bluuebunny/crossref_metadata_2025 huggingface dataset:
Pb()O3-type Perovskites: Part II. Short-range Order Parameter as a Criterion of the Distinction Between Relaxor and Normal Ferroelectrics
Authors: Kim Su-Chan , Jang Hyun M.
Published: March 2008

A classification scheme of Pb()O3-type perovskites with respect to the B-site order parameters was proposed based on the theoretical calculation of the short-range order parameter (σ) using the pair-correlation model. The calculated order parameters predict that a Pb()O3-type perovskite without any charge difference between B′ and B″ cations [e.g., Pb(Zr1/2Ti1/2)O3 (PZT)] is represented by a completely disordered state with the absence of a finite coherence length. On the other hand, a Pb()O3-type perovskite system having different ionic charges is characterized either by the short-range ordering with a nanoscale coherence length or by the macroscopic long-range ordering, depending on the magnitude of ionic charge difference between B′ and B″ ions. The normal ferroelectricity in Pb()O3-type complex perovskites was then correlated either with a completely disordered state (σ = 0) or with a perfectly ordered state (σ = 0), whereas the relaxor behavior was attributed to the nanoscale short-range ordering (0 < σ < 1) in the configuration of the B-site cations.
Thermal stresses in multilevel interconnections: Aluminum lines at different levels
Authors: Shen Y-L.
Published: March 2008

Numerical results on the evolution of thermal stresses in multilevel interconnects are presented. Two levels of aluminum lines with an aspect ratio of unity, aligned vertically or arranged in a staggered manner, are considered by recourse to the finite element analysis. The stresses are found to be significantly higher in the lower-level lines than in the upper-level lines, for both the aligned and staggered arrangements. The stress magnitudes are generally smaller in lines of staggered arrangement, compared to the case of aligned lines. Implications of the present findings are discussed, with directions of future studies highlighted.
Two interferometric methods for the mechanical characterization of thin films by bulging tests. Application to single crystal of silicon
Authors: Bonnotte E. , Delobelle P. , Bornier L. , Trolard B. , Tribillon G.
Published: March 2008

Two optical methods are presented for the mechanical characterization of thin films, namely real time holographic interferometry and a fringe projection method called “contouring.” These two methods are coupled to the interferometry by the phase measurements, thus allowing the displacement field to be measured at all points on the membrane. We discuss the solutions retained in terms of their precision and sensitivity. These methods are then applied to membrane bulging tests, a type of test that is widely used in micro-mechanical studies. The measurements are performed on silicon single crystal and the results are compared to the solutions calculated by finite element methods. In both cases, the good agreement between theory and experiments allows the experimental apparatus to be validated.
Microstructure, electrical properties, and thermal stability of Au-based ohmic contacts to p-GaN
Authors: Smith L. L. , Davis R. F. , Kim M. J. , Carpenter R. W. , Huang Y.
Published: March 2008

The work described in this paper is part of a systematic study of ohmic contact strategies for GaN-based semiconductors. Gold contacts exhibited ohmic behavior on p-GaN when annealed at high temperature. The specific contact resistivity (ρc) calculated from TLM measurements on Au/p-GaN contacts was 53 Ω · cm2 after annealing at 800 °C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current-voltage (I-V) behavior in the as-deposited condition with ρc = 214 Ω · cm2. The specific contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 725 °C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, which coincided with the improvement of contact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN contact, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725 °C for 15 s. The resultant increase in contact resistance is believed to be due to the barrier effect increased by the presence of the low work function Mg metal.
Micro-Raman analysis of residual stresses and phase transformations in crystalline silicon under microindentation
Authors: Lucazeau G. , Abello L.
Published: March 2008

Vickers microindentations obtained with loads between 0.05 N and 2 N were performed on crystalline (100) silicon. The residual stress field and the different structural states induced by loading were studied by mapping the indented zones by their micro-Raman response. A Raman signature of amorphous silicon is found in the center of the impression. The energy of the Γ25 zone center phonon is found to vary from 522 cm−1 when probing the silicon at a distance of 80 μm from the center of the indentation up to 527 cm−1 when probing the pileup region of the impression. When probing cracked zones in the vicinity of the pileup region, wave numbers as high as 536 cm−1 are measured. The stress components induced by a point indentation (1 N) have been calculated from analytical expressions given in the literature. For an average conversion factor of 3.2 cm−1/GPa, the residual local stresses after unloading are found of the same order of magnitude or even larger than the calculated stresses that are generated during loading. A tentative explanation is proposed. Finally a systematic laser-induced thermal treatment of the central area and of the pileup region of indentations was performed. It is shown that the amorphous silicon in the center can partly recrystallize but that the residual stress state in the pileup region cannot be completely relaxed by local laser heating.
A study of the frequency dependence of the dielectrophoretic effect in thermoset polymers
Authors: Bowen C. P. , Shrout T. R. , Newnham R. E. , Randall C. A.
Published: March 2008

Ceramic-polymer composites with a 1–3 connectivity can be created via a novel process called dielectrophoretic assembly. The process involves an electric field which is applied to a suspension of ceramic particles in an uncured thermoset polymer matrix. Under appropriate conditions, the applied electric field acts to induce a spatial redistribution of the particles into a chained or fibril structure. It was shown previously that the electrorheological response and fibril microstructure are dependent on both the frequency and magnitude of the applied alternating electric field.3 This paper will show that the frequency dependence of the uncured thermoset polymer suspensions results from the complex electrical phenomena specific to each thermoset system. Specifically, it will be shown through low field dielectric measurements and high field current-voltage analysis that the dielectrophoretic effect can be limited by electrode polarization, ionic conductivity, and space charge relaxation. It is the frequency dependence of these limiting phenomena that gives rise to the observed frequency dependence in the dielectrophoretic force of attraction being utilized to drive particulate assembly.
Thermal diffusivity maps: Case studies in ceramics
Authors: Wei Lanhua , White Grady S.
Published: March 2008

A new methodology for mapping thermal diffusivity using a photothermal deflection method is introduced. Two case studies are made: fiber-reinforced composite structures and contact damage zones in alumina. In the former, characterization of thermal microstructural features is demonstrated; in the latter, microcrack density is quantified. Experimental data are analyzed and compared with literature results. Advantages and limitations of the technique are discussed.
X-ray photoelectron spectroscopy characterization of barium titanate ceramics prepared by the citric route. Residual carbon study
Authors: Miot C. , Husson E. , Proust C. , Erre R. , Coutures J. P.
Published: March 2008

Powder and ceramics of barium titanate prepared by the citric process were studied by x-ray photoelectron spectroscopy (XPS). Spectra of C1s, O1s, Ti2p, Ba3d, and Ba4d levels are analyzed in powder and ceramics immediately after the sintering step and after several months of exposure in the air. Ar-ion etching allowed one to characterize the material intrinsic carbon. The results are discussed in comparison with works previously published on oxide single crystals.
Characteristics of TiN film deposited on stellite using reactive magnetron sputter ion plating
Authors: Lee Min-Ku , Kang Hee-Soo , Kim Whung-Whoe , Kim Joung-Soo , Lee Won-Jong
Published: March 2008

TiN films were deposited onto stellite 6B alloy (Co base) by the reactive magnetron sputter ion plating. As the substrate bias increases, TiN film changes from columnar structure to dense structure with great hardness and smooth surface due to densification and resputtering by ion bombardment. The content of oxygen and carbon impurities in the TiN film decreases greatly when the substrate bias is applied. The preferred orientation of the TiN films changes from (200) to (111) with decreasing N2/Ar ratio and from (200) to (111) and then (220) with increasing the substrate bias. The change of the preferred orientation is discussed in terms of surface energy and strain energy which are related to the impurity contents and the ion bombardment damage. The hardness of the TiN film increases with increasing compressive stress generated in the film by virtue of ion bombardment. It becomes as high as up to 3500 kgf/mm2 when an appropriate substrate bias is applied.
Bonding behavior of Cu/CuO thick film on a low-firing ceramic substrate
Authors: Lee Sang-Jin , Kriven Waltraud M. , Park Jeong-Hyun , Yoon Young-Soo
Published: March 2008

The adhesion strength between a low-firing substrate consisting of an alumina/glass composite and a copper thick film was affected by the addition of cupric oxide and glass frit to the copper paste in a new co-firing process. An interlayer, 3–4 μm in thickness, was produced in the metal-ceramic interface during the new co-firing process due to the diffusion of copper. At the same time, the adhesion strength was improved by controlling the cupric oxide content. The addition of about 3 wt.% glass frit (softening point = 670 °C, based on the calcium-barium borosilicate glass composition) to the metal paste resulted in highest adhesion strength of 3 kg/mm2 with a shift of the debonding site toward the ceramic substrate within the interlayer. The shift of the debonding site could be observed by comparing the ratios of Al2O3/Cu and Ca concentration at the test pad areas on the substrate after debonding. The shift of the debonding site is attributed to the migration of glass frit into the interfacial region. The migration of glass frit occurred easily when the softening point of the glass frit was compatible with the new co-firing process, regardless of how much frit was used.
Computer simulation of ferroelastic phase transition in LaNbO4
Authors: Parlinski K. , Hashi Y. , Tsunekawa S. , Kawazoe Y.
Published: March 2008

A model of lanthanum orthoniobate which possesses a ferroelastic tetragonalmonoclinic phase transition is proposed. It contains only one particle per unit cell, but it is constructed consistently with symmetry changes at the phase transition. The model parameters are chosen to reproduce the bare soft mode, degree of deformation of the tetragonal unit cell to a monoclinic one, and the phase transition temperature. The ferroelastic system with free boundary conditions was simulated by the molecular dynamics technique, and the second order phase transition was reproduced. The studied annealing process shows formation of the stripe lenticular domain pattern, which has been interrupted by the appearance of a temporary band of perpendicularly oriented lenticular domains. The maps contain W′-type domain walls whose orientations are fixed only by interplay of potential parameters and not by symmetry elements. The simulated domain pattern has the same features as those observed by transmission electron microscopy.
Analytical electron microscopy of planar faults in SrO-doped CaTiO3
Authors: Čeh M. , Gu H. , Müllejans H. , Rečnik A.
Published: March 2008

Oxide-rich planar faults within a perovskite matrix are the prevailing type of extended defects in polycrystalline SrO-doped CaTiO3. These defects form, depending on the temperature of sintering, random networks, or ordered structures. The chemistry of the polytypoid, the isolated planar faults, and the perovskite phase have been studied by spatially resolved electron energy-loss and energy-dispersive x-ray spectroscopies using a dedicated scanning transmission electron microscope. We have found that Sr ions from SrO additions preferably substitute Ca in the CaTiO3 lattice, thus forming a solid solution (Ca1–xSrx)TiO3. The surplus of Ca ions forms single and ordered CaO-rich planar faults in the host (Ca1–xSrx)TiO3 phase. Whereas the excess Ca segregates in a form of single planar faults at lower temperatures, it forms a stable polytypoidic phase at higher temperatures. For materials having up to 25 mol% of SrO additions, this phase has (Ca1–xSrx)4Ti3O10 composition, comprising a sequence of CaO faults followed by three (Ca1–xSrx)TiO3 perovskite layers. Analytical electron microscopy revealed that the composition of the single planar faults, formed at lower temperatures, is identical to that of polytypoids, which are stable at higher sintering temperatures.
Effect of rate controlled sintering on microstructure and electrical properties of ZnO doped with bismuth and antimony oxides
Authors: Agarwal Gaurav , Speyer Robert F.
Published: March 2008

Various rate controlled sintering (RCS) schedules were used on isostatically pressed particulate compacts of ZnO with Bi2O3 and Sb2O3 additives. For low additive content, smaller average grain sizes with more rapid RCS schedules were attributable to thermal schedules which minimized the time at elevated temperatures where grain growth could occur. β–Bi2O3, Zn7Sb2O12, and Zn2Sb3Bi3O14 phases formed during/after sintering. Elevated heat-treatment temperatures favored the formation of Zn7Sb2O12 and additional β–Bi2O3, while Zn2Sb3Bi3O14 was dominant in sintered samples where the RCS schedule did not result in temperatures in excess of 1100 °C. Zn2Sb3Bi3O14 precipitated during sintering, functioning as grain boundary pinning sites which impeded ZnO grain growth. Bismuth and antimony oxide-based liquid facilitated sintering at lower temperatures, which in turn resulted in decreased average grain size. Rapid RCS schedules for samples with low dopant content resulted in lower sintering temperatures, since time was not allowed for Zn2Sb3Bi3O14 precipitation to deplete the liquid phase. For higher dopant contents, liquid phase was adequately plentiful, wherein longer RCS schedules resulted in lower sintering temperatures. Increasing concentration of second phase generally fostered decreased grain size and attenuated the effect of thermal schedule on the microstructure. Electrical resistance and breakdown voltage increased consistent with decreasing ZnO average grain size.
Determination of Young's modulus by spherical indentation
Authors: Huber N. , Munz D. , Tsakmakis Ch.
Published: March 2008

In this paper we consider elastic plastic materials that are tested by spherical indentation. Finite element calculations, which take into account nonlinear geometry properties, are carried out in order to determine the influence of the plastic history on the unloading response of the material. Two different iterative methods are proposed for determining Young's modulus under the assumption of a bilinear plasticity law. The first method deals with loading and unloading parts of the indentation test, whereas the second one deals only with unloading parts of the indentation test.
Friction and wear performance of diamond-like carbon, boron carbide, and titanium carbide coatings against glass
Authors: Daniels B. K. , Brown D. W. , Kimock F. M.
Published: March 2008

Protection of glass substrates by direct ion beam deposited diamond-like carbon (DLC) coatings was observed using a commercial pin-on-disk instrument at ambient conditions without lubrication. Ion beam sputter-deposited titanium carbide and boron carbide coatings reduced sliding friction, and provided tribological protection of silicon substrates, but the improvement factor was less than that found for DLC. Observations of unlubricated sliding of hemispherical glass pins at ambient conditions on uncoated glass and silicon substrates, and ion beam deposited coatings showed decreased wear in the order: uncoated glass > uncoated silicon > boron carbide > titanium carbide > DLC > uncoated sapphire. Failure mechanisms varied widely and are discussed. Generally, the amount of wear decreased as the sliding friction decreased, with the exception of uncoated sapphire substrates, for which the wear was low despite very high friction. There is clear evidence that DLC coatings continue to protect the underlying substrate long after the damage first penetrates through the coating. The test results correlate with field use data on commercial products which have shown that the DLC coatings provide substantial extension of the useful lifetime of glass and other substrates.
Czochralski growth of Yb3+and Pr3+doped Ca-fluoroapatite
Authors: Caprez A. , Mikhail P. , Schwecke C. , Hulliger J.
Published: March 2008

Pure, Pr3+, and Yb3+doped Ca-fluoroapatite (Ca-FAP) crystals were grown by the Czochralski method. The effective distribution coefficientkefffor Yb3+was 0.5. For Pr3+a very highkeffof 1.4 was obtained. Values forkeffare discussed in terms of an elastic model accounting for the strain energy originating from the difference in the size of Ln3+ions. The Ln3+concentrations were measured by absorbance spectroscopy, by inductively coupled plasma optical emission spectroscopy, and by electron microprobe analyses.
Study of fluoride induced dissimilar metal corrosion in a microelectromechanical system
Authors: Prasad Jagdish , Chyan Oliver M. R. , Chen Jin-Jian , Liu Min , Chen Ligang , Xu Fei
Published: March 2008

This paper reports a study of microscopic on-chip corrosion on a 17 μm × 17 μm microelectromechanical device. The active atmospheric corrosion occurred only on the Al−Si−Ti components which were connected directly to the TiW components. Adsorbed fluoride ionic species on the microelectromechanical device were found to activate the observed bimetallic corrosion on the Al−Si−Ti/TiW contacts. Water rinse or replacement of TiW by TiAlx completely eliminates the active corrosion. Electrochemical potential data confirm the dissimilar metal corrosion mechanism. Effective prevention of on-chip corrosion was achieved by the judicious design of the device components to avoid dissimilar metal contacts with large galvanic potential differences.
Improving the wear resistance of Al–Si alloy by ion implantation
Authors: Itoh Y. , Azuma H. , Itoh A. , Hioki T.
Published: March 2008

The mechanical properties of ion-implanted Al–Si alloy were studied using disk samples of alloy irradiated with Ar+, B+, and N2+ ions. Knoop hardness of ASTM 336.0 disks increased from 117 to 165 kgf/mm2 upon N2+ ion implantation. To measure tribological properties, lubricated ball-on-disk tests were performed using steel balls. The coefficients of friction of ion-implanted disks were higher than those of unimplanted ones. Ion implantation improved the wear resistance of the disks, and in the case of N2+ ion-implanted disks, the worn volume was smaller than 10−4 mm3. XPS analysis for the N2+ ion-implanted samples revealed the formation of aluminum and silicon nitride on the sample surface. On the other hand, the cross-sectional image of the ion-implanted surface showed precipitated Si which is held under the implanted N2+ ions.
Calculated phase diagrams for activated low pressure diamond growth from C–H, C–O, and C–H–O systems
Authors: Wang Ji-Tao , Wan Yong-Zhong , Zhang David Wei , Liu Zhi-Jie , Huang Zhong-Qiang
Published: March 2008

Three-dimensional temperature (T)–pressure (P)–composition (X) phase diagrams of binary carbon-hydrogen (C–H) and carbon-oxygen (C–O) systems for activated low pressure diamond growth have been calculated. Based on an approximation of linear combination between C–H and C–O systems, a projective ternary carbonhydrogen-oxygen (C–H–O) phase diagram has also been obtained. There is always a diamond growth region in each of these phase diagrams. Once a supply of external activating energy stops, the diamond growth region will not exist. Nearly all of the reliable experimental data reported in the literature drop into the possible diamond growth region of the calculated projective ternary C–H–O phase diagram under the conditions of 0.01–100 kPa and above 700 K.
Hydrothermal synthesis and sintering of nickel and manganese-zinc ferrites
Authors: Dias Anderson , Buono Vicente Tadeu Lopes
Published: March 2008

The influence of the starting materials on the crystalline phases observed after hydrothermal synthesis of nickel and manganese-zinc ferrites was investigated. The combination of sulfates and sodium hydroxide showed the best results for the conditions studied. The morphological parameters of MnZn ferrites produced at different hydrothermal conditions (110–190 °C, 4–30 h) were analyzed. Changes in lattice parameter, particle size, density, size and total volume of pores, and in the surface area of the particles were analyzed as a function of temperature and processing time. The sintering process was employed in order to verify the reactivity of the hydrothermal powders at controlled atmosphere. High density and surface homogeneous ceramic bodies were obtained, without zinc volatilization. Lattice parameter variations were associated with changes in the cations distribution of the spinel during sintering.
Alumina platelet reinforced reaction bonded aluminum oxide composites: Textured and random
Authors: An Linan , Wu Suxing , Chan Helen M. , Harmer Martin P. , Brandon David G.
Published: March 2008

The RBAO (Reaction Bonded Aluminum Oxide) process and water-based gel casting were combined to produce alumina platelet reinforced RBAO composites. In the RBAO process, a precursor powder mixture of Al metal and Al2O3 is reacted to form 100% ceramic. To obtain composites in which the platelets are highly aligned, tapes consisting of 10 vol.% homogeneously distributed alumina platelets and 90 vol.% RBAO precursor powder were made by water-based gel casting using an extended doctor blade arrangement. Pellets of textured composites were subsequently prepared by stacking sheets cut from the green tapes, and filter pressing. Randomly oriented platelet composites were made using the same starting powders and gelling procedure, but without the tape-casting step. Reaction bonding was carried out in a box furnace in air. Microstructures of the composites were characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of platelet orientation on contact damage behavior was studied using a Hertzian indentation method. It was found that the textured composite exhibited improved damage resistance compared to the random composite.
In situ formation of MoSi2–SiC through reaction of SiO2 or Si3N4 with Mo and carbon
Authors: Krishnarao R. V. , Ramarao V. V. , Mahajan Y. R.
Published: March 2008

Composite powders of molybdenum silicide–SiC were synthesized by reacting mixtures of (Mo–SiO2 –C), (Mo–Si3N4 –C), and (Mo–SiO2 –Si3N4 –C) powders at 1300 °C. In the (Mo–SiO2 –C) system Mo5Si3 and Mo3Si formed predominantly. MoSi2 formed the major constituent of the reaction product from powder mixtures containing Si3N4. Vapor-solid SiC whiskers formed in the (Mo–SiO2 –C) system. Vapor-liquid-solid whiskers of SiC and Mo5Si3C formed in (Mo–SiO2 –Si3N4–C) and (Mo–Si3N4 –C) systems, respectively. The mechanism of formation of the VLS whiskers and molybdenum silicides was identified as follows: initially a thin layer of Mo2C forms on Mo particle; the Si vapor from thermal decomposition of Si3N4 deposits on the Mo2C surface and forms a droplet of ternary “Nowotny phase” Mo<5Si3C<1; an SiC/Mo5Si3C whisker forms by nucleation and growth from the supersaturated ternary phase; after reaction with the Mo2C layer, the SiO/Si vapor further reacts with Mo particle to form bulk silicides.
A study on magnesium diffusion into LiNbO3 single crystal by x-ray diffraction, differential thermal analysis, and scanning electron microscopy
Authors: Que Wenxiu , Lim Siakpiang , Yao Xi , Liu A. Q.
Published: March 2008

The diffusion of magnesium into lithium niobate single crystal under different diffusion conditions has been studied by x-ray diffraction, glancing-incidence x-ray diffraction, differential thermal analysis, and scanning electron microscopy in an attempt to determine the diffusion mechanism and evaluate the crystallinity of the diffused layer. It is found that the magnesium diffused layer exhibits the crystal structure of an unknown compound from the Mg–Li–Nb–O ternary system and MgNb2O6. The MgNb2O6 is in the surface layer of the magnesium diffused layer, while the unknown compound is in the subsurface layer beneath the MgNb2O6. It is proposed that this unknown compound and MgNb2O6 which form during a solid state reaction between a thin layer of MgO and a lithium niobate crystal in a Li2O-rich atmosphere are the real sources for Mg ion indiffusion into lithium niobate crystal. The changes in Curie temperature with diffusion parameters are noted. Reasons of lattice distortion and mechanisms of Mg ion indiffusion are discussed and analyzed.
Characterization and cation exchange properties of zeolite synthesized from fly ashes
Authors: Ma Weiping , Brown Paul W. , Komarneni Sridhar
Published: March 2008

Zeolite P was formed from class F fly ash under hydrothermal conditions. The fly ash was reacted with 2.8 or 5 M NaOH at 100 °C. Zeolite of the above type was produced regardless of the NaOH concentration or the addition of quartz, thus indicating its formation over a wide range of conditions. The zeolite produced was of the NaP-type with a fibrous morphology. Analysis of the pore structure of this zeolite by the BET method indicates a type II isotherm. The specific surface areas of synthesized zeolites increased from 28.5 to 41.1 m2/g when the NaOH concentration was increased from 2.8 to 5.0 M. This zeolite showed a significant selectivity for the uptake of Cs and Sr. Cs uptake ranged from 7.67 to 8.61 meq/100 g while that of Sr ranged from 9.8 to 10.54 meq/100 g. The value obtained depended on the specific synthesis conditions. These values are higher than those observed for tobermorite prepared from the same fly ash even though the tobermorite exhibited a higher specific surface area.
The effect of mixed modifiers on nuclear waste glass processing, leaching, and Raman spectra
Authors: Raman S. V.
Published: March 2008

Borosilicate glasses with different waste loadings were prepared by ambient melting, quenching, and annealing. Some melt compositions partially crystallize to durable phases of zircon and forsterite. The coexisting liquid quenches to glass and endures the leach tests. The waste loading dependent leach rate trends of these glasses are reminiscent of the mixed alkali effect. Raman spectra suggest initial increase in durability with increases in the depolymerization of silicate species. Fluorine and hydroxyl ions also contribute to depolymerization. Tetraborate and metaborate rings are identified in the Raman spectra. The durability is enhanced when tetraborate bands are more intense than the metaborate bands.
Characterization of a new Ca–Cd hydroxide hydrothermally synthesized and its implications for cement isolation of Cd
Authors: Gñni S. , Macías A. , Madrid J. , Díez J. M.
Published: March 2008

Mixtures of CaO–CdO (1 : 1) were hydrothermally treated in a pressure reactor at 200 °C and 200 psi of pressure during a period of 16 h. The evolution of the reaction was followed by x-ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetric (TG and DTG) analysis. Also, the composition of the filtered solutions was analyzed to determine the mechanism of the reaction as well as the thermodynamic solubility constant of the new compound formed. The results show that CaO and CdO react, giving rise to a new CaCd(OH)4 hydroxide whose thermodynamic solubility constant, 1.5 ± 0.4 × 10−11 M2, is six orders of magnitude lower than those of both Ca(OH) 2 and β–Cd(OH) 2. This low solubility constant justifies the Cd2+ concentration measured in the pore solution of cement matrices used to immobilize cadmium containing wastes. The mechanism of the reaction proposed is via dissolution of both Ca(OH) 2 and β–Cd(OH)2, Ca2+ and being the predominant species in solution.
Morphology of wetting reactions of SnPb alloys on Cu as a function of alloy composition
Authors: Liu C. Y. , Tu K. N.
Published: March 2008

We have investigated the wetting angle, side band growth, and intermetallic compound formation of seven SnPb alloys on Cu ranging from pure Sn to pure Pb. The wetting angle has a minimum near the middle composition and increases toward pure Sn and pure Pb, but the side band growth has a maximum near the middle composition. The intermetallic compounds formed are Cu6Sn5 and Cu3Sn for the eutectic and high-Sn alloys, yet for the high-Pb alloys, only Cu3Sn can be detected. While no intermetallic compound forms between Cu and pure Pb, the latter nevertheless wets the former with an angle of 115°. The driving force of a wetting reaction, which may be affected by the free energy gain in compound formation, is discussed by assuming that rate of compound formation is fast.
VHF a–Si: H solar cells: A systematic material and cell study
Authors: van Sark W. G. J. H. M. , Bezemer J. , van der Weg W. F.
Published: March 2008

A systematic study of material quality has been performed for intrinsic a–Si:H layers deposited by plasma enhanced chemical vapor deposition at excitation frequencies between 30 and 80 MHz (VHF). The process conditions were optimized not only for “device quality” opto-electronic properties but also for a uniformity in layer thickness better than 5% over the 10 cm × 10 cm substrate area. We found optimized homogeneities at different pressures depending on the excitation frequency. The effect of frequency at these optimum conditions on the material quality is small. VHF-intrinsic layers have been used in a–Si:H p+-i-n+ solar cells, in which both the p+ and n+ layer were made using 13.56 MHz. There is a clear correlation between material quality and solar cell parameters. Material deposited at low power densities is of so-called “device quality,” which is confirmed by demonstrating an initial efficiency of 10% for cells deposited at 65 MHz using a low power density. The deposition rate still is 2–3 times higher than the one at 13.56 MHz. Light-soaking of the cell leads to stabilization at 6% for the best cells, which compares well to conventional 13.56 MHz cells.
Role of rapid photothermal processing in environmentally conscious semiconductor manufacturing
Authors: Sharangpani R. , Singh R.
Published: March 2008

Compliance with the increasingly stringent environmental laws will force the phasing out of conventional methods for the manufacture of all semiconductor devices. Development of processes with the highest possible material and energy efficiencies is the heart of the present ecological preservation efforts. Besides other benefits, rapid isothermal processing (RIP) also uses less energy than furnace processing. Further increase of material and energy efficiencies is possible by using rapid photothermal processing. Central to this method is the use of quantum photoeffects in conventional RIP systems. This approach can be consolidated with advanced chemical vapor deposition methods that further lower the wastages leading to systems that can give significant improvements over those presently used. Key experimental results and possible future directions are presented.
Molecular orientation in single crystal thin films of N-(4-nitrophenyl)-(L)-prolinol
Authors: Zhou Ligui , Thakur M.
Published: March 2008

Thin single crystal films of N-(4-nitrophenyl)-(L)-prolinol (NPP) were prepared using the modified shear method. The surface orientation of the single crystal films was determined by x-ray diffraction and was found to be [101]. Polarized microscopy showed uniform birefringence and complete extinction when the thin film was rotated under crossed polarization, implying single crystal thin films with uniform surface were obtained. The molecular orientation in the NPP thin film was studied by polarized UV-visible and polarized micro-FTIR spectroscopy along with x-ray diffraction. The orientation of the NPP molecules was found to be almost parallel to the plane of the film. This parallel orientation is because of the polar (hydrogen bonding) interaction of the −(OH) and the N=O groups of the NPP molecule with the hydrophilic substrate surface. The results of the second harmonic generation (SHG) measurements are consistent with such a molecular orientation. These results show that the final molecular and crystallographic orientation in the film is determined by its initial molecule-substrate interaction.
Auto ignition synthesis and consolidation of Al2O3–ZrO2 nano/nano composite powders
Authors: Bhaduri S. , Bhaduri S. B. , Zhou E.
Published: March 2008

An “Auto Ignition” technique was utilized in synthesizing Al2O3 –ZrO2 powders with nano/nano microstructure. The process used the corresponding nitrates as oxidizers and urea as the fuel. The as-synthesized powders were characterized by x-ray diffraction and transmission electron microscopy. It was observed that the microstructure consisted of crystallites of Al2O3 and ZrO2, both of which were nanocrystalline. As opposed to the other nanocomposite ceramics, this feature of the microstructure classifies the present powders as nano/nano type. This nanocrystallinity of the microstructure (crystallite size less than 100 nm) was maintained even after a soaking at 1200 °C for 2 h. Since the microstructure is stable at high temperatures, it was possible to densify the powders by hot isostatic pressing at 1200 °C. The product was 99% of the theoretical density and maintained nanocrystalline grain size. The average hardness and toughness values, as determined by an indentation technique, were 4.45 GPa and 8.38 MPa · m1/2, respectively. These values represent evidence of ductility in these composites since transformation toughening was ruled out in this case. The potential application of these results is expected to be in net shape deformation forming of ceramics.
Improvement in thermoelectric properties of (ZnO)5In2O3 through partial substitution of yttrium for indium
Authors: Kazeoka Masaki , Hiramatsu Hidenori , Seo Won-Seon , Koumoto Kunihito
Published: March 2008

We first measured the thermoelectric properties of layer-structured homologous compounds, (ZnO)mIn2O3 (m = integer), and reported that they would becomecandidate materials for high-temperature thermoelectric energy conversion.1–4 We further tried to improve their thermoelectric properties by partially substituting yttrium for indium in (ZnO)5In2O3. Though the ionic radius of Y3+ is larger than that of In3+, the a-axis (hexagonal system) elongated and c-axis shrank as Y was substituted for In. The thermoelectric properties were found to vary with a varying amount of Y substitution; 3% Y substitution gave rise to the largest thermoelectric figure of merit, i.e., 1.1 - 1.3 × 10-4 K-1 at 960–1100 K. The abnormal change in the lattice structure by Y substitution was responsible for the unusual behavior of the thermoelectric properties.
Evolution of surface structure, microstructure, and superconducting properties during YBa2Cu3O7a-axis thin film growth
Authors: Marshall A. F.
Published: March 2008

The evolution of surface structure, grain microstructure, and superconducting transition temperature ofa-axis YBa2Cu3O7thin films has been studied as a function of film thickness. The grain size increases and develops a bimodal distribution of grain size during film growth, concurrent with an improvement inTc. The surface structure does not represent the grain size, but rather the development of the bimodal grain structure follows the formation of the surface structure. The results are discussed in terms of thin film growth modes.
Effects of hydrogenated amorphous carbon interlayer on diamond nucleation
Authors: Yang W. S. , Kim T. S. , Je Jung Ho
Published: March 2008

Diamond was deposited at 850 °C by microwave plasma chemical vapor deposition (CVD) on the interlayers with various intensity ratios (ID/IG) of the D band (~1400 cm-1) to the G band (~1570 cm-1) in the Raman spectra. Diamond could be grown only on the interlayers with higher ID/IG (≤1.95), and Nd was slightly increased to 3 × 106/cm2with ID/IG. The predeposition at 350 °C, which decreased the full-width at half-maximum of the broad D band, further increased Nd to 5 × 107/cm2. With 300 ÅA Pt overlayer on the interlayer, Nd was much more enhanced to 8 × 107/cm2. We suggest the sp3 bonded carbon clusters within the interlayer contribute to diamond nucleation, but they should be survived against atomic hydrogen etching during diamond deposition by increasing the sp3/sp2 ratio, by increasing the degree in clustering, or by protecting them with overlayer.
Preparation of ceria-gadolinia electrolytes by the tape rolling technique
Authors: Özkan Necati , Briscoe Brian J.
Published: March 2008

The preparation of thin (ca. 200 μm) Ce0.9Gd0.1O1.95planar electrolytes using the tape rolling technique is described. The processing and formation of these electrolytes involved several steps: (i) the production of a processable ceramic paste, (ii) rolling and cutting, (iii) binder burnout, and (iv) sintering. The rheology of these ceramic pastes is characterized by a hardness indentation test. The materials parameters which may be obtained from the hardness indentation test such as the hardness (plastic flow stress), elastic modulus, and plasticity index are provided. The rheology, as characterized by the hardness method, of the pastes is shown to be influenced by the nature and extent of processing aids and also the mixing and milling times. Further, it is shown that by using a paste formulation with appropriate rheological properties, it is possible to produce uniform thin green tapes using a twin roll mill. The binder burnout characteristics of the ceramic pastes were studied by using a specially constructed thermal gravimetric apparatus. It is shown that the heating rate and the ambient atmosphere have strong influences upon the binder burnout kinetics of these green tapes. Finally, it is shown that sintered Ce0.9Gd0.1O1.9electrolytes, with a near theoretical density and with a uniform microstructure as well as a chosen near net shape, may be prepared from the corresponding tape rolled greens.
Combustion synthesis of boron nitride powder
Authors: Hwang Chyi-Ching , Chung Shyan-Lung
Published: March 2008

A combustion synthesis (SHS) process developed in our previous study for the synthesis of Si3N4 has been tested for the synthesis of boron nitride (BN) powder. Boron and NaN3 powders were used as the reactants. In addition to ammonium halides, KHF2, FeCl3, NaNH2, or a mixture of 50 mol% FeCl3 and 50 mol% NaNH2 was added to the reactants to examine their catalytic effect. These powders were mixed and pressed into a cylindrical compact. The compact was wrapped up with an igniting agent (i.e., Mg + Fe3O4) and the synthesis reaction was triggered by the combustion of the igniting agent. It was found that only those reagents containing both halogen and hydrogen can exert effectively the catalytic effect. The BN powder as-synthesized is mostly in the form of agglomerated fine particles (0.1–1 μm in diameter) and is hexagonal in crystalline structure. Effects of various experimental parameters on the product yield were investigated. A possible reaction mechanism was proposed, which explains the effects of the experimental parameters on the synthesis reaction.
A novel Cu(II) chemical vapor deposition precursor: Synthesis, characterization, and chemical vapor deposition
Authors: Devi Anjana , Goswami J. , Lakshmi R. , Shivashankar S. A. , Chandrasekaran S.
Published: March 2008

A nonfluorinated β-diketonate precursor, bis(t-butylacetoacetato)Cu(II) or Cu(tbaoac)2, was synthesized by modifying bis(dipivaloylmethanato)Cu(II) or Cu(dpm)2 for chemical vapor deposition (CVD) of copper. The complex was characterized by a variety of techniques, such as melting point determination, mass spectrometry, infraredspectroscopy, elemental analysis, thermogravimetric and differential thermal analysis, and x-ray diffraction. Cu(tbaoac)2 has a higher sublimation rate than Cu(dpm)2 over the temperature range 90–150 °C. Pyrolysis of Cu(tbaoac)2 leads to the formation of copper films at 225 °C, compared to 330 °C for Cu(dpm)2. As-deposited copper films ere highly dense, mirror-bright, adhered strongly to SiO2, and showed a resistivity of less than 2.9 μΩ-cm at a thickness as low as 1300 Å. A possible mechanism for the decomposition of the ligand tbaoac has been proposed.
In-depth variations of diamond structures on Pt(111) investigated by confocal Raman spectroscopy
Authors: Nishitani-Gamo Mikka , Tachibana Takeshi , Kobashi Koji , Sakaguchi Isao , Ando Toshihiro
Published: March 2008

We have characterized heteroepitaxial diamond films on Pt(111) using the nondestructive technique of confocal Raman spectroscopy to investigate the variation in structure and strain with depth. The spectral depth profiles of heteroepitaxial diamond showed the diamond peak at 1332–1335 cm-1 and four bands centered at 1230 cm-1, 1470–1490 cm-1, 1530–1580 cm-1, and 1640 cm-1 near the surface. The diamond peak shifted to the single crystal peak position at 1332 cm-1 as the linewidth was broadened with free surface proximity. The compressive strain in the heteroepitaxial diamond crystal decreased and turned into the random strain. At the same time, the Raman band at 1470–1490 cm-1 grew in intensity. The constituents of non-diamond phase in the heteroepitaxial growth regions are different from those formed in the randomly oriented regions.
Microstructure characterization of one-directionally oriented ulexite
Authors: Ikuhara Yumi H. , Kondoh Shinji , Kikuta Koichi , Hirano Shin-ichi
Published: March 2008

Microstructures of ulexite were investigated by CTEM and low electron dose HREM. It was found that the longitudinal grains in ulexite were oriented to c-direction to form a bundle structure. There were a number of small-angle grain boundaries and stacking faults inside a grain in the ulexite. Cleavage microcracks and stacking faults were mostly introduced on the {010} of the ulexite. The high-angle grain boundaries mainly consisted of high coincidence boundaries, which was confirmed by a comparison of observed contact angles and calculated degree of coincidence at the boundaries. The light transmittance properties of the ulexite would depend on the defects such as stacking fault, small-angle grain boundary, and high-angle grain boundary.
Synthesis of a bulk amorphous alloy by consolidation of the melt-spun amorphous ribbons under high pressure
Authors: Zhou F. , Zhang X. H. , Lu K.
Published: March 2008

Based on the experimental observation that high pressure will considerably enhance the crystallization onset temperature of amorphous alloys, an attempt was made to consolidate the melt-spun amorphous ribbons into fully densed three-dimensional bulk amorphous materials under high pressures. An amorphous Ni69Cr7Fe2.5Si8B13.5 (at. %) alloy was used as a model material. Under a pressure of 1.5 GPa, the crystallization onset temperature was found to be increased by about 40 K, resulting in a widened supercooled liquid temperature region (about 68 K) beneath the onset of crystallization. The high pressure consolidation of the amorphous ribbons in this temperature region yielded bulk amorphous compacts with the same density of the melt-spun ribbons. This achievement was attributed to the significant homogeneous viscous flow of materials in the supercooled liquid state that could be maintained at higher temperatures during the high pressure compaction.
Preparation of hydroxy double salts exchanged by organic compounds
Authors: Morioka Hiroyuki , Tagaya Hideyuki , Karasu Masa , Kadokawa Jun-ichi , Chiba Koji
Published: March 2008

Hydroxy double salts (HDS's) comprise a class of layered materials that are similar to layered double hydroxides (LDH's) and show a comparable intracrystalline reactivity. Their anion exchange reactions occur with preincorporated anions in the hydroxide layer and with anions bound as gegenions of the positively charged layers, respectively. In this study, nitrate and acetate anions of HDS's were exchanged with anionic monoand di-carboxylic acids, and we confirmed that interlayer spacing of HDS's increased depending on the size of mono- and di-carboxylic acids. Moreover, we have prepared photofunctional materials by exchange reaction with azobenzene-p-carboxylic acid and 4–4′-azobenzenedicarboxylic acid.
Solution processing approaches for solid electrolytes and electrode materials
Authors: Simner Steven P. , Wu Pu-Wei , Dunn Bruce
Published: March 2008

Solution processing methods have been used to prepare a solid electrolyte, copper-doped bismuth vanadate, and several different lithium transition metal oxide cathode materials. Dense thin films of the bismuth vanadate were prepared by pyrolysis of metal organic precursors deposited on various oxide substrates. A high degree of crystal orientation was obtained using single crystal MgO substrates. The Pechini process was used to prepare powders of the different materials and a variety of results were obtained. The bismuth vanadate exhibited a second phase of BiVO4 while LiNiO2 and the LiCoxNi1−xO2 solid solution require further efforts at obtaining the proper phase and stoichiometry. The LiCoO2 system formed readily and exhibited good electrochemical performance.
Synthesis of gold-cadmium selenide co-colloids
Authors: Nayak Rekha , Galsworthy Jane , Dobson Peter , Hutchison John
Published: March 2008

Semiconductor-metal co-colloids of CdSey/Au have been prepared by various synthetic pathways. Their microstructure, including that of Au–CdSe(TOPO) co-colloid in a core-shell structure, has been examined by high resolution transmission electron microscopy (HRTEM) and found to be well defined within the 10 nm size range. The optical absorption spectra of the colloids and of various synthesis stages have been obtained.
Calcium phosphate compound–cellulose fiber composite material prepared in soaking medium at 36.5–60 °C
Authors: Yokogawa Yoshiyuki , Toriyama Motohiro , Kawamoto Yukari , Nishizawa Kaori , Nagata Fukue , Kameyama Tetsuya , Okada Kohji , Okuyama Masahiko
Published: March 2008

Calcium phosphate growth on cellulose fibers phosphorylated in 1.5 × SBF (simulated body fluid) solution at various temperatures from 36.5–60 °C was studied. Cellulose fibers phosphorylated by using urea and H3PO4 and then soaked in saturated Ca(OH)2 solution at ambient temperature were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5 × SBF solution for as little as one day. Soaking in 1.5 × SBF solution at higher temperature produced a thicker layer of calcium phosphate on the fibers, which may be due to the decrease of solubility of calcium phosphate. The specific surface area of the coatings decreased with an increase of soaking temperature and soaking time in 1.5 × SBF solution.