bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deformation Behavior of the Raman Radial Breathing Modes of Single-Wall Carbon Nanotubes in Composites
Authors: Lucas Marcel , Young Robert J. 
Published: April 2011

ABSTRACTRaman spectroscopy is a technique widely used to study the vibrational modes of carbon nanotubes. The low-frequency Radial Breathing Modes (RBMs) are frequently used to characterize carbon nanotube samples. We report a Raman spectroscopic study on the strain-induced intensity variations of the RBMs of Single-Wall Carbon Nanotubes (SWNTs) in epoxy/SWNT composites. The RBM intensities have been found to vary significantly over a range of strain between -0.3% and 0.7%. The trend (increase or decrease) as well as the magnitudes of the intensity variation depends on the nanotube diameter and its chirality. Using tight-binding calculations, we have shown that these intensity variations can be explained entirely by resonance theory. Electronic density of states calculations confirm that the energy separation between the Van Hove singularities shifts with strain. The nanotubes are thus moved closer or further away from resonance, causing the intensity variations. It is demonstrated that through the use of resonance theory, a tentative chirality can be assigned to each type of SWNT from knowledge of its RBM position and the effect of strain upon the RBM intensity, thus determining its entire structure.
Microstructures Of Irradiated And Mechanically Deformed Metals And Alloys: Fundamental Aspects
Authors: Zinkle S.J. , Hashimoto N. , Matsukawa Y. , Stoller R.E. , Osetsky Yu.N. 
Published: April 2011

ABSTRACTRecent molecular dynamics and transmission electron microscopy results on irradiated metallic materials are reviewed, with an emphasis on defect production in the displacement cascade and the fluence- and temperature-dependent accumulation of defect clusters. Materials analyzed include Fe, V, Cu, austenitic stainless steel, V4%Cr4%Ti, and ferritic/martensitic steel. Intrinsic differences between the defect accumulation behavior of body centered cubic (BCC) and face centered cubic (FCC) metals are highlighted. Results on the temperature-dependent vacancy cluster density of Cu are discussed in terms of thermal stability of stacking fault tetrahedra (SFTs). Finally, recent results on deformation behavior of irradiated, quenched, and deformed metals are discussed, with particular emphasis on flow localization mechanisms (e.g., dislocation channeling), and experimental and molecular dynamics studies of the detailed dislocation-defect cluster interactions.
Diffuse Electron Scattering by Nanometer-sized Defects in Gold and Tantalum
Authors: Kirk M. A. , Davidson R. S. , Jenkins M. L. , Twesten R. D. 
Published: April 2011

ABSTRACTDiffuse elastic scattering of electrons by single nanometer-sized defects in ion irradiated Au has been measured quantitatively. Results are given for two dislocation loops and compared with published calculations to establish the loop geometry and interstitial or vacancy nature. Defect images using only diffuse scatttering are achieved with high sensitivity and good resolution by a hollow-cone dark-field method.
Ion Beam-Induced Amorphization of the Pyrochlore Structure-Type: A Review
Authors: Ewing R. C. , Lian J. , Wang L. M. 
Published: April 2011

ABSTRACTThis paper reviews the recent developments in the understanding of the radiation-damage processes in A2B2O7 (Fd3m; Z=8) pyrochlore-structure compounds. Pyrochlore structure compounds display a wide range of behaviors in response to ion beam irradiation. Some compositions, such as Gd2Ti2O7, are amorphized at relatively low doses (∼0.2 dpa at room temperature) while other compositions, such as Gd2Zr2O7, do not amorphize (even at doses of 36 dpa at 25 K) and instead disorder to a defect fluorite structure. The response to ion beam irradiation is highly dependent on compositional changes that affect both the structural distortion from the ideal fluorite structure and the associated energetics of the disordering process. Generally, the ionic size of the cations plays a dominant role in determining the radiation response of different pyrochlore compositions. However, the cation ionic radius ratio criteria cannot be applied all-inclusively in predicting the radiation “tolerance” of a pyrochlore. Systematic irradiation studies of the radiation response of rare-earth (A-site) pyrochlores in which B = Ti, Zr, and Sn have shown that the behavior of the pyrochlore also depends on the cation electronic structure, i.e., the type of bonding, which is closely related to the polyhedral distortion and structural deviation from the ideal fluorite structure. These structural changes affect the dynamic defect recovery process directly linked to the material's response to and recovery from irradiation.
Kinetics of alkali ion exchange of irradiated glasses
Authors: Ojovan Michael I. , Lee William E. 
Published: April 2011

ABSTRACTThe kinetics of alkali ion exchange of irradiated glasses were investigated using the structural energy barrier model for ion exchange of glasses. Derived rates of alkali ion exchange depend both on irradiation dose D(Gy) and dose rate q(Gy/s) illustrating that some effects cannot be simulated by external irradiation and require in-situ measurements. Higher D and q lead to increased ion exchange rates. Significant changes occur in the activation energies demonstrating a 4 – 6 times decrease depending on glass composition. Radiation-induced changes are higher at relatively low temperatures and are diminished by increased glass temperature. Numerical estimations show that changes in alkali ion exchange kinetics occur at D far below damaging doses.
Radiation-induced structural changes, percolation effects and resistance to amorphization by radiation damage
Authors: Trachenko Kostya , Dove Martin T , Pruneda Miguel , Artacho Emilio , Salje Ekhard , Geisler Thorsten , Todorov Ilian , Smith Bill 
Published: April 2011

ABSTRACTWe combine simulation, theoretical and experimental results to study radiation damage effects in complex oxides under irradiation. In zircon, we study large density variations in the damaged structure, and show how damage percolation results in the enhanced transport extending to macroscopic lengthscale, and suggest that percolation threshold serve as a benchmark for acceptable waste load in a waste form. In perovskite, we identify common defects in the damaged structure, and relate their stability to chemical bonding. Finally, we formulate the criterion for resistance to amorphization by radiation damage: a material is amorphizable if it is able to form a covalent network.
Coupled Kinetic Monte Carlo and Molecular Dynamics Simulations of Implant Damage Accumulation in Silicon
Authors: Otto Gustav , Hobler Gerhard 
Published: April 2011

ABSTRACTDamage formation during ion implantation is a complex process that cannot accurately be modeled by binary collision simulations alone. Molecular dynamics (MD) simulations are suited to describe the quenching of collision cascades, while thermally activated processes may be treated with the kinetic Monte Carlo (kMC) method.MD and kMC simulations have widely but separately been used to investigate damage accumulation and annealing in silicon. Simulation of ion implantation at room temperature, however, requires both methods to be coupled. In this paper we describe for the first time a scheme of the coupling between MD and lattice kMC for damage accumulation. Using this scheme we study the dynamic annealing behavior of implantation damage for heavy and light ions.
Thermal Stability of Thin Films of Ion Beam Deposited CNx
Authors: Ingram David C. , Kayani Asghar , Lanter William C. , DeJoseph Charles A. 
Published: April 2011

ABSTRACTA dual ion beam deposition system was used to deposit thin films of CNx from a carbon target. A 1 keV nitrogen ion beam from a 3 cm Kaufman source was used to sputter carbon from a graphite target, and a second nitrogen ion beam of 50 eV, from an RF ion source, was used to bombard the growing film with nitrogen ions. Using this technique, rather than direct ion beam deposition from methane, it is possible to reduce the amount of hydrogen in these films to less than 5% (atomic), and to boost the nitrogen content to over 30%. These films were then subjected to isochronal heating up to 900°C to determine the stability of the films as compared to those with much higher concentrations of hydrogen.CNx is a material that is difficult to fabricate without the inclusion of large amounts of hydrogen. A high hydrogen content has the tendency to make the material sensitive to property changes as it is heated over 200°C. Concomitant with a loss of hydrogen is the loss of nitrogen.In the films that had lower amounts of hydrogen it was found that the loss of nitrogen during heating was delayed until higher temperatures were reached. However, instead of hydrogen being evolved during heating, the amount of hydrogen in the film increases, reaching a maximum concentration of ∼45% at 800°C.
High-speed Processing with Cluster Ion Beams
Authors: Seki Toshio , Matsuo Jiro 
Published: April 2011

ABSTRACTCluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Especially, it is expected that extreme high rate sputtering can be obtained using reactive cluster ion beams. High current SF6 cluster ion beams were recently obtained with new modifications in the basic cluster ion beam technique. The cluster size distribution was measured with Time-of-Flight (TOF) method and the mean size of cluster was about 500 molecules. Si substrates were irradiated with SF6 cluster ions at the acceleration energy of 5–45 keV. Sputtering yield with SF6 cluster ions was increased with acceleration energy and was about 2300 atoms/ion at 45 keV. The sputtering yield was about 1000 times higher than that of Ar monomer ions and was also higher than that of Ar cluster ions. It was found that reactive sputtering occurred with SF6 cluster ion irradiation. These results indicate that high-speed fabrication can be realized with reactive cluster ion irradiation at high energy.
Position Controlled GaN Nano-Structures Fabricated by Low Energy Focused Ion Beam System.
Authors: Nagata Takahiro , Ahmet Parhat , Koida Takashi , Chichibu Shigefusa F. , Chikyow Toyohiro 
Published: April 2011

ABSTRACTWe have demonstrated position controlled GaN nano structures with a combination of surface treatments and nucleation sites control assisted by low energy focused ion beam. Ga ions in the range of 100 eV - 10 keV were irradiated onto the surface of the As-terminated Si (100) to create the nucleation sites. The deposited Ga atoms migrated on the surface and were trapped at the nucleation sites to form Ga droplets. Subsequently an excited atomic nitrogen source was supplied to the surface. By SEM observation, the GaN microcrystals of diameter about 800 nm were found to be allocated every 2 μm periodically on the substrates, and cathodoluminescence peaks from GaN nano structures were observed.
Effects of Substrate Orientation on the Spontaneous Ordering of GaAsSb Epilayers Grown by Molecular Beam Epitaxy
Authors: Gorman Brian P. , Norman Andrew G. , Lukic-Zrnic Reiko , Golding Terry D. , Littler Chris L. 
Published: April 2011

ABSTRACTSpontaneous atomic ordering is investigated in a series of GaAs1−xSbx epilayers (0.51 < x < 0.71) grown by molecular beam epitaxy (MBE) on GaAs substrates with surface orientations of (001), (001) – 8° toward (111)A, (001) – 8° toward (111)B, (115)A, (115)B, (113)A, and (113)B. Atomic ordering in these epilayers was observed from a decrease in the energy gap measured by Fourier transform infrared (FTIR) absorption spectroscopy and corroborated by superlattice reflections in transmission electron diffraction and Raman spectroscopy. Contrary to previous investigations of ordering in III-V alloys, a marked energy gap reduction corresponding to CuPt-B type ordering is observed in the GaAs1−xSbx grown on (111)A-type orientations.
Optical Properties of Quantum-Wires Grown Using Lateral Composition Modulation Induced by (InP)1/(GaP)1 Short-Period Superlattices
Authors: Song J. D. , Kim J. M. , Lee Y. T. 
Published: April 2011

ABSTRACTThe optical properties of quantum wires (QWRs) grown using lateral composition modulation (LCM) were studied by photoluminescence (PL) measurement as a function cryostat temperature (Tcr). 3 stacked arrays of QWRs were formed by sequential growth of ∼ 180 Å-thick LCM layers (lateral period: ∼ 90 Å) induced by (InP)1/(GaP)1 short-period superlattices, and 200 Å-thick InGaP spacers at the growth temperature of 490 °C. The formation of QWRs was confirmed by a transmission electron microscopy measurement. By the analysis of the dependence of PL intensity and peak energy of the QWRs on Tcr, the origin of higher energy peak (H) and lower energy peak (L) were investigated. While behavior of the H peak is similar to that of an ordered InGaP, the L peak shows the insensitivity of PL peak energy to Tcr. This is attributed to compensation of the bandgap by competition of strain in the QWR region and indicates the L peak is related to the QWRs. Strong dependence of the L peak on the position of polarizer also supports this. Additionally, the PL peak intensity of the L peak has the maximum value not at the lowest Tcr (10 K) but at 50 K, while the H peak decrease continuously as T increases. We introduced the idea of compensation of the thermal expansion coefficient to explain this phenomenon.
Room Temperature Resonant Tunneling and Coulomb Blockade in Nanocrystalline Si with Double SiO2
Authors: Wu Barriers L. C. , Chen K. J. , Dai M. , Li W. , Yu L. W. , Huang X. F. 
Published: April 2011

ABSTRACTWe studied electron resonant tunneling and Coulomb blockade in nanocrystalline Si (nc-Si) with double SiO2 barriers, which is fabricated in-situ in a plasma enhanced chemical vapor deposition system. In capacitance-voltage measurements, discrete capacitance peaks due to electron resonant tunneling into energy levels of nc-Si dots and Coulomb blockade charging in nc-Si dots have been observed at room temperature. For smaller dots, capacitance peaks are more distinct due to the stronger Coulomb blockade effect. Meanwhile, conductance plateau in the region of capacitance peaks are also observed due to the charging effect in nc-Si dots. Experimental results are in agreement with theoretical evaluation based on the model of Coulomb blockade.
Nanoengineered Quantum Dot Active Medium for Thermally-Stable Laser
Authors: Tokranov Diodes V. , Yakimov M. , Katsnelson A. , Lamberti M. , Agnello G. , Oktyabrsky S. 
Published: April 2011

ABSTRACTThe influence of a nanoengineering procedure on the properties of single- and multi-layer self-assembled InAs quantum dot (QDs) has been studied using photoluminescence, transmission electron microscopy (TEM), and electroluminescence. Optical properties of QDs were optimized by shape engineering via adjustment of a GaAs overlayer thickness prior to a heating (truncation) step. TEM micrographs have confirmed that the employed growth procedure results in truncated pyramidal QDs covered entirely by AlAs with smooth top interfaces. Truncated QDs with two-monolayer-thick AlAs capping have demonstrated a strong blue shift of ground state (GS) energies and up to 10 meV larger separation between GS and first excited state energy levels as compared to non-capped QDs. We believe that AlAs capping, in combination with truncation procedure, results in significant suppression of carrier transport between QDs within the same layer as well as between QD layers. A record high characteristic temperature for GS lasing threshold, T0 = 380 K up to 55 °C, as well as a maximum saturated gain of 16 (5.3 per layer) cm−1, were measured for a 1.22 μm edge-emitting lasers with this truncated triple layer QD gain medium. A maximum saturated gain, 27 (3.9 per layer) cm−1, and T0 = 110 K have been demonstrated in a 1.19 μm lasers with truncated seven layer QD medium.
Phonon-Polariton Propagation, Guidance, and Control in Bulk and Patterned Thin Film Ferroelectric Crystals
Authors: Ward David W. , Statz Eric , Beers Jaime D. , Stoyanov Nikolay , Feurer Thomas , Roth Ryan M. , Osgood Richard M. , Nelson Keith A. 
Published: April 2011

ABSTRACTUsing time resolved ultrafast spectroscopy, we have demonstrated that the far infrared (FIR) excitations in ferroelectric crystals may be modified through an arsenal of control techniques from the fields of guided waves, geometrical and Fourier optics, and optical pulse shaping. We show that LiNbO3 and LiTaO3 crystals of 10–250 μm thickness behave as slab waveguides for phonon-polaritons, which are admixtures of electromagnetic waves and lattice vibrations, when the polariton wavelength is on the order of or greater than the crystal thickness. Furthermore, we show that ferroelectric crystals are amenable to processing by ultrafast laser ablation, allowing for milling of user-defined patterns designed for guidance and control of phonon-polariton propagation. We have fabricated several functional structures including THz rectangular waveguides, resonators, splitters/couplers, interferometers, focusing reflectors, and diffractive elements. Electric field enhancement has been obtained with the reflective structures, through spatial shaping, of the optical excitation beam used for phonon-polariton generation, and through temporal pulse shaping to permit repetitive excitation of a phonon-polariton resonant cavity.
Design of a New Taper for Light Coupling Between a Ridge Waveguide and a Photonic Crystal Waveguide
Authors: Jamois Cécile , Geppert Torsten , Wehrspohn Ralf B. 
Published: April 2011

ABSTRACTWe propose the design of a new taper to improve light coupling between a photonic-crystal-based W1 waveguide and a ridge waveguide of similar width. The taper design is directly deduced from band structure calculations and allows an adiabatic mode conversion. The comparison between light propagation from the ridge waveguide through the W1 waveguide and through the taper, respectively, shows good improvement of the coupling efficiency.
Dispersion Engineering of Photonic Crystal Devices
Authors: Pustai David M. , Chen Caihua , Sharkawy Ahmed , Shi Shouyuan , Murakowski Janusz , Prather Dennis W. 
Published: April 2011

ABSTRACTWe present and experimentally validate self-collimation in planar photonic crystals as a new means of achieving structureless confinement of light in optical devices. We demonstrate the ability to arbitrarily guide and route light by exploiting the dispersive characteristics of the photonic crystal. Propagation loss as low as 2.17 dB/mm is measured, and the experimental validation of routing structures are presented.
Temperature Controlled Scanning Nonlinear Dielectric Microscopy
Authors: Ohara K. , Cho Y. 
Published: April 2011

ABSTRACTScanning Nonlinear Dielectric Microscopy (SNDM) can obtain the linear and nonlinear dielectric constant distribution of dielectric and ferroelectric materials with sub-nanometer resolution. In this paper, we present the new type of SNDM which can control the sample temperature (80K-730K) in vacuum (less than 5×10−7 Torr), and its application to measure the surface polarization state on LiTaO3 single crystal.
Room Temperature Dielectric Function of Low Dimensional TlMeX2
Authors: Mamedov Nazim , Wakita Kazuki , Akita Seiji , Nakayama Yoshikazu 
Published: April 2011

ABSTRACTRoom temperature ellipsometric measurements of low dimensional TlMeX2 (Me=Ga, In; X=S,Se,Te) were performed in the photon energy range 1.5–6.5e V.Obtained ellipsometric data were then treated with allowance for optical anisotropy of the above materials. The components of dielectric function tensor were determined. The structures of the obtained dielectric function are interpreted in terms of the angle resolved photoemission and band structure results. The contribution of the atomic states of each atom (Tl, In, Se) in the band states in the point M of the Brillouin zone is traced back using LCAO analysis. An ultraviolet window in the joint density of electronic states of some of TlMeX2 is disclosed and substantiated to be a sign of ferroelectricity at room temperature. For the first time the nanorods of TlMeX2 are demonstrated.
Investigation of Valence State of U, Pu, and Am in Crystalline Host-Phases Using in situ Cathodoluminescence Spectroscopy
Authors: Zamoryanskaya Maria V. , Burakov Boris E. , Garbuzov Vladimir M. 
Published: April 2011

ABSTRACTCeramics compounds based on the pyrochlore, (Ca,Gd,Hf,An)2TiO7; zircon, (Zr,An)SiO4, and garnet, (Y,Gd,An‥)3(Al,Ga,An…)5O12, where An = U, Am, Pu, Np, Cm, structures have been investigated to determine their use as durable nuclear waste forms for the immobilization of weapons-grade plutonium and other actinides. U, Pu, and Am were incorporated into synthetic zircon, pyrochlore, and garnet and were investigated using in situ cathodoluminescence (CL) and compared with Ce3+, Ce4+, Eu2+ and Eu3+ in order to determine the valence state of the actinide dopants. The results obtained allow for the identification of Am3+ ions in synthetic zircon and garnet. The CL emission of Am3+ is characterized by narrow bands in the orange-red spectral region and is similar to CL emission of Eu3+ in zircon and garnet. No characteristic CL emission of Pu4+ was observed in zircon, pyrochlore or garnet. This is similar to CL emission of Ce4+, which does not have characteristic CL emission in the visible region of the spectrum. Although ions of Ce3+ were characterized by intense CL emission, no characteristic CL emission of Pu3+ was identified in zircon, pyrochlore, or garnet.The CL study of U-doped garnet and pyrochlore allow for the identification of the presence of two forms of uranium: the uranyl ion, (UO2)2+, and tetrahedral complex, (UO4)2−. Ions of U4+ did not have characteristic CL emission in the visible region. The study of pyrochlore samples doped simultaneously with 238Pu and 238U revealed that CL intensity of the uranyl ion increases with increasing dose of self irradiation from the 238Pu. It was assumed that self-irradiation might cause the change of actinide valence state.
Competition Between Internal and Surface Crystallization in Glass-ceramics Developed for Actinides Immobilization
Authors: Loiseau Pascal , Caurant Daniel , Majerus Odile , Baffier Nöel , Fillet Catherine 
Published: April 2011

ABSTRACTGlass-ceramic matrices containing zirconolite (nominally CaZrTi2O7) as the only crystalline phase in their bulk can be considered as good candidates for actinide-rich nuclear wastes (containing minor actinides or Pu) immobilization. In this study, three different methods are envisaged and compared to prepare such waste forms using neodymium as trivalent actinides surrogate. Independently on the preparation method, zirconolite is shown to be the only crystalline phase to nucleate in the bulk. However, crystallization of silicate phases (titanite CaTiSiO5 + anorthite CaAl2Si2O8) can occur from samples surface and can compete with zirconolite crystallization. The effect of the crystal growth thermal treatment duration (2–300 h) at high temperature (1050–1200°C) on glass-ceramics structure and microstructure is studied. In the oxides system studied here, it appears that zirconolite is not thermodynamically stable in comparison with titanite but, for kinetics reasons, such transformation will not occur during waste forms disposal.