bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Polyquinoline Block Copolymer Using Small Angle Scattering
Authors: Wu Wen-Li , Stille John K. , Tsang Joseph W. , Parker Alex J.
Published: March 2011

To determine the compatibility between the rigid rod and the flexible chain polyquinolines, both small angle x-ray and neutron scattering measurements were conducted on a sample containing deuterated flexible components. The scattering intensities from both x-ray and neutron were reduced to absolute scale in order to remove the scattering contribution from microvoids which tended to overshadow the signal of molecular origin. Quantitative information regarding the extent of molecular segregation in a polyquinoline multi-block copolymer was obtained, the result indicated that the material was strongly associated but not segregated into single component phases.
Morphology of Rigid-Rod Molecular Composites: An Overview
Authors: Krause Stephen J.
Published: March 2011

Rigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. A rigid-rod, extended chain polymer component is used to reinforce a matrix of a ductile polymer with the intent of achieving a “composite” on the molecular level. After synthesis, the key to producing a molecular composite is to control morphology to disperse the reinforcing rod molecules as finely as possible in the matrix polymer. Individual rod molecules or bundles of molecular rods must have dimensions which result in a high ratio of length to width (aspect ratio) for efficient reinforcement. To achieve this, the reinforcing rod component must not phase separate at any stage of processing. Morphological characterization techniques, which can measure the orientation and dispersion (or, conversely, the degree of phase separation) of rod molecules provide the tools for correlating theoretically predicted and experimentally observed mechanical properties. Various morphological techniques which have been applied to molecular composite systems will be reviewed, including wide angle x-ray scattering and scanning and transmission electron microscopy. Structure-property correlations for molecular composite systems will be discussed with regard to models for mechanical properties. Application of new morphological techniques will also be discussed.
Kinetics of Phase Separation in Rigid Rod Polymer and Amorphous Polymer Mixtures
Authors: Nelson Donald S. , Soane David S.
Published: March 2011

Kinetics of phase separation of PBO in methane sulfonic acid are examined by time-resolved small angle light scattering. Thin films of polymer solutions are spincoated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo spinodal decomposition, following Cahn- Hilliard type phase separation kinetics upon exposure to water, leading to an exponential increase in the scattered light intensity at short times.
Solid-State Nmr Studies of Molecular Composites and Thermally Cured Copolymers
Authors: Vanderhart D.L. , Tan Loon-Seng
Published: March 2011

Proton spin diffusion experiments are conducted on two blends of nylon and poly(phenylenebenzobisthiazole) (PBZT). The blends are prepared different ways and utilize either a semicrystalline or fully amorphous nylon. The spin diffusion experiment, which was conducted using three different schemes, yields information about the shortest distances typifying the individual domains. Results suggest that in a 40/60 nylon 6,6/PBZT blend, the nylon and PBZT molecules do not mix on the molecular level, however, each domain is only about 4 nm in its minimum dimension. At the same time, some crystalline nylon regions also exist having somewhat larger dimensions. In contrast, a 50/50 amorphous nylon/PBZT sample, made via a different processing route, showed evidence for similar mixing in only a portion of the material; there was also strong evidence for compositional heterogeneity on a scale larger than 10 nm. The exact stoichiometries describing this compositional heterogeneity could not be uniquely identified on the basis of the spin diffusion studies alone; however the possibilities range from 55% of pure nylon to 35% of pure PBZT being sequestered from the more intimately mixed phase.

In a second set of experiments, the 250°C thermal polymerization chemistry of a benzocyclobutene (BCB), a bismaleimide (BMI) and an equimolar mixture of BCB and BMI was studied. These materials are candidates for thermally polymerizable matrix materials in blends with rigid-rod polymers like PBZT. Polymerization of the BCB homopolymer is found to involve multiple pathways and there is reasonably strong evidence that the reactive carbons generated by thermal ring opening of the cyclobutene moiety not only attack one another; they also attack aromatic carbons adjacent to carbonyl carbons at sites far from the ring opening reaction. Spectra of the BCB homopolymer aged at 300°C in vacuum indicate that significant chemical changes occur. This result casts a shadow on the interpretation of the good apparent thermogravimetric stability of the BCB homopolymer in air at this temperature. The equimolar mixture of BCB and BMI ideally can polymerize via the Diels-Alder mechanism to produce a linear chain of alternating BCB and BMI repeat units. The spectrum of this thermally polymerized mixture suggests a maximum of 50% of the reaction following the Diels-Alder addition; the other 50% follows homopolymerization pathways.
Third-Order Optical Susceptibilities of Molecular and Polymeric Materials. Symmetry, Frequency, and Chromophore Structure Dependence as Probed by π-Electron Theory
Authors: Li D. , Marks T. J. , Ratner M. A.
Published: March 2011

Third-order optical susceptibilities (γijkl) can be efficiently analyzed for a variety of molecular structures employing perturbation theory and a PPP-SCF-SECI-DECI π-electron model Hamiltonian. The key, frequency tripling second hyperpolarizability γijkl(−3ω;ω,ω,ω) is calculated with full single and double CI. It is found that double excitations play a major role in third-order processes, and that γijkl, like the polarizability αij, is sensitive largely to the overall size (volume) of the π system, although charge transfer excitations may also contribute. The frequency dependence of v and correlations between γijkl and conjugation length are found for a series of trans polyenes.
The Birth of Ordered Polymer Technology for Air Force Applications
Authors: Arnold Fred E.
Published: March 2011

Since the late seventies, the Air Force Materials Laboratory and Air Force Office of Scientific Research has had a very energetic program in lyotropic liquid crystalline rigid-rod polymers. The objective of the multifaceted program was the attainment of mechanical properties for a structural material comparable with those currently obtained from fiber reinforced composites. This paper will describe the orgins of this program as derived from the unique aggregation properties of aromatic heterocyclic ladder polymers.
Preparation, Characterization and Conductivity of Li3N, Li3P and Li3As
Authors: Nazri Gholamabbas
Published: March 2011

The superionic conductors lithium nitride and lithium phosphide and the semi-metallic conductor lithium arsenide were synthesized through elemental reactions of lithium melt with nitrogen gas and phosphorus or arsenic powders. A high mobility of the lithium ion was found in this class of compounds. These compounds are hard and brittle and have a dark brown color. The structures of these compounds were studied using x-ray diffraction techniques. All three compounds crystallize in a hexagonal structure with a P6/mm space group. The lattice dimensions expand anisotropically as the size of the anion increases.

The ionic and electronic conductivities of the compounds were studied using reversible lithium electrodes and an ion blocking molybdenum electrode. The temperature dependent conductivity measurements (Arrhenius plot) show a high ionic and a negligible electronic conductivity for both lithium nitride and lithium phosphide. However, lithium arsenide shows semi-metallic behavior with a high electronic conductivity. A higher degree of covalency in the ct direction and a more ionic character in x-y plane were observed. The anisotropic nature of the chemical bonds in these compounds provides a shallow potential well in x-y plane and allows the correlated motion of lithium ions.

Lithium phosphide and nitride are superionic conductors and useful materials for application in batteries and sensors. Lithium nitride decomposes below 0.5 volts and can be used in low voltage and zero current devices. Lithium phosphide is stable up to 2.2 volts and can be used for higher voltage devices. These compounds decompose in contact with water and are air sensitive.
Ion Conductivity of Nasicon Ceramics: Effects of Texture and Doping With B203 and A12 O3
Authors: Høj Jakob W. , Engell John
Published: March 2011

The Nasiconss, Na1+XZr2SiXP3Xo12 O<X<3, includes some of the best solid state sodium conductors known today. Compositions in the interval 1.6<X<2.6 show conductivities comparable to the best aβ-alumina ceramics. It is well known that the ion conductivity of 8-alumina is strongly dependent on the texture of the ceramic. Here a similar behaviour is reported for Nasicon ceramics. Ceramics of the bulk composition Na2.94 Zr1.49Si2. 20P0.80O10.85 were prepared by a gel method. The final ceramics consist of Nasicon crystals with X=2.14 and a glass phase. The grain size and texture of the ceramics were controlled by varying the thermal history of the gel based raw materials and the sintering conditions. The room temperature resistivity of the resulting ceramics varies from 3.65 103 ohm cm to 1.23 10 ohm cm. Using the temperature comparison method and estimates of the area of grain boundaries in the ceramics, the resistivity of the Nasicon phase is estimated to be 225 ohm cm at 25°C. B203 - or Al2O3 -doping of the glass bearing Nasicon ceramic lower the room temperature resistivity by a factor 2 to 5. The dopants do not substitute into the Nasicon phase in substantial amounts.
Ultrasonic Attenuation Peaks Near the Diffuse Transition Temperature in Solid Electrolytes with Fluorite Structure
Authors: Manasreh M. O. , Pederson D. O. , Aurora T. S.
Published: March 2011

Measurements of the ultrasonic attenuation and velocity have been made in solid electrolytes with fluorite structure, PbF2, BaF2, and CdF2, from room temperature to temperature at or above the diffuse solid electrolyte transition temperature, Tc. The ultrasonic attenuation peaks observed in this class of materials are associated only with the ionic conductivity saturation rather than in combination with crystallographic phase transition found in many other solid electrolytes. The relaxation rates and Arrhenius activation energies for anion motion above the transition temperature were obtained from the temperature dependence of the ultrasonic attenuation and the theory of local site fluctuations. The ultrasonic attenuation peaks observed for the first time in CdF2was used to define the diffuse transition temperature in this material. An Anomalous peak is also observed in the linear thermal expansion coefficient of PbF2.
Peo-Based Polymer Electrolytes Containing Divalent Cations
Authors: Farrington Gregory C. , Yang Hong , Hug Rokeya
Published: March 2011

Poly(ethylene oxide) is a non-aqueous solvent which can dissolve high concentrations of a wide variety of monovalent and divalent cation salts. The resulting solutions are generally heterogeneous mixtures of crystalline and amorphous regions. The amorphous components have relatively high ionic conductivities, and PEO ‘quasi-solid’ electrolytes and related polymer materials are arguably a new class of electrolyte, with properties in between those of true solids and true liquids. This paper briefly discusses the preparation and properties of PEO electrolytes containing Mg(II), Zn(II), and Pb(II) salts.
Li ion Conduction in Cross-Linked Peo-LiCF3SO3 Complex
Authors: Tsuchiya Jun
Published: March 2011

Ionic migration of cross-linked amorphous Poly (Ethylene Oxide)-LiCF3SO3was investigated by measuring ionic conductivity and diffusion coefficient. Pulsed-Field-Gradient NMR (PFG-NMR) was used for the diffusion measurement. The measurements were carried out at a temperature region between room temperature and 120°C. The PFG-NMR mea-surement shows the two modes of migration of both cation(Li) and anion (CF3 SO3-) for specimens containing plasticizer (CH30(CHeiH20)gH3C). The two modes of migration for anion are present for specimens without the plasticizer. Li+ transport number is found to be less than 0.1 for specimens without the plasticizer. Plasticizer is found to increase the Li+ ion transport number.
Fe2+ Electronic Transitions in Raman and Infrared Spectra of FePSe3 and FePS3 Crystals
Authors: Jouanne M. , Sanjuan M.L. , Kanehisa M.A. , Balkanski M. , Cavalli P. , Campagnoli G. , Samoggia G. , Scaglioqti M.
Published: March 2011

Polarized Raman scattering and infrared absorption measurements were carried out in FePS3 and FePSe3 as a function of temperature. Features at 700-2000 cm−1 are shown to be essentially due to transitions among the trigonal-field-split 5T2g multiplet of the Fe2+ iron and their phonon sidebands. Though the unpolarized Raman spectra are similar in both compounds, polarized spectra are markedly different. We propose a tentative model to account for this.
Analysis of Transport Phenomena Occurring in Electron-Irradiated Sodium β-Alumina Crystals
Authors: Mariotto Gino , Miotello Antonio
Published: March 2011

Auger analysis of sodium β-alumina crystals provides relevant insights concerning Na- transport along the c-axis. In particular, it allows to prove that sodium ion migration is stimulated by electron-irradiation, a result connected to electron-induced relaxation of lattice. Some aspects of the electric fields induced into a dielectric during Auger analysis are discussed.
Sodium/Beta”-Alumina/Organosulfur Batteries Operating at Intermediate Temperatures
Authors: Visco StevenJ. , Jonghe Lutgard C. De
Published: March 2011

Concurrent with impressive advances in advanced batteries operating at high temperatures such as the Na/Na2 Sx and Li/FeS systems, have been concerns over safety and reliability of such batteries. Accordingly, various efforts have been made to offer alternative high specific energy/power batteries operating at reduced temperatures [ 1, 2, 3 ]. However, since electrode kinetics and mass transport processes in batteries are thermally activated, lower temperature systems often present a compromise between lower power output, and enhanced reliability, safety, and economic factors. Fortunately, lower temperature systems also offer far more flexibility in cell design, allowing geometries with higher electrode surface area than would be feasible with high temperature systems, thereby reducing the necessary current densities for acceptable power output.
Hopping Model for the Non-Debye Dielectric Response in Ionic Crystals
Authors: Wang J. C. , Bates J. B.
Published: March 2011

A model based on ion hopping in potential double-wells is proposed to explain the non-Debye dielectric response in solids. Relying on some assumptions, an attempt is made to remove the “average” nature of previous diffusion theories. This results in a distribution of activation energies, G(E), which decays exponentially on both sides of some given value E0. It is shown that (a) the existence of a dielectric loss peak is a result of the decay of G(E) for E > E0, (b) the constant-phase-angle behavior above the loss peak is associated with the decay of G(E) for E < E0, and (c) G(E) can produce all the main features of the empirical Havriliak-Negami function. An interesting property of this G(E) is that it broadens with increasing temperature, consistent with many experimental observations.
Thin Film Technology in Solid State Ionics.
Authors: Schoonman J.
Published: March 2011

Chemical and physical vapour deposition (CVD, PVD) techniques have been used to fabricate micro–electronic devices for several decades. This success has supported the recent expansion of these thinfilm technologies into areas of ceramic processing. To date the techniques are being used to produce advanced ceramic coatings to improve wear resistance or corrosion resistance, or high efficiency solar cells, or ultra fine ceramic powders.
Hopping Transport in Disordered Systems: Correlation Effects
Authors: Curtin W. A. , Scher H.
Published: March 2011

Starting from a Master Equation description of particle hopping between localized sites in a disordered system, we systematically analyze the influence of spatially-correlated hopping (memory) on the excitation transport. Correlations are introduced by accounting exactly for the hopping among a finite cluster of sites which are coupled in an uncorrelated manner to the remaining sites outside the cluster (background). Our results for quantities such as Ps(t). the probability of being at site s at time t for given initial conditions, compare well with simulation results on systems with both e−r and r−6 hopping rates, the agreement improving systematically with increasing cluster size. A simple interpretation of the time development of the cluster-background coupling is seen to be analogous to the overlapping-sphere construction of the percolation path.
The Effect of Substituting Rdf on the Physical and Environmental Properties of Coal Fly Ash
Authors: Mohamad Ashaari B. , Gress David L.
Published: March 2011

Refuse-derived-fuel (RDF) consisting mainly of waste paper and plastics is a viable fuel source for the production of power. An experimental test burn partially substituting coal with RDF was undertaken by the Public Service of New Hampshire at the Merrimack Power Station.

Five percent and ten percent RDF were substituted, on a BTU basis, for coal in the test bums. The chemical and physical properties of the resulting fly ash were determined. Twelve test burn days were run with 4 days of 5% RDF and 8 days of 10% RDF. Emphasis was placed on investigating the effect of the RDF fly ash on Portland cement concrete.

Most of the chemical and physical properties of the coal-RDF fly ash were found to be comparable with ordinary coal fly ash except for the amount of cadmium and lead, the pozzolanic activity index and the compressive strength of fly ash concrete. Cadmium and lead were at average levels of 5.1 ppm and 102.6 ppm for the 5% RDF, and 7.8 ppm and 198.3 ppm for the 10% RDF, respectively. Although the pozzolanic activity index of coal-RDF fly ash increases over normal coal fly ash, preliminary results show that the 28-day compressive strength of concrete with direct replacement of cement and sand decreases by up to 30%. Leaching tests on crushed concrete were conducted to evaluate the environmental effect of acid rain.
Quantification of Fly Ash in Concrete by Image Analysis Techniques: a Preliminary Investigation
Authors: Ferrell Ray E. , Drew Allison W.
Published: March 2011

The fly ash present in concrete mixtures is readily identified with qualitative electron microscope techniques. Quantification of the fly ash present in samples is more difficult. Visual analysis of a representative sample volume can be accomplished in a reasonable amount of time through use of image analysis techniques.

Our research efforts have focused on the development of an image analysis technique which uses particle shape and composition to quantify the fly ash present in samples. The resultant binary image is filtered to eliminate the smallest particles and pieces of particles. Shape factor analysis distinguishes spherical fly ash particles from irregularly shaped grains of unhydrated cement clinker. The volume percent of nearly spherical particles is calculated and adjusted to compare the percentage of spherical particles in the matrix of fly ash-containing specimens to the percentage in a control specimen with no fly ash.

There is a 2.2-fold increase in the number of spherical particles associated with the substitution of Portland cement by 60 wt% fly ash. Proportional changes in this ratio should be observable in samples with varying amounts of fly ash. The most obvious limitation of the method is related to the requirement that one knows the percentage of high atomic number particles in the fly ash beforehand.
Small Angle Neutron Scattering Studies Of Pore And Gel Structures, Diffusivity, Permeability And Damage Effects
Authors: Allen A. J. , Baston A. H. , Wilding C. R.
Published: March 2011

The pore-gel microstructures of hydrating cement and effects of their interaction with the environment have been studied using the non-destructive technique of small angle neutron scattering (SANS). The results presented for the cement microstructures are statistically representative of such structures over macroscopic sampling volumes.
The Use Of Backscattered Electron Microscopy And Image Analysis To Study The Porosity Of Cement Paste
Authors: Scrivener Karen L.
Published: March 2011

In backscattered electron images of polished sections of cement paste pores can be identified down to a size of about 0.05 microns. Moreover, the contrast between pores and the solid phases is sufficient to allow the pores to be distinguished and quantified by an image analyser. There is a good correlation between measures of porosity obtained by this technique and those obtained by methanol absorbtion methods despite the lower limit to resolution.

The bse method can also be used to study the distribution of the porosity in space. However, as only two dimensional sections can be examined, there are difficulties in determining the connectivity by this method. The possibility of using serial section reconstruction is examined and discussed.

Despite the difficulty in relating two dimensional characterisation to three dimensional properties, several techniques have been used with some success for sandstones. Results from these techniques for cement paste are presented and discussed.
The Effect Of Pore Structure And Cracking On The Permeability Of Concrete
Authors: Bier Thomas A. , Ludirdja Darmawan , Young J. Francis , Berger Richard L.
Published: March 2011

Permeability measurements have been conducted for mortars, concrete and hydrated cement pastes. The permeability with water as the penetrating medium has been measured in a low pressure range (˜ 0.5 psi) and at higher pressures up to 400 psi. Samples never exposed to drying and oven dried samples (105 °C) have been investigated. Pore structure of the investigated samples has been characterized using mercury intrusion porosimetry.

The results are discussed with regard to changes in structure during the experiment due to progressing hydration and healing of cracks.
The Relationship Between The Porosity And Permeability Of The Surface Layer Of Concrete And The Ingress Of Aggressive Ions
Authors: Crumbie Alison K. , Scrivener Karen L. , Pratt P. L.
Published: March 2011

The durability of concrete is strongly dependent on the distribution of porosity particularly in the surface layers. To study this distribution, concretes at different water to cement ratios were studied by methanol counter diffusion and by analysis of backscattered electron images. The distribution of porosity in the surface was compared with that in the bulk. Samples of the same concrete were imnersed in sodium sulphate solutions while others were left in lime water as a control. The effects of the immersion on the microstructure was studied with backscattered electrons in the SEM.
Influence of Water Cement Ratio and Curing on the Permeability and Structure of Hardened Cement Paste and Concrete
Authors: Gräf Herbert , Setzer Max J.
Published: March 2011

Curing affects sincerely the durability of concrete especially in surface regions. This is reflected in the pore structure and in the permeability. In a systematic research the structural changes due to water cement ratio and curing have been studied by mercury porosimetry, by nitrogen adsorption, by oxygen diffusion and by oxygen permeability. Due to these results diffusion and permeability are connected by a power law. Structural changes alter the permeability by four orders of magnitude. The results can be well explained by pore size distribution both for hcp and for concrete. Carbonation and frost action as well as strength and elastic modulus are closely correlated to permeability and therefore to pore structure. For practical application it is possible to give advice for concreting and curing. Service life can be predicted by permeability measurements in an early stage. The results are comparable with Nyames /20/.
Scaling Behavior Of Dynamic Permeability In Porous Media
Authors: Sheng Ping , Zhou Min-Yao , Charlaix E. , Kushnick A. , Stokes J. P.
Published: March 2011

We show that the scaling of the dynamic permeability κ(ω) by its static value κ0 and the frequency ω by a characteristic frequency ω0 particular to the medium results in a dimensionless function , with , which is dominated by the geometry of the throat regions in a porous medium. If the pore cross sectional area S varies slowly near the throat, i.e. dS/dz ≃ 0 where z is the distance normal to the cross section, then is an approximate universal function independent of microstructures. When scaling holds, the dynamic permeability κ(ω) is shown to contain only two pieces of geometric information, and the knowledge of either the low-frequency or the high-frequency asymptotic constants of κ(ω) would enable one to deduce the other missing parameters. In particular, since the high-frequency asymptotic parameters of κ(ω) can be related to the electrical formation factor and the volume-to-surface ratio, the static permeability value κ0 may be directly deduced from such non-permeability measurements.
Pore Structure of Low Porosity DSP Cement Pastes
Authors: Touse Sara A. , Bier Thomas A. , Knepfler Cheryl A. , Young J. Francis , Berger Richard L.
Published: March 2011

The pore structure of low porosity cement pastes containing varying quantities of silica fume has been examined using mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) measurements. The water:solid ratio for all DSP pastes studied was 0.18. It was observed that, as for conventional pastes, removal of water by solvent replacement with methanol minimizes changes to the pore structure. Vacuum or oven drying severely reduces specific surface area and obscures important trends.

It was found that capillary porosity in excess of 10 nm (100 Å) is essentially absent and that the pore volume measured can be considered an intrinsic part of the binding phase. The influence of silica fume and curing times on pore structure has been measured and the implications of the data will be discussed. Comparisons will be made with conventional cement pastes.
An Experimental Observation Related To The Pore Space Between Particles Of Cement In Pastes At Early Ages
Authors: Jennings Hamlin M.
Published: March 2011

Cement paste of water:cement ratios less than about 0.3 usually are not workable, but workability can be maintained at these lower water:cement ratios by using superplasticizers. A typical explanation [1] of the mechanism behind the effectiveness of superplasticizers is that they adsorb on the surface of cement particles and adjust the surface charge so that the particles become deflocculated. The individual particles flow more easily than larger flocs.
Some Experimental Possibilities With Mercury Intrusion Porosimetry
Authors: Winslow Douglas
Published: March 2011

The importance of knowing the pore size distribution of a material, and the utility of mercury intrusion, are briefly reviewed. Mercury intrusion results can be used to obtain the specific surface of a material. Under the right circumstances, this method has many advantages over vapor sorption, and a mercury intrusion test may be desirable for this reason alone. The procedure and limitations are described. Modern instruments allow for the measurement of mercury extrusion as well as intrusion. This opens the possibility of measuring two pore size distributions. One is reversibly intruded, and the other is not. The use of these sub-distributions in seeking correlations with material properties and behavior is discussed. The applied-pressure/diameter-intruded relationship of the Washburn equation depends upon the surface tension and contact angle. Inter-metallic solutions with mercury as the solvent offer the possibility of reducing the surface tension and/or the contact angle. This allows the use of lower pressures to intrude the same diameter pore, or the intrusion of smaller pores at the same pressure. The practical application of using such solutions is described.
Observation of Oxidation-Enhanced and -Retarded Diffusion of Antimony in Silicon: The Behavior of (111) Wafers
Authors: Tan T. Y. , Ginsberg B. J.
Published: March 2011

An experiment was performed to study the oxidation-enhanced and -retarded diffusion (OED and ORD) of Sb in silicon wafers oxidized in dry O2 at 1160°C. The ORD data of (100) wafers agree well with the prediction of a model assuming that Si self-interstitials (I) and vacancies (V) coexist in thermal equilibrium at high temperatures. An adjustment of the I supersaturation values is needed to bring the ORD/OED data of (111) wafers to fit with the model satisfactorily. This indicates the existence of a mechanism which injects V into (111) wafers in addition to the normal mechanism of I injection due to SiO2 growth.
Improved Meltback Procedures for Liquid-Phase-Epitaxial Growth of Planar and Buried Heterostructures
Authors: Chin B. H. , Chin A. K. , Digiuseppe M. A. , Lourenco I. A. , Camlibel I.
Published: March 2011

In the liquid phase epitaxy on indium phosphide, the substrate,just prior to the growth of the first epitaxial layer, is commonly etched back with an indium melt to remove any thermallydegraded surface and to ensure uniform and consistent wetting.This procedure, however, often produces defects which degrade both planar and buried heterostructure devices. For planar edgeemitters and lasers, the resulting rippled surface morphology degrades device performance by scattering light. For buried heterostructures, the meltback in the regrowth step leads to indium-rich inclusions. The effects of meltback on material quality are presented, and a new multiple meltback procedure which maintains flat surface morphology and eliminates inclusions is described.
Electrically Active Defects in Cid Imaging Arrays Fabricated on Hg0.7 Cd0.3Te
Authors: Schaake H.F. , Lewis A.J.
Published: March 2011

CID imaging arrays were fabricated on Hg0.7 Cd0.3Te produced by the solid state recrystallization technique. It was found that the most serious source of dark current was sub-grain boundaries. SEM studies of the microstructure revealed by etching showed that boundaries with a high denisty of dislocations were detectable sources of dark current, while those boundaries with a low density of dislocations, as well as individual dislocations were not. TEM showed that all dislocations were free of precipitates, and most were not dissociated. The sub-grain boundaries were found to arise from misorientation between dendrites which form during the solidification from the melt.
The Structure of a Near Coincidence Σ=5, [001] Twist Boundary in Silicon
Authors: Vaudin Mark , Ast Dieter
Published: March 2011

The dislocation structure of a near coincidence Σ=5 [001]twist boundary in silicon was studied using transmission electron microscopy. Secondary dislocations, with localized cores, were observed in the boundary accommodating a small deviation (<.5°) from perfect coincidence. The O-lattice theory for general low angle boundaries was extended to calculate the expected dislocation content of near coincidence boundaries. Comparison between predictions and observations was used to deduce information on the primary dislocation structure of the boundary.
Ion Irradiation Effects on Pt Contacts To Si with and without Interfacial Chemical Oxide
Authors: Banwell Thomas , Finetti Manuela , Suni Ilkka , Nicolet Marc-A. , Lau S. S. , Scott David M.
Published: March 2011

The electrical properties of ion irradiated metal-semiconductor contacts are investigated. Silicide contacts are fabricated by depositing Pt on chemically clean or slightly oxidized (∼14 Å SiO2) n+-and n-type <111> Si, followed by a Si ion irradiation (1014 − 6×1015 Si/cm2) through the metal-Si interface at various substrate temperatures, and a final thermal annealing in vacuum to form the silicide. Forward I-V measurements are employed for electrical characterization. Metal-Si interaction and substrate damage are measured by MeV ion backscattering and channeling, and interfacial oxygen monitored by nuclear 16O(d,α)14N reaction.

Platinum contacts prepared on clean n-type substrates are Schottky diodes with a barrier height øBn = 0.83 eV. After Si irradiation, the forward I(V) is a power law whose form is largely independent of the dose. Subsequent thermal annealing induces silicide formation, but at a reduced rate compared to irradiated samples. The do characteristics is roughly exponential again, but departures from the original Schottky characteristics remain and are largest for the highest Si doses. The effect is attributed to radiation damage in the Si that is not consumed by the silicide reaction.

Platinum contacts prepared on chemically oxidized samples behave differently for different substrate materials, although the total amount of interfacial oxygen is always the same. On n+-type samples, the silicide formation at 400°C is laterally uniform for Si doses ≥ 2 × 1014 cm−2, but is nonuniform for all doses (≤ 2 × 1015 Si/cm2) on n-type samples. For n+-type samples at 250°C, a dose of 2 × 1015 Si/cm2 is required to induce (uniform) silicide formation; the kinetics displays a time delay compared with that of clean n+ substrates. On oxidized n-type substrates, the I(V) characteristics of Pt contacts before irradiation is not Schottky-like, but power-law-type. After irradiation, the characteristic is the same as for the clean irradiated samples. Thermal annealing induces only incomplete recovery toward an exponential behavior.

These results demonstrate that radiation damage in the unreacted Si remains significant for the electrical behavior of all.

These results demonstrate that radiation damage determines the I(V) characteristics of as-irradiated Pt contacts to n-type Si regardless of the presence of an interfacial oxide layer. After annealing at 400°C for 30 min, radiation damage is still significant, but the oxidized samples recover less than the clean ones. The results are attributed to radiation damage in the unreacted Si substrate.
The Nature of Point Defects and their Influence on Diffusion Processes in Silicon at High Temperatures
Authors: GÖsele U. , Tan T.Y.
Published: March 2011

The paper highlights recent progress in understanding the role of vacancies and self-interstitials in self- and impurity diffusion in silicon above about 700°C. How surface oxidation of silicon leads to a perturbation of the pointdefect population is described. An analysis of the resulting oxidationenhanced or -retarded diffusion of group III and group V dopants shows that under thermal equilibrium as well as under oxidation conditions both vacancies and self-interstitials are present. For sufficiently long times vacancies and self-interstitials attain dynamical equilibrium which involves their recombination and spontaneous thermal creation in the bulk of silicon crystals. The existence and the nature of a recombination barrier slowing down the recombination process are discussed in this context. Recent experimental and theoretical results on the diffusion of gold in silicon enable us to determine the selfinterstitial component of silicon self-diffusion and to obtain an estimate of the respective vacancy contribution. The two components turn out to be of the same order of magnitude from 700°C up to the melting point.
Defects, Dislocations and Degradation of Compound Semiconductors
Authors: Johnston W. Dexter
Published: March 2011

Diode lasers and/or LEDs fabricated from the Ga1 − xAlxAs/GaAs or In1 −xGaxAsyP1−y alloy system provide the basis for rapidly developing optical communications systems. These devices are operated at very high optical and electrical power densities, and the inevitable less-than-perfect efficiency results in intense local thermal and athermal lattice excitation. This in turn can lead to generation, motion and growth of extended defect structures including dislocation networks, precipitation of impurities, or phase separation.

For the AlxGa1−xAs material, a predominant degradation effect is the development of so-called <100> “dark line defects” (DLDs). These have been shown to arise from recombination enhanced climb of threading dislocations giving rise to dipole loops of a primarily interstitial character. A less common form, the <110> DLDs, is associated with slip and typically arises from the strain associated with mechanical damage or careless handling or device processing.

The In1−xGaxAsyP 1−y device material affords less energy per recombina ion event by virtue of its smaller band-gaps, but is likely to have more lattice mismatch strain than Ga1−xAlxAs for typical compositions of device interest. Thus slip, <110> DLDs, and precipitates are the commonly observed features of In1−xGaxAsyP1−y degradation.
Laser Annealing of Ion Implanted Semiconductors
Authors: Narayan J.
Published: March 2011

Photon energy from laser beams can be used to rapidly heat and melt localized regions of semiconductors with a high degree of spatial and temporal selectivity. Pulsed lasers have been successfully used to anneal displacement damage and to remove other defects. However, the number density of trapped defects increases with velocity of solidification and finally thin layers turn directly amorphous after laser-melt quenching. Annealing characteristics are found to be a strong function of ion implantation variables, which determine optical properties of materials. By both solid- and liquid-phase crystallization, supersaturated solid solutions can be formed. Residual defects in SPE grown layers primarily consist of dislocation loops. Device applications utilizing these transient thermal processing techniques are reviewed briefly.
The Friction and Wear Behavior of Ion Beam Assisted Nitride Coatings
Authors: Tetreault Thomas G. , Hirvonen J.K. , Parker G.
Published: March 2011

The method of Ion Beam Enhanced Deposition, (IBED), was used to produce hard films of i-BN, i-SixNy and i-TixNy. The friction, hardness, adhesion, and wear behavior of these nitride coatings were examined using a ball-ondisc friction/wear tester. The friction and wear results were sensitive to stoichiometry and the presence of impurities (e.g., hydrogen) in the film as well as the choice of ball material (400C stainless steel or silicon nitride).
Growth of Stoichiometric Bn Films by Pulsed Laser Evaporation
Authors: Murray P. T. , Donley M. S. , McDevitt N. T.
Published: March 2011

The feasibility of growing stoichiometric thin films of BN by pulsed laser evaporation has been investigated. Films grown under high vacuum conditions were N-deficient. This result is consistent with thermodynamic calculations, which indicate that B metal formation, with concomitant N2 desorption, is energetically favored over BN formation. Stoichiometric films were grown in NH3 with substrate temperatures of 400, 500, and 1000ºC. Analysis of films grown under these conditions by grazing incidence x-ray diffraction indicates the films to be highly oriented, hexagonal BN.
Characterization of TiN Films Prepared by ion Beam Assisted Deposition
Authors: Chang Albert L. , Kant R. A.
Published: March 2011

One of the advantages of the ion beam assisted deposition process is its controllability of the processing parameters such as: ion-to-atom arrival ratio and the ion energy. In this study, the effects of the nitrogen ion energy (from 1 KV to 30KV) on the TiN film morphology and microstructures were systematically investigated as a function of ion-to-atom arrival ratios, using TEM, XTEM, SEM, ESCA and other analytical techniques.
Interfacial Chemical Reactions Between MoS2 Lubricants and Bearing Materials
Authors: Zabinski J.S. , Tatarchuk B.J.
Published: March 2011

X-ray Photoelectron.pectroscopy (XPS) and Conversion Electron M6ssbauer bpectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides depending on the level of excess sulfur in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to theMoS2 basal plane and that alignment, and potentially adhesion, could be variedby appropriate high temperature annealing procedures.
Synthesis and Characterization of MoS2 Thin Films Grown by Pulsed Laser Evaporation
Authors: Donley M. S. , Murray P. T. , McDevitt N. T.
Published: March 2011

The growth and characterization of MoS thin films grown by pulsed laser evaporation is investigated. TOF anafysis of the ions evaporated from an MoS2 target indicates that PLE results primarily in the evaporation of atomic Mo and S species; MoxSy clusters were also detected, but were present at a significantly Iower intensity. TOF velocity analysis indicates an effective plasma temperature of 1500K. Stoichiometric MoS2 films were grown at substrate temperatures between room temperature and 500ºC under the above laser conditions. XPS data is used to develop a Wagner chemical state plot. Analysis of the films by Raman spectroscopy and glancing angle x-ray diffraction indicates the films to be crystalline, hexagonal MoS2, with a tendency for basal plane orientation parallel to the substrate.
A Tribological Study of Mo/Al2O3 in Sliding Contact
Authors: Hong Hyun-Soo , Winer Ward O.
Published: March 2011

This is Part II of a tribological study of metal/ceramic pair in a sliding contact. The tribological behavior of molybdenum against a single crystal A12O3 was investigated at bulk temperatures of 23ºC and 400ºC using a sliding speed of 4 m/s and loads from nine to twenty five Newtons. The role of oxidational wear was confirmed at both temperatures. The linear dependency of wear rate on load was identified at 23ºC tests. At 400ºC, there was a rapid increase of wear rate at a load of about 25 N possibly due to the volatilization of MoO3, which is the limitation of molybdenum oxide as a solid lubricant. However, this study showed that the out-of-contact oxide formation may have prevented the catastrophic oxidation during contact at the real area of contact. It also showed that in-situ formed molybdenum oxide has good lubricating properties (≃ 0.3) and a low wear rate (≃ 10-14 m3/m). Therefore, this molybdenum can be used for a large range of sliding speeds and loads.
The Acoefficient of Friction Between Boron Carbide (B4 C)Surfaces in Air and Ultrahigh Vacuum (UHV)
Authors: DeKoven Benjamin M. , Hagans Patrick L.
Published: March 2011

Friction measurements between two contacting B4C surfaces in airand UHV at room temperature using 0.10-0.13N loads are reported. A novel pin (radius=0.005m) on flat device allowing for interchange in UHV is used. The tribological surfaces can be examined using scanning Auger and XPS in the same UHV system. The coefficient of friction for air exposed surfaces is found to vary between air (0.20-0.25) and UHV (1.2-1.8). Stick-slip behavior, indicating strong adhesion, is observed in UHV while only a smooth friction value is measured in air. Air pressures ≥ 100Pa are necessary toreduce the friction from the high value in UHV. The friction between the clean surfaces in UHV initially is 0.8-1.3, but following mechanical conditioning at a higher velocity the friction drops to 0.17-0.25. In situmechanical conditioning is necessary to obtain reproducible friction values for the clean surface. Exposing the clean surfaces to oxygen (103Pa) while conditioning results in an increase in friction (1.0-1.2). Auger line scans through the scar made using the clean surfaces show enhanced B and reduced C. Similar Auger scans for oxygen exposed surfaces indicate that tearing of the oxide layer may be the reason for the high friction. The friction for a clean pin and an in situ nitrogen-implanted flat (10keV, saturation dose) is 0.70-0.80. Film transfer to the pin is observed.
Continuous High Temperature Lubrication of Ceramics by Carbon Generated Catalytically
Authors: Lauer James L. , Dwyer Scott R.
Published: March 2011

A system for the continuous lubrication of ceramic surfaces at high temperatures by a carbon formed exclusively at the wear surfaces is described. Thelubricant is delivered as a simple gas, ethylene, which is catalytically transformed. No reaction products are left which contain bearing surface material and the only non-volatile product is lubricating carbon. One of the wearing surfaces must contain or have an overlay of nickel (about 1000 A thick in this work) and, preferably, a coating of nickel oxide on top to reducenickel wear during startup. Since the carbon is formed only on nickel and the oxide is worn only in the weartrack, only the wear track is lubricated. The laboratory system consisted of a sapphire pin on a nickel-coated rotating alumina disc. Ethylene was delivered only to the conjunction region, which was surrounded by air. Contact pressures were about 200 MPa, linear speeds between 3 and 9cm/sec. Friction coefficients dropped from 0.6 to 0.06 when ethylene was delivered to the contact at 500°C. Wear rateswere not measureable under operating conditions. Cases other than ethylene and catalysts other than nickel will be explored in further work.
The Binding of Lubricating Films to Ceramic and Refractory Materials
Authors: Bums R. P. , Pierce D. E. , Gabriel K. A.
Published: March 2011

In order to better understand the chemical bonding forces which control lubricating film stability and adhesion, the binding of lead and tin atoms on the ceramics alumina and silica was investigated by laser induced thermal evaporation combined with mass spectrometric detection of the evaporated species. The interaction between lead or tin and alumina and silica was studied as a function of coverage. The sticking probability for the interaction was measured and found to be temperature and coverage dependent. At low coverage the binding energy of lead to alumina and silica was determined as 237and 246 KJ mol1 respectively, while the binding energy of tin to alumina and silica is 313 and 331 kJ mol1, respectively. A binding energy model based on thermochemical and crystallographic data was used to predict corresponding values which agree with the experimental values.

In addition, temperature programmed desorption and\or decomposition (TPD) was used to investigate the thermal and\or chemical stability of MoS2 films on molybdenum supports. The TPD spectra for S2 from MoS 2 were analyzed, and activation energies were found to be dependent on the film application technique. The binding energy model also provided a useful approximation to the experimental activation energies for the S2 production from MoS2 films. Water and carbon impurities were shown to contribute to the decomposition of MoS2 producing SO2 and CS2. The TPD spectra of S2, SO2, and CS2 provide a measure of the onset of lubricant decomposition.