bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Recovery and Ordering in Ni3A1+B
Authors: Karnthaler H. P. , Kozubski R. , Pfeiler W. , Rentenberger C.
Published: April 2011

Defect recovery andlong-range ordering(LRO) in Ni76Al24+0.19at.%B (400 wt.ppm) were studied by means of residual resistometry, TEM methods and microhardness testing. The material was cold-rolled with intermediate annealings and the samples were prepared from sheets exhibiting effective thickness reductions of 8 and 14%, respectively, achieved in the final rolling step.

By TEM two recovery processes were observed. Firstly,superlattice intrinsic stacking faults(SISF) of large density recovered almost completely in the temperature regime between 443 and 700 K showing that they are bounded by dislocations of opposite sign. This indicates that most of the SISF are formed by pulling out dipoles and not by dislocation interactions as recently suggested. Secondly, the recovery of antiphase-boundary (APB) dissociated superlattice dislocations occurred by the annihilation of dipoles within the whole temperature regime leading finally to a loss of all dislocations at 1273 K.

Despite some excess disorder caused by cold-rolling, the mechanical deformation did not influence qualitatively the LRO processes.
Monitoring of Deformation Induced Microcracking in Polycrystalline NiAl
Authors: Wanner A. , Schietinger B. , Bidlingmaier T. , Zalkind H. , Arzt E.
Published: April 2011

Microcracking in polycrystalline near-stoichiometric NiAl produced by room temperature plastic deformation under uniaxial compression was investigated by means of optical microscopy, velocity of sound measurements, and acoustic emission monitoring. Results show that strains greater than 2 % are required to produce microcrack populations which can be evaluated by microscopical investigation or velocity of sound measurements. However, acoustic emission monitoring during compression testing indicates that microcracking starts at about 0.7 % compressive plastic strain which is identical with the typical tensile fracture strain for NiAl. Thus it is concluded that there is little or no stable microcracking prior to failure in tension. Acoustic emission results show also that the process of microcracking does not primarily occur during the applied compressive deformation. A considerable fraction of the microcracking takes place during the quasi-elastic unloading following deformation.
An Hrem Investigation of a {121}L10 Boundary in Tial
Authors: Inkson B. J. , Humphreys C. J.
Published: April 2011

A consideration of {121}L10 boundaries in their unrelaxed form shows that there are at least three ィ2, six ィ3 and three ィ6 variants possible due to the tetragonal ordering of the L10 lattice. Experimental observations of コ-TiAl, obtained by HREM, show that two コ-grains with a true-twin orientation relationship exhibit a rigid body shift between the {111} planes perpendicular to and either side of a {121}L10 interface, and that the interfacial structure is distinct from those previously observed in f.c.c. metals.
The Temperature Dependence of the Mechanical Properties of Gamma TiAl
Authors: Viguier B. , Bonneville J. , Hemker K. J. , Martin J. L.
Published: April 2011

Mechanical properties of a polycrystalline single phased γ Ti47Al51Mn2alloy were studied by compression tests in a wide range of temperature (100 K - 1300 K). We report, in this paper, the temperature dependence of both the flow stress and its strain rate sensitivity. These dependencies show the existence of three temperature domains corresponding to different dislocation motion mechanisms. The temperature dependence of the flow stress strain rate sensitivity is compared with values measured in single crystals1.
Dislocations and Charge Density Distributions of γ Phase in Ti47.5Al2.5V Deformed at Room Temperature and 400°C
Authors: Zhu Jing , Gao Ying , Miao Yu
Published: April 2011

The observations on quantity and configuration of dislocations by TEM conventional diffraction contrast method as well as the determinations of the electron charge density distributions by the quantitative electron crystallography method in Ti47. 5A12. 5V deformed at 400°C and room temperature (R. T.) have been carried out. The metallic bonding between Al—Al or Ti—Ti atom pair along <C110] and Ti — Ti along <C112] direction is strengthened; while the metallic bonding between Ti — Al atom pair both along <C101] and <12l] direction is weakened at 400°C. The quantities of a/2<110], a/2<112] and dissociated a <101] (a[101] →a/2[110] + a/3[112] + SISF+a/6[112] ) dislocations are increased at 400°C, compared with that at R. T.. The a/ 2 < 121] superdislocations have not been seen both at 400°C and R. T..
Dislocation Substructures in Shock-Loaded N13AI
Authors: Albert Diane E. , George T.
Published: April 2011

The deformation substructure and mechanical response of the LI2intermetallic, Ni3Al, subjected to shock-wave loading was studied. Following shock prestrains to shock pressures of approximately 14.0 GPa, 23.5 GPa, and 47.2 GPa, the reload yield strength of Ni3Al was measured to be 750 MPa, 1250 MPa and 1500 MPa, respectively. The effective hardening in the shock-loaded Ni3Al exceeds that quasistatically obtained when deformed to roughly the same equivalent strains. Coarse planar slip on {111} type planes, a high density of stacking faults, and deformation twins with a {111} type twinning plane were observed in the shocked material. An increasing propensity for twinning and stacking fault formation was observed with higher shock peak pressures.
Effect of Ternary Additions on the Intrinsic Ductility of Ni3Al Alloys
Authors: Chiba A. , Hanada S. , Watanabe S.
Published: April 2011

Ductility of binary and ternary Ni3Al alloys with conventional purity, fabricated by isothermal hot-forging, was examined by tensile tests in dry oxygen to eliminate environmental embrittlement. Re crystallized Ni-23A1 doped with approximately 0.4 mol% X(X=Hf, Nb, and Zr) alloys exhibits pronounced ductility, whereas recrystallized Ni-23A1–2X alloys exhibits elongation of less than 3%. Ductility of a highly purified binary Ni-23A1 alloy was also examined and showed remarkable ductility, resulting in trans granular fracture. This indicates that a Ni-rich Ni3Al alloy inherently exhibits marked ductility without intergranular fracture if impurity atoms and other extrinsic factors(e.g., environmental effect and internal microcracks) are eliminated in the alloy. Thus it is found that Hf, Nb and Zr in the significant ductilization of Ni-23A1 can act as a scavenger of harmful impurities when added in a small amount. With further increasing amount of additions of Hf, Nb and Zr, elongation decreases rapidly and reaches almost no ductility at 2 mol% additions, indicating that Hf, Nb and Zr lower the intrinsic ductility of Ni3Al alloy.
Reaction Synthesis of Intermetallics
Authors: Deevi Seetharama C. , Sikka Vinod K.
Published: April 2011

Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.
Microstructures and Properties of Ds in-Situ Composites of Nb-Ti-Si Alloys
Authors: Bewlay B. P. , Jackson M. R. , Reeder W. J. , Lipsitt H. A.
Published: April 2011

In-situ composites based on binary Nb-Si alloys and consisting of a Nb solid solution with Nb3Si or Nb5Si3 have shown a promising combination of low temperature and high temperature mechanical properties. The environmental resistance and room temperature fracture toughness of these composites can be further enhanced by additions such as Ti, Hf, Cr, and Al. In the present study, ternary Nb-Ti-Si alloys were prepared by directional solidification to generate aligned two and three phase composites containing a Nb solid solution with Nb3Si and/or Nb5Si3. The present paper will describe microstructures, phase equilibria and fracture toughness of these composites. The improvement in the room temperature fracture toughness over binary Nb-Nb5Si3 composites is discussed.
High Temperature Corrosion Behavior of Ni3A1-Based Alloys
Authors: Li H. , Guo J. T. , Lai W. H. , Wang S. H. , Tan M. H.
Published: April 2011

The corrosion behavior of a Ni3A1–1 5at%Fe alloy has been studied in air and melted salts, and also that of Ni3Al alloys contained series boron in melted salts. The first alloy has two oxidation rate constants. Its initial oxidation activity energy is 319 kJ / mol. There was much FeAl2O4 formed at 950°C, which possessed better oxidation resistance than NiFe2O4, therefore the alloy had the best oxidation resistance at 950°C. It also had better sulfidation resistance than 00Cr19NillTi stainless steel at 850°C, but the alloy was sulfidized seriously at 950°C. The sulfides were FeS2 at 850°C and A12S3, Ni2S3 at 950°C. There were different initial oxides formed, which were Fe3O4 at 850°C, and mixture oxides of NiO, NiMoO4, A12O3 and NiAl2O4 at 950°C , respectively. The Ni3Al alloys with boron contents from 0 to 3.7at% had better sulfidation resistance than the stainless steel at 850°C, and the alloy with 1.37at%B was the best. The sulfides were the same in the boron containing Ni3Al alloys which were Al2S3 and Ni7S6.
Oxidation Behaviour of Intermetallic Compounds Based on Ti-Al System
Authors: Tomasi A. , Gialanella S. , Orsini P. G. , Nazmy M.
Published: April 2011

In this study we present some results regarding phase and surface stability, with particular reference to the oxidation, of Ti alloys based on the γ-TiAl phase.

We investigated the stability of the metallic phases with TG and DSC methods, according to the temperature range over which the relevant transformations do occur. These tests were particularly useful to select times and temperatures for precipitation hardening treatments and also to evaluate the oxidation resistance.

The isothermal oxidation kinetics were followed with a thermobalance (TG) for time up to 25 hours and, for longer treatments, we put the samples in a furnace and measured their weight changes at fixed time intervals. The microstructure of the oxide scale was investigated with scanning electron microscopy and energy dispersion X-ray analysis and mapping. The identification of the crystalline phases was carried out with X-ray diffraction analysis.

The obtained results afford clear information on the predominant phenomena assisting the observed oxidation kinetics and give indications on the operating conditions suitable for these materials.
TEM Characterization of Al/Al2O3 Composite Fabricated by Reactive Metal Infiltration
Authors: Gao Y. , Jia J. , Loehman R. E. , Ewsuk K. G.
Published: April 2011

The microstructure of Al/α-Al2O3 composites made by infiltrating into dense mullite preforms has been characterized using transmission electron microscopy. Observations revealed that the formation of the Al/Al2O3 composites involves three stages. Initially, infiltrates into a dense mullite preform through grain boundary diffusion, and reacts with mullite at grain boundaries to form a partial reaction zone. Then, a complete reaction takes place in the reaction region between the partial reaction zone and the full reaction zone to convert the dense mullite preform to a composite of α-Al2O3 (matrix) and an Al-Si phase (thin channels). Finally, the reduced Si from the reaction diffuses out of the Al/A2O3 composite through the metal channels, whereas from the molten pool is continuously drawn to the reaction region until the mullite preform is consumed or the sample is removed from the molten pool. Based on the observed microstructure, infiltration mechanisms have been discussed, and a growth model of the composites is proposed in which the process involves repeated nucleation of Al2O3 grains and grain growth.
Polymer-Derived Silicon Carbide Fibers with Near-Stoichiometric Composition and Low Oxygen Content
Authors: Sacks Michael D. , Scheiffele Gary W. , Saleem Mohamed , Staab Gregory A. , Morrone Augusto A. , Williams Thomas J.
Published: April 2011

Fine-diameter (∼ 10–15 µm), polymer-derived SiC fibers were characterized. The average tensile strength of the fibers was ∼ 2.8 GPa, although some lots had average strengths exceeding 3.5 GPa. Microstructure observations showed that fibers had fine grain sizes (mostly ∼0.05–0.2 µm), high densities (∼3.1–3.2 g'cm3), and small residual pore sizes (≤0.1 µm). Elemental analysis showed that fibers had near-stoichiometric composition. Electron and X-ray diffraction analyses indicated that fibers were primarily beta silicon carbide, with a minor amount of the alpha phase. A small amount of graphitic carbon was detected in some samples using high resolution transmission electron microscopy. The residual oxygen content in the fibers was ≤0.1 wt%. Fibers exhibited good thermomechanical stability, as heat treatment at 1800°C for 4h in argon resulted in only an ∼ 8% decrease in strength.
Characterization of BN Rich Layer on Ammonia Treated Nextel™312 Fibers
Authors: Khasgiwale N.R. , Butler E.P. , Tsakalakos L. , Hensley D.A. , Cannon W.R. , Danforth S.C. , Gonczy S.T.
Published: April 2011

A BN rich layer grown on Nextel™312 fibers by appropriate ammonia treatments was evaluated using various complimentary techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM)/ Parallel Electron Energy Loss Spectroscopy (PEELS in TEM). Three different ammonia treatments were studied. Ammonia treatment resulted in crystallization of the Nextel™312 fiber. The BN rich surface layer formed due to ammonia treatment was clearly detected in XPS and PEELS both before and after oxidation. The layer thickness was estimated to be between 5–10 nm. The layer was stable after oxidation treatment at 600°C for 100 hours. High resolution TEM observations of the fiber surface revealed a variable BN rich layer thickness. Patches of turbostratic BN were observed under certain conditions, however mostly the layer appeared to be amorphous.
Effect of Coating Thickness on Interfacial Shear Behavior of Zirconia-Coated Sapphire Fibers in a Polycrystalline Alumina Matrix
Authors: Hellmann John R. , Chou Yeong-Shyung
Published: April 2011

The effect of zirconia (ZrO2) interfacial coatings on the interfacial shear behavior in sapphire reinforced alumina was examined in this study. Zirconia coatings of thicknesses ranging from 0.15 to 1.45 μm were applied to single crystal sapphire (Saphikon) fibers using a particulate loaded sol dipping technique. After calcining at 1100°C in air, the coated fibers were incorporated into a polycrystalline alumina matrix via hot pressing. Interfacial shear strength and sliding behavior of the coated fibers was examined using thin-slice indentation fiber pushout and pushback techniques. In all cases, debonding and sliding occurred at the interface between the fibers and the coating. The coatings exhibited a dense microstructure and led to a higher interfacial shear strength (> 240 MPa) and interfacial sliding stress (>75 MPa) relative to previous studies on the effect of a porous interphase on interfacial properties [1]. The interfacial shear strength decreased with increasing fiber coating thickness (from 389 ± 59 to 241 ± 43 MPa for 0.15 to 1.45 μm thick coatings, respectively). Sliding behavior exhibited load modulation with increasing displacement during fiber sliding which is characteristic of fiber roughnessinduced “stick-slip”. No effect of fiber coating thickness on the interfacial sliding stress was observed for single pushout or pushback events. Heat treatment at 1550°C in air coarsened the fiber surface roughness, resulting in significantly higher interfacial shear strengths (>30%) and interfacial sliding stresses (>60%) relative to the coated fibers in an as-hot-pressed condition. Interfacial sliding resistance decreased significantly after the first sliding cycle. Evidence of substantial “stick-slip” behavior was eliminated from the load displacement plots after one pushout/pushback cycle; however, the pushback plots exhibited evidence of fiber reseating, followed by a decreasing trend in load with increasing displacement of the fiber back to the original position. These results directly support the interphase fragmentation scenario proposed for interface fatigue in ceramic composites.

The high interfacial shear strengths and sliding stresses measured in this study, as well as the potentially strength degrading surface reconstruction observed on the coated fibers after hot pressing and heat treatment, indicate that dense zirconia coatings are not suitable candidates for optimizing composite toughness and strength in the sapphire fiber reinforced alumina system.
Ceramics in the System NbB2 – CrB2
Authors: Talmy I. G. , Wuchina E. J. , Zaykoski J. A. , Opeka M. M.
Published: April 2011

Phase equilibria and properties of ceramics in the NbB2 – CrB2 system were studied. Continuous solid solutions were found showing high activation energy (96 kcal'mol) of formation which is due to large disparity of atomic radii between Cr and Nb. Pure NbB2 and CrB2 ceramics were prepared by hot pressing at 2100 and 1800°C, respectively, at 20 MPa for 0.5 hour. Both materials exhibited closed porosity which was eliminated by the addition of Al2O3 and SiC. Thermogravimetric studies showed different mechanisms of oxidation of the diborides. The presence of Al2O3 and SiC improved the oxidation resistance, hardness, and fracture toughness of CrB2 ceramics. The additives increased the hardness of NbB2 ceramics but did not significantly affect their toughness.
Metal-Ceramic Microstructures in the Fe-Mn-O System – Morphology Control by Impurity Addition
Authors: Subramanian R. , Üstündağ E. , Sass S.L. , Dieckmann R.
Published: April 2011

The influence of the addition of impurities and changes in the oxygen partial pressure on the formation of metal-ceramic microstructures by partial reduction of ternary or higher ceramic oxides was experimentally investigated in the model system Fe-Mn-C at constant temperature and total pressure. Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. It was observed that the addition of dopants such as BaO, CaO, MgO, SrO, Al2O3, Cr2 O3 or ZrO2 to the initial, polycrystalline oxide solid solution (Fel−xMnx)1−ΔO strongly influences the location and rate of metal precipitation during reduction. Experimental observations are discussed based on solubility limits and the segregation of dopants.
Characterization of Phosphorus Segregation in Neutron-Irradiated Pressure Vessel Steels by Atom Probe Field Ion Microscopy
Authors: Miller M. K. , Jayaram R. , Russell K.F.
Published: April 2011

An atom probe field ion microscopy characterization of A533B and Russian VVER 440 and 1000 pressure vessel steels has been performed to determine the phosphorus coverage of grain and lath boundaries. Field ion micrographs of grain and lath boundaries have revealed that they are decorated with a semi-continuous film of discrete brightly-imaging precipitates that were identified as molybdenum carbonitride precipitates. In addition, extremely high phosphorus levels were measured at the boundaries. The phosphorus segregation was found to be confined to an extremely narrow region indicative of monolayer-type segregation. The phosphorus coverages determined from the atom probe results of the unirradiated materials were in excellent agreement with predictions based on McLean's equilibrium model of grain boundary segregation. The boundary phosphorus coverage of a neutron-irradiated weld material was significantly higher than that observed in the unirradiated material.
Gamma Ray-Induced Embritilement of Pressure Vessel Alloys
Authors: Alexander Dale E. , Farrell K. , Stoller R. E. , Rehn L. E.
Published: April 2011

High-energy gamma rays emitted from the core of a nuclear reactor produce displacement damage in the reactor pressure vessel (RPV). The contribution of gamma damage to RPV embrittlement has in the past been discounted. However, in certain reactor designs the gamma flux at the RPV is sufficiently large that its contribution to displacement damage can be substantial. For example, gamma rays have been implicated in the RPV embrittlement observed in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory.

In the present study, mechanical property changes induced by 10-MeV electron irradiation of a model Fe alloy and an RPV alloy of interest to the HFIR were examined. Tensile specimens were irradiated with high-energy electrons to reproduce damage characteristic of the Compton recoil-electrons induced by gamma bombardment. Substantial increases in yield and ultimate stress were observed in the alloys after irradiation to doses up to 5.3x10−3 dpa at temperatures (~50°C) characteristic of the HFIR pressure vessel. These measured increases were similar to those previously obtained following neutron irradiation, despite the highly disparate nature of the damage generated during electron and neutron irradiations.
Precipitation in Zr-2.5Nb During 10 MeV Electron Irradiation
Authors: Woo O.T. , Hutcheon R.M. , Coleman C.E.
Published: April 2011

The corrosion resistance of Zr-2.5Nb is increased by neutron irradiation at 570K. This is due to the radiation-enhanced precipitation of β-Nb within the ∝-Zr grains, and the associated reduction in the Nb concentration in the ∝-Zr matrix during irradiation. This microstructure was observed in annealed Zr-2.5Nb irradiated with neutrons at 670K and 770K, and also with protons between 770 and 720K to 0.9 dpa. In this study, the same annealed Zr-2.5Nb, in the form of four 8 mm diameter, 0.5 mm thick discs, was irradiated with 10 MeV electrons for 370 hours. The damage accumulated on the discs ranged from 0.5 to 1.2 dpa, while the temperature of each disc varied from 720K at the centre to 600K at the edge. TEM examination of the 1.2 dpa, 710K sample revealed needle-like precipitates in the ∝-Zr matrix. These precipitates, having widths of I or 2 nm and lengths up to 70 nm, were shown by EDX analysis to contain Zr and Nb. Dark field observations using a precipitate reflection confirmed that the precipitates were β-Nb with about 88 % Nb. Specimens made from the same Zr-2.5Nb that were annealed at 720K for 370 hours but unirradiated had clear ∝-Zr grain interiors, with no precipitates. Thus electron irradiation produced a microstructure similar to that produced by neutrons and protons.
Medium-Range Order in Metamict Silicas
Authors: Qin L.C. , Hobbs L.W.
Published: April 2011

The first sharp diffraction peak from various forms of aperiodic silica was studied. Materials examined include vitreous silica, electron-metamict quartz, neutron-metamict quartz, and Si+ ion-implanted quartz. The peak is attributed to the dominant structural rings existing in the materials, or modification thereof. The anomalous behavior of this peak is also discussed.
The Effect of Crystal Structure on Sputtering: Molecular Dynamics Calculations
Authors: Chang Che-Chen , Chen Horng Huah , Wu Paul
Published: April 2011

Molecular dynamics calculations have been used to study the ion-etching process by a focused-ion beam. Ion-induced atomic displacement in a Ag surface initiates collision cascades which lead to particle sputtering from the surface. Tracing collision cascades reveals that the sputtering is mainly caused by a surface atom being sideswiped by its neighboring atom traveling in a surface channel oriented a certain angle away from the direction of ejection. Depending on the angle of detection and on the kinetic energy of sputtering, the ejecting particles may proceed along crystallographic directions parallel to either the close-packed or the non-close-packed rows of atoms in the surface. The preferred direction of ejection is sensitive to variations in the polar angle of detection and in the ejection energy. For those residual atoms initially located within four lattice spacings from the target atom, the most probable distance of displacement is less than one eighth of the equilibrium bond length in the crystal bombarded by Ar† ions of I keV energy. The structural perturbation increases as the ion energy is increased from 0.2 keV to I keV, but decreases as the energy is increased further.
Microstructure of Ybco Irradiated with 200 Kev Protons and 1 Mev Fluorine Ions
Authors: Kulik Joseph , Wu J.Z. , Zhang Z.H. , Yu N. , Chu W.K.
Published: April 2011

Transmission electron microscopy (TEM) has been used to study the effects of 200 keV proton and 1 MeV fluorine ion irradiation on the microstructure of YBa2Cu3O7-δ (YBCO). Proton irradiation at fluences on the order of 1016 cm−2 results in more visible defects than can reasonably be expected solely from high energy transfer events; medium energy transfer events also contribute to visible defects. Defects arising from cascade events can be as large as 2 to 3 nm, and high resolution imaging suggests that they consist of small volumes of structurally disordered material. Fluorine irradiation to similar displacement levels results in significantly more visible defects.
Peculiarities in the Epitaxial Regrowth of Ion-Implanted Si1−xGex Alloy Layers Grown on Compositionally Graded Buffers
Authors: Fyhn M. , Shiryaev S. Yu. , Larsen A. Nylandsted , Hansen J. Lundsgaard
Published: April 2011

Solid phase epitaxial regrowth of ion-implanted relaxed Si1-xGex layers was studied as a function of alloy composition (0.15< x <0.5) by a combination of Rutherford backscattering/ channeling spectrometry and transmission electron microscopy. The samples were grown by molecular beam epitaxy on compositionally graded buffers at different growth conditions. It was found that the regrowth velocity follows an Arrhenius curve in the investigated composition range and increases with increasing Ge content. The activation energies of the epitaxial regrowth were found to be higher than those expected from a linear interpolation between the values for pure Si and Ge. It is demonstrated that the regrowth velocities in the samples grown at 550 and 750°C and with low-rotational speed of the substrate during growth depend on the lateral position on the wafer and that they can be reduced by a preannealing treatment at high temperatures (σ920°C). We suggest that these effects arise from a compositional modulation in the alloy layer and, therefore, from a symmetrized strain, which can be reduced by a high temperature annealing.
Numerical Simulation of Thermal Effects in Nonlinear Optical Materials
Authors: Kowalski Gregory J. , Wahl Edward H. , Roach Joseph F.
Published: April 2011

A numerical simulation of the nonlinear optical and thermal response of a material is described. The code is divided into preprocessor, simulation and postprocessing functions. The simulation function is a transient, three dimensional, finite difference algorithm which describes the thermal response and the optical phase change that occurs due to 3rd order nonlinearity and thermal effects. Irradiance changes due to linear and nonlinear absorption mechanisms are included in the code. In the postprocessing function a Gaussian beam decomposition technique is used to calculate the irradiance and transmitted power at a far field location and the temperature time response of the material. Examples of using the code to simulate Z-scan experiments are presented and compared to those reported in the literature. Results are presented that demonstrate that the code can be used as a tool to investigate using thermal transport mechanisms to modify the nonlinear optical response of the material. Limitations of the code are discussed.
Solvent Effects on C60 Excited State Cross Sections
Authors: McLean Daniel G. , Brandelik Donna M. , Brant Mark C. , Sutherland Richard L. , Frock Lynn
Published: April 2011

A survey study of solvent effects on the linear and nonlinear absorption properties of C60 has been done. The nonlinear absorption measurements are done at 694 nm with a Q-switched Nd:YAG pumped dye laser. In conjunction with this study a three level rate equation system has been solved analytically and the model results used to extract effective excited state cross sections. A difference and a ratio are calculated from the effective excited state cross section and the ground state cross section. The analysis demonstrates that it is this difference and the initial transmission which determine the critical fluence for the onset of nonlinear absorption. The saturation behavior is determined by the ratio of the cross sections and the initial transmission. Based on these findings C60 is shown to have some of the highest reported nonlinear absorption properties at 694 nm. The effective excited state cross sections at 694 nm are reported for the solutions and correlations to the solvent types demonstrated.
Optical Limiting with Liquid Crystalline Cylindrical Guided Wave Optical Elements
Authors: Khoo I. C. , Li H. , Lee Ming , Yarnell B. K. , Wood M. V.
Published: April 2011

Using micro-capillaries and capillary arrays, we have fabricated dye- and C60-doped liquid crystal cored fibers and image transmission plates of various core diameters and lengths. We have observed nonlinear pulse propagation and limiting effect using nanosecond 0.53 μm Nd:Yag laser. Typical threshold fluence is on the order of < 1 J/cm2 in a 7 mm long fiber. A theoretical modelling of the observed effect is also presented.
Silicon-Hydrogen Bonding and Hydrogen Diffusion in Amorphous Silicon
Authors: Van De Walle Chris G. , Street R. A.
Published: April 2011

Despite its importance for technological applications, the behavior of hydrogen in amorphous silicon is not fully understood. In particular, the anomalously low activation energy (1.5 eV) for hydrogen diffusion has remained unexplained. We investigate the interaction of hydrogen with dangling bonds using first-principles pseudopotential-density-functional calculations. Our analysis shows that the diffusion activation energy should be measured from the hydrogen chemical potential, and that this level should be identified with the formation energy of Si-H bonds. A quantitative identification of the energy levels with experimental observables is then possible.
Properties and Crystallization of Amorphous Si1-xPx Alloy Thin Films
Authors: Carisson J. R. A. , Li X.-H. , Madsen L. D. , Hentzell H. T. G.
Published: April 2011

The properties of amorphous Si1-xPx alloy thin films with 20–44 at.% P were studied. The results showed that these alloys have a wide bandgap Eo ranging from 1.5 to 2.15 eV, where the alloy films with 20 at.% P have the widest bandgap (1.75–1.82 eV) at annealing temperatures ≤600 °C. Conductivity measurements showed that two electron conduction processes mainly exist: hopping conduction in the band tail at low temperatures and extended-state conduction in the conduction band at high temperatures. Crystallization studies showed that the alloys are thermally stable and crystallize at temperatures between 850 and 1100 °C. A new phosphide, Si7P3 was formed by annealing the alloys with 30–44 at.% P at temperatures ≥950 °C depending on the P concentration.
Dopant Activation in Boron-Doped a-Si:H and a-SiC:H by Thermal Annealing and Light-Soaking
Authors: Isomura Masao , Hishikawa Yoshihiro , Tsuda Shinya
Published: April 2011

The effects of thermal history and light-soaking are systematically studied on boron-doped a-Si:H and a-SiC:H. Light-soaking increases dark conductivity at a low carbon content but decreases it at a high carbon content. This reaction is reversible, and the dark conductivity recovers to the initial value with thermal annealing. The effect of thermal history is also influenced by carbon content in samples deposited at a relatively low temperature (110°C). The increase in dark conductivity occurs with thermal annealing at a higher temperature than the deposition temperature at a high carbon content. But this effect is not significant at a low carbon content. These phenomena can be explained by the hydrogen passivation of four-fold boron, and the hydrogen motion and trapping in the network. The present model suggests that a microstructure containing deep traps of mobile hydrogen contributes to improvement in the stability of a-Si:H and its alloys.
Analysis of Fill Factor Losses in a-Si and a-SiGe Alloy Solar Cells Using a New Technique
Authors: Banerjee A. , Xu X. , Yang J. , Guha S.
Published: April 2011

A new technique to diagnose fill factor losses occurring in single-junction amorphous silicon (a-Si) alloy based nip solar cells has been explored. The method consists of the measurements of the fill factor of the device under blue and red light illumination and the current-collection loss obtained from the ratio of the quantum efficiency versus wavelength spectra at zero and reverse bias. Normally, the losses are higher at low and high wavelengths. It has been observed that there is a strong correlation between the values of the blue and red fill factors and the current collection losses at the pli interfaces and the bulk of the i-layer, respectively. The losses have been attributed to back diffusion of carriers at the pli interface and to the bulk of the i-Layer. There is a sensitive dependence between these losses and the texture of the substrate: textured substrates lead to higher losses compared to specular substrates. The technique has been used successfully to enhance the values of the red, blue, and AM 1.5 fill factors of both a-Si and amorphous silicon-germanium (a-SiGe) alloy single-junction cells on back reflectors by the optimization of device fabrication parameters. The optimized cells on textured back reflectors exhibit reduced losses. The paper presents an analysis of the experimental results.
Electrophotographic Patterning of a-Si:H
Authors: Gleskova H. , Wagner S. , Shen D. S.
Published: April 2011

A novel laser-printing method for the manufacturing of the backplane circuits of active-matrix liquid-crystal displays (AMLCD) is proposed and demonstrated. Xerographic toner is used as an etch mask for amorphous silicon (a-Si:H) and for the seeding of metal lines. We also demonstrate for the first time the direct-print patterning of silicon on ∼ 50 μm thick glass foil.
Detection Limit of Large Area Id Thin Film Position Sensitive Detectors Based in a-Si:H P.I.N. Diodes
Authors: Martins R. , Lavareda G. , Soares F. , Fortunato E.
Published: April 2011

The aim of this work is to provide the basis for the interpretation of the steady state lateral photoeffect observed in p-i-n a-Si:H ID Thin Film Position Sensitive Detectors (ID TFPSD). The experimental data recorded in ID TFPSD devices with different performances are compared with the predicted curves and the obtained correlation's discussed.
Studies of a Polymer Dispersed Ferroelectric Liquid Crystal
Authors: Allan Guymon C. , Hoggan Erik N. , Bowman Christopher N.
Published: April 2011

Ferrorlrtric liquid crystals (FLCs) have shown great potential for use in electro-optic and display technology due to theri inherently fast switching speeds. Recently within this area a great deal of attention has also been given to FLCs dispersed within a polymer networks. Adding the polymer may act to enhance certain electro-optic properties and will substantially increase the mechanical strenth on the FLC system. This study examines the effects of adding either a diacrylate monomer or a polymer network to a FLC mixture of known composition. The monomer depresses the phase transition temperatures to more orderd phases for both first and second order transitions and causes a marked decrease in the amount of liquid crystal which exhibits typical transitions behavior. During polymerization the network phase separates forming two cocontinuous phases and allows the liquid crystal transitions to return close to values seen in polymer systems. As a result of this decrease, the rotational viscosity decrease for these same samples. Maximum double bond conversions and polymerization rate maxima increase with monomer concentration until saturation on monomer in the liquid crystal is reached. The rate maxima then decreases as the monomer as the monomer must dissolute into the liquid crystal and diffuse to the reactive sites.
Deviation from Stoichiometry and Lattice Properties of Semiconducting SnTe Phase
Authors: Rogacheva E. I. , Gorne G. V. , Nashchekina O. N.
Published: April 2011

The temperature dependences of lattice thermal conductivity λp in the range of 300-650 K were obtained for SnTe1+x semiconducting phase with x =0-0.04. It is established that the nonstoichiometric vacancies are centers of effective scattering of phonons. The scattering cross-section calculated from experimental data is in a good agreement with the theoretical calculations based on the Klemens theory. The linear change of thermal resistance with temperature is observed, which evidences the prevalence of three-phonon scattering processes. The additional thermal resistance grows as the concentration of cation vacancies increases.
Growth and Characterization of the Binary Defect Alloy Cu2-xSe and the Relation to II–VI/I–III–VI Heterojunction Formation
Authors: Nelson Art J. , Sinha K. , Moreland John
Published: April 2011

Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu2Se heterojunction interface. Cu2−xSe layers were deposited on GaAs (100) by molecular beam epitaxy from Cu2Se sources. Raman spectra reveal a strong peak at 270 cm−1, indicative of the Cu2−xSe phase. Atomic force microscopy reveals uniaxial growth in a preferred (100) orientation. CdS overlayers were then deposited in-situ, at room temperature, in steps on these epilayers. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Se3d and Cd4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu2−xSe and heterojunction valence band discontinuity and the consequent heterojunction band diagram. These results are compared to the valence band offset (ΔEv) for the CdS/CuInSe2 heterojunction interface.
Enhanced Hydrogenation Due to Ultrasound Treatment in Polycrystalline Silicon: New Approach to Thin Film Defect Engineering
Authors: Ostapenko S. , Henley W. , Karimpanakkel S. , Jastrzebski L. , Lagowski J.
Published: April 2011

We applied the ultrasound treatment (UST) to improve properties of poly-Si thin films on glass substrates for thin-film transistor applications. A strong decrease of the sheet resistivity in hydrogenated films subjected to UST was observed. UST improves the film homogeneity as monitored by spatially resolved surface photovoltage mapping. Studies of hydrogenated thin-film transistors demonstrated remarkable UST induced improvement in transistor characteristics, especially, a reduction of leakage current by as much as one order of magnitude. All these effects are explained in terms of UST enhanced hydrogenation of poly-Si film.
Characterization of Fast Diffusing Charged Defects in Semiconductors
Authors: Heiser T. , Zamouche A. , Mesli A.
Published: April 2011

A novel technique is introduced to study fast diffusing charged defects in semiconductors. It is based on the capacitance change induced by ion drift in a reverse biased Schottky barrier. It is shown that such charge movement yields exponential capacitance transients, which contain information about the defect concentration and mobility. The method is checked on Li-diffused samples, where the extracted diffusion coefficient are in good agreement with literature data. It is next applied to interstitial copper (Cui) in silicon. In the proposed experiment Cui gives rise to a well defined signal which enables us to investigate near room temperature defect reactions involving Cui. The diffusion data extracted from copper diffused and quenched silicon samples establishes the origin of the signal. Near room temperature precipitation kinetics of Cui are studied and energy barriers are extracted.
Photoluminescence of Extended Defects in Silicon-on-Insulator Formed by Implantation of Oxygen
Authors: Qian Y. H. , Evans J. H. , Giles L. F. , Nejim A. , Hemment P. L. F.
Published: April 2011

PL and TEM have been carried out on SIMOX structures before and after thinning the silicon overlayer by a process of sacrificial oxidation. The implantation and high temperature annealing schedules involved in fabricating SIMOX material result in threading dislocations and stacking fault tetrahedra and pyramidals in the silicon overlayer. The optical activity of these extended defects is found to be low. However, after the sacrificial oxidation, strong dislocation related luminescence is observed, which is attributed to the presence of oxidation-induced stacking faults now present in the overlayer.
Type II Dislocation Loops and their Effect on Strain in Ion Implanted Silicon as Studied by High Resolution X-ray Diffraction
Authors: Thompson R. H. , Krishnamoorthy V. , Liu J. , Jones K. S.
Published: April 2011

P-type (100) silicon wafers were implanted with 28Si+ ions at an energy of 50 keV and to doses of 1 × 1015, 5 × 1015 and 1 × 1016 cm−2, respectively, and annealed in a N2 ambient at temperatures ranging from 700°C to 1000°C for times ranging from 15 minutes to 16 hours. The resulting microstructure consisted of varying distributions of Type II end of range dislocation loops. The size distribution of these loops was quantified using plan-view transmission electron microscopy and the strain arising from these loops was investigated using high resolution x-ray diffraction. The measured strain values were found to be constant in the loop coarsening regime wherein the number of atoms bound by the loops remained a constant. Therefore, an empirical constant of 7.7 × 10−12 interstitial/ppm of strain was evaluated to relate the number of interstitials bound by these dislocation loops and the strain. This value was used successfully in estimating the number of interstitials bound by loops at the various doses studied provided the annealing conditions were such that the loop microstructure was in the coarsening or dissolution regime.
Ellipsometric Monitoring of Defects Induced by Electron Cyclotron Resonance Etching of GaAs
Authors: Snyder P. G. , Ianno N. J. , Wigert B. , Pittal S. , Johs B. , Woollam J. A.
Published: April 2011

Spectroscopic ellipsometry (SE) measurements were made during and after electron cyclotron resonance (ECR) etching of GaAs. The spectral range for ex situ measurements, 1.24–5 eV, included the E1, E1+A1 critical points. The Ej, Ei+Aj structure was red shifted by about 50 meV, and broadened, by etching with a mixture of methane, argon, and hydrogen. Exposure to a pure H2 plasma caused greater red shifting and broadening, while a pure Ar ECR plasma produced only a slight red shift. The red shift is consistent with an increase in lattice constant of the order of 1%, in the top 10-30 nm. Broadening is consistent with crystalline lattice damage.
Degradation of InGaAs High Electron Mobility Transistors: The Role of Channel Composition and Thickness
Authors: Meshkinpour Marjohn , Goorsky Mark S. , Streit Dwight C. , Block Thomas R. , Wojtowicz Mike
Published: April 2011

In this study, we examined the performance of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors with varying channel layer thicknesses for indium mole fractions of 0.21 and 0.24. For both compositions, we find that there is an optimum channel thickness above which the device performance is impaired. As expected the effective critical thickness of the In0.2iGa0.79As layer is higher. Surprisingly, however, transmission electron microscopy of the device structures indicates that the device performance is not impaired by the presence of a linear array of misfit dislocations. In fact, the devices with highest performance have misfit dislocations indicating that defect engineering may lead to improved performance in these structures. Furthermore, we find that device structures with poor performance have misfit dislocations along both of the <110> directions. Triple axis x-ray diffraction provides a non-destructive estimate of the dislocation densities present.
Effect of Fermi Level Pinning at the Surface During OMVPE Growth
Authors: Cohen R. M. , Chen C. Y. , Li W. M. , Simons D. S. , Chi P. H.
Published: April 2011

During organometallic vapor phase epitaxy of GaAs, the Fermi energy is found to be pinned ≈200 meV below the intrinsic Fermi energy on a (lOO)-oriented surface. This was determined by making the first comparison of Zn concentration, Nzn. obtained from growth with that obtained at equilibrium, all under the same nominal ambient conditions. Donor solubility has been found to be virtually unchanged during growth of n- or p-type GaAs, and this is strong evidence that the Fermi level remains pinned at essentially the same energy during growth of n- or p-type GaAs. Consistent with Fermi level pinning, we find (1) the NZn is supersaturated in the epilayer for the ambient growth conditions used, (2) a large excess concentration of positively charged Ga interstitials can be grown into n-type GaAs and which diffuses into nearby p-type layers, causing (3) the Zn diffusivity, DZn ∼10−13 cm2/s, out of buried npn layers to be essentially independent of the ambient conditions. Annealing of a heavily Zn-doped layer at the surface can lead to 10−16<DZn<10−13 cm2/s at T=800°C simply by varying the Zn partial pressure over its commonly used range. Use of In-doped spikes in n- and p-type GaAs suggest that interstitial point defects have a strong effect on the group III diffusion.
Computation of the Onset of Point Defect Aggregation in Crystalline Silicon Using an Empirical Interatomic Potential
Authors: Sinno T. , Brown R.A.
Published: April 2011

The Stillinger-Weber interatomic potential is used in molecular dynamics simulations to investigate the equilibrium, transport and aggregation properties of self-interstitials and vacancies in crystalline silicon at temperatures ranging from 500K to the melting point. The simulations predict equilibrium configurations of a < 110 > dumbbell for the single self-interstitial and an inwardly relaxed structure for the single vacancy. Both single-defect structures exhibit significant derealization at high temperatures resulting in strongly temperature dependent entropies of formation, as suggested by diffusion experiments. Diffusion coefficients and mechanisms for the single defects are predicted as a function of temperature. The results for the single point defects are discussed in the context of the existing literature values. Aggregation of two point defects is investigated by the computation of binding energies and entropies for these structures. Interstitials exhibit significant aggregation driving forces across the entire temperature range under simulation conditions, while vacancies aggregate less readily.
Defect Reaction and Electrical Properties of Iron in N-Type Silicon
Authors: Kitagawa Hajime , Tanaka Shuji
Published: April 2011

Since the first report by our group in 1992, iron-related defects in n-type silicon has been found to exhibit unusual in-diffusion and annealing properties. We review in this paper the recent progress in understanding the electrical and diffusion properties of iron-related defects in n-type silicon. We have shown from DLTS and Hall effect that iron in n-type silicon is electrically ionized and introduce one donor level at Ec-0.41 eV (level C) and, at least, one acceptor level at Ec-0.21 eV (level B). The donor character of former level has been confirmed by a Poole-Frenkel effect. The concentrations of two centers introduced are in the order of 1013 cm−3 at maxima. In-diffusion behavior of levels B and C show that these levels are intermediate states in a consecutive reaction of iron-related complex formation. Low-temperature isothermal annealing experiments from the room temperature to 200°C suggest that iron-related donor is formed, in part, by the electrostatic attractive force between two point charges.