bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron Irradiation of 4H SiC by TEM: An Optical Study
Authors: Sridhara S. G. , Persson P. O. Å. , Carlsson F. H. C. , Bergman J. P. , Janzén E. , Evans G. , Steeds J. W. 
Published: April 2011

ABSTRACTAn intrinsic defect spectrum, commonly observed after ion-implantation, electron, proton or neutron irradiation and even after SIMS measurements is investigated using photoluminescence techniques. The spectrum is associated with carbon related isoelec-tronic centers having a pseudodonor like behaviour. Vacancy-interstitial pair complexes are tentatively suggested as the defect centers responsible for this intrinsic spectrum.
Simulations of Quantum Confinement in Self-Assembled InAs/GaAs Island Quantum Dot Arrays
Authors: Johnson H.T. , Nguyen V. , Bower A. F. 
Published: April 2011

ABSTRACTQuantum confinement and photoluminescence properties of self-assembled InAs quantum dot arrays on GaAs substrates are studied theoretically using a coupled morphology/electronic structure finite element approach. Simulations of island evolution due to strain energy driven diffusive mass transport are first used to generate realistic island arrays. The resulting finite element meshes are input to a continuum, single charge-carrier model in which band structure properties are prescribed using a k•p Hamiltonian formulation. The results of the electronic properties analysis are spectra of electron and hole energies and corresponding wave functions. The electron and hole states have characteristics unique to arrays, the most prominent of which are the energy separations due to size and shape variations among dots in the array. This feature is shown to lead directly to inhomogeneous broadening in the photoemission spectra. Other phenomena observed here include the onset of a discrete density of states at the point of island formation during growth; the presence of states with wave functions coupling multiple dots in the array; and the nature of wetting layer states in the system.
InAs Quantum Dots Grown on an AlGaAsSb Strain-Relief Buffer
Authors: Gray A.L. , Dawson L. R. , Lin Y. , Stintz A. , Xin Y.-C. , Garza A.A. , Lester L. F. 
Published: April 2011

ABSTRACTAn In(Ga)As-based self-assembled quantum dot laser test structure grown on strain-relief Al0.5Ga0.5As1-ySby strain-relief buffer layers (0≤y ≤ 0.24) on a GaAs substrate is investigated in an effort to increase dot size and therefore extend the emission wavelength over conventional InAs quantum dots on GaAs platforms. Cross-section transmission electron microscopy, and high-resolution x-ray diffraction are used to monitor the dislocation filtering process and morphology in the buffer layers. Results show that the buffer layers act as an efficient dislocation filter by drastically reducing threading dislocations, thus providing a relaxed, low dislocation, compositionally modulated Al0.5Ga0.5Sb0.24As0.76 substrate for large (500Å height x 300Å width) defect -free InAs quantum dots. Photoluminescence shows a ground-state emission of the InAs quantum dots at 1.45 μm.
Formation of Quasicrystalline Phases in the Equilibrium Immiscible Co-Cu and Fe-Cu Systems by Ion Mixing/Solid-State Reaction
Authors: Li Z.F. , Lai W.S. , Yang G.W. , Zhang Q. , Liu B.X. 
Published: April 2011

AbstractAnomalous structural evolution was induced in the equilibrium immiscible Co-Cu and Fe-Cu systems by 100 or 200 keV xenon ion irradiation at 77 K or room temperature. In the Co15Cu85 and Fe70Cu30 multilayered films, nanosized quasicrystals were formed in an amorphous matrix, through a two-step transition of crystal-to-amorphous-to-quasicrystal. The obtained quasicrystals are Co-Cu dodecagonal and Fe-Cu icosahedral phases with twelve-fold and five-fold rotational symmetries, respectively. The real compositions of the amorphous matrix were determined to be close to Co10Cu90 and Fe70Cu30, while those for quasicrystals are nearly Co20Cu80 and Fe50Cu50, respectively. Moreover, the same dodecagonal and icosahedral phases were also obtained in the specifically designed Co50Cu50 and Fe50Cu50 multilayered samples upon thermal annealing at 500°C and 850°C, respectively, confirming the existence of these new metastable states in the respective systems. Besides, our molecular dynamics study showed that either Co or Fe could be mixed with Cu at an atomic scale in forming some metastable alloy phases. The amorphous-to-quasicrystal transition was discussed in terms of the similarity in the atomic configuration between the quasicrystal and amorphous short-range orders.
The Ten-Fold Surface of The Decagonal Al72Ni11Co17 Quasicrystal Studied by Leed, Spa-Leed, Aes and Stm.
Authors: Cox Erik J. , Ledieu Julian , Mcgrath RÓn'n , Diehl Renee D. , Jenks Cynthia J. , Fisher Ian 
Published: April 2011

AbstractThe ten-fold surface of the decagonal Al72Ni11Co17 (d-Al-Ni-Co) quasicrystal has been investigated using low energy electron diffraction (LEED), spot profile analysis LEED (SPA- LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM). This was done as a function of both annealing temperature and annealing time. The long-range order of the surface, as indicated by LEED, increases both as a function of annealing time and temperature. STM shows the surface to be rough and cluster-like at low annealing temperatures (≤725 K), whilst annealing to temperatures in excess of 725 K results in the formation of terraces. These terraces are small (≤ 100 Å width) at lower annealing temperatures and increase in size (100 Å ≤ x ≤ 500 Å) as the annealing temperature is increased (≥ 850 K). They are characterised by the presence of three-fold protrusions which align preferentially. STM images show single height steps as expected due to the periodicity of d-Al-Ni-Co in the z direction. To date it has not been possible to obtain atomic resolution, although this work is continuing.
Origin of Magnetism in Al-Pd-Mn and Al-Mn Quasicrystals and Approximants
Authors: Hippert Françoise , Simonet Virginie , Audier Marc , Calvayrac Yvonne , Bellissent Robert , Laissardière Guy Trambly de , Mayou Didier 
Published: April 2011

AbstractLocalized moments are observed on a small fraction of the Mn atoms in Al-Pd-Mn and Al-Mn quasicrystals while a large proportion of magnetic moments is found in liquids in equilibrium with these quasicrystalline phases. As magnetic sites cannot be identified in quasicrystals because of the very small number of Mn atoms involved, we have studied the case of approximant phases in both Al-Mn and Al-Pd-Mn systems. Most of the approximants are non- magnetic but magnetic moments are present on a fraction of the Mn sites in the μ-Al4Mn phase and in the Mn-rich TAlPdMn phase. From both experimental and theoretical investigations, the magnetic sites are identified in these phases. The moment formation can be explained by analysing the local environment of the Mn atoms and indirect Mn-Mn interactions mediated by conduction electrons on relatively large distances. A clear picture of the origin of magnetism in quasicrysals, approximants and liquids in the Al-Mn and Al-Pd-Mn systems can therefore be obtained.
Modeling Thermopower in AlPdMn Based Quasicrystalline Systems
Authors: Pope A. L. , Zawilski B. M. , Gagnon R. , Tritt T. M. , Strom-Olsen J. , Schneidmiller R. , Kolis J. 
Published: April 2011

AbstractWe report room temperature thermopower values and the temperature dependence for several AlPdMn based quasicrystals. In an effort to further understand the complexities of electrical transport in quasicrystalline systems, thermopower data for icosahedral Al71Pd21Mn8-XReX will be presented and discussed. A relation of room temperature thermopower to the curvature of the thermopower is demonstrated. We propose an empirical fit to the thermopower data, utilizing three free variables. The physical significance of the fit parameters is discussed. These results are discussed in brief concerning the relation to the application of quasicrystals for use as thermoelectric materials.
Quasicrystalline Coatings Through Laser Processing: A Study on Process Optimisation and Microstructure Evolution
Authors: Chattopadhyay K. , Biswas K. , Bysakh S. , Phanikumar G. , Weisheit A. , Galun R. , Mordike B. 
Published: April 2011

AbstractComposite coatings containing quasicrystalline (QC) phases in Al-Cu-Fe alloys were prepared by laser cladding using a mixture of the elemental powders. Two substrates, namely pure aluminum and an Al-Si alloy were used. The clad layers were remelted at different scanning velocities to alter the growth conditions of different phases. The process parameters were optimized to produce quasicrystalline phases. The evolution of the microstructure in the coating layer was characterized by detailed microstructural investigation. The results indicate presence of quasicrystals in the aluminum substrate. However, only approximant phase could be observed in the substrate of Al-Si alloys. It is shown that there is a significant transport of Si atoms from the substrate to the clad layer during the cladding and remelting process. The hardness profiles of coatings on aluminum substrate indicate a very high hardness. The coating on Al-Si alloy, on the other hand, is ductile and soft. The fracture toughness of the hard coating on aluminum was obtained by nano-indentation technique. The K1C value was found to be 1.33 MPa m1/2 which is typical of brittle materials.
Where are the Atoms in Quasicrystals? Experimental and Theoretical Studies of Ternary and Quaternary Approximants
Authors: Miller Gordon J. , Lee Chi-Shen , Tsai Wen-Jiuan 
Published: April 2011

AbstractProblems concerning complete structural characterization of quasicrystals involve locating the atomic positions as well as determining the distribution of elements at each site. Quasicrystalline approximants provide models for potential building units of quasicrystals, but a clear determination of the elementaldecorations in such approximants also remains incomplete. We report experimental and theoretical studies of new, quaternary Bergman phases in the Li-Mg-Zn-Al system and a new, quasicrystalline approximant Li10Mg6Zn31Al3(A16M34-type). A theoretical model using averaged Mulliken populations provides a means to track the segregation of elements (and vacancies) onto different sites as a function of valence electron concentration. As the Li content decreases, vacancies begin to occur at a specific site in the Bergman structure. The new approximant demonstrates how truncated tetrahedra can play an important role in forming clusters with possible fivefold symmetry in quasicrystalline structures.
Fundamental Cluster and Hydrogen Sites in Ti-Zr-Ni Quasicrystals
Authors: Majzoub E.H. , Hennig R.G. , Kelton K.F. , Gibbons P.C. , Misture S.T. 
Published: April 2011

AbstractA Rietveld refinement confirmed by ab initio calculations [1] has shown that the structure of the related W-phase [2] 1/1 approximant consists of Bergman clusters connected by “glue” sites. To investigate if the quasicrystal structure contains the same cluster we construct two constrained icosahedral glass models using the Bergman or Mackay cluster, respectively. A comparison with neutron diffraction data yields better agreement if the Bergman cluster is used, suggesting that this is a frequently occurring element in the quasicrystalline structure. Since absorbed hydrogen is known to locate preferentially in tetrahedral interstitial sites in many metals, the tetrahedral sites in the constrained glass were filled with hydrogen. The calculated powder neutron diffraction spectra are similar to the experimental data. It was not possible, however, to differentiate between possible tetrahedral sites where the hydrogen atoms sit. Hydrogen site energies from ab initio calculations indicate preferences that are consistent with fillings of non-Ni bearing tetrahedral sites.
Dislocation Glide Resistance in a Model Quasicrystalline Lattice
Authors: Tamura R. , Takeuchi S. , Edagawa K. 
Published: April 2011

AbstractThe glide resistance of edge dislocations gliding along a two-dimensional quasiperiodic lattice (Burkov II model of the decagonal quasicrystal) has been calculated. The glide resistance consists of τphason and τPeierls components and the τPeierls component depends strongly on the orientation of the dislocation. For the orientation of large τPeierls component, the τphason component is about half of the τPeierls component for individual dislocation glide but becomes negligibly small for glide of a pair of dislocations. The largest τPeierls component is about 0.1G (G: the shear modulus).
Phase Transitions in Quasicrystals Induced by Friction and Wear
Authors: Dong Chuang , Wu Jinsong , Zhang Liming , Dubois Jean-Marie , Brunet Pierre , Zhou Qinggang , Wang Dehe , Zhang Huichen 
Published: April 2011

AbstractCertain ductility may occur during friction tests on quasicrystalline materials that are intrinsically brittle. This is, at least in part, due to a solid-state phase transition from the icosahedral to a BCC phase. The present paper first summarizes phase transition features of quasicrystals and then examines the microstructural mechanism of scratch indentation on an icosahedral Al-Cu-Fe sample. The last part of this paper is devoted to a discussion of the correlation of this phase with respect to quasicrystals.
Influence of Grain Orientation on Friction and Wear Behavior in Quasicrystalline Alloys
Authors: Duckham Alan , Shechtman Dan , Grushko Benjamin 
Published: April 2011

AbstractThe influence of grain orientation on the friction and wear behavior of single-phase quasicrystalline alloys is investigated. Pin-on-disc wear tests and friction coefficient measurements have been performed on bulk samples of icosahedral phase AlPdMn and decagonal phase AlNiCo alloys. Wear behavior has been evaluated by optical microscopy, scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Coefficient of friction values of the decagonal AlNiCo alloy are found to be widely scattered (between 0.03 and 0.55) compared to the far more consistent values of the icosahedral alloys. This is explained by considering the significant variation in wear behavior that is observed between different – sometimes adjacent – oriented grains in the decagonal specimens.
Comparative Study of the Tribological and Oxidative Properties of AlPdMn Quasicrystals and Their Cubic Approximants
Authors: Mancinelli Chris , Ko Jeff S. , Jenks Cynthia J. , Thiel Patricia A. , Ross Amy R. , Lograsso Thomas A. , Gellman Andrew J. 
Published: April 2011

AbstractAn experimental comparison has been made between the properties of the surfaces of an Al70Pd21Mn9 quasicrystal and its Al48Pd42Mn10 approximant. The Al70Pd21Mn9 sample was a single grain icosahedral quasicrystal cut to expose its five-fold symmetric (000001) surface. The approximant was polycrystalline β-phase Al48Pd42Mn10, which has a CsCl-type cubic structure. Surfaces of both were prepared under ultra-high vacuum (UHV) conditions and then used for comparative measurements of their frictional properties and oxidation rates. Both materials are oxidized by reaction with O2 to form a thin film of aluminum oxide that ultimately passivates their surfaces. The interesting difference between the two is that the rate of oxidation of the approximant is significantly higher than that of the quasicrystal in spite of the fact that the bulk Al concentration of the approximant is lower than that of the quasicrystal. Friction measurements were made under UHV conditions between pairs of quasicrystals and pairs of approximants whose surfaces were either clean or oxidized to varying degrees. The friction between pairs of the approximant surfaces is significantly higher than that measured between the quasicrystal surfaces under all conditions of surface oxidation.
An Investigation of Sputtered Al-Cu-Fe-Cr Quasicrystalline Films Via Synchrotron Diffraction
Authors: Daniels M.J. , Maciejewski J. , Zabinski J.S. , Rek Z.U. , Yalisove S.M. , Bilello J.C. 
Published: April 2011

AbstractAnalysis of the phase relationships of Al-Cu-Fe-Cr based sputtered films, before and after various annealing treatments, was carried out via grazing incidence x-ray scattering (GIXS) at SSRL on beamline 7-2. The “as-deposited” films were composed primarily of nanoscale grains whose structure were mainly quasicrystalline (QC) and its approximants, plus a nano-crystalline phase was also observed in one sample. None of these precursor films exhibited any degree of amorphous character. GIXS studies, in the symmetric and asymmetric modes, revealed that grain growth due to the post-deposition heat treatments caused a decagonal QC phase to evolve and dominate the crystalline phases, which composed the film. These ≍10 µm thick films were created by sputter deposition with a DC magnetron source via an Al-Cu-Fe-Cr powder pressed target, giving a nominal sample composition of Al75Cu4Fe8Cr10O3. Two types of annealing treatments were performed using an Argon atmosphere. Anneal of a precursor film for 4 hours at 500°C showed a large fraction of decagonal and approximant phases, while anneal of a precursor film for 2 hours at 400°C and 2 hours at 550°C showed a large fraction of the crystalline phase.
Aluminum-Based Quasicrystals Studied by Slow Positron Beam Technique
Authors: Sato K. , Uchiyama H. , Kanazawa I. , Tamura R. , Kimura K. , Komori F. , Suzuki R. , Ohdaira T. , Takeuchi S. 
Published: April 2011

AbstractIcosahedral quasicrystals Al71.5Pd20.3Mn8.2, Al70.7Pd21.34Re7.96, Al62.5Cu25.5Fe12.5, and α-Al68.31Mn21.21Si10.48 1/1- approximant were investigated by using a monoenergetic slow positron beam. The structural vacancy densities in the first three samples were determined to be 5.0×1020, 7.7×1020, and 4.7×1020 cm−3, respectively, by analyzing the measured S-parameter.
Experimental Studies and Molecular Dynamics Simulations of the Sliding Contact of Metallic Glass
Authors: Fu Xi-Yong , Falk Michael L. , Rigney David A. 
Published: April 2011

AbstractTribological properties of bulk metallic glass Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 were studied experimentally using a pin/disk geometry without lubrication. Experimental observations were compared with 2D molecular dynamics simulations of amorphous material in sliding contact. The friction coefficient and the wear rate of bulk metallic glass (BMG) depend on normal load and test environment. The sliding of annealed BMG re-amorphizes devitrified material. A mechanically mixed layer is generated during sliding; this layer has enhanced oxygen content if the sliding is in air. The MD simulations show that atomic scale mixing occurs across the sliding interface. The growth kinetics of the mixing process scales with the square root of time. In the simulations, a low density region is generated near the sliding interface; it corresponds spatially to the softer layer detected in experiments. Subsurface displacement profiles produced by sliding and by simulation are very similar and are consistent with the flow patterns expected from a simple Navier-Stokes analysis when the stress state involves both compression and shear.
Abrasive Wear Resistance of Bulk Metallic Glasses
Authors: Greer A. Lindsay , Myung Wha-Nam 
Published: April 2011

AbstractThis paper reviews work on the wear of metallic glasses in general, as well as reporting recent results on the abrasive wear of bulk metallic glasses. The distinctive mechanical properties of metallic glasses make their wear resistance of fundamental interest. Metallic glasses, and the partially or fully crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Standard wear laws are followed, with behaviour similar to that of conventional hardened alloys. The microhardness and abrasive wear resistance are measured for four bulk metallic glasses (based on La, Mg, Pd or Zr). The hardness and wear resistance correlate well with the Young's modulus of the glass.
Plasticity at Crack Tips in Zr-Based Bulk Metallic Glasses
Authors: Li Jing , Gu Xiaofeng , Xing Li-Qian , Livi Ken , Hufnagel T. C. 
Published: April 2011

AbstractWe have examined the structure of plastic deformation zones ahead of the tips of microcracks in Zr-based bulk metallic glass Zr57Ti5Cu20Ni8Al10. We have used an axially aligned dark field transmission electron microscopy technique, with the objective aperture placed to form images using electrons from several different areas of the diffraction patterns. We also compared Fourier transforms of the high resolution transmission electron microscopy images of deformed and undeformed regions to extract additional structural information. The plastic zones produce enhanced low-angle scattering of electrons and an apparent broadening of the amorphous halo, suggesting increased disorder and the presence of voids in the deformed zones. These results are consistent with an increased degree of atomic-scale disorder and enhanced free volume in highly deformed regions, which may provide a partial explanation of the manner in which plastic deformation occurs in metallic glasses.
Shaping of Bulk Metallic Glasses by Simultaneous Application of Electrical Current and Low Stress
Authors: Yavari A.R. , Oliveira M. F. de , Botta W.J. 
Published: April 2011

AbstractUsing the intrinsic materials properties of bulk metallic glasses (BMG), namely electrical resistivities two orders of magnitude higher than good conductors and a Newtonian viscous-flow regime of deformability, a new electromechanical process has been developed for shaping, joining and engraving of BMGs. The wider the liquid supercooled region between the glass transition temperature Tg and the crystallisation temperature Tx of the bulk metallic glass, the easier the application of the new process. In this range, the undercooled liquid deforms in a quasi-Newtonian way, allowing thermomechanical shaping in the low viscosity range as for oxide glasses. The new electromechanical processing technology has been used for economical and rapid shaping at low applied stresses by eliminating the thermal mass of the furnace and the need to heat the deformation dies. The process parameters are adaptable for the full maintenance of the glassy state or when desired, for appropriate compositions, for nanocrystallisation during the joining or shaping operation.
Glass Formation and Glass Forming Ability of Alloys Near Eutectic Composition
Authors: Li Y. 
Published: April 2011

AbstractOnset temperature, Tm and offset temperature (liquidus) Tl of melting of a series of bulk glass forming alloys based on La, Mg, and Pd have been measured by studying systematically the melting behaviour of these alloys using DTA or DSC. Bulk metallic glass formation has been found to be most effective at or near their eutectic points and less effective for off-eutectic alloys. Reduced glass transition temperature Trg given by Tg/Tl is found to show a stronger correlation with critical cooling rate or critical section thickness for glass formation than Trg given by Tg/Tm.