bluuebunny/crossref_metadata_2025_split huggingface dataset:
Size-dependence of Magnetic Properties of Bismuth Ferrite Nanopowders
Authors: Li J. , He H. , Lü F. , Duan Y. , Song D. 
Published: April 2011

ABSTRACTA series of BiFeO3 nanopowders were prepared by the sol-gel process. X-ray diffraction analysis shows that their rhombohedral crystal symmetry remains unchanged. However, as the particle size decreases, the edge length of the unit cell increases markedly and the angle between the edges deviates increasingly from 60°. Magnetic measurements show obvious weak ferromagnetism. The magnetization and magnetic susceptibility increase with decreasing particle size. Mössbauer studies reveal that the spin canting angles in the smaller particles are bigger and have a wider distribution. The magnetic structure in these particles is a complicated uncompensated antiferromagnetic spin arrangement.
Refractive Index Engineering of Nano-Polymer Composites
Authors: Kambe Nobuyuki , Kumar Sujeet , Chiruvolu Shiv , Chaloner-Gill Benjamin , Blum Yigal D. , Brent MacQueen D. , Faris Gregory W. 
Published: April 2011

ABSTRACTHighly homogeneous nanoparticles-polymer composite materials are being developed to meet high demands of photonic materials covering a broad range of the refractive index. Refractive index engineering can be achieved by controlling loading level of metal-oxide nanoparticles within an organic host material. The uniformity and small size of nanoparticles are critical to maintain a low level of light scattering, particularly in the visible to infrared regions. First observations of index variation for these nanoparticle-polymer composites to our knowledge are presented.
Intracellular uptake of poly(ethylene glycol) and folic acid modified magnetite nanoparticles
Authors: Zhang Yong , Kohler Nathan , Zhang Miqin 
Published: April 2011

ABSTRACTSuperparamagnetic magnetite nanoparticles were surface-modified with poly (ethylene glycol) (PEG) or folic acid, to resist the protein adsorption and avoid their recognition by macrophage cells, and to improve their cell internalization and ability to target specific cells. The nanoparticle uptake into human osteosarcoma cells, MG63, was visualized using both fluorescence and confocal microscopy, and quantified using inductively coupled plasma emission spectroscopy (ICP) measurement. Fluorescence and confocal microscopy results showed that the nanoparticles were internalized into the cells after the cells were cultured for 48h in the medium containing the nanoparticles modified with PEG or folic acid. ICP measurements indicated that both the PEG and folic acid modification increased the amount of the nanoparticle uptake into the cells, in comparison with that of unmodified nanoparticles.
Modeling the Effects of Dislocation-Grain Boundary Interactions in Polycrystal Plasticity: Identification and Characterization of Unit Mechanisms
Authors: de Koning M. , Miller R. , Bulatov V.V. , Abraham F. 
Published: April 2011

ABSTRACTIn this paper we focus on one of the key issues in polycrystalline plasticity: the unit mechanisms involving the interactions between dislocations and grain boundaries (GB). Using a combination of large-scale molecular dynamics simulations based on an embedded atom potential and an analysis in terms of the line-tension model we identify and characterize the geometrical parameters that govern the occurrence of slip transmission, absorption, blockage, etc. in dislocation-GB interactions. The results provide a guideline for the development of quantitative micro-constitutive equations for dislocation-GB interactions to be used in meso-scale simulations of polycrystal plasticity.
Ab-initio modelling of atomic and molecular Hydrogen adsorption in graphite
Authors: Letardi Sara , Celino Massimo , Cleri Fabrizio , Rosato Vittorio , Volpe Manuela 
Published: April 2011

ABSTRACTAb-initio electronic structure calculations have been used to evaluate the binding energy of atomic and molecular hydrogen to graphite lattice defects. Results show that graphite defects (Stone- Wales, vacancy) are preferred binding sites with respect to regular lattice sites. We find that molecular hydrogen can be physisorbed between the graphite planes, but cannot diffuse across a graphitic plane.
Development of an Ab-initio Model of the Lattice Thermal Conductivity in Semiconductor Thin Films and Nanowires
Authors: Zou Jie , Balandin Alexander 
Published: April 2011

ABSTRACTA model for calculating the lattice thermal conductivity in semiconductor thin films and nanowires is developed. It is based on the solution of phonon Boltzmann equation and takes into account phonon dispersion modification due to confinement effects and non-equilibrium phonon redistribution. Phonon spatial confinement at the structure boundaries leads to modification of the acoustic phonon dispersion and corresponding drop in the mode-averaged group velocity. Scattering from rough boundaries and interfaces introduces a change in the non-equilibrium phonon distribution as compared to bulk. These effects lead to a reduction in the in-plane lattice thermal conductivity in both thin films and nanowires. The predicted values for the lattice thermal conductivity and their temperature and interface roughness dependence are in good agreement with available experimental data.
High Resolution X-Ray Characterization of Tl-2212 Superconducting Thin Films
Authors: Daniels M.J. , Bilello J.C. , Rek Z.U. , Hyland D. , Dew-Hughes D. , Grovenor C.R.M. 
Published: April 2011

AbstractThallium based high temperature superconducting films were formed on LaAlO3 (LAO) substrates by thalliation of sputtered amorphous precursor films by reaction with Tl2O. High resolution strain measurements and diffraction topographic imaging studies were performed using the synchrotron at Stanford Synchrotron Radiation Laboratory (SSRL). From these results, we have reached preliminary conclusions regarding the effect of film strain and substrate twinning on the superconducting properties of Tl-2212 films on LAO substrates. High- resolution strain measurements showed a correlation between film strain and microwave properties. The relative strain in samples in which Q>105 at 5.55 GHz (at 50 K) was approximately 30% lower than that in samples in which Q<104 when tested under the same conditions. Examination of samples where Q<104 at 5.55 GHz (at 50 K) by SEM also indicated microstructure defects that are typical in films with a high level of residual stress. White beam x-ray diffraction topographic analysis was used to quantitatively measure the degree of twinning in the substrate. The results will discuss the relationship between the measured Q values of the microwave cavity and the strain state, microstructure and defect morphology in the superconducting film/substrate couple.
Energy-Tunable X-Ray Diffraction in Polycrystalline Materials: a Look at Microstructure in Seashells
Authors: Zolotoyabko Emil , Quintana John P. 
Published: April 2011

AbstractWe developed a depth-sensitive x-ray diffraction technique in which diffraction profiles are measured at x-ray energies that are varied by small steps. The method is intended for synchrotron beam lines and provides non-destructive mapping of structural characteristics in inhomogeneous polycrystalline materials. Depth resolution is achieved due to an energy dependence of the x-ray penetration length. Application of this technique to seashells allowed us to extract spatial distributions of preferred orientation and strain components, which revealed pronounced variations of the shell microstructure in three dimensions. The results shed light on “engineering solutions” by mollusk. The developed technique can be used to characterize various laminated structures and composite materials.
Mapping the Distribution of Corrosion Products in Cement Exposed to Sulfate using Energy Dispersive X-ray Diffraction
Authors: Wilkinson Angus P. , Lind Cora , Stock Stuart R. , Kurtis Kimberly E. , Naik Nikhila , Haeffner Dean R. , Lee Peter L. 
Published: April 2011

AbstractThe use of energy dispersive X-ray diffraction (EDXRD) to produce 1 D maps of the phases present inside both an alumina-aluminum test specimen and a 1.0 cm diameter cylinder of type I portland cement paste is discussed. The surface of the cement paste sample was found to be rich in calcium carbonate and deficient in portlandite relative to the bulk. After 7 days exposure to 1000 ppm Na2SO4 there was no evidence for the formation of a surface layer rich in crystalline sulfate containing phases. EDXRD appears to be a powerful tool for the study of sulfate attack on portland cements.
Xanes and Exafs Analysis of Ball-Milled Fe-Ni
Authors: Schilling P.J. , Tittsworth R.C. , Palshin V. , Xu J. , Ma E. , He J.-H. 
Published: April 2011

AbstractEXAFS and XANES analysis have been applied in a study of ball-milled nano-crystalline iron-nickel alloys prepared with overall compositions spanning the two-phase region. EXAFS analysis was used to determine bond distances for like and unlike atom pairs in single phase face-centered cubic Fe-Ni alloys, demonstrating the presence of bond dilation for unlike neighbors. Using XANES analysis, the compositions of the two coexisting solid solutions were determined to characterize the ball-milled two-phase region. The compositions of the coexisting face-centered and body-centered cubic phases were found to be consistent with the overall composition of the mixture. The results obtained for the negative heat-of-mixing Fe-Ni system were used for comparison to the positive heat-of-mixing Fe-Cu system.
Influence of Spontaneous and Piezoelectric Polarizations on the Lattice Dynamics of III-Nitride Structures
Authors: Gleize Jérôme , Frandon Jean , Renucci Marie A. , Bechstedt Friedhelm 
Published: April 2011

ABSTRACTThe influence of pyroelectric and piezoelectric polarizations on the lattice dynamics of strained III-nitride based structures is investigated within a macroscopic framework. New relationships between stress and strain are derived, which take into account the piezoelectric fields, which appear in the strained III-nitride layers. Consequently, the strained phonon frequencies in such systems differ from those calculated within the elasticity theory framework. In the case of strained, free-standing GaN/AlN superlattices grown along the [0001] axis, the difference of the spontaneous polarizations of GaN and AlN also contributes to the change in the effective strain along the growth direction. The corresponding shift of the zone center phonon frequencies of GaN and AlN might be negligible or significant, depending on the value of the ratio of the GaN and AlN layer thickness.
Preparation of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
Authors: Lu Hai , Schaff William J. , Hwang Jeonghyun , Eastman Lester F. 
Published: April 2011

ABSTRACTInN is an important III-V compound semiconductor with many potential microelectronic and optoelectronic applications. In this study, we prepared epitaxial InN on (0001) sapphire with an AlN buffer layer by molecular beam epitaxy, and its variation, migration enhanced epitaxy. A series of samples were grown with different substrate temperatures ranging from 360°C to 590°C. The optimum growth temperature for InN was found to be between 450°C and 500°C. We also found that thicker AlN buffer layers result in the best InN quality. With increasing thickness of an AlN buffer layer, the Hall electron mobility of InN increases while the carrier concentration decreases. The surface morphology is also improved this way. Hall mobility greater than 800 cm2/Vs with carrier concentration 2-3×1018 cm−3 at room temperature can be routinely obtained for ∼0.1[.proportional]m thick InN films. Various InN-based heterostructures with AlInN or AlN barrier were fabricated. X-ray diffraction study clearly shows the barrier and InN layers. A 2-dimensional electron gas resulting from polarization induced electrons was observed in capacitance-voltage measurements. Some results on Mg doping of InN will be discussed as well.
MOCVD growth of GaN on flat and misoriented A-plane sapphire substrates
Authors: Someya T. , Hoshino K. , Arakawa Y. 
Published: April 2011

ABSTRACTWe have grown high-quality GaN with smooth surface morphology on vicinal a-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD). The misorientation angles of vicinal a-plane sapphire substrates were changed systematically from 0° to 0.75°. Surface morphology and crystalline qualities are found to be very sensitive to misorientation angles of a-plane sapphire substrates and the misorientation angle was optimized to be 0.25°.
Ionization Energy and Electron Affinity of Clean and Oxidized AlxGa1−xN(0001) Surfaces
Authors: Nienhaus H. , Schneider M. , Grabowski S.P. , Mönch W. , Dimitrov R. , Ambacher O. , Stutzmann M. 
Published: April 2011

ABSTRACTIonization energies and electron affinities of clean AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy over the whole composition range. The samples were cleaned with cycles of N+-ion sputtering and annealing partly within a Ga atom flux. The ionization energy is measured as 6.5 eV and is almost independent of the aluminum content in good agreement with the general chemical trend. The electron affinity decreases linearly with composition from 3.1 eV for GaN to 0.25 eV for AlN. No evidence for negative electron affinity at AlN(0001) surfaces was found. Adsorption of oxygen at room temperature leads to a significant increase of the ionization energy and electron affinity. With AlN(0001) surfaces, an oxygen uptake of 0.6 monolayers is observed after exposures of 108 Langmuirs and the ionization energy increases by approximately 2 eV.
Extraction of Trap Characteristics from Excess Noise in GaN Devices
Authors: Balandin Alexander A. 
Published: April 2011

ABSTRACTCharacteristics of traps are extracted from excess noise spectra of the doped-and undoped-channel GaN/AlGaN heterostructure field-effect transistors. The two types of excess noise that have been analyzed include flicker, e.g. 1/fγ noise, and generation-recombination noise. The average trap density determined for the undoped and doped devices is 1.1 × 1016 cm−3 and 7.1 × 1017 cm−3, respectively. Two distinct trap time constants τ determined for doped devices were 16 μsec and 0.1 msec. The trap characteristics obtained from the analysis of the excess noise spectra are in agreement with data provided by other techniques.
Pt Schottky contacts on Ga- and N-face surfaces of free-standing GaN
Authors: Karrer U. , Miskys C.R. , Ambacher O. , Stutzmann M. 
Published: April 2011

ABSTRACTThick GaN films, grown by hydride vapor phase epitaxy (HVPE), were separated from their sapphire substrate with a laser-induced lift-off process. After cleaning and polishing, these films offer the most direct way to investigate and compare the influence of crystal polarity on the electronic properties of Ga-face and N-face surfaces, respectively. Different barrier heights for Pt Schottky diodes evaporated onto Ga- and N-face GaN are determined from the dependence of the effective barrier height versus ideality factor by I-V measurements to 1.15 eV and 0.80 eV, respectively. The charge neutrality condition at the surface is modified by the spontaneous polarization due to the polarization induced bound sheet charge. This effect has to be included in the electronegativity concept of metal induced gap states (MIGS) and can also be illustrated by different band bending of the conduction and valence band, inferred from the self-consistent solution of the Schrödinger-Poisson equation. Furthermore, temperature dependent I-V characteristics are compared to simulated behavior of Schottky diodes, exhibiting excellent agreement in forward direction, but showing deviations in the reverse current.
Effects of hydrothermal aging on the dielectric properties of epoxy molding compounds
Authors: Gonon Patrice , Sylvestre Alain , Teysseyre Jérôme , Prior Christophe 
Published: April 2011

ABSTRACTWe studied the influence of hydrothermal aging on the dielectric properties of epoxy molding compounds used for integrated circuits packaging. Samples were subjected to two different aging (JEDEC 1 and JEDEC 3 procedures, followed by a thermal stress at 240°C for a few minutes). Resistance to aging was studied as a function of crosslinking density. Water uptake increases with crosslinking. Aging leads to a reduction in the dielectric constant and to an increase in the loss factor. Post-mold curing is found to slightly enhance the resistance against hydrothermal aging.
Microthermomechanical Analysis of Lead-Free SN-3.9AG-0.6CU Alloys; Part I : Viscoplastic Constitutive Properties
Authors: Haswell Peter , Dasgupta Abhijit 
Published: April 2011

ABSTRACTThis is part I of a two-part paper on the mechanical behavior of lead-free solders. The constitutive properties of Sn3.9Ag0.6Cu lead-free alloy are presented and compared against baseline data from eutectic Sn63Pb37 solder. Monotonic, displacement-controlled and load-controlled tests are performed over various temperatures, strain rates and stresses using the thermo-mechanical-microstructural (TMM) test system. It is shown that the lead-free alloy exhibits creep strain rates that are from one to five orders of magnitude lower than the eutectic SnPb alloy, depending on the stress level and the homologous temperature.
Novel Materials and Joinings for Power Electronics Module Packaging
Authors: Wolfgang Eckhard , Mitic Gerhard , Lefranc Guy , Schwarzbauer Herbert 
Published: April 2011

ABSTRACTPower electronics modules consist of several layers of different materials according to their function. A base plate is necessary for mounting the module to the cooling unit, an insulating layer provides protection against high voltages, the power semiconductor chips with metal electrodes on both sides are used for switching currents, and finally passivation layers have to protect the chips against high electric fields and environmental impacts. The combination of semiconductors, metals and insulators and their different coefficients of thermal expansion leads to stresses and fatigue during temperature excursions. Some major trends require the use of new materials and joinings: higher voltages (up to 6.5 kV), higher currents (above 2000 A), and higher operating temperatures, e.g. in automotive applications (up to 200°C). To reduce the influence of the thermal mismatch between the base plate and the insulator (Alumina, AlN), metal matrix composites such as AlSiC have been used for several years in power modules. To minimize the partial discharge of the ceramics substrate, an amorphous coating (a-Si:H) was tested at high voltages up to 15 kV. A low-temperature joining technique based on silver powder processed under high pressure and at low temperatures works well at higher temperatures. Finally a concept for securing reliability is discussed.
Working with Industry and a Professional Organization to Offer Students a National Certification
Authors: Schemmel John J. , Griffith Frances , Glover Earl 
Published: April 2011

ABSTRACTAs part of their required curriculum, undergraduate students in the Civil Engineering Department at the University of Arkansas take a course that studies the materials commonly used in the construction of buildings, bridges, highways, and the like. This course is titled CVEG 2113 - Structural Materials. A focal point for this course is the examination of concrete, its production, engineering properties, and uses in structures.Since concrete can be delivered to a job site while still in a workable form, it is often necessary to perform a series of tests on the “fresh” material prior to its placement in a structure. Prior to the mid-1980's results from the field testing of concrete were often dubious. In an effort to improve the quality of testing, and thus the reliability and accuracy of the test data, organizations such as the American Concrete Institute (ACI) initiated programs to certify field testing technicians. With the students in CVEG 2113 already receiving instruction relative to testing, as well as having the opportunity to perform the applicable tests in the laboratory, it quickly became evident that ACI certification could, and should, be incorporated into the course syllabus. Being certified adds a tangible skill to a student's resume thus making the student more marketable for summer and long-term employment. The concrete industry benefits from an increased pool of highly qualified engineers. The Department of Civil Engineering benefits from an enhanced reputation from the perspective of both the students and industry.
The Materials World Module Series and the Polymer Module: A Design-Oriented Approach to Teach Scientific Concepts to Grades 9-12 Students through Materials Science
Authors: Nguyen SonBinh T. , Cocson Jennifer K. , Colby Carol L. , Chang Robert P. H. , Miller Keith E. 
Published: April 2011

ABSTRACTThe Materials World Modules (MWM), funded by the National Science Foundation, is a series of nine short texts that introduce science and scientific concepts to high school students through guided investigations of the materials that surrounds us in the modern world. Designed to be flexible, these modules can be incorporated into a high school science curriculum as a learning-by-inquiry addition to the main science texts. Depending on the time that the teacher has, each module can be covered in 8 to 15 class periods. Using an inquiry method of learning, the modules prompt the students to generate questions about a subject and find experimental approaches which will lead them to the answers. The modules encourage the students to learn by carrying out simple experiments using readily available materials. The Polymers Module of the MWM series aims at introducing the concepts of polymer chemistry and polymeric materials to an audience that has had some exposure to general chemistry. It asks the students to investigate their surroundings to find polymer-based objects and to infer the properties of those objects from knowing the structures of the monomeric building blocks. It introduces the relation between polymer properties and structure and that between polymer properties and molecular weight by suggesting experiments that students can do with poly(vinyl alcohol) and poly(vinyl acetate) films. Finally, it encourages the students to use what they have learned to design simple devices using polymeric materials. An example of such a device is a humidity sensor that is fabricated from thin polymer films.
Integration Processes and Properties of Pt/Pb5Ge3O11/(Zr, Hf)O2/Si One Transistor Memory Devices
Authors: Li Tingkai , Hsu Sheng Teng , Ulrich Bruce , Stecker Lisa 
Published: April 2011

AbstractThe basic mechanism for one transistor memory device has been studied. Ferroelectric material, Pb5Ge3O11 (PGO) was selected for MFOS (M: Metal, F: Ferroelectrics, O: oxide, S: silicon) memory transistor fabrication. Processing of one-transistor memory devices dealt with the following issues: decomposition of ferroelectric materials, the etching damage of ferroelectric materials, the forming gas annealing damage of ferroelectric materials, the selective deposition of ferroelectric materials, the alignment for device making processes. The integration processes for one transistor memory device have been optimized to reduce process-induced damages. The gate dielectric material is (Zr, Hf)O2. Extremely high c-axis oriented Pb5Ge3O11 thin films were successfully deposited on high k gate oxide. Memory transistors having 0.6, 3 and 10μm channel length and 10 μm channel width have been fabricated. The memory windows are around 1 - 2V. The memory windows are almost saturated from operation voltage of 4V. After programming at -5V (on “off” state), the drain current (ID) at VD of 1V and VG of 2.5 V is about 1.15 ×10−10A. After programming at 5 V (on “on” state) the drain current (ID) at VD of 1V and VG of 2.5 V is measured about 6.4 ×10−8 A, which was 2.5 order higher than that of “off” state.