bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Induced Periodic Surface Structure
Authors: Van Driel H.M. , Young Jeff F. , Sipe J.E.
Published: March 2011

Laser induced periodic surface structure can be understood as a universal phenomenon which occurs when high intensity pulses are absorbed near the surface of solids or liquids. The phenomenon occurs on metals, semiconductors and insulators because of the interference between the incident pulse and an induced “radiation remnant”. This scattered field may be enhanced by the existence of true surface modes such as surface plasmons or phonon-polaritons but this is not essential. The universality characteristics include beam polarization, since we show that circularly polarized light can induce surface ripples, with the damage structure showing a dependence on the sense of rotation. We also present time resolved results of the formation of the ripples to illustrate the essential dynamical processes that occur.
Impurity Diffusion in Silicon Annealed by Semi-Continuous Laser
Authors: Bouree Jean-Eric , Leray Claude , Rodot Michel
Published: March 2011

The diffusion of an impurity into a solid which is irradiated by laser pulses of some milliseconds duration has been analysed in terms of effective diffusion time and temperature. In the case of Fe in Si, the diffusion coefficient is found to be similar to that measured by COLLINS and CARLSON, and independent of boron doping. In the case of Al in Si, a value of 2.10–10 cm2/ at 1400°C has been found both for single crystals and for fine-grained polycrystals.
Search for Vacancies in Laser Annealed Silicon
Authors: Stein H. J. , Peercy P. S.
Published: March 2011

In an effort to enhance vacancy trapping and detection in laser-annealed Si, float zone Si was implanted with oxygen to achieve concentrations between one and two orders of magnitude greater than the equilibrium saturation limit. Oxygen, which is known to be an effective trap for vacancies, was found to incorporate efficiently into Si regrown with Q-switched laser annealing Interstitial oxygen, oxygen-vacancy defects and divacancies were observed after implantation. The laser-regrown layers, however, were free of detectable vacancy-associated defects.
Microprobe Raman Analysis of Picosecond Laser Annealing of Implanted Silicon
Authors: Sapriel J. , Nissim Y.I. , Oudar J.L.
Published: March 2011

Picosecond laser annealing has been performed on implantationamorphised silicon. A multiannular (up to five rings) recrystallization pattern has been generated by a single~30 psec pulse at 1.06 μM and 0.53 μm wavelength and energy density just below the damage threshold. The different patterns have been investigated by scanning the surface with a Raman microprobe with a 1pm spacial resolution. Information are thus given on the different phases (amorphous or crystalline) and on lateral as well as in depth dimensions of the different rings.
Analysis of Temperature and Stress Profiles Induced by a cw Line Scanned Electron Beam in <100> Oriented Silicon
Authors: Bentini G. G. , Correra L.
Published: March 2011

Evaluation of thermal profiles along the scan direction of a line shaped e-beam as well as the topographic distribution of the thermally induced stresses have been performed by solving the heat diffusion equation for several incident power values. The resulting stresses have been computed in the “nearly isotropic” approximation but taking into account that the slip planes, in <100> oriented silicon crystals, are{lll} and the slip directions in the plane are <110>.The threshold of damage introduction has been evaluated by comparing the computed stresses with the yield stress of the material at any annealing temperature. Experimental observations based on X-Ray topography have been performed in order to study the damage introduction on <100> silicon samples annealed in the same conditions used for stress computation. A very good agreement between computed and experimental results was found.
Ising Model Simulations Of Impurity Trapping in Silicon
Authors: Gilmer George H.
Published: March 2011

Laser annealing experiments on silicon have shown that rapid solidification can trap large amounts of certain impurities in the crystal lattice. Concentrations that exceed the equilibrium solubility limits by several orders of magnitude have been obtained. In this paper we discuss the impurity trapping process using Monte Carlo simulation data from the kinetic Ising model. The dependence of the impurity concentration in the crystalon the solidification rate is calculated. The simulation data are compared with recent laser annealing results for bismuth and indium. Excellent agreement between the model and the bismuth experiments is obtained. The larger trapping rate on the (111) relative to the (100) orientation is found to be caused by the slower crystallization kinetics on the (111) face. Similar results are obtained for indium, although the difference in trapping on the (111) and (100) faces is somewhat smaller in the model than in the experiment.
Amorphous Si, Crystallization And Melting
Authors: Poate J. M.
Published: March 2011

Recent experiments dealing with the thermodynamics of crystallization and melting of amorphous Si are reviewed. differential scanning calorimetry measurements give the heat of crystallization of implanted, amorphous Si to be 11.3±t.8 kJ/mole. Gibbs free energy calculation based on these measurements indicate that amorphous Si melts at a temperature of 1460°K compared to the crystalline value of 1685°K. Evidence for this reduced melting temperature also comes from rapid heating measurements using a) structural information after solidification and b) dynamic conductance measurements during the melt. Solid phase epitaxial regrowth experiments which apparently do not show such a depression in amorphous melting temperature will be discussed.
Segregation and Crystallization Phenomena in Germanium
Authors: Clark G. J. , Cullis A. G. , Jacobson D. C. , Poate J. M. , Thompson Michael O.
Published: March 2011

While many studies have been made of liquid phase epitaxy impurity trapping and segregation in Si little is known about the equivalent processes in Ge. In this paper we have laser annealed Ge <100> and <111> crystals implanted, at liquid nitrogen temperature, with 200 keV 210Bi ions to doses of 2 × 1015 and 1016 ions cm−2. The samples were annealed with Q-switched ruby lasers and an XeCl excimer laser. We have observed 1) velocity and orientation dependence of the Bi segregation coefficient 2) interface instability and cell formation resulting from constitutional supercooling and 3) amorphization and defect production at high velocities. The phenomena are shown to be analogous to those seen in Si.
Effect of Pulse Duration on the Annealing of Ion Implanted Silicon With A XeCl Excimer Laser And Solar Cells
Authors: Young R. T. , Narayan J. , Christie W. H. , van der LEEDEN G. A. , Rothe D. E. , Sandstrom R. L.
Published: March 2011

The advantages of pulsed excimer lasers for semiconductor processing are reviewed. Studies of XeCl excimer laser annealing with pulses of 25 and 70 nsec duration and energy densities in the range from 0.5–3.0 J/cm2 are discussed. The annealing characteristics are described in terms of the results of melt depth, dopant profile spreading, and electrical properties (sheet resistivity, diode characteristics) measurements. Solar cells with efficiencies as high as 16.7% AMI have been fabricated using glow discharge implantation and XeCl laser annealing.
Pulsed Electron Beam Annealing Induced Deep Level Defects in Virgin Silicon
Authors: Barbier D. , Kechouane M. , Chantre A. , Laugier A.
Published: March 2011

DLTS has been used to investigate deep level defects induced by Pulsed Electron Beam Annealing (PEBA) in virgin (100) boron doped silicon. Various PEBA conditions were selected resulting in different molten layer thicknesses, melt front velocities and thermal gradient distributions. Discrete hole traps distributed in the regrowth layer were observed in all the annealed samples. The activation energies and thermal signatures of these levels do not correspond to already known defects except for one level which has been assigned to the carbon interstitial substitutional pair. Carbon contamination during irradiation is the most probable explanation for the creation of this defect. Other discrete hole trap levels are likely to be generated by quenching of the molten layer as far as their profiles do not extend beyond the regrowth layer. Moreover, a broad band of levels, characteristic of extended defects, has been observed only on the samples which have suffererd the highest thermal stresses. This band of levels might be related to the generation of dislocation networks as recently observed by means of T.E.M. on the same PEBA processed samples.
Zone-Melting Recrystallization of Semiconductor Films
Authors: Geis M. W. , Smith Henry I. , Tsaur B-Y. , Fan John C. C. , Silversmith D. J. , Mountain R. W. , Chapman R. L.
Published: March 2011

The use of zone melting recrystallization (ZMR) to prepare large-grain(and in some cases single-crystal) semiconductor films is reviewed, with emphasis on recent work on Si on SiO2. Encapsulants are generally required to minimize contamination and decomposition, induce a crystalline texture,improve surface morphology and prevent agglomeration. In the case of Si, the solid-liquid interface is faceted, which gives rise to subboundaries. These can be entrained by laterally modulating the temperature through the use of an optical absorber on top of the encapsulant. Control of thermal gradients and in-plane crystallographic orientation are important for reliable entrainment.
Beam Shaping for Cw Laser Recrystallization of Polysilicon Films
Authors: Zorabedian P. , Drowley C.I. , Kamins T.I. , Cass T.R.
Published: March 2011

A shaped laser beam has been used for laterally seeded recrystallization of polysilicon films over oxide. Direct maps of the shaped-beam intensity distribution in the wafer plane are correlated with the grain structure of the recrystallized polysilicon. Using 60% overlapping of shaped-beam scans along <100> directions, we have obtained seeded areas one mm wide and 50 to 500μm long. These consist of 40μm-wide adjacent single-crystal strips regularly separated by low-angle grain boundaries extending laterally away from the seed openings. The spacing between grain boundaries is equal to the scan spacing, providing a means for controlling the location of grain boundaries in otherwise defect-free, single-crystal films.
Transient Annealing of Ion Implanted Gallium Arsenide
Authors: Williams J.S.
Published: March 2011

This paper provides a brief overview of the application of transient annealing to the removal of ion implantation damage and dopant activation in GaAs. It is shown that both the liquid phase and solid phase annealing processes are more complex in GaAs than those observed in Si. Particular attention is given to observations of damage removal, surface dissociation, dopant redistribution, solubility and the electrical properties of GaAs. The various annealing mechanisms are discussed and areas in need of further investigation are identified.
Rapid Isothermal Annealing of Si Implanted Semi-Insulating GaAs by Means of High Frequency Induction Heating.
Authors: Cetronio A. , Bujatti M. , D'eustacchio P. , Ciceroni S.
Published: March 2011

Experimental results obtained by rapid isothermal annealing of Si implanted semi-insulating GaAs are presented and compared with results obtained by electron-beam and conventional furnace annealing. We shall show that for high Cr-doped material the problem of redistribution cannot be avoided and that for undoped material, this technique yields very good activation (near 100%) and high mobility (approximately 4400 cm2 /V.sec).
Electron Beam Processing of Semiconductors
Authors: Ahmed B. , McMahon R.A.
Published: March 2011

Electron beams can transfer energy very efficiently to semiconductors. Systems have been developed for rapid heating to temperature around 1000°C under a variety of conditions from adiabatic to isothermal. Pulsed, focused, line and synthesized shaped beams are used to obtain a wide range of thermal cycles. The following applications are described: the annealing of ion-implanted Si, particularly the activation of As implants and shallow implants (Rp<150Å), the annealing of Si and Se in GaAs, the e-beam processing of implanted silicon devices and the improvement of SOS substrate quality. Localized annealing by a computer controlled e-beam and the recrystallization of deposited films on insulators are also considered.
Optical and Electrical Properties of Cd Te Laser-Synthetized
Authors: Baufay L. , Pigeolet A. , Andrew R. , Laude L.D.
Published: March 2011

Optical and electrical characterization of CdTe synthetized by laser irradiationofamultilayer film of alternately Cd and Te is achieved. Optical absorption measurements evidence the good quality of these films and show that they have behaviour comparable to the single crystal. The influence of the irradiation conditions on the electrical properties of such CdTe films is discussed; they are compared to single crystal from the point of view of resistivity. It is shown that it is possible to prepare by this means samples devoid of impurity states in the middle of the forbidden gap. Finally, the ohmicity of Au, Al, Cr, ITO and non irradiated Cd/Te sandwich contacts is tested.
Impurity Redistribution Studies on Laser-Formed Silicides
Authors: Wakita A. S. , Sigmon T. W. , Gibbons J. F.
Published: March 2011

4He+ Backscattering and SIMS were used to study impurity redistribution during laser formation of refractory silicides. Thin films of Mo and W were evaporated on to <100> p-type silicon substrates, which were As or B implanted to doses of 1 ×1015 to 1 ×1016cm−2 . These samples were laser reacted with multiple or single laser scans at various powers. Analysis of these films indicate impurity movement into the forming silicide layer. Impurity concentrations in the films were observed to be as high as 7.8×1020 cm−3−> for As in WSi2 , however a reduction in this concentration occurred with subsequent thermal annealing.
Processing/Microstructure Relationships in Surface Melting
Authors: Schaefer R. J. , Mehrabian R.
Published: March 2011

The development of predictive models for rapid surface melting and resolidification requires coupling of realistic heat flow models to emerging theories of rapid solidification processing. Attainment of unique microstructures and phases,for example through plane-front solidification and solute trapping, can be correlated to solid/liquid interface velocity,temperature and temperature gradients, and to theories of morphological stability. However, there are important limitations on achievable solid/liquid interface velocity depending upon the heating mode and heat flux distribution,melt thickness and location of the interface within the molten zone.

An overview is given of the emerging guidelines for prediction and control of rapid solidification conditions and microstructures. Homogenization of the liquid by convection and diffusion is also discussed. Electron beam surface melting of alloy substrates is used as an example of these processes.
Metastable Fe(Pd) Alloys Formed By Pulsed Electron Beam Melting
Authors: Follstaedt D. M. , Knapp J. A.
Published: March 2011

Fe(Pd) surface alloys formed by either ion implanting Pd into Fe or by vapor depositing Pd on Fe have been examined after pulsed (∼70 nsec) electron beam melting. TEM and ion backscattering/channeling showed that the implanted alloys with up to 9.6 at.% Pd were bcc and epitaxial with the substrate, inspite of predictions of initial solidification to the fcc phase by the Fe-Pd phase diagram. The resolidified Pd films, however, were fcc as predicted by the diagram. The defect structures observed in these alloys are discussed.
Amorphous Al(Ni) Alloy Formation by Pulsed Electron Beam Quenching
Authors: Picraux S. T. , Follstaedt D. M.
Published: March 2011

The Microstructural Transition From The Epitaxial Crystalline To Amorphous State As A Function Of Ni Concentration Is Examined In Al(Ni) Alloys Formed By Ion Implantation And E-Beam Melt Quenching. The Evolution From Epitaxial Crystalline Al At ≲ 3.5 At.% Ni To Amorphous Phase Formation At 15–30 At.%Ni Is Characterized In Detail For 8, 10 And 12% Ni Uniform Concentration Samples By Ion Channeling And Transmission Electron Microscopy. The Transition Occurs Via Complete Loss Of Epitaxial Regrowth At 9 At.% And The Formation Of A Finegrained Polycrystalline Al, With Grain Size Decreasing With Increasing Ni From 20–100 Å At 10% Ni Concentration To ≲ 10–50 Å At 12% Ni.
Mineralogy of the Residues from an Underground Coal Gasification Test
Authors: McCarthy Gregory J. , Stevenson Robert J. , Oliver Robert L.
Published: March 2011

Detailed mineralogical characterization by X-ray diffraction, scanning electron microscopy and electron microprobe analysis has been performed on a suite of residues and on three samples of unaltered overburden excavated from a 1983 underground coal gasification (UCG) test conducted at a mine site near Centralia, Washington. The residues were classified into nine zones based on their appearance and location in the burn cavity. Because they were isochemical with the overburden, six of these zones could be identified as altered overburden and proved to be particularly useful for correlations of mineralogy with the temperature and redox atmosphere prevailing in these materials during the UCG process. A previously unrecognized, moderate temperature, reaction between reduced iron phases and clay minerals to form an Al-rich hercynite-spinel solid solution (Al-spinel), (Fe,Mg)Al2O4, was identified. This reaction is a precursor to the well-known formation of Fe-cordierite, (Mg,Fe)2 Al4Si5O18 from SiO2 and the Al-spinel at higher temperatures. The mineralogies of altered overburden were analogous to high-temperature, low pressure, metamorphic rocks of the sanidinite facies, and to thermally altered rocks from natural coal combustion. Modeling of the mineral phase assemblages was successfully performed using a phase diagram for the system (FeO+MgO)-Al2O3-SiO2 constructed from literature diagrams. Melting relations were also modeled with this diagram. Deviations from the assemblages predicted by this diagram were attributed to oxidizing conditions.
Evaluation of Acid-Leached Fly Ash as a Pozzolan
Authors: Hemmings R. T. , Berry E. E. , Cornelius B. J. , Golden D. M.
Published: March 2011

Direct acid leaching (DAL) with HCl to recover Al and other metal values from fly ash has been examined extensively by the Electric Power Research Institute (EPRI) under RP2422. Large scale utilization of the solid residues from the DAL-process (DAL-residues) could significantly influence the economics of resource recovery. This paper describes a study of the potential use of DAL-residue as a pozzolan in the concrete industry.

Samples of six ashes from a range of coal types were beneficiated to remove magnetic particles and particles larger than 45 gim. The beneficiated fractions were leached with 6M HCl at 105°C to determine metals recovery for Al, Fe, Ca, Mg, Na, K, and Ti. The corresponding DALresidues were characterized by chemical composition, morphology and mineralogical content, and examined as potential concrete pozzolans by standard ASTM tests. One DAL-residue from a highrank coal was examined more extensively in Portland cement mortars.

The greatest yields of Al were from low-rank coal ashes, but were obtained at the ‘cost’ of substantial salt-cake production and high acid consumption. The DAL-residues from all ash types showed high-Si content: those from high-rank coals being spherical pseudomorphs of the original ash particles, and those from low-rank coals containing substantial quantities of gel-like materials.

All of the residues were pozzolanic, but those from low-rank coals caused an unfavorable increase in water demand in mortars. DAL-residues from beneficiated high-rank coal ashes are enhanced pozzolans conforming to standard specification requirements with pozzolanic indices in excess of 100%.
Fly Ashes Used For Blended Portland Cement: Effect Of Grinding on Cement Quality
Authors: Stoltenberg-Hansson Erik
Published: March 2011

Tests have been performed with Class F fly ashes used for the production of interground 20% fly ash cement. Unground and ground fly ashes were mixed with a reference high fineness Portland cement and tested for strength in mortar (ISO/CEN method). The fly ashes were also tested for chemical composition, bulk density and specific gravity, fineness (Blaine) and particle size distribution (laser method). There are considerable variations in the specific weights of the asdelivered fly ashes. It is shown that even a small amount of grinding increases the specific gravity significantly, and improves and homogenizes the particle size distributions, resulting in higher strength. The strength increase corresponds to the decrease in air void content.

Intergrinding of fly ash and clinker in large scale mills reduces the power consumption, giving the same 28-day strength as mixed fly ash cement with higher fineness.
Similarities and Differences in Shale, Aggregate Mixes and Concrete Containing Fly Ash
Authors: Zenieris Petros E. , Laguros Joakim G.
Published: March 2011

Fly ash technology has been very effective in providing stability in roadway base courses composed either of shale or aggregate materials, and also in partly replacing Portland cement in concrete. X-ray diffractometry and scanning electron microscopy observations indicate that there are certain similarities among these three types of mixes concerning the hydration process; on the other hand, there is evidence of distinct differences in the hydration products which are found to act either as a filler, a chemical agent, or both. Fly ash suppresses the intensity of the clay minerals in shale, speeds up the hydration process in concrete and acts partly as a filler in aggregate mixes. The net practical result is strength development which varies not only in terms of the maximum level attained, but also in regard to its rate. The conversion of ettringite to monosulfoaluminate proceeds at a rate which is considered high in concrete, moderate in aggregate mixes, and moderate to low in shale. X-ray diffraction analyses help to identify other dissimilarities in the minerals produced. The modification which takes place in the fabric and the matrix of the mixes is morphologically the same; in contrast, the growth of crystallites at the “particle”/fly ash interface is explicitly different. Preliminary quantification of matrix changes resulting from new hydration products is also explored.
Performance Characteristics of Concrete Produced with Fluidized Bed Combustion Ash Residue
Authors: Bland A. E. , Jones C. E. , Rose J. G. , Harness J. L.
Published: March 2011

Over the last five years, the Kentucky Energy Cabinet (KEC) and the Tennessee Valley Authority (TVA) have developed and demonstrated the production of concrete from atmospheric fluidized bed combustion (AFBC) spent bed (SB) ash, and pulverized fuel ash (PFA). This AFBC concrete contains no cement and relies on the reaction of residual lime in the SB ash to react with the pozzolan PFA to form cementitious products. The SB ash is prehydrated in order to reduce exothermic lime hydration reactions and minimize molar volume expansion. Laboratory tests were conducted to establish the performance characteristics of AFBC concretes relative to conventional concrete. AFBC concretes exhibit slower strength gain characteristics, but long term (60 day), unconfined compressive strengths of 5,000 psi have been documented. This slow strength development is typical of pozzolanic concretes. AFBC concrete is more flexible and less brittle than conventional Portland cement concrete, as evidenced by its much lower modulus of elasticity. Setting times for AFBC concretes are extended, requiring the use of accelerators under certain applications. Field demonstrations of the AFBC concretes in ready mix concrete, masonry units, and road base applications have indicated excellent workability and finishing characteristics and confirm the laboratory performance characteristics.

The paper describes the results of the testing program with emphasis on the ash chemistry/conditioning, the performance characteristics and field demonstrations.
Pore Structure, Permeability, and Chloride Diffusion in Fly Ash-and Slag-Containing Pastes and Mortars
Authors: Malek R. I. A. , Roy D. M. , Fang Y.
Published: March 2011

The transport of ions through cement pastes and mortars with variable contents of fly ashes and granulated blast-furnace slag from different sources and with variable composition has been investigated. The research included the determination of chloride diffusion rate and chloride permeability in relation to microstructure development. The median pore size generally was much diminished in mature blended material compared with Portland cement (PC) pastes and mortars. It appears that, at the same age, a finer microstructure is generally developed in blended specimens compared to PC specimens. Also, it was found that the microstructure approaches a limiting value at longer ages of hydration. That limiting value may be reached at earlier ages with the blends. The chloride diffusion rates and permeabilities in the blends were significantly lower than PC mixes. A comparison between the blends containing fly ashes and those containing slag was made.
Densification and Migration of Ions in Blast Furnace Slag-Portland Cement Pastes
Authors: Feng Q. L. , Lachowski E. E. , Glasser F. P.
Published: March 2011

Well-cured slag cement blends are known to give rise to paste matrices of low permeability. Electron microscopy has been used to follow microstructural development in slag cement pastes. An initially dense layer of hydrated product develops around the slag grains. Its chemistry and microstructure are not constant but evolve with time. These variations have been explored by analytical electron microscopy, X-ray diffraction, etc. Mg is concentrated in this zone and serves as a useful chemical marker. However an outer matrix of mixed hydration products also develops, to which slag and cement both contribute. The additional contribution of Ca, Al and Si derived from slag to this matrix is considered to explain its gradual densification and resultant low permeability.
Microstructure and Porosity of Metakaolin Blended Cements
Authors: Bredy P. , Chabannet M. , Pera J.
Published: March 2011

Five compositions with 10% to 50% metakaolin for cement substitution were studied. The rate of hydration was studied from the compressive strength after up to 6 months of curing and from the hydrates formed (DTA-XRD). The metakaolin addition considerably reduced portlandite content in the hydrated cement and contributed to the formation of hydrated gehlenite which is not present in OPC paste. The microstructure study (SEM) shows that pozzolanic cement pastes were less crystallized than plain pastes. Mercury intrusion was used to measure porosity of hydrated cement pastes. The porosity with blended cements was higher than that with OPC, except for 10 and 20% metakaolin substitution. Evolution of the pore size distribution was studied: the pozzolanic pastes enhance small diameters.
Evidence for Minimal Pozzolanic Reaction in a Fly Ash Cement During the Period of Major Strength Development
Authors: Diamond Sidney , Sheng Qizhong , Olek Jan
Published: March 2011

Strengths developed in fly ash concretes usually equal or exceed that of similar plain concrete after a few months, with much of the response usually attributed to “pozzolanic” reaction between ash and secondary calcium hydroxide (CH). The CH contents of pastes made with five different fly ashes were determined by DTA for periods up to six months. The CH contents found did not decrease notably over the period, and were substantially identical to that expected for plain cement pastes diluted with the same amount of inert material as the amount of fly ash used. Scanning electron microscope examination of the pastes showed only minimal evidence of reaction even up to 1 year of age, although many fly ash grains were in intimate contact with CH. Non-evaporable water contents of the fly ash pastes were substantially higher than expected at each age, suggesting that the fly ash promoted more complete cement hydration or that the hydration products formed bound substantially greater amounts of water than plain cement paste ordinarily does.
Ontario Hydro's R&D on Sorbent Injection Waste Part I. Characterization and Conditioning
Authors: Mozes M. S. , Mangal R. , Thampi R.
Published: March 2011

The effects of furnace sorbent injection on waste characteristics and the performance of electrostatic precipitators (ESPs) have been studied under conditions simulating full scale operation at Ontario Hydro's 640 MJ/h Combustion Research Facility. Twice as much waste was produced as with coal ash; the waste was found to contain high levels of calcium compounds (CaO, CaSO4, etc.). In situ resistivity and impactor data were obtained using various sorbents injected either as a dry powder or in the form of a slurry while burning coals with sulphur content ranging between 1.4 to 2.8%. Resistivities were found to increase 2- to 3-orders of magnitude from a baseline level of 108 ohm.cm, and the size distribution of particles suspended in the flue was slightly finer than the baseline ash. Experiments with flue gas conditioning showed that the resistivity of the ash/sorbent mixture produced from limestone injection could be reduced by 1- to 2.5-orders of magnitude during SO3 conditioning and 3-orders of magnitude during water conditioning. Both agents improved the performance of the ESP and reduced particulate emissions by a factor of 1.2 to 4.
By-Product Sulfur from the Stabilization of Coal Solid Wastes
Authors: Gokhalea A. J. , Burnet G.
Published: March 2011

A stabilization process for coal cleaning and coal combustion-related wastes has been developed that uses the energy derived from the fuel contained in the coal cleaning wastes. The wastes are pulverized, when necessary, formed into granules in a rotary pan agglomerator, and then fired to a sintering temperature. The result is a readily disposable product that is highly resistant to environmental degradation. Granules of refuse only, and of refuse/fly ash and refuse/FGD sludge mixtures have been investigated. About 90 wt% of the sulfur in the refuse/sludge mixtures is evolved as SO2 during the combustion/sintering portion of the process. Studies using a microreactor system have shown the generation of SO2 to be a function of temperature and to parallel the decomposition of the sulfur-containing compounds present. Based on laboratory tests, SO2 concentrations of 4–8 vol% are predicted in the SO2-rich off-gases. By-product sulfur recovery from the off-gases appears practical and attractive using current technology that is proven and well established.
The Microstructure of National Bureau of Standards Reference Fly Ashes
Authors: Qian J. C. , Lachowski E. E. , Glasser F. P.
Published: March 2011

A suite of three fly ashes, National Bureau of Standards* Standard Reference Materials (SRMs) 2689, 2690 and 2691, was studied by transmission electron microscopy and by analytical electron microscopy (aem): sample preparation techniques are described. The chemical compositions of the glassy phase, analyzed by aem, showed a wide dispersion of values although the mean composition of the glass remained close to that of the whole fly ash.

The microstructure of these materials is complex: besides crystalline inclusions, the aluminasilica glasses have undergone phase separation on a nanometer scale, and consist of two glassy phases. Since liquid-liquid phase separation has also been found in British fly ashes, it appears to be a characteristic feature of the glassy phase in Class F ashes and is also encountered in occasional Al-Si rich particles in Class C ashes. High iron content glass was found in fly ash SRM 2689, and its phase separation and crystallization were investigated.
Predicting Properties of Solids at Finite Temperatures
Authors: Joannopoulos J.D. , Rabe K.M. , Needels M.
Published: March 2011

A method for performing ab-initio investigations of the equilibrium properties of real material solids at finite temperature is discussed. Examples involving surface and bulk structural transitions are presented.
Pseudoatomic Orbital Compact Basis Sets: Applications to Metallic Systems
Authors: Jansen Robert W. , Klein B. H.
Published: March 2011

A self-consistent orbital-based scheme is applied to metallic systems and is found to be efficient for these materials. The technique uses the local density approximation in the pseudopotential framework, but replaces the planewave basis by a basis pseudoatomic orbitals constructed directly from the pseudoatoms. Free electron-like wavefunction components are handled by orthogonalizing the orbital basis to a few low energy planewaves as needed for good eigenvalue and total energy convergence. The method is fast and versatile enough to be used for a variety of problems. Applications to bulk bandstructures, total energies, and forces in Al and Nb are presented.
First-Principles Phonon Calculations for LA2CUO4
Authors: Cohen R. E. , Pickett W. E. , Krakauer Henry
Published: March 2011

Full potential linearized augmented plane wave (LAPW) total energy calculations predict that the breathing mode in La2CuO4 is a high frequency mode, in agreement with experiment and contrary to previously published results. We also find the experimentally observed tilt mode to be unstable within the local density approximation (LDA). Eight other modes were studied, as well as the static structural parameters, and excellent agreement with experiment was found, indicating that LDA gives accurate total energies and static density response for the high temperature superconductors. Our results also suggest that phonons in the high Tc superconductors are not heavily dressed by magnetic or excitonic fluctuations, and thus that the isotope effect observed in the oxide superconductors is probably due to direct involvement of phonons in the superconductivitymechanism.
Quantum Chemical Molecular Dynamics
Authors: Caro A. , Victoria M.
Published: March 2011

We propose a simple electronic model for the cohesive energy of metals which explicitely considers eigenfunctions and eigenvectors in a single-particle LCAO approach. From them, forces are obtained to perform molecular dinamics or static relaxation. As a first application we compare the model predictions to full many-body ab-initio and Embedded Atom Model calculations of structure and energetics of small metallic clusters. Adventages and limitations of this approach as well as size restrictions are discussed.
Solid Solutions of AB2C4 Defect Semiconductors
Authors: de Pascale T.M. , Marinelli M. , Meloni F. , Mula G. , Serra M. , Borghesi A. , Guizzetti G. , Nosenzo L.
Published: March 2011

AB2C4 defect semiconductors can be thought of as generalized zincblende compounds, in which the presence of two different cations and of vacant sites favours the formation of several crystalline phases. In this work we present a theoretical study of the structural stability of the ZnxCdl-xIn2S4 solid solutions. The end compounds crystallize in a layer (x = 1) and in a spinel structure (x = 0). Total energy first principle calculations have been performed for both phases and for various values of x. The theoretical structural stability diagram compares very well with experiment.
Vibrational Localization and Vibrational Spectra in Amorphous Silicon
Authors: Biswas R. , Bouchard A. M. , Kamitakahara W. A. , Grest G. S. , Soukoulis C. M.
Published: March 2011

Amorphous silicon structures have been generated by quenching liquid silicon configurations using molecular-dynamics simulations. Localized vibrational modes have been identified in these models. The presence of under-coordinated atoms in these a-Si models leads to extra resonant modes at low frequencies. The vibrational densities of states, and dynamic structure factors for localized, resonant and extended modes, are discussed and compared with neutron scattering data. The amorphous networks have also been adapted to model amorphous silicon-germanium systems. Densities of states and localization characteristics have been calculated for a-SixGe1-x alloys and a-Si/a-Ge superlattices, and are compared to Raman measurements.
Structure of Unhydrogenated Amorphous Silicon Carbide
Authors: Kelires P. C. , Tersoff I.
Published: March 2011

Simulations of unhydrogenated amorphous silicon carbide, formed by condensing a vapor of silicon and carbon atoms, indicate partial chemical ordering, with heteronuclear bonds predominating. We find no evidence of phase separation. Carbon atoms are predominantly three-fold coordinated while silicon atoms have four-fold coordination. By combining these results with results of experimental studies, we speculate on the role of hydrogenation in determining the structure of amorphous silicon carbide.
Properties of Liquid As: A First Principles Calculation
Authors: Li X.-P. , Allen P.B. , Car R. , Parrinello M.
Published: March 2011

The structural and electronic properties of liquid arsenic are calculated using density-functional quantum theory to calculate forces and trajectories of atoms. A semiconducting gap of 0.4 eV is found, and a coordination number of 2.8, close to the experimental values of 0.5 eV and 3. Our results support the existence of a Peierls-type distortion in liquid arsenic.
Native Defects in Diamond, Sic, and Si: Energetics and Self-Diffusion
Authors: Antonelli A. , Wang C. , Bemholc J. , Davis R. F.
Published: March 2011

We have investigated, via first principles total energy calculations, the energetics of elementary native defects in group IV semiconductors. Its implications on the relative abundance of these defects and self-diffusion phenomena are analyzed. The results show that in diamond the self-diffusion is dominated by vacancies, because the interstitial and direct exchange mechanisms have much greater activation energy. In SiC stoichiometry plays an important role. For Si-rich compound, Sic-antisite is the dominant defect in the intrinsic and p-type material, while the carbon vacancy is dominant in the n-type material. For C-rich material, the Csi-antisite is dominant regardless the position of the Fermi level. In Si, it well-known that the vacancy, interstitial and direct exchange mechanisms have very similar activation energies. Our results suggest that self-diffusion experiments carried out at various pressures can determine the relative contribution of each of these mechanisms.
Atomistic Simulation of Ionic and Electronic Defects in YBa 2 Cu3O7
Authors: Baetzold Roger C. , Islam M. Saiful
Published: March 2011

An empirical two-body potential model has been developed in order to describe the electronic and ionic defect properties of orthorhombic YBa 2 Cu307. The potential model was derived starting from known potentials and calculated potentials and fits the crystal structure to better than 0.03 A for the major bonds. Oxygen vacancy formation and hole trapping as a localized polaron are most favorable at the chain oxygen ion site. Hole trapping on Cu + ions is most favorable for ions in the copper-oxygen plane. Divalent impurity ions such as Ni+2, Zn+2 and Cd+2 can dissolve in the crystal preferentially at the Cu+2 plane site.
Derivation of Many-Body Potentials for Examining Defect Behavior in Bcc Niobium
Authors: Eridon James M. , Rao Satish
Published: March 2011

Many-body potentials, in either the Embedded Atom or Finnis-Sinclair form, have gained wide popularity recently. The major difficulty in implementing the method concerns the derivation of suitable forms for the pair potential, electron density, and embedding, function which reproduce a range of empirically observable parameters such as elastic constants, defect formation energies, and defect Green's functions. This is a particularly difficult problem for niobium, which shows a variety of anomalous features in its phonon dispersion. Embedding functions which match only elastic constants may do a poor job of reproducing short wavelength behavior, and hence provide poor defect modeling. A straightforward method of deriving embedding functions for homonuclear BCC and

FCC metals will be presented which provides excellent agreement with experimental phonon dispersion curves and elastic constants, as well as Griineisen coefficients, vacancy formation energies, lattice constants and heats of sublimation. The results of the application of a set of many-body potentials derived in this fashion to nitrogen irradiated niobium will be presented.
Point and Extended Defect Properties in H.C.P. Metals Revealed by Atomic-Scale Calculations
Authors: Bacon D.J.
Published: March 2011

Recent modelling of defects in the h.c.p, metals is discussed, including the properties of vacancies and self-interstitials, and the structure of twin-boundary dislocations. Most simulations have used pair potentials, and their strengths and weaknesses are described. It is shown that an understanding of the atomic structure of h.c.p, defects is at last emerging.
Atomic Structure of a 60° Dislocation in Bulk Silicon and Germanium, and at Ge/Si Interface.
Authors: Nandedkar A. S. , Narayan J.
Published: March 2011

Atomic structures of 60° dislocations were calculated in bulk Si and Ge ,and at Ge/Si interfaces, using energy minimization techniques. An empirical three body potential developed by Stillinger-Weber was used for Si ,and the same potential with modified parameters was used for Ge. Two different configurations of a 60° dislocation (shuffle and glide) were compared. Energetics of a 60° dislocation in shuffle configuration in bulk Si and Ge , and at Ge/Si interfaces are discussed.
Electronic Structure of Extended Defects in Close-Packed Metals
Authors: Crampin S. , Vvedensky D.D. , Maclaren J.M. , Eberhart M.E.
Published: March 2011

Stacking faults in close-packed metals are known to play a crucial role in determining mechanical behaviour. Extending recent layer Korringa-Kohn-Rostoker calculations on twin faults in a variety of FCC crystals, we study in detail the aluminium defect and develop an atomistic understanding of the modifying behaviour of small concentrations of impurity atoms.
Nanometer-Scale Shock-Front Structure in Metals
Authors: Taylor Paul A. , Dodson Brian W.
Published: March 2011

Molecular dynamics shock wave simulations have been performed, which for the first time include a realistic many-body description of the atomic interactions. The structural instabilities observed in the shock-front structure are dramatically influenced by the many-body effects of these atomic interactions.
Molecular Dynamics Study of A Model Langmuir-Blodgett Film
Authors: Bareman James P. , Cardini Gianni , Klein Michael L.
Published: March 2011

Molecular dynamics calculations have been carried out on a primitive model of a Langmuir-Blodgett film. The model consists of a patch of 151 molecules, each with a head group and a 19 pseudoatom tail, physisorbed on a planar substrate at room temperature. The aggregated patch is found to be a stable entity for the duration of the calculation (200 ps), with structural features similar to those found in previous calculations on a monolayer system which employed periodic boundary conditions but no explicit headgroup. Results are presented for the density distribution normal to the surface, the average chain tilt angle distribution and for the number of gauche defects.
First Principles Study of Hydrogen Adsorption and Diffusion on Transition Metal Surfaces: Application to the Ru (0001) Surface
Authors: Chelikowsky-al James R. , Chou M.-Y.
Published: March 2011

Hydrogen adsorption and diffusion on the (0001) surface of ruthenium is investigated using ab initio pseudopotentials within the local density approximation. The adsorption energies at a number of different sites and bond lengths were investigated via total energy calculations. Using these calculated values a potential surface was constructed and an estimate for the activation barrier for hydrogen diffusion was obtained. The calculated value of 4.0 kcal is in good accord with the value of ≈ 4 kcal as determined from laser-induced thermal desorption experiments.
Computer-Generated Structural Models for a-Si:H
Authors: Lewis Laurent J. , Mousseau Normand , Drolet FranÇois
Published: March 2011

A new algorithm for generating fully-coordinated hydrogenated amorphous silicon models with periodic boundary conditions is presented. The hydrogen is incorporated into an a-Si matrix by a bond-switching process similar to that proposed by Wooten, Winer, and Weaire, making sure that four-fold coordination is preserved and that no rings with less than 5 members are created. After each addition of hydrogen, the structure is fully relaxed. The models so obtained, to be used as input to molecular dynamics simulations, are found to be in good agreement with experiment. A model with 12 at.% H is discussed in detail.
Hyperfine Interactions in Dangling-Bond Defects
Authors: Cook Michael , White C.T.
Published: March 2011

In a recent theoretical study of the Pb center at the Si(lll)/SiO2 interface, 1,2 we pointed out the importance of spin-polarization effects for the accurate theoretical description of ESR hyperfine interactions. The small superhyperfine tensor in the Pb center, for example, could not have been definitely assigned to a subset of the second neighbors of the defect atom rather than its nearest neighbors without an explicit consideration of spin polarization effects.
Thermodynamics, Kinetics and Interface Morphology of Reactions Between Metals and GaAs
Authors: Lin Jen-Chwen , Chang Y. Austin
Published: March 2011

The chemical stability of interfaces between metals and GaAs was discussed in terms of reaction sequence and diffusion path concepts. The factors which determine interface morphology were also given. These general ideas can be applied to any interfacial reactions between two dissimilar materials.
Characterization of Interfaces Between Polymers and Metals by Static Sims
Authors: Van Ooij W.J.
Published: March 2011

The use of static Secondary Ion Mass Spectrometry (SIMS) in the characterization of polymer surfaces and interfaces between polymers and metals is described. Examples are given of the use of SIMS to study the effects of plasma treatments on polyimide surfaces and for the analysis of the interface in metallized polytetrafluoroethylene (PTFE).
Xps Identification of Al-Pva Complex
Authors: Akhter S. , Jo S.K. , Zhou X.-L. , White J.M.
Published: March 2011

Aluminum was deposited on a polyvinyl alcohol film surface by reaction with trimethyl aluminum at 300 K. XPS analysis indicated a carbon free deposition of a monolayer of Al. The Al forms an oxy-carbide complex, AIOC, which exhibits a stoichiometry of 1:1:1 for Al, 0 and C. Within this complex Al is bonded to both C and 0 resulting in the appearance of low binding energy peaks in C(ls) and O(ls) spectra. The complex is oriented such that Al forms the outer-most layer. The Al modified surface was hydrophobic compared to the hydrophilic PVA. A reaction mechanism is proposed based on XPS and mass spectrometric data.
New Simulation of Polymers on Surfaces
Authors: Aguilera-Granja F. , Kikuchi Ryoichi
Published: March 2011

A new method of simulation based on the output of the analytical equilibrium calculation of the Cluster Variational Method (CVM) is used to obtain information about the properties of the polymers adsorbed on a surface. We find a strong preferential adsorption of longer chains, in agreement with experimental observations. This tendency is more pronounced in neutral polymers than in polyelectrolytes. Other geometrical properties like trains, tails, and loops of adsorbed polymers are also calculated.