bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Improvement in the Electrical Properties of Lead-zinc-niobate–based Ceramics by Thermal Treatments
Authors: Fan Huiqing , Park Gun-Tae , Choi Jong-Jin , Ryu Jungho , Kim Hyoun-Ee
Published: March 2008

The piezoelectric and dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN)-based ceramics were investigated. The perovskite structure of PZN ceramics was stabilized by the addition of Pb(Zn0.47Ti0.53)O3 (PZT). The highest piezoelectric properties were observed for the composition of 0.5PZN–0.5PZT, which lies on the two-phase zone of morphotropic phase boundary. For further improvements in electric properties, the specimens were thermally treated in a flowing O2 atmosphere at temperatures ranging from 860 to 1030 °C. The thermal treatment eliminated the PbO-rich amorphous intergranular layer by lead evaporation. As a result of this improvement in structure, the dielectric constant (ε′), the piezoelectric coefficient (d33), and the electromechanical coupling factor (kp), were enhanced markedly after thermal annealing at 960 °C for 8 h in an O2 atmosphere.
Atomic-scale simulations of multiple ion–solid interactions and structural evolution in silicon carbide
Authors: Gao F. , Weber W. J.
Published: March 2008

Molecular dynamics (MD) were employed in atomic-level simulations of fundamental damage production processes due to multiple ion–solid collision events in cubic SiC. Isolated collision cascades produce single interstitials, vacancies, antisite defects, and small defect clusters. As the number of cascades (or equivalent dose) increases, the concentration of defects increases, and the collision cascades begin to overlap. The coalescence of defects and clusters with increasing dose is an important mechanism leading to amorphization in SiC and is consistent with the homogeneous amorphization process observed experimentally in SiC. The driving force for the crystalline– amorphous (c–a) transition is the accumulation of both interstitials and antisite defects. High-resolution transmission electron microscopy (HRTEM) images of the defect accumulation process and loss of long-range order in the MD simulation cell are consistent with experimental HRTEM images and disorder measurements. Thus, the MD simulations provide atomic-level insights into the interpretation of experimentally observed features associated with multiple ion–solid collision events in SiC.
Dielectric properties of epitaxial KNbO3 ferroelectric thin films
Authors: Chattopadhyay Soma , Nichols B. M. , Hwang Jin-Ha , Mason T. O. , Wessels B. W.
Published: March 2008

The dielectric response of KNbO3 epitaxial ferroelectric thin films was measured as a function of bias, frequency, and temperature. Thin films with a thickness of 80 to 350 nm were deposited on spinel substrates by low-pressure metalorganic chemical vapor deposition. Bias dependence measurements showed hysteresis in the dielectric response. The dielectric constant decreased with bias, and the tunability was calculated to be between 35% and 42% for an applied field of 7 MV/cm. The frequency dependence of the dielectric constant followed a power law. A pronounced thickness effect was observed in the dielectric response, especially at the Curie temperature. With decreasing thickness, the dielectric constant and the loss tangent decreased. A diffuse ferroelectric phase transition was observed for films with a thickness less than 350 nm.
Porous reaction-sintered AlN tapes for high-performance microelectronics application
Authors: Boey F. Y. C. , Tok A. I. Y. , Clegg W. J.
Published: March 2008

A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method involved polymer microspherical powders used as a sacrificial mold to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 °C for 12 h to create porous AlN tapes. This work builds upon a previously developed novel reaction sintering process that densified and converted Al2O3-rich tapes (Al2O3–20 wt% AlN–5 wt% Y2O3) to AlN tapes at a relatively low sintering temperature of 1680 °C. The sintering behavior of the porous tapes was investigated, and the effects of the microsphere particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constants of the AlN tapes were reduced to about 6.8 to 7.7 while thermal conductivity values were reasonable at about 46 to 60 W/mK. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of 4.4 × 10−6 to 4.8 × 10−6/°C, showing good CTE compatibility with silicon at 4.0 × 10−6/°C. The added porosity did not significantly affect the CTE values.
Formation of in-situ reinforced microstructure in α–sialon ceramics I: Stoichiometric oxygen-rich compositions
Authors: Shen Zhijian , Peng Hong , Nygren Mats
Published: March 2008

The abnormal grain growth in α–sialon ceramics was investigated. The preparations had stoichiometric compositions on the oxygen-rich phase boundary, and they were stabilized by Y, Nd, Sm, Dy, and Yb, respectively. Specimens were prepared from α–Si3N4 as precursor powder by applying conventional hot pressing and a novel rapid consolidation process, namely spark plasma sintering (SPS). Single-phase α–sialon ceramics with in situ reinforced bimodal microstructure, i.e., large elongated grains embedded in a matrix consisting of small equiaxed grains, were obtained above 1750 °C in all systems compacted by SPS and above 1800 °C in systems stabilized by Nd and Sm but not Dy, Y, or Yb by a two-step hot-pressing procedure. It was observed that the formation of abnormally grown α–sialon grains was strongly temperature-dependent, indicating that it was encouraged by the formation of a transient liquid phase that stimulated the dissolution of any remaining nitride precursors and early formed small α–sialon grains and sequentially facilitated supersaturation by the α–sialon constituents. The presence of elongated grains improves fracture resistance in the obtained materials.
Effects of an interposed Cu layer on the enhanced thermal stability of C49 TiSi2
Authors: Wang Ming-Jun , Lin Wen-Tai , Pan F. M.
Published: March 2008

The effects of an interposed Cu layer and a surface Cu layer on the C49–C54 TiSi2 transformation temperature were studied. For the Ti/Cu/(100)Si samples the interposed Cu layer significantly enhanced the thermal stability of C49 TiSi2. The temperature for complete C49–C54 TiSi2 transformation was raised from 710 to 735 to 750 °C with the thickness of the interposed Cu layer increasing from 0 to 1.5 to 3.5 nm, correspondingly. Cu was insoluble in C54 TiSi2. For the Cu/Ti/(100)Si samples, the surface Cu layer did not at all enhance the thermal stability of the C49 phase. In the present study, the enhanced thermal stability of C49 TiCuxSi2–x can be attributed to its reduced electron/atom ratio and larger grain size relative to those of C49 TiSi2.
Coble-creep response and variability of grain-boundary properties
Authors: Tong W. S. , Rickman J. M. , Chan H. M. , Harmer M. P.
Published: March 2008

A microstructural model of steady-state creep that couples grain-boundary transport, micromechanics, and grain sliding is employed to investigate the grain-boundary diffusional creep response of an idealized microstructure with variable boundary diffusivities. Both numerical and analytical methods were used to determine the stress state and, in some cases, the strain rate associated with an applied uniaxial, tensile stress. Various types of boundaries are considered, and the implications of our results for more general microstructures are discussed.
Interfaces between solution-derived LiMn2O4 thin films and MgO and Au/MgO substrates
Authors: Ikuhara Yumi H. , Ma Xiuliang , Iwamoto Yuji , Ikuhara Yuichi , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

Spinel LiMn2O4 thin films have been prepared on MgO(110) and Au/MgO(110) substrates by a chemical solution deposition method. The interfaces between film and substrate were characterized by means of high-resolution transmission electron microscopy (HREM) as well as x-ray diffraction. Cross-sectional HREM observation revealed that LiMn2O4 films grew epitaxially on the MgO(110) and Au/MgO(110) substrates. In the LiMn2O4/MgO system, misfit dislocations formed to accommodate the lattice strain at the LiMn2O4/MgO interface. In the LiMn2O4/Au/MgO system, Au grew epitaxially on the MgO substrate with its surface facetted along {111} planes, probably because the surface energy of this plane is relatively low. The formation of these facets is considered to have a favorable effect on the growth of {111} planes of LiMn2O4 when deposited on the Au film.
Effects of precursor additives on the stability of plasma enhanced chemical vapor deposited a-GeC(O):H films
Authors: Grill A. , Guilley S. , Patel V. , Babich K.
Published: March 2008

Germanium- and carbon-based films were deposited by plasma-enhanced chemical vapor deposition from tetramethylgermane (TMGe) with additions of oxygen, hydrogen, or argon. The index of refraction, extinction coefficient, and optical gap and Fourier transform infrared spectra of the films were measured as well as their stability in regular ambiance. It was found that the films deposited from pure TMGe were stable in time only if deposited at a negative bias above −250 V direct current. Films deposited at a bias of −150 V direct current could be stabilized by significant additions of oxygen to the plasma and complete stabilization was achieved at O2/TMGe ratios larger than 3 in the gas feed when GeOx films containing small amounts of C and H were obtained. Additions of hydrogen or argon to TMGe had only slight effects in improving the stability off the films.
Kinetics of PbTiO3 perovskite phase formation via an interfacial reaction
Authors: Sung Yun-Mo , Kwak Woo-Chul , Kim Sungtae
Published: March 2008

The kinetics of the formation of PbTiO3 at the PbO/TiO2 interface has been analyzed. The flux of Pb2+ and O2− ions through the PbTiO3 layer was used to derive the kinetics equation for the formation of the PbTiO3 phase. On the basis of the parabolic growth kinetics of the PbTiO3 interlayer, the reaction rate constant (k) for PbTiO3 formation was determined as a function of the average diffusion coefficient of the Pb2+ ions (DPb2+). By employment of the data from diffusion couple experiments and the free energy values for the formation of the PbTiO3 phase () into the present kinetics equation, DPb2+ in the PbTiO3 interlayer was calculated with respect to the corresponding temperature. The activation energy for diffusion (Q) and the diffusion constant (D0) of Pb2+ ions in the PbTiO3 layer could be evaluated from the Arrhenius plot of DPb2+.
Nanomechanical properties of energetically treated polyethylene surfaces
Authors: Klapperich C. , Pruitt L. , Komvopoulos K.
Published: March 2008

The effects of energetic treatments, crosslinking, and plasma modification on the surface mechanical properties and deformation behavior of ultrahigh molecular weight polyethylene (UHMWPE) were examined in light of nanoindentation experiments performed with a surface force microscope. Samples of UHMWPE were subjected to relatively high-dose gamma irradiation, oxygen ion implantation, and argon ion beam treatment. A range of crosslinking was achieved by varying the radiation dose. In addition, low-temperature plasma treatment with hexamethyldisiloxane/O2 and C3F6 was investigated for comparison. The surface mechanical properties of the treated UHMWPE samples are compared with those of untreated UHMWPE samples used as controls. Surface adhesion measurements obtained from the nanoindentation material responses are also discussed in terms of important treatment parameters. Results demonstrate that high-dose oxygen ion implantation, argon ion beam treatment, and low-temperature C3F6 plasma modification are effective treatments for enhancing the surface mechanical properties of UHMWPE.
Effects of powder bed conditions on the liquid-phase sintering of Si3N4
Authors: Lee Sea-Hoon , Rixecker Georg , Aldinger Fritz , Choi Sung-Churl , Auh Keun-Ho
Published: March 2008

The effects of the active and passive protection mechanisms of powder beds on the sintering of Si3N4 were investigated. Shrinkage, density, and coloring behavior of sintered samples were analyzed using different compositions and packing conditions of powder beds based on BN and Si3N4 with different additives. Y2O3 additive in the powder bed influences the weight change and phase formation behavior of the samples, although it has a very low vapor pressure at the sintering temperature. When MgO/Y2O3 was used as sintering additives, the packing density and thickness of the powder bed had a much stronger effect than in the case of Al2O3/Y2O3. For the optimization of the powder bed conditions, the vapor pressure and chemical stability of sintering additives at the sintering temperature has to be considered.
Indentation load–displacement curve, plastic deformation, and energy
Authors: Malzbender J. , de With G.
Published: March 2008

Various methods to access indentation data are considered on the basis of the load P–displacement h curve, its derivative, or its integral. This paper discusses and extends the various analytical models to estimate the indentation P–h curve, the slope, and the dissipated energy to aid the development of a concise methodology to analyze indentation data. Special consideration is given to the effect of pile-up and sink-in. Relationships for sharp and spherical indenters are presented and in addition for sharp indenters with a rounded tip. An overview over analytic expressions for the P–h curve is given and compared to finite element simulations and experimental data. An expression derived for the representative strain at the onset of yield under sharp and spherical indenters compares well with literature results. The effect of a rounded tip on the yielding under a sharp indenter is discussed. The ratio of loading to unloading slope and the ratio of the plastically dissipated energy to the total energy is related to hardness and elastic modulus. In combination these ratios can be used to determine the strain-hardening coefficient.
Growth and Characterization of Series Nd:GdxLa1-xVO4 (x = 0.80, 0.60, 0.45) Crystals
Authors: Zhang Huaijin , Wang Changqing , Zhu Li , Liu Xuesong , Zhang Guanghui , Yu Wentao , Meng Xianlin , Chow Y. T.
Published: March 2008

In this paper, series crystals Nd:Gd0.8La0.2VO4, Nd:Gd0.6La0.4VO4, and Nd:Gd0.45La0.55VO4 were grown by the Czochralski method. The structure and lattice constants of the series crystals were measured. The morphology of Nd:Gd0.8La0.2VO4 is discussed, and it is composed of {100} and {101} simple forms. The thermal expansion and specific heat of the Nd:Gd0.8La0.2VO4 crystal were also measured. The absorption and emission spectra of the Nd:Gd0.8La0.2VO4 and Nd:Gd0.6La0.4VO4 crystals were measured at room temperature. The laser outputs at 1.06 and 1.34 μm were determined when a crystal sample of Nd:Gd0.8La0.2VO4 was pumped by a laser diode at 808 nm, and the visible green and red laser outputs of the intracavity frequency double at 0.53 and 0.67 μm were determined when nonlinear KTiOPO4 and LiB3O5 crystals were used.
Electrical Conductivity of Open-cell Metal Foams
Authors: Dharmasena K. P. , Wadley H. N. G.
Published: March 2008

Cellular metal foams are of interest because of the ability to tailor their mechanical, thermal, acoustic, and electrical properties by varying the relative density and cell morphology. Here, a tetrakaidecahedral unit-cell approach is used to represent an open-cell aluminum foam and a simplified electrical resistor network derived to model low frequency current flow through the foam. The analysis indicates that for the range of relative densities studied (4–12%), the conductivity of tetrakaidecahedral foams has a linear dependence upon relative density. The distribution of metal in the cell ligaments was found to significantly affect the conductivity. Increasing the fraction of metal at the ends of the ligaments resulted in a decrease in electrical conductivity at a fixed relative density. Low frequency electrical conductivity measurements of an open-cell aluminum foam (ERG Duocel) confirmed the linear dependence upon density, but the slope was smaller than that predicted by the unit-cell model. The difference between the model and experiment was found to be the result of the presence of a distribution of cell sizes and types in real samples. This effect is due to the varying number of ligaments, ligament lengths, and the cross-sectional areas available for current conduction across the cellular structure.
Thermal Decomposition Kinetics of Functionalized Polynorbornene
Authors: Wedlake Michael D. , Kohl Paul A.
Published: March 2008

The mechanism and kinetic parameters for the thermal decomposition of four functionalized addition-polymerized polynorbornenes were studied by dynamic and isothermal thermogravimetric analyses and by mass spectrometry. The dynamic and isothermal thermogravimetric analyses showed a first-order degradation reaction mechanism with an activation energy of 229.6 ± 12.5 kJ/mol. Based on the polymer structure, reference mass spectra for related molecules, and a cross-comparison of the mass spectra, the backbone, free-radical scission mechanism was found to occur by cleavage of the linkages between bicyclic rings and the production of volatile monomer and oligomers. The degradation of polynorbornene occurred via a depropagation and transfer reaction process. Initially, the depropagation pathway was preferred, but with increasing conversion, intra- and intermolecular hydrogen transfer reactions dominated.
Icosahedral Phase Formation Domain in Al–Cu–Fe System by Mechanical Alloying
Authors: Barua P. , Murty B. S. , Mathur B. K. , Srinivas V.
Published: March 2008

A systematic composition dependence study on icosahedral phase (i-phase) formation in the Al–Cu–Fe system has been carried out. Structural evolution during mechanical alloying and on subsequent heat treatment has been investigated by x-ray diffraction and transmission electron microscopy. The i-phase is observed to evolve from the reaction between the Al2Cu and b phases. The influence of the Cu to Fe ratio (RCuFe), Al to transition metal ratio (RAlTM), and the electron to atom ratio (e/a) on the volume fraction of the i-phase has been studied. The analysis of the present results and those published earlier indicates that quasicrystal-forming ability correlates better with the RAlTM and e/a ratios. The volume fraction of the i-phase is maximum when the RAlTM ˜ 2.3 and e/a ratio ˜ 2.0. Formation of the i-phase in Al65Cu25Fe10 by mechanical alloying is reported for the first time.
Effects of Creep and Thermal Drift on Modulus Measurement Using Depth-sensing Indentation
Authors: Feng G. , Ngan A. H. W.
Published: March 2008

In modulus measurement by depth-sensing indentation, previous considerations assume elastic recovery to be the sole process during unloading, but in reality creep and thermal drift may also occur, causing serious errors in the measured modulus. In this work, the problem of indentation on a linear viscoelastic half-space is solved using the correspondence principle between elasticity and linear viscoelasticity. The correction term due to creep in the apparent contact compliance is found to be equal to the ratio of the indenter displacement rate at the end of the load hold to the unloading rate. A condition for nullifying the effect of thermal drift on modulus measurement is also proposed. With this condition satisfied, the effect of thermal drift on the calculated modulus is negligible irrespective of the magnitude of the drift rate.
Subcritical Crack Growth in Single-crystal Silicon Using Micromachined Specimens
Authors: Fitzgerald A. M. , Iyer R. S. , Dauskardt R.H. , Kenny T. W.
Published: March 2008

A micromachined specimen with a test section only 150-μm thick was developed for investigating subcritical crack growth in silicon. Crack growth rates in the range 10−4–10−10m/s were measured as a function of applied stress intensity (v–Kcurves) during tests in humid air and dry nitrogen lasting up to 24 h. The fracture toughness,KIcof {110} silicon was also measured at 1.15 ± 0.08 MPa m1/2. While some evidence MPa-m1/2of subcritical crack growth appeared to occur in the region 0.9KIc 0.98KIc, the extremely high crack growth exponent (n100) and the high ratio of the apparent stress corrosion threshold,KIscc, to the fracture toughness,KIscc/KIc> 0.9, suggests that no clear evidence exists for a stress corrosion process in silicon exposed to humid air.
Formation of Zr70Ni23Ti7 Glassy Alloy and Phase Transformation upon Annealing
Authors: Wang Limin , Li Chunfei , Ma Liqun , Inoue Akihisa
Published: March 2008

Zr70Ni23Ti7 alloy contains a single amorphous phase when it is melt-spun at a wheel surface velocity over 20 m/s. The crystallization of these amorphous ribbons takes place through two exothermic reactions and shows a significant supercooled liquid region of about 30 K, indicating that the Zr70Ni23Ti7 alloy has a good glass-forming ability. The crystallization products of the first exothermic reaction for the ribbon prepared at a wheel surface velocity of 40 m/s are mainly an icosahedral quasicrystalline phase (I-phase) and some Zr2Ni phases. Further heating to a higher temperature will lead to the transformation of the metastable I-phase to Zr2Ni. Some icosahedral atomic clusters with a structure similar to those in face-centered-cubic Zr2Ni may exist in the alloy after rapid quenching, and most of them may act as nuclei of I-phase. The formation of I-phase in this alloy without any noble metals may be due to the proper atomic ratios in the system.
Biomimetic apatite formation on poly(lactic acid) composites containing calcium carbonates
Authors: Maeda Hirotaka , Kasuga Toshihiro , Nogami Masayuki , Hibino Yoshitaka , Hata Ken-Ichiro , Ueda Minoru , Ota Yoshio
Published: March 2008

Poly(lactic acid) composites containing a mixture of calcium carbonates (vaterite, aragonite, and calcite) were prepared by a carbonation process in methanol. Soaking of the composites for 3 h in simulated body fluid (SBF) at 37 °C resulted in the deposition of bonelike apatite particles on the composite surface. After soaking the composites, vaterite phase in the composites was forward to dissolve rapidly, resulting in increase the supersaturation of the apatite in SBF. 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca2+ ion and the COO- group, which induces the apatite nucleation. These results may elucidate the mechanism of means to reduce the induction period for apatite formation.
Hardness of cubic silicon nitride
Authors: Tanakaa I. , Oba F. , Sekine T. , Ito E. , Kubo A. , Tatsumi K. , Adachi H. , Yamamoto T.
Published: March 2008

We report that polycrystalline cubic-Si3N4 with a spinel structure and low oxygen concentration (<0.5 wt%) shows Vickers hardness of 43 GPa when measured with the indentation load of 10 mN. The hardness decreases with the increase of the indentation load, which can be ascribed to the presence of weak grain boundaries. The high hardness can be well explained by its large shear modulus as predicted by first-principles calculations.
Mechanism of liquid-phase epitaxy growth of NdBa2Cu3O7−xfilm from low-peritectic-temperature YBa2Cu3O7−xseed film
Authors: Huang D. X. , Yao X. , Nomura K. , Wu Y. , Nakamura Y. , Izumi T. , Shiohara Y.
Published: March 2008

NdBa2Cu3O7-x (NdBCO) superconducting films were successfully grown on MgO substrates by liquid-phase epitaxy (LPE) using YBa2Cu3O7-x (YBCO) seed films which have lower peritectic temperatures. Microstructural characterizations using optical and electron microscopes revealed that most of the seed grains decomposed at the high processing temperature and dissolved when they touched the solution. The NdBCO grains were formed first by the quasi-homoepitaxial growth of NdBCO units on the few surviving YBCO seed grains and then grew pendently to cover the large bare surface areas of the MgO substrates quickly by lateral overgrowth. A micrometer-thick melt layer was entrapped between the film and the substrate. Through the few links provided by the surviving seed grains, a stable film/substrate orientation relationship could still be maintained. A semiquantitative analysis was done for the lateral overgrowth process, and two different lateral overgrowth stages were observed with about 50 times difference in the lateral overgrowth rate. Then, a semiquantitative understanding for the entire YBCO-seeded NdBCO LPE growth process was finally reached.
Dielectric properties of BaTiO3–BaZrO3 ceramics under a high electric field
Authors: Tsurumi T. , Yamamoto Y. , Kakemoto H. , Wada S. , Chazono H. , Kishi H.
Published: March 2008

Multilayered ceramic capacitors (MLCCs) with BaTiO3–BaZrO3 (BTZ) dielectric layers were fabricated, and the dielectric permittivity of the BTZ layers with different thicknesses in MLCCs was measured. The dielectric permittivity of the BTZ ceramic disk was also measured under various ac electric fields. The variation in the dielectric behaviors with the thickness of BTZ layers in MLCCs was explained by the ac-field dependence of dielectric permittivity observed in the BTZ ceramic disk. The ac-field dependence of dielectric permittivity of BTZ was markedly observed below the temperature of a broad maximum in the dielectric permittivity versus temperature (є versus T) curve. It was found that the temperature of the broad maximum shifted to the low-temperature side and the peak shape became asymmetric with increasing ac field. These changes in the dielectric properties under high ac fields were explained by a model of relaxors with the concept of the formation of polar microregions (PMRs) and the freezing of fluctuating ipoles in PMRs.
Fabrication of β–BaB2O4 thin films with (00l) preferred orientation through the chemical solution deposition technique
Authors: Kobayashi Takeshi , Ogawa Ryo , Miyazawa Kun'ichi , Kuwabara Makoto
Published: March 2008

β–BaB2O4 (β-BBO) films with the (00l) preferred orientation were successfully fabricated on Si(100) and fused quartz substrates by the chemical solution deposition technique. The films were characterized by x-ray diffractometry in out-of-plane and in-plane geometry, reciprocal space mapping, transmission electron microscopy, and scanning electron microscopy. The degree of orientation of the films is as high as 95% and the full width at half-maximum (FWHM) of the rocking curve for the films is as low as 2.9°. The films have a mosaic structure. The (00l) planes of some of the crystallites tilt to the substrate and the in-plane orientation of each crystallite is random. The size of each crystallite is 0.5–1.5 μm, and crystallite thickness is equal to the film thickness. The degree of orientation of the films increases and the FWHM of rocking curve for the films decreases with increasing film thickness. The thicker the films are, the larger the crystallite size and the more definite the crystallite boundaries are. These phenomena are thought to be closely related with the increase in internal stress with film thickness. The films irradiated by Nd3+: YAG laser light generated second harmonic wave.
Evaluation of thermal aging embrittlement of austenitic stainless steels JN1, JJ1, and JK2 by cryogenic small-punch testing
Authors: Saucedo-Muñoz Maribel L. , Liu Shi Cheng , Komazaki Shin-Ichi , Kwon Il-Hyun , Hashida Toshiyuki , Takahashi Hideaki , Nakajima Hideo
Published: March 2008

Small-punch tests were conducted at 4, 77, and 293 K on three newly developed cryogenic austenitic stainless steels, JN1, JJ1, and JK2, which were solution treated, water-quenched, and then aged at 923, 973, 1023, and 1073 K for 5 h. Small-punch test energy was employed for the evaluation of the aging-induced embrittlement behavior in these materials. An SEM analysis of the fracture surface for the solution-treated steel specimens indicated a ductile fracture, having the highest SP test energy values. On the contrary, intergranular brittle fracture was observed in aged specimens. The small-punch test energy of materials decreased significantly as the aging process progressed. The highest and lowest decrease in small-punch test energy with aging temperature occurred in JN1 and JK2 steels, respectively. The decrease in small-punch test energy was shown to follow appropriately the aging-induced embrittlement in these materials. The difference in aging-induced embrittlement behavior for these steels was explained on the basis of the volume fraction of intergranular precipitates in aged samples.
Residual stresses in DLC/Si and Au/Si systems: Application of a stress-relaxation model to the nanoindentation technique
Authors: Lee Yun-Hee , Kwon Dongil
Published: March 2008

Residual stress in a thin film was analyzed by the nanoindentation technique. Two dominant effects of residual stress to indentation were summarized as the slope change in loading curve and the invariant value of intrinsic hardness. A stress-sensitive reversibly deformed zone around contact was modeled to explain the indentation behaviors under a residually stressed state. Finally, the residual stress was evaluated from the changes in contact shape and applied load during stress relaxation under the condition of constant indentation depth. The residual stresses in diamond-like carbon and Au films analyzed from this model agreed well with the average values measured by the curvature method.
Reactive wetting of a metal/ceramic system
Authors: Chen Jian , Gu Mingyuan , Pan Fusheng
Published: March 2008

The mechanism of reactive wetting of metal/ceramic was investigated on the basis of a detailed description of the thermodynamics of interfacial reactions. The interfacial reaction of the metal/ceramic system has been treated as the reaction between the surface phase of the metal matrix and that of the substrate. It is concluded that reactive wetting is governed not only by the term accounting for the intensity of interfacial chemical reactions but also by the term accounting for the physicochemical properties of the resulting interface. In some cases, only one of them contributes dominantly to wetting. The criteria for the choice of an alloying element to promote wetting should not only include its reactivity with the substrate but also its ability to favorably modify the metal/substrate interface.
Transparent Lead Lanthanum Zirconate Titanate Ceramics Derived from Oxide Mixture Via a Repeated Annealing Process
Authors: Kong L. B. , Ma J. , Zhang T. S. , Zhang R. F.
Published: March 2008

Lead lanthanum zirconate titanate (PLZT9/65/35) ceramics were prepared from their oxide mixture via reactive sintering without involving a calcination step. PLZT ceramics sintered at 1000 °C for 4 h possessed a grain size of 3–4 μm, a dielectric constant of 3670, a dielectric loss of 0.033 at 1 kHz, and a remnant polarization of 5.7 μC/cm2 and coercive field of 4.6 kV/cm, respectively. Transparent PLZT ceramics were obtained by annealing the sintered samples at 1125 °C for 6 h repeatedly for 4 times without using hot pressing or oxygen flow. The grain size of PLZT ceramics increased to 4–6 μm, with dielectric constant of 5187 and dielectric loss (1 kHz) of 0.036, and remnant polarization of 11 μC/cm2 and coercive field of 5.3 kV/cm. The transparent PLZT ceramics demonstrated a transmittance of 42% at a wavelength of 550 nm.
Dependence of the Au/Ni/Si/Ni Contact Properties on the Si-layer Thickness and the Annealing Temperature in p-type GaN Epilayers
Authors: Yang S.J. , Kang T.W. , Kim T.W. , Chung K.S.
Published: March 2008

The dependences of the properties of Au/Ni/Si/Ni contacts, deposited on p-GaN epilayers by using electron-beam evaporation, on the Si layer thickness and the annealing temperature were investigated with the goal of producing contacts with low specific resistances. The results of the current–voltage (I–V) curves showed that the lowest specific contact resistance obtained for the Au/Ni/Si/Ni contact with a 1200-Å- thick Si layer on p-type GaN annealed at 700 °C for 1 min in a nitrogen atmosphere was 8.49 × 10-4 Ω cm2. The x-ray diffraction (XRD) measurements on the annealed Au/Ni/Si/Ni/p-GaN/sapphire heterostructure showed that Ni3Si, GaAu, and NiGa layers were formed at the Au/Ni/Si/Ni/p-GaN interfaces. While the intensities corresponding to the Ni3Si layer decreased with increasing annealing temperature above 700 °C, those related to the GaAu and the NiGa layers increased with increasing temperature. These results indicate that the Au/Ni/Si/Ni contacts with 1200-Å-thick Si layers annealed at 700 °C hold promise for potential applications in p-GaN-based optoelectronic devices.
Electrodeposition of Fe–Co Alloys into Nanoporous p-type Silicon: Influence of the Electrolyte Composition
Authors: Hamadache F. , Duvail J-L. , Scheuren V. , Piraux L. , Poleunis C. , Bertrand P. , Belkaïd M. S.
Published: March 2008

The cathodic deposition of iron–cobalt alloys inside the pores of anodically formed nanoporous silicon (PS) from p-type Si substrate is investigated with respect to the electrolyte composition. The samples were characterized by scanning electron microscopy, energy dispersive spectrometry, Auger electron spectroscopy, and Fourier transform infrared spectroscopy. Results showed that the nucleation of pure cobalt started at the bottom of the pores and the nucleation of pure iron occurred all over the pore walls, leading to a preferential deposition on top surface of the porous layer. Nevertheless, a low concentration of Co2+ ions (5 at.%) in the electrolyte drastically improved the penetration of iron into the pores. As a result, a good filling of the pores with Co metal as well as with Fe–Co alloys was achieved. It was also shown that the deposition process oxidizes the structure mainly at the pore walls. The results of our investigation indicate that the mechanisms occurring during the electrodeposition of metals on porous p-type silicon substrates are completely different depending on the kind of electrolyte used: pure iron-based electrolyte or cobalt-based solutions. A complete understanding of the deposition process requires further analyses of the carrier transport in PS and of the charge exchange at the Si/electrolyte and PS/electrolyte interfaces. These new results involving the deposition of iron-group materials into porous p-type silicon are useful for future silicon technologies.
Phase Diagram of the W-doped Pb(Zn1/3Nb2/3)O3–BaTiO3– PbTiO3 System Around a Morphotropic Phase Boundary Composition
Authors: Zhu W. Z. , Yan M. , Kholkin A. L. , Mantas P. Q. , Baptista J. L.
Published: March 2008

The morphotropic phase boundary (MPB) composition that is characterized by the coexistence of rhombohedral and tetragonal phases in the Pb(Zn1/3Nb2/3)O3–BaTiO3– PbTiO3 system was modified by W-doping at the B site of a perovskite structural block. To maintain the electrical neutrality, creation of A-site vacancies was intentionally introduced in the formulation of the examined compositions. Incorporation of W ions was revealed to stabilize the tetragonal phase against the rhombohedral one, shifting the MPB toward the PZN-rich end at room temperature. High-temperature x-ray diffraction examination in combination with dielectric measurements discloses two successive phase transitions as a sample is cooled from high temperature, namely, paraelectric cubic to ferroelectric rhombohedral followed by ferroelectric rhombohedral to ferroelectric tetragonal. W addition appears to suppress the first transition while promoting the second one.
Characterization of Free Volume in a Bulk Metallic Glass Using Positron Annihilation Spectroscopy
Authors: Flores K. M. , Suh D. , Dauskardt R. H. , Asoka-Kumar P. , Sterne P. A. , Howell R. H.
Published: March 2008

The free volume of metallic glasses has a significant effect on atomic relaxation processes, although a detailed understanding of the nature and distribution of free volume sites is currently lacking. Positron annihilation spectroscopy was employed to study free volume in a Zr–Ti–Ni–Cu–Be bulk metallic glass following plastic straining and cathodic charging with atomic hydrogen. Multiple techniques were used to show that strained samples had more open volume, while moderate hydrogen charging resulted in a free volume decrease. It was also shown that the free volume is associated with zirconium and titanium at the expense of nickel, copper, and beryllium. Plastic straining led to a slight chemical reordering.
Growth and Characterization of Na0.5K0.5NbO3 Thin Films on Polycrystalline Pt80Ir20 Substrates
Authors: Wang Xin , Olafsson Sveinn , Madsen Lynnette D. , Rudner Staffan , Ivanov Ivan P. , Grishin Alex , Helmersson Ulf
Published: March 2008

Na0.5K0.5NbO3 thin films have been deposited onto textured polycrystalline Pt80Ir20 substrates using radio frequency magnetron sputtering. Films were grown in off- and on-axis positions relative to the target at growth temperatures of 500–700 °C and sputtering pressures of 1–7 Pa. The deposited films were found to be textured, displaying a mixture of two orientations (001) and (101). Films grown on-axis showed a prefered (001) orientation, while the off-axis films had a (101) orientation. Scanning electron microscopy showed that the morphology of the films was dependent on the substrate position and sputtering pressure. The low-frequency (10 kHz) dielectric constants of the films were found to be in the range of approximately 490–590. Hydrostatic piezoelectric measurements showed that the films were piezoelectric in the as-deposited form with a constant up to 14.5 pC/N.
Formation of Single-phase CuO Quantum Particles
Authors: Borgohain Kavita , Mahamuni Shailaja
Published: March 2008

CuO nanocrystals of three different sizes 3.5, 6.5, and 10.0 nm were synthesized by a novel electrochemical route. Quantum size effects in these nanocrystals are evident from the optical absorption spectra. The optical absorption feature is observed to be blue shifted by about 1 eV with size reduction. The CuO q-particles were found to be single-phased and very stable as far as the size and phase is concerned.
Structures of AlN/VN Superlattices with Different AlN Layer Thicknesses
Authors: Li Quan , Kim I. W. , Barnett S. A. , Marks L. D.
Published: March 2008

AlN/VN superlattices with different periods were studied using x-ray diffraction and transmission electron microscopy (TEM). A phase transformation of the AlN from an epitaxially stabilized rock-salt structure to a hexagonal wurtzite structure was observed for an AlN layer thickness greater than 4 nm. A structural model is proposed on the basis of TEM results for the orientation of the transformed phase. The VN layer grown on top of the hexagonal AlN was observed to be reoriented compared to that in the stabilized B1-AlN/VN. The VN nucleated by taking the w-AlN(002) plane as its (111) plane instead of the (002) plane.
Microwave Electromagnetic Characteristics of a Microcoiled Carbon Fibers/paraffin Wax Composite in Ku Band
Authors: Du Jin-Hong , Sun Chao , Bai Shuo , Su Ge , Ying Zhe , Cheng Hui-Ming
Published: March 2008

The complex relative permittivity ∈γ and permeability μγ of microcoiled carbon fibers (MCCFs) imbedded in paraffin wax were measured at Ku band frequencies (12.4–18 GHz). Both the real and imaginary parts of the complex relative permittivity of the MCCFs/paraffin wax composite decreased with increase of the frequency. The real part of the complex relative permeability of the composite increases with increase of the frequency, and the imaginary part is nonzero and nearly constant over the measured frequency range. The dielectric loss tangent (tan δ∈), the magnetic loss tangent (tan δm), and amplitude attenuation factor (α) were determined as well. On the basis of the experimental results, the MCCFs/paraffin wax composite is mainly a kind of dielectric lossy material with small magnetic loss and diamagnetism in the Ku band.
Mechanical Relaxation Time Scales in a Zr–Ti–Ni–Cu–Be Bulk Metallic Glass
Authors: Suh Daewoong , Dauskardt Reinhold H.
Published: March 2008

The relaxation time scales in a commercial-grade Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at.%) bulk metallic glass were examined using transient and dynamic mechanical experiments. The viscoelastic and sub-Tg relaxations were well described by the Kohlrausch–Williams–Watts relaxation function. A large activation energy (4.0 eV) and small nonexponentiality parameter (approximately 0.5) were observed for viscoelastic relaxation above Tg consistent with the cooperative nature of atomic movements leading ultimately to viscous flow. Conversely, a small activation energy (0.1 eV) and large nonexponentiality parameter (approximately 0.9) were observed for the sub-Tg relaxation suggesting localized atomic adjustments which may involve different structural units or mechanisms. The glass transition was manifested as a decoupling of the sub-Tg and viscoelastic relaxation. The resulting transition temperature determined at a selected time scale was in agreement with the value obtained from calorimetric studies.
Crystallization Mechanism of Nd1+xBa2−xCu3O7−y and YBa2Cu3O7−y Films Deposited by Metalorganic Deposition Method Using Trifluoroacetates
Authors: Shibata Junko , Honjo Tetsuji , Fuji Hiroshi , Araki Takeshi , Hirabayashi Izumi , Hirayama Tsukasa , Izumi Teruo , Shiohara Yuh , Yamamoto Takahisa , Ikuhara Yuichi
Published: March 2008

YBa2Cu3O7−y(Y123) and Nd1+xBa2−xCu3O7−y (Nd123) films were deposited by the metalorganic deposition method, and the growth mechanism of these films was investigated by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. The Y123 and Nd123 films were prepared by spin-coating LaAlO3 (001) and SrTiO3 (STO) (001) substrates, respectively, with solutions including trifluoroacetates. Then, the samples were heat treated at 673 K in a humid O2 gas flow to form amorphous precursor films. Finally, the precursor films were heated at higher temperatures for 0–30 min in a humid Ar/O2 gas flow and cooled rapidly from those annealing temperatures. It was found that CuO crystals with a size of 10–20 nm are segregated in the Y123 and Nd123 amorphous precursor films. In the Y123 quenched film prepared by cooling the precursor film rapidly after the heat-treatment at 1048 K for 30 min, a polycrystalline film including Y2Cu2O5, BaF2, and CuO crystals was found to be generated on the c-axis-oriented Y123 film. In contrast, in the Nd123 quenched films, (NdBa)2CuO4(Nd201) phase was found to be formed first on the surface of the STO substrate. In conclusion, the c-axis-oriented Y123 film is formed by diffusion and reaction of Y2Cu2O5, BaF2, and CuO crystals, and the Nd201 phase reacts with BaF2 and CuO crystals in a humid atmosphere to form a c-axis-oriented Nd123 film.
Preparation and Properties of Novel Aerodynamic Pressure-sensitive Paint Via the Sol-gel Method
Authors: Jiang Feng-Zhi , Xu Ren , Wang Duo-Yuan , Dong Xing-De , Li Gui-Chun , Zhu Dao-Ben , Jiang Lei
Published: March 2008

A novel aerodynamic pressure-sensitive paint (PSP) was prepared by using the sol-gel process for measuring the pressure distribution variation on an aerodynamic surface with an oxygen-containing gas flow. In this PSP, RuIIcomplexes as oxygen-sensitive probe molecules excited with visible light of 436 nm were dispersed into the organic modified silica matrix film prepared by the sol-gel method. A linear relationship between the emission intensity and the oxygen partial pressure was achieved in the airflow pressure range of 10.1–405 kPa, and the slope that represents the sensitivity of PSP for oxygen quenching reaches 0.75. A pressure distribution map was demonstrated showing a spatial resolution of 0.25 mm.
Optical Characterization of GaAs/Si Layers Grown by the Conformal Method (Confined Lateral Epitaxial Growth)
Authors: Ardila A. M. , Martínez O. , Avella M. , Jiménez J. , Gil-Lafon E. , Gérard B.
Published: March 2008

Optical studies of conformal GaAs layers grown on silicon substrates were carried out by cathodoluminescence, photoluminescence imaging, and micro-Raman spectroscopy. These techniques revealed, in the conformal GaAs layers, local variations of the luminescence intensity with the shape of stripes both parallel and perpendicular to the GaAs seed, associated with local variations of tensile stress. The cathodoluminescence and micro-Raman spectra suggest that this distribution of tensile stress plays an important role in the formation of mid-gap states responsible for the variations of the luminescence intensity. The high luminescence emission of the conformal GaAs layers compared to the emission of the GaAs seed grown directly on the Si substrate is consistent with the high quality of the conformal layers.
Flame-made Ceria Nanoparticles
Authors: Mädler L. , Stark W. J. , Pratsinis S. E.
Published: March 2008

Flame spray pyrolysis (FSP) has been used to synthesize high-surface-area ceria from cerium acetate in acetic acid solution. With the addition of an iso-octane/2-butanol mixture to that solution, homogeneous CeO2 nanoparticles were obtained. The specific surface area of the powders ranged from 240 to 101 m2/g by controlling the oxygen dispersion and liquid precursor flow rates through the flame. Furthermore, for production rates from 2 to 10 g/h a constant average primary particle size could be obtained at selected process parameters. The ceria showed high crystallinity and primary particles with a stepped surface. The powder exhibited good thermal stability and conserved up to 40% of its initial specific surface area when calcinated for 2 h at 900 °C. This shows the potential of FSP made ceria for high-temperature applications as in three-way catalysts or fuel cells.
Grain-boundary Voiding in Self-passivated Cu–1 at.% Al Alloy Films on Si Substrates
Authors: Weiss D. , Kraft O. , Arzt E.
Published: March 2008

The new generation of semiconductor metallization is based on Cu-film technology. In this paper we report on detrimental changes in surface morphology of self-passivated-Cu–1 at.% Al films which were magnetron-sputtered on Si substrates. Large voids appeared at grain boundaries after annealing, oxidation at temperatures at or above 500 °C, and cooling to room temperature under vacuum. Grain-orientation imaging with electron backscatter diffraction revealed that preferentially high-energy grain boundaries were voided. Contrary to reports in the literature, void growth was not prevented by the extremely clean ultrahigh-vacuum conditions during film fabrication nor by the strong and very sharp grain texture. Instead, it was clearly correlated with the stable surface oxide on the self-passivated films. Void growth was not found after annealing passivation-free films such as pure Cu or unoxidized Cu–1 at.% Al films.