bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient Nucleation in Co-Zr Metallic Glasses
Authors: Köster Uwe , Blank-Bewersdorff Margret 
Published: April 2011

AbstractCrystallization kinetics and crystal size distributions in Co33Zr67-glasses have been analyzed by quantitative electron microscopy. The polymorphic crystallization of spherical CoZr2 crystals is very suitable reaction for such an analysis. Calculated crystal size distributions at different temperatures were compared to those experimentally revealed. Parameters controlling crystallization were varied within reasonable limits until theoretically calculated and experimentally observed crystal size distributions were in good agreement. It has been found that crystal size distribution can be explained by transient nucleation; the time lag and its temperature dependence can be evaluated. These results are discussed in the light of recent theories on transient nucleation.
Interphase Boundary Diffusion in Eutectic Alloys
Authors: Chadwick G. A. 
Published: April 2011

AbstractTurnbull and co-workers have shown that the noble metals Cu, Ag, and Au diffuse into single crystals of Pb and Sn by an interstitialcy mechanism with measured diffusion coefficients of ∼10−6cm2s−1. These experiments have been extended to study the diffusion rates of the noble metals along the interphase boundaries of single crystal of Pb-Sn eutectic alloys and to measure the diffusion coefficient of silver along the interphase boundaries of Ag-Cu eutectic single crystals.The measured interphase boundary diffusion coefficients of the noble metals in the Pb-Sn single crystals are extremely high, being 2.6 × 10−3cm2s−1for Cu and ∼10−4cm2s−1for Ag and Au at room temperature. These results again imply an interstitialcy mechanism of diffusion at the interphase boundaries. In contrast, the diffusion coefficient of Ag110in a Ag-Cu eutectic single crystal worked out to be ∼8×10−9cm2s−1at 500°C, two orders of magnitude lower than the value obtained by Turnbull and Hoffman for self-diffusion along low-angle (8∼10°) boundaries in silver.
Kinetics of the Nucleation of a Crystalline Droplet from the Melt
Authors: Grant Martin , Gunton J. D. 
Published: April 2011

AbstractTheory for the rate of nucleation of a crystalline solid from its melt is discussed. An expression for the dynamical prefactor of the nucleation rate is presented, which is derived using Langer's field theory of nucleation. The theoretical result generalizes the classical theory of Turnbull and Fisher, and can be tested experimentally. The analysis makes use of the formalism of Ramakrishnan and Yussouff, as extended to solid-melt interfaces by Oxtoby, Haymet, and Harrowell.
Optical Spectroscopy of Single Self Assembled Quantum Dots
Authors: Dekel E. , Gershoni D. , Ehrenfreund E. , Garcia J.M. , Petroff P.M. 
Published: April 2011

ABSTRACTWe applied low temperature diffraction limited confocal optical microscopy to spatially resolve, and spectroscopically study photoluminescence from single self-assembled semiconductor quantum dots. Using selective wavelength imaging we unambiguously demonstrated that a single photoexcited quantum dot emits light in a few very narrow spectral lines. By solving numerically a many body Hamiltonian for a model quantum dot, we show that the multi-line emission spectrum is due to optical transitions between confined exciton multiplexes. We explain the measured spectrum and its dependence on the power of either cw or pulsed excitation by analytically solving the coupled rate equations for the excitation relaxation between these exciton multiplexes.
Optical Property Characterization of Silicon Quantum Wires
Authors: Yu D. P. , Bai Z. G. , Zou Y. H. , Wang J. J. , Zhang H. Z. , Ding Y. , Feng S. Q. 
Published: April 2011

ABSTRACTThe recent success of bulk synthesis of pure nano-scale silicon quantum wires (SiQW's) enables us to evaluate their photoluminescence (PL) characteristics under ultra-violet photoexcitation. Intense multiple light emissions ranging from dark red to blue regions were revealed for as-grown and partially oxidized SiQW samples. The physical origin of the multiemissions is discussed on the basis of quantum confinements, or defect centers.
Few-Particle Effects in Nonlinear Optical Spectra of Semiconductor Quantum Dots
Authors: Hohenesteri Ulrich , Rossi Fausto , Molinari Elisa 
Published: April 2011

ABSTRACTWe present a density-matrix approach for the description of nonequilibrium carrier dynamics in optically excited semiconductor quantum dots, that explicitly accounts for exciton-exciton as well as exciton-carrier interactions. Within this framework, we analyze few-particle effects in the optical spectra and provide a consistent description of additional peaks appearing at high photoexcitation density. We discuss possible applications of such optical nonlinearities in future coherent-control experiments.
Controlling Growth of InAs/GaAs Self-Assembled Quantum Dots to Give 1.3 μm Room Temperature Emission
Authors: Malik Surama , Siverns Philip , Childs David , Roberts Christine , Hartmann Jean-Michel , Murray Ray 
Published: April 2011

ABSTRACTWe have investigated the extent to which the emission wavelength of self-assembled InAs/GaAs quantum dots can be controlled by growth parameters using conventional solid source MBE. Changing from conventionally high growth rates to a very low growth rate (LGR) and a relatively high substrate temperature, tunes the photoluminescence (PL) emission from 1.1 μm to 1.3 μm at room temperature. Atomic force micrographs obtained from uncapped samples reveal that these LGRQDs are larger, lower in density and extremely uniform in size. The improved size uniformity is reflected in the reduction of the PL linewidth from 78 meV to 22 meV. Under conditions of high excitation, emission from the ground and two excited states each separated by ∼70 meV is observed. This implies a parabolic confining potential. Time resolved photoluminescence (TRPL) measurements of dots grown under the various growth conditions yield radiative lifetimes which reflect the depth of the confining potential. A comparison of the decay times measured for the excited states show that the relaxation of carriers within the dots cannot be ascribed to phonon effects.
Morphological Changes to InAs Quantum Dots Caused by GaAs Overgrowth
Authors: Smathers J.B. , Ballet P. , Salamo G.J. 
Published: April 2011

ABSTRACTWe have used in-situ scanning tunneling microscopy (STM) to study the morphological changes to InAs quantum dots (QD's) caused by overgrowth of a GaAs capping layer. We demonstrate that the InAs islands are highly unstable during GaAs overgrowth and that this morphological instability confirms that significant cation intermixing occurs during overgrowth. In particular, the anisotropic nature of the volume redistribution indicates that In surface diffusion is the specific mechanism of In transfer away from the islands. Images taken after 10 monolayers or more of overgrowth reveal that more rapid GaAs overgrowth better preserves the 3D-islands morphology.
Early Stages of Growth of Ge Quantum Dots
Authors: Tognini P. , Patrini M. , Stella A. , Tonova D. , Cheyssac P. , Kofman R. , Bottani C. E. , Gemmi M. 
Published: April 2011

ABSTRACTThe present work is concentrated on the investigation of the initial stages of growth of Ge nanoparticles embedded in an amorphous A1203 matrix on suitable substrates. The growth technique is based on self-organization processes related to the balance of the interface energies involved. Combined data from complementary optical techniques (absorption, Raman scattering, spectroscopic ellipsometry) give evidence of a behaviour which can be ascribed to the existence of a wetting layer, not detectable by conventional transmission microscopy.
Growth by Low Pressure Chemical Vapor Deposition of Silicon Quantum Dots on Insulator for Nanoelectronics Devices
Authors: Baron T. , Martin F. , Mur P. , Wyon C. , Dupuy M. , Busseret C. , Souifi A. , Guillot G. 
Published: April 2011

ABSTRACTWe present the first comparative study of nucleation and growth of Si quantum dots on SiO2, SiOxNy and Si3N4 substrates using silane Low Pressure Chemical Vapor Deposition at low temperature (570–610°C). The samples are investigated by Atomic Force Micoscopy, Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and Spectroscopic Ellipsometry. We confirm that the chemical nature of the surface and precisely the presence of SiO bonds decreases the Si quantum dot density. By optimising the deposition parameters, a Si dot density of 1012 cm−2 can be obtained below 600°C on a pure Si3N4 surface. The influence of hydrogen, provided by silane decomposition, on the Si nucleation mechanism will be discussed.
The Formation of Close-Packed Two-Dimensional CdSe Colloidal Films by Electric-Field-Induced Deposition
Authors: Xu L. , Huang X.F. , Chen H.M. , Chen W. L. , Liu Z.G. , Chen K.J. 
Published: April 2011

ABSTRACTMonodispersed CdSe nanocrystals with average diameter of ∼5 nm were synthesized from SeSO32− and rich Cd2+ ionic reagents in aqueous solution. Two-dimensional (2D) close-packed colloidal CdSe films were formed on the electrode surface by electric-field induced deposition method. Transmission electron microscopy (TEM) images show that colloidal CdSe films exhibit different states, named “gas”, “liquid” and “solid” states, which can be transformed by adjusting applied field (E) or deposition time (T). The experimental results demonstrate that the average nearest-neighbor distance of clusters on the electrode surface is inversely proportional to the ET product.
Electron Beam Induced Current Imaging of Ferroelectric Thin Films
Authors: Lubomirsky Igor , Wang Tzu Yu , Gartsman Konstantin , Stafsudd Oscar M. 
Published: April 2011

AbstractWe have observed Electron Beam Induced Current imaging of thin film ferroelectrics. The Electron beam irradiation of a thin ferroelectric film creates a local temperature gradient that induces a polarization gradient and therefore a local electric field. Although the temperature difference is small the gradient is on the order of thousands K/cm and results in a corresponding electric field of a few MV/cm. The thermally induced electric field drives the electron beam created carriers toward an electrode thus inducing an externally measurable current. Despite the very small carrier life time (<1 ns) in ferroelectrics, the induced electric field is strong enough to collect carriers from a few hundred nm depth before recombination. An EBIC gain of 5 to 20 was measured experimentally with BaTiO3 and LiTaO3 films on silicon substrates. This method is insensitive to charge traps and provides a resolution better than 1 μm.
Lattice Defects in SrRuO3 Thin Films and Their Contribution to film Resistivity
Authors: Zakharov N. D. , Satyalakshmi K. M. , Koren G. , Hesse D. 
Published: April 2011

AbstractLattice defects present in PLD-grown, epitaxial SrRuO3 thin films on (001) SrTiO3 substrates are analyzed by high resolution transmission electron microscopy (HRTEM). Before the preparation of TEM samples, the electrical resistivity of films grown at different substrate temperatures was determined. Films grown at 775 °C exhibited a low electrical resistivity of only 200 μΩcm. They were found to be of orthorhombic structure and contained only few lattice defects. Films grown at 700 °C showed a high electrical resistivity of 1400 μΩcm. They were of cubic lattice symmetry, while films grown at temperatures above 800 °C showed resistivities between 300 and 900 μΩcm. The latter films mainly consist of an orthorhombic-cubic phase mix and involve lattice defects of high density, such as twins and antiphase boundaries (APBs). These defects are mainly located in between the islands and obviously contribute to the high film resistivity observed. For example, the APBs contain an extra single SrO layer, which is certainly insulating. Moreover, Ru vacancies are present in these films.
Transparent Conducting Coatings Made from Redispersable Crystalline Nanoscaled Powders
Authors: Goebbert C. , Bisht H. , Nonninger R. , Aegerter M. A. , Schmidt H. 
Published: April 2011

AbstractA new wet chemical concept is presented for the preparation of electrically conducting SnO2:Sb (ATO) and In2O3:Sn (ITO) coatings. It is based on the deposition by spin, dip or spray techniques of a solution containing crystalline nanoscaled particles fully redispersable in a solvent. The particle synthesis is carried out in a solution at temperatures < 200 °C by a controlled growth reaction using SnCl4 and InCl3 as precursors and SbCl3 and SnCl4 as dopant, respectively. The aggregation of the particles is avoided by in-situ surface modification with bifunctional organic molecules. After drying the nanocrystalline particles can be fully redispersed in ethanol at pH < 6 (for ITO) or water at pH > 8 (for ATO) with solid contents up to 8.8 vol. %. Single layers with thickness up to 200 nm (ATO) and 400 nm (ITO) have been fabricated. Their sheet resistance decrease with the sintering temperature. Typical lowest values are 430 Ω□ (550 °C) for ATO and 90 Ω□ (900 °C) for reduced ITO. The resistivity of as fired ATO and ITO coatings is stable but it slightly increases with time for ITO in the reduced state. All coatings have a transmission in the visible range of about 90 %. Anti-glare conducting coatings on glass with 70 GU as well as antistatic coatings (R□ ≈ 1 MΩ□) on polycarbonate substrates have been obtained with chemically modified ITO suspensions.
High Energy Density Capacitors Fabricated by Thin Film Technology
Authors: Wagner Andrew V. , Johnson Gary W. , Barbee Troy W. 
Published: April 2011

AbstractLow energy density in conventional capacitors severely limits efforts to miniaturize power electronics and imposes design limitations on electronics in general. We have successfully applied physical vapor deposition technology to greatly increase capacitor energy density. The high dielectric breakdown strength we have achieved in alumina thin films allows high energy density to be achieved with this moderately low dielectric constant material. The small temperature dependence of the dielectric constant, and the high reliability, high resistivity, and low dielectric loss of Al2O3, make it even more appealing. We have constructed single dielectric layer thin film capacitors and shown that they can be stacked to form multilayered structures with no loss in yield for a given capacitance. Control of film growth morphology is critical for achieving the smooth, high quality interfaces between metal and dielectric necessary for device operation at high electric fields. Most importantly, high rate deposition with extremely low particle generation is essential for achieving high energy storage at a reasonable cost. This has been achieved by reactive magnetron sputtering in which the reaction to form the dielectric oxide has been confined to the deposition surface. By this technique we have achieved a yield of over 50% for 1 cm2 devices with an energy density of 14 J per cubic centimeter of Al2O3 dielectric material in 1.2 kV, 4 nF devices. By further reducing defect density and increasing the dielectric constant of the material, we will be able to increase capacitance and construct high energy density devices to meet the requirements of applications in power electronics.
Dielectric Response of free Standing Strontium Titanate Thin Films from 10 Khz to 1 Ghz as A Function of Temperature and Applied Voltage
Authors: Dalberth M. J. , Price J. C. , Rogers C. T. 
Published: April 2011

AbstractUsing pulsed laser ablation, we have grown epitaxial bilayers of strontium titanate (STO) and yttrium barium copper oxide (YBCO) on (110) neodymium gallate (NGO) substrates. Using a selective acid etch, we have removed the YBCO from the middle of the bilayer and lifted off the STO films from their parent substrates. Using coplanar interdigital capacitors patterned on the surface of the films, we have measured the capacitance and loss as a function of frequency (from 10 kHz to 1 GHz), temperature (from 300 K to 4 K), and applied electric field (up to roughly 2 V/μm). We have seen frequency dependent loss peaks in the films that indicate thermally activated behavior, and an improvement in the tuning quality.
Oxygen Diffusion in Tantalum Oxide Metal-Oxide-Metal Capacitor Structures
Authors: Chang J. P. , Steigerwald M. L. , Fleming R. M. , Opila R. L. , Alers G. B. 
Published: April 2011

AbstractWe have studied structures used in MOM capacitors including Ta2O5/TiN/Ti, Ta2O5/Ti, Ta2O5/TaN/Ti, Ta2O5/WN/Ti, and Ta2O5/M where M = Ta, Pt, W, Al, and Si using X-Ray Photoelectron Spectroscopy. We find that Ti and Al are able to reduce the Ta2O5 to Ta, forming oxides of Ti and Al, respectively. The diffusion barrier TiN hampers the diffusion of oxygen and therefore postpone the reduction of Ta2O5 to higher temperatures. The oxygen migrates from the Ta2O5 layer and through the TIN layer to the Ti layer during the heat treatment. As judged by the temperatures at which the reduction of Ta2O5 occurs, TaN and WN are more effective oxygendiffusion barriers than TiN. Leakage current observed in AI/Ta2O5/TaN/Ta capacitors is one to two orders of magnitude lower than that observed in Al/Ta2O5/TiN/Ti capacitors.
Electrical Noise in Ultra Thin Giant Magnetoresistors
Authors: Lisauskas A. , Khartsev S. I. , Grishin A. M. , Palenskis V. 
Published: April 2011

AbstractWe report measurements of low frequency 1/f excess noise for the series of La0.75Sr0.25MnO3 (LSMO) giant magnetoresistive thin epitaxial films with thickness of 42, 50, 100, and 600 Å. Fabricated manganite films experience semiconductor-normal metal (paramagnetic-ferromagnetic) phase transition with the temperature change. The transition manifests itself by the sharp change of resistivity and characteristic peak of magnetoresistivity. Thickness decrease results in lowering the transition temperature and increasing of resistivity. The noise spectra has 1/fa behavior with a ≈ 1± 0.2. The voltage fluctuations spectral density shows quadratic dependence on current indicating that observed noise is caused by the resistance fluctuations. Noise level, temperature coefficient of resisistvity and magnetoresistance increase for thin films. Therefore, the operation point (transition temperature) can be tailored from 330 K to 220 K by changing only the film thickness while the performance of temperature and magnetic field LSMO sensors can be maintained almost constant in thickness range down to 100 Å.
Critical Microscopic Processes in Semiconductor Lasers
Authors: Hybertsen Mark S. , Alam M. A. , Baraff G. A. , Smith R. K. 
Published: April 2011

ABSTRACTThe cascade of microscopic processes relevant to semiconductor laser operation is outlined. An integrated laser simulator which encapsulates these processes is applied to illustrate the connection between an accurate model of the optical gain in the quantum wells and measured characteristics of representative 1.3 μm InGaAsP/InP lasers. These results highlight the impact of carrier transport effects on the observed optical gain and the modulation response of semiconductor lasers.
Silicon Crystal Growth on a Ni Silicide Seeding Layer by DC Magnetron Sputtering
Authors: Guliants E. , Anderson W.A. 
Published: April 2011

AbstractDirect current (d.c.) magnetron sputtering was applied to polycrystalline Si growth and yielded a uniform Si film at a deposition temperature below the glass softening point. The approach involved the deposition of a thin Ni film over SiO2 prior to Si sputtering. The interaction of a fine-grained metallic Ni with an atomic Si provided by a sputtering gun resulted in the formation of Ni silicide at the Ni-Si interface immediately after the onset of Si deposition. The phase composition of the nickel silicide was controlled by the temperature of deposition and the Si-to-Ni concentration ratio. The silicide region exhibited a layered structure where the bottom layer consisted of the mixture of several NixSiy phases and the top layer represented the pure NiSi2 phase. This Ni disilicide layer provided the nucleation sites for the epitaxial Si crystal growth. As a result, the polycrystalline silicon film consisted of 0.1-0.5µm grains with preferred (11) or (110) orientation without an indication of an amorphous phase. The carrier lifetime of 11 µs indicated good electrical properties which make the film potentially applicable to fabrication of thin film transistors and solar cells. The Ni prelayer thickness in the 5-100nm range dramatically influenced the crystal size and preferential crystal orientation. Possible mechanisms responsible for the nickel silicide induced grain growth of silicon and the correlation between the Ni silicide and silicon microstructure is discussed.
Characterization of Epitaxial Growth of Semiconducting Rhenium “Disilicide” Films
Authors: Misra A. , Verdier M. , Mahan J.E. , Mitchell T.E. 
Published: April 2011

AbstractWe have characterized, through transmission electron microscopy (TEM), the ReSi2−x thin films grown by reactive deposition on (001) Si. ReSi2−x thin films exhibit a distorted body-centered tetragonal MoSi2-type structure, and have excellent epitaxy on (001) Si since the face diagonal of the Si unit cell is equal to the c lattice parameter of silicide. The Si-deficient composition in the “disilicide” may be accommodated by collapse and shear of missing Si planes to form planar faults. Kirkendall voids are also observed at the film-substrate interface. The engineering of the defect and interface structures of these complex, non-stoichiometric silicides for optimized optoelectronic properties are discussed.
Growth of Epitaxial Cu/TiN/6H-SiC(0001) Heterostructures by Pulsed Laser Deposition
Authors: Kvit A. , Sharma A.K. , Narayan J. 
Published: April 2011

AbstractEpitaxial Cu/TiN heterostructures were grown on hexagonal (6H)-SiC(0001) substrate by pulsed laser deposition using the domain epitaxy, where integral multiple of lattice constant or major planes match across the interface1. Such layers are needed for metallization of SiC bond integrated circuit devices. These Cu and TiN layers on SiC(0001) were grown at 600 degrees centigrade in a high vacuum (<10−6 Torr). This structure was characterized using X-ray diffraction technique and transmission electron microscopy. The X-ray diffraction recorded only (111) and (222) reflection of Cu and TiN. The full-width at half maximum of ω-rocking curve of (111) reflection of Cu (0.4 degree) and TEM results indicated a high epitaxial quality. The plan view transmission electron micrograph shows that Cu forms three-dimensional islands indicating that the Cu/TiN interface energy is very high. The island size varies from 0.2 to 2 μm. Analysis of selective aperture diffraction patterns and cross-sectional transmission electron microscopy, including high-resolution imaging, showed relationships Cu(111)//TiN(111)//6H-SiC(0001). The TiN/SiC an interface was locally atomically sharp and free from secondary phases or obvious interdiffusion. The typical defects in the TiN(111) layers consisted of threading domain boundaries. The mechanism of three-dimension growth of copper on TiN layers was discussed.
Role of a Free Energy Action Principle in Predicting Microstructure Formation
Authors: Kirkaldy J.S. 
Published: April 2011

AbstractIt is demonstrated that some twenty representative free boundary diffusion-reaction and hydrodynamic patterning systems fall within the compass of the isothermal variational principle where the Lagrangian density is the free energy density g, and η is an appropriate order parameter. To illustrate the universality of the formulation we survey in some detail its degree of equivalence to twenty-one currently adopted or promoted procedures for resolving pattern degeneracies, and critically reappraise theoretical descriptions of grain growth, ordinary diffusion, spinodal decomposition and Ostwald Ripening and their predictive success. The importance of a hierarchy of kinetic scaling laws is discussed. The physics of fluctuations is essential to understanding.