bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation between Structural and Optical Properties of Si Nanocrystals in SiO2: Model for the Visible Light Emission
Authors: López M. , Garrido B. , González O. , García C. , Pérez-Rodríguez A. , Morante J.R. , Bonafos C. , Carrada M. , Rodríguez R.J. , Montserrat J. 
Published: April 2011

ABSTRACTThe correlation between the structural and optical properties of Si nanocrystals embedded in SiO2 is the key factor to understand their emission mechanism. However, there is a great difficulty in imaging Si nanocrystals in SiO2 and measuring their size distribution because of the lack of contrast in electron microscopy. We have used here a new method for imaging Si nanocrystals by using high resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Regarding the optical properties, the band-gap energies and photoluminescence have been measured by direct and independent methods. The results have allowed experimental determination, for the first time in this material, of the experimental Stokes shift between absorption and emission as a function of crystallite size. The experimental band-gap versus size correlates well with the most accurate theoretical predictions. Moreover, the photoluminescence energy emission versus crystallite size shows a parallel behaviour to that of band-gap energy. Consequently, the experimental Stokes shift is independent of nanocrystal size and is found to be 0.26±0.03 eV. This value is almost twice the energy of the Si-O vibration (0.134 eV). These results suggest that the dominant emission of Si nanocrystals passivated with SiO2 is a fundamental transition spatially located at the Si-SiO2 interface and with the assistance of a local Si-O vibration.
Determination of the Distribution of Ion Implantation Boron in Silicon
Authors: Wang Te-Sheng , Cullis A.G. , Collart E.J.H. , Murrell A.J. , Foad M.A. 
Published: April 2011

ABSTRACTBoron is the most important p-type dopant in Si and it is essential that, especially for low energy implantation, both as-implanted B distributions and those produced by annealing should be characterized in very great detail to obtain the required process control for advanced device applications. While secondary ion mass spectrometry (SIMS) is ordinarily employed for this purpose, in the present studies implant concentration profiles have been determined by direct B imaging with approximately nanometer depth and lateral resolution using energy-filtered imaging in the transmission electron microscopy. The as-implanted B impurity profile is correlated with theoretical expectations: differences with respect to the results of SIMS measurements are discussed. Changes in the B distribution and clustering that occur after annealing of the implanted layers are also described.
Post Annealing Studies of C60 Ion Implanted Thin Films
Authors: Dharmarasu Nethaji , Narayanan Kannan L. , Kojima Nabuaki , Ohshita Yoshio , Yamaguchi Masafumi 
Published: April 2011

ABSTRACTPhysical properties of multiple-energy B-ion implanted C60 thin films were investigated for various doses. Fourier Transform Infra-red Spectroscopy (FTIR) results indicate the structural transformation of C60 to amorphous carbon phase during implantation. The conductivity type of the implanted films is found to be p-type and the conductivity measurements reveal a dramatic increase in the conductivity with ion implantation. Temperature dependent conductivity shows the semiconducting nature of the B-ion implanted films. The optical absorption coefficient and optical gap of the implanted films have been observed as a function of B-ion dose. Measurements on implanted films subjected to thermal annealing indicate the removal of the defects caused during the implantation. Ion implantation-induced defects are found to partially annihilate with the annealing temperature. Electrical conductivity and optical gap are determined in the post-implanted films. The observation of the systematic increase in the conductivity of the annealed films is due to the removal of the defects and the formation of defect free boron impurity acceptor.
Stress Driven Phase Transformations and Recrystallization Processes in Two-Phase Titanium Aluminide Alloys
Authors: Appel Fritz , Oehring Michael 
Published: April 2011

ABSTRACTThe paper presents an electron microscope study of phase transformation and recrystallization in an intermetallic α2(Ti3Al) + γ(TiAl) titanium aluminide alloy, after long-term creep. The mechanisms are closely related to the atomic structure of the α2/γ phase boundaries and are probably driven by a non-equilibrium of the phase composition leading to the dissolution of the α2 phase. The α2 /γ transformation is accompanied by the formation of precipitates, because the γ(TiAl)phase has a significantly lower solubility for interstitial impurities than the α2(Ti3Al) phase.
Morphological Evolution of a Fully Faceted Grain Boundary
Authors: Medlin D.L. , Lucadamo G. 
Published: April 2011

ABSTRACTWe examine the morphological evolution of faceted grain boundaries in gold during annealing. Experiments were performed on <111> oriented gold films composed of two Σ=3 related orientation variants. The boundaries between these variants initially possess a high density of finely spaced (<25 nm) facets on {112} type planes. During annealing a large proportion of these fine-scale corrugations are annihilated, and the facet distribution coarsens significantly. Through in situ transmission electron microscopy (TEM), we directly observe this coarsening process. These results show a more complex behavior than geometric models for facet evolution would suggest and point to the need for an improved understanding of facet-junction properties and the interactions between grain boundary facets and dislocations.
Phase-Field Simulation of Domain Structure Evolution in Ferroelectric Thin Films
Authors: Li Y. L. , Hu S. Y. , Liu Z. K. , Chen L. Q. 
Published: April 2011

ABSTRACTA phase-field model for predicting the domain structure evolution in constrained ferroelectric thin films is developed. It employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions. In particular, the model is applied to the domain structure evolution during a cubic→tetragonal proper ferro- electric phase transition. The effect of substrate constraint on the volume fractions of domain variants, domain-wall orientations, and domain shapes is studied. It is shown that the predicted results agree very well with existing experimental observations in ferroelectric thin films.
Interface Structure in Ferritic/Austenitic Stainless Steel Bicrystals
Authors: Taisne Aude , Décamps Brigitte , Priester Louisette 
Published: April 2011

ABSTRACTElementary mechanisms of deformation by fatigue in duplex stainless steels bicrystals are studied by transmission electron microscopy (TEM). An attempt is made to correlate the bicrystal macroscopic behaviour with the interphase interface crystallography.
Fracture Toughness of Amorphous Precursor Derived Si-C-N Ceramics
Authors: Bauer A. , Zimmermann A. , Aldinger F. 
Published: April 2011

ABSTRACTFully amorphous ceramics in the system silicon-carbon-nitrogen were produced with the polymer precursor route using the commercially available polysilazane CerasetTM. Besides their high temperature thermal stability, these ceramics show excellent high temperature creep resistance. Not many investigations have been dedicated to the fracture mechanics of these materials. This paper provides data on toughness measurements utilizing bulk and indentation techniques. The double cantilever beam method (DCB) was used to study crack propagation. To determine the intrinsic toughness, the crack opening displacements (COD) of indentation cracks were determined.
Interaction of Slip Bands with Grain Boundary - in situ TEM Observation
Authors: Gemperlová Juliana , Jacques Alain , Gemperle Antonín , Zárubová Niva 
Published: April 2011

ABSTRACTMechanism of the slip transmission across the grain boundaries was studied on Σ3 bicrystals of Fe-4at%Si by transmission electron microscopy. In situ straining experiments as well as post mortem observations were performed. Three distinct events were observed in dependence on the angle α between the slip and grain boundary planes, namely transformation of the tertiary slip system in one grain into the secondary slip system in the other grain for α ≍ 90°, cross slip of dislocations of the primary slip system into the {112} plane parallel to the grain boundary for α ≍21°, and an abrupt formation of a sub-grain boundary in one grain for α ≍49°. Reasons for these diverse phenomena will be discussed in terms of interactions between the slip dislocations and the grain boundary dislocations.
A Novel Approach for the Complete Removal of Threading Dislocations from Mismatched Heteroepitaxial Layers
Authors: Zhang X. G. , Rodriguez A. , Li P. , Jain F. C. , Ayers J. E. 
Published: April 2011

ABSTRACTThe application of mismatched combinations of heteroepitaxial semiconductors has been quite limited due to the presence of high threading dislocation densities. In recent years, great progress has been made toward solving this problem using compliant substrates and lateral epitaxial overgrowth. We have proposed another approach which we call patterned heteroepitaxial processing (PHP), and which involves post-growth patterning and thermal annealing. In this paper we describe the successful application of the PHP technique to the ZnSe/GaAs (001) material system.Epitaxial layers of ZnSe on GaAs (001) were grown to thicknesses of 2000 - 6000 Å by photoassisted metalorganic vapor phase epitaxy (MOVPE). Following growth, layers were patterned by photolithography and then annealed at elevated temperature under flowing hydrogen. Threading dislocation densities were determined using a bromine/methanol etch followed by microscopic evaluation of the resulting etch pit densities.We found that as-grown layers contained more than 107 cm-2 threading dislocations. The complete removal of threading dislocations was accomplished by patterning to 70 μm by 70 μm square regions followed by thermal annealing for 30 minutes at temperatures greater than 500°C. Neither post-growth annealing alone nor post-growth patterning alone had a significant effect. By studying the annealing temperature dependence, we have determined that the dislocation removal by PHP is thermally activated. It appears that the maximum dimension for patterned regions in PHP is determined by the annealing temperature rather than an effective range for image forces.These results show that PHP can be used to completely remove threading dislocations from lattice-relaxed heteroepitaxial layers. In principle this approach should be generally applicable to mismatched heteroepitaxial materials.
Effects of Y and Zr Dopants on Grain Boundary Structure in Creep Resistant Polycrystalline Alumina
Authors: Cargill G. S. , Wang C. M. , Rickman J. M. , Chan H. M. , Harmer M. P. 
Published: April 2011

AbstractDopants Y and Zr at 100 ppm levels in high purity, micron grain-size polycrystalline alumina are mainly segregated to the alumina grain boundaries and strongly reduce high temperature creep. Information about this segregation has come from high resolution STEM composition mapping experiments. Information about local structural surroundings of the dopant atoms has come from EXAFS experiments, and information about local bonding of the dopant atoms has come from XANES experiments. Structural models for dopant grain boundary segregation provide a context for these experimental results and for effects of dopant incorporation on grain boundary mediated transport. Recent experimental and theoretical results are discussed in this paper.
Atomic and Electronic Structure of Symmetric Tilt Boundaries in ZnO
Authors: Oba Fumiyasu , Nishitani Shigeto R. , Adachi Hirohiko , Tanaka Isao , Kohyama Masanori , Tanaka Shingo 
Published: April 2011

AbstractWe have investigated the atomic and electronic structure of symmetric tilt boundaries in ZnO by a first-principles plane-wave pseudopotential method. Equilibrium boundary geometries with distorted- and dangling-bonds are obtained. Localized electronic states form mainly at the lower valence band and the bottom of the upper valence band owing to the bond disorder. However, the electronic states near the band gap are not significantly affected; deep states are not generated in the band gap. The small effects of the bond disorder on the electronic structure can be attributed to the band structure characteristic of ZnO.
Atomic Scale Characterization of Oxygen Vacancy Segregation at SrTiO3 Grain Boundaries
Authors: Klie R.F. , Browning N. D. 
Published: April 2011

AbstractWe have examined the structure, composition and bonding at an un-doped 58° [001] tilt grain-boundary in SrTiO3 in order to investigate the control that the grain boundary exerts over the bulk properties. Room temperature and in-situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements indicate that the widely observed electronic properties of grain boundaries may be due to an excess of mobile oxygen vacancies that cause a highly doped n-type region in the close proximity ( ≍ 1 unit cell) to the boundary. These results are shown to be consistent with both theoretical models and lower resolution chemical analysis.
Interfacial Structure of BaRuO3 Thin Films Grown On (111) SrTiO3
Authors: Tian W. , Lee M. K. , Eom C. B. , Pan X. Q. 
Published: April 2011

AbstractBaRuO3 thin films were grown on (111) SrTiO3substrate by 90° off-axis rf-sputtering. Transmission electron microscopy studies revealed that the films consist of the metastable 4H hexagonal polymorph of BaRuO3 along with few defects. The films are c-axis oriented, single crystalline with the in-plane orientation relationship with respect to the SrTiO3substrate of [112 0] BaRuO3 // [110] SrTiO3. High-resolution transmission electron microscopy (HRTEM) studies of the film-substrate interface revealed the existence of a thin intermediate layer of the 9R hexagonal polymorph of BaRuO3 between the (111) SrTiO3 substrate and the 4H film. The formation mechanism for the intermediate layer is not fully understood though. Through the combination of HRTEM and quantitative image simulations, the atomic structure of the interface between the 9R intermediate layer and the underneath (111) SrTiO3 was constructed. Three initial growth modes were observed, each of them adopting the local continuity of the oxygen octahedral sublattice across the interface.
Atomic Force Microscopy Studies of Fracture Surfaces From Oxide / Polymer Interfaces
Authors: Jenkins Maura , Snodgrass Jeffrey , Chesterman Aaron , Dauskardt Reinhold H. , Bravman John C. 
Published: April 2011

AbstractAtomic Force Microscopy (AFM) is used to characterize fracture surfaces in silicon oxide / silane adhesion promoter / BCB polymer systems. Fatigue striations were found on some samples, and these were correlated with the crack growth rate per fatigue cycle. X-ray Photoelectron Spectroscopy (XPS) was used to identify the species present on each surface, and it was found that striations only form when the fracture path is through the polymer.
The Interfacial Reaction Products and Mechanical Properties with Oxidized Layer Thickness of SiC Particle in 2014Al/SiC Composites
Authors: Kim Youngman , Jeong Jong-Hoon , Lee Jae-Chul 
Published: April 2011

AbstractMetal matrix composites (MMC's) are known to have wide applications in parts of transportation devices such as automobiles and aircraft. Al matrix composites using SiC particles as reinforcements are especially spotlighted because of low cost, superior specific modulus, specific strength, wear resistance and high temperature stability. However, Al4C3 formed by the interfacial reaction between Al and SiC weakens the interfacial bonding strength. It is also known to be unstable in the water-soluble atmosphere.In this study, the passive oxidation of SiC powder is used as protective layer against the reaction between the Al matrix and the SiC particle. We investigated the changes in interfacial product of the composites and mechanical properties such as interfacial bonding strength, and tensile strength in terms of the oxidized layer thickness of the reinforcement.
Segregation of Yttrium at Grain Boundaries in α-Al2O3
Authors: Nufer Stefan , Kurtz Wolfgang , Rühle Manfred 
Published: April 2011

AbstractQuantitative X-ray analysis allows the investigation of yttrium-doped grain boundaries. In the present study well-defined bicrystal interfaces were characterized. The quantitative comparison of segregation at different bicrystals requires a correction of artifacts in the X-ray spectra due to mass absorption, fluorescence, and beam spread. Mean grain boundary excess values of 3 Y/nm2 and around 5 Y/nm2 were found at a ∑17 and ∑37 symmetrical grain boundary, respectively. Additionally, with the ∑17 bicrystal YAG precipitation and presence of silicon was found.
Ellipsometry as a Sensitive Technique to Probe film -Substrate Interfaces: Al2O3 on Si(100)
Authors: Singh M. P. , Raghavan G. , Tyagi A. K. , Shivashankar S. A. 
Published: April 2011

AbstractAn attempt has been made to study the film-substrate interface by using a sensitive, non- conventional tool. Because of the prospective use of gate oxide in MOSFET devices, we have chosen to study alumina films grown on silicon. Film-substrate interface of alumina grown by MOCVD on Si(100) was studied systematically using spectroscopic ellipsometry in the range 1.5-5.0 eV, supported by cross-sectional SEM, and SIMS. The (ε1,ε2) versus energy data obtained for films grown at 600°C, 700°C, and 750°C were modeled to fit a substrate/interface/film “sandwich”. The experimental results reveal (as may be expected) that the nature of the substrate -film interface depends strongly on the growth temperature. The simulated (ε1,ε2) patterns are in excellent agreement with observed ellipsometric data. The MOCVD precursors results the presence of carbon in the films. Theoretical simulation was able to account for the ellipsometry data by invoking the presence of “free” carbon in the alumina films.
Relationships between Film Chemistry, Structure, and Mechanical Properties in Titanium Oxide
Authors: Pang M. , Eakins D.E. , Norton M.G. , Bahr D.F. 
Published: April 2011

AbstractTitanium oxides were grown anodically to selected final potentials on grade II polycrystalline titanium under different anodization rates. XPS and RBS results show that the oxide consists of primarily TiO2with a non-stoichiometric oxide/metal interface, with the slower growth rate associated with a thicker layer at the interface. Characterization using TEM reveals that the structure of the oxide evolves from a primarily amorphous phase to islands of crystallites in an amorphous matrix, to an entirely crystalline phase by increasing the polarization potential. Slower growth rates tend to remain crystalline at higher potentials. The mechanical strength of oxide films extracted from load-depth data by nanoindentation varies dramatically for oxide films grown by different rates at 9.4 V, and to a lesser extent at lower potentials. The variation of film strength is associated with both compositional and structural characteristics.
Influence of Pre-Gate Cleaning ON Si/SiO2 Interface and Electrical Performance of Cmos Gate Oxide
Authors: Duan X. , Kisslinger K. , Mayes L. , Ruby S. , Barrett J. 
Published: April 2011

AbstractThe Si/SiO2 interface is attracting new interest as gate dielectrics in MOS devices become ultra thin. In this paper, the impact of pre-gate cleaning on the morphology of the Si/SiO2 interface and the electrical performance of CMOS gate oxides has been systematically investigated. Using the High-Resolution Transmission Electron Microscopy (HRTEM) technique, we observed the Si/SiO2 interface at an atomic level. We have found a direct experimental relationship between the pre-gate cleaning scheme, Si/SiO2 interface morphology, and the electrical properties of CMOS gate oxides. When the ratio of H2O2:NH4OH ≥ 1.45, the roughness of the Si/SiO2 interface was dramatically improved, which, in turn, increased the Charge-to-Breakdown to an ideal value.
A Subnanoscale Study of Segregation at CdO/Ag(Au) Heterophase Interfaces
Authors: Sebastian Jason T. , Hellman Olof C. , Seidman David N. 
Published: April 2011

AbstractThree-dimensional atom-probe (3DAP) microscopy permits the atom-by-atom reconstruction of a small volume (typically 10 nm × 10 nm × 100 nm) of a material with respect to both the positions and chemical identities of individual atoms. It is, therefore, ideally suited for the study of solute segregation at internal heterophase interfaces. We present recent results of a 3DAP microscopy study of solute segregation at ceramic/metal (C/M) heterophase interfaces prepared by internal oxidation. In particular, results on the CdO/Ag(Au) (where Au is the segregating species) system are presented. In the 3DAP atomicreconstructions, the interfaces of nanometer-size CdO ceramic particles are delineated as Cd isoconcentration surfaces. The distribution of the segregating species as a function of distance to the isoconcentration surfaces is determined with the proximity histogram (or proxigram) method. Two interfaces are investigated in detail. The first shows no appreciable Au segregation, while the second exhibits segregation with a Gibbsianinterfacial excess of 1.65 nm-2at 650°°C.
Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent Surface Processes
Authors: Diebold Ulrike 
Published: April 2011

AbstractSurface defects are important in oxide surface chemistry, because they change not only the surface geometric structure, but also affect the local electronic structure. Scanning Tunneling Microscopy (STM) images with atomic-scale resolution, in combination with area-averaging surface spectroscopies, is an ideal tool to study local surface defects and their relationship to surface reactivity. We report STM results onTiO2(110) surfaces which show the surprising influence of bulk defects on surface properties. Thereduced crystals used in this and other surface science studies contain Ti interstitials and oxygen vacancies. Re-oxidation at elevated temperatures results in the growth of additional TiO2 layers with Ti coming from the bulk of the crystal and O from the gas phase. This often result in partially incomplete surface structures with many undercoordinated atoms. The esorption behavior of elemental S, dosed at room temperature, depends on the reduction state of the sample. This is explained by a mechanism where desorption froma weaklybound precursor state competes with the availability of new adsorption sites in the form of oxygen vacancies which migrate from the bulk to the surface.