bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of a high active photocatalyst, K2La2Ti3O10, by polymerized complex method and its photocatalytic activity of water splitting
Authors: Ikeda Shigeru , Hara Michikazu , Kondo Junko N. , Domen Kazunari , Takahashi Hiroyuki , Okub Toru , Kakihana Masato
Published: March 2008

A layered perovskite type oxide, K2La2Ti3O10, was prepared by a gel technique using the polymerized complex (PC) method. A single phase K2La2Ti3O10 was obtained by adding twice the potassium required for stoichiometry. The Ni–K2La2Ti3O10 catalyst prepared by the PC method exhibited a higher photocatalytic activity for decomposition of H2O into H2 and O2 than that prepared by a conventional solid state reaction.
Preparation of porous niobium oxide by the exfoliation of K4Nb6O17 and its photocatalytic activity
Authors: Abe Ryu , Shinohara Kiyoaki , Tanaka Akira , Hara Michikazu , Kondo Junko N. , Domen Kazunari
Published: March 2008

A new porous material was prepared from a layered compound, K4Nb6O17, through the exfoliation of its layers. A composite of the niobate sheets and MgO particles were obtained by precipitating the exfoliated two-dimensional niobate sheets with MgO fine particles. Porous niobium oxide was obtained by removal of the MgO particles from the composite after thermal treatment. It had a large surface area and showed higher photocatalytic activity than the original H+/K4Nb6O17 for H2 evolution from various aqueous alcohol solutions.
Hydrothermal growth of millimeter-sized aluminosilicate sodalite single crystals in noble metal capsules
Authors: Hayashi Tomohiro , Shiga Hidemoto , Sadakata Masayoshi , Okubo Tatsuya , Yoshimura Masahiro
Published: March 2008

Aluminosilicate sodalite Na8[SiAlO4]6Cl2 single crystals are synthesized by hydrothermal processing at 873–973 K and 100–150 MPa in noble metal capsules to avoid contamination. The starting material is aluminosilicate gel, and spontaneous nucleation followed by its growth takes place. The largest size of the single crystals obtained is 1 mm across. Longer aging and heating result in larger single crystals. It is also found that the aluminum source in the synthesis gel and the element used in the noble metal capsules influence the single crystal growth. Judging from x-ray diffraction (XRD) (powder and single-crystal), optical microscopy, and thermogravimetry and differential thermal analysis (TG-DTA), the sodalite single crystals grown have good quality compared with the conventional powder.
Potential oscillations during the electrochemical self-assembly of copper/cuprous oxide layered nanostructures
Authors: Switzer Jay A. , Hung Chen-Jen , Huang Ling-Yuang , Miller F. Scott , Zhou Yanchun , Raub Eric R. , Shumsky Mark G. , Bohannan Eric W.
Published: March 2008

Layered nanostructures of copper metal and cuprous oxide are electrodeposited from alkaline solutions of Cu(II) lactate at room temperature. No subsequent heat treatment is necessary to effect crystallization. The electrode potential spontaneously oscillates during constant-current deposition. At a fixed current density the oscillation period decreases as either the pH or temperature is increased. The oscillations are periodic in stirred solution, but show period doubling and evidence of quasi-periodic or chaotic behavior in unstirred solution. The phase composition and resistivity of the films can be controlled by varying the applied current density. The resistivity of the films can be varied over ten orders of magnitude. Scanning electron microscopy shows that the films are layered.
One-step electrodeposition of CdS/ZnS bilayer from an aqueous mixture of Cd2+ and Zn2+
Authors: Yamaguchi Koichi , Yoshida Tsukasa , Sugiura Takashi , Minoura Hideki
Published: March 2008

Electrochemical thin film deposition in aqueous mixtures containing Cd2+, Zn2+, and thioacetamide has been investigated. It has been found that the atom-by-atom growth of well-crystallized CdS thin film preferentially takes place at the early stage of the reaction, followed by the cluster-by-cluster growth of the poorly crystallized ZnS outer layer, thus resulting in the formation of CdS/ZnS bilayer by a one-step synthesis.
Synthesis of hollandite-type KxGaxSn8−xO16 fine particles by the sol-gel method
Authors: Fujimoto Kenjiro , Watanabe Mamoru , Mori Toshiyuki , Ito Shigeru
Published: March 2008

KxGaxSn8−xO16 (x ≤ 2) powders with hollandite structure were prepared by the sol-gel method using metal alkoxides. Dried gels, when being annealed at 973 K, changed to well-crystallized hollandite powders with about 22 m2/g in BET value which consisted of needle-like crystallites 25 nm wide and 65 nm long in average. The specific surface area was nearly 100 times larger than that of the hollandite produced at 1648 K by the conventional method, and the preparation temperature was lowered by 500 to 700 K. The powders obtained at 973 K were characterized as an attractive porous material showing a pore size distribution profile sharply monodispersed at 10.7 nm in the mesopore range.
A kaolinite-NMF-methanol intercalation compound as a versatile intermediate for further intercalation reaction of kaolinite
Authors: Komori Yoshihiko , Sugahara Yoshiyuki , Kuroda Kazuyuki
Published: March 2008

A kaolinite-organic intercalation compound containing methanol was proved to be a versatile host for further displacement reaction with alkylamines. Kaolinite-organic intercalation compounds with polar molecules, such as N-methylformamide (NMF) and formamide, were used as the starting materials. After stirring the kaolinite-NMF intercalation compound with methanol, the basal spacing increased to 1.11 nm. The 13C MAS NMR result of the product indicated that methanol was intercalated into kaolinite by partial displacement with NMF. By use of the methanol-treated kaolinite intercalation compound as the intermediate, alkylamines were intercalated into the interlayer space of kaolinite by displacing with methanol.
Interfacial precipitation in titania-doped diphasic mullite gels
Authors: Hong Seong-Hyeon , Lee Naesung , Carim Altaf H. , Messing Gary L.
Published: March 2008

Interfacial precipitation in sol-gel derived, titania-doped diphasic mullite gels was investigated using conventional and high resolution transmission electron microscopy. Rutile, anatase, and brookite precipitated on the interface between {110} planes of mullite and glass pockets in the sintered body. The formation of brookite may be attributable to the Si- and Al-rich environment during precipitation. Each polymorph of titania has a unique morphology and orientation relationship with mullite. Brookite exhibits a truncated pill box shape, and anatase displays a vermicular morphology. Quenching experiments suggest that the precipitates grow and undergo phase transformations during cooling.
Phase transition, dielectric and electrostrictive behaviors in (1 – x)PYN–xPMN
Authors: Kang Dong Heon , Lee Yong Hwa , Yoon Ki Hyun
Published: March 2008

A system of (1 − x)Pb(Yb1/2Nb1/2)O3 (PYN)–xPb(Mg1/3Nb2/3)O3 (PMN) (0 ≤ x ≤ 1) has been investigated with regard to its phase transition, densification, and dielectric and electrostrictive properties. According to the XRD study, a crystal structure transformed from orthorhombic to pseudocubic at approximately x = 0.22. The superlattice peaks were gradually weakened with increasing x, and disappeared above x = 0.22. Increasing x led to an increase in the maximum dielectric constant and a decrease in transition temperature over the entire composition range. As a result of P-E hysteresis loops, successive phase transitions of ferroelectric-antiferroelectric-paraelectric were observed to occur in the range of 0.18 ≤ x ≤ 0.25 with increasing temperature, while the direct transition into the paraelectric region was found to take place for x ≥ 0.3. From the field-induced strain measurement, high electrostrictive coefficients, 7.3–8.2 × 10−2 (m4/C2), were determined in the PYN-rich range (x ≤ 0.1). Based on the results, a phase diagram of the system was constructed with variations in x and temperature.
Leakage current of Al- or Nb-doped Ba0.5Sr0.5TiO3 thin films by rf magnetron sputtering
Authors: In Tae-Gyoung , Baik Sunggi , Kim Sangsub
Published: March 2008

The effects of Al and Nb doping on the leakage current behaviors were studied for the Ba0.5Sr0.5TiO3 (BST) thin films deposited on Pt/Ti/SiO2/Si(100) substrate by rf magnetron sputtering. Al and Nb were selected as acceptor and donor dopants, respectively, because they have been known to replace Ti-sites of the BST perovskite. The BST thin films prepared in situ at elevated temperatures showed relatively high leakage current density and low breakdown voltage. However, the BST thin films deposited at room temperature and annealed subsequently in air showed improved electrical properties. In particular, the leakage current density of the Al-doped BST thin film was measured to be around 10−8 A/cm2 at 125 kV/cm, which is much lower than those of the undoped or Nb-doped thin films. The results suggest that the Schottky barriers at grain boundaries in the film interior could determine the leakage behavior in the BST thin films.
Microstructure and optical loss in epitaxial (Pb, La)TiO3 thin films on (001) MgO
Authors: Kang Young Min , Baik Sunggi
Published: March 2008

Surface morphologies and microstructures of epitaxial (Pb1−xLax)TiO3 (PLT, x = 0.00, 0.08, 0.16, and 0.24) thin films grown on (001) MgO have been investigated using SEM, AFM, and TEM. Surface roughness of PLT films varies severely with La concentration. For 0.08La-PLT film, very smooth surface has been achieved with 9.3 Å of RMS roughness. 0.00La- and 0.08La-PLT films show 90° domain structure, and periodic dimension of the domain is reduced by La substitution. 0.16La- and 0.24La-PLT films show the presence of triangular grains, causing rough surface and poor crystal quality. However, they are distributed uniformly in 0.16La-PLT film while agglomerated in 0.24La-PLT film. Optical propagation losses of PLT films measured by prism coupling technique were 22.3, 6.0, 11.4, and 20.7 dB/cm for x = 0.00, 0.08, 0.16, and 0.24, respectively. Such a variation in optical losses seemed to be due to the surface morphology and abundance of domain boundaries that change continuously as a function of La concentration in epitaxial PLT thin films.
On the design of 1–3 piezocomposites using topology optimization
Authors: Sigmund O. , Torquato S. , Aksay I. A.
Published: March 2008

We use a topology optimization method to design 1–3 piezocomposites with optimal performance characteristics for hydrophone applications. The performance characteristics we focus on are the hydrostatic charge coefficient , the hydrophone figure of merit , and the electromechanical coupling factor . The piezocomposite consists of piezoelectric rods embedded in an optimal polymer matrix. We use the topology optimization method to design the optimal (porous) matrix microstructure. When we design for maximum and , the optimal transversally isotopic matrix material has negative Poisson's ratio in certain directions. When we design for maximum , the optimal matrix microstructure is layered and simple to build.
Epitaxial growth of SrTiO3 (00h), (0hh), and (hhh) thin films on buffered Si(001)
Authors: Sáanchez F. , Aguiar R. , Trtik V. , Guerrero C. , Ferrater C. , Varela M.
Published: March 2008

Epitaxial SrTiO3(STO) thin films have been grown successfully on Si(001) buffered with single and double buffer layers by pulsed laser deposition. Depending on the buffer structure and under appropriate substrate temperature and oxygen pressure values, epitaxial films are grown with single orientations. Epitaxial STO films with (0hh), (00h), and (hhh) out-of-plane orientation have been obtained for the first time on yttria-stabilized zirconia (YSZ)ySi(001), CeO2/YSZ/Si(001), and TiN/YSZ/Si(001), respectively. Secondary ion mass spectrometry analyses show sharp interfaces and good uniformity of the elements in each layer. The films are practically free of droplets, and the rms value of roughness is smaller than 0.5 nm.
Electron microscopy study of interfacial structure and reaction of Yba2Cu3O7/Y-ZrO2 films on LaAlO3 substrates
Authors: Dai J. Y. , Kaatz F. H. , Markworth P. R. , Buchholz D. B. , Liu X. , Chiou W. A. , Chang R. P. H.
Published: March 2008

The detailed structure and interfacial reaction of epitaxial Yba2Cu3O7/Y-ZrO2 (YBCO/YSZ) films grown by chemical vapor deposition (CVD) on LaAlO3 (LAO) substrates are investigated by means of high-resolution electron microscopy (HREM), analytical transmission electron microscopy, and scanning transmission electron microscopy (STEM). The epitaxial relations of YBCO/YSZ/LAO are [100]YBCO // [110]YSZ // [100]LAO and (001)YBCO // (001)YSZ // (001)LAO. The optimum atomic configuration at the YSZ/LAO interface, in which oxygen is the first atomic layer on LAO, is proposed by using HREM combined with image simulation based on the atomic structure models of the interface. Near the YBCO/YSZ interface, two localized interfacial reaction products are formed: (i) a Y-rich modulated ZrO2 structure at the surface of the YSZ film, which may be caused by the diffusion of Y into the YSZ grains; (ii) an intergranular BaZrO3 phase formed by the diffusion of Ba along the columnar grain boundaries of the YSZ film during YBCO growth.
The development of microstructure of Ni3Al during rapid cooling and heating
Authors: Wang Luhong , Liu Haozhe , Chen Kuiying , Hu Zhuangqi
Published: March 2008

The processes of rapid solidification from liquid to solid and heating from glass to crystalline for Ni3Al are simulated using molecular dynamics method. An amorphous state can be obtained by rapid solidification as long as the cooling rate is sufficiently large, which is very difficult to get in experiment. An fcc-type crystalline is obtained by heating the amorphous with a small heating rate. Based on the pair analysis technique, the microstructures of liquid, supercooled liquid, amorphous, and crystalline states of Ni3Al have been analyzed. Furthermore, the effects of cooling rate and heating rate on microstructures of Ni3Al during rapid solidification and heating processes have been discussed.
Hi-Nicalon fiber-reinforced celsian matrix composites: Influence of interface modification
Authors: Bansal Narottam P. , Eldridge Jeffrey I.
Published: March 2008

Unidirectional celsian matrix composites having 42–45 vol% of uncoated or BN-SiC coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 ± 35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 ± 35 MPa and 0.27 ± 0.01%, respectively, with ultimate strength as high as 960 MPa. The elastic Young modulus of the uncoated and coated fiber-reinforced composites were 184 ± 4 GPa and 165 ± 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of composite with uncoated fibers is due to degradation of the fiber strength from mechanical damage during processing. Because both the coated- and uncoated-fiber-reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.
Fabrication of on-chip barium strontium titanate capacitors by metallo-organic decomposition
Authors: Catalan Antonio B. , Chang Shih-Chia , Poisson Roger J. , Baney William J. , Benci John E.
Published: March 2008

Metallo-organic thin film decomposition (MOD) was used in forming barium strontium titanate (BST) thin film capacitors on phosphorus doped polysilicon films deposited on 4 in. silicon wafers. A single step deposition process yielded highly uniform, crack-free BST films ranging up to 0.25 εm in thickness and having various step heights and dimensional area. Scanning electron microscopy (SEM) showed very good step coverage and planarization of the BST. The capacitors had capacitance densities above 200 nF/cm2, leakage current densities less than 1.55 εA/cm2 at a bias voltage of 10 V, and a dielectric breakdown field above 1 MVycm. Small temperature coefficients of capacitance and dissipation (tan δ) were also observed. Frequency response measurements were made using the BST capacitors and on-chip resistors in low pass and high pass circuit configurations. A plot of relative gain and phase angle versus frequency showed excellent agreement with predicted results.
Sol-gel synthesis of phosphate ceramic composites II
Authors: Cao Zhicheng , Lee Burtrand I. , Samuels William D. , Wang Li-Qiong , Exarhos Gregory J.
Published: March 2008

Phosphate ceramics were synthesized using sol-gel technique of direct reaction of P2O5 with tetraethoxy silane (TEOS) or titanium tetraethoxide (Ti(OEt)4). The reaction mechanism of P2O5 and TEOS was deduced using liquid and solid-state NMR. Hexacoordinated silicon in phosphosilicate gels was observed. A specially structured titanium phosphate-layered Ti(HPO4)2 · 2H2O was synthesized for the first time through the sol-gel method. The gelation process and phase transformations were investigated.
Improvement on the degradation of microwave sintered ZnO varistors by postannealing
Authors: Chen Chang-Shun , Kuo Cheng-Tzu , Lin I-Nan
Published: March 2008

The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 °C/min after sintering, followed by 600 °C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N2 (or air) or loss of Zn species in these regions when annealed at 750 °C (900 °C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.
W–Ti–O layers for gas-sensing applications: Structure, morphology, and electrical properties
Authors: Sangaletti L. , Bontempi E. , Depero L. E. , Salari R. , Zocchi M. , Nelli P. , Sberveglieri G. , Galinetto P. , Ferroni M. , Guidi V. , Martinelli G.
Published: March 2008

The kinetics of phase transitions and phase segregation induced by annealing temperature on the Ti–W–O gas-sensing layer was studied by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The main goal was to identify, on the basis of kinetics studies, structurally stable Ti–WO3 thin film phases and compare their response to polluting gases in order to determine possible correlations between structural and electrical properties of the sensing layers.
The role of microstructure and processing on the proton conducting properties of gadolinium-doped barium cerate
Authors: Haile Sossina M. , West David L. , Campbell John
Published: March 2008

The influence of grain boundary conductivity and microstructure on the electrical properties of BaCe0.85Gd0.15O3–δhave been examined. Grain sizes were varied by sintering at various temperatures. Impedance data were analyzed using the brick layer model, and some new consequences of this model are presented. The specific grain boundary conductivity exhibits an activation energy of ~0.7 eV, and for similar processing routes, is independent of grain size. An isotope effect was observed, indicating that protons (or deuterons) are the mobile species. TEM investigations showed the intergranular regions to be free of any glassy phase that could account for the differences in bulk and grain boundary properties. Single-crystal fibers, grown by a modified float zone process, were notably barium deficient, and exhibited a low conductivity, comparable to that of polycrystalline Ba0.96Ce0.85Gd0.15O3–δ.
Mechanically induced reaction between alkaline earth metal oxides and TiO2
Authors: Welham N. J.
Published: March 2008

This paper outlines the formation of alkaline earth metal titanates, of the general formula MTiO3, directly from the metal oxides and rutile by mechanical activation in a laboratory ball mill at room temperature. X-ray diffraction analysis showed that the reaction was essentially complete within 100 h for all metals except magnesium. The titanates formed all had a Scherrer crystallite size of 11–12 nm and a lattice strain of 0.5–0.6%, neither of which were affected by extended milling. Annealing studies confirmed that the titanate was formed during milling and showed that grain growth could be achieved at temperatures below that generally used for their formation. Mixed cation titanates could also be formed by milling, but tended to be barium rich until annealed.
Grain morphology and cation composition heterogeneity of Pb(ZrxTi1–x)O3 thin films deposited by metal-organic chemical vapor deposition
Authors: Tsu I-Fei , Bai G-R. , Foster C. M. , Merkle K. L. , Liu K. C.
Published: March 2008

The preferred orientation, grain morphology, and composition heterogeneity of the polycrystalline Pb(ZrxTi1–x)O3 (PZT) thin films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and x-ray energy dispersive spectroscopy (EDS). PZT thin films with nominal x = 0.5 were grown by metal-organic chemical vapor deposition (MOCVD) on (110)- and (101)-textured RuO2 bottom electrodes at temperatures ≤525 °C. Columnar grain microstructure with strongly faceted surface morphology was observed in both films. The grain morphology and surface roughness of the PZT films were observed to depend on those of the underlying RuO2 layers. TEM-EDS analysis shows notable cation composition heterogeneity in length scales of 0.2–2 μm. Pronounced Pb composition deficiency and heterogeneity were also observed in PZT/(110)RuO2 in length scales above 40 μm. The grain morphology and cation heterogeneity of the PZT films are discussed on the basis of diffusion-limited columnar growth mechanism.
Reverse burning phenomenon in self-propagating high-temperature synthesis
Authors: Lee Jou-Hong , Lee Ai-Yi , Chen Chien-Chong
Published: March 2008

An interesting reverse burning phenomenon was observed during the combustion synthesis of zirconium-based materials. When an external heat was applied to one end of a green pellet, the ignition was initiated at the other end. Also, the ignition position, measured from the heated end, was proportional to the apparent green density of the compact. The possible explanations for this reverse burning phenomenon are discussed.
An experimental device for depth-sensing indentation tests in millimeter-scale
Authors: Huber N. , Tsakmakis Ch.
Published: March 2008

A device for spherical indentation using a tip radius of 2 mm and loads up to 10 kN is presented. This facility can be applied, for example, to verify methods for characterizing the behavior of materials exhibiting homogeneous and isotropic constitutive properties. The indentation device can be driven both load- and depth-controlled. The accuracy of measurements is about 1 N for load and 0.2 μm for depth at a total depth of 200 μm. Two materials, an austenitic steel and an aluminum alloy, have been tested and their Young's moduli have been determined. For determining Young's modulus from spherical indentation data, use is made of a so-called Lt method, which had been developed in Ref. 1. Results obtained in this way are compared with corresponding values measured by one-dimensional homogeneous tensile experiments.
Simultaneous real-time study of initial hillocking and changes in overall stress in evaporated Al films during heating
Authors: Kylner C. , Mattsson L.
Published: March 2008

Optical quality Al films were evaporated by an electron beam onto Si wafers in an ultrahigh vacuum system. The as-deposited samples were radiative heated at a rate of 3 °C/s in air environment. During heating, measurements ofinitialhillocking and changes in overall film stress were performed simultaneously and in real time as a function of time and temperature with a specially designed optical instrument. The physical principles of this instrument are based on laser beam deflection caused by film stress induced wafer bending and partial integrated light scattering from surface roughening. The experimental results show how theinitialhillocking is accompanied by changes in the overall stress and yield a very good correlation between the onset of hillock formation and the maximum change in overall stress.
Atomic force microscopy studies of ZnS films grown on (100) GaAs by the successive ionic layer adsorption and reaction method
Authors: Valkonen Mika P. , Lindroos Seppo , Kanniainen Tapio , Leskelä Markku , Resch Roland , Friedbacher Gernot , Grasserbauer Manfred
Published: March 2008

In this study zinc sulfide thin films were grown by the successive ionic layer adsorption and reaction (SILAR) technique on (100) GaAs substrates from aqueous precursor solutions. The atomic force microscopy (AFM) method was used to study the growth of the films up to a thickness of 180 nm. The ZnS thin films on (100) GaAs were smooth with an rms roughness of 0.2–1.9 nm depending on the film thickness. After the GaAs surface was covered with ZnS, the growth appeared to be nearly layerwise. In addition, in situ AFM studies were carried out to analyze the dissolution of (100) GaAs in water, which is a process competing with the thin film deposition by the SILAR.
Diffusion-limited and asymmetric growth of amorphous layer in Ni/Zr bilayer upon annealing
Authors: Lai W. S. , Liu B. X.
Published: March 2008

Asymmetric growth of amorphous layer in a Ni/Zr bilayer, in which a thin disordered interlayer is preset, upon annealing at medium temperatures is observed by molecular-dynamics simulation with an n-body potential. It is shown that the amorphous layer is extended from the interlayer with different speeds toward two opposite directions and that the growth kinetics follows time dependence of t1/2, indicating amorphization upon annealing in the Ni/Zr bilayer is indeed through a diffusion-limited reaction. Besides, two low temperature limits allowing the growth of amorphous layer toward Ni and Zr layers are also obtained.
Measured and calculated thermoelastic properties of supersaturated fcc Ni(Al) and Ni(Zr) solid solutions
Authors: Bøttiger J. , Karpe N. , Krog J. P. , Ruban A. V.
Published: March 2008

Metastable face-centered cubic (fcc) solid solutions of Ni1–xAlx and Ni1–xZrx have been prepared in thin-film form using dc planar magnetron sputtering in a UHV system. In both these alloy systems, extended solubilities in the fcc phase and a pronounced (111) texture are observed after sputter deposition. An amorphous phase is found to form in Ni1–xAlx for x ≥ 0.30 and in Ni1–xZrx for x ≥ 0.05. Lattice constants, thermal expansion coefficients, and Debye temperatures were derived from x-ray diffraction measurements. These parameters were also calculated by using ab initio methods in the framework of the local-spin density and coherent potential approximations for the electronic subsystem and the Debye–Grüneisen model for the vibrational properties of the nuclei subsystem. Experiment and theory are compared and discussed.
Formation of cubic C-BN by crystallization of nano-amorphous solid at atmosphere
Authors: Yao Bin , Liu L. , Su W. H.
Published: March 2008

An amorphous carbon-boron nitride (C-BN) solid was prepared by ball milling the mixture of graphite and hexagonal BN powders for a period of 120 h. After annealing the amorphous C-BN solid for 1 h at atmosphere in the temperature range from 800 to 900 K and then quenching it to room temperature, a small amount of cubic C-BN solid solutions with diamond-like structure, which belong to a high energy phase and can only be synthesized previously under high pressure and temperature (30 GPa, 2000 K), were observed in the annealed amorphous C-BN solid. The lattice constant of the cubic C-BN solid solution was 0.3587 nm, and its grain size was in the range of 10 to 50 nm.
Direct current electrical degradation of iron-doped titania ceramics
Authors: Sheng Jianxin , Fukami Tatsuo , Karasawa Junich
Published: March 2008

An anomalous increase of current was found in Fe-doped titania ceramics subjected to a constant field of 105 V/m. It is suggested that the space charge rises from blockage of O2(g) → O2−(s) ion transfer at the cathode. This leads to an increase of n-conductivity in the cathodic region and p-conductivity in the anodic region according to the specific defect equilibrium. This viewpoint was reinforced by two newly observed phenomena: (i) the I-V plot shows a linear feature at the initial stage, but it gradually becomes a rectifying feature with time; and (ii) an edge-located electrode shows lower current density and faster current saturation compared with a normal electrode.
High resolution transmission electron microscopy of Ba1−xKxBiO3 superconductor-insulator-superconductor grain boundary tunnel junctions
Authors: Chan Siu-Wai , Kussmaul A. , Hellman E. S. , Hartford E. H.
Published: March 2008

High angle boundaries in Ba1−xKxBiO3 are superconductor-insulator-superconductor (SIS) Josephson tunnel junctions of a quality unequaled among the high temperature superconducting oxides. Electron microscopy of 24° [001] tilt boundaries reveals nominally symmetric and straight boundaries of aperiodic structure with reappearing structural units. Low {hk0} atomistic facets are predominant. A segregation layer of only 1 nm thick is identified straddling the boundary. This layer which forms naturally is insulating, pin-hole free, and surprisingly robust with a breakdown voltage which exceeds 1 × 106 V/cm, yet thin enough to allow quasiparticle tunneling, yielding reliable gap energies for theoretical comparison.
Gd-doping effects on properties of amorphous silicon films prepared by electron beam evaporations
Authors: Gan Runjin , Liu Fengmin , Qi Li , Wang Jizheng
Published: March 2008

Gd-doped amorphous silicon films have been prepared by the electron beam evaporation technique, employing the experimental methods of dc conductivity temperature properties, ESR (electron spin resonance) spectra, and optical band gap Eopt measurements. We have investigated the optical and electrical properties of the films. The results show that at 290 K < T < 330 K, hopping conduction in Gd impurity states near Fermi level is predominant, and at 330 K < T < 500 K extended state conduction dominates due to electrons exited from the impurity states. At a Gd concentration of about 1.0 at.% spin density Ns, peak-peak width ΔBpp and line-shape factor l of ESR spectra change their dependence on Gd contents. The optical gap of the films narrows with increasing Gd contents in the films from 1.68 eV to 0.42 eV. The results were explained on the basis of the partial compensation of Gd atoms for dangling bonds .
Auger electron spectroscopy and x-ray photoelectron spectroscopy analysis of angle of incidence effects of ion beam nitridation of GaAs
Authors: Pan J. S. , Huan C. H. A. , Wee A. T. S. , Tan H. S. , Tan K. L.
Published: March 2008

Ion beam nitridation (IBN) of GaAs at room temperature was studied as a function of N2+ ion incident angle at ion energy of 10 keV. The ion beam bombardment surface area of GaAs was characterized in situ by both Auger electron spectroscopy (AES) and small spot-size x-ray photoelectron spectroscopy (XPS). Thin GaN reaction layers are formed at all N2+ ion incident angles, whereas the formation of As–N bonds has not been found. However, the degree of nitridation of Ga decreases with increasing incident angle. The observed angular dependence of the N incorporation can be explained in terms of sputtering yield, indicating that the growth kinetics can be described as a dynamic process comprising the accumulation of N and sputter removal of the surface layer. N2+ ion bombardment causes the depletion of As from the surface region because of the preferential sputtering of As from GaAs. The preferential sputtering of As reduces with increasing N2+ ion incident angle. The angular dependent behavior of preferential sputtering of As by 10 keV N2+ ions can be attributed to the angular dependence of GaN surface layer formation.
Aluminum nitride-silicon carbide solid solutions grown by plasma-assisted, gas-source molecular beam epitaxy
Authors: Kern R. S. , Rowland L. B. , Tanaka S. , Davis R. F.
Published: March 2008

Solid solutions of aluminum nitride (AlN) and silicon carbide (SiC) have been grown at 900–1300 °C on vicinal α (6H)-SiC(0001) substrates by plasma-assisted, gas-source molecular beam epitaxy. Under specific processing conditions, films of (AlN)x(SiC) 1−x with 0.2 ≤ x ≤ 0.8, as determined by Auger electron spectrometry (AES), were deposited. Reflection high-energy electron diffraction (RHEED) was used to determine the crystalline quality, surface character, and epilayer polytype. Analysis of the resulting surfaces was also performed by scanning electron microscopy (SEM). High-resolution transmission electron microscopy (HRTEM) revealed that monocrystalline films with x ≥ 0.25 had the wurtzite (2H) crystal structure; however, films with x < 0.25 had the zincblende (3C) crystal structure.
A comparison of two aluminizing methods for corrosion protection in the wet seal of molten carbonate fuel cells
Authors: Indacochea J. Ernesto , Bloom Ira , Krumpelt Michael , Benjamin Thomas G.
Published: March 2008

The corrosion behavior of aluminized Type 310S stainless steel (SS) in the wet seal of molten carbonate fuel cells was investigated. Coupons of Type 310S SS were aluminized by two different aluminizing methods: thermal spray and slurry-coating. In both types of samples Fe and Cr diffused readily into the Al layer at 650 °C. At first this interdiffusion is limited to the interfacial area. With time, Fe and Cr aluminides precipitate in the Al layer. The slurry-coated layer contains a higher concentration of FeAl and Fe3Al than does the thermal spray layer. Consequently, the slurry-coated layer also displays a greater degree of corrosion than the thermal spray layer.
Interactions between bismuth oxide and ceramic substrates for thick film technology
Authors: Immovilli Simona , Morten Bruno , Prudenziati Maria , Gualtieri Alessandro , Bersani Massimo
Published: March 2008

We investigated the interactions between screen printed and fired layers of Bi2O3 and ceramic substrates of alumina and beryllia. It was found that the reaction products are invariably crystalline in nature. Several transitions of Bi2O3 in its polymorphic phases were found to occur on BeO substrates, while newly formed compounds have been observed to grow on alumina substrates, i.e., Al4Bi2O9 on 99.9% Al2O3 and Bi12SiO20 on 96% Al2O3. Bismuth deeply penetrates in the ceramic interstices in all the cases. Until Bi2O3 is not completely reacted, this penetration is diffusion limited (penetration depth , where td is the reaction time) with values of the activation energy ranging from 3.7 ± 0.6 eV (BeO substrate) to 1.4 ± 0.06 eV (96% Al2O3 substrate). It is shown that these processes are notably different to those occurring in PbO/ceramic systems; moreover, they imply different adhesion phenomena of thick films on different substrates.
Detection of contact damage in ceramics by an ultrasonic method
Authors: Ahn Hyo Sok , Jahanmir Said , Slotwinski John A. , Blessing Gerald V.
Published: March 2008

A pulse-echo ultrasonic technique consisting of focused normal-incident compressional waves was used for the detection and evaluation of surface and subsurface damage in micaceous glass-ceramic and silicon nitride samples. The damage was produced by indentation with a tungsten carbide ball. The nature of the damage was found to be material-dependent and was classified into two types: Hertzian cone cracks in the silicon nitride, and distributed subsurface microcracks in the glass-ceramic. While the cone cracks were visible on the surface as circular ring cracks, the distributed subsurface microcracks were not associated with any visible surface cracks. Both the cone cracks and the distributed subsurface microcracks were easily detected by the ultrasonic technique. In addition, the ultrasonic beam was focused to different depths below the surface of the glass-ceramic sample to probe the subsurface region containing the microfracture damage.
System Bi–Sr–O: Synergistic measurements of thermodynamic properties using oxide and fluoride solid electrolytes
Authors: Jacob K. T. , Jayadevan K. P.
Published: March 2008

Phase equilibrium and electrochemical studies of the ternary system Bi–Sr–O indicate the presence of six ternary oxides (Bi2SrO4, Bi2Sr2O5, Bi2Sr3O6, Bi4Sr6O15, Bi14Sr24O52, and Bi2Sr6O11) and three solid solutions (δ, β, and γ). An isothermal section of the phase diagram is established at 1050 K by phase analysis of quenched samples. Three compounds, Bi4Sr6O15, Bi14Sr24O52, and Bi2Sr6O11, contain Bi5+ ions. The stability of these phases is a function of oxygen partial pressure. The chemical potentials of SrO in two-phase fields are determined as a function of temperature using solid-state cells based on single crystal SrF2 as the electrolyte. Measurement of the emf of cells based on SrF2 as a function of oxygen partial pressure in the gas at constant temperature gives information on oxygen content of the compounds present at the electrodes. The chemical potentials of Bi2O3 in two-phase fields of the pseudobinary Bi2O3–SrO are measured using cells incorporating (Y2O3)ZrO2 as the solid electrolyte. The standard free energies of formation of the ternary oxides are calculated independently using emfs of different cells. The independent assessments agree closely; the maximum difference in the value of of component binary oxides. The results are discussed in the light of the phase diagram and compared with calorimetric and chemical potential measurements reported in the literature. The combined use of emf data from cells incorporating fluoride and oxide electrolytes enhances the reliability of derived data.
Evolution of stresses in passivated and unpassivated metal interconnects
Authors: Gouldstone A. , Shen Y-L. , Suresh S. , Thompson C. V.
Published: March 2008

This paper discusses computational simulations of the evolution of stresses and deformation in unpassivated and SiO2-passivated Al lines on Si substrates. The finite element model accounts for elastic-plastic deformation in the Al lines during etching, passivation, and subsequent thermal cycling, by recourse to a generalized plane strain formulation within the context of a unit cell with appropriately constrained boundary conditions. The effects of different controlled variations in thermal history, and in the width, height, spacing, and yield behavior of the Al lines are analyzed; all these factors are seen to have potentially strong effects on the evolution of stresses within the lines. The predictions of the computations presented in this work are amenable for direct comparisons with experiments of curvature evolution along and perpendicular to the lines upon patterning, passivation, and thermal loading. The predicted stresses in metal interconnects can be directly used for reliability modeling purposes.
Appropriate passivation structure in dynamic random access memory devices to improve stress-related reliability performance after plastic packaging
Authors: Lee Seong-Min
Published: March 2008

This work attempts to determine an appropriate passivation structure in the real integrated circuit (IC) pattern to improve stress-related reliability problems after the plastic packaging. Several different types of amorphous passivation materials were first tested to learn how effectively they protect underlying Al interconnection lines during thermal displacement-induced fatigue at temperature ranges from −65 °C to 150 °C. It was also studied how effectively the occurrence of cracking in a passivation layer can be suppressed by the improvement of its topological feature or increase in its thickness. According to the experimental results, an increase in passivation thickness up to 21,000 Å (7000 Å for oxide and 14,000 Å for SiN, respectively) was found to be a highly effective way to suppress stress-induced passivation damage on the inside of the chip in plastic IC packages. However, at the edges of the chip, smoothing of the passivation layer by a sloping metal sidewall was more important for the improvement of thermal cycling performance than thickening of the passivation layer.
Synthesis of a Mo/Nb mixed carbide
Authors: Teixeira da Silva V. L. S. , Schmal M. , Schwartz V. , Oyama S. T.
Published: March 2008

Molybdenum and niobium carbides (β−Mo2C, NbC), as well as mixed carbides of molybdenum and niobium, were synthesized by the temperature-programmed carburization method (TPC) using a 20 vol% CH4/H2 gas mixture. The starting materials were MoO3, B-Nb2O5, and physical mixtures of B-Nb2O5/MoO3 with Nb/(Nb + Mo) atomic ratios varying from 0.2 to 0.8, respectively. Results from catalytic and temperatureprogrammed oxidation (TPO) measurements indicate that during the carburization of the Nb2O5/MoO3 physical mixture with Nby(Nb + Mo) = 0.8 there is, besides β−Mo2C and NbC formation, the appearance of a carbidic phase not detectable by x-ray diffraction (XRD). This phase appears to be highly active and selective for the dibenzothiophene hydrodesulfurization (HDS) reaction.
Large Faraday effect and local structure of alkali silicate glasses containing divalent europium ions
Authors: Tanaka Katsuhisa , Fujita Koji , Matsuoka Nobuaki , Hirao Kazuyuki , Soga Naohiro
Published: March 2008

Measurements of Faraday and Mössbauer effects have been performed at room temperature for alkali silicate glasses containing a large amount of Eu2+ ions to examine the relation between local structure and magnitude of Verdet constant. The Mössbauer spectra indicate that about 80% of europium ions are present as a divalent state. The effective transition wavelength and effective transition probability for the 4f7 → 4f65d transition of Eu2+, which causes the Faraday effect, are derived from the wavelength dependence of Verdet constant. Both effective transition wavelength and effective transition probability are large compared with borate glasses, leading to the large magnitude of Verdet constant of the alkali silicate glasses. The variation of effective transition wavelength with glass composition is connected with the change of 6s-electron density of Eu2+ evaluated from the Mössbauer spectroscopy.
Preparation and characterization of epitaxial iron oxide films
Authors: Gao Y. , Kim Y. J. , Chambers S. A.
Published: March 2008

Well-ordered, pure-phase epitaxial films of FeO, Fe3O4, and γ–Fe2O3 were prepared on MgO(001) by oxygen-plasma-assisted MBE. The stoichiometries of these thin films were controlled by varying the growth rate and oxygen partial pressure. Selective growth of γ–Fe2O3 and α–Fe2O3 was achieved by controlling the growth conditions in conjunction with the choice of appropriate substrates. Growth of the iron oxide epitaxial films on MgO at ≥350 °C is accompanied by significant Mg outdiffusion. The FeO(001) film surface exhibits a (2 × 2) reconstruction, which is accompanied by a significant amount of Fe3+ in the surface region. Fe3O4 (001) has been found to reconstruct to a structure. γ–Fe23 (001) film surface is unreconstructed.
Structural characterization of carbons obtained from polyparaphenylenes prepared by the Kovacic and Yamamoto methods
Authors: Endo M. , Kim C. , Hiraoka T. , Karaki T. , Nishimura K. , Matthews M. J. , Brown S. D. M. , Dresselhaus M. S.
Published: March 2008

The structure of polyparaphenylene (PPP)-based carbons prepared by the Kovacic and Yamamoto methods heat-treated at 650–3000 °C have been characterized comparatively by using x-ray diffraction, SEM, TEM, and Raman spectroscopy. Both kinds of carbons indicate not typical but poor graphitizing behavior, especially for the case of PPP Yamamoto samples, and much less for PPP Kovacic samples, by heat treatment up to 3000 °C. The Kovacic-based samples heat-treated at 600–2400 °C have a more developed layer structure than that of Yamamoto-based samples. In contrast, for HTT's (heat-treatment temperature) more than about 2400 °C, PPP Yamamoto-based carbons exhibit a more developed crystallite structure than PPP Kovacic-based carbons. At a given HTT, PPP Kovacic-based carbons have a much more quinoid-like structure and graphene-type structure than PPP Yamamoto-based carbons, as indicated by the carbon yield and Raman scattering measurements. It is suggested that the detailed structure of the starting polymers influences the texture as well as the microstructure of resultant carbons even though both are obtained from the same kinds of precursors. These microstructures also largely influence the anode performance when these carbons are used in Li ion batteries.
Experimental investigation of the Y2BaCuO5 surface free energy during peritectic solidification of YBCO
Authors: Lo Wai , Cardwell D. A. , Chow J. C. L. , Leung H-T.
Published: March 2008

The characteristic inhomogeneous distribution of nonsuperconducting Y2BaCuO5 (211) inclusions in melt-processed YBa2Cu3O7−δ (123) grains has generally been attributed to 211 particle pushing by 123 growth fronts during peritectic solidification on the basis of reduced total surface free energy. Analysis of the morphology of the interfaces at the 211–211–123 and 211–211-liquid triple points in seeded melt-processed samples invalidates this assumption for the pure YBCO system and has implications of the mechanism of 211 particle segregation.
Role of bonding and coordination in the atomic structure and energy of diamond and silicon grain boundaries
Authors: Keblinski P. , Wolf D. , Phillpot S. R. , Gleiter H.
Published: March 2008

The high-temperature equilibrated atomic structures and energies of large-unit-cell grain boundaries (GB's) in diamond and silicon are determined by means of Monte-Carlo simulations using Tersoff's potentials for the two materials. Silicon provides a relatively simple basis for understanding GB structural disorder in a purely sp3 bonded material against which the greater bond stiffness in diamond combined with its ability to change hybridization in a defected environment from sp3 to sp2 can be elucidated. We find that due to the purely sp3-type bonding in Si, even in highly disordered, high-energy GB's at least 80% of the atoms are fourfold coordinated in a rather dense confined amorphous structure. By contrast, in diamond even relatively small bond distortions exact a considerable price in energy that favors a change to sp2-type local bonding; these competing effects translate into considerably more ordered diamond GB's; however, at the price of as many as 80% of the atoms being only threefold coordinated. Structural disorder in the Si GB's is therefore partially replaced by coordination disorder in the diamond GB's. In spite of these large fractions of three-coordinated GB carbon atoms, however, the three-coordinated atoms are rather poorly connected amongst themselves, thus likely preventing any type of graphite-like electrical conduction through the GB's.
Precipitates in GaN epilayers grown on sapphire substrates
Authors: Kang Junyong , Ogawa Tomoya
Published: March 2008

Precipitates in GaN epilayers grown on sapphire substrates were investigated by atomic number contrast (ANC), wavelength-dispersive x-ray spectrometry (WDS), energy-dispersive spectrometry (EDS), and cathodoluminescence (CL) techniques. The results showed that the precipitates are mainly composed of gallium and oxygen elements and distribute more sparsely and inhomogeneously in directions in the sample grown on substrate nitridated for a longer period. Yellow luminescence intensity was imaged to be stronger in the precipitates. The results suggest that the precipitates are formed on dislocations and grain boundaries by substituting oxygen onto the nitrogen site, and result in the formations of deep levels nearby.