bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lateral Coupling of Self-Assembled Quantum Dots Studied by Near-Field Spectroscopy
Authors: Robinson H.D. , Goldberg B.B. , Merz J.L. 
Published: April 2011

ABSTRACTLateral coupling between separate quantum dots has been observed in a system of In0.55A10.45As self-assembled quantum dots. The experiment was performed by taking photoluminescence excitation (PLE) spectra in the optical near-field at 4.2 K. The high spatial resolution afforded by the near-field technique allows us to resolve individual dots in a density regime where interactions between neighboring dots become apparent. In the PLE spectra, narrow resonances are observed in the emission lines of individual dots. A large fraction of these resonances occur simultaneously in several emission lines, originating from different quantum dots. This is evidence of interdot scattering of carriers, which additional data show to be mediated by localized states at energies below the wetting layer exciton energy. A very rich phonon spectrum generated by the complicated interfaces between barrier and dot material is also evident in the data.
Oxide Film Formation on Metals and Alloys by Thermal, Electrochemical and Plasma Oxidation and Prediction of Resulting Structures
Authors: Cocke D. L. , Promreuk S. , Schennach R. , Mollah M. Y. , Naugle D. G. 
Published: April 2011

AbstractMulticomponent oxide films are needed to meet the increasing demands of the electronics industry. Three main methods that involve oxidation of a metallic substrate are thermal, anodic and plasma oxidation. Today we do not have an adequate fundamental physical-chemical model of how multicomponent oxides evolve on alloys under these oxidizing conditions to design a wide range of materials for electronic devices. The three methods will be discussed in terms of physical/chemical parameters that influence the chemical nature and structure of the resulting oxides. By using surface studies of the oxidation behavior of numerous metals and alloys we have been able to delineate the factors which are most important to the oxide formation process and provide insight into the prediction of oxide layer structures. The electrochemical processes that occur during the materials reaction with a chosen environment will be used to discuss the physical and chemical mechanisms involved. Intrinsic and extrinsic electric fields will be shown to influence the chemical and structural nature of the resulting oxide structures. Examples will be presented from a number of metal and alloy systems that have been examined in our laboratory. These include Al, Ti, Zr, Nb, Mn, Cu and Ni and some of their selected alloys. The models that have developed from these studies are providing some predictive power in how the complex oxide overlayer will be chemically speciated and on its structure.
Ultraviolet Assisted Pulsed Laser Deposition of Thin Oxide Films
Authors: Craciun V. , Howard J. , Singh R. K. 
Published: April 2011

AbstractThe properties of Y2O3, ITO (indium tin oxide), and TaSi2 thin layers grown using a new in-situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. X-ray diffraction investigations showed that with respect to conventional PLD grown films under similar conditions, but without UV illumination, UVPLD grown films exhibited better crystallinity, especially for growth at low substrate temperatures, from 200 °C up to 450 °C, depending on the material. X-ray photoelectron spectroscopy investigations showed that UVPLD layers contained less physisorbed oxygen than the conventional PLD layers, exhibiting a better overall stoichiometry. These results suggest that during the ablation-growth process, UV radiation increases the surface mobility of adatoms and provides more reactive gaseous species. Both factors contribute to the crystalline growth and are especially effective at moderate processing temperatures, where the thermal energy available for the process is comparatively low.
Micromachined Array Studies of Tin Oxide Films: Nucleation, Structure and Gas Sensing Characteristics
Authors: Panchapakesan B. , DeVoe D. L. , Cavicchi R. E. , Walton R. M. , Semancik S. 
Published: April 2011

AbstractThe ability to fabricate sensitive and stable gas sensors which can detect low concentrations of gaseous species is necessary for many critical applications such as environmental safety monitoring. Although highly sensitive gas sensors have been produced by dispersion of catalytic metals on oxide sensing films, fouling of catalysts can cause instability in sensor performance. We have examined an approach which involves fine tuning the microstructure of tin oxide sensing films by vapor depositing an ultra-thin film of seed layer metals prior to tin oxide deposition. Metals including Fe, Sn and Pt have been investigated for their influence on tin oxide growth. Systematic studies of the growth mechanism and microstructure of CVD tin oxide using four-element arrays of “microhotplates” have revealed a number of different film morphologies which result from seeding. Enhancements in sensitivity for seeded growth relative to unseeded growth suggest a method of producing sensitive gas sensors which may not require the addition of surface catalytic layers. In this study we also demonstrate the use of microhotplates not only as sensing devices, but as excellent platforms for materials research.
Preparation of Na0.5K0.5NbO3/La0.6Sr0.2Mn1.2O3/LaAlO3 Thin Film Structures by Pulsed Laser Deposition
Authors: Cho Choong-Rae , Khartsev S. I. , Grishin A. M. , Lindbäick Ture 
Published: April 2011

AbstractWe report on ferroelectric/giant magnetoresistive Na0.5K0.5NbO3/La0.6Sr0.2Mn1.2O3 (NKN/LSMO) heterostructures grown onto LaAlO3 (001) single crystal using KrF pulsed laser ablation of stoichiometric ceramic target. Main processing parameters have been optimized to obtain smooth LSMO template layer, avoid NKN-LSMO interdiffusion, preserve NKN stoichiometry against the lost of volatile potassium and sodium and achieve reasonable reliability of NKN film performance. X-ray diffraction θ- 2θ scans and rocking curves evidence for single-phase content and high c-axis orientation both in template LSMO and top NKN layers. Ferroelectric measurements yield remnant polarization Pr of 1.5 [C/cm2 and spontaneous polarization Ps of 7 μC/cm2 at electric field strength of 130 kV/cm. At room temperature, dielectric permittivity ε′ and dissipation factor tan δ have been found to vary from 595 to 555 and 0.046 to 0.029 respectively in the frequency range of 0.4 to 20 kHz. At 10 kHz dielectric permittivity linearly increases from 410 to 650 in the temperature range 77 K to 415 K while the dissipation factor below 320 K does not exceed 3%.
Improvement of the Electrical Properties of YMnO3 Thin Films in A Metal/Ferroelectric/Si Structure
Authors: Yi Woo-Chul , Seo Chang-Su , Kwun Sook-Il , Yoon Jong-Gul 
Published: April 2011

AbstractHighly (0001)-oriented films of YMnO3 were grown on n-type Si(100) substrates by a chemical solution deposition with a modified precursor solution. Spin-coated films were crystallized by rapid thermal annealing at 650 °C, and showed improved structural and electrical properties. Capacitance-voltage (C-V) measurements at 1 MHz showed a counterclockwise hysteresis, with a memory window of 1.9 V at 9 V, due to ferroelectric polarization, and a dielectric constant of 25. The effects of mobile ionic charge and effective interface charge in the C-V measurements were found to be small by investigating the bias sweep rate dependence and flat-band voltage shift, respectively. The interface trap density near the Si midgap was obtained to be about 1.3 × 1011 cm−2eV−1 through conductance measurements. Current-voltage characteristics showed a leakage current density of 16 nA/cm2 at 3 V. An asymmetric polarization-voltage (P-V) hysteresis curve became symmetric one with a remanent polarization value of 0.1 μ C/cm2 under He-Ne laser illumination. The depolarization field in the ferroelectric film and charge compensation by the light-generated minority carriers may be responsible for the observed P-V characteristics. The low temperature fabrication of this YMnO3 film showed good structural and electrical properties for application to nonvolatile ferroelectric memory devices.
Low Loss Ferroelectric Films Grown on Polycrystalline Ferrite Substrates for Dual-Tuning Microwave Devices
Authors: Jiang H. , Hu W. , Liang S. , Fouflyguine V. , Zhao J. , Jia Q. X. , Groves J. R. , Arendt P. , Vittoria C. , How H. 
Published: April 2011

AbstractWe successfully deposited high quality biaxially oriented BaxSr1-xTiO3 thin films on polycrystalline yttrium iron garnet substrates using both the metal-organic chemical liquid deposition and pulsed laser deposition methods with biaxially oriented MgO and yttriumstabilized- zirconia buffer layers. The dielectric losses of the films range from 0.005 to 0.015 while 25% of dielectric constant change was observed with 40V bias voltage up to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range. A dual-tuning microwave phase shifter using a BST film grown on an MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in a wide frequency range when an electric bias or a magnetic field was applied to the device.
Metal-Organic Chemical Vapor Deposition of Metal Oxides: from Precursor Synthesis to Thin Films
Authors: Belot J. A. , Wang A. , Edleman N. L. , Babcock J. R. , Metz M. V. , Marks T. J. , Markworth P. R. , Chang R. P. H. 
Published: April 2011

AbstractThis contribution describes the synthesis, characterization, and implementation of new lanthanide and main group metal-organic chemical vapor deposition precursors based on the 2,2-dimethyl-5-N-2-methoxyethylimino-3-hexanonato ligand system. The new homoleptic, fluorinefree, low melting, and highly volatile complexes are ideally suited for oxide MOCVD, and in many applications are superior to standard β-diketonates while maintaining ease of synthesis and low cost. This is explicitly demonstrated by the growth of high quality CeO2/YBa2Cu3O7-δ multilayers.
Thin Film Dielectrics for Electronics Using Combustion Chemical Vapor Deposition
Authors: Lin Wen-yi , Huang Hai , Cullen D. Kacy , Shoup Shara S. , Cousins Donald , Schmitt Jerome J. , Hunt Andrew T. , Romanofsky Robert R. , VanKeuls Fred W. , Miranda Félix A. , Mueller Carl H. 
Published: April 2011

AbstractThis paper reviewed work to date on multicomponent oxides deposited, utilizing openatmosphere Combustion Chemical Vapor Deposition for electronic applications. Epitaxial barium strontium titanate and strontium titanate thin films were deposited on (100) MgO single crystal substrates. They were patterned to form interdigitated structures for electrically tunable devices, namely, coupled microstripline phase shifters (CMPS). The undoped, as-deposited perovskite dielectrics exhibited a figure of merit of 53°/dB at 20 GHz and 23°C, indicating high degree of tunability and fairly low loss. High-permittivity (ε=263), polycrystalline BST and SrTiO3 were studied for dynamic random access memory, and leakage current density of 10−7 A/cm2 was measured. Intended for non-volatile ferroelectric memory, lead zirconium titanate was deposited onto a seed layer of perovskite structure to prevent the growth of the unwanted pyrochlore phase. To function as buffer layers for superconductor applications, epitaxial CeO2, YSZ, SrTiO3, LaAlO3, Y2O3, and Yb2O3 coatings on single crystal and textured nickel substrate were investigated. Electronic analyses and characterization, using SEM, EDS, XRD, and X-ray pole figures, were presented.
First-Principles Calculations of Positron Annihilation in Solids
Authors: Barbiellini B. , Hakala M. , Nieminen R. M. , Puska M. J. 
Published: April 2011

ABSTRACTWe present first-principles approaches based on density functional theory for calculating positron states and annihilation characteristics in condensed matter. The treatment of the electron-positron correlation effects (the enhancement of the electron density at the positron with respect to mean-field density) is shown to play a crucial role when calculating the annihilation rates. A generalized gradient approximation (GGA) takes the strong inhomogeneities of the electron density in the ion core region into account and reproduces well the experimental total annihilation rates (inverses of the positron lifetimes) by suppressing the rates given by a local density approximation (LDA). The GGA combined with an electron-state-dependent enhancement scheme gives a good description for the momentum distributions of the annihilating positron-electron pairs reproducing accurately the trends observed in the angular correlation (ACAR) or Doppler broadening measurements of the annihilation radiation. The combination of the present positron lifetime and momentum density calculations with the corresponding measurements yields a unique tool for defect identification. Especially, the investigation of various vacancy-type defects in semiconductors able to trap positrons will be an important field for these methods. We will show that the identification of vacancy-impurity complexes in highly n-Type Si and the study of the SiO2/Si interface are particularly interesting applications.
Initial Crystallization Reactions
Authors: Perepezko J.H. , Allen D.R. 
Published: April 2011

AbstractDuring the initial stage of phase formation reactions nucleation conditions often apply a controlling influence on the phase selection, product phase number density and grain size. In most cases the operation of nucleation control is also associated with the development of significant undercooling or supersaturation in order to initiate crystallization. Under this constraint it is common to observe different forms of alloy metastability. In fact, a hierarchy of equilibria can be identified based upon the severity of the kinetic constraints that act during transformation. One consequence of the different levels of metastability is the development of precursor reactions before the initial crystallization. In other cases a kinetic competition between different reaction modes or structures can yield a change in the transformation pathway during reaction. The appearance of kinetic transitions is one consequence of the competition between concurrent reactions and provides a valuable opportunity for kinetics analysis and modeling. In cases where sequential reactions are separated by temperature or time intervals other kinetic constraints operate to expose metastability due to diffusional growth limitations. The identification of the reaction control provides the foundation for kinetics analysis and the development of alloy design strategies. These features can be considered in terms of the observed crystallization behavior during rapid solidification and solid state interface reactions.
Kinetic Limitations to Shape Equilibration of Liquid Pb Inclusions In Al
Authors: Gabrisch H. , Kjeldgaard L. , Værnholt Olesen A. , Johnson E. , Dahmen U. 
Published: April 2011

AbstractThe shape of liquid Pb inclusions in Al was investigated by in-situ electron microscopy over a temperature interval from 300 to 500°C. The inclusion shape was found to depend on size and temperature. During isothermal annealing after melting, small inclusions rounded off while larger inclusions remained faceted until the temperature was raised to about 500°C. During subsequent cooling, inclusions refaceted, although less strongly than during heating. The shape hysteresis between heating and cooling cycles was found to be due to the barrier of ledge nucleation necessary to advance the faceted interfaces. The observations show that the step energy depends on temperature and its disappearance at about 540-600°C indicates a roughening transition.
Coupling The Nano and Micro Scales In Modelling The Formation of Metallic Microstructures
Authors: Chirazi A. , Rafii-Tabar H. 
Published: April 2011

AbstractWe have developed a model of dendritic grain growth in the solidification process of metallic alloys in which the output of a nanoscopic molecular dynamics simulation, based on the use of many-body interatomic potentials, provides the input into the microscopic nucleation and growth model of Rappaz et al. The microscopic model itself is also extended by the introduction of a stochastic dynamics, via the Ito stochastic calculus, to account for the random fluctuations in the growth trajectory of the dendrite tip. The model is applied to the industrially important Sn-Pb alloy and its result is compared with that obtained with the Rappaz model.
Atomic Structure of Alloys Close to Phase Transitions
Authors: Van Tendeloo G. , Schryvers D. 
Published: April 2011

AbstractPhase transitions are often accompanied by pre-transition effects. These effects have been studied on an atomic scale by high resolution electron microscopy. For the diffusion controled phase transitions we discuss short range ordering effects in Ni-Mo and Cu-Pd. For the displacive transitions we discuss the martensitic nucleation in Ni-Al and the nanoscale domain formation in the Ni-Ti R phase.
On The Effect of Au Addition and the Role of B on Nanocrystallization of Fe-Zr-B Amorphous Alloy
Authors: Zhang Y. , Wanderka N. , Czubayko U. , Zhu F. , Wollenberger H. 
Published: April 2011

AbstractUsing atom probe field ion microscopy (APFIM) we examined the local chemical compositions of Fe-7Zr-5B-lAu and Fe-14B amorphous alloys in the course of primary crystallization. Au rich clusters are formed during primary crystallization of Fe-7Zr-5B-lAu alloy. However, these clusters do not act as nucleation sites for α-Fe particles. In the early stage of primary crystallization, heterogeneities of Fe and B evolve in the amorphous phase. Heterogeneous distribution of B was found in the as-melt-spun Fe-14B amorphous alloy. During primary crystallization, B is highly supersaturated not only in the nanometer sized α-Fe particles in Fe-7Zr-5B-lAu alloy, but also in those of large diameters in Fe-14B alloy. From the results it is concluded that presence of B lowers the nucleation barrier for primary crystallization.
Diffusion Pathway of Interface Reactions in Amorphous-SiC/Ni
Authors: Dong Z.F. , Perepezko J. H. , Edelstein A.S. 
Published: April 2011

AbstractA multilayer sample of amorphous SiC (α-SiC) and polycrystalline Ni was prepared by ionbeam sputtering, and was used as a model, prototype system to study the stability of metal contacts with SiC against interdiffusion reactions near the interface. The modulation wavelength is around 80 nm and with equal thickness of α-SiC and Ni layers. By use of XRD, TEM and energy dispersive spectroscopy (EDS), information on the structural evolution and composition distribution during heat treatment was obtained. The diffusion of Ni into the SiC layer, and Si and C into the Ni layer appears to take place concurrently during the annealing process. An amorphous reaction layer was formed during the heat treatment that is distinct from the α-SiC. The increase in thickness of the reaction layer followed a parabolic time dependence in the initial stage, until further reaction was limited by the precipitation of a graphite layer near the original α-SiC/Ni interface. A metastable intermediate phase and a NiSi phase were identified in the original Ni layer due to the diffusion of Si and C based on the decomposition of the α-SiC.
Thin Film Growth and Ion-Beam Modification: Md Simulations Going Beyond Simple Systems
Authors: Haddeman Edwin F. C. , Bunnik Bouke S. , Thijsse Barend J. 
Published: April 2011

AbstractMolecular Dynamics computer simulations were used to explore a number of complex phenomena that occur during film growth and ion-surface interactions. A few examples are discussed. (1) Strong surface patterns develop when a Mo film is grown on a Mo(110) substrate, whereas they are absent for Mo on Mo(100). (2) Depositing a Mo film on a substrate containing two antiparallel (100)/(910) grain boundaries leads to complicated film morphologies in the grain boundary regions. Stresses, mosaic spread, and regions of fcc Mo are observed, and their stability is examined. (3) Cu films deposited on a Mo(110) substrate, a model system for interconnects in modern IC technology, are affected by the strong fcc/bcc interface mismatch. The Cu film properties are analyzed for thermally evaporated films and for films grown by argon ion-beam assisted deposition (IBAD).
Enhancement in the Growth of Textured HFCVD Diamond Coatings on Ti-6Al-4V Substrates by Excimer Laser Processing
Authors: Galeev Mikhail T. , Vedawyas M. , Sivanathan G. , Kumar Ashok 
Published: April 2011

AbstractIn this work we address the studies of enhancement in diamond growth on Ti-6AI-4V metal alloy by modifying the surface using the excimer laser ablation technique, prior to deposition of diamond. Ti-6Al-4V is chosen for its technological importance in aerospace industry, dental and bio-implant applications. Analysis of the structures of the film is done using X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Ablation of the alloy by excimer laser pulses produces periodically hill/valley structures on the surface, thus increasing the density of diamond nucleation and film adhesion. The roughness of the alloy surface was measured to be in the 0.5μm – 1μm range with an average distance between peaks of the hill/valley structure measuring 1.5μm.
Deposition of Cubic-SiC Thin Films on Si (111) using the Molecular Ion Beam Technique
Authors: Matsumoto T. , Mimoto K. , Kiuchi M. , Sugimoto S. , Goto S. 
Published: April 2011

AbstractSiC thin films were formed on Si (111) at growth temperatures of 750–1000 °C using the molecular ion beam technique, with a precursor of methylsilicenium ions (SiCH3+). The chemical bindings and surface structures of SiC thin films were analyzed by Raman spectroscopy and reflection high-energy electron diffraction. As a result, 3C-SiC (111) was grown on Si (111) substrates without carbonized treatments.
Ain Thin Films Prepared by Reactive Ion Beam Coating
Authors: Cheng L. L. , Yu Y H. , Sundaravel B. , Luo E. Z. , Lin S. , Lei Y M. , Ren C. X. , Cheung W. Y. , Wong S. P. , Xu J. B. , Wilson I. H. 
Published: April 2011

AbstractAluminum Nitride (AIN) is a promising material for a variety of technological applications because it has many exceptional properties, such as wide band gap (WBG) and negative electron affinity (NEA). AIN thin films were prepared by Reactive Ion Beam Coating. The properties of the AIN thin films may be a function of one of the preparation conditions: the beam energy. We used the non-Rutherford backscattering (non-RBS) and Auger Electron Spectroscopy (AES) results to analyze the composition of the AIN thin films. Atomic Force Microscopy (AFM) was applied to study the morphology of films. On the other hand, electron field emission properties were also studied to find the relationship between the compositional, morphological and electron field emission properties of the AIN thin films.