bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Deviation from Stoichiometry on Deformation Behavior of Hard-Oriented NiAl Single Crystals
Authors: Srinivasan R. , Savage M. F. , Noebe R. D. , Mills M. J. 
Published: April 2011

ABSTRACTNi-44A1, Ni-50Al and NiAl-0.3 at.% Hf single crystals have been studied in compression to understand the effects that alloying additions and deviation from stoichiometry can have on the mechanical response of NiAl-based single crystals. While all three single crystals deform through a<111> slip at lower temperatures, the active slip systems differ at higher temperatures. Climb of a<010> dislocations contributes to deformation in Ni-50AI single crystals beyond the slip transition temperature, while Ni-44Al and NiAl-0.3Hf crystals deform through a<101> glide. But several microstructural differences have been observed in the mode of deformation between Ni-44Al and NiAl-0.3Hf crystals. In addition, significant strengthening is exhibited in the Hf-doped crystals at higher temperatures. The post-deformation microstructure is also observed to be sensitive to both strain and strain rate. A possible explanation is offered for some of the observed differences in deformation behavior between the three alloys.
Joining of NiAl to Nickel-Base Alloys by Transient Liquid Phase Bonding
Authors: Abdo Z. A. M. , Guan Y. , Gale W. F. 
Published: April 2011

ABSTRACTA transmission and scanning electron microscope investigation is undertaken to study microstructural development during transient liquid phase (TLP) bonding of NiA1 to Ni-base substrates. The bonds were produced through a conventional technique employing a Cu foil interlayer or a widegap technique using a composite preform containing powders of NiAl and Cu. The time required for completion of isothermal solidification was greatly reduced in wide-gap bonds as compared to conventional bonds. Microstructural features of conventional TLP bonds of polycrystalline-NiAl/Ni were controlled by the ratio of Al: Cu across the joint. The precipitation of the a phase encountered in polycrystalline- NiAl/Martin Marietta 247 superalloy (MM247) bonds was suppressed in wide-gap bonds of single crystal-NiAl(Hf) and MM247. In general, the extent of second phase precipitation, in the asbonded condition, was greatly reduced by the use of the wide-gap technique. However, extensive precipitation of HfC and W-rich phases was observed after post-bond heat treatments.
Crystal Structure Of Hexagonal Phases And Its Relation To Icosahedral Quasicrystalline Phase In Zn-Mg-RE (RE = Rare Earth) System
Authors: Takakura Hiroyuki , Sato T. J. , Tsai A. P. , Sato A. , Yamamoto A. 
Published: April 2011

AbstractA relationship between hexagonal phases in the Zn-Mg-RE (RE=rare earth) system and icosahedral quasicrystalline phase is discussed. There are three hexagonal phases in the vicinity of Zn6Mg3RE1which are related with a lattice parameters by a ratio 3:5:7 but with approximately the samecparameters. A structural model for the phase with medium a lattice parameter is proposed based on the structures of the other two phases recently determined. We also show a preliminary result of X-ray diffraction study of the Zn-Mg-Ho icosahedral phase.
Structural Phase Transitions Of Decagonal Quasicrystals
Authors: Steurer W. 
Published: April 2011

AbstractA two step model for the transformation of decagonal quasicrystals (DQC) to their crystalline approximants is presented. First, a partially disordered approximant domain structure results rapidly from small atomic displacements. Subsequently, atomic diffusion leads very slowly to an ordered approximant crystal (AC) structure. The model is discussed on atomic scale. Its basic idea is to describe the structure of a quasicrystal (QC) as incommensurately modulated structure (IMS). In that description, the average structure (AS) of a QC is at the same time the AS of all its irrational and rational approximants. In this approach, the positional quasicrystal- to-approximant-crystal (QC-AC) transformation can be performed by atomic displacements smaller than any interatomic distance. This mechanism, however, leads inherently to to a certain amount of chemical disorder. In most cases also some positional disorder will result. The tools developed for the description of phase transitions of IMS can analogously be used for QC. Examples for one- and two-dimensional quasiperiodic structures are discussed.
Room Temperature Oxidation Of AI-Cu-Fe and Al-Cu-Fe-Cr Quasicrystals
Authors: Pinhero Patrick J. , Sordelet Daniel J. , Anderegg James W. , Brunet Pierre , Dubois Jean-Marie , Thiel Patricia A. 
Published: April 2011

AbstractWe have investigated formation of oxides on quasicrystalline and crystalline alloy surfaces of similar composition, in different oxidizing environments. This includes a comparison between a quaternary orthorhombic approximate of Al-Cu-Fe-Cr quasicrystal and the ternary Al-Cu-Fe quasicrystalline and crystalline phases. We noted that each sample showed the following common trends: preferential oxidation of the Al, enrichment in the concentration of Al present at the surface upon oxidation, water concentration is directly related to oxide thickness, and the oxide thickness displays a strong correlation with the bulk concentration of Al in the sample.
A New Series Of Al-Pd-Based Ordered Icosahedral Quasicrystals And Their Electrical Resistivities
Authors: Tamura R , Asao T , Tamura M , Takeuchif S , Shibuya T 
Published: April 2011

AbstractX-ray measurements on samples of Al-Pd-(Fe,Ru,Os) systems with various annealing temperatures and times have been performed in order to gain insights into formations of icosahedral (I) phases and related approximants and to produce single phases of them. As a result, well ordered I phases have been obtained in Al-Pd-(Ru,Os) systems when annealed at 1000 °C for several hours. Formations of the (1/0-1/0-1/0) and the (2/1-2/1-2/1) approximants have been observed in wide compositional ranges in Al-Pd-(Fe,Ru,Os) and Al-Pd-(Ru,Os) systems, respectively. Electrical resistivity measurements of I phases and related approximants are performed as a function of temperature. The resistivity of I phases at room temperature is as high as that of highly resistive I phases such as Al-Pd-Mn and AI-Cu-(Fe,Ru) systems and the resistivity ratio (P12K/P300K) reaches about 1.5 in Al-Pd-Ru I phases. A negative temperature coefficient of the resistivity is observed in (1/0-1/0-1/0) approximants of Al-Pd-(Fe,Ru) systems, which indicates the electronic transport is quite anomalous even in the lowest approximant of the I phase.
Influence Of Hydrogen On The Thermal Stability Of Zr-Based Quasicrystals
Authors: Zander D. , Köster U. , Eliaz N. , Eliezer D. , Plachke D. 
Published: April 2011

AbstractThe high number of tetrahedrally coordinated sites for interstitial hydrogen and the favorable hydrogen-metal chemistry make quasicrystalline Zr-Cu-Ni-Al alloys a candidate for hydrogen storage applications. The icosahedral phase in Zr69.5Cu12Ni11Al7.5 has been shown to absorb electrochemically hydrogen up to H/M = 1.6. Only partially desorption of hydrogen was observed by TDA at about 500°C. Since hydrogen desorption seems to be hindered by a surface barrier, the hydrogen remains in the quasicrystal thus influencing their thermal stability. Such effects of hydrogen were studied by DSC and microstructural investigations. With increasing hydrogen content the decomposition of icosahedral Zr69.5. Cu12Ni11A17.5 is shifted to lower temperatures. Quasicrystals decompose by a discontinous transformation into the tetragonal Zr2Cu phase, the tetragonal Zr2Ni and the hexagonal Zr6NiAl2. Hydrogenation does not influence the phases formed during decomposition, but leds to the formation of a finer microstructure. We assume that the defects formed during the hydrogenation accelerate the nucleation of the stable crystalline phase.
Experimental Observations And Theoretical Modelling Of Equilibrium Quasicrystalline Phase In A Commercial Maraging Steel
Authors: Nilsson J.-O. , Liu P. , Dzugutov M. 
Published: April 2011

AbstractA recently developed maraging steel of type 12%Cr-9%Ni-4%Mo-2%Cu-l%Ti in which precipitation strengthening is caused by quasicrystalline precipitates is presented. The steel is used in its tempered condition as surgical instruments such as surgical needles and dental reamers. The high strength and the resistance to tempering induced softening is in part attributable to the formation of quasicrystalline precipitates of icosahedral symmetry. Profuse nucleation in combination with slow coarsening of precipitates are explicable in terms of a low surface energy associated with quasicrystallinity. There is experimental evidence supporting the conclusion that the quasicrystalline precipitates in the present material are formed under thermal equilibrium conditions. To rationalise this conclusion, we compare it with the thermodynamics and kinetic properties of an equilibrium quasicrystalline phase simulated by molecular dynamics. The simulation has demonstrated that the stability of this quasicrystal with respect to the crystalline ground state may be attributed to the large configurational entropy arising from the thermally activated phason dynamics. We argue that this mechanism, suggested by the random tiling model, may account for the observed equilibrium quasicrystalline precipitates in metallic alloys.
Self-Similar Porosity In Quasicrystals
Authors: Janot C. , Loreto L. , Farinato R. , Mancini L. , Baruchel J. , Gastaldi J. 
Published: April 2011

AbstractSingle grains of real quasicrystals have been investigated using X-ray imaging techniques at a third-generation synchrotron radiation source (ESRF). Facetted microholes have been observed. The experimental results are discussed with reference to a description of the quasicrystal structure in terms of overlapping atomic clusters (self-similar packing or random covering modifications). Relations between holes and quasicrystal formation are also discussed.
Voltage Creep in Holographic PDLC Gratings
Authors: Klosterman A.M. , Pogue R.T. , Schmitt M.G. , Natarajan L.V. , Tondiglia V.P. , Tomlin D. , Sutherland R. L. , Bunning T.J. 
Published: April 2011

ABSTRACTIn holographic Bragg gratings formed by anisotropic photopolymerization of free-radical monomers, an electric field is required to switch the grating between a diffracting and a transmitting state. The voltage necessary to turn the grating completely off is defined as the switching voltage. In this work, we report on the gradual increase of this switching voltage with time after initial fabrication. The switching field increases approximately 60% over a seven-day period for a pentaacrylate/E7 material system. Using dielectric measurements, it is observed that the resistance of the cell does not change over time while the capacitance decreases. FT-IR spectroscopy was also used to explore the continued post-polymerization after fabrication of the gratings. Increases in switching field were observed for samples fully illuminated with light as well as those kept in the dark. We speculate that the rise in the switching voltage is caused by post polymerization of residual reactive moieties located near the polymer/nematic droplet interface. An increase in the amount of interfacial area generated by post-polymerization yields more surface area for the LC molecules to bind; thus a larger field is needed to switch.
In-Situ Observation of Thermal Amplification of Photogenerated Optical Anisotropy of Films of Azobenzene Polymers
Authors: Kidowaki Masatoshi , Fujiwara Takenori , Morino Shin'ya , Ichimura Kunihiro , Stumpe Joachim 
Published: April 2011

ABSTRACTThin films of polymers containing p-cyanoazobenzene side chains were studied to reveal its applicability for optical storage media, surface grating optics and aligning films for liquid crystal (LC) display devices. We followed the generation of optical anisotropy of LPLirradiated films of three polymethacrylates with azobenzene side chains exhibiting amorphous, crystalline and liquid-crystalline natures during heat treatment by mean of an ellipsometry and polarized UV-visible spectroscopy. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photo-induced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers amplified optical anisotropy was maintained even at 300°C whereas partial decomposition was observed.
Light Absorption Properties of Anthraquinone Dyes and Guest-Host Liquid Crystal Displays
Authors: Wang Shuangxi , Abeygunaratne Sugat , Chien Liang-Chy 
Published: April 2011

ABSTRACTThe light absorption properties of anthraquinone dye in different hosts are compared in order to demonstrate the influence of the dye-liquid crystal interactions on dye order parameter. Surprisingly, the anthraquinone dye have a higher order parameter in liquid crystalline mixtures of positive dielectric anisotropy as well as in a liquid crystalline mixture of negative dielectric anisotropy (S = 0.71-0.82). We studied the Heilmeier displays use homogeneous alignment. The display is operated at the reverse mode, transparent at zero field. The switching voltage between the bright and dark states for these displays is 2-4 volts, depending on host liquid crystal and cell configuration.
Antiferroelectric Liquid Crystals from Achiral Molecules And A Liquid Conglomerate
Authors: Walba David M. , Körblova Eva , Shao Renfan , Maclennan Joseph E. , Link Darren R. , Clark Noel A. 
Published: April 2011

ABSTRACTUntil recently, it was an empirical fact that creation of a chiral liquid crystal phase required enantiomerically enriched molecules. In addition, to date known ferroelectric and antiferroelectric smectics have also been composed of enantiomerically enriched molecules. Herein are described the first examples of the formation of chiral and antiferroelectric supermolecular liquid crystalline structures from achiral molecules. In one case (apparently metastable) the liquid crystal structure is macroscopically chiral, with samples composed of heterochiral macroscopic domains: a liquid conglomerate.
Rheo-Optics Studies in the Development of Hybrid Liquid Crystalline Based Mwir Polarizers
Authors: Mather P.T. , Barnes W. , Hood P.J. , Bunning T.J. 
Published: April 2011

ABSTRACTWe present here a rheo-optical study of the flow behavior of two cholesteric liquid crystals, one with a large pitch and one with a small pitch. The large pitch compound has been investigated as a possible fixed wavelength polarizer in the mid-wavelength infra-red region (3-5 micron). The investigation of these compounds is driven by their low melt viscosity and ability to vitrify order, and thus functionality, into films with a wide range of thickness. In our attempts to obtain consistent thin films with reproducible contrast ratios, we explored the defect textures of both compounds under a polarizing optical microscope. These materials were sheared at various strain rates and at various temperatures in an attempt to determine the best processing window for defect free films. The pitch lengths of the two materials investigated were 160 and 1330 nm. The flow behavior of the large pitch material resembles a pure nematic with defect refinement taking place under flow. The short pitch material exhibited the typical Grandjean oily streaks upon shearing followed by coarsening. Observations made during this rheological study were used to identify a processing technique for the large pitch materials. Upon application of a conventional buffed alignment layer, films with consistent quality were routinely made. The measured polarization contrast of >70:1 exceeds the values obtained from state-of-the art commercial polarizers in this wavelength regime.
Mechanisms for Microstructure Evolution in Electroplated Copper Thin Films
Authors: Harper J. M. E. , Cabral C. , Andricacos P. C. , Gignac L. , Noyan I. C. , Rodbell K. P. , Hu C. K. 
Published: April 2011

ABSTRACTWe present a model which accounts for the dramatic evolution in the microstructure of electroplated copper thin films near room temperature. Microstructure evolution occurs during a transient period of hours following deposition, and includes an increase in grain size, changes in preferred crystallographic texture, and decreases in resistivity, hardness and compressive stress. As the grain size increases from the as-deposited value of 0.05–0.1 μm up to several μm, the decreasing grain boundary contribution to electron scattering lowers the resistivity by tens of percent to near-bulk values. Concurrently, as the volume of grain boundaries decreases, the stress is shown to change in the tensile direction by tens of MPa. The as-deposited grain size is also shown to be consistent with grain boundary pinning.
Magnetic Exchange-Coupling In Copt/Co Bilayer Thin Films
Authors: Kim J. , Barmak K. , Lewist L. H. , Crewt D. C. , Welcht D. O. 
Published: April 2011

ABSTRACTThin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700°C and fully transformed from the FCC phase to the magnetically hard, ordered LI0 phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8–225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.
Structured Abrasive CMP: Length Scales, Subpads, and Planarization
Authors: Goetz D. P. 
Published: April 2011

Chemical-Mechanical Planarization with structured abrasive uses a subpad to manage the pressure variations due to loading over a range of length scales. The effect of subpad construction on pressure responses related to those scales is illustrated.A minimum length scale for the effect of the subpad is established via contact mechanics. Differences between one- and two-layer subpads are shown. Uniform compression, point loading, and edge exclusion are considered briefly. A model of the subpad as a plate on an elastic foundation is applied to the problem of die doming. The roles of process pressure, die size, and subpad construction are illustrated. Planarization at the intra-die, die, and wafer scales are related to the subpad construction.
Passivation of (111) Si/SiO2 Interfacial Defects by Molecular Hydrogen
Authors: Gheorghita Ligia , Ogryzlo Elmer 
Published: April 2011

ABSTRACTThe reaction of molecular hydrogen with Pb defects at the (111) Si/SiO2 interface has been studied using a remote radio frequency (RF) probe to continuously monitor the rate of removal of electrically active defects. The kinetic parameters calculated from these experiments are compared with the earlier work of Brower and Stesmans. Although the data confirms the non-exponential nature of the reaction reported by Stesmans the activation energy of the process is found to be somewhat different.
Effects of Inversion Layer Quantization and Polysilicon Gate Depletion on Tunneling Current of Ultra-Thin SiO2 Gate Material
Authors: Saha S. , Srinivasan G. , Rezvani G. A. , Farr M. 
Published: April 2011

ABSTRACTWe have investigated the impact of inversion layer quantization and polysilicon-gate depletion effects on the direct-tunneling gate-leakage current and reliability of ultra-thin silicon-dioxide gate dielectric. The gate-leakage current was measured for nMOSFET devices with gate oxide thickness down to 3 nm. A simulation-based methodology was used to determine the physical oxide thickness from the measured capacitance data, and the corresponding effective gate oxide thickness at inversion was computed from the simulation data obtained with and without the quantum mechanical and polysilicon depletion effects. The simulation results indicate that the effective gate oxide thickness is significantly higher than the physically grown oxide thickness due to inversion layer quantization and polysilicon depletion effects. The increase in oxide thickness is strongly dependent on the supply voltage and is more than 0.6 nm at 1 V. Our data, also, show that in order to maintain a leakage current ≥ 1 A/cm2 for 1 V operation, the effective gate oxide thickness must be ≥ 2.2 nm.
Soft Breakdown in Ultra-Thin Oxides
Authors: Weir B. E. , Silverman P. J. , Alers G. B. , Monroe D. , Alam M. A. , Sorsch T. W. , Green M. L. , Timp G. L. , Ma Y. , Frei M. , Liu C. T. , Bude J. D. , Krisch K. S. 
Published: April 2011

ABSTRACTAn understanding of dielectric breakdown mechanisms is critical for continued oxide scaling. Although working transistors have been demonstrated with sub-2nm SiO2 gate dielectrics, the manufacturability of such devices hinges on the reliability of the oxide. As oxides become thinner and operating voltages become lower, a fundamentally different mode of dielectric breakdown occurs. This has been called soft breakdown and is considered to be the formation of a small, localized tunneling path through a dielectric. For transistors with 2-nm gate oxides, threshold voltage and maximum transconductance are not affected by soft breakdown, implying that circuits may continue to operate after soft breakdown. The increase in gate current or voltage noise associated with soft breakdown is not a limiting factor for many applications. However, some cases will be shown in which soft breakdown does degrade device function.In order to make comparisons of ultra-thin oxide quality, it is important to be able to reliably detect soft breakdown. J-ramp, a commonly used ramped-current measurement to determine oxide quality, is unable to detect soft breakdown in ultra-thin oxides. We will demonstrate the incorporation of noise measurements in a commercial J-ramp algorithm.
Structure and Bonding in Nitrided Oxide Films by Sims and Xps
Authors: Novak S. W. , Shallenberger J. R. , Cole D. A. , Marino J.W. 
Published: April 2011

ABSTRACTThe N distribution and bonding in five types of oxynitride films have been investigated using SIMS and XPS. Films were grown using N2O, NO-O2 and NH3 gas sources, a remote plasma N source and a Helicon plasma source. The SIMS measurements show different N distributions for each type of sample. XPS measurements show only N≡Si3 bonding in the gas source films, N≡Si3 and O-N-Si2 bonding in the remote plasma sample, and N≡Si3, O-N≡Si2, and O2≡N-Si bonding in the Helicon plasma sample. Angle-resolved XPS measurements show that the O2≡N-Si bonding is deepest in the sample whereas the O-N≡Si2 bonding is associated with a surface oxide.