bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Study of Stresses in Ag/Cu Thin Film Multilayers During Deposition
Authors: Shull Alison L. , Zolla Howard G. , Spaepen Frans
Published: April 2011

Ag/Cu multilayers are deposited onto a thin Si(100) cantilevered substrate in ultra high vacuum. During deposition, the force per unit width (F/w) in the multilayers is measured continuously from the substrate curvature by a laser scanning technique. Mechanical stability and sample temperature are monitored continuously. The evolution of stress in the film during a layer deposition depends on the thicknesses of the layers beneath it. During deposition of thicker layers of either Cu or Ag, we observe increasing tensile F/w at the start of each layer. The F/w increases up to a few N/m at ∼20 nm layer thickness, and then decreases. When the thickness of each layer is less than 30 nm, the tensile stress sometimes continues to decrease even after a new interface is created. This result does not support a model for the origin of compressive stress that is based on coherent propagation of compressive strain.
Effect of Structure, Stress, Strain, and Alloying on the Hardness of Fe(001)/Pt(001) Epitaxial Multilayers
Authors: Daniels B. J. , Nix W. D. , Clemens B. M.
Published: April 2011

The hardness of epitaxial sputter-deposited Fe(001)/Pt(001) multilayers grown on single crystal MgO(001) has been previously evaluated as a function of composition wavelength, Λ. Nanoindentation results reveal that the hardness is enhanced over that expected from a simple rule of mixtures by a factor of approximately 2.5 for bilayer spacings from 20 to 125 Å. In this paper we investigate possible causes of this hardness enhancement by determining the stress, strain, and alloying in each layer of the multilayer as a function of Λ. Accurate in-plane and out-of-plane lattice parameter measurements were obtained via x-ray diffraction using synchrotron radiation. The stress state and the extent of alloying in each layer as a function of Λ was determined by using the appropriate elastic constants for each component. The stress, strain, and amount of alloying in the Pt layer were near zero for 25≤Λ≤121 Å. The Fe layer exhibited large stresses and strains which relaxed with increasing Λ for 44≤Λ≤121 Å. For Λ=25 Å, the metastable FCC structure was adopted by the Fe film. The amount of alloying also varied from approximately 11 at.% Pt for Λ=44 Å to 5 at.% Pt for Λ=121 Å. Since the structure, film stress, amount of strain relaxation, and extent of alloying vary over this range of Λ while the hardness does not, we conclude that the hardness enhancement in these films must be controlled by other factors. Nevertheless the investigation of these basic film properties has enhanced our understanding of the structure-property relationships that give rise to strengthening in multilayer thin films.
Three Dimensional Surface Waviness of an Epitaxial Layer Due to Surface Diffusion Induced by Interface Misfit Dislocations
Authors: Jonsdottir F.
Published: April 2011

It has been observed that, for some strained epitaxial layer systems, the surface of the layer develops roughness or waviness which correlates spatially with the positions of underlying interface misfit dislocations which partially relax the elastic mismatch strain. A model based on redistribution of mass by surface diffusion is analyzed to estimate the waviness of the three dimensional thermodynamic equilibrium surface due to intersecting arrays of interface misfit dislocations.
Effect of Mechanical Stress on Electromigration Failure Mode During Accelerated Electromigration Tests
Authors: Pramanick S. , Brown D. D. , Pham V. , Besser P. , Sanchez J. , Bui N. , Hijab R. , Yue J. T.
Published: April 2011

The electromigration failure mode and failure rate during accelerated electromigration testing is expected to be strongly affected by the mechanical stress state of Al lines, since tensile stress and compressive stress states favor void growth and hillock formations (extrusions), respectively. During electromigration testing, the mechanical stress state or evolution of mechanical stress of an interconnect is a function of current density and temperature, the two principal variables in electromigration testing. In our experiments, we have observed two different electromigration failure modes by varying the current density and temperatures where (i) the passivated Al lines tested at high current density and high temperatures failed by extrusion or hillock type failure and (ii) the interconnect lines tested at low current density and moderate temperature failed by voiding. A mechanical stress model which incorporates both the thermally generated stress and electromigration induced mechanical stress is invoked to explain the electromigration failure mode selection observed in our experiments.
Stress Effects in Drying Polymer Films
Authors: Tam S. Y. , Scriven L. E. , Stolarski H. K.
Published: April 2011

A model is developed to predict the magnitude and pattern of stress due to drying of polymer films. This model combines diffusion-and-convection equation with large deformation elasto-viscoplasticity, utilizing concentration dependent elastic and viscoplastic material properties to better represent the behavior of drying thin films.

The results show that the highest stress occurs at film surface where the concentration depletion is the highest. The magnitude of this stress is induced by increasing mass transfer across the film surface but reduced by increasing diffusion coefficient. The edge effect is significant but local, limited to about four film thicknesses. Similarly, change in substrate induces extra stress.
Indentation Creep of Molybdenum: Comparison Between Thin Film and Bulk Material
Authors: Yoder K. B. , Stone D. S. , Lin J. C. , Hoffmann R. A.
Published: April 2011

Indentation creep, load relaxation, and rate-change experiments probe room temperature and 80°C creep properties of a 1.3 μm-thick molybdenum film on silicon. The film, with 0.51 GPa compressive stress, 8 GPa hardness and estimated 40 nm grain size, was deposited using steered-arc evaporation at -17V bias. Despite its small grain size and high hardness, the thin film behaves like bulk molybdenum does: the rate sensitivity of the hardness is only weakly-dependent on measurement path (as with bulk material), and activation volumes calculated based on strain rate sensitivity are consistent with those of bulk molybdenum We suspect deformation mechanisms are similar to those in bulk molybdenum under similar conditions.
Hydrogen Effects on the Fracture of Thin Tantalum Nitride Films
Authors: Moody N. R. , Venkataraman S. K. , Bastasz B. , Angelo J. E. , Gerberich W. W.
Published: April 2011

In this study we used nanoindentation and continuous microscratch testing to determine the effect of hydrogen on the work of adhesion and fracture toughness of thin tantalum nitride films. These films were sputter-deposited on sapphire substrates to a thickness of 600 nm followed by the heating of some films in deuterium and some in vacuum at 300°C. Deuterium was used in this study because it is much easier to detect and measure than hydrogen. Ion beam spectroscopy showed that exposure to deuterium produced a uniform internal deuterium concentration of 2000 appm. Nanoindentation showed that exposure to deuterium at 300°C and vacuum annealing at 300°C had little effect on elastic modulus and hardness values of these films at room temperature. In contrast, the microscratch tests at room temperature revealed that the work of adhesion decreased from 24.5 J/m2 after vacuum annealing to 9.1 J/m2 after deuterium charging and demonstrated that tantalum nitride films have a strong susceptibility to hydrogen embrittlement.
Influence of Aging Processes on Adhesion Properties of Metallic and Oxidic Thin Films
Authors: Ottermann C. R. , Tomita Y. , Ishiyama M. , Bange K.
Published: April 2011

Adhesion of oxidic and metallic films with thicknesses between 40 nm and 350 nm has been investigated by means of a scratch-test method based on a vibrating diamond micro-indenter. SiO2 and TiO2 films are precipitated on fused silica substrates by sol-gel techniques (SG), reactive evaporation (RE), reactive low-voltage ion plating (IP), and plasma impulse chemical vapour deposition (PICVD), and Cr-layers are produced by rf magnetron sputtering (SP). The influence of aging effects on film adhesion is investigated in respect of several conditions, like storage under ambient surroundings with differences in relative humidity or temperature treatment. A method is presented allowing control of the long-term stability of the scratch-test conditions. Temperature treatment up to 600 °C is found to have the most significant impact on adhesion properties. Adhesion increases for some SiO2 films, whereas for TiO2 layers an opposite behavior is observed. Here, the adhesion of the originally amorphous titania films is reduced due to the phase transition to polycrystalline anatase, which correlates with a significant increase in film stress.
Die Attach Adhesion and Void Formation at the Gaas Substrate Interface
Authors: Strifas Nickolaos , Christou Aris
Published: April 2011

A model is constructed to consider the stresses (analytically and with Finite Element Analysis (MiA)) which result from the thermal mismatch between the die and the substrate. FHA is used to simulate thermal stresses induced from temperature cycling with voids and without voids in the die-attach at the die-substrate interface. Local stress concentration caused by voids is found to be dependent on the location of the voids. The presence of an edge void at the die-attach interface changes the local stress and creates a longitudinal stress field. It is also observed that for die-attachment without voids or some center voids there will be no cracking whereas specimens with voids near the edge of the die are likely to have vertical die cracks. Using the void growth, stress relaxation equations, the void growth is simulated yielding an exponential relationship to void grow th and a saturation of void volume w ith time. Stress relaxation and void growth during cool down are simulated, once the material parameters and cooling rates are known. It yields a time dependence of the relative void volume (exponential decay).
Shape Memory Behavior of Ti-Ni Thin Films Annealed at Various Temperatures
Authors: Ishida A. , Takei A. , Sato M. , Miyazaki S.
Published: April 2011

Ti-Ni thin films with three different types of compositions, titanium-rich Ti-Ni, near equiatomic TiNi and nickel-rich Ti-Ni were prepared by sputtering. The sputter-deposited films were annealed at various temperatures between 773 and 973K in order to crystallize. After the heat treatment, the shape memory behavior was examined with a thermomechanical tester. The shape memory behavior of the near equiatomic composition films was not affected by the heat treatment. On the other hand, the shape memory behavior of the other composition films strongly depended on the annealing temperature. As the annealing temperature increases, the martensitic and reverse martensitic transformation temperatures of the nickel-rich films decreased and those of the titanium-rich films increased. These opposite behaviors of the transformation temperatures can be explained by the opposite dependence of the precipitation of the second phase on the annealing temperature. All the nickel-rich films exhibited good shape memory effect over a wide range of stress, while all the titanium-rich films exhibited a small plastic strain only in the stress range where the shape changes associated with both the R-phase and the martensitic transformations were observed.
An Experimental Examination of Mems Microactuator Material Issues
Authors: Cooney T. G. , Glumac D. E. , Robbins W. P. , Francis L. F.
Published: April 2011

Thermally induced interactions between materials in complex microactuator structures were investigated. The device structure contained a combination of a piezoelectric layer (lead zirconate titanate - PZT) an electrode with adhesion layer (Pt/Ti), buffer layer (SiO2 or TiO2), structural material (polysilicon and/or silicon nitride), and sacrificial oxide (SiO2). The presence of a SiO2 sacrificial layer did not affect either the bottom electrode or PZT layer. XRD results showed significant platinum and titanium silicide formation in the Pt/Ti electrode at 700 °C (PZT crystallization temperature) on both polysilicon and silicon nitride structural materials when no buffer layer was used. Auger analysis shows that the Ti adhesion layer oxidizes, that measured levels of silicon increase in the electrode zone, and that electrode elements diffuse into the structural material. Buffer layers of SiO2 (0, 0.1, 0.73, 1.3, 1.5 μm) and amorphous TiO2 (0.065 μm) were inserted between the electrode and the structural material. XRD and sheet resistance measurements demonstrated that SiO2 thicknesses greater than 0.73 μm reduced pyrochlore formation in the PZT and reduced the degradation of the electrode. However, this thickness was incompatible with overall surface micromachining processes. The TiO2 layer effectively prevented pyrochlore formation and electrode degradation, while being compatible with overall actuator processing.
Electrical Characteristics of Barium Strontium Titanate-Oxide Composite Films
Authors: Sengupta S. , Sengupta L.C. , Stowell S. , Vijay D.P. , Desu S.B.
Published: April 2011

In a previous work. composites of BSTO combined with other nonelectrically active oxide ceramics have been formulated and have demonstrated adjustable electronic properties which can be tailored for use in various electronic devices. One application has been for use in phased array antennas and insertion has been accomplished into several working antenna systems. To further accommodate the frequencies required by these phased array antennas, thin films of the composites have been fabricated using a Krypton Fluoride excimer laser as an ablation source. The electrical properties, including the dielectric constant and the tunability (change in the dielectric constant with applied voltage) have been measured. The results have been compared to those obtained for the bulk, ceramic composites and other BSTO/oxide composite thin film structures.
Relationship Between the Ductility and Impurity Hydrogen in Ni3Al
Authors: Chikaizumi R. , Itoh G. , Kanno M. , Okada H.
Published: April 2011

Tensile tests were carried out on B-doped and undoped Ni3Al having different hydrogen contents in order to examine whether the amount of impurity hydrogen affects the ductility of Ni3Al. Specimens were melted either in a high vacuum of ∼10−3Pa or argon, isothermally forged and finally annealed for 15hr at 430°C in an ultra high vacuum of ∼10−3Pa or in argon, respectively. Measurement of hydrogen gas evolved from the specimen during the annealing at 430°C in an ultra high vacuum of ∼10−7Pa confirmed that vacuum treated specimen had actually smaller hydrogen content than the argon treated one. The ductility of vacuum treated specimens both B-doped and undoped was found to be larger than that of argon treated ones, which means a detrimental influence of hydrogen. Hydrogen evolution behavior during the test on B-dopcd specimens in an ultra high vacuum of ∼10−8Pa revealed that the amount of hydrogen gas evolved at the moment of fracture was smaller in vacuum treated specimens than in argon treated one. Impurity hydrogen atoms were considered to move and enhance the formation and growth of voids, accelerating transgranular fracture.
Service Limitations for Oxidation Resistant Intermetallic Compounds
Authors: Smialek J. L. , Nesbitt J. A. , Brindley W. J. , Brady M. P. , Doychak J. , Dickerson R. M. , Hull D. R.
Published: April 2011

Oxidation resistant intermetallic compounds based on NiAl, TiAl, and MoSi2 are of interest for high temperature applications. Each system exhibits different life-limiting degradation modes due to oxidation. β-NiAl forms protective α-Al2O3 scales. Breakdown follows well-established diffusion controlled processes resulting in survival for thousands of hours. The effect of thermal cycling and spalling is well established. Ti3Al and TiAl compounds form less protective mixed TiO2 and A12O3 scales. However at realistic use temperatures (600°–800 °C), scale growth rates are acceptably low. The critical factor is embrittlement due to interstitial oxygen diffusion over a matter of hours. Solutions based on alloy development and coatings have not been satisfactory. MoSi2 materials exhibit very low oxidation rates at very high temperatures. However, low temperature (500°C) pest oxidation can be a catastrophic transient effect. Material integrity is a key factor. Fracture occurs because of accelerated growth of non-protective mixed MoO2–SiO2 scales in pores and microcracks.
Microstructure/Oxidation/Microhardness Correlations in γ-Based And ツ-Based Ai-Ti-Cr Alloys
Authors: Brady Michael P. , Smialek J. L. , Humphrey D. L.
Published: April 2011

The relationships between alloy microstructure and air oxidation kinetics and alloy microstructure and microhardness in the Al-Ti-Cr system for exposures at 800°C and 1000°C were investigated. The relevant phases were identified as τ (Ll2), γ (Ll0), r-Al2Ti, TiCrAl (laves), and Cr2Al. Protective alumina formation was associated with τ, Al-rich TiCrAl, and γ/TiCrAl mixtures. Brittleness was associated with the TiCrAl phase and τ decomposition to Al2Ti + Cr2Al. It was concluded that two-phase γ + TiCrAl alloys offer the greatest potential for oxidation resistance and room temperature ductility in the Al-Ti-Cr system.
Stoichiometry and Alloying Effects on the Phase Stability and Mechanical Properties of TiCr2-Base Laves Phase Alloys
Authors: Chen Katherine C. , Allen Samuel M. , Livingston James D.
Published: April 2011

Ti-Cr alloys near the TiCr2 composition have been studied to determine the single-phase Laves field and the associated defects accompanying off-stoichiometry. A combination of metallography, x-ray diffraction, lattice parameter measurements, density measurements and electron microprobe analysis have been used to establish a narrow single-phase region extending towards Ti-rich compositions. All three Laves crystal structures (C14, C36 and C15) were found to exist at different temperatures. Hardness and fracture toughness values determined by Vickers microindentation were studied as a function of alloy composition. Effects of adding Fe, Nb, Mo, and V to TiCr2 on lattice parameter, crystal structure, hardness and fracture toughness are reported.
Numerical Simulations of Tensile Deformation Behavior in Two Phase α2 + γ Lamellar Tial Alloys
Authors: Kad Bimal K. , Dao Ming , Asaro Robert J.
Published: April 2011

Deformation microstructures in γ-TiAl + α2Ti3Al based fully lamellar (FL) and nearly lamellar (NL) microstructures have been simulated using micro-mechanical methods. The deformation is extremely inhomogenous resulting in a large accumulation of hydrostatic stresses at the grain boundaries, thereby promoting intergranular fracture initiation. In particular, the increase in ductility with increasing equiaxed γ-grain volume fraction (with compliant deformation characteristics) in nearly lamellar alloys is explained by the reduction of the hydrostatic stress buildup at the boundaries, consequently mitigating fracture.
Extension of the Two Parametric Approach to Fatigue Crack Growth in Intermetallics
Authors: Sadananda K. , Vasudevan A. K.
Published: April 2011

Fatigue crack growth in intermetallics and their composites published in the literature have been examined in the light of the new concepts developed by the authors. It is shown that the two parametric approach can adequately account for the observed behavior without resorting to an extraneous factor such as crack closure. Implication of the two parametric approach in design is discussed.
The Phenomenon of Superplasticity in Feal-Ti Alloy with Large Grains
Authors: Li Dingqiang , Shan Aidang , Liu Yi , Lin Dongliang
Published: April 2011

The phenomenon of superplasticity in an ordered FeAl based alloy is reported in this paper for the first time. The behavior of superplastic deformation for the FeAl based alloy (Fe-36.5at.%-2at.%Ti) with large grains of above 300 μm has been examined at 1000°C in a strain rate range from 1.39×10− 4 /s to 2.78×l0−2 /s. The maximum elongation of 208% for the FeAl based alloy with large grains has been obtained and the index of strain rate sensitivity, the m value, has a range of values from 0.25 to 0.42. The reason for the large elongation is ascribed to the dynamic recovery and recrystallization during deformation in this large grained alloy at high temperatures.
Atomistic Simulation of Defect Structure in Ternary Intermetallics
Authors: Jones Chris C. , Ternes J. K. , Farkas D.
Published: April 2011

Interatomic potentials of the Embedded Atom type were used to study defect structure in ternary intermetallics. Interatomic potentials with appropriate inner consistency were developed for the modeling of ternary systems. Alloys were considered in the Nb-Al-Ti and in the Ni-Al-Ti systems. The stability of ternary phases in these systems was studied, particularly the B2 phase in Nb rich alloys of the Nb-Al-Ti system. The effects of increasing Ti additions in these alloys were studied, as well as the APB energies in these ternary alloys.
Atomistic Study of Cleavage and Dislocation Emission in NiAl
Authors: Ludwig M. , Gumbsch P.
Published: April 2011

The atomistic processes during fracture of NiAl are studied using a new embedded atom (EAM) potential to describe the region near the crack tip. To provide the atomistically modeled crack tip region with realistic boundary conditions, a coupled finite element - atomistic (FEAt) technique [1] is employed. In agreement with experimental observations, perfectly brittle cleavage is observed for the (110) crack plane. In contrast, cracks on the (100) plane either follow a zig-zag path on (110) planes, or emit dislocations. Dislocation generation is studied in more detail under mixed mode I/II loading conditions.
Serrated Yield Behavior in Nial Single Crystal
Authors: Brzeski J. M. , Hack J.E. , Darolia R.
Published: April 2011

Dynamic strain aging has been characterized in standard purity NiAl single crystals during compression testing. The activation energy for the process suggests carbon and oxygen as the most likely agents. Experimental data is compared with a recent model and implications for the fracture behavior of NiAl are considered.
Characterization of Deformation Structures in B2 CoAL
Authors: Crimp M. A. , Zhang Y.
Published: April 2011

B2 CoAl single crystals with a number of orientations have been deformed at 1300 K and 1000 K. The deformation substructures have been characterized using TEM diffraction contrast techniques supported by image simulations. While <100> slip is found to be the predominant slip mode at these temperatures, <111> and <110> dislocations have also been observed. In particular, in hard orientations <110> dislocations appear to play an active role in initiating the deformation. Additionally, <110> dislocations are often observed as junctions of <100> type dislocations. Under the conditions tested, changes in alloy stoichiometry do not result in any modifications to the dislocation slip behavior.
Thermodynamical Estimations on the Amount of Liquid Phase During Reaction Synthesis of Nickel-Aluminides
Authors: Miura Seiji , Mishima Yoshinao
Published: April 2011

The amounts of intermetallic compounds and liquid phase are estimated as a function of temperature during reaction syntheses for Ni–Al binary alloys having arbitrary compositions under adiabatic conditions. It is assumed that the phases that would present during the process are only those appearing in the equilibrium binary phase diagram. Calculations are done by using available data on heat of formation of intermetallic compounds and those on enthalpy of liquid phase. The results obtained arc discussed in view of the estimation and control of the amount of liquid phase, which is significant for the densification and shape change of materials.
Phase Stabilities in Some B2 Type Ordered Ni-Al-X Alloys
Authors: Shinoda Tetsumori , Mishima Y. , Suzuki T.
Published: April 2011

The difference in developing of solubility lobe (s.l.) of B2 phase from the B2 NiAl point on each isothermal phase diagram of Ni-Al-Co, Ni-Al-Fe and Ni-Al-Mn is expected to be explained in terms of the pattern of free energy minimum (f.e.m.) line in the B2 phase region of these phase diagrams. To calculate such the f.e.m. line, a simple way has been proposed based on the tetrahedron approximation of the cluster variation method (CVM) making use of a relationship to correlate the conventional chemical potential of a species with some kinds of the CVM variables. The calculated results show that the f.e.m. line well reflects the solubility lobe developing of the B2 phase for both Ni-Al-Fe and Ni-Al-Co while some disagreement arises with Ni-Al-Mn. The results also show a theoretical possibility of transition from the high ordered state B2 to a low ordered one under a relatively low temperature regime so far as the present free energy model are concerned.
The Influence of Boron Additions in Cast Ti-47AL-2Cr-2Nb-0.8B
Authors: Schwartz Daniel S. , Shih Donald S.
Published: April 2011

Morphology, fine structure, and chemistry of phases formed in cast Ti-47Al-2Cr-2Nb-0.8B due to boron addition were examined in detail. Boron acts an inoculant, refining and stabilizing the cast grain size. A curving ribbon-shaped phase was present throughout the material, related to the ordered phase Ti2AlCr. The ribbon phase had the B2 structure, with a0∼0.318nm. Many ribbons had a low degree of order, i. e. the material was a BCC mixture of Ti, Al, Nb, and Cr. Ribbon phase composition was variable, measured to be: Ti-(20–30)Al-(2–4)Nb-(5–16)Cr. TiB2 was present in small amounts, always in intimate contact with the ribbon phase. A (100)ribbon ‖ {1100}TiB2, (011)ribbon ‖ {1122}TiB2 orientation relationship was observed. It is proposed that the ribbon phase is a remnant of the high-temperature titanium aluminide β-phase, stabilized by dissolved boron.
Nickel Aluminide (Ni3Al) Fabricated By Reactive Infiltration
Authors: Chen Yuyong , Chung D.D.L.
Published: April 2011

Nickel aluminide Ni3Al in single phase form, with grain size ∼ 10 μm, porosity ∼ 5%, tensile strength 425 MPa, modulus 92 GPa and ductility 9.5% at room temperature, was fabricated by reactive infiltration at 800˚C of liquid aluminum into a porous preform containing 78 vol.% nickel and made by sintering 3–7 μm size nickel particles.
Melting, Casting, and Processing of Nickel and Iron Aluminides
Authors: Sikka Vinod K
Published: April 2011

A process for successful melting of Ni3Al- and Fe3Al-base alloys is described. Casting and welding of these alloys are also briefly described.
Properties of Hot-Pressed Cr-Cr3Si
Authors: Newkirk Joseph W. , Price Joseph E.
Published: April 2011

Previously, Cr-Cr3Si in-situ composites produced by arc-melting were shown to have good strengths at high temperatures1. For example, samples of a 25% Cr and 75% Cr3Si composite achieved bend strengths of 135 MPa at 1200°C. However, there is potential for even higher strengths at high temperatures and a need for improvement in the low temperature strength and toughness. In order to improve the properties, two approaches were taken. The first used powder metallurgy to develop a better microstructure than in the cast alloys, to try to improve both strength and toughness. The second approach was to incorporate erbia into the composites, to improve the strength and stability of the microstructure at elevated temperatures.

High density samples of hot pressed Cr-15.5Si and Cr-18.6Si have been produced by mixing Cr and Gr3Si powders and hot pressing in a graphite die. Erbia powders have been incorporated into some compacts for comparison.

Micros true tures have been characterized and mechanical properties determined. Both the hot pressing and the erbia affected the properties. In addition the erbia had a significant effect on consolidation of the samples.
Susceptibility of Iron-Rich Fe-Al Alloys to Embrittlement by Hydrogen and Water
Authors: Lynch R. J. , Heldt L. A.
Published: April 2011

Iron-rich Fe-Al alloys have been tensile tested in moist air and dry oxygen at a strain rate of 3.3×10−4 s−1. Moist air did not cause embrittlement until the composition reached 18-20% Al. Alloys with lower aluminum contents were embrittled when tested in hydrogen gas. The environmental sensitivity of these alloys was further investigated by examining the effects of strain rate on the ductility. For the most part, no significant strain rate effects were observed in the low aluminum alloys; strain rates of up to 3.3×10−1 s−1 were not fast enough to prevent embrittlement. In contrast, the ductility of Fe-35 at.% Al did increase with increasing strain rate in air and hydrogen; at a strain rate of 3.3×10−1 s−1 the elongations approached that of vacuum.
Fabrication of Sic Matrix Composites by Liquid Phase Infiltration with a Polymeric Precursor
Authors: Interrante Leonard V. , Whitmarsh C.W. , Sherwood W.
Published: April 2011

A process for the fabrication of SiC matrix composites has been developed which employs aliquid, highly branched, polycarbosilane (AHPCS). This polymer thermosets on heating at 200-400 °C (or at 100 °C with catalyst) and yields an amorphous SiC with low excess C and O content in 60-80% yield on pyrolysis to 1000 °C. Preforms consisting of C-coated Nicalon SiC fiber cloth, unidirectional Textron SiC SCS-6 fiber layups, or Mo boats packed with SiC whiskers, were infiltrated with the polymer, cured in an autoclave, and pyrolyzed to 1000 °C. Five to eight infiltration cycles gave net shape composites with final densities at 85-94 % of theoretical. The results of 4-point flexure tests on the as-prepared Nicalon composites indicate flexure strengths (aver. 378 MPa) that are comparable to or better than similarly reinforced CVI-SiC matrix composites. The whisker and SCS-6 composites showed a small weight loss (10-20%) on heating to 1500 °C in Ar and little or no weight change or obvious embrittlement in air at 1000 °C.
Microstructure and Mechanical Properties of 2D SiC-Reinforced Carbon Matrix Composites
Authors: Bourrat Xavier , Evans Anthony. G.
Published: April 2011

Fiber-reinforced composites consisting of combination of SiC and C have been explored as materials having thermostructural characteristics suitable for elevated temperature applications [1–4]. There are two opposing strategies. One uses C fibers and a matrix of SiC, usually produced by CVI [5, 6]. The other uses SiC fibers and a matrix consisting of C ; those are designated CERACARBTM and were studied in this paper.
Solid Solubility and Diffusivity in an Alumina/Zirconia System
Authors: Stough Matithew A. , Hellmann John R.
Published: April 2011

Polycrystalline zirconia-coated single crystal sapphire fiber displays reconstruction of the sapphire surface in regions of contact with zirconia grains. This is a concern where ZrO2 -coated sapphire fiber is desired for reinforcement of ceramic matrices. Previous work has demonstrated pitting is partially attributed to impurity-induced transient liquid phase formation with local dissolution of alumina; however, the extent of reconstruction witnessed via microscopy suggests that other mechanisms are active. The present study has addressed the issue of solid solubility and interdiffusivity to more thoroughly understand the solid state mechanisms contributing to pitting. Single crystal sapphire and zirconia were ion implanted with zirconium and yttrium, and aluminum, respectively, and then subjected to diffusion anneals at 1200° - 1600°C to study redistribution of implanted cations. Secondary Ion Mass Spectroscopy (SIMS) was used to profile the redistribution of implanted ions for measurement of diffusion coefficients and solubility limits after heat treatments. The results will offer a significant set of data on interface stability in the alumina/zirconia system.
Radiation-Induced Grain Boundary Segregation in Austenitic Stainless Steels
Authors: Bruemmer S. M. , Charlot L. A. , Vetrano J. S. , Simonen E. P.
Published: April 2011

Radiation-induced segregation (RIS) to grain boundaries in Fe-Ni-Cr-Si stainless alloys has been measured as a function of irradiation temperature and dose. Heavyion irradiation was used to produce damage levels from 1 to 20 displacements per atom (dpa) at temperatures from 175 to 550°C. Measured Fe, Ni, and Cr segregation increased sharply with irradiation dose (from 0 to 5 dpa) and temperature (from 175 to about 350°C). However, grain boundary concentrations did not change significantly as dose or temperatures were further increased. Although interfacial compositions were similar, the width of radiation-induced enrichment or depletion profiles increased consistently with increasing dose or temperature. Impurity segregation (Si and P) was also measured, but only Si enrichment appeared to be radiation-induced. Grain boundary Si peaked at levels approaching 8 at% after irradiation doses to 10 dpa at an intermediate temperature of 325°C. No evidence of grain boundary silicide precipitation was detected after irradiation at any temperature. Equilibrium segregation of P was measured in the high-P alloys, but interfacial concentration did not increase with irradiation exposure. Comparisons to reported RIS in neutronirradiated stainless steels revealed similar grain boundary compositional changes for both major alloying and impurity elements.
Radiation Enhanced Diffusion in Fcc Alloys
Authors: SchÜle Wolfgang
Published: April 2011

Diffusion mechanisms in fcc materials during irradiation with high energy particles due to vacancies, interstitials, di-interstitials, and dynamic crowdions are discussed. It is shown that in most alloys an increase in the degree of order is obtained by migrating vacancies and interstitials, and only in ∝-copper-zinc alloys mainly interstitials and in nickel-chromium alloys mainly vacancies are able to increase the degree of order during irradiation. The migration activation energies of interstitials and of vacancies for these two alloys are derived.

Mass transport also by channeling and by dynamic crowdions is shown for Ni63 in nickel irradiated with 1.85 MeV electrons.
Amorphization of Complex Ceramics by Heavy-Particle Irradiations
Authors: Ewing R.C. , Wang L.M. , Weber W.J.
Published: April 2011

“Complex” ceramics, for the purpose of this paper, include materials that are generally strongly bonded (mixed ionic and covalent), refractory and frequently good insulators. They are distinguished from simple, compact ceramics (e.g., MgO and UO2) by structural features which include: 1.) open network structures, best characterized by a consideration of the shape, size and connectivity of coordination polyhedra; 2.) generally, complex compositions which characteristically lead to multiple cation sites and lower symmetry; 3.) directional bonding; 4.) bond-type variations, from bond-to-bond, within the structure. The heavy particle irradiations not only include ion-beam irradiations, but also recoil-nucleus damage resulting from a-decay events from constituent actinides. The latter effects are responsible for the radiation-induced transformation to the metamict state in minerals. The responses of these materials to irradiation are complex, as energy may be dissipated ballistically by transfer of kinetic energy from an incident projectile or radiolytically by conversion of radiation-induced electronic excitations into atomic motion. This results in isolated Frenkel defect pairs, defect aggregates, isolated collision cascades or bulk amorphization; all may occur concurrently. Thus, the amorphization process is heterogeneous. Only recently have there been systematic studies of heavy particle irradiations of “complex” ceramics on a wide variety of structure-types and compositions as a function of dose and temperature. In this paper, we review the conditions for amorphization for the tetragonal orthosilicate, zircon [ZrSiO4]; the hexagonal orthosilicate/phosphate apatite structure-type [X10(ZO4)6(F,Cl,O)2]; the isometric pyrochlores [A1-2B2O6(O,OH,F)o-1pH2O] and its monoclinic derivative zirconolite [CaZrTi2O7]; the olivine (derivative - hcp) structure types, α-VIA2IVBO4, and spinet (ccp,) γ-VIA2IVBO4.
Effects of Ion Dose and Irradiation Temperature on the Microstructure of Three Spinel Compositions
Authors: Wang L.M. , Gong W.L. , Bordes N. , Ewing R.C. , Feit Y.
Published: April 2011

Three compositions with the spinel structure (γ-AIVB2VIO4), MgAl2O4, FeCr2O4 and γ-SiFe2O4, have been irradiated with 1.5 MeV Kr+ ions over a temperature range (20 to 873 K). In situ TEM and HRTEM afterwork were conducted to characterize the effects of the ion irradiation on the microstructure. MgAl2O4 was the most “radiation-resistant” among the three materials. After irradiation to lx1016 ions/cm2 at 20 K, the cations were completely disordered among all possible tetrahedral and octahedral sites, but the oxygen sublattice remained intact. At room temperature, a high density of dislocation loops developed after this same dose, but there was no evidence of cation disordering. However, γ-SiFe2O4, a spinel structure type, formed under high pressure (7.0 GPa), was easily amorphized at low ion doses (σ1014 ions/cm 2) below 723 K, even lower than required for radiation-induced amorphization of its olivine polymorph, fayalite (α-SiFe2O4; HCP). At 873 K, the amorphous phase recrystallized to magnetite (Fe2+Fe 3+2O4, an inverse spinel structure) and quartz (SiO2) during continued Kr+ irradiation. Chromite (ideally FeCr2O4) with an actual composition of (Fe0.6Mg0.4)(Cr0.7A10.3)2O4 amorphized at 6x1015 ions/cm2 at 20 K, a dose about 20 times as high as that required to amorphize most other AB2O4 phases under the same irradiation conditions. A structural parameter, which quantifies the deviation from ideal packing in the spinel structure was developed and correlates with themeasured doses required for amorphization among these three spinel compositions.
Fabrication of Optical Channel Waveguides in the GaAs/AlGaAs System by Mev Ion Beam Bombardment
Authors: Taylor T. , Ila D. , Zimmerman R. L. , Ashley P. R. , Poker D. B.
Published: April 2011

We have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3x1013 and 3x1014 ions/cm2. Although disordering of GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors' knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 μm.
Stability of Cascades Under ion and Electron Irradiation in Germanium
Authors: Abe Hiroaki , Kinoshita Chiken , Denda Yasutaka
Published: April 2011

Concurrent irradiation with ions and electrons has been done in a high voltage electron microscope interfaced with an ion accelerator. The objective is to clarify the stability of cascades in Ge in terms of the elementary processes associated with the concurrent irradiation. Amorphous-like cascade contrast is observed under ion irradiation and increases in number eventually leading to saturation. The cascade contrast is produced within cascade regions through sequential overlaps of cascades and heavier ions form more stable cascade regions. The concurrent or subsequent electron irradiation recrystallizes cascade regions through shrinkage of the cascade contrast. Point defects and their diffusion induced by electrons contribute to the recrystallization of cascade regions.
Helium and Hydrogen Induced Growth of Microcavities in Silicon; Application to Gas And Impurity Collection
Authors: Veen A. Van , Schut H. , Hakvoort R.A. , Fedorov A. , Westerduin K.T.
Published: April 2011

Thermal helium desorption spectrometry and positron beam analysis have been used to monitor the growth of helium vacancy clusters during room temperature helium irradiation of silicon and during subsequent annealing to 1300 K. Experimental results obtained with hydrogen irradiation show that also hydrogen can be used to create cavities. There is a rather sharp threshold dose for creating cavities that will survive 1300 K annealing. It appears that positrons form a sensitive probe for the trapping and release of impurities inside the cavities. Results of atomistic calculations are used to discuss thermal stability of helium vacancy complexes. The results are related to recent impurity gettering studies based on impurity trapping at helium induced gettering centers.
Wavelength Dependence of the Non-Linear Transmission of Hitci Using the Z-Scan Technique
Authors: Swatton Stewart , Welford Kevin , Ray Cameron , Till Steven
Published: April 2011

The excited state properties of dyes become important under intense illumination of a short laser pulse. The pulse induces a significant population in an excited state which will have different absorptive properties, this causes a change in absorption of the incident pulse within its duration. An increase in absorption arises from molecules in an excited state having an absorption greater than the corresponding ground state.

The z-scan technique has been used to measure the induced absorption of a carbocyanine dye 1,1′,3,3,3′,3′- Hexamethylindtricarbocyanine Iodide (HITCI) for laser pulses of different wavelengths. An optical parametric oscillator pumped by the third harmonic of a Q-switched Nd:YAG laser was used. Z-scans were taken at a number of different wavelengths between 460 and 630 nm. Data is presented which shows the spectral region where induced absorption occurs. An eight level rate equation model is used to predict the non-linear behaviour and to fit to the experimental data, good correlation is found between the model and data.
Development of Solid State Non-Linear Absorbers - Dyes in Polymer Hosts
Authors: Kolinsky Peter V. , Hall Simon R. , Venner Mark R. W. , Croxall Derek F , Welford Kevin , Swatton Stewart
Published: April 2011

This paper describes the development of high quality solid state optical components which have been made by the incorporation of the reverse saturable dye chloro aluminium phthalocyanine (CAP) into polymeric host material.

In particular, the effect of using different host materials with CAP is investigated in terms of key parameters such as solubility, integrity of the dye molecules in the polymer host, hardness of the resulting polymer, ease of polishing to the production of a good optical finish, induced stress, and non-linear absorption performance.

Results are presented highlighting the above considerations, and problems encountered in material preparation will be described together with details on how, by careful choice of guest/host combination, good optical quality samples can be produced.
Optical Limiter Based on Nonlinear Interface Fibers
Authors: Zhu Zi Zhong , Jiao Hua , Hu Yi
Published: April 2011

This paper presents a design for an optical limiter composed of an optical fiber with a nonlinear interface. Our analysis of this device shows that high linear transmittance is obtained for weak incident light, while at the same time, intense light is attenuated below allowable values through continuous reflection. Moreover, the bandwidth of the device may be quite large when the fibers have small amounts of dispersion. Theoretical calculations are presented along with a characteristic analysis.
Simultaneous Relaxation of Network and Defects in Silicon-Implanted a-Si:H
Authors: Nakata J. , Sherman S. , Wagner S. , Stolk P. A. , Poate J. M.
Published: April 2011

We report extensive optical and electronic transport data on silicon-implanted a-Si:H, annealed in steps in the dark or with additional illumination. All measured properties relax gradually with increasing annealing temperature. The dark conductivity of the as-implanted film is dominated by hopping conduction via midgap defects. This channel is pinched off during the initial stages of annealing. The midgap defect density and the Urbach energy follow an annealing path that agrees qualitatively with the trajectory postulated by the equilibrium theory of the dangling-bond density. Therefore, the silicon network and the defect density equilibrate continuously during network relaxation.
Vacancy-Interstitial Pair-Formation Mechanism of X-Ray-Irradiation-Induced Crystallization in Amorphous Silicon Studied by ab initio Molecular Dynamics Simulation
Authors: Matsumura T. , Katayama-Yoshida H. , Orita N.
Published: April 2011

We have studied the microscopic mechanism of the X-ray-irradiation-enhanced crystallization in amorphous silicon (a-Si) based upon an ab initio molecular-dynamics simulation. We find that the bistable dangling-bonds (sp3- and sp2-like structures) exhibit a large lattice relaxation and are strongly related to the X-ray-irradiation-induced vacancy-interstitial-pair formation. The vacancy-interstitial-pair formation reduces the formation energy of the vacancy to zero and enhances the crystallization with small migration energy of the vacancy. The crystallization rate in X-ray-irradiated a-Si is dominated by the migration energy of the vacancy in this mechanism because the formation energy is zero in X-ray-irradiated a-Si and one order of magnitude larger than the migration energy without X-ray irradiation.
Hydrogen Bond Configuration Changes in PECVD Silicon Nitride Films During RTA
Authors: He S. S. , Shannon V. L.
Published: April 2011

PECVD silicon rich (x<4/3) and nitrogen rich (x>4/3) silicon nitride films have been deposited using a silane, ammonia, and nitrogen mixture at 400°C in a dual frequency parallel plate reactor. From FTIR measurements, most of the bonded hydrogen was observed to be present as N-H in the nitrogen rich films and as Si-H in the silicon rich films. In this study, the movement of hydrogen in the various nitride films as a result of Rapid Thermal Annealing (RTA) in N2 for 30 seconds has been investigated. While the intensity of the N-H stretching band was always found to decrease from that measured for the as-deposited film, the intensity of the Si-H stretching band was observed to increase for anneal temperatures up to 650°C. During the anneal process some hydrogen effusion takes place and some of hydrogen changes its bonding to silicon atoms from previous nitrogen atoms in the film. Consistent with the FTIR results, Hydrogen Forward Scattering (HFS), shows that only a small amount of hydrogen effuses from the silicon nitride film as a result of the RTA process below 650°C.
Spin-Dependent Recombination Effects in a-SI:H Pin Solar Cell Devices: A New Characterization Technique
Authors: Lips Klaus
Published: April 2011

Electrically detected magnetic resonance (EDMR) - also often referred to as spin-dependent photoconductivity - is a particularly attractive technique for the investigation of the electronic properties of semiconductor devices. This method detects the paramagnetic states involved in transport and recombination by recording changes of the sample current induced by a resonant enhancement of the recombination rates. This is in contrast to ESR which monitors the resonant enhancement of microwave absorption. Therefore, EDMR is more sensitive by many orders of magnitude than conventional ESR and can be used to investigate a-Si:H solar cell devices under standard operating conditions.

In this report we review the EDMR technique and discuss, in detail, the spin-dependent processes controlling dark and photocurrent of standard a-Si:H pin solar cells. In particular, we show that EDMR is sensitive to changes in the internal field of the i layer. We compare the experimental results to numerical calculations of the potential profiles and of EDMR-related quantities. We arrive at the conclusion that degradation by both high forward current and illumination increases the defect density mainly in the i layer, rather than at the pi interface.