bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of SiC whiskers by VLS process
Authors: Urretavizcaya G. , López Porto J.M.
Published: September 2007

β-SiC whiskers were synthesized by the vapor-liquid-solid (VLS) process using Fe catalyst. Whiskers show smooth surfaces and no ramifications. They have uniform diameter (0.5-1 μm) and lengths between 50 and 300 μm. A catalyst droplet was observed on the tip of almost all the whiskers. The transport of iron from the substrate surface to the SiO generators, where growth took place, occurs fundamentally via vapor phase. Fe was deposited over surfaces containing C, and whisker growth was produced where there were Fe droplets of appropriate size and SiO available in great quantity. The need for reaching a threshold size (2–3 μm) of the catalyst droplet before whisker growth is proposed as a possible explanation for the formation of whiskers with uniform size in zones with a high partial pressure of SiO.
Ion implantation of silicon wafers for defect-reduced doped layer formation with low dopant atom diffusion
Authors: Shigenaka Naoto , Ono Shigeki , Hashimoto Tsuneyuki , Fuse Motomasa , Owada Nobuo
Published: September 2007

A new process for ion implantation into silicon wafers was proposed. This process has an additional implantation step to form an amorphous phase. At first self-ions are implanted into a cooled wafer (< −30 °C) to form the amorphous phase, and subsequently dopant atoms are implanted to form a doped layer within the amorphous layer. After annealing above 650 °C, the silicon wafer is completely recrystallized, and no defects with sizes detectable by TEM are present near the doped layer. There is indeed a defect layer in the wafer; however, it lies along the amorphous/crystal interface that is behind the doped layer. The concentration profile of the dopant atoms is not changed during epitaxial recrystallization, and further dopant atom diffusion during annealing is limited to about 0.05 μm, because defect-enhanced diffusion does not occur. The double implantation method is considered to be effective for doped layer formation in the VLSI fabrication process.
Magnetic characterization of calcium-nickel-potassium oxide catalysts
Authors: Perry Dale L. , Berdahl Paul , Perrino Charles
Published: September 2007

SQUID magnetometer characterization of Ca–Ni–K–O catalyst materials reveals complex magnetic behavior. The magnetic properties are generally determined by the antiferromagnetic material NiO, but samples with traces of elemental nickel show marked effects of ferromagnetism. Potassium doping enhances the formation of metallic nickel. Further deviations from bulk NiO properties can be attributed to NiO particle size effects (superparamagnetism) and to the presence of paramagnetic impurities, possibly Ni3+ ions.
Plasma enhanced chemical vapor deposition of silicon nitride films from a metal-organic precursor
Authors: Hoffman David M. , Rangarajan Sri Prakash , Athavale Satish D. , Deshmukh Shashank C. , Economou Demetre J. , Liu Jia-Rui , Zheng Zongshuang , Chu Wei-Kan
Published: September 2007

Silicon nitride films are grown by plasma enhanced chemical vapor deposition from tetrakis(dimethylamido)silicon, Si(NMe2)4, and ammonia precursors at substrate temperatures of 200-400 °C. Backscattering spectrometry shows that the films are close to stoichiometric. Depth profiling by Auger electron spectroscopy shows uniform composition and no oxygen or carbon contamination in the bulk. The films are featureless by scanning electron microscopy under 100,000X magnification.
Epitaxial Y1Ba2Cu3O7−δ thin films with (103)/(110)- and (100)/(010)-orientation on NdGaO3 and SrTiO3 substrates grown by ion-beam sputter deposition
Authors: Krumme J-P. , Doormann V. , Welz F. , Eckart R. , Dössel O. , Dingen W. , Schiffmann K.
Published: September 2007

A fully oxygen-compatible ion-beam sputter deposition process (IBS) has been implemented for investigation of four film/substrate couples: (103)/(110)YBCO on (110)SrTiO3 (STO) and on (100)NdGaO3 (NGO), and (100)/(010)YBCO on (110)NGO and on (100)STO. For comparison, some (103)/(110)YBCO films have also been prepared by off-axis rf-magnetron sputtering. Below about 600 °C semiconducting, sub-nm flat, and perfectly single-crystalline YBCO films crystallize on these substrates with a crystallographic unit cell of about 1/3 of the Cu-O subcell of YBCO and perfect registration with the Ti4+-O and Ga3+-O sublattice of STO and NGO, respectively. At higher temperature superconducting YBCO films grow coherently epitaxially in the first ∼100 nm thickness; in thicker films the lattice-misfit strain relaxes to the “free” lattice constants. Above ∼680 °C a faceted (103)YBCO orientation grows on (110)STO and (100)NGO substrates with uniform in-plane orientation of the [010]YBCO direction parallel to [001]STO and [001]NGO. Along [010]YBCO the (103)YBCO films exhibit high crystalline perfection and intrinsic superconducting properties approaching those of (001)YBCO films in the plane; i.e., Tc,0 > 88 K, ΔTc,0 < 0.6 K, R300/R100 > 2.9, ρ100 > 250 μ°Cm, and jc (77 K) ⋚106 A/cm2. Practical use of (103)YBCO films is hampered by the large surface roughness. Above ∼680 °C a mixed (100)/(010)YBCO orientation grows on (110)NGO substrates, exhibiting a very smooth surface but less attractive superconducting properties; typically, Tc,0 ⋚ 80 K, ΔTc,0 ∼ 1 K, R300/R100 ∼ 1.2, ρ100 > 3 m°Cm, and jc (77 K) ⋚105 A/cm2. On (100)STO substrates the YBCO film orientation varies from pure (100)YBCO between ∼580 and ∼630 °C and mixed (100)/(010)YBCO below ∼660 °C to pure (001) YBCO above ∼670 °C. With rising temperature the surface roughness increases from <2 to ∼6 nm-rms, while the other parameters continuously improve to state-of-the-art values for c⊥-oriented films. Specifically, mixed (100)/(010)YBCO films reach Tc,0 > 86 K, δc,0 ∼ 1 K, R300/R100 > 2.8, ρ100 < 3 m°Cm, and jc (77 K) > 105 A/cm2. (100)/(010)YBCO films on (100)STO are a promising candidate for sandwich-type SIS-JJ.
Evolution of the two-phase microstructure L12 + DO22 in near-eutectoid Ni3(Al,V) alloy
Authors: Bendersky L.A. , Biancaniello F.S. , Williams M.E.
Published: September 2007

Transmission electron microscopy and powder x-ray diffraction methods have been used to investigate the evolution of two-phase (L12 + DO22) microstructures from the quenched fcc phase of the Ni-5Al-20V (at. %) alloy. The microstructure after annealing in a temperature range from 650 to 900 °C differs from the eutectoid structure which might be expected for the alloy according to the eutectoid-type phase diagram of the Ni3Al-Ni3V section. This structure results from fast kinetics of ordering in the fcc → L12 and fcc → DO22 phase transitions. Four main stages in the microstructural evolution were observed. Stage I is the formation of spheroidal coherent L12 clusters in a disordered fcc matrix. During stage II the L12 clusters transform into cuboidal precipitates, and the fcc matrix orders into three DO22 variants (which may have interfaces that are wetted by thin fcc layers). In stage III accommodation of misfit (elastic energy) between different phases and variants occurs by formation of (110) twins or a single variant of the DO22 phase and tetragonally strained lamellae of the L12 phase. Stage IV is a discontinuous coarsening process in which a coarse incoherent two-phase structure replaces the fine coherent one. Grains of the coarse structure are nucleated on high-angle boundaries of primary fcc or other surfaces. Many of the grains are found twinned.
ARXPS studies of SiO2-SiC interfaces and oxidation of 6H SiC single crystal Si-(001) and C-(001) surfaces
Authors: Hornetz B. , Michel H-J. , Halbritter J.
Published: September 2007

The main puzzle in oxidation of hexagonal SiC is the slower rate of the Si-terminated surface as compared to the C-terminated surface, which is blamed on an unknown interface compound. ARXPS is a unique method to identify minor amounts of interface compounds, especially for smooth surfaces. Our ARXPS analysis of oxidized Si-(001) and C-(001) surfaces of 6H SiC reveals the interface oxide Si4C4−xO2 (x < 2), likely a reaction product of a peroxidic O2-bond to a SiC double layer. Si4C4−xO2 occurs in larger thickness (≃1 nm) at the slowly oxidizing Si-(001) surface, whereas the C-(001) surface shows smaller amounts, diminishing fast with oxidation above 1000 K. Evidence is presented that with increasing amount of Si4C4−xO2 the oxidation of SiC to SiO2 is reduced. ARXPS is consistent with a layer of SiO2 containing less than 3% Si4C4O4 being an oxidation product of Si4C4−xO2. At the surface of SiO2, graphite and some Si4C4O4 exist, aside from standard adsorbates.
Epitaxial thin films of PbTiO3/SnO2 heterostructures on sapphire
Authors: Chang H.L.M. , Zhang H. , Shen Z. , Wang Q.
Published: September 2007

Epitaxial films of single-layer SnO2 and PbTiO3/SnO2 heterostructures were obtained on (0001) sapphire (α-Al2O3) substrates by metal-organic chemical vapor deposition. X-ray diffraction and transmission electron microscopy were used to characterize the structural properties of these films. The epitaxial relationship for the heterostructure PbTiO3/SnO2/sapphire was found to be (111) [011]PbTiO3 ‖ (100) [001]SnO2 ‖ (0001) [1100]α-Al2O3. The fact that epitaxial ferroelectric films were obtainable in such a structurally highly heterogeneous system suggests that a wide range of material selection is possible in exploring the kind of applications that need to utilize epitaxial ferroelectric films in a multilayered heterostructure.
Room temperature copolymerization to improve the thermal and dielectric properties of polyxylylene thin films by chemical vapor deposition
Authors: Gaynor Justin F. , Desu Seshu B.
Published: September 2007

Polyxylylene thin films grown by chemical vapor deposition (CVD) have long been utilized for uniform, pinhole-free conformal coatings. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We show room temperature copolymerization with previously untested comonomers during the CVD process. Samples were studied with wavelength dispersive analysis, FTIR, scanning variable angle ellipsometry, and x-ray diffraction. Copolymerizing chloro-p-xylylene with perfluoro-octyl methacrylate results in dielectric constants at optical frequencies as low as 2.19, compared to 2.68 for the homopolymer. Copolymerizing p-xylylene with 4-vinylbiphenyl resulted in films whose onset of weight loss in TGA measurements was 450 °C, compared to 270 °C for the homopolymer.
Mechanical properties of compositionally modulated Au-Ni thin films: Nanoindentation and microcantilever deflection experiments
Authors: Baker Shefford P. , Nix William D.
Published: September 2007

The mechanical properties of compositionally modulated Au-Ni films were investigated by submicrometer depth-sensing indentation and by deflection of micrometer-scale cantilever beams. Films prepared by sputter deposition with composition wavelengths between 0.9 and 4.0 nm were investigated. Strength was found to be high and invariant with composition wavelength. Experimental and data analysis methods were developed to provide more accurate and precise measurements of elastic stiffness. Large enhancements in stiffness (the “supermodulus effect”) were not observed. Rather, relatively small but significant minima were observed at a composition wavelength of about 1.6 nm by both techniques. These variations were found to be strongly correlated with variations in the average lattice parameter normal to the plane of the film. Both structural and mechanical property variations are consistent with a simple model in which the film consists of bulk-like Au and Ni layers with interfaces of constant thickness.
Microstructure and mechanical properties of aluminum nitride-aluminum composite
Authors: Huang Jow-Lay , Li Ching-Hsiung
Published: September 2007

In a new approach to sinter Al/AlN composites in an overpressure environment of Al, the effects of sintering temperature and Al content on the microstructure, density, shrinkage, and mass gain were investigated. Fracture behavior and toughness were correlated with microstructure and composition of Al/AlN composites.
Simplified preparation of REBa2Cu3O7−x via the acetate method
Authors: McHale J. , Myer G.H. , Salomon R.E.
Published: September 2007

High-quality bulk REBa2Cu3O7−x (RE = Y,Eu,Gd,Nd,La) was synthesized by a solution method. Stoichiometric amounts of yttrium, barium, and copper acetates were dissolved in glacial acetic acid. The acid was boiled away leaving a glassy acetate precursor. This precursor has shown amorphous scattering in XRD, a phenomenon consistent with atomic level mixing of reactants. The glassy precursor was subsequently heat-treated with a 5 °C/min ramp to 900 °C and a 2 h soak at 900 °C in air. The final product was obtained after heat treatment under oxygen at 550 °C with slow cooling to room temperature. Final products were analyzed by XRD, SEM, and four probe de-resistivity measurements. The mechanism of both precursor and product formation was examined through substitution studies and XRD. It was found that a combination of a rare earth acetate, barium acetate, and acetic acid was necessary for the formation of an amorphous precursor.
Elastic constants and microcracks in YBa2Cu3O7
Authors: Shindo Yasuhide , Ledbetter Hassel , Nozaki Hideaki
Published: September 2007

We analyze theoretically the effect of microcracks and voids on the apparent elastic constants of polycrystalline YBa2Cu3O7. Using measurements by Holcomb and Mayo, we calculate crack density and crack aspect ratio. We obtain reasonable intrinsic elastic constants. For the bulk modulus, for example, we predict values close to these obtained by neutron-diffraction studies: 123 GPa for a polycrystal and 122 GPa for a monocrystal.
Optical measurement of the elastic moduli and thermal diffusivity of a C–N film
Authors: Yang Yongwu , Nelson Keith A. , Adibi Farshid
Published: September 2007

The elastic properties of carbon nitride (CNx) film adhered to a silicon substrate were characterized through impulsive stimulated thermal scattering (ISTS). The lowest-order pseudo-Rayleigh acoustic mode of the film was excited and monitored optically. From the measured acoustic phase velocities, the elastic moduli of the film were determined. The ISTS technique also permits measurements of the CNx thermal diffusivity. The noninvasive optical measurements described can provide a useful guide to refinements in thin film fabrication procedures and for optimization of mechanical and thermal transport properties.
Zirconia-mullite ceramics made from composite particles coated with amorphous phase: I. Effect of zirconia addition
Authors: Shyu Jiin-Jyh , Chen Yuan-Chieh
Published: September 2007

Mullite-based ceramics added with 0–20 vol % stabilized zirconia have been prepared by alumina/zirconia particles coated with an amorphous silica layer. All samples can be densified through the viscous flow of the amorphous silica layer in the typical temperature range of 1100–1310 °C. For the ZrO2-free mullite ceramics, the viscous densification kinetics is inhibited by increasing the content of the alumina inclusion particles and by crystallization of the amorphous silica layer. However, for the zirconia-mullite ceramics, the addition of the zirconia inclusion particles accelerates the viscous densifcation kinetics. Mullitization kinetics is also enhanced by the addition of zirconia. As the sintering temeperature is high, a porous, duplex microstructure is observed in samples with or without zirconia. Zirconia addition enhances the development of this microstructure. As the sintering temperature and/or zirconia content is increased, ZrO2 particles tend to coarsen, resulting in a decreased tetragonal to monoclinic ratio. Fracture toughness KlC increases with the zirconia content. Mullite-20 vol % ZrO2 composite sintered at 1600 °C has a KlC of 3.8 MPa · m1/2.
Submicrometer zinc oxide particles: Elaboration in polyol medium and morphological characteristics
Authors: Jézéquel Didier , Guenot Jean , Jouini Noureddine , Fiévet Fernand
Published: September 2007

A novel and easy route for preparing submicrometer particles of zinc oxide, involving hydrolysis of zinc salt in a polyol medium, is proposed. Zinc acetate dihydrate and diethyleneglycol appear to be the best candidates for obtaining a high yield of particles with well-defined morphological characteristics. Monodisperse spherical particles in the submicrometer range (0.2−0.4 μm) have been obtained for a salt concentration less than 0.1 mol 1−1. The particle size depends mainly on the heating rate. The particles are microporous (surface area: 80 m2 g−1) and are formed by aggregation of small crystallites (10 nm). Calcination at moderate temperature drastically reduces this porosity without significant interparticle sintering. At higher concentration, no aggregation occurs and tiny single crystallite particles are obtained.
Effect of machining residual stresses on the repetitive impact behavior of silicon nitride
Authors: Srinivasan Sreeram , Blau Peter J. , Bjerke Julia L.
Published: September 2007

Silicon nitride is a candidate valve material for internal combustion engines. Its low density and attractive mechanical properties relative to conventional metallic alloys portend significant improvements in valve performance. The production of valves involves a significant amount of machining, especially grinding. Grinding of ceramic materials may result in surface and subsurface damage in the form of fracture or residual stresses which may affect impact behavior and, consequently, the behavior of silicon nitride ceramic materials as valves. The effects of residual stresses due to grinding on the impact wear behavior of one silicon nitride composition ground under various conditions have been investigated.
Microprobe Raman spectroscopy of TiN coatings oxidized by solar beam heat treatment
Authors: Franck M. , Celis J-P. , Roos J.R.
Published: September 2007

Physical vapor deposited TiN coatings oxidized by solar beam heat treatment in air were examined by microprobe Raman spectroscopy. The Raman spectra of TiN treated at 400 °C indicated incipient oxidation by the presence of anatase TiO2 and additionally showed a broadband feature around the forbidden TiN vibrational mode. Inhomogeneous mixtures of rutile TiO2 and small amounts of anatase polymorph (< 10%) were detected for the treatments at 600 °C only during the initial stage of oxidation. Prolonged treatment at 600 °C resulted in a complete anatase-to-rutile conversion. Rutile was identified as the single product of oxidation of the TiN samples treated at 800 °C. Peak analysis of the rutile spectra revealed no substantial spectral shifts, demonstrating an oxide growth of nearly stoichiometric rutile with an estimated composition in the range of TiO2±0.02. The Raman scattered light intensity could be correlated with the rutile layer thickness.
Partial melting and segregation behavior in a superplastic Si3N4/Al–Mg alloy composite
Authors: Koike J. , Mabuchi M. , Higashi K.
Published: September 2007

AJ-Mg alloy (5052) composite reinforced with Si3N4 particulates was investigated by transmission electron microscopy and electron energy loss spectroscopy. Partial melting was observed at matrix/reinforcement interfaces and matrix grain boundaries at a temperature near an optimum superplastic temperature. Segregation of solute elements (Mg and Si) was observed at the interfaces and grain boundaries. Both partial melting and solute segregation were found to depend on grain boundaries. The obtained results were explained by a decrease of the solidus temperature due to segregation whose extent depends on the type of the grain boundary structure.
Retention of nanostructure in aluminum oxide by very rapid sintering at 1150 °C
Authors: Risbud Subhash H. , Shan Chien-Hua , Mukherjee Amiya K. , Kim Moon J. , Bow J.S. , Holl Richard A.
Published: September 2007

Aluminum oxide powders doped with MgO (300 to 500 nm) were sintered to almost theoretical density within just 10–15 min at 1150 °C using a plasma-activated sintering process based on charging the loosely filled powders with an electric discharge prior to densification by resistance heating. The microstructure of the consolidated disks was examined by high resolution transmission electron microscopy (HREM) and electron energy loss spectroscopy (EELS) and revealed excellent grain to grain contact with virtually no grain growth and structurally clean grain boundaries.
Investigation of the electroplastic effect using optical and conventional techniques
Authors: Stanton C.T. , Coffey C.S. , Zerilli F.
Published: September 2007

The electroplastic effect in materials is an interesting and potentially useful phenomenon in which an applied electric field affects the plastic flow properties of materials under strain. We have undertaken a study to use optical methods to monitor changes in alkali halide crystals undergoing the electroplastic effect. Some preliminary results from this work are presented along with more conventional quasi-static measurements of the electroplastic effect.
(Mn,Zn,Fe)1−xO thin films showing ferrimagnetic property deposited by ion beam sputtering
Authors: Cho Hae Seok , Ha Sang Ki , Kim Min Hong , Kim Hyeong Joon
Published: September 2007

We deposited (Mn,Zn,Fe)1−xO thin films of a wüstite structure on SiO2/Si(100) by ion beam sputtering using a single-crystal Mn-Zn ferrite target. The wüstite structure of the as-deposited film, confirmed by XRD, TEM, and XPS analysis, appeared to originate from an oxygen-deficit ambient and also from the preferential resputtering of the oxygen ions in films during deposition. The as-deposited films showed ferrimagnetic characteristics having quite a large Ms in spite of their crystallographic structure, wüstite. Such an unusual phenomenon is presumably due to the different magnetic moments of the constituent cations with disordered distribution. This wüstite phase could be transformed into the spinel ferrite phase with the same preferred orientation during postannealing under an appropriate oxygen partial pressure. The interplanar distance of the as-deposited films decreased with increasing Ts due to a release of compressive stress. The Ms of the film had a maximum value at about 275 °C, while the resistivity, mainly governed by the grain boundaries, was almost the same irrespective of Ts.
Precursors of amorphization in supersaturated Nb-Pd solid solutions
Authors: Krill C.E. , Li J. , Garland C.M. , Ettl C. , Samwer K. , Yelon W.B. , Johnson W.L.
Published: September 2007

The possibility that crystal-to-amorphous phase transformations can be induced by one or more underlying instabilities of the crystalline phase has been investigated in highly supersaturated solid solutions of Nb-Pd. Several unusual properties were discovered that may be identified as precursor effects of the collapse of the bcc α-Nb terminal solution to the amorphous phase. Elastic neutron diffraction measurements of α-Nb solutions found, with increasing Pd concentration, an anomalously large increase of the average atomic root-mean-square displacement to about half of the value at which the Lindemann criterion predicts the lattice should melt. Low-temperature heat capacity measurements yielded a concomitant decrease in the Debye temperature, suggesting that supersaturation causes an elastic modulus to soften. Single crystals of α-Nb solutions at high supersaturations have a highly anisotropic structure that is visible in transmission electron microscopy images; it is consistent with the development of a soft phonon mode leading to a bcc-to-ω phase transformation. Considered together with the results of other recent experiments, these findings suggest that shear instability of the crystalline phase plays an important role in the crystal-to-amorphous transformation and that the average static mean-square displacement of atoms in the lattice acts as a useful parameter for the stability of the crystal with respect to amorphization.
Low pressure chemical vapor deposition of B-N-C-H films from triethylamine borane complex
Authors: Levy R.A. , Mastromatteo E. , Grow J.M. , Paturi V. , Kuo W.P. , Boeglin H.J. , Shalvoy R.
Published: September 2007

In this study, films consisting of B-N-C-H have been synthesized by low pressure chemical vapor deposition using the liquid precursor triethylamine borane complex (TEAB) both with and without ammonia. When no NH3 is present, the growth rate was observed to follow an Arrhenius behavior in the temperature range of 600 to 800 °C with an apparent activation energy of 11 kcal/mol. A linear dependence of growth rate is observed as a function of square root of flow rate for the TEAB range of 20 to 60 sccm, indicating that the reaction rate is controlled by the adsorption of borane. The addition of NH3 to TEAB had the effect of lowering the deposition temperature down to 300 °C and increasing the apparent activation energy to 22 kcal/mol. Above 650 °C, the carbon concentration of the deposits increased significantly, reflecting the breakup of the amine molecule. X-ray diffraction measurements indicated the films to be in all cases amorphous. Infrared spectra of the films showed absorption peaks representing the vibrational modes of B-N, B-N-B, B-H, and N-H. The index of refraction varied between 1.76 and 2.47, depending on composition of the films. Films deposited with no NH3 above 700 °C were seen to be compressive while films below that temperature were tensile. In the range of 350 to 475 °C, the addition of NH3 to TEAB resulted in films that were mildly tensile, while below 325 °C and above 550 °C, the films were found to be compressive. Both the hardness and Young's modulus of the films decreased with higher temperatures, reflecting the influence of the carbon presence.
Effects of Nb2O5 in (Ba,Bi,Nb)-added TiO2 ceramic varistors
Authors: Yang Seng-Lu , Wu Jenn-Ming
Published: September 2007

Novel (Ba,Bi,Nb)-added TiO2 ceramic was previously proved to be potentially useful as a varistor material, and by varying atmosphere compensation the roles of barium and bismuth have been explored. The present work attempted to investigate how the third additive, niobium, operates on varistor characteristics. The content of added niobium is in the range from 0.125 to 1.0 cat. %, while that of the other additives is always maintained at a constant value. The results show that an adequate addition of niobium, 0.25 cat. % Nb, is beneficial to the improvement of varistor characteristics. The variations of varistor behavior are discussed in terms of a point defect model. Two kinds of charge compensation, for the substitutional incorporation of niobium into the titanium rutile lattice, are also used to illustrate the variation. The detailed results and discussions are shown in this paper.
Effects of heat treatment on Ag particle growth and optical properties in Ag/SiO2 glass composite thin films
Authors: Tanahashi I. , Yoshida M. , Manabe Y. , Tohda T.
Published: September 2007

Small Ag particles were embedded in SiO2 glass thin films by a multi-target sputtering method. The mean diameter of Ag particles in the as-deposited film with 28.0 at. % of Ag was estimated to be 4.4 nm and it was increased to 24.0 nm when the film was heat-treated at 700 °C for 3 h. The diameter was proportional to the cube root of the heat-treatment time, suggesting that the Ag particles grew in the supersaturated solid solution. In the optical absorption spectra of the heat-treated films, the absorption peak due to the surface plasmon resonance of Ag particles was observed about 410 nm. The peak intensity became large and the full width at half maximum of the absorption band was decreased with increasing the diameter of Ag particles.
In situ x-ray CT under tensile loading using synchrotron radiation
Authors: Hirano T. , Usami K. , Tanaka Y. , Masuda C.
Published: September 2007

Internal damage in metal matrix composite (MMC) under static tensile loading was observed by in situ x-ray computed tomography based on synchrotron radiation (SR-CT). A tensile testing sample stage was developed to investigate the fracture process during the tensile test. Aluminum alloy matrix composites reinforced by long or short SiC fibers were used. The projection images obtained under tensile loading showed good performance of the sample stage, and matrix deformation and breaks of the long SiC fibers could be observed. In the CT images taken at the maximum stress just before failure, debondings of the short SiC fibers to the matrix, many pullouts of the fibers, and matrix cracking could be clearly observed. The in situ SR-CT allowed the observation of generation and growth of such defects under different tensile stress levels. The results from the nondestructive observation revealed that the MMC was broken by propagation of the matrix cracks which might be caused by stress concentration at the ends of the short fibers. A three-dimensional CT image reconstructed from many CT images provided easy understanding of the fiber arrangement, crack shape, and form of the void caused by fiber pullout. In situ SR-CT is a useful method for understanding failure mechanisms in advanced materials.
Nucleation and selected area deposition of diamond by biased hot filament chemical vapor deposition
Authors: Zhu W. , Sivazlian F.R. , Stoner B.R. , Glass J.T.
Published: September 2007

This paper describes a process for uniformly enhancing the nucleation density of diamond films on silicon (Si) substrates via dc-biased hot filament chemical vapor deposition (HFCVD). The Si substrate was negatively biased and the tungsten (W) filaments were positively biased relative to the grounded stainless steel reactor wall. It was found that by directly applying such a negative bias to the Si substrate in a typical HFCVD process, the enhanced diamond nucleation occurred only along the edges of the Si wafer. This resulted in an extremely nonuniform nucleation pattern. Several modifications were introduced to the design of the substrate holder, including a metal wire-mesh inserted between the filaments and the substrate, in the aim of making the impinging ion flux more uniformly distributed across the substrate surface. With such improved growth system designs, uniform enhancement of diamond nucleation across the substrate surface was realized. In addition, the use of certain metallic wire mesh sizes during biasing also enabled patterned or selective diamond deposition.
A study of temperature and pressure-induced structural and electronic changes in SbCl5intercalated graphite: Part III. Analysis of theTandpdependence of thec-axis resistivity
Authors: Sundqvist B. , Andersson O.E. , McRae E. , Lelaurain M. , Maréché J.F.
Published: September 2007

We present experimental data for thec-axis electrical resistivity of SbCl5intercalated graphite between 20 and 300 K. The data are analyzed together with our previous results for these and other samples [O. E. Anderssonet al., J. Mater. Res.7, 2989 (1992)]. Before the analysis, we correct the experimental data to constant volume, as assumed by theorists. We show that the correction factor is much larger for these materials than for normal metals. Although the original data showed significant nonlinearities withT, the corrected data are linear inTto within the experimental accuracy for low-stage compounds below the intercalate crystallization temperature. We compare our results with several models and conclude that both the temperature dependence, the pressure dependence, and the relative changes in the in-plane andc-axis resistivities associated with intercalate crystallization can be best described by a band conduction model.
Characterization of PbTiO3 thin films deposited on Pt/Ti/SiO2/Si substrates by ECR PECVD
Authors: Chung Sung-Woong , Shin Jung-Shik , Kim Jae-Whan , No Kwangsoo , Chun Sung-Soon , Lee Won-Jong
Published: September 2007

The electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) method is used to prepare ferroelectric PbTiO3 films. Single-phase perovskite PbTiO3 films with smooth surfaces and fine grain size were successfully fabricated on Pt/Ti/SiO2/Si substrates at low temperatures of 400–500 °C using metal-organic (MO) sources. The chemical compositions, structural phases, surface morphologies, and depth profiles of the PbTiO3 thin films were investigated using EDS, XRD, SEM, RBS, and AES. Variations of those properties with process temperature and gas supply ratio are discussed. When the process temperature was above 450 °C, the stoichiometric perovskite PbTiO3 films could be obtained even though the MO source supply ratio was varied in a wide range if the oxygen supply was sufficient.
An incommensurate-commensurate phase transformation in antiferroelectric tin-modified lead zirconate titanate
Authors: Xu Z. , Viehland Dwight , Payne D.A.
Published: September 2007

Antiferroelectric tin-modified lead zirconate titanate ceramics (PZST), with 42 at. % Sn and 4 at. % Ti, were studied by hot- and cold-stage transmission electron microscopy and selected area electron diffraction techniques. The previously reported tetragonal antiferroelectric state is shown to be an incommensurate orthohombic state. Observations revealed the existence of incommensurate 1/x 〈110〉 superlattice reflections below the temperature of the dielectric maximum. The modulation wavelength for this incommensurate structure was found to be metastably locked-in near and below room temperature. An incommensurate-commensurate orthorhombic antiferroelectric transformation was then observed at lower temperatures. However, an intermediate condition was observed over a relatively wide temperature range which was characterized by an intergrowth of 〈110〉 structural modulations, which was strongly diffuse along the 〈110〉. These structural observations were correlated with dispersion in the dielectric properties in the same temperature range. No previous reports of an incommensurate orthorhombic antiferroelectric state or an incommensurate-commensurate orthorhombic antiferroelectric transformation are known to exist.
Characterization of hydroxyapatite laser ablation plumes by fast intensified CCD-imaging
Authors: Serra P. , Palau J. , Varela M. , Esteve J. , Morenza J.L.
Published: September 2007

ArF excimer laser pulses (193 nm, 20 ns, 150 mJ) have been focused on a hydroxyapatite (HA) target in similar conditions to those normally used for thin film deposition. Fast intensified CCD images of HA laser ablation plumes have been taken in vacuum and under different water vapor pressures ranging from 0.01 mbar to 1 mbar. Images of HA ablation in vacuum have shown a plume freely expanding at a constant velocity of 2.3 × 106 cm/s. HA ablation under a water vapor pressure of 0.01 mbar has revealed an expansion behavior very similar to that of ablation in vacuum. Images taken under a water vapor pressure of 0.1 mbar have shown the formation of a shock structure in the plume. Finally, HA ablation under a water vapor pressure of 1 mbar has revealed the development of some irregularities in the shape of the plume.
Environmentally benign vacuum deposition with air-to-vacuum-to-air technology
Authors: Barth K.L. , Sampath W.S.
Published: September 2007

The deposition of thin films and coatings frequently results in the generation of toxic waste, volatile organic compounds, or large amounts of waste water and sludge. Vapor deposition in vacuum offers a more environmentally benign alternative, but is not prevalent outside of the microelectronics industry due to economic reasons. However, vacuum coating could be more widely accepted, and could potentially replace nonvacuum deposition methods, if either the cycle time or costs associated with vacuum coating were reduced. In order to reduce the cycle time for vacuum deposition, a robust system for continuous air-to-vacuum-to-air (AVA) transportation of discreet substrates has been developed and constructed in this study. This technology allows the insertion of discrete components into vacuum at high rates, without the need for venting the deposition chamber. Substrates have been repeatedly transported from atmosphere to 10−5 Torr in under a second. The capability of the AVA technology was studied through the deposition and characterization of CdS and CdTe films and photovoltaic devices. With the AVA technology, the need for venting the vacuum chamber to insert the substrates and subsequent pumping of the system for deposition is eliminated. The AVA technology could be applied to the processing of silicon wafers, compact disks, optical components, solar cells, cutting tools, and fasteners.
Aerosol synthesis of AlN by nitridation of aluminum vapor and clusters
Authors: Pratsinis Sotiris E. , Wang Guizhi , Panda Siddhartha , Guiton Theresa , Weimer Alan W.
Published: September 2007

Aluminum nitride (AlN) powders were produced in an aerosol flow reactor by direct nitridation of aluminum vapor with ammonia and nitrogen in flowing argon. In the presence of excess NH3, pure AlN powders were obtained from 1400 to 1873 K. These powders had higher specific surface areas than commercially available AlN powders. The effects of reactor temperature and gas flow rate on AlN purity, yield, and grain and crystallite size were investigated. The BET grain diameter of AlN increased as the process temperature increased, indicating sintering controlled particle formation and growth. Both the crystallite size and the BET grain size of pure AlN powders slightly decreased as ammonia flow rate was increased. Increasing temperature and flow rate increased the AlN yield.
Biocompatible whiskers with controlled morphology and stoichiometry
Authors: Suchanek Wojciech , Suda Hiroyuki , Yashima Masatomo , Kakihana Masato , Yoshimura Masahiro
Published: September 2007

Hydroxyapatite whiskers have been prepared by the hydrothermal method. The crystals had diameter, length, and aspect ratio in the range of 1–10 μm, 30–50 μm, and 5–20, respectively. Their Ca/P molar ratio varied from 1.59 to 1.62. The morphology of the crystals can easily be controlled by the concentrations of species in the starting solution, while the Ca/P ratio is almost independent of them. Through the reaction with calcite powder at 600 °C, the Ca/P ratio of the whiskers has been improved even to the stoichiometric value of 1.67. Taking into account morphology and chemical composition of the HAp whiskers, they should not be health hazardous and may find applications as substitutes for asbestos and other fibrous materials which presently have restricted use because of their carcinogenic natures.
A study of the ultrasonic technique applied in fabrication of SiC fiber-reinforced aluminum composites
Authors: Pan J. , Yang D.M. , Yin X.F. , Fukunaga H.
Published: September 2007

By comparing the ultrasonic cavitation in several kinds of transparent liquid mediums, we have investigated the cavitation effect in liquid. It is considered that the shock wave created by the cavitation in aluminum melt induces a high pressure and an elevated temperature field around the fibers, which can promote the wetting between fiber and aluminum and have aluminum melt infiltrate into the fibers. Moreover, the experiment result shows that the fiber resonance matching with the cavitation is also an important factor for SiC/Al composites preparation. There exists a damage of the ultrasonic vibration on SiC fiber, if the fiber is acted long enough.
Fiber strength utilization in carbon/carbon composites: Part II. Extended studies with pitch- and PAN-based fibers
Authors: Zaldivar Rafael J. , Rellick Gerald S. , Yang J.M.
Published: September 2007

Measurements of fiber strength utilization (FSU) in unidirectional carbon/carbon (C/C) composites as a function of heat-treatment tempcrature (HTT) have been extended beyond the original group of DuPont pitch-based E-series fibers to include additional pitch- and PAN-based fibers. Fibers and composites were characterized by tensile strength, optical microscopy, SEM, fiber preferred orientation, and a single-fiber composite (SFC) fragmentation test to provide a relative measure of fiber-matrix interfacial shear strength (IFSS). Results show that fracture behavior and FSU are dominated by the degree of fiber-matrix bonding, as inferred from microscopic observations and measurements of IFSS. In the very high modulus pitch-based fibers, the behavior of the F,130 is strikingly different from that of the Amoco and Nippon Oil fibers, in that it retains good bond strength and high FSU even with HT to 2400 °C, in contrast to the other very high modulus pitch-based fibers that are already weakly bonded at the lowest HTT of 1100 °C. All PAN-based fibers and lower modulus pitch fibers are characterized by strong bonding, brittle fracture, and low FSU for the 1100 °C HTT. Subsequent heat treatment of these composites to 2150 and 2400 °C, in most cases, results in significant recovery of FSU, suggesting an optimum IFSS for each composite. It is suggested that the difference in bonding between the pitch-based E-series and P-series may be related to the similarity in fine structure between the E-fibers and high-modulus PAN-based fibers.
Change of the critical thickness in the preferred orientation of TiN films
Authors: Oh U.C. , Je Jung Ho , Lee Jeong Y.
Published: September 2007

Recently it was observed through cross-sectional TEM that the preferred orientation of the TiN thin film was changed from (200) to (111) with thickness. In this study, the process of the change in the preferred orientation was studied near the critical thickness by x-ray diffraction, and the value of the critical thickness could be estimated. The change of the critical thickness was also investigated with the strain energy per unit volume. The strain energy could be changed by controlling the energy of the bombarding particle, i.e., by adjusting the rf power, the working pressure, and the substrate bias in sputtering. The critical thickness was decreased monotonically in all cases as the energy of the bombarding particle or the strain energy per unit volume was increased. These results surely show the dependence of the change of the preferred orientation on the strain energy in the TiN thin films.
Mechanical solid state reaction for synthesis of β–SiC powders
Authors: Sherif El-Eskandarany M. , Sumiyama Kenji , Suzuki Kenji
Published: September 2007

Stoichiometric β-SiC powders have been successfully prepared by solid state reaction of elemental silicon and carbon powders via the mechanical alloying process. The mechanical alloying process was performed in a high-energy ball mill under argon gas flow at room temperature. The solid-state reacted alloy powders have been characterized as a function of the milling time by means of x-ray diffraction, infrared absorption, scanning and transmission electron microscopy, and chemical analysis. Complete fcc-SiC (β-phase) alloy powders were obtained after 1080 ks of continuous milling. The lattice parameter (a0) of the formed β-SiC was calculated to be 0.4357 nm. No free silicon and/or carbon crystals were observed. The existence of transverse optical (TO) and longitudinal optical (LO)-like phonon modes is observed for the end-product alloy powders. Mechanically alloyed β-SiC powders are stable at elevated temperatures (1773 K) and did not transform to any other phases. The end-product β-SiC alloy powders possess excellent morphological properties, such as homogeneous shape (spherical morphology) with fine and smooth surface relief and uniform size (less than 0.5 μm in diameter). The fabricated β-SiC alloy powders have fine cell-like structure with nanoscale dimensions of about 7 nm.
Synthesis and characterization of TiO2 thin films on organic self-assembled monolayers: Part II. Film formation via an organometallic route
Authors: Shin H. , Collins R.J. , De Guire M.R. , Heuer A.H. , Sukenik C.N.
Published: September 2007

Crystalline, uniform, adherent, ultrathin films of TiO2 were deposited onto OH-functionalized organic self-assembled monolayers (SAMs) on single-crystalline Si at low-temperature (<100 °C) from anhydrous ethanolic solutions of titanium isopropoxide. The films were identified as TiO2 by x-ray photoelectron spectroscopy, electron diffraction, and energy-dispersive x-ray microanalysis. Transmission electron microscopy showed the films to be uniform in thickness (2 ± 0.5 nm) and continuous. On bare Si, in contrast, there was no evidence of TiO2 deposition under identical conditions. Unlike the anatase films deposited on SAMs from aqueous solutions (described in the preceding paper), the electron diffraction patterns of the films deposited from alkoxide solutions suggest that they were the rutile phase. It is suggested that the functionalized SAMs enable the anchoring of the Ti alkoxide and initiate the formation of an adherent oxide film, and that they are sufficiently uniform that the resulting film is continuous and uniform in thickness.
Fabrication of Sr2Nb2O7 thin films by sol-gel processing
Authors: Prasadarao Alamanda V. , Selvaraj Ulagaraj , Komarnenici Sridhar
Published: September 2007

Sol-gel Sr2Nb2O7 thin films were deposited on Si(100) and Pt-coated Si substrates for the first time by spin-coating. The Sr2Nb2O7 precursor solution was prepared from strontium metal dissolved in 2-methoxyethanol, acetylacetone, and niobium ethoxide. The formation of phase pure Sr2Nb2O7 occurred via an intermediate perovskite phase of composition close to Sr0.82NbO3. Crack-free Sr2Nb2O7 films of ∼0.4 μm thickness were deposited on these substrates using a single-coating followed by heat treatment at 850 °C for 12 h. SEM microstructure and thin film XRD results indicated the deposition of a grain-oriented film on the Pt-coated Si substrate. The room temperature dielectric constant and the loss values of the film measured at 10 kHz are 45 and 0.045, respectively.
Synthesis of β-sialon from coals or natural graphite
Authors: Narciso F.J. , Linares-Solano A. , Rodriguez-Reinoso F.
Published: September 2007

The synthesis of β-sialon has been carried out by heat treatment in nitrogen flow of Spanish coals or mineral graphite, both with a high content of mineral matter. The results were compared with those obtained with conventional clay/carbon mixtures. The coals and, especially, the mineral graphite produced a very high yield of β-sialon, with a faster reaction rate than the clay/carbon mixtures due to the more intimate contact among the reactants, with the additional advantage of forming much a lower proportion of vitreous phases. On the other hand, the results show that in the particular case of graphite, the use of high temperatures (even above 1450 °C) does not lead to changes in the crystalline phases of the product, allowing the synthesis to be carried out over a wider temperature range than that used for clay/carbon mixtures. The mechanical properties of the sintered artifacts obtained with the sialon synthesized from natural graphite are superior to those prepared from clay/carbon mixtures and comparable (or even superior) to commercial artifacts manufactured from much more expensive precursors.
Effects of radiation on SiC-based Nicalon fibers
Authors: Snead L.L. , Osborne M. , More K.L.
Published: September 2007

This paper presents neutron and ion radiation effects in the Nicalon SiC polymer precursor fiber. It is shown that the serious structural degradation of this fiber and its composites (e.g., CVD SiC/Nicalon) previously reported for the standard grade of Nicalon is primarily due to the presence of the silicon oxycarbide phase. Results supporting this interpretation include microstructural analysis as well as post irradiation mechanical property measurements. Preliminary results of the effects of irradiation on low-oxygen Nicalon fibers are presented. The reduced oxygen content fibers exhibit radiation-induced density, strength, and Weibull's and Young's moduli changes typical of monolithic ceramic materials. This contrasts sharply with the poor irradiation behavior of the standard Nicalon fiber and suggests that improved radiation resistance can be expected in SiC/SiC composites fabricated with low oxygen Nicalon fibers.