone shell. The relative orientations of calcite and aragonite grains exhibit some differences from the idealizations reported previously. Long calcite grains impinge the nacre–prismatic boundary at 45° angles, suggestive of nucleation on (104) planes followed by growth along the c axis. In the region within 100 μm of the boundary, calcite and aragonite crystals lose their bulk orientational order, but we found no evidence for qualitative changes in long-range order such as ideal powder texture or an amorphous structure factor. XRD rocking curves determined the mosaic of calcite crystals in the prismatic region to be no broader than the 0.3° resolution limit of the beamline’s capillary optics, comparable to what can be measured on geological calcite single crystals.
SrTiO3 films on platinized (0001) Al2O3: Characterization of texture and nonstoichiometry accommodation
Authors: Klenov Dmitri O. , Taylor Troy R. , Stemmer Susanne
Published: May 2005

Transmission electron microscopy and x-ray diffraction were used to study SrTiO3 films grown on platinized (0001) Al2O3 substrates. The Pt films were epitaxial with an orientation relationship described by (111)Pt‖(0001)Al2O3 and [110]Pt‖[10¯10]Al2O3. SrTiO3 films with two different Sr to Ti ratios, 1.02 and 1.4, were deposited by radio-frequency magnetron sputtering. In the film with a large amount of Sr excess, the grain sizes were smaller and a high density of planar defects was observed. The films were predominantly (111) textured, but a weaker (110) texture component was also found, independent of stoichiometry. While the (111) texture could be explained with the excellent lattice match with (111) Pt, the (110) textured grains had a large mismatch with the Pt electrode. We propose that the presence of the (110) oriented grains is due to nucleation at Pt surface defects. Planar defects in the films with a large amount of Sr excess served to accommodate the nonstoichiometry. Comparison with homoepitaxial SrTiO3 films showed that the density of planar defects in the SrTiO3 films on (111)Pt/Al2O3 is insufficient to accommodate all the excess Sr. The influence of the film microstructure on the dielectric properties is also discussed.
Structure and mechanical properties of cast quasicrystal-reinforced Mg–Zn–Al–Y base alloys
Authors: Yuan Guangyin , Amiya Kenji , Kato Hidemi , Inoue Akihisa
Published: May 2005

The structure and mechanical properties of Mg–Zn–Al–Y base cast alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were investigated. Mg–8Zn–4Al–xY base bulk alloys containing the i-phase were prepared by casting into a copper mold at moderate cooling rates. The Y addition was effective for decreasing the size of the i-phase and the increasing the homogeneity of its dispersed state. The mechanical properties examined by compression tests at room temperature were much superior to those of a conventional AZ91 Mg alloy. The creep tests at elevated temperatures indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg–Zn–Al–Y cast alloy. The strengthening mechanism was also discussed.
Ultrahigh strength Al-based amorphous alloys containing Sc
Authors: Inoue Akihisa , Sobu Shintaro , Louzguine Dmitri V. , Kimura Hisamichi , Sasamori Kenichiro
Published: May 2005

Amorphous metallic alloys possess high strength characteristics, which are superior to crystalline materials. Here we report an influence of Sc addition on glass-forming ability, glass-transition behavior, supercooled liquid region, and mechanical properties of an Al84Y9Ni5Co2 glassy alloy. This paper also aims to present a promising (Al0.84Y0.09Ni0.05Co0.02)95Sc5 amorphous alloy. This alloy has an ultrahigh tensile fracture strength exceeding 1500 MPa, which surpasses those for all the other Al-based fully crystalline and amorphous alloys reported to date, in addition to high Young’s modulus of 78 GPa. The fracture surface of this new alloy exhibited vein pattern typical for amorphous alloys with good ductility, and multiple shear bandswere observed on the lateral surface. The ultrahigh tensile strength of the (Al0.84Y0.09Ni0.05Co0.02)95Sc5 amorphous alloy results from an increase in the interatomic constraint force by the addition of Sc, an element having highly negative enthalpy of mixing with Al, Ni, and Co and the highest chemical affinity with Al among the alloying elements.
Generation of silver/palladium nanoparticles by liquid flame spray
Authors: Keskinen H. , Mäkelä J.M. , Vippola M. , Nurminen M. , Liimatainen J. , Lepistö T. , Keskinen J.
Published: May 2005

Ag–Pd alloy nanoparticles have been generated from silver and palladium nitrate precursors using a high temperature aerosol method, the liquid flame spray (LFS) process. In the LFS process, a spray aerosol of precursor liquid is introduced into a high-temperature H2–O2 flame. The primary micron-sized spray droplets evaporatein the flame, and the final particulate product is a result of the nucleation of the pure metal vapors shortly after the flame. In the study, three Ag–Pd molar ratios—10:90, 50:50, and 90:10—were used in the precursor. As a result of the synthesis, metalalloy nanoparticles with practically the same concentration ratios, correspondingly, were produced with the method. In the experiments, metal mass flow rates of 0.01–0.8 g/min were covered. The size of the particles was determined to be in the rangeof 10–50 nm by aerosol instrumentation. The particles were spherical and slightly agglomerated. It was concluded that the particle size can be controlled via the total precursor mass flow rate, and the composition can be controlled by the molar ratio of Ag and Pd compounds in the precursor liquid.
Facile method of infilling photonic silica templates with rare earth element oxide phosphor precursors
Authors: Silver J. , Ireland T.G. , Withnall R.
Published: May 2005

A method for preparing rare-earth element-doped yttrium oxide phosphor photonic band gap crystals (PBG) is described, which obviates the necessity for multiple infilling of the opal-like template. The method utilizes (i) the re-dissolving and the concentration of previously precipitated spherical phosphor particles made by homogeneous precipitation methods into a viscous precursor phosphor solution, and (ii) formation of an opal-like template of polystyrene or silica spheres. A procedure is outlined that permits the precursor solution to be drawn into the template in a controlled manner that can be easily monitored using an optical microscope. Attenuation of the strong, red cathodoluminescent emission is observed in Y2O3:Eu3+ phosphor PBG crystals that are engineered to have a stopband overlapping the emission bands in the red region. This attenuation results from Bragg diffraction of the light emitted within the PBG phosphor crystals.
Using self-assembling monolayers to study crack initiation in epoxy/silicon joints
Authors: Kent M.S. , Reedy E.D. , Yim H. , Matheson A. , Sorenson J. , Hall J. , Schubert K. , Tallant D. , Garcia M. , Ohlhausen T. , Assink R.
Published: May 2005

The effect of the density and in-plane distribution of interfacial interactions on crack initiation in an epoxy-silicon joint was studied in nominally pure shear loading. Well-defined combinations of strong (specific) and weak (nonspecific) interactions were created using self-assembling monolayers. The in-plane distribution of strong and weak interactions was varied by employing two deposition methods: depositing mixtures of molecules with different terminal groups resulting in a nominally random distribution, and depositing methyl-terminated molecules in domains defined lithographically with the remaining area interacting through strong acid-base interactions. The two distributions lead to very different fracture behavior. For the case of the methyl-terminated domains (50 μm on a side) fabricated lithographically, the joint shear strength varies almost linearly with the area fraction of strongly interacting sites. From this we infer that cracks nucleate on or near the interface over nearly the entire range of bonded area fraction and do so at nearly the same value of local stress (load/bonded area). We postulate that the imposed heterogeneity in interfacial interactions results in heterogeneous stress and strain fields within the epoxy in close proximity to the interface. Simply, the bonded areas carry load while the methyl terminated domains carry negligible load. Stress is amplified adjacent to the well-bonded regions (and reduced adjacent to the poorly bonded regions), and this leads to crack initiation by plastic deformation and chain scission within the epoxy near the interface. For the case of mixed monolayers, the dependence is entirely different. At low areal density of strongly interacting sites, the joint shear strength is below the detection limit of our transducer for a significant range of mixed monolayer composition. With increasing density of strongly interacting sites, a sharp increase in joint shear strength occurs at a methyl terminated area fraction of roughly 0.90. We postulate that this coincides with the onset of yielding in the epoxy. For methyl-terminated area fractions less than 0.85, the joint shear strength becomes independent of the interfacial interactions. This indicates that fracture no longer initiates on the interface but away from the interface by a competing mechanism, likely plastic deformation and chain scission within the bulk epoxy. The data demonstrate that the in-plane distribution of interaction sites alone can affect the location of crack nucleation and the far-field stress required.
Use of aluminum in air-brazing aluminum oxide
Authors: Kim Jin Yong , Hardy John S. , Weil K. Scott
Published: May 2005

A commercial aluminum foil was used to braze alumina plates in air. Although the outer surface of the aluminum oxidizes in air, the majority of the aluminum underneath remains unoxidized during brazing, allowing the ceramic pieces to be joined together with adequate strength. Joint strength testing and subsequent examination of the fracture surfaces of the joints indicate that the joints are inherently ductile, even after long-term, high-temperature air exposure.
The microstructure of Sn in near-eutectic Sn–Ag–Cu alloy solder joints and its role in thermomechanical fatigue
Authors: Henderson Donald W. , Woods James J. , Gosselin Timothy A. , Bartelo Jay , King David E. , Korhonen T.M. , Korhonen M.A. , Lehman L.P. , Cotts E.J. , Kang Sung K. , Lauro Paul , Shih Da-Yuan , Goldsmith Charles , Puttlitz Karl J.
Published: May 2005

During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.
Field decrystallization and structural modifications of highly doped silicon in a 2.45-GHz microwave single-mode cavity
Authors: Peelamedu Ramesh , Roy Rustum , Agrawal Dinesh , Drawl William
Published: May 2005

Highly doped n-type silicon powder responds aggressively to a 2.45-GHz microwave E-field, whereas it remains unperturbed in the H-field. In the E-field, after about 30 s of treatment, the silicon powder attained submelting temperatures and thus coagulated to a bulk solid piece. X-ray diffraction analysis of the surface and the cross section of this solid material failed to show any detectable peaks, ascertaining the fact that the material had decrystallized. The Raman spectra of the material had broad and shallow peaks quite different from the thin, sharp lines exhibited by Si wafer. It appears that the E-field treatment has considerably distorted the lattice structure creating lattice strains throughout the sample. These lattice strains were relieved by grinding (recrystallized).
Fabrication of β-boron by chemical-reaction and melt-quenching methods at high pressures
Authors: Brazhkin V.V. , Taniguichi T. , Akaishi M. , Popova S.V.
Published: May 2005

The dependence of boron crystallization upon melt cooling has been investigated, as well as boron formation as a result of the chemical reaction of boron oxide with magnesium at a pressure of 7.7 GPa. Crystallization from the melt and the chemical reaction produce a rhombohedral β-boron phase, which is evidence of this phase stability at all temperatures up to the melting curve within the pressure range up to7.7 GPa. The melting temperatureTmat 7.7 GPa is 2480 ± 50 K, which points to a slight positive slope of the melting curve equal to approximately 10 K/GPa. Well-shaped single crystals of boron are formed as a result of the chemical reaction and the subsequent cooling from the melt at a rate of approximately 1 K/s, indicating low viscosity of the liquid phase.
Nanotopography impact in shallow-trench isolation chemical mechanical polishing—analysis method and consumable dependence
Authors: Park Jea-Gun , Katoh Takeo , Paik Ungyu
Published: May 2005

The nanotopography of the surface of silicon wafers has become an important issue in ULSI device manufacturing, as it affects the post–chemical mechanical polishing (post-CMP) uniformity of the thickness deviation of dielectric films. A spectral method is proposed to examine quantitatively how the nanotopography impacts the film thickness deviation during CMP. The nanotopography impact was investigated in terms of its dependence on the characteristics of consumables, such as the polishing pad hardness and the wafer manufacturing method. In addition, the effects of the surfactant and the abrasive size in ceria slurry on nanotopography impact were investigated. It was found that the magnitude of the post-CMP oxide thickness deviation due to nanotopography increased with the surfactant concentration in the case of smaller abrasives but was almost independent of the concentration in the case of larger abrasives. These results demonstrate that the nanotopography impact can be controlled by manipulating the slurry characteristics.
New lead-free relaxors based on the K0.5Na0.5NbO3–SrTiO3 solid solution
Authors: Kosec Marija , Bobnar Vid , Hrovat Marko , Bernard Janez , Malic Barbara , Holc Janez
Published: May 2005

New lead-free relaxors have been produced from the K0.5Na0.5NbO3–SrTiO3 (KNN-STO) system. The solid solubility within the studied range of compositions (1 - x) K0.5Na0.5NbO3–xSrTiO3 was observed for x up to 0.33. A pseudo-cubic perovskite structure was determined for x = 0.15 to 0.25. The high density and the uniform distribution of fine grains and pores were confirmed by the translucency of these ceramics. The 0.85KNN-0.15STO composition reaches the dielectric permittivity of above 3000 at room temperature. Dielectric spectroscopy measurements revealed that, as with lead-based complex perovskites, the cationic distribution disorder is reflected in relaxorlike properties, thus suggesting possible applications based on this environmentally friendly lead-free ceramic system.
Microwave-assisted synthesis of calcium phosphate nanowhiskers
Authors: Jalota Sahil , Tas A. Cuneyt , Bhaduri Sarit B.
Published: May 2005

Calcium phosphate [single-phase hydroxyapatite (HA), single-phase tricalcium phosphate (TCP), and biphasic HA-TCP] nanowhiskers and/or powders were produced by using a novel microwave-assisted “combustion synthesis (auto ignition)/molten salt synthesis” hybrid route. This work is an example of our “synergistic processing” philosophy combining these three technologies while taking advantage of their useful aspects. Aqueous solutions containing NaNO3, Ca(NO3)2·4H2O and KH2PO4 (with or without urea) were irradiated in a household microwave oven for 5 min at 600 watts of power. The as-synthesized precursors were then simply stirred in water at room temperature for 1 h to obtain the nanowhiskers or powders of the desired calcium phosphate bioceramics.
Quantifying improvements in adhesion of platinum films on brittle substrates
Authors: Cordill M.J. , Moody N.R. , Bahr D.F.
Published: May 2005

This study used nanoindentation coupled with stressed overlayers to evaluate the effect of titanium interlayers on the interfacial fracture energy of platinum films on SiO2substrates. Interfacial fracture energy was calculated three ways: from platinum buckles that formed spontaneously upon deposition of the film, from buckles that formed upon deposition of a stressed tungsten overlayer, and from blisters triggered by indentation of a platinum film with a tungsten stressed overlayer. The calculated values for the interfacial fracture energy of the Pt-SiO2interface were 0.2 and 0.5 J/m2for indentation blisters and spontaneous buckles, respectively. The effect of a titanium interlayer on adhesion was examined using a tungsten stressed overlayer coupled with nanoindentation. The addition of a titanium layer improved the adhesion of the platinum film on SiO2from 0.2 to 1.0 J/m2.
Carbon nanotubes grown on different-sized rectangular patterns
Authors: Pan Lujun , Nakayama Yoshikazu , Shiozaki Hideki , Inazumi Chikashi
Published: May 2005

Carbon nanotubes have been synthesized by chemical vapor deposition using a thin iron film as catalyst on the silicon substrate with different-sized rectangular patterns. It is found that the carbon nanotubes grow vertically to the substrate in a high density with a surface shape similar to that of the substrate when the line width of the patterns are larger than 1 μm, However, when the line width of the pattern is reduced to below 0.5 μm, carbon nanotubes cannot grow vertically anymore. This phenomenon might be caused by the relaxation of stress in catalyst film and the coalescence of the catalyst clusters to form particles or grains, which contributes to the migration of catalyst from edge to inner part during the nucleation process. These results are very useful for the fabrication of field-emission displays and other devices using patterned carbon nanotubes.
Phase transition of iron inside carbon nanotubes under electron irradiation
Authors: Kim Hansoo , Kaufman Michael J. , Sigmund Wolfgang M.
Published: May 2005

Selective encapsulation of different materials or phases of a material inside a carbon nanotube leads to controlling local properties of the nanotube. We report a method of synthesizing stable γ-Fe selectively inside a carbon nanotube by transforming α-Fe through electron irradiation in situ inside a transmission electron microscope. Therefore, this method enables a single nanotube to encase both high (γ-Fe) and low (α-Fe) temperature phases of iron simultaneously. γ-Fe produced by this method may be used as a novel catalyst, and its presence inside a carbon nanotube may affect the physical properties of the nanotube, which therefore can be used to modify the nanotube.
Ferroelectric property of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method
Authors: Morita Takeshi , Wagatsuma Yasuo , Morioka Hitoshi , Funakubo Hiroshi , Setter Nava , Cho Yasuo
Published: May 2005

Deposition of thin films via hydrothermal method has various advantages: low deposition temperature, high purity, deposition on a three-dimensional structure,and a large thickness. Although an epitaxial lead zirconate titanate (PZT) thin-film deposition has been reported, the ferroelectric measurement has not been conducted due to the peel-off morphology of the film. The current paper investigates the improvement of an epitaxial PZT thin film deposited via a hydrothermal method. By adjusting the position at which the substrate was suspended in the solution, smooth morphology surface was successfully obtained. As a bottom electrode, a 200-nm SrRuO3 thin film was deposited on SrTiO3 single crystals, and the PZT thin film was deposited on SrRuO3. The remanent polarization 2Pr and coercive electric field for PZT on SrRuO3/SrTiO3 (001) were 17.1 μC/cm2 and 36 kV/cm, respectively, and those of PZT on SrRuO3/SrTiO3 (111) were 32.7 μC/cm2 and 59 kV/cm, respectively. The reason for large imprint electrical field, 91 kV/cm and 40 kV/cm for each film, was unclear at this stage, although it is associated with self–alignment poling direction. This self–alignment poling direction was confirmed via scanning nonlinear dielectric microscopy and is thought to have been related to the deposition mechanisms.
Microstructure of SrTiO3 buffer layers and itseffects on superconducting properties ofYBa2Cu3O7-δ coated conductors
Authors: Wang H. , Foltyn S.R. , Arendt P.N. , Jia Q.X. , MacManus-Driscoll J.L. , Stan L. , Li Y. , Zhang X. , Dowden P.C.
Published: May 2005

A thin layer of SrTiO3 (STO) has successfully been used as a buffer layer to grow high-quality superconducting YBa2Cu3O7-δ(YBCO) thick films on polycrystalline metal substrates with a biaxially oriented MgO template produced by ion-beam-assisted deposition. Using this architecture, 1.5-μm-thick YBCO films with an in-plane mosaic spread in the range of 2.5° to 3.5° in full width at half-maximum and critical current density over 2 × 10 6A/cm2 in self-field at 75 K have routinely been achieved. It is interesting to note that the pulsed laser deposition growth conditions of SrTiO3 buffer layers, such as growth temperature and oxygen pressure, have strong effects on the superconducting properties of YBCO. Detailed studies using transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used to explore the microstructures of STO deposited at different conditions and to understand further their effects on the growth and properties of YBCO films.
Synthesis and characterization of polyether structure carbon nitride
Authors: Mu Tiancheng , Huang Jun , Liu Zhimin , Han Buxing , Li Zhonghao , Wang Yong , Jiang Tao , Gao Haixiang
Published: May 2005

Carbon nitride powder with an atomic N/C ratio of 1 has been prepared by reaction of cyanuric chloride with sodium metal. X-ray diffraction, Fourier transform infrared spectra, and x-ray photoelectron spectroscopic data provide substantial evidence for a graphite-like sp2-bonded structure composed of building blocks of s-triazine rings bridged by carbon-carbon atoms in the bulk carbon nitride. The electron-microscopy results reveal that the material is spherical particles with an average diameter of 50 nm. The optical properties and thermal stability are also characterized. Based on the experimental results, it is deduced that the structure of as-prepared material carbon nitride has polyether structure.
Organic solar cells: An overview
Authors: Hoppe Harald , Sariciftci Niyazi Serdar
Published: May 2005

Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.
Organic molecular-beam deposition of perylene on Cu(110): Results from near-edge x-ray absorption spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy
Authors: Hänel K. , Söhnchen S. , Lukas S. , Beernink G. , Birkner A. , Strunskus T. , Witte G. , Wöll Ch.
Published: May 2005

The growth of the polycyclic aromatic hydrocarbon perylene on (110) oriented copper substrates has been studied by means of x-ray photoelectron spectroscopy, near-edge x-ray absorption spectroscopy, and atomic force microscopy. In the monolayer regime, the molecules are orientated with their molecular plane parallel to the substrate, whereas they adopt a tilted arrangement in multilayer films. For multilayers with thicknesses exceeding 10 nm, the molecules grow in a bulk-like structure with their long axes orientated upright to the substrate surface.
Degradation of organic field-effect transistors made of pentacene
Authors: Pannemann Ch. , Diekmann T. , Hilleringmann U.
Published: May 2005

This article reports degradation experiments on organic thin film transistors using the small organic molecule pentacene as the semiconducting material. Starting with degradation inert p-type silicon wafers as the substrate and SiO2 as the gate dielectric, we show the influence of temperature and exposure to ambient air on the charge carrier field-effect mobility, on-off-ratio, and threshold-voltage. The devices were found to have unambiguously degraded over 3 orders of magnitude in maximum on-current and charge carrier field-effect mobility, but they still operated after a period of 9 months in ambient air conditions. A thermal treatment was carried out in vacuum conditions and revealed a degradation of the charge carrier field-effect mobility, maximum on-current, and threshold voltage.
Metal ion and N co-doped TiO2 as a visible-light photocatalyst
Authors: Sakatani Yoshiaki , Ando Hiroyuki , Okusako Kensen , Koike Hironobu , Nunoshige Jun , Takata Tsuyoshi , Kondo Junko N. , Hara Michikazu , Domen Kazunari
Published: May 2005

Powders of TiO2 doped with a metal ion and N species were prepared by a polymerized complex method and the visible-light photocatalytic activities of the products are investigated. Of the metal ions studied (K+, Ca2+, Sr2+, Ba2+, Nb5+, Fe3+, Zn2+, and Al3+), the photocatalyst prepared with Sr2+ exhibits the highest activity for acetaldehyde decomposition under visible-light irradiation. Results obtained from x-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) analyses suggest that the doped N species reside at interstitial lattice positions in the catalyst. It was also found by XPS and ESR measurements that the doped N species combine with lattice oxygen to give rise to a paramagnetic property. The visible-light response of the catalyst is driven by the formation of paramagnetic N species at interstitial positions in the TiO2 lattice.
Sol-gel coatings to improve processing of aluminium matrix SiC reinforced composite materials
Authors: Rams J. , Campo M. , Ureña A.
Published: May 2005

This paper analyses the influence of the inner structure of a SiO2 coating deposited on SiC particles by a sol-gel route on reactivity and wettability between SiC particles and molten aluminium during composite manufacturing. Different heat treatments were applied to the sol-gel coatings to change the porous structure of the amorphous silica. The coatings subjected to the mildest heat treatment were more reactive with molten aluminium, enriching the Si content of the matrix composite, and hence inhibiting direct reaction of the SiC particles and the formation of aluminium carbide. Thermal analysis showed that Si enrichment altered the solidification behavior of the aluminium matrix and its resultant microstructure, influencing the manufacturing conditions and final properties of the fabricated composites.
Transmission electron microscopy and electron energy loss spectroscopy analysis of ultrathin amorphous carbon films
Authors: Wan D. , Komvopoulos K.
Published: May 2005

Transmission electron microscopy (TEM) and analytic TEM were used to study the microstructure of amorphous carbon (a-C) films of thickness in the range of 5–100 nm deposited on Si(100) by radio-frequency (rf) sputtering. High-resolution cross-section TEM revealed a two-layer structure consisting of the a-C film and an ultrathin interface layer, in agreement with electron energy loss spectroscopy results. The presence of a 35-Å-thick interface layer (regardless of the deposition conditions) indicates that nucleation and initial growth of the a-C films were mainly controlled by the substrate surface condition. Mass-thickness contrast in bright-field TEM images showed an interface layer denser than the a-C film. This layer, believed to consist of Si, a-C, and SiC, enhances the adhesion of the film to the silicon substrate and accommodates the residual stress in the film. High-resolution cross-section TEM images revealed the presence of platelike nanocrystallites (∼35 Å in size) randomly distributed in the a-C film and oriented parallel to the surface. The possible mechanisms leading to the formation of these nanocrystalline structures are discussed in terms of sputtering phenomena occurring during film deposition.
First solar cells based on CdTe nanoparticle/MEH-PPV composites
Authors: Kumar Sandeep , Nann Thomas
Published: May 2005

Hybrid bulk heterojunction composites are promising material for low-cost organic solar cells. Fundamental measurements with CdTe nanocrystal/MEH-PPV poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] composites and the first realization of a solar cell based on this material are presented. Optical and electrochemical properties are discussed as well as the current voltage characteristic of the resulting cell. It was found, that CdTe nanocrystal/MEH-PPV composites are well suited for an organic solar cell, even though the technological realization needs to be improved.
Chemical solution deposition of lanthanum zirconate barrier layers applied to low-cost coated-conductor fabrication
Authors: Sathyamurthy S. , Paranthaman M. , Zhai H.Y. , Kang S. , Aytug T. , Cantoni C. , Leonard K.J. , Payzant E.A. , Christen H.M. , Goyal A. , Li X. , Schoop U. , Kodenkandath T. , Rupich M.W.
Published: May 2005

Epitaxial lanthanum zirconate (LZO) buffer layers have been grown by sol-gel processing on Ni–W substrates. We report on the application of these oxide films as seed and barrier layers in coated conductor fabrication as potentially simpler, lower cost coated-conductor architecture. The LZO films, about 80–100-nm thick, were found to have dense, crack-free surfaces with high surface crystallinity. Using 0.2-μm YBCO deposited by pulsed laser deposition, a critical current density of 2 MA/cm2 has been demonstrated on the LZO films (YBCO/LZO/Ni–W). Using 0.8-μm YBCO deposited using metal organic decomposition, a critical current density of 1.7 MA/cm2 and a critical current of 135 A/cm have been demonstrated on the LZO barrier layer with a sputtered CeO2 cap layer (YBCO/CeO2/LZO/Ni–W). These results offer promise to replace several of the vacuum-deposited layers in the typical coated conductor architecture (YBCO/CeO2/YSZ/Y2O3/Ni/Ni-W).
Crystalline silica nanowires
Authors: Deepak F.L. , Gundiah Gautam , Seikh Md. Motin , Govindaraj A. , Rao C.N.R.
Published: May 2005

α-Cristobalite nanowires of 50–100 nm diameter with lengths of several microns have been synthesized for the first time by the solid-state reaction of fumed silica and activated charcoal. The nanowires have been characterized by x-ray diffraction, electron microscopy, photoluminescence, and Raman scattering. The nanowires are single crystalline as revealed by high-resolution electron microscope images. The crystalline nanowires are clad by an amorphous silica sheath when the carbon to fumed silica ratio in the starting mixture is small. Use of hydrogen along with Ar helps to eliminate the amorphous sheath.
Formation of in situ reinforced microstructures in α-sialon ceramics: Part III. Static and dynamic ripening
Authors: Peng Hong , Shen Zhijian , Nygren Mats
Published: May 2005

Dual cation (Yb + Y)-stabilized α-sialon ceramics with either stoichiometric composition or nonstoichiometric composition that yield less than 3 vol% of an additional intergranular liquid/glass phase were consolidated by spark plasma sintering (SPS). This process allows very fast heating and cooling, thus providing a unique possibility to monitor and manipulate the kinetics of phase transformation and grain growth during sintering. Below a temperature threshold, full densification and complete α-sialon formation are accompanied by very limited grain growth. The grain growth kinetics were investigated both by post heat-treatment of SPS pre-consolidated monophasic α-sialon bodies consisting of sub-micron sized equiaxed grains in a conventional graphite furnace using extended holding times (hours) and directly rapid annealing in the SPS apparatus above the temperature threshold (within minutes). Post heat treatment in the graphite furnace yielded in situ reinforced microstructures consisting of interlocking elongated grains only in the presence of an additional intergranular liquid/glass phase. Direct annealing by SPS process yielded in situ reinforced microstructures whether or not an additional liquid/glass was involved. The former microstructures are formed via the static Ostwald ripening mechanism whereas the latter ones are generated via a dynamic ripening mechanism. This demonstrates that the dynamic ripening provides an efficient means of developing in situ reinforced microstructure in α-sialon ceramics with improved mechanical properties.
Chemical and physical characterization of C(N)-doped W–S sputtered films
Authors: Nossa A. , Cavaleiro A.
Published: May 2005

The load-bearing capacity of self-lubricating W–S films can be improved by doping with nitrogen or carbon. In this study, the chemical composition, the atomic bonding, the structure, and the surface and cross section morphologies of sputtered W–S–C(N) films were analyzed. The addition of the doping element leads to a progressive broadening of the x-ray diffraction (XRD) peaks indicating a loss of crystallinity. In W–S–N films, amorphous structure could be obtained. In W–S–C films, W–C compounds were detected in conjunction with the hexagonal WS2 phase. For the highest C contents, a nanocomposite structure, including those phases and graphite, was suggested for the film. X-ray photoelectron spectroscopy results showed different types of bonds in the W4f peak in good agreement with the XRD results, i.e., when W–C(N) compounds were indexed W–S, W–C, and W–N bonds are present in the W4f peak. For the highest C content film, the detection of C–C bond in the C1s peak confirmed the formation of graphite.
Liquidus projection of the ternary Ag–Sn–Ni system
Authors: Chen Sinn-wen , Hsu Hsiu-feng , Lin Chih-wei
Published: May 2005

The liquidus projection of the ternary Sn–Ag–Ni system at the Sn-rich side was determined experimentally. No ternary compound was found, and the ζ–Ag4Sn, Ag3Sn, and Sn existed as the primary solidification phases only in very small compositional portions of the ternary Sn–Ag–Ni system. In more than half of the compositional regime of the ternary system, the Ni3Sn2 phase was the primary solidification phase. The differential thermal analysis technique was used to determine the reaction temperatures and solidification sequences of various Sn-rich Sn–Ag–Ni alloys. Three invariant reactions were found: L = Sn + Ni3Sn4 + Ag3Sn, L + ζ–Ag4Sn = Ni3Sn4 + Ag3Sn and L + Ni3Sn2 = ζ–Ag4Sn + Ni3Sn4. Their reaction temperatures have been determined to be 219, 488, and 516.5 °C, respectively.
Effect of as-deposited residual stress on transition temperatures of VO2 thin films
Authors: Tsai Kuang Yue , Chin Tsung-Shune , Shieh Han-Ping D. , Ma Cheng Hsin
Published: May 2005

Transmittance loops upon thermal cycling of VO2 thin films were found to change among films with different fabrication conditions that lead to different transition temperatures (Tts) from that of a strain-free VO2 single crystal, 68 °C. The residual stresses in the films quantitatively determined from x-ray diffractometry were used to explain this variation. Electron spectroscopy for chemical analysis spectra showed that the difference in the binding energy of core electrons 2p1/2 and 2p3/2 of the vanadium atom are affected by residual stress and proportional to Tts of the films. The bond length between vanadium and oxygen atoms at room temperature varies with different residual stresses and, furthermore, affects the movements of both atoms during phase change (and hence the Tt of VO2 thin films). Residual stresses also affect the hysteresis span of the transmittance loop. The relationship between the residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen atoms are also delineated in detail.
Study of decagonal approximant and γ-brass-type compounds in Al–Cr–Fe thin films
Authors: Demange V. , Ghanbaja J. , Beeli C. , Machizaud F. , Dubois J.M.
Published: May 2005

This paper reports the preparation conditions and structure characteristics of Al–Cr–Fe very thin films (10–30 nm) obtained by the flash evaporation technique. The films are either amorphous or crystallized, depending on the thickness of the sample and temperature of the substrate. Annealing of amorphous films leads to crystallization of intermetallic phases that are all linked with quasicrystals. In particular, we have identified by transmission electron microscopy the following structures: body-centered-cubic (bcc) γ-brass phase, monoclinic λ–Al13(Cr,Fe)4phase, and orthorhombic O1-phase, all of them already observed in this system, together with four new structures, i.e., a face-centered-cubic (fcc) γ-brass phase (superstructure of the bcc phase), monoclinic λ′-phase (related to the λ-phase) and two orthorhombic phases (1/1/; 1/1) and (1/0; 2/1) approximants of the decagonal phase). In this study, we point out the occurrence of twin defects of the λ–Al13(Cr,Fe)4phase. Films prepared directly in the crystalline state comprise the O1approximant. Electron energy loss spectroscopy measurements show that all films are not oxidized except for the presence of a native oxide layer that forms in ambient atmosphere with a thickness that cannot exceed 0.3 nm. Optical properties were investigated and show that films need to be large enough (>30 nm) to reproduce the properties of bulk alloys. Finally, contact angle wetting measurements reveal that the presence of such films on a substrate, even at very low thickness, considerably decreases the wetting behavior by water.
Preparation of cathode active materials for lithium ion secondary batteries utilizing microwave irradiation: Part II. Electronic structure of lithium manganese oxide
Authors: Kobayashi Shota , Usui Tatsuya , Ikuta Hiromasa , Uchimoto Yoshiharu , Wakihara Masataka
Published: May 2005

The microwave irradiation technique (MWIT) was applied to synthesize lithium manganese oxide having spinel structure using LiOH·H2O and ε–MnO2 as starting materials. The crystal and electronic structure depends on the irradiation time; x-ray diffraction patterns of the sample irradiated for 9 min were in good agreement with that of cubic structure without showing the peak of MnO2. The electronic structure of synthesized samples before and after lithium ion intercalation and/or deintercalation was investigated by Mn L-edge and O K-edge x-ray absorption spectroscopy.
Photochromism in spiropyran impregnated fluorinated mesoporous organosilicate films
Authors: Bae Jae Young , Jung Ji-In , Bae Byeong-Soo
Published: May 2005

Fluorinated mesoporous organosilicate films were synthesized by sol-gel spin-coating on a quartz substrate using (heptadecafluorodecyl)trimethoxysilane, tetramethylorthosilicate, and n-cetyltrimethylammonium chloride as the fluoro-precursor, silica source, and supramolecular template, respectively. The photochromism efficiency of photochromic dyes (spiropyran) increases in the order non-porous < hexagonal mesoporous < fluorinated mesoporous organosilicate films. The relatively high efficiency of the photochromism of spiropyran in fluorinated mesoporous organosilicate films suggests that such films are promising materials for applications as optical shutters and light modulators.
New method of producing well-aligned ZnO nanorods on a Si-SiO2 substrate
Authors: Hung N.C. , Wang G.Z. , Yau M.Y. , Ng Dickon H.L.
Published: May 2005

Well-aligned ZnO nanorods arrays were fabricated by sintering powder Zn underneath a Si–SiO2 substrate. In this fabrication, ZnO was produced by the displacement reactions between Zn and SiO vapors. We found that these ZnO nanorods grew toward the [0001] direction. The diameter and the alignment of these nanorods strongly depended on the sintering temperature. When the temperature was increased from 740 to 800 °C, the diameter of the rods was increased from 30–70 nm to 300–700 nm, and their alignment was also improved. A model is proposed to describe the formation of these nanorods.
Erratum: “Magnetic properties of undoped and Co-doped n-type β-FeSi2.5 single crystals” [J. Mater. Res. 17, 2960–2965 (2002)]
Authors: Arushanov E. , Ivanenko L. , Eckert D. , Behr G. , Rößler U.K. , Müller K.-H. , Schneider C. , Schumann J.
Published: May 2005

In the title of this paper (and also in several places in the text), the chemical notation for the orthorhombic semiconducting iron disilicide is given incorrectly. In the whole paper, the chemical formula “β-FeSi2.5” should be replaced by the formula “β-FeSi2”.
Aluminum-containing intergranular phases in hot-pressed silicon carbide
Authors: Zhang Xiao Feng , De Jonghe Lutgard C.
Published: May 2005

Using transmission electron microscopy, we studied aluminum-containing intergranular phases and secondary-phase particles at triple-junctions in SiC (hot-pressed with aluminum, boron, and carbon additions). This study of statistical high-resolution electron microscopy of intergranular films indicated that a large fraction of the vitreous intergranular films (in the as-hot-pressed SiC) crystallized during post-annealing in argon above 1000 °C. However, brief heating to 1900 °C indeed re-melted 25% of the crystallized intergranular films. The structural transitions were reflected in the statistical width distributions of the amorphous grain-boundary layers. At triple-junctions, Al2O3, Al2OC-SiC solid solution, and mullite phases were newly identified. These phases, together with others reported before, are represented in a quaternary phase diagram for 1900 °C. It is proposed that a SiC-Al2OC liquid domain should be included in this phase diagram.
Surface biofunctionalization of materials by amine groups
Authors: Martín-Palma R.J. , Manso M. , Pérez-Rigueiro J. , García-Ruiz J.P. , Martínez-Duart J.M.
Published: May 2005

A novel deposition technique for the bio-functionalization by amine groups of surfaces of materials is presented. The process is based on the activation at high temperature of 3-aminopropyltrietoxysilane (3-APTS) molecules in vapor phase immediately before impinging on the substrate. Materials such as silicon, porous silicon, and titanium were chosen to demonstrate the validity of the process on surfaces with very different chemical properties. The effect of the activation process on the surface was evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction (XRD). In addition, the reactivity under mild reaction conditions of the functionalized surfaces was determined by using a fluorescent reagent that specifically reacts with amine groups. From the experimental results it can be concluded that the proposed activation method induces amino-group fixation on the surface of materials, ranging from semiconductors to metals and insulating materials.
Effect of lead zinc niobate addition on sintering behavior and piezoelectric properties of lead zirconate titanate ceramic
Authors: Lee Sung-Mi , Yoon Chang-Bun , Lee Seung-Ho , Kim Hyoun-Ee
Published: May 2005

We investigated the effect of lead zinc niobate (PZN) on the sintering behavior and piezoelectric properties of lead zirconate titanate (PZT) ceramics. The addition of PZN improved the sinterability of PZT ceramic so remarkably, that at additions of more than 10%, the specimens were fully dense at a temperature as low as 900 °C. The phase of the PZT-PZN ceramics was affected by PZN content and the Zr/Ti ratio in the PZT. With increasing PZN content, a lower Zr/Ti ratio was required for the morphotropic phase boundary (MPB). Specimens with the MPB composition showed the highest piezoelectric properties; d33 = 500 pC/N, kp = 0.68, and S33 = 0.38% at 2 kV/mm.
An irreversible disappearance of the mechanical loss peak of an yttria-doped silicon nitride
Authors: Akatsu T. , Kawakami Y. , Tanabe Y. , Yasuda E. , Yamada K. , Kamiya N.
Published: May 2005

The internal friction of a silicon nitride with a sintering aid of yttrium oxide was measured from room temperature to 1400 °C. A mechanical loss peak was typically observed at 1000 °C on heating the as-sintered specimen; however, it disappeared on cooling. Also, the peak was not observed upon heating a specimen that had been heated above 1400 °C. When we carried out thermal cycling, raising terminal temperatures from 1050 to 1400 °C, the integrated intensity of the peak gradually decreased due to the progressive crystallization of a grain-boundary amorphous phase.
An effective Cu-Sn barrier layer for Au bump used in optoelectronic devices
Authors: Liu C.Y. , Wang S.J.
Published: May 2005

By studying reactions between Au foils and Sn(Cu) alloys, we found that the Au consumption rate depended on the Cu-content of the Sn(Cu) solders. The higher Cu-content alloys had faster Au consumption rates. When the Au foil was pre-coated with a Ni layer and then reacted with Sn(Cu) alloys having a Cu-content of morethen 1.5 wt%, a stable ternary (Cu,Ni)6Sn5 compound layer was observed on theAu foil. This ternary compound layer then served as a barrier layer that effectively prevented the Au foil from reacting with the molten solder. This result enabled the implementation of a flip-chip assembly process for the fabrication of optoelectronic devices.