bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hematite Nano Cubes and the Prototypes of Their Self Assembly Investigated Using Tem
Authors: Yu San , Kan Shihai , Zou Guangtian , Peng Xiaogang , Li Dongmei , Sun Haiping , Zhang Xingtong , Xiao Liangzhi , Li Tiejin 
Published: April 2011

AbstractMonodisperse hematite cubes about 30nm in size have been prepared by aging a refluxing acidified aqueous solution of FeCl3 in an open vessel. The as grown nano cubes were determined to be single crystalline hematite in perfect cubic shapes using transmission electron microscope and electron diffraction. The nano cube is one of the equilibrium shapes of hematite, which is resumed to be formed by preferential growth in certain crystallographic directions through the species diffusion in the aqueous solutions.Some self-assembly prototypes have been observed, such as the short range ordered buildup consisting of several brick-like hematite nano cubes and the nano box consisted of square plates of hematite nanocrystals. The drive force for the formation of the above assemblies is assumed to be the unique magnetic feature of the single crystalline hematite nano cubes.The perfect shape and the self-assembly feature give a possibility to fabricate bulk ceramics orderly assembled using hematite nano cubes.
Hydroxyapatite Ceramics From Powders Prepared by Precipitation Method
Authors: Silva Viviane V. , Fernandes Rosana Z. D. 
Published: April 2011

AbstractHydroxyapatite (HA), specifically, calcium hydroxyapatite, is the main inorganic compound of human bone and teeth. The utilization of synthetic powders of this material in dental and medical implants has increased in the recent days.In this paper, synthetic hydroxyapatite powder was prepared by a precipitation method, compacted and sintered at 800, 900, 1000, 1100, 1200 and 1300° C. The powder and its ceramics were analysed by X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. The influence of experimental conditions on the microstructure and densification is discussed.Some measurements of the hydroxyapatite ceramics obtained in this work were compared with those of the hydroxyapatite ceramics produced from a commercial powder. It was shown that calcium hydroxyapatite is probably the only phase present for the precipitated samples sintered below 1100° C.
Corrosion Resistant Coatings for Aluminum by Hydrothermal Film Formation in Alkaline Li-Salt Solutions
Authors: Buchheit R.G. , Martinez M.A. , Cooper C.B. 
Published: April 2011

AbstractNew methods of forming corrosion resistant inorganic coatings on Al and Al alloys are required due to environment and work safety hazards associated with the currently used Cr-based coatings technologies. In this paper we report on certain specific aspects of Al surface film formation that can be exploited to form highly corrosion resistant coatings. The aspects discussed include: formation of hydrotalcite surface films, Li2[Al2 (OH)6]2 CO3nH2O, by exposure to Li-salt solutions, elimination of unwanted Cu compounds that accumulate surface films formed on Cubearing Al alloys, and generation of high corrosion resistance by precipitating transition metal oxides on to alkaline hydrotalcite coated surfaces.
Chemical, Hr-Xrd and Spectroscopic Approaches to Short-Time Dissolution Behavior of Kaolin1tic Soils
Authors: Malengreau N. , Sposito G. 
Published: April 2011

AbstractBatch experiments were conducted at varying proton concentrations on a representative tropical soil in order to investigate its dissolution behavior over a 12h period. The release kinetics of Al, Fe, Si and C were investigated over a 2 to 6 pH range. The pH-dependence exhibited a “point of minimum dissolution” at pH ≈ p.z.n.c. Light scattering measurements on supernatant solutions indicated that colloids were dispersed mainly at pH > p.z.n.c. These results suggested a two-pathway dissolution process, with organic matter playing a role in both pathways. High-resolution X-ray diffraction as well as electron spin resonance and diffuse reflectance spectroscopies, were applied to characterize solid-phase transformations in the course of dissolution. With the exception of quartz, all mineralogical phases (kaolinite, and minor phases such as Fe-, Al- and Ti-oxides) remained unchanged or were slightly affected. A significant loss of quartz (about 10% by mass) was observed after a 12h dissolution at pH 2. Minor phases might have played an important role in stabilizing kaolinite, and dissolved silica may have hindered the dissolution of minor phases.
Issues in the Energetics of Metastable Oxides and Oxyhydroxides
Authors: Navrotsky Alexandra 
Published: April 2011

AbstractIn both low temperature materials synthesis (sol gel processing, chimie douce) and low temperature geochemistry (weathering, geothermal and hydrothermal reactions, diagenesis) metastable and/or poorly crystalline materials are encountered. Despite the lack of equilibrium, energetic considerations play a major role in the formation and transformation of such phases. Recent calorimetric studies on heats of formation of zeolites and related metastable frameworks, on nanophase alpha and gamma alumina, and on manganese oxides and hydroxides are summarized. These studies illustrate the effects of framework topology, cation content, hydration and surface energy on the formation, persistence, and eventual transformation to more stable phase assemblages of these environmentally important materials.
Interaction of Organic Additives With Ceramic Surfaces In Colloidal Slurries
Authors: Sigmund W. M. , Wang L. , Sindel J. , Rotov M. , Aldinger F. 
Published: April 2011

AbstractThree different dispersants, a low molecular weight compound (aminoalkanol), a polymer (polyelectrolyte) and a block-co-polymer (block polyethylenoxide-polyacrylic acid) were investigated with AFM and rheology in an aqueous system in order to elucidate the influence of the size and structure of the molecule on the dispersion stabilization. The AFM studies indicate that the aminoalkanol gives repulsive forces due to electrostatic repulsion only. The polyelectrolyte seems to stabilize the dispersion with both steric and electrostatic repulsive forces. A new compound that was designed for pure steric stabilization in aqueous media a block-co-polymer consisting of a polar anchor block and a stabilizing neutral chain was investigated for its behavior. The AFM measurements show that it is likely that this compound causes repulsion of silicon nitride surfaces due to steric repulsion only. Rheological measurements of aqueous powder slurries show that the adsorption of the organic additives is of great importance. Due to a more silicon dioxide like acidic surface of the investigated Si3N4 - powder the carboxylate anions of the block-co-polymer adsorb badly. Therefore, no sterically repulsive forces can be built up. This then causes an increase in the slurry's viscosity.
Electrode Materials for Ferroelectric Capacitors: Properties of Reactive DC Sputtered IrO2 Thin Films
Authors: Balu Venkatasubramani , Chen Tung-Sheng , Jiang Bo , Kuah Shao-Hong , Lee Jack C. , Chu Peir , Jones Robert E. , Zurcher Peter , Taylor Deborah J. , Gillespie Sherry 
Published: April 2011

AbstractDue to its low resistivity and excellent thermal stability, IrO2 has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. In this work, IrO2 films deposited using reactive DC magnetron sputtering were studied. Film properties such as resistivity, crystallinity and morphology were examined as a function of deposition condition. Optimum process parameters to obtain high quality IrO2 thin films are suggested.
Voltage Shifts and Defect-Dipoles in Ferroelectric Capacitors
Authors: Warren W. L. , Pike G. E. , Dimos D. , Vanheusden K. , Al-Shareef H.N. , Tuttle B. A. , Ramesh R. , Evans J. T. 
Published: April 2011

AbstractWe review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from nearinterfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.
Retentivity Studies on Lead Zirconate Titanate Thin Film Capacitors
Authors: Yoo In K. , Kim Chang J. , Desu Seshu B. 
Published: April 2011

AbstractRetention characteristics of various ferroelectric memory cell structures, based on lead zirconate titanate (PZT) capacitors, were investigated under different test conditions. Test of retentivity without any pre-treatment, revealed very high rates of polarization loss with time for partially polarized PZT capacitors. However, when different structures were subjected to a thermal cycle before retentivity study, they indicated significant polarization loss or polarization reversal in FRAM and MFMIS(metal-ferroelectric-metal-insulatorsemiconductor) structures. This thermal cycle dependent retentivity problem was attribute to pyroelectric charges that are developed during the temperature cycle.For each memory cell structure, the underlying mechanisms for the rapid polarization. loss were discussed. Furthermore, guidelines for improving the memory retention were proposed based on the theoretical interpretation of the phenomena.
Electronic Structure of the Layered Ferroelectric Perovskite SrBi2Ta2O9
Authors: Robertson J , Chen C W , Warren W L 
Published: April 2011

AbstractThe band structure of the Bi layered perovskite SrBi2Ta2O9 (SBT) has been calculated by the tight binding method. We find both the valence and conduction band edges to consist of states primarily derived from the Bi-O layer rather than the perovskite Sr-Ta-O blocks. The valence band maximum arises from 0 p and some Bi s states, while the conduction band minimum consists of Bi p states, with a band gap of 5.1 eV. It is argued that the Bi-O layers largely control the electronic response of SBT while the ferroelectric response originates from the perovskite Sr-Ta-O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for the excellent fatigue properties of SBT.
Preparation and Characterization of (Sr1−xTix)O3 and (Ba1−xSrx)TiO3 Thin Films using ECR Plasma Assisted MOCVD
Authors: No Kwangsoo , Lee Joon Sung , Song Han Wook , Lee Won Jong , Yu Byoung Gon , Jiang Zhong-Tao 
Published: April 2011

AbstractBa(TMHD)2, Sr(TMHD)2 and Ti-isopropoxide were used to fabricate the (SrxTi1 x)O3 and (Ba1 x Srx)TiO3 thin films. The decomposition and degradation characteristics of Ba(TMHD)2 and Sr(TMHD)2 with storage time were analyzed using a differential scanning calorimeter (DSC). The thin films were fabricated on Si(p-type 100) and Pt/SiO2/Si substrates with Ar carrier gas using ECR plasma (or without ECR plasma) assisted MOCVD. Experimental results showed that the ECR oxygen plasma increased the deposition rate, the ratio of Sr/Ti, the dielectric constant and the leakage current density of the film. The dependency of the crystallinity and the electrical properties on the Sr/Ti ratio of films were investigated. However, almost of the films deposited with Ar carrier gas had slightly high dielectric loss and high leakage current density and showed non-uniform compositional depth profiles. NH3 gas was also used to decrease the degradation of the MO-sources. Mass spectra in-situ monitoring of source vapors in ECR-PAMOCVD system were obtained. By introducing NH3 as a carrier gas, a significant improvement was achieved in the volatility and the thermal stability of the precursors, and the vaporization temperatures of the precursors were reduced compared to Ar carrier gas. The uniform compositional depth profile, less hydrogen and carbon content and the good electrical properties of (SrxTi1−x)O3 thin films were obtained with NH3 carrier gas. The (Ba1−xSrx)TiO3 thin film were fabricated to have very fine and uniform microstructure, the dielectric constant of 456, the dielectric loss of 0.0128, the leakage current density of 5.01 × 10−8A/cm2 at 1V and the breakdown field of 3.65MV/cm.
Synthesis of Carbon Nitride Composite Thin Films Prepared by Pulsed Laser Deposition Method
Authors: Kumar Ashok , Inturi R. B. , Ekanayake U. , Chan H. L. , You Q. , Watiuhewa G. , Barnard J. A. 
Published: April 2011

AbstractCarbon nitride/titanium nitride composite coatings have been deposited on Si (100) and 7059 coming glass by in-situ pulsed laser deposition technique. A pulsed laser (λ = 248 nm) has been used to ablate the both pyrolytic graphite and TiN targets. It has been shown that TiN provides a lattice-matched structural template to seed the growth of carbon nitride crystallites (W. D. Sproul et. al., Appl. Phys. Lett. Vol. 67, 203–205; 1995). This paper describes the same approach to grow carbon nitride composite coatings with varying thicknesses of buffer layer and carbon nitride films at different temperatures and pressures. Our preliminary results show the superior mechanical properties (hardness and modulli). The films have been characterized by Xray diffractometer, SEM, FTIR and Raman spectroscopic techniques.
Toughening Mechanisms in Al/Al-SiC Laminated Metal Composites
Authors: Lesuer D. R. , Wadsworth J. , Riddle R. A. , Syn C. K. , Lewandowski J. J. , Hunt W. H. 
Published: April 2011

AbstractThe fracture toughness of laminated metal composites consisting of alternating layers of a metal matrix composite (Al6090/SiC/25p) and a monolithic aluminum alloy (Al5182) has been studied as a function of the volume fraction of the component materials. Finite element simulations of the fracture toughness tests have been used to study the mechanisms of crack growth and extrinsic toughening. The mechanisms responsible for toughening in laminated metal composites are described.
Toughness and Subcritical Crack Growth in Nb/Nb3Al Layered Materials
Authors: Bloyer D. R. , Rao K. T. Venkateswara , Ritchie R. O. 
Published: April 2011

AbstractA brittle intermetallic, Nb3Al, reinforced with a ductile metal, Nb, has been used to investigate the resistance curve and cyclic fatigue behavior of a relatively coarse laminated composite. With this system, the toughness of Nb3Al was found to increase from ∼1 MPa√m to well over 20 MPa√m after several millimeters of stable crack growth; this was attributed to extensive crack bridging and plastic deformation within the Nb layers in the crack wake. Cyclic fatigue-crack growth resistance was also improved in the laminate microstructures compared to pure Nb3Al and Nb-particulate reinforced Nb3Al composites with crack arrester orientations in the laminate providing better fatigue resistance than either the matrix or pure Nb.
Fabrication, Structure and Properties of Aluminum-Aluminide Layered Composites
Authors: Alman D. E. 
Published: April 2011

AbstractThe fabrication of aluminum-aluminide layered composites by reactive bonding of elemental Al and Ni foils was investigated. It was observed that after hot-pressing, thin Ni foils were converted to NiAl. The as-processed Al-NiAl layered structure could be heat-treated to produce an equilibrium Al-Al3Ni layered composite. Tensile tests revealed that composites could be produced that failed in a “tough” manner and were stronger and stiffer than aluminum.
FGMs by Sedimentation
Authors: He Y. , Subramanian V. , Lannutti J. 
Published: April 2011

AbstractSimple sedimentation in organic solvents followed by hot-pressing is used to produce alumina-NiAI functionally graded materials (FGMs). Varying degrees of agglomeration influenced the phase arrangement in the mixed layer(s) producing microstructural variation. We discovered a pronounced structural dependence on NiAl stoichiometry. Slight variations in Al content are known to influence Tdb and these apparently lead to large increases in residual stress. Zirconia - NiA1 FGMs were better able to accorrunodate these levels of residual stress possibly due to accommodation by enhanced tetragonal phase retention. However, these FGMs undergo transformation of the tetragonal phase to the monoclinic fonn, starting from the surface. Finally, variable microstructures result in detectable changes in the stress-strain behavior of alumina-NiAl FGMs.
Finite Element Studies of the Influence of Pile-up on the Analysis of Nanoindentation Data
Authors: Bolshakov A. , Oliver W. C. , Pharr G. M. 
Published: April 2011

AbstractMethods currently used for analyzing nanoindentation load-displacement data give good predictions of the contact area in the case of hard materials, but can underestimate the contact area by as much as 40% for soft materials which do not work harden. This underestimation results from the pile-up which forms around the hardness impression and leads to potentially significant errors in the measurement of hardness and elastic modulus. Finite element simulations of conical indentation for a wide range of elastic-plastic materials are presented which define the conditions under which pile-up is significant and determine the magnitude of the errors in hardness and modulus which may occur if pile-up is ignored. It is shown that the materials in which pile-up is not an important factor can be experimentally identified from the ratio of the final depth after unloading to the depth of the indentation at peak load, a parameter which also correlates with the hardness-to-modulus ratio.
Stress Reduction in PACVD Amorphous Diamond Coatings by Boron Addition
Authors: Wagner V. , Dekempeneer E. H. A. , Geurts J. , IJzendoorn L. J. van , Sporken R. , Caudano R. 
Published: April 2011

AbstractThe applications of super hard coatings of diamond-like carbon (DLC) films are often limited by adhesion problems caused by intrinsic stress in the deposited layer due to the PACVD growth process. One approach to reduce the stress are less optimal process parameters. However, they also affect the desired high hardness of the films. Our approach in this study is to add B2H6 to the gas mixture, which shifts the composition towards another very hard compound (B4C). A sequence of amorphous BxC1-x:H films with a thickness of 0.5μm and a boron content between 0 and 50 at.-% were deposited on silicon substrates using a capacitively coupled r.f PACVD reactor. The tribological film properties and the internal stress were determined by depth-sensing indentation and laser reflection measurements. For an addition of x ≥5 at.-% boron the decrease of the internal film stress is found to be clearly larger than the effect on the hardness value. For boron contents x > 18% the internal stress is reduced by a factor of 5 while the reduction of hardness is only a factor of 2.3. For microscopic structure analysis Raman and infrared spectroscopy are applied. They reveal an increasing hydrogenation of the carbon network. Therefore, the softening is attributed to a boron induced modification to a more polymeric-like material.
Nanoindentation of Soft Films on Hard Substrates:The Importance of Pile-Up
Authors: Tsui T. Y. , Oliver W. C. , Pharr G. M. 
Published: April 2011

AbstractNanoindentation is a common technique for measuring the mechanical properties of thin films. Here, we address the potential measurement errors caused by pile-up when soft films deposited on hard substrates are tested by nanoindentation methods. Pile-up is exacerbated in soft film / hard substrate systems because of the constraint the substrate exerts on plastic deformation of the film. To experimentally examine pile-up effects, aluminum films with thicknesses of 240 and 1700 nm were deposited on hard glass substrates and tested by standard nanoindentation techniques. The aluminum/glass system is interesting because the film and substrate have similar elastic moduli; thus, any unusual behavior in the nanoindentation results may be attributed to differences in the plastic flow characteristics alone. A detailed scanning electron microscopy examination of nanoindentation hardness impressions in the film revealed that common methods for analyzing nanoindentation data underestimate the true contact areas by as much as 80%, which results in overestimations of the hardness and modulus by as much as 80% and 35%, respectively. The sources of these errors and their influence on the measurement of hardness and elastic modulus are discussed, and a simple model for the composite hardness of the film/substrate system is developed. The model could prove useful in measuring the hardness and elastic modulus of soft-film / hard substrate systems when it is not possible to make indentations shallow enough to avoid the substrate influences.
Mechanical Properties of CaF2Single Crystal Substrates Determined from Nanoindentation Techniques
Authors: Aruga A. , Inturi R. B. , Barnard J. A. , Bradt R. C. 
Published: April 2011

AbstractCaF2single crystals are interesting substrate materials for deposition of thin films. Its structure is cubic and it cleaves on {111} planes. CaF2, whose hardness has been reported to be 4 on the Moh's scale, is plastic and soft. In this study, the mechanical properties such as hardness(H) and Young's modulus(E) of single crystal CaF2mineral were measured by using a nanoindenter with a Berkovich indenter normal to (100) and (111) planes. A normal indentation size effect (ISE) in accordance with the traditional power law and the proportional specimen resistance model (PSR) of Li and Bradt [1] was observed. The values of E and H on (100) plane are larger than those on (111) plane and these values on both planes decrease with increase in time during the hold segment. The effect of displacement rate on mechanical properties of (100) and (111) surfaces is also studied.
Effect of Film Thickness and Substrate Surface Treatment on Substrate Deformation: DLC on MgO
Authors: Strojny A. , Lilleodden E. T. , Wang G. , Sivertsen J. V. , Gerberich W. W. 
Published: April 2011

AbstractDiamond-Like Carbon films with thicknesses controlled in the 10 to 100 nm range were sputter-deposited on single crystals of MgO. The substrates were prepared with varying roughness from 5 to 50 nm and varying surface dislocation densities from 100 to 2000 disl./μ2. Mechanical properties of the film and film-substrate interactions were investigated with an atomic force microscope retrofitted with a diamond indenter.The load bearing capacity of the substrate increased with increasing film thickness. As the indenter approached the film-substrate interface, load excursions occurred for the thinner films. No excursion was found for the thick film. Load excursions may be attributed to dislocations nucleating at the interface and/or film delamination.