bluuebunny/crossref_metadata_2025 huggingface dataset:
Lubricity of zinc oxide thin films: Study of deposition parameters and Si as an additive
Authors: Nainaparampil J. J. , Zabinski J. S.
Published: March 2008

Zinc oxide preferentially crystallizes into a wurzite structure and has a unique set of properties. There have been numerous studies on doped zinc oxide thin films as an optical coating or as a semiconductor material. However, very little work has been reported on its tribological properties. Recent reports from this laboratory revealed that ZnO has good potential for controlling friction and wear. ZnO has an open structure and favorable coordination number, which permits zinc to freely move to different positions in the crystal lattice and to accommodate external atoms as substitutes. The nature of the substitution and the concentration of Zn interstitials may be used to control tribological performance. In this work, thin films of zinc oxide were deposited by pulsed laser ablation while silicon was added simultaneously by magnetron sputtering. The effects of deposition geometry and oxygen partial pressure on stoichiometry and microstructure were evaluated. It was found that the angle of deposition and oxygen partial pressure control coating texture. Depositions normal to the sample surface, along with 10 mtorr of oxygen, produced strong (002) texture. These conditions were selected for Si-doping studies. The tribological characteristics of Si-doped coatings were evaluated at both room and high temperature. Addition of Si around 7–8% gave a coefficient of friction of about 0.2 at 300 °C, decreasing to 0.13 around 500 °C.
High grain size stability of nanocrystalline Al prepared by mechanical attrition
Authors: Zhou F. , Lee J. , Dallek S. , Lavernia E. J.
Published: March 2008

Grain growth in nanocrystalline (nc) Al with a grain size of 26 nm produced by cryogenic mechanical milling was studied through x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Grain growth kinetics resembled those of ball-milled nc Fe. For homologous temperatures (T/TM) of 0.51–0.83, the time exponentnfromD1/n−D01/n= ktwas 0.04–0.28, tending toward 0.5 asT/TMincreased. Two grain-growth regimes were distinguished: belowT/TM= 0.78 growth ceased at an approximate grain size of 50 nm while at higher temperatures, grain growth proceeded steadily to the submicrometer range. Grain growth over the range of temperatures studied cannot be explained in terms of a single thermally activated rate process. The observed high grain size stability was attributed primarily to impurity pinning drag associated with the grain growth process.
Origins of stored enthalpy in cryomilled nanocrystalline Zn
Authors: Zhang Xinghang , Wang Haiyan , Kassem Magdy , Narayan Jagdish , Koch Carl C.
Published: March 2008

Nanocrystalline Zn was prepared by cryomilling (mechanical attrition at liquid nitrogen temperature). Differential scanning calorimetry (DSC), x-ray diffraction, and transmission electron microscopy were used to study the structural changes and grain size distribution with milling time and subsequent annealing. Maxima in both stored enthalpy (for the low-temperature DSC peak) and lattice strain on the Zn basal planes were observed at the same milling time. Dislocation density on the basal planes is proposed as a major source for lattice strain and the measured stored enthalpy. The released enthalpy that might be due to grain growth is very small.
Embedded-atom-method functions for the body-centered-cubic iron and hydrogen
Authors: Wen Mao , Xu Xue-Jun , Fukuyama Seiji , Yokogawa Kiyoshi
Published: March 2008

A new reliable embedded atom method potential for hydrogen in body-centered-cubic (bcc) iron is developed by fitting not only to the properties of hydrogen in a perfect bcc iron lattice but also to the properties of hydrogen binding to vacancies. The validity of the potential is examined by calculating the properties of hydrogen trap binding to surfaces and dislocations that are in good accordance with the experiments. A brief application of the potential by molecular dynamic simulation reveals that hydrogen accumulated ahead of the crack tip induces serious hydrogen embrittlement.
Hydrodynamic cavitation as a tool to control macro-, micro-, and nano-properties of inorganic materials
Authors: Find J. , Emerson S.C. , Krausz I.M. , Moser W.R.
Published: March 2008

Hydrodynamic cavitation was shown to be a powerful tool for the synthesis of nanostructured catalysts, ceramics, and piezoelectrics in high phase purities. The macro-, micro-, and nano- properties of solid-state materials could be controlled through adjusting the cavitational regime during synthesis by simple mechanical adjustment. The synthesis of nanostructured titania, piezoelectrics, perovskites, supported and unsupported cobalt molybdates, and Pd and Ag supported on alumina illustrate changes in morphology and size of crystals, growth in a preferred orientation of crystallites, and control of crystallographic strain and size compared to classically prepared materials. The high shear and cavitational forces during synthesis induce micro-strain into the materials and are a function of the Reynolds and cavitation numbers.
Formation of Al2O3 grains with different sizes and morphologies during the pulse electric current sintering process
Authors: Wang S. W. , Chen L. D. , Hirai T. , Guo Jingkun
Published: March 2008

Commercial micrometer Al2O3 powder was sintered at 1550 °C under a mechanical pressure of 30 MPa by pulse electric current sintering (PECS). Microstructure observation was performed on polished, thermal-etched cross sections parallel to the direction of mechanical pressure. Platelike Al2O3 grains formed when the powder was heated at a heating rate of 5 °C/min, while a heating rate of 200 °C/min resulted in equiaxed grains. These results indicated that PECS is an effective approach to hinder grain growth by application of a higher heating rate. However, Al2O3 grains at the upper edge were larger than those at the side edge of the samples in both cases. It implied that there were different temperatures at the upper edge and the side edge of the Al2O3 powder compacts during the PECS process.
Mechanical and thermal properties of combustion-synthesized perovskites, La1−xSrxCr0.2Fe0.8O3
Authors: Chou Yeong-Shyung , Kerstetter K. , Pederson L. R. , Williford R. E.
Published: March 2008

This paper examined the room-temperature thermal and mechanical properties of a mixed conducting perovskite La1−xSrxCr0.2Fe0.8O3 (x = 0.2 to 0.8). Powders were made by the combustion-synthesis technique and sintered at 1250 °C in air. Sintered density, crystal phase, and grain size were characterized. Linear thermal expansion in air was also tested. Young's and shear moduli, microhardness, indentation fracture toughness, and biaxial flexure strength were determined. It was found that the linear coefficient of thermal expansion increased with increasing Sr content, while elastic modulus appeared to decrease with increasing Sr content. Young's modulus of 128 to 192 GPa and shear modulus of 51 to 74 GPa were measured. A biaxial flexure strength of 243 MPa was measured for the lowest Sr content batches. Batches with higher Sr concentrations (x = 0.6 to 0.8) showed extensive cracking. Indentation toughness showed a decrease with increasing Sr content. In addition, fractography was used to characterize the critical flaw and the fracture mode.
Scanning probe microscopy generated out-of-plane deformation maps exhibiting heterogeneous nanoscale deformation resulting from thermal cycling of Cu–polyimide damascene interconnects
Authors: Gross Todd S. , Kamsah Nazri bin , Tsukrov Igor I.
Published: March 2008

Room-temperature scanning probe microscopy was used to generate out-of-plane deformation maps around Cu vias and polyimide mesas in single-level Cu–polyimide damascene interconnect structures subjected to a room-temperature to 350 °C thermal cycle. The deformation maps are obtained by taking the difference between the images obtained before and after thermal processing. The deformation of the Cu is shown to be highly heterogeneous on the submicrometer scale. Direct evidence of Cu–Ta interfacial sliding, Cu–Cu grain boundary sliding, and diffusion creep is presented. The direction of Cu–Ta sliding is shown to depend on polyimide mesa size. A hot-stage atomic force microscope was used to show that hillock/extrusion growth occurs at temperatures between 130 and 180 °C. We propose that this hillock/extrusion growth is correlated with dips in stress–temperature plots for blanket, uncapped Cu films in the same temperature range and that the absence of dips for nitride-capped Cu films is due to suppression of the hillock/extrusion growth.
Minima in the strength of MnZn ferrites
Authors: Donners M. A. H. , Dortmans L. J. M. G. , de With G. , de Graaf M. J. M.
Published: March 2008

Like many other oxides, MnZn ferrite shows a considerably decreased strength in a humid environment. Conventionally one explains this behavior by subcritical crack growth, i.e., a kinetic effect affecting the oxygen–metal bond breaking rate at the crack tip via a reaction with water. The dissociation of water in a proton and hydroxyl ion is considered as crucial. However, it appears that also other gases have a detrimental effect on the strength. In this paper the effect of H2O, H2S, NH3, NO, and CO on the strength of MnZn ferrite have been studied experimentally. For water a clear minimum in strength occurs at relative low partial pressure. For the other gases the data also indicate a minimum. An adsorption model taking into account the presence of competitive adsorption mechanisms, involving dissociative and nondissociative adsorption of the adsorbate and the (non)dissociative adsorption of the ever present N2, is presented. This model can explain the experimentally observed features well. Although kinetic effects induce subcritical crack growth in MnZn ferrites, it is concluded that adsorption is an important strength lowering effect for MnZn ferrite when exposed to active gases.
Metalorganic chemical vapor deposition of very thin Pb(Zr,Ti)O3 thin films at low temperatures for high-density ferroelectric memory applications
Authors: Kim Hye Ryoung , Jeong Seehwa , Jeon Chung Bae , Kwon Oh Seong , Hwang Cheol Seong , Han Young Ki , Yang Doo Young , Oh Ki Young
Published: March 2008

The metalorganic chemical vapor deposition of very thin (<50 nm) Pb(Zr,Ti)O3 (PZT) thin films was performed for high density (>32 mega bit) ferroelectric memory devices. The growth temperatures were set between 450 and 530 °C to obtain a smooth surface morphology and prevent damage to the underlying reaction barrier layer. The average grain size of a 50-nm-thick film on a Pt electrode was about 34 nm with a size distribution (σ2) of 11 nm. These values are much smaller than the sol-gel-derived PZT films (55 and 25 nm, respectively). Very thin films with a thickness of approximately 30 nm were prepared at wafer temperatures ranging from 500 to 525 °C. Even with the very small thickness, the films showed good ferroelectric properties with a typical remanent polarization from 10 to 15 μC/cm2 and an extremely low coercive voltage of 0.3 V. However, the leakage current density was rather high resulting in nonsaturating polarization versus voltage curves. Even though good ferroelectric properties were obtained, the formation of PtxPby alloys on top of the Pt electrode was consistently observed. This precludes the reliable control of film composition and electrical performance. The adoption of an Ir electrode successfully eliminated intermetallic alloy formation and resulted in better and reproducible process control. A 50-nm-thick PZT film on an Ir/IrO2/SiO2/Si substrate also showed a reasonable ferroelectric performance.
Origin of the anomalous volume expansion in Al–Si alloys above liquidus
Authors: Wang W. M. , Bian X. F. , Wang H. R. , Wang Zhen , Zhang L. , Liu Z. G. , Liu J-M.
Published: March 2008

The sessile-drop method and high-temperature small-angle x-ray diffraction technique were used to characterize the density of liquid Al–Si alloys with Si contentC= 0 to 22 wt%. A distinct abnormal volume expansion of the hyper-eutectic melts was identified just above the liquidus (withinTL–Tk) during the heating sequence (h.s.), which is irreversible during the cooling sequence (c.s.). This phenomenon is explained by the segregation of Si atoms from the supersaturated “quasi-eutectic” structure and formation of silicon clusters in the superheated melt. In addition, a pre-peak in the x-ray diffraction spectrum of Al–14% Si melt was observed at 850 °C, which is associated with the silicon clusters. The pre-peak remains when the superheated melt is cooled down to the liquidus (670 °C); this result is in accord with the density measurements.
Laser-induced surface perturbations in silicon
Authors: Pedraza A. J. , Jesse S. , Guan Y. F. , Fowlkes J. D.
Published: March 2008

In this paper it is shown that the initial stages in the laser-induced roughening in silicon is independent of the atmosphere used, whether it is Ar, vacuum, or SF6. It is also shown that the morphology that results after a few hundred laser pulses strongly depends on the crystallographic orientation of the surface. The morphological features that appear in this first stage have been related to the nature of the solidification process that follows laser melting. A second stage in the roughening process with a dramatic change in morphology takes place when a surface with deep depressions and hills is further irradiated in SF6. Very deep etching occurs in the depressions promoting the formation of microholes that with further irradiation lead to cone formation. It is further shown that the distance between microholes is equal to the distance between the depressions that formed as the initial perturbations developed. Then the wavelength of the initial perturbation and by extension the distance between microholes has been estimated.
Irradiation-disorder Creation in SrTiO3
Authors: Soulet S. , Chaumont J. , Sabathier C. , Krupa J-C.
Published: March 2008

The chemical durability of crystalline matrices loaded with actinides can be stronglyreduced when α-decays generate enough disorder to induce a crystalline to amorphoustransition. The alpha decay of actinides in SrTiO3 (α-recoils and α-particles) was simulated using Pb and He irradiation. This study shows that the He-ion annealingprocess that operates in some apatitic structure is negligible in SrTiO3 where thedisorder evolution at room temperature has a strong sigmoid dependence on dose. Thedirect-impact/defect-stimulated model, the cascade quenching/epitaxial recrystallizationmodel, and a direct-impact/cascade-overlap model were used to reproduce the SrTiO3-disorder evolution under Pb-ion irradiation.
Thermal Stability and Wetting Properties of Cr–O–C Coatingssynthesized by Plasma Immersion Ion Processing
Authors: He Xiao-Ming , Hakovirta Marko , Walter Kevin C. , Trkula Mitchell , Nastasi Michael
Published: March 2008

Microcrystalline Cr-O-C films, synthesized by the plasma immersion ion processing technique, were annealed in vacuum and air at 700 °C for different times so their thermal stability could be evaluated. The study showed that annealing does not greatly change the chemical composition of the Cr–O–C films but induces a transformation ofthe film structure from the mixed phases of Cr2O3, CrO2, and CrC1.13O0.12 to the dualphases of Cr3C2, and Cr2O3. In addition, the annealed Cr–O–C films exhibit excellentnonwetting qualities to liquid aluminum despite the presence of pin holes. The contactangle of resolidified molten aluminum against the Cr–O–C films was found to be ashigh as 120–150°. The aluminum contact angle was found not to vary with thermal aging of the Cr–O–C films. The Cr–O–C films showed high hardness (16–24 GPa) and good wear resistance as compared to the steel substrates (H13 and 304 stainless steels)used in this study.
Interface Shape Effects on the Tensile Strength for T-type Structure Bonded Dissimilar Materials
Authors: Nagasawa Shigeru , Yokoyama Yuji , Fukuzawa Yasushi , Tateno Masayoshi
Published: March 2008

To estimate the effect of the spherical interface of the T-type joint structure on bonding strength, thermal residual stress on the outer surface and in the interface were investigated by thermal elastoplastic finite element analysis, in terms of principal stress and principal axis direction. These numerical results were compared with experimental fracture patterns and the tensile strength. The relationship between the maximum principal stress around the interface edge and the joint angle was studied. As a result,an optimal joint angle was shown by the experimental data and also by the principal stress calculated.
Green Density-based Sintering Predictions
Authors: Sweeney Sean M. , Mayo Merrilea J.
Published: March 2008

Prediction of density–time curves, i.e., using the sintering curves for one green density to predict those of another during isothermal sintering, was demonstrated for 3 mol% yttria-stabilized zirconia and titania, as well as for data from the literature on various ceramic powder compacts. The predictions utilized only a median green pore size term as the scaling parameter for densification rates between samples of different green densities. Despite the simplicity of the approach, the resulting predictions of density–time curves were in relatively good agreement with the measured data.
Diffuse Dielectric Anomaly in MnO2-doped Pb0.9La0.1TiO3 Ceramic in the Temperature Range of 400–700 °C
Authors: Kang Byung Sung , Choi Si Kyung
Published: March 2008

The diffuse dielectric anomaly observed in the temperature range of 400–700 °C was investigated in MnO2-doped Pb0.9La0.1TiO3 ceramic. The frequency and the temperature dependence of the dielectric relaxation behavior in the diffuse dielectric anomaly were analyzed with the modified Debye equation. The dielectric relaxation strength was considered an important fitting variable in the modified Debye equation. The temperature-dependent behavior of the diffuse dielectric anomaly was successfully described by introduction of the exponential decay form for the relaxation strength inthe modified Debye equation.
Analysis of the Reservoir Length and its Effect on Electromigration Lifetime
Authors: Le H.A. , Ting Larry , Tso N.C. , Kim C-U.
Published: March 2008

This report studies the electromigration performance of W-plug via structures under the reservoir effect. The lifetime improvement factor M was observed to be a weak function of the stressing current and approximately equal to 2. A Simple model is included in the report to explain this observation. The model also predicts the most effective reservoir length for electromigration lifetime improvement.
Evaluation of Strain Rate During Equal-channel Angular Pressing
Authors: Kim Hyoung Seop
Published: March 2008

Strain rate is an important factor in plastic deformation because it determines the constitutive behavior of rate sensitive materials, e.g., dislocation density and flow stress evolution, deformation heat generation, etc. In the present study, the strain rate of workpiece materials during equal-channel angular pressing (ECAP) was evaluated by a geometric approach. The results were compared to those of the finite element analyses of a model ideally plastic material with various mesh sizes. The derived equation for strain rate is in reasonably good agreement with the results of the finite element method. The effects of the die geometry (a channel angle and a corner angle) were investigated. The strain rate during ECAP increases with punch speed and decreases with die channel angle, die corner angle, and the width of the workpiece. The relation obtained can be used for analytical calculations of the deformation, thermal, and microstructural evolution behavior of materials during ECAP. In particular, the size of the deforming zone and the effect of the finite element size are discussed.
Preparation and Characterization of Ester-derived BaFe12O19 Powder
Authors: Yu Hsuan-Fu , Huang Kao-Chao
Published: March 2008

Ultrafine BaFe12O19 powder with crystallite sizes less than 200 nm was prepared via a citric acid precursor method. Citric acid was added into an aqueous solution, containing nitrates of Ba2+ and Fe3+ in a stoichiometric ratio to form barium ferrite, to chelate metallic ions in the solution. The pH of aqueous solutions was adjusted with NH4OH. After ethylene glycol was added into the solution and the system temperature was raised, esterification and dehydratation led to the formation of solid ester precursor. The distribution and contents of metallic ions in the ester are affected by the [citric acid]/[metallic ions] molar ratio used and the pH of starting solutions. When the ester-precursor obtained at pH = 9 with [citric acid]/[metallic ions] = 1.5 was used, crystalline BaFe12O19 appeared at temperatures as low as 923 K, and pure barium ferrite was obtained at 1073 K. According to the experimental results obtained, the reaction mechanism involved in the pyrolysis of esters is proposed and discussed.
Chemical vapor deposition of cobalt using novel cobalt(I) precursors
Authors: Choi Hyungsoo , Park Sungho , Jang Ho G.
Published: March 2008

The deposition of cobalt thin films from cobalt hydride complexes, HCo[P(OR)3]4, where R = methyl, ethyl, i-propyl, and n-butyl, by a chemical vapor deposition method is reported. The new cobalt precursors deposited high-purity cobalt films at substrate temperatures as low as 300 °C without employing hydrogen. The deposited Co films showed smooth and dense surface morphology. The microstructure and growth rate of the deposited films depended on the reaction conditions such as substrate temperature and precursor feed. No gas phase reactions were observed during the deposition process.
Disordering behavior and helium diffusion in He+ irradiated 6H–SiC
Authors: Jiang W. , Weber W. J. , Wang C. M. , Zhang Y.
Published: March 2008

Single-crystal 6H–SiC wafers were irradiated at 300 K with 50 keV He+ ions to fluences ranging from 7.5 to 250 He+/nm2. Ion-channeling experiments with 2.0 MeV He+ Rutherford backscattering spectrometry were performed to determine the depth profile of Si disorder. The measured profiles are consistent with SRIM-97 simulations at and below 45 He+/nm2 but higher than the SRIM-97 prediction at both 100 and 150 He+/nm2. Cross-sectional transmission electron microscopy study indicated that the volume expansion of the material is not significant at intermediate damage levels. Results from elastic recoil detection analysis suggested that the implanted He atoms diffuse in a high-damage regime toward the surface.
Fabrication of TiNi shape memory alloy thin films by pulsed-laser deposition
Authors: Chen X. Y. , Lu Y. F. , Ren Z. M. , Zhu S.
Published: March 2008

Thin films of TiNi shape memory alloy have been prepared by pulsed-laser deposition at different substrate temperatures. The stoichiometry and crystallinity of the deposited films as functions of the substrate temperature were investigated. The deposition rate, surface morphology, crystallization temperature, and phase transformation behavior of the films were studied. It was found that both the substrate temperature and the laser fluence play important roles in the composition control and crystallization of the films. The deposition rate is of the order of 10−2 nm/pulse. The Ni content ranges from 46.7 to 52.0 at.%. The crystallization temperature of the amorphous Ti–51.5 at.% Ni films is around 460 °C. The activation energy of the crystallization process was determined by Kissinger's method to be 301 kJ/mol. The martensitic transformation temperature of the annealed Ti–51.5 at.% Ni film was determined to be −20.8 °C.
Growth of boron suboxide crystals in the B–B2O3 system at high pressure and high temperature
Authors: He Duanwei , Akaishi Minoru , Scott Brian L. , Zhao Yusheng
Published: March 2008

B6O crystal growth from the B–B2O3 system was investigated at 1700–2200 °C and 4.5–6.5 GPa by using two different sample assemblies. Single B6O crystals over 100 μm in size have been synthesized at 5.5 GPa and 2100 °C. This makes it possible to study the properties of this interesting material. The factors affecting the B6O crystal morphology, size, color, and growth process were discussed. The solubility of B6O in B2O3 flux was estimated at 5.5 GPa and different temperatures. On the basis of the experimental results, we suggest two methods to grow large B6O crystals.
Grain boundary faceting in YBa2Cu3O7–x bicrystal thin films on SrTiO3 substrates
Authors: Jin Qiang , Chan Siu-Wai
Published: March 2008

The structure of [001] tilt boundaries in YBa2Cu3O7–x (YBCO) thin films deposited on [001] tilt SrTiO3 (STO) bicrystal substrates has been characterized by transmission electron microscopy (TEM). These boundaries are (100)/(210), (310)/(510), (410)/(310), (510)/(210), (210)/(410), and (210)/(310), with corresponding misorientation angles of 26°, 29°, 32°, 37°, 40°, and 44°. It was found that the YBCO film boundaries were meandering along the relatively straight substrate boundaries. High-resolution lattice images indicated that the microscopic meandering of the film boundary essentially consisted of many straight segments of facets at the atomic scale. On the basis of the observed facets, three competing factors controlling the formation of facets are discussed. First, the boundary plane is defined by Miller indices (hk0) in both crystals with sufficiently small h, k (i.e., h, k ≤ 5) and sufficiently large effective interplanar spacing (i.e., deff > 0.06 nm). Second, the closure failure defined by the difference between the local misorientation from the design misorientation is small, i.e., less than 2°. Third, the deviation of a local facet plane is observed to be less than 30° from the design boundary plane. Higher values of deffs are observed to give tolerance to higher deviation angles.
Grain growth of precursor-derived nanocrystalline gallium nitride powder
Authors: Puchinger M. , Kisailus D. J. , Lange F. F. , Wagner T.
Published: March 2008

Nanocrystalline gallium nitride powder was synthesized from a gallium dimethylamide-derived polymeric precursor by pyrolysis in ammonia atmosphere to study the grain growth mechanisms in the temperature range 800–1150 °C. In particular, growth exponents and activation energies were determined. Up to 900 °C, grain growth was inhibited, whereas, above 1000 °C, evaporation–condensation was identified as the dominant material transport path.
Squeeze casting of SiCp/Al-alloy composites with various contents of reinforcements
Authors: Chen Liang-Guang , Shue Kung-Hsien , Chang Shou-Yi , Lin Su-Jien
Published: March 2008

Aluminum matrix composites reinforced with various contents and sizes of silicon carbide particles (SiCp) were fabricated by squeeze casting. A lower melting point AA A383 aluminum alloy (A383 Al) was squeezed into the higher melting point SiCp/pure aluminum (SiCp/pure Al) and SiCp/AA 6061 aluminum alloy (SiCp/6061 Al) preforms. The volume percents of the ceramic reinforcements were effectively lowered from traditional 50 to 8–25 vol% by the addition of pure Al and 6061 Al powders in the preforms. The SiC particles uniformly distributed within the matrices, and no pore was found in these composites. The growth of silicon precipitates in A383 Al alloys was limited by the addition of the aluminum alloy powders and SiC particles, and the tensile properties of the alloys were effectively enhanced by the refinement of the silicon precipitates. The tensile strengths and elongations of the SiCp/pure Al/A383 Al and SiCp/6061 Al/A383 Al composites were both better than those of the A383 Al alloy. The T6-treated 12-μm SiCp/6061 Al/A383 Al composite exhibited the highest tensile strength of 301 MPa.
Synthesis of phenyl-MSU-1 and bi-functionalized silica mesophases
Authors: Gong Yan Jun , Li Zhi Hong , Wu Dong , Sun Yu Han , Deng Feng , Luo Qing , Yue Yong
Published: March 2008

Template-directed co-condensation was used to synthesize phenyl-modified MSU-1 and bi-functionalized MSU-1 silica containing binary moieties of covalently linked phenyl along with methyl or ureidopropyl [H2NCONH(CH2)3]. The texture properties of these materials from x-ray diffraction, Fourier transform infrared, nuclear magnetic resonance, scanning electron microscopy, high-resolution transmission electron microscopy, N2adsorption, thermogravimetric analysis data, varied with the type of alkoxylsilane precursor and the amount of organosiloxane in the mixture. Small-angle x-ray scattering results, for the as-synthesized and surfactant-extracted organo-modified MSU-X, showed that the templates remaining in the mesostructures gave positive deviation from Porod's law while the incorporated organic groups led to a negative deviation, which formed an interfacial layer between the pore and silica matrix.
Preparation of alumina ceramics from aqueous suspensions employing the hydrolysis of aluminum nitride
Authors: Novak S. , Kosmac T.
Published: March 2008

This paper summarizes the effects of selected processing parameters on the behavior of aqueous alumina suspensions during hydrolysis-assisted solidification and on the properties of the green and sintered parts prepared by this technique. Measurements of the changes in viscosity, the pH, and the impedance of aqueous suspensions with time were performed to evaluate the process. Using impedance spectroscopy, the effects of the addition of AlN, the solids content in the ceramic suspension, and the effect of the solidification temperature on the progress of solidification were followed. It was demonstrated that the solidification temperature significantly affects not only the solidification rate but also the properties of the green and sintered parts. A transmission electron microscopy analysis of dry green parts revealed that the host ceramic particles are bound by a predominantly amorphous AlOOH phase, which results in a high strength for the green parts.
Effect of substrate pregrowth treatments on characteristics of low-temperature diamondlike carbon films prepared by very-high-frequency chemical vapor deposition
Authors: Waqar Zafar , Titkov Alexander Nikolaivech , Andronov Alexander Nikolaivech , Kosarev Andrey , Makarenko Igor
Published: March 2008

Diamondlike carbon (DLC) films were grown on Si and ceramic substrates by very-high-frequency chemical vapor deposition at temperature of approximately 250 °C. Thin metal coatings from Ti, Ni, Pt, and Cu were deposited on the substrates before DLC film deposition. The impact of the pregrowth treatments of the substrates on surface morphology and emission properties of the grown DLC films was studied. The films deposited on ceramic substrates pretreated by Ti, Ni, and Pt coatings, with grainlike structures, demonstrated good emission currents and low threshold voltages among the deposited DLC films.
Selective DNA attachment of micro- and nanoscale particles to substrates
Authors: Hartmann D. M. , Heller M. , Esener S. C. , Schwartz D. , Tu G.
Published: March 2008

Materials formed from micro- and nanoscale particles are of interest because they often exhibit novel optical, electrical, magnetic, chemical, or mechanical properties. In this work, a means of constructing particulate materials using DNA strands to selectively attach micro- and nanoparticles to substrates was demonstrated. Unlike previous schemes, the DNA was anchored covalently to the particles and substrates, rather than through protein intermediaries. Highly reproducible selective attachment of 0.11–0.87 mm-diameter particles was achieved, with selective:nonselective binding ratios >20:1. Calculations showed that at most 350 and 4200 DNA strands were involved in the binding of the small and large particles, respectively. Experiments showed that the DNA was bent at an angle, relative to the surfaces of their solid supports.
Transmission electron microscopy study of Ge implanted into SiC
Authors: Gorelik T. , Kaiser U. , Schubert Ch. , Wesch W. , Glatzel U.
Published: March 2008

Hexagonal 6H– and 4H–SiC wafers were implanted with (1−1.5) × 1016 cm−2 germanium ions at room temperature and at 700 °C with subsequent annealing between 1000 and 1600 °C. Structural changes in the SiC matrix were studied in detail by means of transmission electron microscopy (TEM). After implantation at room temperature the hexagonal SiC matrix becomes amorphous and, after annealing, recrystallizes into cubic SiC. The latter process was accompanied by the creation of voids and cracks. In case of high-temperature (700 °C) implantation, where amorphization was avoided, no polytype change in as-implanted and annealed SiC wafers was observed. In annealed samples nanocrystalline precipitates with high Ge content were observed in high-resolution TEM images.
High Critical Current Density of a MgB2 Bulk Superconductor High-pressure Synthesized Directly from the Elements
Authors: Jin C-Q. , Li S-C. , Zhu J-L. , Li F-Y. , Liu Z-X. , Yu R-C.
Published: March 2008

We report the property studies of a MgB2 superconductor with high critical current density. The MgB2 superconductor was readily fabricated through a direct high-pressure synthesis of the respective elements. The obtained high-density MgB2 undergoes a sharp superconducting transition at 39 K. The bulk critical current density (Jc) of the sample was calculated on the basis of Bean's critical state model, and rather high critical current densities over a wide temperature range were obtained in comparison with the ambient prepared samples. The results highlight that high-pressure sintering would be a promising way to produce and search for this kind of intermetallic boride and the related superconductors.
Simultaneous Synthesis and Consolidation of Nanostructured MoSi2
Authors: Gras Christophe , Bernard Frédéric , Charlot Frédéric , Gaffet Eric , Munir Zuhair A.
Published: March 2008

A new process combining electric field activation and the imposition of pressure from mechanically activated powder mixtures is demonstrated as a means to simultaneously synthesize and densify nano-MoSi2 in one step. Nanophase reactants (Mo + 2Si) produced by mechanical activation are reacted by field activation with the simultaneous application of a uniaxial pressure. Mo + 2Si powders were comilled in a specially designed planetary mill to obtain nanometric reactants but to avoid formation of any product phases. These were then subjected to high alternating currents (1600 A) and pressures of 106 MPa. Under these conditions, a reaction is initiated and completed within a short period of time (3–6 min). The relative density of the product ranged from 82 to 93%. The crystallite size of the MoSi2 compound was determined by x-ray diffraction line-broadening analysis using the Langford method. The size ranged from 58 to 75 nm.
Nitrogen Effects on Crystallization Kinetics of Amorphous TiOxNy Thin Films
Authors: Hukari Kyle , Dannenberg Rand , Stach E. A.
Published: March 2008

The crystallization behavior of amorphous TiOxNy (x ≫ y) thin films was investigated by in situ transmission electron microscopy. The Johnson–Mehl–Avrami–Kozolog (JMAK) theory was used to determine the Avrami exponent, activation energy, and the phase velocity pre-exponent. Addition of nitrogen inhibited diffusion, increasing the nucleation temperature, while decreasing the growth activation energy. Kinetic variables extracted from individual crystallites were compared to JMAK analysis of the fraction transformed, and a change of 6% in the activation energy led to agreement between the methods. From diffraction patterns and index of refraction the crystallized phase was found to be predominantly anatase.
Growth of KTiOPO4 Films on KTi1-xGexOPO4 Substrates by Liquid-phase Epitaxy
Authors: Solé R. , Nikolov V. , Vilalta A. , Carvajal J. J. , Massons J. , Gavaldà Jna. , Aguiló M. , Díaz F.
Published: March 2008

The epitaxial growth of KTiOPO4 (KTP) films on different natural faces of KTi1-xGexOPO4 substrates was studied. The growth on faces (100) and (201) is generally of high quality, irrespective of the growth time or concentration of germanium in the substrates. On the other hand, the epitaxial growth on the face (101) is always of poor quality, and the defects are pyramids, even when the germanium content in the substrate is low and the growth time is short. The films on faces (011) and (110) generally have small hillocks as defects and for high concentrations of Ge in the crystals some cracks begin to appear. The film thickness, depending on the growth time and the face considered was measured by scanning electron microscopy (SEM) using backscattered electrons. The diffusion of germanium from the substrate to the film is very low, as demonstrated by electron probe microanalysis measurements and SEM observations. The difference in the refractive indices ny and nz of KTP and KTi0.92Ge0.08OPO4 are on the order of 0.01, which could be enough to produce wave guides. Finally, it was observed that the second harmonic generation response of KTP substituted with Ge decreases as the Ge content in the crystal increases.
Iron and Iron-oxide on Silica Nanocomposites Prepared by the Sol-gel Method
Authors: Ennas G. , Casula M. F. , Piccaluga G. , Solinas S. , Morales M. P. , Serna C. J.
Published: March 2008

γ–Fe2O3/SiO2 and Fe/SiO2 nanocomposites, with a Fe/Si molar ratio of 0.25, were prepared by the sol-gel method starting from ethanolic solutions of tetraethoxysilane and iron (III) nitrate. After gelation the xerogels were oxidated or reduced. Samples were investigated by transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, and thermogravimetry. Magnetic properties of the samples were investigated at room temperature (RT) and at 77 K. Nanometric particles supported in the silica matrix were obtained in all cases. Bigger particles (10 nm) were obtained in the case of Fe/SiO2 nanocomposites with respect to the γ–Fe2O3/SiO2 samples (5–8 nm). A slight effect of sol dilution on particle size was observed only in the case of γ–Fe2O3/SiO2 nanocomposites. A superparamagnetic behavior was shown at RT only by γ–Fe2O3/SiO2 nanocomposites. Iron-based composites exhibited coercivity values higher than 700 Oe at RT.
Multilayered Structures of SrNb0.1Ti0.9O3/La0.8Sr0.2MnO3/SrTiO3 Prepared by Laser Molecular Beam Epitaxy
Authors: Ma X. L. , Lu H. B. , Chen F. , Chen Z. H. , Yang G. Z.
Published: March 2008

Multilayer oxides of SrNb0.1Ti0.9O3/La0.8Sr0.2MnO3/SrTiO3 have been grown by computer-controlled laser molecular beam epitaxy and characterized by transmission electron microscopy. Electron microdiffractions and high-resolution imaging reveal that the as-prepared thin film of La0.8Sr0.2MnO3 with thickness of 200 nm is epitaxially grown on the SrTiO3(001) substrate and the SrNb0.1Ti0.9O3 with thickness of 250 nm epitaxially on the as-received La0.8Sr0.2MnO3 film. The microstructures in the La0.8Sr0.2MnO3 film are clarified in terms of the oriented microdomains. In contrast, microstructures in SNTO are featured by the formation of superstructures due to charge ordering. Crystallographic relationships of these domains are discussed on the basis of an orthorhombic cell and rationalized by theoretical calculations based on a geometrical model.
Effect of Barium Titanate Seed Particles on the Sintering and Lattice Parameters in PbMg1/3Nb2/3O3 Ceramics
Authors: Spagnol P. D. , Zaghete M. A. , Paiva-Santos C. O. , Andrade A. V. C. , Cavalheiro A. A. , Tebcherani S. M. , Varela J. A.
Published: March 2008

PbMg1/3Nb2/3O3 (PMN) powder was prepared by citrate organic solution, and barium titanate (BT) seed particles were added to encourage the perovskite phase formation. Sintering was followed using the constant heating rate mode of a dilatometer, and it was observed that the seed concentration affected the PMN shrinkage rate and crystal structure. The study of the lattice parameters of the samples after the sintering process indicates that the diffusion of the titanium and of the barium inside perovskite and pyrochlore PMN phases occurs. Moreover, this substitution provoked a decrease of the lattice parameters as showed by the Rietveld refinement.
Formation of Bulk Glassy Fe75–x–yCrxMoyC15B10 Alloys and Their Corrosion Behavior
Authors: Pang Shujie , Zhang Tao , Asami Katsuhiko , Inoue Akihisa
Published: March 2008

Formation of bulk Fe-based glassy alloys with high corrosion resistance was succeeded in the Fe75–x–yCrxMoyC15B10 alloy system. A large temperature interval of supercooled liquid region (ΔTx) of 40–90 K was obtained over a wide composition range for the Fe75?x–yCrxMoyC15B10 alloys. The Fe75–x–yCrxMoyC15B10 alloys were prepared in a bulk glassy form with diameters of 1.0–2.5 mm by copper mold casting. The bulk glassy Fe75–x–yCrxMoyC15B10 alloys exhibited high corrosion resistance in 1 N HCl solution. The glassy alloys containing Cr were spontaneously passivated with a wide passive region before the transpassive dissolution of Cr. The passive current density decreased significantly with an increase of alloying Cr content, indicating that the addition of Cr was effective on enhancing the corrosion resistance. Excess addition of Mo for replacing Fe in the present alloys was detrimental for the corrosion resistance.
Improved magnetic properties of self-assembled epitaxial nickel nanocrystallites in thin-film ceramic matrix
Authors: Kumar D. , Zhou H. , Nath T. K. , Kvit Alex V , Narayan J. , Craciun V. , Singh Rajiv K.
Published: March 2008

Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles was investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in the case of the TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in the Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization–field (M–H) hysteretic behavior, of the Ni–TiN sample (approximately 190 K) is significantly higher than that of Ni–Al2O3 sample (approximately 30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles in amorphous alumina matrix. The high values of TB and Hc of Ni–TiN samples with respect to TB of N–A12O3 samples are believed to be associated with preferred alignment of nanocrystallites.
Microstructure and adhesion properties of Sn–0.7Cu/Cu solder joints
Authors: Bae Kyoo-Sik , Kim Si-Jung
Published: March 2008

The microstructure and adhesion strength of the Sn–0.7Cu/Cu solder joints were examined. The acicular η(Cu6Sn5)-phase was formed inside the solder and at the solder/Cu interface, mostly in the direction normal to the interface. Compared to the Sn–3.5Ag alloy, the Sn–0.7Cu solder showed comparable wettability, but lower microhardness and joint strength. After aging, the acicular η-phase grew into a round and scallop-shaped morphology, thin є(Cu3Sn)-phase evolved just above the Cu substrate, and the joint strength decreased linearly with aging time.
Solid-solution directionally solidified eutectic oxide composites: Part I. Eutectic growth and characterization
Authors: Brewer L. N. , Dravid V. P. , Dhalenne G. , Velázquez M.
Published: March 2008

In this work, the solid solution series directionally solidified eutectic, Co1−xNixO/ZrO2(CaO), 0 ≤ x ≤ 1, was examined as a possible model system for interfacial fracture studies. These materials were grown by the optical floating zone method in an image furnace under controlled atmospheres to prevent the formation of Co3O4. For all compositions, lamellar microstructures were produced. The interface plane orientation relationship {111} Co1−xNixO║{100} ZrO2(CaO) was maintained throughout the solid solution series. The phase compositions were close to nominal values with some solubility of CoO in ZrO2(CaO). Preliminary indentation measurements demonstrate the onset of interfacial delamination for compositions of x <0.2.
Solid solution directionally solidified eutectic oxide composites: Part II. Co1-xNixO single-crystal growth and characterization
Authors: Brewer L. N. , Dravid V. P. , Velázquez M. , Revcolevschi A.
Published: March 2008

The growth and structure of the Co1−xNixO series of single crystals with 0 ≤ x ≤ 1 were investigated with the goal of achieving a single-phase crystal over several centimeters of bulk growth. The single crystals were grown via the floating zone method controlling the partial pressure of oxygen to prevent secondary phase precipitation. The resulting crystals were single phase for all compositions. CoO was a single-domain crystal but contained microvoids. The lattice parameters followed a rule-of-mixtures trend, but the coefficient of thermal expansion exhibited a maximum in the middle of the solid solution, which was attributed to enhanced vacancy formation.
Different routes to the formation of C54 TiSi2 in the presence of surface and interface molybdenum: A transmission electron microscopy study
Authors: Zhang Z-B. , Zhang S-L. , Zhu D-Z. , Xu H-J. , Chen Y.
Published: March 2008

Direct evidence revealing fundamental differences in sequence of phase formation during the growth of TiSi2 in the presence of an ultrathin surface or interface Mo layer is presented. Results of cross-sectional transmission electron microscopy showed that when the Mo layer was present at the interface between Ti films and Si substrates, C40 (Mo,Ti)Si2 formed at the interface, and Ti5Si3 grew on top after annealing at 550 °C. Additionally, both C54 and C40 TiSi2 were found in the close vicinity of the C40 (Mo,Ti)Si2 grains. No C49 grains were detected. Raising the annealing temperature to 600 °C led to the formation of C54 TiSi2 at the expense of Ti5Si3, and the interfacial C40 (Mo,Ti)Si2 also began to transform into C54 (Mo,Ti)Si2 at 600 °C. When the Mo was deposited on top of Ti, the silicide film was almost solely composed of C49 TiSi2 at 600 °C. However, a small amount of (Mo,Ti)5Si3 was still present in the vicinity of the sample surface. Upon annealing at 650 °C, only the C54 phase was found throughout the entire TiSi2 layer with a surface (Mo,Ti)Si2 on top of TiSi2. Hence, it was unambiguously shown that in the presence of surface versus interface Mo, different routes were taken to the formation of C54 TiSi2.
Room-temperature oxidation of ultrathin TiB2 films
Authors: Huang Feng , Liu W. J. , Sullivan J. F. , Barnard J. A. , Weaver M. L.
Published: March 2008

Titanium diboride has been claimed as a very promising candidate material for protective applications in the magnetic recording. Its oxidation resistance at room temperature is a critical criterion in assessing this application potential. In this paper, the oxidation characteristics of ultrathin TiB2 thin films, such as overcoat erosion and oxide thickness, are investigated via a combination of x-ray reflectivity, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy. It was found that a <2-h exposure to air at room temperature led to the formation of approximately 15-Å-thick, well-defined oxides at the expense of an approximately 9-Å erosion of the TiB2 overcoats, coupled with the existence of a sharp oxide/TiB2 interface. XPS studies confirmed the existence of the oxides. Considering the decreasing allowable thickness for such protective overcoats, oxidation and the resultant thickness gain negate such a potential of ultrathin TiB2 films. The results in our current report provide a new perspective on its potential as protective overcoats in magnetic recording.