bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inert Gas Condensation of Iron and Iron-Oxide Nanoparticles
Authors: Baker C. , Ismat Shah S. , Hasanain S. K. , Ali B. , Shah L. , Li G. , Ekiert T. , Unruh K. M. 
Published: April 2011

ABSTRACTAn inert gas condensation technique has been used to prepare nanometer-sized particles of metallic iron by evaporation and agglomeration in a flowing inert gas stream. The resulting Fe nanoparticles were protected from complete oxidation either by the formation of a thin Fe-oxide surface passivation layer or by immersion in an oil bath. X-ray diffraction and transmission electron microscopy measurements indicated that the nanoparticles were typically between 10 and 20 nm in size, that the thickness of the Fe-oxide surface passivation layer was between 3 and 4 nm, and that the oil immersed samples exhibited a significant smaller volume fraction of Fe-oxides than did the surface passivated samples. Room temperature magnetization measurements were also carried out and the coercivity and saturation magnetization of the surface passivated and oil immersed samples determined. Although the coercivities and saturation magnetization values of both samples were very similar, the Fe/Fe-oxide samples exhibited a single component hysteresis loop while the Fe/oil samples exhibited a two component loop.
Chemically Functional Alkanethiol Derivitized Magnetic Nanoparticles
Authors: Fleming David A. , Napolitano Michael , Williams Mary Elizabeth 
Published: April 2011

ABSTRACTChemically functional magnetic nanoparticles, comprised of an Fe core encased in a thin Au shell, have been prepared by sequential high temperature decomposition of organometallic compounds in a coordinating solvent. A novel approach to encapsulate the Fe core in Au has been developed. TEM analysis confirms that the nanoparticles are monodisperse (∼20%) with average diameters of 8nm. The nanoparticles were subsequently functionalized with alkanethiolate ligands, which prevent aggregation, enable solubility in a range of solvents (both hydrophobic and hydrophilic), and permit subsequent derivatization (e.g., via ligand exchange reactions). The functionalized particles are characterized using high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and ultraviolet-visible (UV-Vis) absorption spectroscopy.We have utilized place-exchange to impart chemical functionality to the nanoparticles by attaching either (1) thiol-derivatized redox moieties (e.g., ferrocene) or (2) alkanethiols with terminal reactive groups such as alcohols, amines and carboxylic acids. This paper presents our preliminary investigations of the voltammetry of the former class of these magnetic core/shell nanoparticles.
Epitaxial Growth and Magnetic Behavior of (Ni,Zn)Fe2O4 Thin Films on Si Substrate Using Designed Buffer Layers for Novel Memory Application
Authors: Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu 
Published: April 2011

ABSTRACTEpitaxial nickel zinc ferrite (Ni,Zn)Fe2O4 (NZF) thin films were successfully deposited on (MgO-Al2O3)/CeO2/YSZ/Si(001) substrates, where (MgO-Al2O3) is MgO doped with Al2O3. The crystallographic orientation and magnetic properties (saturation magnetization: Ms, and squareness: Mr/Ms where Mr is remanent magnetization) of NZF thin films were considerably changed with the amount of Al2O3 addition. If the amount of Al2O3 addition was less than 7 mol%, (001)-oriented epitaxial NZF thin films were obtained and the films had low squareness (around 45%). If the amount of Al2O3 addition was more than 7 mol%, (111)-oriented epitaxial NZF thin films were obtained and the films had high squareness (around 60–81%). Maximum squareness (81%) was obtained if the amount of Al2O3 addition was 26 mol%. For the sample with this Al2O3 content, the lattice mismatch between NZF and (MgO-Al2O3) buffer layer was 3.2%. The fact that high squareness was not obtained if lattice mismatch was very small (-0.3% on MgO) but obtained if lattice mismatch was 3.2% suggests that lattice mismatch to a certain content is important to avoid the formation of antiphase boundaries (APBs). This consideration was confirmed by examining other buffer layers having various lattice mismatches with NZF.
SiO2 Formation at the Aluminum Oxide/Si(100) Interface
Authors: Chowdhuri A. Roy , Takoudis C. G. , Klie R. F. , Browning N. D. 
Published: April 2011

ABSTRACTThin films of aluminum oxide were deposited on clean Si(100) substrates using trimethylaluminum and oxygen at 300°C. Infrared spectroscopic and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate or SiO2 phase formation at the film/substrate interface. The O/Al ratio in the as deposited film was found to be higher than that in stoichiometric Al2O3. On annealing the as deposited samples in Ar at higher temperatures, a peak due to the transverse optical phonon for the Si-O-Si stretching mode appeared in the infrared spectra. A combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Z-contrast images and electron energy loss spectra, obtained while heating the sample inside the scanning transmission electron microscope were used to follow the interfacial SiO2 formation.
In situ investigation of the stress evolution during deposition of Ti/Al-multi layer films as a function of layer thickness and substrate temperature.
Authors: Lackner St. , Abermann R. 
Published: April 2011

ABSTRACTIn order to further investigate the origin of growth instabilities in aluminium rich Ti/Al-alloy films, formed by simultaneous deposition of the two alloy components, from separate evaporation sources, we have investigated the growth stress of multilayer-films under UHV-conditions, formed by a variable number of double layers of Ti and Al, by in situ internal stress measurements. The thickness of the respective Ti/Al-double layer was varied between 6.25 nm and 25 nm and the thickness of the respective titanium and aluminium layer was chosen to achieve an overall composition of Ti25Al75in a 150 nm thick film. The multilayer films were deposited on 10 nm thick alumina substrate films at substrate temperatures of 350°C and 450°C. Microstructure and phase formation was investigated by TEM/TED-experiments.In summary, these experiments show diffusion of aluminium (compressive stress) into the underlying film during deposition of the first monolayers and then formation (stress free or small tensile stress) of aluminium precipitates on the surface of the multilayer film during each aluminium deposition. During the subsequent titanium deposition the aluminium surface precipitates spread in a circular region under alloy formation (tensile stress) (see also accompanying paper). The respective stress contributions are strongly dependent on the double-layer thickness and substrate temperature. The increasing magnitude of the different stress contributions in the early growth stage are interpreted to indicate that the various processes are limited to specific surface regions, which get larger as the number of double-layers increases. The average film stress built up in the respective multilayer film by superposition of the stress contributions mentioned above, is also strongly dependent on double layer thickness and substrate temperature.
Dehydrogenation and Polymerization of TiOxHy Films in Obtaining Anatase Coating at Low Temperature
Authors: Takayama Kouichi , Ohshio Shigeo , Saitoh Hidetoshi 
Published: April 2011

ABSTRACTChemical-vapor-deposition of titanium tetra-isopropoxide (TTIP) under the atmosphere at low temperature has been conducted. The structure of the obtained films was assessed using Fourier transform infrared spectroscopy, X-ray diffractometry and Raman spectroscopy. These analyses indicated that amorphous TiOxHy films were obtained at gas temperatures in the range of 150–300 °C, and crystalline anatase-TiO2 film was formed at 350 °C. This distinction is accounted for by plausible chemical reactions as follows; the hydroxyl reaction of TTIP below 350 °C promotes the formation of the amorphous TiOxHy. As the temperature goes up to 350 °C, dehydrogenation of the TiOxHy films promotes to form crystalline TiO2. Also the obtained amorphous films were annealed for 10 min under the atmosphere in assessing the transformation proceeding in the solid state. The structural change is shown at 350 °C, indicating that the crystalline phase would be formed via dehydrogenation and polymerization on the surface of the amorphous phase under the atmosphere. The crystal size of the annealed films was evaluated in assessment for the transformation.
Adatom Diffusion on Strained Si(001)-(2×1) Surface
Authors: Kuronen Antti , Henriksson Krister , Kaski Kimmo 
Published: April 2011

ABSTRACTThe effects of a buried germanium island inside silicon substrate on the silicon adatom diffusion on the substrate surface have been studied by kinetic Monte Carlo simulations. The confinement of adatoms caused by the strain field of the germanium island can clearly be seen. Moreover, due to the anisotropy in adatom diffusion the confinement in directions parallel and perpendicular to the dimer rows of the surface take place in different temperatures.
Deposition Mechanism of Oxide Thin Films Manufactured by a Focused Energetic Beam Process
Authors: Wanzenboeck H.D. , Harasek S. , Langfischer H. , Bertagnolli E. 
Published: April 2011

ABSTRACTChemical vapor deposition (CVD) is a versatile deposition technique for both dielectrics and metals. CVD is based upon the adsorption of a volatile species from the gas phase and the decomposition of the adsorbed molecules on the sample surface resulting in the deposition of solid material. In contrast to thermal CVD or plasma assisted CVD used for large area coatings this work focuses on a method for locally confined deposition. A focused energetic beam is used to provide the necessary activation energy for CVD. With a focused beam material could be deposited locally within a strictly confined area down to the nanometer range. The deposition of silicon oxide microstructures utilizing two precursor gases - siloxane and oxygen - was performed by direct-write nanolithography. For initiating the CVD process energy is introduced by local ion exposure utilizing a scanning focused ion beam (FIB). The influence of the different ion fluxes and the effect of the mixture ratio of precursors were studied. Deliberate changes in the process parameters allowed adjusting the physical properties and the chemical composition of the solid silicon oxide. Process control allows tailoring of material properties according to requirements of the application.
Nanocluster Epitaxy by Annealing: Ag on H-terminated Si (111) Surfaces
Authors: Li B.Q. , Shi Y.F. , Bording J. , Zuo J.M. 
Published: April 2011

ABSTRACTWe report an experimental investigation on the morphology and orientation of Ag nanoclusters by RT deposition and subsequent annealing. We show that epitaxial Ag clusters of 2 ∼ 6 nm in diameter can be synthesized in this way. The RT self-assembled Ag clusters grow as mostly single-crystal crystallites with Ag(111)//Si(111), but the in-plane orientation has a dispersion of ∼ 9° centering at Si[110] direction. Upon annealing, the Ag clusters drastically rotated to the epitaxial configuration with the in-plane orientation aligned to the Ag[110] //Si[110] direction. The rotation and epitaxy of the Ag nanoclusters are explained based on a coincident site lattice model and interface energy minimization.
Sintering of Metal(100) Homoepitaxial Islands: Kink Rounding Barriers, Modified Size Scaling, and Experimental Behavior
Authors: Liu Da-Jiang , Stoldt C. R. , Thiel P. A. , Evans J. W. 
Published: April 2011

ABSTRACTNear-square islands form during sub-monolayer homoepitaxial growth on metal (100) surfaces. Diffusion of these islands after deposition leads to collision of island pairs, typically corner-to-corner creating dumbbell-shaped clusters. Subsequent coalescence (or sintering) recovers a near-square equilibrium shape. This process is mediated by periphery diffusion (PD) and its study can provide detailed insight into the underlying dynamic processes and energetics. Atomistic modeling reveals that the size scaling of the characteristic relaxation time, τ, depends on the detailed energy barriers of various hopping processes that contribute to PD. Simulations without an extra kink or corner rounding barrier for PD reveals τ ∼ L4, while behavior approaching τ ∼ L3 is observed with a significant extra kink rounding barrier for PD. The latter is consistent with experimental observations for Ag/Ag(100) at 300 K.
Atomic Structure of Ultrathin Iron Silicide Films on Si(111): Metastable Phases and a New Template Structure
Authors: Starke U. , Walter S. , Krause M. , Blobner F. , Bandorf R. , Weiss W. , Müller S. , Hammer L. , Heinz K. 
Published: April 2011

ABSTRACTThe initial stages of iron silicide growth on Si(111) were investigated using LEED, AES and STM experiments together with DFT calculations. In 1:1 stoichiometry, a cubic FeSi develops showing a (1×1) surface periodicity which is stable up to 300°C. The epitaxial strain energy stabilizes this bulk-unstable B2 (CsCl-type) phase for up to 250 Å thickness. The surface is Si terminated, the interface coordination of the so-called B8 type. After annealing at ≈ 600°C, a (2×2)-FeSi2 phase of higher Si content is observed which possesses cubic crystal structure. It is stable below 10 monolayers (ML) initial Fe coverage and grows in an island-like morphology. In the initial growth stage, however, a c(8×4) phase forms that completely covers the surface at 1.5 ML Fe content and appears as potential template for further growth of homogeneous films. The interpretation of atomically resolved STM images suggests that the film contains three Si and two Fe layers in B2 structure with vacancies on Fe positions. The vacancy arrangement seems to be responsible for the c(8×4) periodicity displayed by the Si adatoms in T4-position.
EFFECT OF LANTHANUM MANGANITE MODIFICATION BY CALCIUM AND/OR FLUORINE ON THE BONDING STRENGTH, MOBILITY AND REACTIVITY OF THE LATTICE AND SURFACE OXYGEN
Authors: Sadykov V. A. , Kuznetsova T. G. , Simakov A. V. , Rogov V. A. , Zaikovskii V. I. , Moroz E. M. , Kochubei D. I. , Novgorodov B. N. , Ivanov V. P. , Trukhan S. N. , Litvak G. S. , Bulgakov N. N. , Lunin V. V. , Kemnitz E. 
Published: April 2011

ABSTRACTCa and/or F-modified samples of LaMnO3have been prepared by the Pechini method. The bulk structure of samples was characterized by TEM, EXAFS and XRD, while the surface composition was studied by SIMS. Thermal analysis, O2TPD, H2TPR and isothermal pulse/flow samples reduction by CO were applied to characterize the accessible surface/bulk oxygen mobility and reactivity. A reasonable description of the experimental energetic spectrum of the surface oxygen for various types of regular and defect surface sites on the perovskite faces was achieved by using semiempirical Interacting Bonds Method in the slab approximation with a due regard for the surface face termination and relaxation. Fluorine was found to decrease the surface coverage by reactive weakly bound oxygen forms while increasing the bulk oxygen excess and mobility. Calcium generated reactive weakly bound oxygen forms while decreasing the oxygen excess in the lattice and converting the regular M-O oxygen forms into the bridging ones through migration to the surface.
A Structural Comparison of Si(100) Oxidized by Atomic and Molecular Oxygen
Authors: Randjelovic Maja , Yang Judith C. 
Published: April 2011

ABSTRACTWe compared the structural characteristics of a silica layer formed on Si(100) by oxidation in hyperthermal atomic oxygen and molecular oxygen at 493K. The laser detonation method was used to create primarily neutral atomic oxygen with kinetic energy of 5.1eV. The silicon oxides were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). We determined that atomic oxygen forms amorphous silica that is almost twice as thick and nearly double the surface roughness as compared to molecular oxygen - formed silica at the same temperature and time conditions.
Observations of TiO2 Surfaces Using Totally Reflected X-ray In-plane Diffraction Under UV Irradiation
Authors: Horiuchi T. , Ochi H. , Kaisei K. , Ishida K. , Matsushige K. 
Published: April 2011

ABSTRACTSurface lattice displacements of titanium dioxide (TiO2: rutile) during ultra-violet (UV) light irradiation have been investigated using a total reflection x-ray diffraction, which provides a high signal to noise ratio (S/N) and superior in-plane surface diffraction. Under the environments in vapors of H2O, CH3OH, C2H5OH and C3H6OH, the photo-catalytic activities of TiO2 (110), (100) and (001) surfaces subject to UV irradiation have been measured. It is found that the diffraction peaks and their full width half maxima (FWHMs) show some peculiarities with respect to the photo-catalytic activities in both surface lattices and adsorbed molecules in vapors. Furthermore, Kelvin force microscopy (KFM) has showed that there exists a very high surface potential, probably due to surface atom displacements induced by UV irradiation. With regard to the origin of the photo-catalytic activities, the induced surface potentials are discussed.
Effect of the Supercooled Liquid Region on Al85Ni7Gd8 Metallic Glass Crystallization Products
Authors: Guo F. Q. , Poon S. J , Shiflet G. J. 
Published: April 2011

ABSTRACTThe effect of the supercooled liquid region on the primary crystallization of Al85Ni7Gd8 metallic glass, which exhibits a clear glass transition before its primary crystallization, was evaluated systematically under different annealing conditions, including isothermal annealing at different temperatures and non-isothermal annealing employing different heating rates. It was found that isothermal annealing within the supercooled liquid region and non-isothermal annealing at small heating rates (≤ 5 °C/min) result in the co-precipitation of fcc-Al and Al compound(s). When isothermal annealing is done at temperatures where partial crystallization is involved, or non-isothermal annealing is carried out at a larger heating rate, the primary crystallization product is a single phase of fcc-Al. The effect of the supercooled liquid region on the crystallization product is discussed in detail.
Effect of high pressure on glass transition in Zr-Ti-Cu-Ni-Be bulk metallic glass
Authors: Wang Wei Hua , Wen Ping , Hui Zhao Yan , Xiang Pan Ming , Qian Zhao De 
Published: April 2011

ABSTRACTA new method is developed to directly exhibit glass transition in Zr-Ti-Cu-Ni-Be bulk glass-forming alloy under high pressure in metallic glass. Via the method, we derive an increase of glass transition temperature,Tgwith pressure of 5.6 K/GPa, and a formation volume (ΔVf) of 6.5 Å3for diffusion and the migration volume (ΔVm) of 6.5 Å3. The glass transition under high pressure is simulated based on the free-volume theory, and the simulations are consistent with the experimental observations.
Computer Simulations of Hydration, Alteration, and Release from Waste Glasses Using A Cell Model
Authors: Pérez-Cárdenas Fernando C. , Gan Hao , Pegg L. 
Published: April 2011

ABSTRACTA probabilistic cell model to study the hydration, alteration, and elemental release into solution from nuclear waste glasses is presented. This computational model considers the glass alteration as the product of hydration and multiple phase transformations. The model reveals that the elemental redistribution occurring as a consequence of these transformations can produce transport barriers that would affect the glass alteration and release into a surrounding aqueous solution. Importantly, the model also exhibits anapparentsaturation concentration in solution, which has a kinetic origin and is lower than the true thermodynamic value. We also highlight the interplay among the different mechanisms that give rise to the glass corrosion process.
Modeling Element Concentrations in Äspö Groundwaters
Authors: Emrén Allan T. 
Published: April 2011

ABSTRACTThe chemical properties of groundwater entering a repository for nuclear wastes, have a major impact on the performance of natural and engineered barriers. Thus, accurate models for the chemical evolution of the groundwater are important in connection with performance assessments. Simple mixing of waters is inadequate for describing most chemical properties, like concentrations of iron, pH or redox potential.In the present work, ground waters from Äspö at the Swedish east coast have been modeled. In the model it is assumed that ancient waters (end member waters) have been able to reach a steady state with respect to the minerals in the fracture walls. Due to groundwater flow, end member waters have been mixed to form intermediate waters. In the sampling process (by pumping), waters from a large number of small units are mixed too rapidly for mineral reactions to be of importance. After the sampling mixture has been formed, the water reaches equilibrium with respect to homogeneous reactions (in the aqueous phase) but not with respect to heterogeneous reactions.The CRACKER program has been used to simulate groundwater formation and sampling process according to the model. It has been found that the end member waters are fairly stable with respect to observed mineral sets.Conservative elements like Cl have been used to find the initial mixing ratios for intermediate waters. Evolution of the mixtures was simulated and finally mixing and speciation of waters from some 900 locations have been simulated to describe the final solution. It is found that the model is able to give a good agreement between observed and modeled concentrations for the ten most important elements as well as pH and redox potential.
Effect of Elevated Curing Temperature on Early Hydration and Microstructure of Composite Cements
Authors: Hill J , Whittle B R , Sharp J H , Hayes M 
Published: April 2011

ABSTRACTThe heat of hydration of a number of composite cement systems has been studied using isothermal conduction calorimetry (ICC) from ambient temperature to 90°C. The resulting hardened cement paste, from the high temperature regime, was then examined by scanning electron microscopy. Results showed that increasing the hydration temperature increased the rate of heat output for all systems and, at early ages, decreased the porosity of the sample.
Modelling of Biochemical Processes in Rocks: Oxygen Depletion by Pyrite Oxidation – Model Development and Exploratory Simulations
Authors: Sidborn Magnus , Neretnieks Ivars 
Published: April 2011

ABSTRACTThe purpose of this work is to gain understanding about one of the potential oxygen consuming processes occurring in deep subsurface crystalline rocks. A model for the depletion of oxygen by microbially mediated oxidation of pyrite along a deep subsurface conducting fracture was developed. In the model, a previously undisturbed fracture is suddenly invaded by oxygenated water. This could happen after a glacial period when the melt water penetrates down in the deep rock. We assume that no degradable organic matter is present. The oxygen in the water will be scavenged by the pyrite minerals in the rock matrix and in secondary minerals in any fracture infill. In this study the intrusion depth of oxygenated water is simulated assuming microbially mediated oxidation of pyrite mineral in the rock matrix as the main oxygen consuming reaction. Bacterial growth was modelled using Monod's dual limitation equation with oxygen and dissolved pyrite as the two limiting substrates. The bacteria grow as a biofilm on the fracture surface and are also present in the flowing water. The oxygen is transported to the microbes in the biofilm by the flowing water in the fracture. The ferrous iron and the sulphur from the pyrite move by molecular diffusion in the rock matrix. The rock matrix, near the fracture, is gradually depleted of pyrite and a dissolution front propagates away from the fracture.