bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray Magnetic Linear Dichroism of Fe-Ni Alloys on Cu(111)
Authors: Johnson T.F. , Chiang S. , Sato Y. , Arena D.A. , Morton S.A. , Hochstrasser M. , Tobin J.G. , Shine J.D. , Giacomo J.A. , Thayer G.E. , Land D.P. , Zhu X.D.
Published: April 2011

We have prepared FexNi1−x multilayers on Cu(111) in order to learn how to control the structure and magnetism of these thin alloy films, which are relevant to the giant magnetoresistance (GMR) effect used in magnetic disk drive heads. Using the Spectromicroscopy Facility (7.0.1.2) on Undulator Beamline 7.0 at the Advanced Light Source, we have measured X-ray magnetic linear dichroism (XMLD) signals from both Fe and Ni 3p lines for fourteen different thin Ni-Fe alloy films on Cu(111), with Fe concentration ranging from 9% to 84% and for a variety of film thicknesses. The Curie temperature for all of these samples was in the range 200K to 500K. For many of these films, the Curie temperature was considerably lower than was previously seen for similar films deposited on Cu(100). For a particular Fe concentration x, the Curie temperature increases with alloy film thickness. For a specific film thickness, the Curie temperature has a maximum near x≍0.4.
Effect of scattering noise on the data fidelity of holograms recorded in photorefractive crystals
Authors: Qin Mingyan , Tao Shiquan , Liu Guoqing , Ding Xiaohong , Wang Dayong
Published: April 2011

In this paper a method is proposed to investigate how the scattering noise of photorefractive crystals influences the quality of an input data page in holographic storage. By illuminating the crystal under investigation with an intense coherent light beam, and measuring the signal-to-noise ratio (SNR) of an image formed through the crystal before and after the exposure, the loss of SNR provides a good assessment for the suitability of the crystal for data storage. A variety of doped lithium niobate crystals were investigated. The results show that the intensity of fanning light increases with increase of the doping concentration, but there is no strict correlation between the fanning strength and the fidelity degradation. Owing to the low noise and high data fidelity, iron-and- zinc co-doped lithium niobate crystal is a potential material for high-density holographic data storage.
Synthesis of Ultrathin Ta-C Films by Twist-Filtered Cathodic Arc Carbon Plasmas
Authors: Anders André , Kulkarni Ashok V.
Published: April 2011

The application of cathodic-arc-deposited films has been very slow due to the infamous macroparticle problem. We report about the application of the open Twist Filter as the key component to an advanced filtered cathodic arc system. Ultrathin tetrahedral amorphous carbon (ta-C) films have been deposited on 6 inch wafers. Film propertieshave been investigated with respect to application in the magnetic data storage industry. Films can be deposited in a reproducible manner where film thickness control relies on arc pulse counting once deposition rates have been calibrated. Films of 3 nm thickness have been deposited that passed acid and Battelle corrosion tests. Monte Carlo Simulation of energetic carbon deposition shows the formation of an intermixed transition layer of about 1 nm. The simulation indicates that because the displacement energy of carbon isnot smaller than of magnetic materials, films thinner than 2 nm are either not high in sp3 content or represent a carbidic phase.
Elastic Constants of Nanometer Thick Diamond-like Carbon Films
Authors: Beghi Marco G. , Bottani Carlo E. , LiBassi Andrea , Pastorelli Rosanna , Tanner Brian K. , Ferrari Andrea C. , Robertson John
Published: April 2011

Carbon films of thickness down to 2 nanometers are necessary to achieve a storage density of 100 Gbit/in2 in magnetic hard disks. Reliable methods to measure the properties of these ultrathin films still have to be developed. We show for the first time that combining Surface Brillouin Scattering (SBS) and X-ray reflectivity measurements the elastic constants of such films can be obtained. Tetrahedral amorphous carbon films were deposited on silicon, by an S bend filtered cathodic vacuum arc, which provides a continuous coverage on large areas free of macroparticles. Films of thickness down to 2 nm and density of ∼3 g/cm3 were produced and characterized. The dispersion relations of surface acoustic waves are measured by SBS for films of different thickness and for the bare substrate. Waves can be described by a continuum elastic model. Fitting of the dispersion relations, computed for given film properties, to the measured dispersion relations allows the derivation of the elastic constants. Fora 8 nm thick film we find a Young's modulus E around 400 GPa, with a shear modulus G lying in the 130 – 210 GPa interval. For a 4.5 nm thick film, E is around 240 GPa, with G lying in the 70 – 130 GPa interval. Results for even thinner films become highly sensitive to the precision of the substrate properties, and indicate that the above values are lower bounds. We thus show that we can grow and characterize nanometer size tetrahedral amorphous carbon films, which maintain their density and mechanical properties down to the nm range.
Comparison of CPM, PDS and Optical Transmittance of Amorphous Carbon Nitride Films Made by a Nitrogen Radical Sputter Method
Authors: Katsuno Takashi , Nitta Shoji , Habuchi Hitoe
Published: April 2011

Amorphous carbon nitride films a-CNX, deposited in our laboratory by a radical sputter method, show high photosensitivity PS, where PS is the ratio of photoconductivity sP and dark-electrical conductivity sd. A-CNX made a layer-by-layer method, LLa-CNX, has the highest photosensitivity in our various preparation conditions. The photoconductivity in a-CNX and LLa-CNX shows dependence on photon energy in the range 2 eV to 6.2 eV. The constant photocurrent method (CPM), photothermal deflection spectroscopy (PDS) and optical transmittance spectra are used to obtain the information in the optical energy band gap and defect states. A-CNX and LLa-CNX are good photoconductors especially at energy higher than 3 eV. Therefore it is not difficult to obtain CPM spectra in the high photon energy region. CPM spectra are obtained by dc- and ac- measurements. The value of the absorption coefficient a spectra obtained by dc-CPM is larger than that of ac-CPM, which increases with increasing frequency of the measurement. In this paper, CPM data is used to discuss a model of density of states (DOS) of a-CNX by comparison with PDS and optical transmittance spectra.
Nanodevice fabrication on hydrogenated diamond surface using atomic force microscope
Authors: Tachiki Minoru , Fukuda Tohru , Seo Hokuto , Sugata Kenta , Banno Tokishige , Umezawa Hitoshi , Kawarada Hiroshi
Published: April 2011

Nanofabrication on a hydrogen-terminated diamond surface is performed usingan atomic force microscope (AFM) anodization. Locally insulated areas less than 30 nm aresuccessfully obtained. Side-gated field effect transistors (FETs) are fabricated using the local anodization, and they operate successfully. Single hole transistors composed ofone side-gated FET and two tunneling junctions are also fabricated and operate at liquid nitrogen temperature (77 K).
Designability of Graphitic Cones
Authors: Treacy M. M. J. , Kilian J.
Published: April 2011

We show that, with topologically flexible seeds which are allowed to explore different growth modes, graphitic cones are inherently more “designable” than flat graphitic disks. The designability of a structure is the number of seed topologies encoding that structure.

We illustrate designability with a simple model, where graphite grows onto Cn (5≤n≤30) ring seeds. For a wide range of ring sizes, cones are the most likely topological outcome. Results from the model agree well with data from special cone-rich carbon black samples.

The concept of designability allows entropy to be incorporated into the “pentagon road” model of the formation of curved graphitic structures.
Nano-Sized [60]Fullerene-Cyclodextrin Molecules
Authors: Park Jeong-Seo , Kang Han-Chang , Geckeler Kurt E.
Published: April 2011

As [60]fullerene is a very hydrophobic macromolecule, there have been a number of attempts to make it more hydrophilic for biomedical applications. By attaching hydrophilic moieties such as poly(oxyethylene)(POE) chains and cyclodextrin molecules to [60]fullerene, novel water-soluble and biocompatible materials have been successfully prepared [1,2].

The synthesis of novel macrocyclic fullerene conjugates which are water-soluble is reported. The telechelic fullerene derivatives have been prepared via addition reaction of POE-based arms with covalently bonded β-cyclodextrin (CD) to [60]fullerene. To this end, a mono-tosylated CD derivative has been prepared in pyridine and then reacted with an amino-functional POE in the presence of triethylamine. The subsequent reaction of [60]fullerene with the hydrophilic POE-conjugated CD-derivative yielded the macrofullerene after separation and purification procedures.

The macrocyclic [60]fullerene derivatives obtained were soluble in water and characterized by UV-VIS and FT-IR spectroscopy as well as light scattering measurements and thermogravimetric analysis.
Ab Initio Study of Si Doped Carbon Nanotubes: Electronic and Structural Properties
Authors: Fazzio A. , Baierle R. J. , Fagan Solange B. , Mota Ronaldo , da Silva Antônio J. R.
Published: April 2011

We report the electronic and structural properties of silicon doped carbon nanotubes using first principles calculations based on the density-functional theory. In the doped metallic nanotube a resonant state appears about 0.7 eV above the Fermi level and for the semiconductor tube the Si introduces an empty level at approximately 0.6 eV above the top of the valence band.
Surface Patterns by Solvent Evaporation of Colloidal Zeolite Suspension
Authors: Wang Huanting , Wang Zhengbao , Huang Limin , Mitra Anupam , Yan Yushan
Published: April 2011

Surface patterns of porous zeolite structures such as knotted-rope web and wrinkled honeycomb were obtained by dynamic self-assembly of zeolite nanoparticles during solvent evaporation of colloidal zeolite suspension. The study shows that extra ethanol in zeolite synthesis solution is crucial for pattern formation. The addition of ethanol helps produce zeolite nanoparticles with a specific range of particle size during the hydrothermal synthesis. It also provides uniform dynamic driving force for pattern formation during its preferential evaporation. In addition, surface patterns vary with suspension compositions. The patterned zeolite structures have a well-defined bimodal pore size distribution (i.e., 0.55 nm and 2.6 nm) with high BET surface area of 680∼750m2&/g.
A Novel Low Temperature Synthesis Method for Semiconductor Nanowires
Authors: Sharma Shashank , Sunkara Mahendra K. , Miranda Raul , Lian Guoda , Dickey Elizabeth C.
Published: April 2011

We present a novel synthesis technique to grow bulk quantities of semiconductor nanowires at temperatures less than 500 °C. Gallium is used as the liquid medium in a mechanism similar to vapor-liquid-solid (VLS). We demonstrated this low temperature technique with silicon and carbon nanowires. Gallium exhibits extremely low solubility for several elemental semiconductors. This property enables nucleation and growth of nanometer scale wires from large sized gallium droplets (>1 μm) eliminating the need for creation of quantum sized metal droplets.
Synthesis of Silicon Nano-Dendrites
Authors: Sinha Saion , Gao Bo , Zhou Otto
Published: April 2011

Recent interests on the science at nanometer-scale, have led to successful synthesis of a growing number of nanostructures such as zero-dimension semiconductor quantum dots [1] and C60 fullerene [2] and one-dimensional carbon nanotubes [3], metallic nanowires [4] and inorganic nanorods [5]. More complex structures/junctions beyond simple dots and lines that are essential for eventual molecular electronic applications, however, have not been realized via non-lithographic methods. Here we report the synthesis of a new branched silicon nanostructure which we call Silicon Nano-Dendrite (SiND) by Laser ablation.
Eu3+-Doped Y2O3-SiO2 Nanocomposite Obtained by a Sol-Gel Method
Authors: Cannas Carla , Casu Mariano , Licheri Roberta , Musinu Anna , Piccaluga Giorgio , Speghini Adolfo , Bettinelli Marco
Published: April 2011

A Y2O3-SiO2 nanocomposite doped with Eu3+ was obtained by a sol-gel method and characterized by X-ray diffraction, IR, 29Si NMR and laser-excited luminescence spectroscopy. It was found that small (2-3 nm) yttria nanoparticles are homogeneously dispersed in, and interacting with, the amorphous silica matrix. Luminescence spectroscopy indicates that the Eu3+ ion is preferentially located inside or at the surface of highly disordered Y2O3 nanoparticles. These luminescent nanocomposites form a class of materials which could find applications in the field of phosphors.
Ultrasound-Enhanced Spray Drying of Polymer Micro-emulsions for Nanoparticles Synthesis
Authors: Tsai Shirley C. , Chen C. Y. , Song Y. L. , Tsai C. S. , Tsai H. S. , Chiu W. Y.
Published: April 2011

In this paper we report the experimental results that polymer micro-emulsions (up to 10 wt%) behave like Newtonian liquids in ultrasound-modulated two-fluid (UMTF) atomization. Specifically, the emulsion drops generated are much smaller and more narrowly sized than those generated in conventional ultrasonic atomization (without air). After spray drying, the PMMA emulsion drops yield uniform nanoparticles that were originally dispersed in the micro-emulsion. Contrary to the conventional view that viscoelastic liquids are more difficult to atomize than Newtonian liquids, we found that ultrasound enhanced atomization of viscoelastic liquids such as gel-forming xanthan gum solutions. Under similar aerodynamic conditions using UMTF atomization at 54 kHz, 40-μm-diameter uniform drops were obtained for Xan solutions, but not for Newtonian aqueous glycerol of same viscosity.
Magnetic Properties of Co Nanoparticles in an AlMCM41 Mesoporous Host
Authors: Jung Jin-Seung , Kim Jun-Yong , Chae Weon-Sik , Kim Yong-Rok , Jun Jong-Ho , Malkinski Leszek , Zhou Weilie , Kumbhar Amar , Viciu Marilena L. , Wiley John B. , O'Connor Charles J.
Published: April 2011

Ultrafine cobalt particles in AlMCM41 silica tubes have been synthesized by ion exchange and the reduction with sodium borohydride. The role of this stable host matrix of AlMCM41 silica is to prevent agglomeration of the magnetic particles attached to the walls of AlMCM41 silica pores. The size of the host pores naturally limits the particle dimensions and thus improves their size distribution. Both magnetic susceptibility measurements and transmission electron microscopy (TEM) show a narrow distribution size of the nanoparticles. Well controlled insertion of the magnetic material to the host channel excludes formation of bulk particles outside the host material grains, which was confirmed by the TEM studies. X-ray diffraction data did not show peaks corresponding to a crystalline cobalt, but this maybe due to small size of particles and their relatively small volume fraction. The content of Co in the AlMCM41 host was measured using both magnetic measurements and elemental analysis.
Applications of ZnS:Mn2+ nanocrystals
Authors: Suyver J. F. , Meijerink A. , Kelly J. J.
Published: April 2011

Nonstoichiometric precursor-ratios for the synthesis of ZnS:Mn2+ are discussed and the significant influence on the luminescence features and crystal size is explained. From the temperature quenching of the ZnS photoluminescence a luminescence excitation model is proposed. Measurements of the photoelectrochemical properties of nanocrystalline ZnS electrodes doped with Mn2+ are also presented and discussed. The observation of both anodic and cathodic photocurrent is direct evidence for the nanocrystalline nature of the system. In-situ photoluminescence measurements showed stable Mn2+ related photoluminescence over a large potential range.
Size-dependence of Magnetic Properties of Bismuth Ferrite Nanopowders
Authors: Li J. , He H. , Lü F. , Duan Y. , Song D.
Published: April 2011

A 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

Highly 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

Superparamagnetic 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

In 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

Ab-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

A 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

Thallium 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

We 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

The 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

EXAFS 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

The 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

InN 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

We 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

Ionization 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

Characteristics 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

Thick 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

We 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

This 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

Power 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

As 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

The 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

The 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.
Crystallization Kinetics of Seeded SBT ( Sr0.7Bi2.4Ta2O9 ) Powders from Sol-Gel Derived Precursors
Authors: Kumar Gopinathan M. A. , Kwak Woo-Chul , Jung Se-Yon , Hwang Seung-Joon , Sung Yun-Mo
Published: April 2011

Strontium bismuth tantalate (SBT) having composition of Sr0.7Bi2.4Ta2O9 has been prepared through sol-gel method using their corresponding metal alkoxides as precursors. Seeded SBT powder was prepared by the addition of 5 wt.% of nanometer sized SBT particles to the sol followed by pyrolysis. By applying non-isothermal kinetic analysis to the DTA results, activation energy values for the unseeded and seeded samples were determined. Enhanced crystallization kinetics was observed for the seeded one and the activation energy for the aurivillius phase formation was found to be 318 kJ/mol, while 375 kJ/mol for the unseeded. The Avrami exponent values for the seeded and unseeded were found to be 2.80 and 0.96 respectively.
Pyroelectric Properties of Alanine Doped TGS Single Crystalline Thick Films under Constant Electric Stress
Authors: Pintilie Lucian , Matei Ion , Pintilie Ioana , Alexandru Horia V. , Berbecaru Ciceron
Published: April 2011

Pyroelectric properties of triglycine sulfate (TGS) thick films, separately doped with L and D alanine were investigated. Internal bias field of about 1 kV/cm, induced by the two dopants, stabilize the polarization in the opposite direction on the ferroelectric axis. Pyroelectric current (under constant stress) was recorded with a computer controlled Keithley 6517 electrometer, crossing up and down the Curie point. A reverse external electric field was applied on doped materials during heating, crossing up the Curie point. It is shown that the pyroelectric coefficient can be increased about four times at room temperature under un optimized DC electric field applied on the pyroelectric wafer.
Direct Nanoscale Observation of Size Effect on Polarization Instability in Pb(Zr,Ti)O3 film capacitors
Authors: Stolichnov Igor , Colla Enrico , Tagantsev Alexander , Hong Seungbum , Cross Jeffrey S. , Tsukada Mineharu
Published: April 2011

Mapping of polarization distributions in Pb(Zr,Ti)O3 ferroelectric capacitors with sizes down to 0.5 × 0.5 μm has been studied using scanning probe microscope (SPM) with detection of piezoelectric response through the top electrode. A well reproducible anomaly in polarization distribution namely elevated polarization at the edges and inverse polarization in the center has been observed for the FeCaps of several μm size. This polarization pattern is found to be insensitive to the poling voltage polarity and voltage stress prehistory but strongly dependent on the FeCAP size. Specifically, the polarization anomaly tends to disappear as the FeCAP size scales down to the submicron range. Tentative interpretation of this phenomenon in terms of strain-induced phase transitions in combination with depolarization effects is discussed.
Process Induced Modification of the High Frequency Dielectric Behavior of (100) Textured BaxSr1−xTiO3 (x = 0.5 and 0.6) Thin Films
Authors: Majumder S.B. , Jain M. , Martinez A. , Katiyar R.S. , Fachini E.R. , Keuls F.W. Van , Miranda F.A. , Sahoo P.K. , Kulkarni V.N.
Published: April 2011

Paraelectric BaxSr1−xTiO3 (BST) (x = 0.5 and 0.6) thin films are attractive candidates for the fabrication of various microwave dielectric devices including phase shifters, resonators, filters, oscillators etc. In the present work we have studied the effect of annealing temperature and ambient on the epitaxial quality, surface morphology, dielectric, and phase shifter characteristics of BST thin films deposited on LaAlO3 substrates. The epitaxial quality of the film was markedly improved as the annealing temperature was increased from 1050 to 1100°C. The degree of phase shift increased from 221 to 328° (measured at 14.5 GHz applying a field of 30V/μm) with the improvement of the epitaxial quality of the film. The insertion loss was also increased with the increase in annealing temperature and therefore the effective phase shifter κ factor (defined by the ratio of the degree of phase shift and insertion loss) remained low (∼30°/dB), while annealing these films in N2 ambient significantly reduced the insertion loss, their dielectric breakdown was observed at relatively lower applied voltage as compared to air and oxygen annealed films. The observed electrical behavior was correlated with the composition, chemical state of the constituents and epitaxial quality of the films synthesized under different annealing conditions.
Ferromagnetic and Paramagnetic Semiconductors Based upon GaN, AlGaN, and GaP
Authors: Overberg Mark E. , Thaler Gerald T. , Frazier Rachel M. , Gila Brent P. , Abernathy Cammy R. , Pearton Stephen J. , Theodoropoulou Nikoleta A. , Arnason Stephen B. , Hebard Arthur F. , Park Yun D.
Published: April 2011

Epitaxial growth of the ferromagnetic semiconductors GaMnP:C and GaMnN has been investigated by Gas Source Molecular Beam Epitaxy (GSMBE). GaMnP:C films grown with 9.4% Mn are found to be p-type with hysteretic behavior to room temperature. GaMnN films grown at 700 °C with 2.8% Mn show hysteresis at 300 K, while temperature-dependent magnetization measurements indicate that the magnetism may persist to much higher temperatures (> 325 K). Samples of AlGaMnN have also been prepared for the first time that show improved surface morphology compared to GaMnN but which show only paramagnetic behavior.
First-principles Modeling of Co/SrTiO3/Co Magnetic Tunnel Junctions
Authors: Oleinik I.I. , Tsymbal E.Y. , Pettifor D.G.
Published: April 2011

The atomic and electronic structure of Co/SrTiO3/Co (001) magnetic tunnel junctions (MTJs) was investigated by first-principles density-functional theory. We considered different interface terminations and the most stable structure with the TiO2 termination has been identified based on energetics of adhesion. The electronic structure of the TiO2-erminated MTJ shows an exchange coupling between the interface Co and Ti atoms mediated by oxygen. This coupling induces the magnetic moment of 0.25 μB on the interface Ti atom, which is aligned antiparallel to the magnetic moment of the Co layer. We argue that this might cause the inversion of the spin polarization of tunneling across the SrTiO3 barrier that was found in recent experiments.
Kinetic Exchange Vs. Room Temperature Ferromagnetism in Diluted Magnetic Semiconductors
Authors: Blinowski J. , Kacman P. , Dietl T.
Published: April 2011

Guided by the internal-reference rule and the known band o sets in - and - diluted magnetic semiconductors, we discuss the feasibility of obtaining p-type conductivity, required for the carrier-induced ferromagnetism, as well as the cases for which the doping by shallow impurities may lead to the ferromagnetism driven by the double exchange. e consider the dependence of kinetic exchange on the p-d hybridization, on the electronic con gurations of the magnetic ions, and on the energies of the charge transfer betw een the valence band of host materials and the magnetic ions. n the case of n-based - compounds, the doping by acceptors is necessary for the hole-induced ferromagnetism. he latter is, how ever, possible without any doping for some of Mn-, Fe- or Co-based - magnetic semiconductors. n nitrides with Fe or Co carrier-induced ferromagnetism with TC > 300 is expected in the presence of acceptor doping.
Successes and Predictions of A Pseudopotential Approach in Anion-Mixed Nitrides
Authors: Bellaiche L. , Al-Yacoub A. , Modine N. A. , Jones E. D.
Published: April 2011

The construction and the parameters of a new-strain dependent empirical pseudopotentials method are described and provided, respectively. This method is shown to reproduce with a very high accuracy some observed unusual properties in various complex anion-mixed nitride alloys. This method is also used to predict and understand anomalous effects that remain to be experimentally discovered in Ga1−yInyAs1−xNx quaternaries and GaAs0.5−xP0.5−xN2x solid solutions.