bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation Of Pozzolanic Binders Using Sulpho-Calcic Fly Ashes
Authors: Pera J. , Momtazi A. Sadr , Dejean J.
Published: March 2011

Because of their high SO3 content (∼11%), sulfo-calcic fly ashes cannot be used as a cement admixture without pretreatment. The fly ashes contain mainly quicklime (CaO), anhydrite (CaSO4) and larnite (BC2S). At ambient temperatures and at normal consistency, their hydration leads to the formation of ettringite, slaked lime and gypsum. As a result, cracking and splitting of the hydrated product quickly occurs due to the crystallization of the ettringite.

The ability of these fly ashes to produce Portlandite, Ca(OH)2, led the authors to investigate pozzolanic binders by the addition of artificial pozzolans — siliceous fly ashes, slag and clay minerals — which had been calcined at moderate temperatures.

The sulfo-calcic fly ashes are ground, then slaked either in ambient or hydrothermal conditions (2 or 6 hours at 130°C). In the case of slaking under ambient conditions, ettringite is quickly produced with a definitive crystallographical structure. As a result, no volume change is observed after re-hydration of the material. By comparison, autoclave slaking does not lead to this phenomenon, and only slaked lime is produced.

The rate of hydration is studied through the development of compressive strength and by analyses of the products by differential thermal analysis (DTA) and X-ray diffraction (XRD) at various hydration times. The best results are obtained using calcined laterite or blast furnace slag.
Factors Affecting the Ability of a Fly Ash to Contribute to the Sulfate Resistance of Fly Ash Concrete
Authors: McCarthy G. J. , Tikalsky P. J. , Carrasquillo R. L. , Manz O. E. , Thedchanamoorthy A.
Published: March 2011

The objective of this summary is to report on work in progress that is examining parameters, measurable through chemical and XRD analyses, that could indicate whether a fly ash will enhance, degrade or have no effect on the sulfate resistance of fly ash concrete.

Mehta [1–4] has discussed the factors that contribute to attack of sulfates on fly ash concrete. As noted in his review paper on this subject in the preceding volume in this series [1], the agents responsible for concrete expansion and cracking are alumina-bearing hydrates, such as calcium monosulfoaluminate and calcium aluminate hydrate, that are attacked by the sulfate ion to form ettringite, calcium trisulfoaluminate. Acidic type interactions between sulfate ions and calcium hydroxide also lead to strength and mass loss.
Mineralogy of Weathered Flue Gas Desulfurization Sludges
Authors: Mattigod S. V. , Rai Dhanpat , Zachara J. M. , Amonette J. E.
Published: March 2011

Samples of flue gas desulfurization sludge were characterized chemically and mineralogically. X-ray diffraction analysis indicated that the major crystalline components in the sludge samples were calcite, hannebachite, gypsum, and quartz. Identification of major compounds was confirmed through morphological and chemical analyses using scanning electron microscopy with energy dispersive X-ray analysis. In a related study, equilibrium solubility measurements of these samples corresponded with known solubilities of calcite, hannebachite, and gypsum.
Ontario Hydro's R&D on Sorbent Injection Waste Part II. Handling and Disposal
Authors: Golomb Arnold , Nott Babu R.
Published: March 2011

Canadian utilities are investigating the use of Furnace Sorbent Injection (FSI) for control of acid gas emissions from thermal generating stations. Typically, limestone or slaked lime is injected into the furnace [1,2] and is calcined to calcium oxide (CaO), which reacts with sulphur dioxide (SO2) and oxygen, forming calcium sulphate:

or

The by-product is removed with the fly ash, using back-end particulate control equipment. The resulting solid waste usually contains substantial amounts (e.g., 20 to 40% w/w) of unreacted CaO, which can cause handling and disposal problems because of its vigorous exothermic reaction on contact with water:

The solid waste can set prematurely in the handling equipment. It can also produce a harmful dust and/or yield a highly alkaline leachate that could affect local ground and/or surface water supplies.
Semi-Quantitative X-Ray Diffraction Analysis of Fly Ash by the Reference Intensity Ratio Method
Authors: McCarthy Gregory J. , Thedchanamoorthy A.
Published: March 2011

A protocol for relatively inexpensive and rapid semi-quantitative x-ray diffraction analysis of fly ash mineralogy by the Reference Intensity Ratio (RIR) method is described. RIR's for the common crystalline phases in fly ashes derived from low rank and bituminous coal are given. The method is semi-quantitative for some phases because of unavoidable overlaps of the stronger peaks suitable for quantitation. Use of the protocol is illustrated with the four fly ash Standard Reference Materials supplied by the National Institute of Standards and Technology. Recommendations for implementation of this protocol in other laboratories and for improvements in quantitation of fly ash mineralogy are given.
A Tight-Binding Hamiltonian for the High-Temperature Superconductor YBa2Cu3O7
Authors: DeWeert M.J. , Papaconstantopoulos D.A. , Pickett W.E.
Published: March 2011

We present a highly accurate tight-binding parametrization of the LAPW band structure of the high-temperature superconductor YBa2Cu3O7, discuss the methodology used in obtaining this fit, and its potential application to a Tight-Binding Coherent-Potential Approximation (TB-CPA) calculation of the effects of oxygen vacancies on the electronic structure.
Coherency Strain Modeling of Elastic Moduli in CU/NB Multilayers
Authors: Jankowski A. F.
Published: March 2011

An anomalous decrease in the elastic moduli of Cu/Nb multilayers has been observed via acoustic wave measurements. The decrease occurs for (111) fcc Cu and (110) bcc Nb layered structures with repeat periods between 1 and 5 nm. The coherency strain model has been used to simulate modulus enhancement in noble/transition metal multilayers. This approach addresses the atomic displacements corresponding with the lattice distortions of biaxially stressed layers. Elastic moduli are derived with respect to higher order differentials of a Born-Mayer type potential for nearest neighbor ions. The elastic moduli anomalies of Cu/Nb multilayers will be modelled within this conceptual framework.
First-Principles Theory of Alloy Phase Diagrams
Authors: Zunger Alex , Ferreira L. G. , Wei S.-H.
Published: March 2011

Temperature-composition phase diagrams of alloys are calculated by a new method combining (i) first principles total energy calculations (at T=0) for ordered structures, using the local density formalism, with (ii) finite-temperature statistical-mechanics approach (the Cluster Variation Method) to the solution of the multi-spin Ising model, using volume-dependent interaction energies obtained from (i). Novel features, including the appearance of metastable long-range ordered compounds at low temperatures are discovered.
Numerical Simulations of the Lattice Stability of β-Phase Hume-Rothery “ALLOYS”
Authors: De Graef M. , Verlinden B. , Delaey L.
Published: March 2011

A new empirical potential model is proposed which can be used for a full fit to second and third order elastic moduli. The lattice stability of the β-phase of Cu-based martensitic alloys is known to depend strongly on these moduli. The pair potential is then used to compute the eigenvalues of the effective elastic moduli tensor for different deformations such as uniaxial z-distortion and (110)[110] shear. The results of these simulations are compared with the predictions of linear elasticity theory.
Application of a New Three-Body Potential to Vitreous Silica and Sodium Silicate Glasses
Authors: Feuston B. P. , Newell R. N. , Garofalini S. H.
Published: March 2011

An empirical three-body potential, suitable for molecular dynamics (MD) simulations, has been developed to model the natural covalency of the Si-O bond in vitreous silica and silicate glass systems. Through the addition of a small directional-dependent three-body term to a previously used modified ionic pair interaction, a narrow distribution of tetrahedral angles and a low concentration of defects were obtained, in good agreement with experiment. The structure of bulk silica resulting from the MD technique also contained a larger average ring size, no edge-sharing tetrahedra, and a calculated static structure factor in good agreement with neutron diffraction results. The simulated sodium silicate glass was also largely improved over previous simulations using pair interactions alone. All silicon atoms were found to be exactly four coordinated while the number of non-bridging oxygen nearly equaled the number of sodium ions present with a reasonable distribution of Qi species.
An Ab-Initio Multicenter Tight-Binding Model for Molecular Dynamics Simulations
Authors: Sankey Otto F. , Niklewski David J.
Published: March 2011

A new, approximate method has been developed for computing total energies and forces for a variety of applications including molecular dynamics simulations of covalent materials. The method is tight-binding-like and is based on the local density approximation within the pseudopotential scheme. Slightly excited pseudo-atomic-orbitals are used, and the tight-binding Hamiltonian matrix is obtained in real space. The method is used to find the total energies for five crystalline phases of Si and the Si 2 molecule. Excellent agreement is found with experiment. A molecular dynamics simulated annealing study has been performed on the Si 3 molecule to determine the ground state configuration.
Monte Carlo Simulation of Precipitate Nucleation and Growth: Time Dependent Results
Authors: Lavine James P. , Hawkins Gilbert A.
Published: March 2011

A three-dimensional Monte Carlo computer program has been developed to study the heterogeneous nucleation and growth of oxide precipitates during the thermal treatment of crystalline silicon. In the simulations, oxygen atoms move on a lattice with randomly selected lattice points serving as nucleation sites. The change in free energy that the oxygen cluster would experience in gaining or losing one oxygen atom is used to govern growth or dissolution of the cluster. All the oxygen atoms undergo a jump or a growth decision during each time step of the anneal. The growth and decay kinetics of each nucleation site display interesting fluctuation phenomena. The time dependence of the cluster size generally differs from the expected 3/2 power law due to the fluctuations in oxygen arrival at and incorporation in a precipitate. Competition between growing sites and coarsening are observed.
Calculating Barriers to Oxygen Penetration on Metal Oxides with the Effective-Medium Theory
Authors: Ronay Maria , Nordlander Peter
Published: March 2011

We estimated surface penetration barriers for interstitial oxygen using a simple calculational scheme, the effective-medium theory for a single atom. In this theory the single parameter describing the host is the electron density. Since the electron density depends primarily on the interatomic distances, i.e. the structure of the host, we found that the barrier to oxygen penetration in oxides depends primarily on the structure of the oxide, the closest-packed isotropic oxides with the smallest lattice constants having the highest barriers.
Dislocation Core Properties in Bulk and Layered Materials
Authors: Duesbery M.S. , Grossmann B. , Joo B.
Published: March 2011

The dislocation core is now recognised as a major contributor to many physical properties in bulk materials, for example the plasticity of metals. Less well known is that the dislocation core can be similarly important in two-dimensional (2D) systems such as surface films. Core properties in bulk materials are reviewed briefly, with emphasis on the diversity of behavior and on unifying concepts. Dislocation cores in 2D matter are considered in more detail, with particular reference to the role of the dislocation core in the melting transition.
Ab-Initio Molecular Dynamics Approach to the Study of Grain Boundaries in Semiconductors
Authors: Tarnow E. , Bristowe P. D. , Joannopoulos J. D. , Payne M. C.
Published: March 2011

Using an ab-initio molecular dynamics approach based on the Car-Parrinello method, the detailed atomic and electronic structure of a high-angle grain boundary in germanium is determined by investigating its energy-translation surface. Information concerning the coordination of the lowest energy configuration, its translation state, volume change, structure factor and local density of states is obtained.
The Energetics Associated with the Formation of Interfaces, Multilayers and Adlayers
Authors: Watson R. E. , Weinert M. , Fernando G. W. , Davenport J. W.
Published: March 2011

A combination of bulk and slab total energy calculations have been done to disentangle the energetics of metal adlayer and multilayer formation. Results have been obtained for Pd/Nb(110), Pd/Nb(001), Ag/Nb(ll0), Ag/Nb(001) and Nb/Pd(111) which provide a picture consistent with what is known experimentally for these systems.
Fluorine-Silicon Reactions and the Etching of Crystalline Silicon
Authors: Van De Walle Chris G. , Mcfeely F. R. , Pantelides S. T.
Published: March 2011

The interaction between F atoms and crystalline Si, which is essential for etching processes in semiconductor device fabrication, is investigated with state-of-the-art theoretical techniques. The theory is based on the pseudopotential-density-functional method in a supercell geometry. A comprehensive picture of F reactions with the Si surface, the bulk, and the near-surface region is obtained, in terms of which the etching process is elucidated. Insertion of F into Si-Si bonds becomes possible because of relaxed steric constraints in the near-surface region. Dependence of the etch rate on doping follows naturally, in agreement with observations. Similarities and differences between F-Si and H-Si reactions are discussed.
The Interaction of an Atom with a Surface: A Model Based on Effective Medium Theory
Authors: Karimi M. , Vidali G.
Published: March 2011

The interaction potential between an atom and a surface is constructed using the “effective medium theory” (EMT) for the repulsive part of the interaction, and the damped dipole-dipole and dipole-quadrupole Van der Waals terms for the attractive part. This model is then applied to the following systems: He/MgO, LiF, NaCl, Ag and Cu.
First Principles Calculations of Surface Stress
Authors: Meade Robert D. , Vanderbilt David
Published: March 2011

Only recently have there been fully quantum-mechanical calculations of two-dimensional surface stress tensors. We have calculated total energies and stresses of semiconductor surfaces within the Local Density Approximation, using norm-conserving pseudopotentials. In order to hasten convergence of the stress with respect to basis size, it is useful to remove a fictitious tensile stress. We have calculated surface stress for the relaxed Si (111) 1×1 and 2×2-adatom surfaces, as well as for the relaxed Ge (111) 1×1 and 2×2-adatom surfaces. We have also calculated the surface stress for several chemisorbed systems, including Ga, Ge and As chemisorbed onto Si. We find a dramatic correlation between the electronic structure and chemistry of the surface, and its elastic properties.
Tersoff-Type Potentials for Carbon, Hydrogen and Oxygen
Authors: Brenner Donald W.
Published: March 2011

The application of Tersoff-type potentials are illustrated for examples from three distinct classes of chemical systems: a covalently-bonded solid (carbon), a gas-phase few-body reactive system (H3), and a molecular solid (oxygen). For carbon, the potential energy expression yields stable planar graphite layers as well as a stable diamond phase, both with correct densities and binding energies. The potential also predicts the π-bonded chain structure to be the energetically-preferred reconstruction on the {111} surface of diamond, in agreement with ab initio studies. For hydrogen the potential provides a quantitative description of accurate ab initio energies. The oxygen potential describes both the O2 and O3 molecules, and qualitatively describes intramolecular bonding in the condensed phase.
Interatomic Potentials in Ioncovalent Solids
Authors: Cormack A.N. , Catlow C.R.A.
Published: March 2011

The use of interatomic potentials in the simulation of ionocovalent solids is discussed. Some of the problems that may arise in the application of atomistic simulations to these solids are highlighted and some criteria for the validation of interatomic potentials for this class of solids are presented.
Calculation of the Hubbard-Type Many Body Interaction Parameters using Constrained Density Functional Theory
Authors: Schluter Michael , Hybertsen Mark S. , Christensen Niels E.
Published: March 2011

The constrained density functional approach is used to calculate the energy surface as a function of local charge fluctuations in La2CuO4. This energy surface is then mapped onto a self consistent mean field solution of the Hubbard model which allows extraction of the Coulomb interaction parameters when combined with oneelectron parameters derived from band structure results. The present calculations indicate that La2CuO4 is intermediate between the extreme spin or charge fluctuation regimes. This severly restricts the range of parameter space for theories of quasiparticles, optical excitations and possible pairing mechanism based on the extended Hubbard model.
Applications of Sims to Spatially Modified Polymer Film Characterization
Authors: Linton Richard W. , Judy Cheryl L. , Maybury Susan G. , Corcoran Sean F.
Published: March 2011

The predominant application of secondary ion mass spectrometry (SIMS) to organic polymeric solids has been the molecular monolayer analysis of thin films in the “static” mode. The primary emphasis in this paper, however, is the evaluation of SIMS for two or three dimensional compositional mapping studie of spatially modified polymer. This often requires the use of the “dynamic” SIMS mode to provide lateral images, depth profiles, or 3-D image depth profiles. Selected applications are presented including SIMS studies of surface derivatized polymers, metal-doped conductive polymer films, and patterned polymeric materials or fibers. One analytical objective is to assess the extent to which compositional information is limited by primary beam damage. The outlook for SIMS instrumentation combining high lateral spatial resolution with minimal primary beam damage to surface molecules is summarized, for example the combination of microfocused liquid metal ion sources and time-of-flight mass spectrometry.
High Resolution Electron Microscopy of Grain Boundaries in Nanophase Palladium
Authors: Thomas G. J. , Siegel R. W. , Eastman J. A.
Published: March 2011

Using high resolution electron microscopy, consolidated nanophase palladium samples were examined following electrolytic thinning after a hydriding - dehydriding cycle at 310 K. Due to the small size and random orientations of the individual grains, a large number of grain boundaries were available for examination. Some of these yielded adequate imaging conditions to allow observation of the lattice structure in the grain boundary regions. Image simulations were performed to determine the sensitivity of the technique to lattice disorder. The results of these studies suggest that grain boundary structures in nanophase palladium are similar to those in conventional coarse-grained polycrystals.
Surface Enrichment in Polymer Blends: Simple Theory and an Experimental Test
Authors: Jones R.A.L. , Kramer E.J. , Rafailovich M.H. , Sokolov J. , Schwarz S.A.
Published: March 2011

If a polymer mixture which is in the bulk one-phase region is next to an interface - this may be with another polymer, with a non-polymeric solid, or with the air - the composition of the mixture at the interface will be different from the bulk [1-4]. There are two questions we would like to understand: what determines the composition of the mixture at the interface, and how does that composition increment decay back to the bulk value. This surface or interface segregation has important practical consequences; in the surface case such segregation will profoundly affect wettability, with consequences for the strength of adhesive joints and the biocompatibility of polymeric surgical implants, as well as influencing friction and wear; at interfaces with non-polymers segregation is important for the adhesion of mixed polymer phases to non-polymer phases such as reinforcing fibres or fillers. In this paper we describe some experiments on surface segregation in a very well characterised model system and we describe a recent theory that can be quantitatively tested by our data. We will consider the consequences of this new understanding of surface segregation in polymer mixtures, and we will argue that many of these conclusions may be carried over to the more general case of interface segregation, which opens up a number of interesting technological possibilities.
Rutherford Backscattering Spectrometry Studies on Copper and Chromium Diffusion in Polyimide
Authors: Paik Kyung W. , Ruoff Arthur L.
Published: March 2011

Diffusion of Cu in polyimide(PI) film was observed after Cu evaporation on PI at room temperature. Annealing treatment significantly enhanced the diffusion of Cu. The diffusion coefficient measured at 200 and 400 C using the Fickian erfc solution are 3 × 10−14 and 1 × 10−13 cm2/sec, respectively. Cu shows the Fickian diffusion behavior. In contrast to Cu, no clearly measurable diffusion had occurred for an as-deposited Cr specimen and a specimen annealed at 400 C for 1 hour. However, for longer annealing times a slight amount of Cr diffused into PI because of the growth of the intermixed region. The diffusion coefficients of Cr at 200 and 400 C for less than 20 hours are 2 × 10−15 and 7 × 10−15 cm2/sec, respectively. The diffusion of Cr in PI shows non-Fickian behavior.
In Situ Ftir Investigations of Polymer Surface Modification in Downstream Microwave Plasma Etching
Authors: Leu Jihperng , Jensen K.F.
Published: March 2011

In situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy investigations of etching of thin polyimide and poly(methyl methacrylate) films (200-1500Å) in downstream microwave NF3/O2/Ar plasmas are reported. Etch rates and surface chemistry are monitored as a function of gas phase composition, plasma treatment conditions and time. NF3/Ar plasma treatment leads to significant surface fluorination characterized by the formation of aliphatic fluorine compounds (CFx), acyl fluorides, benzoyl fluoride, and polyfluorinated benzene. Addition of oxygen to the etching gas reduces the degree of surface fluorination and modifies the chemical structure. The absorption bands due to CFx structures decrease gradually while polyfluorinated benzene rings and benzoyl fluoride are absent for NF3/O2 mixtures with more than 20% oxygen. The effect of humidity on the plasma-modified polymers is studied by comparing infrared spectra collected in situ with those after air exposure. For NF3/O2 plasma-treated polyimides significant changes are observed while samples fluorinated in NF3 show no changes after exposure to air overnight. The FTIR data are supplemented by XPS analysis.
Moisture Intrusion in Sio2/Epoxy Interfaces
Authors: Takahashi Ken M.
Published: March 2011

In-situ interfacial impedance measurements were used to study the effects of moisture at 80 °C on the interface between oxidized silicon and a diglycidyl ether of bisphenol A (DGEBA) epoxy cured with diethylene triamine (DETA). Using two electrode configurations, admittances attributable to bulk and interfacial conduction processes were distinguished. Bulk impedance measurements followed Randles behavior; conduction in the bulk epoxy was ionic, and was diffusion controlled at low frequencies. Equivalent circuit models were used to demonstrate that an apparent interfacial conduction process was caused by distributed current leakage into the silicon subphase, not a true interfacial conduction path that would indicate water adsorption or interfacial aggregation. However, transitions in diffusivity and bulk epoxy permittivity behavior above a 70-80% relative humidity threshold were observed. Effective epoxy permittivity (∈c) jumped to values indicative of a water cluster induced Maxwell-Wagner relaxation. The humidity threshold corresponds to a level that has been associated with adhesion loss in epoxies. It appears that epoxy adhesion losses result from bulk epoxy property changes at high humidity rather than interfacial bond displacement or delamination.
Morphology of Lignin-Polyurethane Blends
Authors: Feldman D. , Lacasse M.A.
Published: March 2011

The morphology of blended polyurethane (PU) sealants was studied by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The PU was modifided by mechanical mixing with various amounts of Lignin (L) to achieve a homogeneous blend. Specimens were subjected to control (C), accelerated weathering (AW), and natural weathering (NW) conditions. Results obtained from SEM analysis reveal an even distribution of L particles in the PU matrix. Furthermore, the SEM photomicrographs clearly emphasize the differing morphologies of the constituent phases. They also depict the differences in surface texture between control and aged specimens. The DSC analysis shows that the two phases are immiscible which is in agreement with observations by microscopy.
Effect of Oxygen Plasma Treatments on Polypropylene-Epoxy Interfacial Strength
Authors: Occhiello E. , Morra M. , Morini G. , Garbassi F.
Published: March 2011

The effect of oxygen plasma treatment on adhesion and surface properties of polypropylene (PP) was assessed. An oxygen rich modified PP layer, immiscible with bulk PP, was formed by the treatment. Contact angle measurements showed that macromolecular motions led with time to rearrangements of the surface layer drastically decreasing its wettability, while its composition, measured by XPS, remained unaffected.

The shear strength of PP-epoxy joints increased after plasma treatment. The locus of failure was found to occur at the PP/epoxy interface for untreated PP, within PP in the case of oxygen-plasma-treated samples, close to the modified PP/bulk PP interface. This result suggests that the plasma treament improves the interaction at the PP/epoxy interface, but weakens the mechanical strength of the surface layer thereby creating a weak point at the modified PP/bulk PP interface.
Study of Nanophase TiO2 Grain Boundaries by Raman Spectroscopy
Authors: Melendres C. A. , Narayanasamy A. , Maroni V. A. , Siegel R. W.
Published: March 2011

Raman spectra have been recorded for as-consolidated nanophase TiO2 samples with differing grain sizes and on samples annealed in air at a variety of temperatures up to 1273 K. The nanophase samples with the smallest grain size, about 12 nm average diameter, could have 15-30% of their atoms in grain boundaries; nevertheless, the strong Raman-active lines representative of the rutile structure were found to dominate all of the observed spectra, independent of grain size and annealing treatment. These lines were quite broad in the as-consolidated nanophase samples, equally in 12 nm and 100 nm grain-size compacts, but sharpened considerably upon annealing at elevated temperatures. The Raman data give no indication of grain-boundary structures in nanophase TiO2 that are significantly different from those in conventional polycrystals. However, defect structures within the grains, which anneal out at elevated temperatures, are evidenced by changes in the Raman spectra.
Fluorinated Monomolecular Assemblies: Model Systems to Probe Chemical Interactions at the Polymer-Metal Interface
Authors: Chau Lai-Kwan , Porter Marc D.
Published: March 2011

Monomolecular assemblies of n-perfluorocarboxylic acids [CF3 (CF2)nnCOOH,n=-6,7, and 8] have been adsorbed at silver by spontaneous adsorption from dilute alcoholic solutions. Infrared reflection spectroscopy indicates that the monolayers form by the reactive chemisorption of the carboxylic acid to a carboxylate salt. Ellipsometrically-determined film thicknesses increase linearly with an increase in the perfluorocarbon chain length. Contact angle measurements indicate that the packing density of the films increases with increasing chain length, resulting in an interface with a low surface free energy. The structure and properties of these interfaces are compared to those for monolayers of n-alkanoic acids. The potential utility of such assemblies to probe fundamental chemical and physical interactions at polymer-metal interfaces are also discussed.
Adhesion of Copper to Polytetrafluoroethylene
Authors: Kim Yong-Kil , Chang Chin-An , Schrott A.G. , Andreshak J. , Cali M.
Published: March 2011

An enhancement of the adhesion between copper and polytetrafluoroethylene (PTFE) has been studied. Thin-films of copper were electron-beam deposited on the surface of the polymer substrates. Peel test measurements showed that, without any treatment of the substrates, the adhesion was poor with a peel strength of 1-2 g/mm. A pronounced enhancement of the adhesion has been obtained when the fluorocarbon substrates were treated by either an ultraviolet (UV) irradiation, an ion-beam presputtering prior to the metal deposition, or heat treatments after the deposition. Among the treatments employed, the ion-beam sputtering was the most effective in improving the adhesion. The roles of the treatments and possible reasons for the enhanced adhesion are discussed in conjunction with the studies of interface morphology and chemistry using Scanning Electron Microscopy, Rutherford Backscattering Spectroscopy, and X-ray Photoelectron Spectroscopy.
The Aspects of Thermal Anneal to Intrinsic Stress and Hicrostructure of Multilayer Thin Films
Authors: Yang C. H. , Chen P.C.
Published: March 2011

Adhesion degradation mechanism at the interface of a multilayer thin film was studied as a function of annealing temperature. The multilayer thin films employed for current investigation of the temperature effect were constructed by sputtering 500 Å Cr and 10K Å Cu on both sides of kapton. A steady decrease of adhesion strength was found as a result of increasing the annealing temperature from 150°C to 350°C. Thin film and interfacial properties in association with degradation of adhesion were characterized by several techniques, including intrinsic stress measurement, Auger, TEN and SIMS. Several changes were observed by elevating the annealing temperature. It was found that the intrinsic stress in each layer changed. Both Cu and Cr grain size increased with the annealing temperature. The interface at kapton and metal became more defined. The Cu atoms were found to become mobile and diffused into Cr and kapton layer after a 350 degree annealing. In addition, a change of molecular orientation and chemistry in kapton near the interface was observed by SIMS and XPS studies. A combination of these factors resulted in a decline of adhesion strength.
Measurement of Micromechanical Properties Using Atomic Force Microscope with Capacitative
Authors: Neubauer Gabi , Cohen Sidney R. , McClelland Gary M.
Published: March 2011

A new UHV atomic force microscope for the study of micromechanical properties is described. A capacitance technique is used, which enables simultaneous measurement of forces perpendicular and parallel to the surface (i.e., load and friction), and has low noise down to frequencies below 0.1 Hz. Preliminary results for Ir- and W-tips sliding on graphite and silicon, respectively, demonstrate the capabilities of this new instrument.
Design, Development, and Applications of Novel Techniques for Studying Surface Mechanical Properties
Authors: Miyoshi Kazuhisa
Published: March 2011

This paper reviews the author's research of the adhesion, friction, and micromechanical properties of materials and presents examples of the results. The ceramic and metallic materials studied include silicon carbide, aluminum oxide, and iron-base amorphous alloys. The design and operation of a torsion balance adapted for study of adhesion from the Cavendish balance are discussed first. The pull-off force (adhesion) and shear force (friction) required to break the interfacial junctions between contacting surfaces of the materials were examined at various temperatures in a vacuum. The surface chemistry of the materials was analyzed by x-ray photoelectron spectroscopy. Properties and environmental conditions of the surface regions which affect adhesion and friction - such as surface segregation, composition, crystal structure, surface chemistry, and temperature were also studied.
Fracto-Emission from Interfacial Failure
Authors: Dickinson J. T.
Published: March 2011

Fracto-Emission is the emission of particles and photons during and after fracture of materials. The observed emission includes electrons, negative and positive ions, neutral species in both ground states and in excited states, and visible photons. This emission can often serve as a sensitive probe of crack growth and may prove to be a useful tool for investigating molecular and microscopic events accompanying crack growth and for studying the details of failure modes in a variety of materials. Interfacial failure provides unique fracto-emission signals due to the extensive charge separation accompanying separation of dissimilar materials. Here we present the results of several recent studies of interfacial failure involving a variety of materials and relate them to electronic and mechanical processes accompanying failure.
Elastic Properties of Grain Boundaries in Copper
Authors: Adams James B. , Wolfer Wilhelm G. , Foiles Stephen M.
Published: March 2011

The elastic constants of a Σ5 (100) twist grain boundary are calculated on a monolayer-by-monolayer basis, and the elastic behavior is shown to differ by up to an order of magnitude from bulk-like behavior. This unusual elastic behavior is found to be similar to that of uniaxiallystrained crystals, since the grain boundaries themselves are regions which are strained (expanded) in one direction.
Role of the Interface in the Adhesion of Cu to SiO2
Authors: Kellock Andrew J. , Baglin John E.E.
Published: March 2011

The adhesion of thin evaporated Cu films directly to SiO2 is generally poor. The adhesion can be improved by a variety of treatments, ranging from a pre-deposition Ar ion bombardment of the substrate, to post deposition bombardments with ion beams, photons or electrons. Also, if a thin layer of partially oxidized Cr is deposited onto the SiO2 prior to Cu deposition, the Cu adheres more strongly. The intrinsic mechanism responsible for these adhesion improvements remains to be understood.

We have attempted to characterize the interface of these structures by a combination of Rutherford Backscattering Spectrometry (RBS) and an adhesion peel test to determine the role each treatment plays in the adhesion process.
Precipitation at Grain Boundaries in Irradiated Austenitic Fe-Cr-Mn Alloys
Authors: McCarthy J. M.
Published: March 2011

In previous work, the phase stability of Fe-Cr-Mn alloys during irradiation was investigated in a study that included simple binaries, simple ternaries and commercially produced alloys. These low activation alloys are being considered for fusion reactor service in the first wall and in other structural applications subject to high neutron doses. In addition to phase instabilities observed within the grains, grain boundaries were susceptible to varying levels of precipitation dependent upon alloy composition, displacement dose and irradiation temperature. This paper describes the grain boundary microstructures that developed in these Fe-Cr-Mn alloys during irradiation.
An Arxps Investigation of the Initial Growth of Aluminum Films on the (0001) Face of Sapphire.
Authors: Arbab Mehran , Chottiner Gary S. , Hoffman R. W.
Published: March 2011

The (0001) face of α-Al2O3 and the initial growth of ultra-thin aluminum, films deposited on this surface were studied by a combination of low energy electron diffraction, angle resolved x-ray photoelectron spectroscopy and thermal desorption techniques. At high temperatures, the (0001) face of α-Al2O3 reconstructs to form a (√31×√31)R±9° structure which remains stable at lower temperatures, as evidenced by IEED. ARXPS shows that the annealed sanple retains its bulk composition up to the solid-vacuum interface.

Thin Al films were deposited on the above surface by in situ evaporation. ARXPS results indicate a uniform growth of the initial monolayer of aluminum. Further growth (<3 A°) deviated fr the layer by layer adsorption mechanism.
Novel Approach for High Resolution Tem Studies of Ceramic-Ceramic Interfaces
Authors: Datye Abhaya K. , Paine Robert T. , Narula Chaitanya K. , Allard Lawrence F.
Published: March 2011

Ceramic coatings on oxides can be studied by high resolution transmission electron microscopy (HRTEM), with minimal sample preparation, if the substrate consists of nonporous particles of simple geometric shape. Interfaces suitable for ‘end-on’ examination by HRTEM can be readily obtained without any necessity for ion-beam thinning. All the interface orientations that are thermodynamically stable are available for examination from a single sample. This technique is of general applicability and can be used for studies of metal-ceramic and ceramic-ceramic interfaces. We have examined the nature of boron nitride interfaces with oxides such as MgO, TiO2 and Al2O3 and find that BN appears to wet the oxide surface and form tough, adherent coatings. The hexagonal crystalline BN grows with the (0001) planes always being locally parallel to the oxide surface in every instance.
Deep-Level Dominated Current-Voltage Characteristics of Novel Semiconductor Heterostructures
Authors: Das K.
Published: March 2011

Current-voltage characteristics of Au contacts formed on buried implanted oxide silicon-on-insulator structures and molecular beam epitaxially grown GaAs on (1012) sapphire and silicon-on-sapphire substrates indicate that the dominant transport mechanism in these films is space-charge-limited current conduction in the presence of deep-level states. The deep-level parameters, determined using an analysis of the current-voltage characteristics, appear to be sensitive to the nature of crystallographic defects present in the grown layers. Conduction in the GaAs film on SOS was dominated by one discrete state located ~ 0.28eV below the conduction band-edge, which is close to the El center uniquely observed in the molecular beam epitaxially grown GaAs-on-Si. Discrete levels are also observed in annealed buried implanted oxide silicon-on-insulator films. In contrast, the GaAs films deposited directly on (1012) sapphire substrates and rapid-thermally annealed high-dose As implanted buried oxide SOI films appear to have a continuous distribution of states. The distributed states in GaAs films deposited directly on sapphire probably arise from the electrical activity of the double-position boundaries present in this material system.
Surface Structure of Sulfur Coated GaAs
Authors: Fujisaki Yoshihisa , Goto Shigeo
Published: March 2011

Surface structure of (NH4)2S treated GaAs. is investigated using PL (PhotoLuminescence), XPS (X-ray Photoelectron Spectroscopy) and RHEED (Reflection of High Energy Electron beam Diffraction). The data taken with these techniques show the strong dependence upon the crystal orientations coming from the stabilities of chemical bonds of Ga-S and As-S on GaAs crystals. The greater enhancement of PL intensity, the clearer RHEED patterns and the smaller amount of oxides on (111)A than (111)B implies the realization of a more stable structure composed mainly of the Ga-S chemical bond.
Evidence for Strong Trapping by Ionized Donors of Free Excitions in Excited States for High Purity GaAs and AlGaAs
Authors: Zemon S. , Lambert G.
Published: March 2011

Striking increases in the intensity of donor-related, photoluminescence transitions are observed in undoped (1014-1015 cm-3) GaAs for excitation energies (Ee) in the vicinity of the band-gap energy (Eg). The enhancement has maxima at Ee consistent with excitation of the n=2 and 3 states of the free exciton (Xn=2,3) and appears to be correlated to the concentration of ionized donors, suggesting that the effects are related to capture of electron-hole pairs by ionized donors through trapping of Xn=2,3. The enhancement decreases monotonically as Ee increases to values as much as 12 meV above Eg.
Optical Absorption of Deep Defects in Neutron Irradiated Semi-Insulating GaAs.
Authors: Manasreh M. O. , Pearah P. J.
Published: March 2011

Two defects were observed in thermal neutron irradiated semi-insulating liquid-encapsulated Czochralski (LEC) GaAs materials by using the infrared absorption technique. The first defect was observed before thermal annealing and it has a broad peak at ~0.83 eV. The second defect was observed after annealing the sample at 250 °C for 15 min. The latter defect is an EL2 - like defect, but is thermally unstable at 400 °C with a concentration of about an order of magnitude larger than [EL2] observed in as grown LEC materials. Both defects were found to photoquench with white light or 1.1 eV monochromatic light at 9 K and thermally recovered at 150 K. The concentration of the EL2 - like defect is reduced from 8.5×1016cm3 after annealing the sample at 300 °C for 15 min to 2×1016cm-3 after annealing at 400 °C for 15 min. This defect becomes unquenchable after the latter annealing conditions. An explanation for this behavior is offered.
New, Germanium - Related Defect in Neutron - Irradiated Gallium Phosphide
Authors: Barczynska J. , Goldys E.
Published: March 2011

GaP crystals were irradiated with thermal neutrons with a fluence 1.4 * 10 19 neutrons / cm2 . The isochronal annealing at temperatures up to 800°C resulted in n - type conductivity of irradiated samples. After 800°C anneal 10% of transmuted Ge atoms become neutral donors. Simultaneously the absorption spectrum shows a broad band centered at 1 eV. The similar feature is observed in photoconductivity. The origin of the absorption band is discussed. The band is most likely due to germanium - related defect.
Anomalous Luminescence Properties of GaAs grown by Molecular Beam Epitaxy
Authors: Szafranek I. , Plano M.A. , McCollum M.J. , Jackson S.L. , Stockman S.A. , Cheng K.Y. , Stillman G.E.
Published: March 2011

A shallow acceptor-like defect labeled “A” is frequently incorporated in molecular beam epitaxial GaAs. We report here anomalous photoluminescence effects that are induced by this defect. With increasing concentration of the “A” defect: (1) neutral and ionized donor-bound exciton peaks disappear almost completely even for donor concentration as high as 7×1014 cm-3 and compensation ratio ND/NA≈0.3; (2) a new, sharp line emerges at 1.5138 eV, and (3) the relative intensity and line shape of the free exciton transition change dramatically. These observations are discussed in the perspective of previous reports, where similar effects were, in our opinion, misinterpreted.
Infrared Studies of the Double Acceptor Zinc in Silicon
Authors: Dörnen A. , Kienle R. , Thonke K. , Stolz P. , Pensl G. , Grünebaum D. , Stolwijk N.A.
Published: March 2011

In the present paper, optical absorption studies on the neutral charge state of the double acceptor zinc in silicon are presented. Measurements were carried out in the mid infrared (MIR) and in the near infrared (NIR) region. The MIR absorption spectra show the excitation series of an effective-masslike hole, from which the Zn° level position is calculated to be at Ev + 319. 1 meV. A splitting of the ground state into 3 sublevels is assigned to hole-hole coupling and crystal-field splitting. Absorption spectra obtained in the NIR are interpreted in terms of an A° X-type bound exciton.
Luminescence Due to Mn Doped GaP
Authors: Monteiro Teresa , Pereira Estela
Published: March 2011

In n-type GaP doping with Mn gives rise to a deep centre due to Mn+2. Its luminescence occurs in the near infrared.

The behaviour of this centre is studied as a function of temperature and the thermal quenching of the luminescence interpreted as due to a non-radiative process to the ground state. The behaviour of another band that appears upon doping with Mn is also discussed.
Generation and Dissociation of Iron-Boron Pairs in Silicon
Authors: Suezawa Masashi , Sumino Koji
Published: March 2011

The generation and dissociation processes of Fe-B pairs in Si crystal are investigated by means of the measurements of electron paramagnetic resonance of Si crystals of various B concentrations doped with Fe. Fe-B pairs are generated due to annealing of the crystals at temperatures around 300 K obeying to the first order reaction kinetics. The activation energy for pair generation is determined to be about 0.65 eV which is almost equal to the migration energy of Fe impurity in a Si crystal. Fe-B pairs are found to be dissociated at tempeatures higher than 150°C leading to the precipitation of Fe.
Novel Luminescence Band in Silicon Implanted with Phosphorus and Boron
Authors: Srivastava A.K. , Sharma D.K. , Narasimhan K.L. , Sarkar D. , Premchandran V.
Published: March 2011

Photoluminescence measurements on silicon implanted with boron, phosphorus, and dual implanted with phosphorus and boron are reported. A high intensity luminescence band between 0.9–1.03 eV is observed in the samples with dual implantation of boron and phosphorus. The luminescence band has similar spectral characteristics as that of the 1.018 eV W or II band which is observed in silicon samples irradiated with neutrons or ions. However the annealing behaviour of the luminescence band observed in our samples differs considerably from that of the W band, whose intensity increases on annealing at 525 K and is quenched on heating to 600 K. The luminescence band in our samples is not annealed out even at 900 C. The temperature dependence of the intensity of the luminescence band is also studied. It shows excitonic behaviour with an activation energy of 52 meV.
Electronic Structure of Vacancy-Phosphorus Impurity Complexes in Silicon
Authors: Xu Hongqi , Lindefelt U.
Published: March 2011

We present a systematic theoretical investigation on four vacancy-phosphorus impurity complexes in silicon, i.e., a vacancy with one through four phosphorus impurities on the nearest neighbour sites of the vacancy, using a semi-empirical self-consistent tight-binding theory. The calculations are based on the Lanczos-Haydock recursion Green’s function method. The predicted energy levels in the band gap for the five cases, the isolated Si vacancy and the four complexes, show a remarkable regularity. We shed light on this regularity by relating it to the localization of the wavefunctions on the Si and P atoms surrounding the vacancy. We compare our results with experimental work.
New DLTS Peaks Associated with New Donors and Rodlike Defects in Czochralski Silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: March 2011

We have studied the effects of low-temperature preannealing and carbon on new donor formation at 650°C in phosphorus-doped Czochralski (CZ) silicon by deep-level transient spectroscopy (DLTS). In not preannealed carbon-lean samples, only a weak continuous DLTS spectrum often reported so far was observed. The intensity of this broad feature became significantly stronger in not preannealed carbon-rich samples. On the contrary, preannealed samples showed no such continuous spectra but two new DLTS peaks arising from shallow donor levels. Carbon enhanced the low-temperature peak, but retarded the high-temperature one. The latter peak is in strong correlation with the rodlike defect.