bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Ceramic Foams from Crystals of AlCl3(Pri2O) complex
Authors: Grader G. S. , Shter G. E. , Hazan Y. de
Published: March 2008

In this paper we report a novel process for the production of ultralight cellular ceramics. The foams are generated by the heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri2O)]. The crystals, which are the only foam precursor, are obtained from concentrated solutions of AlCl3, Pri2O, and CH2Cl2. The foams consist of an arrangement of closed cells, 50–300 μm in diameter, having cell walls approximately 1–2 μm thick. An exceptionally high porosity is obtained ranging from 94 to 99%, and the cellular structure is retained during heating at 1500 °C. The foaming mechanism involves two consecutive nonhydrolytic sol-gel chemical reactions and physical processes including crystal dissociation, solvation, phase separation, and foaming. While other foaming mechanisms cited in the literature utilize one or more of the processes above, no analog mechanism exists in the organic, ceramic, or metal foam production processes. The effectiveness of the process originates from an initial precursor which contains all the necessary foaming components in such a way that the application of mild heating accelerates its transformation to a solid, dry, ultralight foamed material.
Synthesis of Sr2KNb5O15 Thin Films by Chemical Solution Deposition Method
Authors: Sakamoto Wataru , Yogo Toshinobu , Kuroyanagi Takae , Hirano Shin-ichi
Published: March 2008

Crack-free and transparent Sr2KNb5O15 (SKN) thin films have been synthesized by the chemical solution deposition method. A homogeneous and stable precursor solution was prepared via controlling the reaction of metal alkoxides. SKN precursor was found to be the complex alkoxide between Sr[Nb(OEt)6]2 and KNb(OEt)6 with high structural symmetry. SKN powders and thin films on fused silica substrates directly crystallized to the polycrystalline tetragonal tungsten bronze phase at 600 °C. Highly oriented SKN thin films with the tetragonal tungsten bronze phase were fabricated on MgO(100) and Pt(100)/MgO(100) substrates. Two crystal lattice planes of SKN were intergrown at an orientation of 18.5° on MgO(100). The dielectric constant of SKN thin films on Pt(100)/MgO(100) was about 590 at 20 °C at 1 kHz.
Growth and Characterization of Epitaxial NiMnSb/PtMnSb C1b Heusler alloy superlattices
Authors: Mancoff F. B. , Bobo J. F. , Richter O. E. , Bessho K. , Johnson P. R. , Sinclair R. , Nix W. D. , White R. L. , Clemens B. M.
Published: March 2008

We have sputter deposited NiMnSb/PtMnSb Heusler alloy superlattices with bilayer periods from 9–160 Å. X-ray diffraction and cross-sectional transmission electron microscopy (TEM) measurements indicate that even for short bilayer periods, the superlattices are compositionally modulated, epitaxial, and maintain the Heusler alloy C1b structure. Low- and high-angle diffraction profiles are in agreement with simulations of the superlattice peaks. TEM images reveal defects, including stacking faults, which help relieve lattice mismatch strain. Energy minimization calculations of the stacking fault density are within a factor of 3 of the density observed by TEM. The saturation magnetization of the superlattices is close to bulk PtMnSb and NiMnSb, with a tendency for perpendicular magnetization at short bilayer periods.
Perovskite NdTiO3 in Sr- and Ca-doped BaO–Nd2O3–TiO2 Microwave Dielectric Ceramics
Authors: Ubic R. , Reaney I. M. , Lee W. E.
Published: March 2008

Ba6–3xNd8+2xTi18O54 (BNT) is a useful dielectric resonator at microwave frequencies. Recent work has shown that the major secondary phase in this system can be indexed as Nd4Ti9O24 (JCPDS 33–943). The present study has evealed that when half of the stoichiometric Ba+2 is replaced with Ca+2 or Sr+2, a third, tilted perovskite-structured phase, NdTiO3, is also present. It forms as coherent intragranular regions within BNT grains and always contains some of the divalent dopant species. The orientational relationship between NdTiO3 and BNT has been established.
Al–Ta Bilayer as an Oxidation Resistant Barrier for Electrode Structures in High Dielectric Constant Capacitors
Authors: Grill A. , Cabral C.
Published: March 2008

Aluminum-tantalum bilayers have been investigated for their potential to serve as conductive barriers to oxygen diffusion when annealed at conditions corresponding to crystallization of perovskite dielectrics such as lead lanthanum titanate (PLT). Ta (50 nm)/Al (15 nm) structures have been deposited on Si substrates and annealed in oxygen at 650 and 700 °C for various amounts of time. The as-deposited and annealed structures have been characterized by x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and Auger electron spectroscopy (AES) analysis and by four-point probe electrical measurements. It has been found that the Al–Ta structures can withstand complete oxidation when exposed to oxygen at 650 °C for 30 min or 700 °C for 1 min and the oxide layer formed at the surface of the structure acts as a barrier to further oxygen diffusion. When a PLT film was deposited directly on the Al–Ta structures intermixing took place. It was therefore necessary to insert a Pt layer between the Al–Ta barrier and PLT layer. In such a case the PLT showed electrical properties similar to those obtained when deposited on SiO2/Pt; however, the Al–Ta structure did interact with Pt during the perovskite formation anneal. It has been found that this interaction can be prevented by preannealing the Al–Ta, in oxygen, prior to the deposition of Pt.
Layered TaSiN as an Oxidation Resistant Electrically Conductive Barrier
Authors: Grill A. , Jahnes C. , Cabral C.
Published: March 2008

TaSiN films deposited as layered TaN–SiN structures of various compositions have been examined for their oxidation resistant properties during annealing in oxygen at annealing conditions commonly used to prepare perovskite dielectrics. The films have been characterized by Rutherford backscattering analysis (RBS), x-ray diffraction (XRD), and electrical resistivity measurements. Films with less than 15 at.% Si showed some resistance to oxidation after annealing for 1 min at 650 °C but became fully oxidized after longer anneals. Increasing the Si content up to 28 at.% increasingly improved the oxidation resistance of the alloys to the point where the films resisted complete oxidation for up to 5 min at 700 °C. For alloys with greater than 28 at.% Si, no oxidation could be detected by RBS or electrical measurements for anneals up to 5 min at 700 °C. Furthermore, these high Si content alloys were still conductive with resistivities of near 1000 μΩ cm. It was also found that TaSiN and lead lanthanum titanate (PLT) interact strongly during annealing, and another nonoxidizing barrier metal, such as Pt, is required between the two materials if TaSiN is to be used as an electrode/barrier with lead-based perovskites.
Oxygen Gettering Effect During the Reactive Evaporation of Manganese Oxide Films
Authors: Isai Masaaki , Yamaguchi Katsuma , Iyoda Haruhiko , Fujiyasu Hiroshi , Ito Yasumitsu
Published: March 2008

Manganese oxide films for lithium secondary batteries were prepared using a reactive evaporation method. Mn was evaporated from a molybdenum boat by resistive heating and deposited on a glass slide under oxygen atmosphere. These films were examined with x-ray photoelectron spectroscopy (XPS) and x-ray diffraction. The Mn oxide films with a wide valency of Mn were prepared in this study. A rapid change of the back pressure was found as the deposition of Mn was started. This implies that Mn atoms start to react with O2. This means that in situ detection of reactive evaporation process can be utilized.
Subsolidus phase equilibria in the La2O3−CeO2−Co2O3 system
Authors: Hrovat Marko , Holc Janez , Bernik Slavko
Published: March 2008

Subsolidus equilibria in air in the La2O3−CeO2−Co2O3 system were studied with the aim to obtain information on possible interactions between LaCoO3-based cathode and CeO2-based solid electrolyte in solid oxide fuel cells (SOFC). No ternary compound was found. The tie line is between LaCoO3 and CeO2.
Promotion of phase transformation and single-phase formation in silver-doped Tl–Ba–Ca–Cu–O superconducting thin films
Authors: Koo Horng-Show , Tseng Tseung-Yuen
Published: March 2008

Phase transformation and physical characteristics of the spray-pyrolyzed Tl–Ba–Ca–Cu–O superconducting films with 3 mol% silver dopant have been studied using electrical resistivity, x-ray diffraction, and scanning electron microscopy. The major phase formed in the resultant film, annealed at a temperature of 885 °C for 3 min, was found to be the nearly single-phase, high-Tc Tl2Ba2Ca2Cu3Oy (Tl-2223). The multiple phase of Tl2Ba2Ca2Cu3Oy and TlBa2Ca2Cu3Oy (Tl-1223) appeared at annealing temperatures lower and higher than 885 °C. It was also observed that Ag dopant effectively reduces normal resistivity at 300 K and enhances the phase transformation of single-Tl-layer Tl-1223 to double-Tl-layer Tl-2223 phases and further helps to form the nearly single-phase Tl-2223 within a short duration. Critical transition temperature (Tc,zero) and current density (Jc, 77 K, 0 Tesla) of the best resultant film were shown to be 123 K and 5.7 × 104 A/cm2, respectively.
Temperature and porosity dependence of the thermoelectric properties of SiC/Ag sintered materials
Authors: Kato K. , Asai K. , Okamoto Y. , Morimoto J. , Miyakawa T.
Published: March 2008

We have studied the thermoelectric properties of a SiC-based thermoelectric semiconductor with Ag and polysilastylene (PSS) as a dopant and as a sintering additive, respectively. Ag is an effective dopant to decrease the electrical resistivity of the SiC-based p-type thermoelectric semiconductor. It introduces carrier (hole) concentration 103−104 times larger than the case of Al-doped SiC with the typical doping concentration. PSS can control the sample density, which is one of the important factors in decreasing the electrical resistivity and thermal conductivity of the sintered samples. The figure of merit of the sample with Ag 2.0 wt% and PSS 0.1 wt% was estimated to reach 4 × 10−4 K−1 at 700 °C. This value implies that the SiC/Ag system is one of the promising thermoelectric materials for a high-temperature region.
Solidification of undercooled molten Cu30Ni70
Authors: Xiao J. Z. , Kui H. W.
Published: March 2008

Recently, it was demonstrated that grain refinement in undercooled Cu30Ni70 is brought about by a remelting of those initially formed dendrites (termed novel dendrites) which are unstable against melting. Also, it was found that in the same transition regime, there is a sharp drop in the specific volume of the undercooled specimens. Before entering into the transition regime, the novel dendrites found in an undercooled specimen are arranged in a regular pattern and the microstructures consist of large dendrites. Voids are found mainly at the dendritic spacings of the large dendrites. On the other hand, near the upper end of the transition regime, the microstructures consist of equiaxed refined grains. Furthermore, each of these grains contains a novel dendrite. Voids have moved to the interdendritic or grain boundaries. Based on these observations, a solidification mechanism of undercooled molten Cu30Ni70 is proposed.
Characterization of Fe–Ni(C) nanocapsules synthesized by arc discharge in methane
Authors: Dong X. L. , Zhang Z. D. , Jin S. R. , Sun W. M. , Zhao X. G. , Li Z. J. , Chuang Y. C.
Published: March 2008

Ultrafine Fe–Ni(C) particles of various compositions were prepared by arc discharge synthesis in a methane atmosphere. The particles were characterized by x-ray diffraction, transmission electron microscopy, energy disperse spectroscopy, chemical analysis, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and magnetization measurement. The carbon atoms solubilizing at interstitial sites in γ–(Fe, Ni, C) solution particles have the effects of forming austenite structure and changing microstructures as well as magnetic properties. A carbon layer covers the surface of Fe–Ni(C) particles to form the nanocapsules and protect them from oxidization. The mechanism of forming Fe–Ni(C) nanocapsules in the methane atmosphere was analyzed.
Characterization of sol-gel Pb(Zr0.53Ti0.47)O3films in the thickness range 0.25–10 μm
Authors: Kurchania Rajnish , Milne Steven J.
Published: March 2008

Films of nominal composition Pb(Zr0.53Ti0.47)O3(PZT) in the thickness range 0.25−10 μm have been fabricated on Pt/Ti/SiO2/Si substrates using a propanediol-based sol-gel route. The spun-on coatings were prefired at 350 and 600 °C between successive depositions before firing the multilayer stack at 700 °C for 15 min. The variations in crystallite orientation, microstructure, and dielectric and ferroelectric properties were determined as a function of film thickness. For a constant applied field of 150 kV cm−1, remanent polarization decreased progressively from 35 to 17 μC cm−2as film thickness decreased in the range 10–0.25 μm; values of coercive field were reasonably constant, 18–19 kV cm−1, for films between 2 and 10 μm, but increased sharply below 2 μm, reaching 46 kV cm−1for a 0.25 μm film. Relative permittivity (εr) decreased from approximately 1400 to approximately 940 with most of the reduction occurring in films less than 2 μm in thickness. These trends are discussed in terms of the presumed influence of interfacial phenomena on the measured electrical response.
Planar defects in ZnO thin films deposited on optical fibers and flat substrates
Authors: Sagalowicz Laurent , Fox Glen R.
Published: March 2008

The microstructure and the defects of ZnO coatings deposited at room temperature by sputtering onto fibers and flat substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction (XRD). XRD shows that the films have a [0001] preferred orientation and a large angular width of the 0002 reflection. According to TEM observations, the film microstructure consists of columnar grains which contain large concentrations of basal planar defects and dislocations. High-resolution transmission electron microscopy analysis and the associated image simulation are in full agreement with the presence of single (type I) and double (type II) stacking faults. The relation between the observed defects and the 0002 peak broadening is discussed.
The effect of Zn(OH)2 addition on the electrode properties of nickel hydroxide electrodes
Authors: Chen J. , Bradhurst D. H. , Dou S. X. , Liu H. K.
Published: March 2008

Nickel hydroxide powders currently used in the positive electrode of nickel-metal hydride (Ni–MH) batteries require cobalt or cobalt oxides to make them viable and attractive. As a step to eliminate the cobalt-containing materials, spherical nickel hydroxide powders coprecipitated with Zn(OH)2 were prepared by a spraying technique. These powders, which have a higher tapping density and a much smaller pore volume than conventional powders, were used as the active materials of nickel hydroxide electrodes. The effects of the Zn(OH)2 additions on the electrode properties, such as percentage utilization and cycle life, were studied, and the relationship between the electrode performance and the formation of γ–NiOOH was investigated. The cycle life was increased because there was less electrode swelling due to much reduced formation of γ–NiOOH.
A self-propagating high-temperature synthesis method for synthesis of AlN powder
Authors: Chung Shyan-Lung , Yu Wen-Liang , Lin Chun-Nan
Published: March 2008

A new self-propagating high-temperature synthesis (SHS) process has been developed for synthesis of AlN powder under low nitrogen pressures. Al and NH4X (X = F, Cl, Br, or I) powders were mixed and pressed into a compact, which was placed in a reaction chamber filled with nitrogen. The combustion synthesis reaction was ignited by heating directly the compact, and high product yields (∼90%) were obtained under nitrogen pressures of around 0.5 MPa. The product yield was affected by the reactant composition, the nitrogen pressure, and the compact-forming pressure. The powder as synthesized consists mainly of fibers, coarse granules, and agglomerated fine particles, which become mostly smaller than 10 μm after grinding. A reaction process was also proposed that explains the effects of the experimental parameters on the product yield.
Structural characterization of deuterated titanium thin films
Authors: Checchetto R. , Scardi P.
Published: March 2008

Pure and deuterated titanium thin films 140 nm thick were deposited on 〈100〉 Si wafers by electron beam evaporation, keeping the substrate temperature at 150, 300, and 450 °C. Pure Ti samples were deposited in a high-vacuum condition, while for deuterated samples, deuterium high-purity gas was introduced in the deposition chamber during the process. Film composition was studied by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA), whereas structural characterization of the deposited layers was carried out by x-ray diffraction (XRD) using both the traditional Bragg–Brentano geometry and a parallel beam setup for pole figure measurements. Titanium films deposited in a high vacuum showed the hexagonal Ti structure (α−Ti) and grew with a double orientation at each of the examined substrate temperatures. Deuterated titanium films deposited at 150 °C had a compositional ratio Ti: D = 1: 0.35 and grew with a [111] oriented fcc structure, suggesting the formation at low temperature of a substoichiometric δ hydride phase. Deuterated films deposited at higher substrate temperatures revealed a lower deuterium content and XRD reflections corresponding to the hexagonal Ti phase. The present results were interpreted according to a temperaturedependent D2 adsorption mechanism at the surface of the continuously growing Ti film.
Corrosion performance of ferrous and refractory metals in molten salts under reducing conditions
Authors: Indacochea J. E. , Smith J. L. , Litko K. R. , Karell E. J.
Published: March 2008

A lithium reduction technique to condition spent fuel for disposal has been developed at the Argonne National Laboratory. There is a need to ensure adequate vessel longevity through corrosion testing and, if necessary, materials development. Several ferrous alloys and tantalum specimens were submitted to a corrosion test at 725 °C for thirty days in an argon atmosphere, using a lithium-chloride salt saturated with lithium metal and containing small amounts of lithium oxide and lithium nitride. The samples did not show dimensional or weight change, nor could corrosion attack be detected metallographically. The lithium-saturated salt system did not show any behavior similar to that of liquid lithium corrosion. From testing in other gas compositions, it appears that the presence of oxygen in the system is necessary to produce severe corrosion.
Formation of C54–TiSi2 in titanium on nitrogen-ion-implanted (001)Si with a thin interposing Mo layer
Authors: Cheng S. L. , Jou J. J. , Chen L. J. , Tsui B. Y.
Published: March 2008

Formation of TiSi2 in titanium on nitrogen-implanted (001)Si with a thin interposing Mo layer has been investigated. The presence of a Mo thin interposing layer was found to decrease the formation temperature of C54–TiSi2 by about 100 °C. A ternary (Ti, Mo)Si2 phase was found to distribute in the silicide layer. The ternary compound is conjectured to provide more heterogeneous nucleation sites to enhance the formation of C54–TiSi2. On the other hand, the effect of grain boundary for decreasing transformation temperature was found to be less crucial. For Ti/Mo bilayer on 30 keV BF2+ or As+ + 20 keV, 1 × 1015/cm2 N2+ implanted samples, a continuous C54–TiSi2 layer was found to form in all samples annealed at 650–950 °C. The presence of nitrogen atoms in TiSi2 is thought to lower the silicide/silicon interface energy and/or the silicide surface energy to maintain the integrity of the C54–TiSi2 layer at high temperatures.
Niobium and zirconium telluride thin films prepared by sputtering
Authors: Pailharey Daniel , Mathey Yves , Kassem Mohamad
Published: March 2008

A versatile procedure of sputter deposition, well-adapted for getting a large range of Te/M ratios (with M = Zr or Nb), has led to the synthesis of several highly anisotropic zirconium and niobium polytellurides in thin film form. Upon tuning the two key parameters of the process, i.e., the Te percentage in the target and the substrate temperature during the deposition, preparation of systems ranging from ZrTe0.72 to ZrTe6.7, on the one hand, and from NbTe1.28 to NbTe7.84, on the other, has been achieved. Besides their amorphous or crystalline (with or without preferential orientations) behavior and their relationship to known structural types, the most striking feature of these films is their large departure from the stoichiometry of the bulk MTex reference compounds. This peculiarity, together with the possible changes of composition under annealing, are described and interpreted in terms of variable amounts of Te and M atoms trapped or intercalated within the parent structures.
Formation mechanism of spherical oxide particles containing dye
Authors: Wu Sixin , Zhu Congshan
Published: March 2008

2-[3-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidine)-1-propenyl]-1,3,3-trimethyl-3H-indolium idoide (HICI) dye-doped SiO2 particles were synthesized by sol-gel method. Dimension, diameter, distribution, and homogeneity of the particles are closely related to the positively charged dye concentration, corresponding to the zeta potential of the particles. When the dye concentration reaches about 7.8 × 10−4 mol/mol SiO2, corresponding to the isoelectric point of the particles, the maximum particle size and the most homogeneity can be reached.
Anodic dissolution of diamondlike carbon film-coated type 301 stainless steel
Authors: Srividya C. , Moskowitz I. , Babu S. V.
Published: March 2008

The resistance of thin diamondlike carbon (DLC) films to anodic breakdown in aqueous electrolytes was investigated using voltammetry. The films were less than 0.5 μm thick and were deposited on type 301 stainless steel substrates using plasma-assisted chemical vapor deposition (PACVD) from either methane, acetylene, or 1,3-butadiene precursors with argon or hydrogen as diluent. A 10 nm thick polysilicon (PS) film was plasma-deposited prior to DLC film deposition to improve adhesion. The electrolytes used for corrosion testing were mixtures of 0.1 M NaCl and 0.1 M Na2SO4 and 0.1 M HCl and 0.1 M Na2SO4 in de-ionized water. The measured anodic current was lowest for the films deposited from butadiene and highest for those deposited from methane. The anodic current also increased with an increase in the hydrogen content in the feed gas mixture. In addition, the DLC films deposited at higher gas flow rates offered more resistance to anodic dissolution than those deposited at lower gas flow rates. Annealing improved the film performance. There appears to be an optimum DLC film thickness which provides the maximum resistance to anodic dissolution. In the best case, the DLC films reduced the anodic dissolution of bare stainless steel by about 4 orders of magnitude in the passive region. Atomic force microscopy studies of coated and uncoated stainless steel showed that the DLC films conformed to the steel substrate surface and had no effect on surface roughness, while DLC coated silicon substrates showed no evidence of pores.
Influences of thermal annealing and humidity exposure on surface structure of (100) single-crystal MgO substrate
Authors: Delplancke-Ogletree M. P. , Ye M. , Winand R. , de Marneffe J. F. , Deltour R.
Published: March 2008

We studied the influence of thermal annealing on the surface structure of (100) singlecrystal MgO substrates by atomic force microscopy (AFM). By annealing MgO substrates at various temperatures for 4 h in flowing oxygen, we showed that the surface reconstruction could be explained by considering surface diffusion, surface evaporation, and condensation. At an annealing temperature of 1473 K, a stepped structure was formed with screw dislocations acting as step sources. The influence of humidity on the surface morphology of MgO substrates was also studied by exposing them to a constant humidity of 40 and 80% for different times. After an exposure time of 1.5 h in 80% humidity, the substrate surface was already covered by reaction products. For the 40% humidity, the corresponding time is 10 h. The major reaction product was identified as Mg(OH)2 by x-ray diffraction.
Study on the structure of PbS nanoparticles coated with dialkyldithiophosphate
Authors: Chen Shuang , Liu Weimin , Yu Laigui
Published: March 2008

PbS nanoparticles modified with di-n-hexadecyldithiophosphate (DDP) were prepared by the chemical surface modification method. The structure of the PbS nanoparticles coated with DDP was investigated by means of infrared spectroscopy (ir), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM), and 31P nuclear magnetic resonance spectroscopy (31P NMR). The thermal stability of DDP coating on the PbS nanoparticles was compared with that of pyridinium di-n-hexadecyldithiophosphate (PyDDP) using a thermogravimetric analyzer (TGA). It was found that coated PbS nanoparticles had an average diameter of about 5 nm. Surface modification with DDP prevented water adsorption and effectively improved the dispersive capacity and antioxidative stability of PbS nanoparticles. The thermal stability of DDP coating on the surface of nano-PbS particles was higher than that of modifier PyDDP because of the chemical interaction between PyDDP and PbS during the coating process.
Determination of elastic modulus of thin films and small specimens using beam bending methods
Authors: Menčík J. , Quandt E.
Published: March 2008

Elastic modulus of small specimens and thin films can be determined in bending tests using cantilever or three-point arrangement. The paper presents the basic formulae for these measurements, analyzes the errors which can arise, and shows how they can be reduced. The use of the method is illustrated on glass, silicon, and glass coated with TbDyFe.
Microstructure modification of amorphous carbon films by ion-implantation techniques
Authors: Wei B. , Komvopoulos K. , Brown I. G.
Published: March 2008

Microstructure modification of amorphous carbon films containing about 30 at.% hydrogen (a-CHx) and nonhydrogenated amorphous carbon (a-C) films was accomplished with a vacuum arc metal plasma implanter and a cathodic arc plasma system, respectively. The films were implanted with Si, Ti, Hf, W, and Al of ion doses approximately equal to 1 and 3 × 1016 ions/cm2 and mean ion kinetic energies in the range of 3–70 keV, depending on the implantation method. Simulation results demonstrated a profound effect of the size of implant species, ion dose, mean ion kinetic energy, and implantation processes on the implant spatial distributions. Statistical roughness results showed a negligible effect of ion implantation on the film surface topography. Elastic recoil spectroscopy revealed a decrease in the hydrogen content of the a-CHx films due to the ion bombardment. A monotonic decrease in the Raman scattering intensities and a downward shift of the carbon peak position occurred with increasing ion dose for both types of films and implantation techniques. Nanoindentation experiments demonstrated an effect of ion implantation on the apparent film hardness, depending on the flux and kinetic energy of implanted species. Changes in the hardness characteristics of the implanted films are interpreted in terms of the chemical reactivity of implant elements and microstructure modifications caused by irradiation damage, dehydrogenation, and higher contents of tetrahedral (s p3) carbon hybridization due to carbide bond formation.
Microstructural characteristics of TiC-reinforced composite coating produced by laser syntheses
Authors: Wu Xiaolei
Published: March 2008

An in situ method has been developed to produce a Ni alloy composite coating reinforced by in situ reacted and gradiently distributed TiC particles by one-step laser cladding. The dispersed, ultrafine TiC particles in the coating are observed. Most of TiC particles, evidently with a gradient distribution, are uniformly distributed within interdendritic regions due to the trapping effect of advanced solid–liquid interface. The TiC/γ–Ni interface is clean and free from deleterious surface reactions. The microhardness of the coating also has a gradient variation, with the highest value being 1250 Hv 0.2.
Early stages of oxidation of aluminum nitride
Authors: Geng Yongjun , Norton M. Grant
Published: March 2008

The early stages of oxidation of aluminum nitride have been studied by transmission electron microscopy and electron diffraction. It has been found that the oxide layer grows by the Stranki–Krastonow mechanism, where an initial uniform layer is followed by island formation. The onset of oxidation occurs at 800 °C and the initial oxide phase that forms is γ–Al2O3, one of the transition aluminas. The orientation relationship between the oxide layer and the underlying nitride is (440)γ∥(1120)AINand [112]γ∥[0110]AIN.
Preparation of highly oriented Pb(Zr0.52Ti0.48)O3thin films by sol-gel-hydrothermal process
Authors: Zeng Jianming , Lin Chenglu , Li Jinhua , Li Kun
Published: March 2008

A novel sol-gel-hydrothermal process for preparation of highly oriented thin films of Pb(Zr0.52Ti0.48)O3is reported. Pb(Zr0.52Ti0.48)O3thin films with fully (111) orientation were successfully prepared on platinized silicon substrates at low temperature (100–200 °C) by combining a conventional sol-gel process and hydrothermal method, i.e., sol-gel-hydrothermal technique. The x-ray rocking curve for the (111) reflection as measured by a high-resolution four-crystal diffractrometer showed a narrow full width at half-maximum value of 0.20° for the as-prepared films. A dense, pinhole-free, and uniform surface morphology was observed from atomic force microscopy images of the films. The low leakage current density of the prepared films was also found.
X-ray and neutron diffraction of yttrium–barium–copper–oxide: Modeling diffraction intensity variations produced by surface leaching
Authors: Watkins Seth A. , Cocks F. Hadley
Published: March 2008

High normal current fluences have long been reported to produce major changes in the x-ray diffraction pattern of YBa2Cu3O7−x (YBCO). These x-ray diffraction effects have now been shown to result from the removal of barium from the YBCO near-surface lattice together with the formation of a thin barium oxide overlayer. Neutron diffraction reveals that the bulk crystallographic structure remains unaltered by charge fluences of more than 40 million C/cm2, and Auger electron spectroscopy confirms the presence of surface barium enrichment.
Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography
Authors: Seraphin S. , Beeli C. , Bonard J-M. , Jiao J. , Stadelmann P. A. , Châtelain A.
Published: March 2008

The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was established by simulation.
Kinetics and mechanism of anatase-to-rutile phase transformation in the presence of borosilicate glass
Authors: Jean Jau-Ho , Lin Shih-Chun
Published: March 2008

The effects of borosilicate glass (BSG) on the kinetics and mechanism of anataseto- rutile phase transformation have been investigated. The displacive anatase-to-rutile phase transformation kinetics of TiO2 were greatly enhanced in the presence of BSG. The transformation kinetics followed the Avrami equation, and the results showed an apparent activation energy of 260–370 kJ/mol, which was close to the bond strength of Ti–O, suggesting a reaction-controlling mechanism. The values of the Avrami exponent were in the range of 1.4–2.3, which could be interpreted as two-dimensional reaction-controlled growth at zero nucleation rate. The rutile particles obtained by the phase transformation were always much larger than the starting anatase powders, which was explained by a mechanism of phase-transformation–induced particle coalescence.
Nucleation mechanisms in chemically vapor-deposited mullite coatings on SiC
Authors: Hou Ping , Basu S. N. , Sarin V. K.
Published: March 2008

Dense, uniform, and adherent chemically vapor-deposited mullite coatings were deposited on SiC substrates using the AlCl3–SiCl4–H2–CO2 system. Typical coating morphology consisted of a thin interfacial layer of γ–Al2O3 nanocrystallites embedded within a vitreous SiO2-based matrix. When a critical Al/Si ratio of 3.2 ± 0.29 was reached within this nanocrystalline layer, mullite crystals nucleated and grew as columnar grains. The thickness of the nanocrystalline layer decreased as the input AlCl3/SiCl4 ratio was increased. In all cases, the Al/Si composition in the coating increased from the coating/substrate interface to the coating surface. Critical factors leading to the nucleation and growth of mullite crystals are discussed in this article.
Origin of strength change in ceramics associated with the alteration of spray dryer
Authors: Hotta T. , Nakahira K. , Naito M. , Shinohara N. , Okumiya M. , Uematsu K.
Published: March 2008

A significant difference of strength was noted in alumina ceramics made through the powder compaction process with spray dryers of two sizes. The origin of the change was examined by new characterization methods involving optical microscopy. The granules were found to have irregular shape. Defects in compacts were formed from these dimples and also from the nonuniform packing of powder particles at the granule boundaries. These defects are responsible for major defects in sintered bodies. The change of strength in the ceramics can be explained by the change of granule size with the spray dryer. The size of granules was found to directly affect the size of defects in the green and sintered bodies. The size of granules, defects in granules, green bodies, and sintered bodies were approximately 20–30% smaller for granules made with the small spray drier. There was a direct correlation between the size of defect and the strength of ceramics.
Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W
Authors: Kriese Michael D. , Gerberich William W. , Moody Neville R.
Published: March 2008

Sputtered copper and tungsten thin films both with and without tungsten and chromium superlayers were tested by using nanoindentation probing to initiate and drive delamination. The adhesion energies of the films were calculated from the induced delaminations using the analysis presented in “Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics.” Copper films ranging in thickness from 150 to 1500 nm in the as-sputtered condition had measured adhesion energies ranging from 0.2 to 2 J/m2, commensurate with the thermodynamic work of adhesion. Tungsten films ranging in thickness from 500 to 1000 nm in the as-sputtered condition had measured adhesion energies ranging from 5 to 15 J/m2. The superlayer was shown to induce radial cracking when under residual tension, resulting in underestimation of the adhesion energy when the film was well adhered. Under conditions of weak adherence or residual compression, the superlayer provided an excellent means to induce a delamination and allowed an accurate and reasonably precise quantitative measure of thin film adhesion.
The role of the dispersed-phase remnant magnetization on the redispersibility of magnetorheological fluids
Authors: Phulé Pradeep P. , Mihalcin Matthew P. , Genc Seval
Published: March 2008

The influence of the remnant magnetization of the soft magnetic particulates, used as a dispersed phase, on the redispersibility of magnetorheological (MR) fluids is discussed. Calculations of the magnetic interaction energy showed that for 33-vol% MR fluids based on particles of iron (∼6 μm), manganese zinc ferrite (∼2.3 μm), and nickel zinc ferrite (∼2.1 μm), the ratios of the magnetic interaction energy to the thermal energy were 161,000, 6400, and 3900, respectively. These calculations showed that even the seemingly small levels of remnant magnetization, associated with particulates employed in MR fluids, introduced significant dipole–dipole interparticle interactions. It is proposed that this interaction causes most MR fluids to show a tendency for “cake formation,” which makes it difficult to redisperse these fluids. Our modeling presented here also suggests practical strategies to enhance the redispersibility of MR fluids.
Electromechanical anisotropy behavior in Pb0.88Eu0.08Ti1−yMnyO3 system: Role of 90° domain reversal
Authors: Martínez O. Pérez , Blesa J. M. Saniger , Barranco A. Peláiz , Piñar F. Calderón
Published: March 2008

An indirect observation of 90° domain reversal under the influence of a poling field process was undertaken by an x-ray diffraction study in the Pb0.88Eu0.08Ti1™y MnyO3 (y = 0, 0.01, 0.02, and 0.03) piezoelectric anisotropic system. The optimum condition kp → 0 was achieved for y = 0.02 composition. A large percentage of 90° domain rotation was necessary, but not a sufficient condition for the ultrahigh electromechanical anisotropy manifestation. A large microstrain originated by structural defects in unpoled samples seemed to play a crucial role in the attainment of this piezoelectric anisotropy. A breaking in the translational periodicity due to induced vacancy in Pb and O sites by Eu3+ and Mn2+ substitutions was manifested in the nonuniform variance of the tetragonality (c/a), the large microstrain, and the detriment of crystallinity observed.
Eu-doped Y2O3 phosphor films produced by electrostatic-assisted chemical vapor deposition
Authors: Choy K. L. , Feist J. P. , Heyes A. L. , Su B.
Published: March 2008

Europium-doped yttrium oxide (Y2O3:Eu) thermographic phosphor films were deposited on Ni-alloy substrates using a novel and cost-effective electrostatic-assisted chemical vapor deposition (EACVD) technique. The thermoluminescence properties were studied under irradiation by an ultraviolet laser. It was found that crystallized Y2O3: Eu films could be deposited at a temperature as low as 550 °C. Annealing of the as-deposited films at higher temperatures (>1000 °C) improved the luminescence properties due to further crystallization processes. The correlation of the lifetime decay and temperature change of the films showed that the EACVD-deposited films are suitable for use in phosphor thermometry for high-temperature applications.
Structural mechanisms underlying near-zero thermal expansion in β-eucryptite: A combined synchrotron x-ray and neutron Rietveld analysis
Authors: Xu Hongwu , Heaney Peter J. , Yates Douglas M. , Von Dreele Robert B. , Bourke Mark A.
Published: March 2008

The structures of ordered and disordered β-eucryptite have been determined from Rietveld analysis of powder synchrotron x-ray and neutron diffraction data over a temperature range of 20 to 873 K. On heating, both materials show an expansion within the (001) plane and a contraction along thecaxis. However, the anisotropic character of the thermal behavior of ordered β-eucryptite is much more pronounced than that of the disordered compound; the linear expansion coefficients of the ordered and disordered phases are αa= 7.26 × 10−6K−1; αc= −16.35 × 10−6K−1, and αa= 5.98 × 10−6K−1; αc= −3.82 × 10−6K−1, respectively. The thermal behavior of β-eucryptite can be attributed to three interdependent processes that all cause an increase inabut a decrease incwith increasing temperature: (i) Si/Al tetrahedral deformation, (ii) Li positional disordering, and (iii) tetrahedral tilting. Because disordered β-eucryptite does not exhibit tetrahedral tilting, the absolute values of its axial thermal coefficients are smaller than those for the ordered sample. At low temperatures, both ordered and disordered β-eucryptite exhibit a continuous expansion parallel to thecaxis with decreasing temperature, whereasaremains approximately unchanged. Our difference Fourier synthesis reveals localization of Li ions below room temperature, and we suggest that repulsion between Li and Al/Si inhibits contraction along theaaxes.
Effects of carbonization atmosphere and subsequent oxidation on pore structure of carbon spheres observed by scanning tunneling microscopy
Authors: Inagaki M. , Vignal V. , Konno H. , Morawski A. W.
Published: March 2008

The surface of carbon spheres was studied by using field-emission scanning electron microscopy and scanning tunneling microscopy paying particular attention to the effects of atmosphere during carbonization and of subsequent oxidation on shape and size of the entrance of micropores. Commercial spheres of glasslike carbon prepared by carbonization of phenol resin spheres in either N2 or CO2 atmosphere were subjected to the oxidation by immersing into nitric acid and then heating in air at 400 °C. The size distribution of pore entrance at nanoscopic scale was determined from scanning tunneling microscope images. Carbon spheres prepared in CO2 atmosphere had predominantly ultramicropores, but those prepared in N2 had a very low porosity. The behavior during the oxidation process in air was found to be quite different on these two carbon spheres; spheres carbonized in N2 were oxidized heterogeneously, but those in CO2 showed homogeneous oxidation, giving a high density of ultramicropores.
On the grain size and coalescence stress resulting from nucleation and growth processes during formation of polycrystalline thin films
Authors: Thompson Carl V.
Published: March 2008

When polycrystalline films form by nucleation, growth, impingement, and coalescence of islands on a substrate surface, the grain size at impingement depends on the relative magnitudes of the nucleation rate, the growth rate, and the dimension of the zone from which adatoms diffuse to a growing island. A simple description of the interdependence of these parameters is developed. It is used to discuss the dependence of the grain-size-at-impingement and the intrinsic stress resulting from coalescence on the deposition rate and the substrate temperature, and to discuss how these might affect texture evolution during film growth.
Microtexture of shock reaction products of niobium and silica mixtures
Authors: Murao Reiko , Kikuchi Masae , Fukuoka Kiyoto , Aoyagi Eiji , Atou Toshiyuki , Syono Yasuhiko
Published: March 2008

Shock compression experiments on powder mixtures of niobium metal and quartz were conducted for the pressure range of 30–40 GPa by a 25-mm single-stage propellant gun. Chemical reaction occurred above 35 GPa, and products were found to be mainly so-called “Cu3Au-type” Nb3Si, which contained a small amount of oxygen. Microtextures of the specimen were examined by scanning and transmission electron microscopy. A field-emission transmission electron microscope was used for energy-dispersive x-ray analysis of microtextures in small particles found in the SiO2 matrix, and various species with different Nb/Si ratio and oxygen content were shown to be produced through the nonequilibrium process of shock compression.
A novel approach for identifying and synthesizing highdielectric materials
Authors: Park J.-H. , Parise J. B. , Woodward P. M. , Lubomirsky I. , Stafsudd O.
Published: March 2008

Modern telecommunications require materials with high dielectric constants (κ). The number of suitable elements ultimately limits one approach to the discovery of new materials, targeting compositions with high atomic polarizabilities (α). By decreasing the molar volume of compositions with high α, however, we anticipated dramatic increases in κ and demonstrated that this approach works. The quenched high-pressure perovskite polymorph of Na2MTeO6 (M = Ti, Sn) showed a twofold increase in κ, compared to the ilmenite form. This result suggested the highest values of κ occur for compositions with high α, which form quenchable compounds at high pressures and temperatures.
Effect of oxygen plasma treatment on gas adsorption behavior and surface structure of carbon spheres derived from phenol resin
Authors: Inagaki M. , Sunahara M. , Shindo A. , Vignal V. , Konno H.
Published: March 2008

Plasma treatment was applied on glasslike carbon spheres to modify their gas adsorption behavior. After the oxygen plasma treatment, a selective adsorption of CO2 gas was obtained, almost no nitrogen adsorption being detected, at low temperatures. Surface morphology observed by using field-emission scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy was found to be changed after the oxygen plasma treatment.
Stress-driven surface evolution in heteroepitaxial thin films: Anisotropy of the two-dimensional roughening mode
Authors: Ozkan Cengiz S. , Nix William D. , Gao Huajian
Published: March 2008

We have analyzed the anisotropic behavior of surface roughening in Si1−xGex/Si(001) heterostructures by use of methods of elastic analysis of undulated surfaces and perturbation analysis on the basis of global energy variations associated with surface evolution. Both methods have shown that the two-dimensional stage of surface roughening preferentially takes place in the form of ridges aligned along the two orthogonal 〈100〉 type directions. This prediction has been confirmed by ex situ experimental observations of surface evolution by use of atomic force microscopy and transmission electron microscopy in both subcritically and supercritically thick Si1−xGex films grown on Si(001) substrates. Further experiments in supercritically thick films have revealed a remarkable interplay between defect formation and surface evolution: the formation of a network of 〈110〉?misfit dislocations in the latter stages alters the evolution process by rotating the ridge formations toward the 〈110〉 type directions.
Epitaxial growth of magnesia and spinel on sapphire during incongruent reduction in molten magnesium
Authors: Kumar P. , Dregia S. A. , Sandhage K. H.
Published: March 2008

The types and structures of oxide phases produced during the incongruent reduction of sapphire (single-crystal Al2O3) by molten magnesium were examined. Polishedfaces of sapphire were exposed to molten magnesium at 1000 °C for 100 h. Such exposure resulted in the formation of a continuous, epitaxial layer of spinel (MgAl2O4) on sapphire and a continuous, epitaxial layer of magnesia (MgO) on the spinel. X-ray pole figure analyses indicated that two variants of spinel and magnesia had formed in a manner consistent with the following orientation relationships: