bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dislocation Configurations Around Nanoindentations in Reconstructed Au(001)
Authors: Fuente O. Rodríguez de la , González M.A. , Rojo J.M. 
Published: April 2011

ABSTRACTNanoindentations resulting from STM tungsten tip contacts with the 5×20 reconstructed surface of a Au(001) crystal around the indentation point have been studied by Scanning Tunnel Microscopy (STM). A novel defect structure is recognised: a row of hillocks extending along more than a hundred nm along the <110> directions stemming from the indentation point. These hillocks have about 7 nm of side and 0.06 nm of height. With the help of simulation models we identify individual hillocks as dislocation configurations consisting of two stacking fault ribbons encompassed by Shockley partials having a stair-rod dislocation as a ridge. It is proposed that hillocks are generated by plastic flow, from an initially nucleated V-shaped dislocation loop intersecting the surface.
The Effects of Creep on Elastic Modulus Measurement Using Nanoindentation
Authors: Feng G. , Ngan A.H.W. 
Published: April 2011

ABSTRACTDuring the unloading segment of nanoindentation, time dependent displacement (TDD) accompanies elastic deformation. Consequently the modulus calculated by the Oliver-Pharr scheme can be overestimated. In this paper we present evidences for the influence of the measured modulus by TDD. A modification method is also presented to correct for the effects of TDD by extrapolating the TDD law in the holding process to the beginning of the unloading process. Using this method, the appropriate holding time and unloading rate can be estimated for nanoindentation test to minimise the effects of TDD. The elastic moduli of three materials computed by the modification method are compared with the results without considering the TDD effects.
Mechanism of Al-Cu-Fe Quasicrystal Plastic Deformation Studied by Instrumented Sharp Indentation
Authors: Dub Sergey N. , Milman Yuly V. , Lozko Dina V. , Belous Anton N. 
Published: April 2011

ABSTRACTCyclic nanohardness tests of Al65Cu23Fe12 quasicrystal reveals a different mechanism of plastic deformation as compared with a regular metal. For a polycrystalline metal, the indent depth increases monotonically with load, while for a quasicrystal, it increases stepwise. Probably, the step formation in the Al-Cu-Fe quasicrystal loading curve is due to the structural transformation in the indent. It is known that the quasicrystal structure destroys at high pressure and transforms into a regular crystalline structure. Therefore, it is possible to attribute the pressure drop in the indent to the transformation of the quasicrystalline structure into the crystalline one and extrusion of the plastic polycrystalline metallic phase out from indent. The observation of thin layers extruded out of the indent in Al-Cu-Fe quasicrystal supports this assumption.
Determining the Area Function of Spherical Indenters for Nanoindentation.
Authors: Bushby Andrew J. , Jennett Nigel M. 
Published: April 2011

ABSTRACTNanoindentation with spherical tipped indenters provides a powerful technique for exploring surface mechanical properties through the application of Hertzian mechanics. The full range of mechanical response can be obtained from elastic, through the yield point to a range of permanent deformation. However, the successful application of the technique requires accurate calibration of the indenter tip geometry. In this paper methods based on indentation into a number of reference materials are used to characterise a range of spherical tipped indenters with nominal radii from 5 to 50 microns. A traceably calibrated metrological AFM is also used to determine the actual shape of one of the indenters. The sensitivity of each method to test parameters is discussed. Coincidence of the data from both methods validates the determined shape of the indenter and offers the opportunity to cross-correlate the calibration of both instruments with high sensitivity.
Influence of Tipradius and Substrate on the Nanotribological Characterization of Thin DLC Coatings
Authors: Staedler Thorsten , Schiffmann Kirsten I. 
Published: April 2011

ABSTRACTIn this work diamond-like carbon films deposited via plasma enhanced chemical vapor deposition with a thickness of 250nm on different substrates are characterized by nanoindentation and microscratching in combination with scanning probe microscopy. The substrates (SU8 photoresist, quartz glass, Si(100) and AlTiC ceramic) provide a wide range of combinations between film and substrate properties. The experimental configuration allows the testing of samples with loads between 1μN and 10mN and a high local resolution. The tribological response of the various film/substrate systems is analysed in two different ways. A single scratch test with linear increasing load and an oscillating wear tests at constant loads is used. The tip radii of the conical diamond tips utilized vary between 0.6 and 6μm. Both, the substrates as well as the tip radii, show a significant influence on the tribological behavior of the systems.
Microstructure and Post-Irradiation Annealing Behavior of 20% Cold-Worked 316 Stainless Steel
Authors: Cole J. I. , Allen T. R. , Kusanagi H. , Dohi K. , Ohta J. 
Published: April 2011

ABSTRACTMicrostructural examination and in situ post-irradiation annealing studies were carried out on 20% cold-worked 316 stainless steel (SS) hexagonal duct material following irradiation in the reflector region of the EBR-II reactor. Stainless steel hexagonal ducts were used to house reactor subassemblies and provide a valuable source of information on irradiation behavior of reactor structural materials at lower dose-rates (on the order of 10-8 dpa/sec) than previously examined. The microstructural development of samples irradiated to doses of 1, 20 and 30 dpa is examined, while the post-irradiation annealing behavior of a sample irradiated to 20 dpa is described. Annealing studies were performed at 370 and 500°C to examine the kinetics of radiation damage recovery as a function of annealing temperature. The initial (pre-annealed) microstructures consists of a substantial density of irradiation induced chromium-rich M23C6 and M6C carbides which form both on the grain boundaries and within the grain interiors. Recovery of the cold- work is evident in the 1 dpa sample while samples irradiated to 20 and 30 dpa possess dense populations of voids and dislocation structures consisting of networks of line dislocations and faulted dislocation loops. Results indicate that post-irradiation annealing of the samples at 370°C for 1 hour has little effect on the microstructure, while further annealing at 500°C for 1 hour results in void shrinkage, the formation of small cavities, and a reduction in the dislocation loop and network density.
Molecular Dynamic Simulation of Cascade Overlap and Amorphization in 3C-SiC
Authors: Gao Fei , Weber William J. 
Published: April 2011

ABSTRACTMolecular dynamics (MD) simulations have been employed to study cascade overlap and defect accumulation processes during amorphization in 3C-SiC. A large number of 10 keV displacement cascades were randomly generated in a model crystal to achieve the amorphous state, and the corresponding dose is consistent with experimental observations. The results show that most defects are single interstitials and mono-vacancies at low dose, whereas the amorphous or disordered clusters, which consist of interstitials and antisite defects, appear at intermediate dose levels. These local disordered regions play an important role in the amorphization of SiC. At higher doses, a significant proportion of antisite defects is created during continued cascade overlap. The increase in interstitials and antisite defects with increasing dose suggests that the primary driving force for the crystalline-to-amorphous transition under these ion irradiation conditions in SiC is due to the accumulation of both Frenkel pairs and antisite defects.
Atomic Level Characterization of Neutron Irradiated Pressure Vessel Steels
Authors: Miller M. K. , Pareige P. 
Published: April 2011

ABSTRACTAtom probe tomography provides one of the most effective tools to characterize the solute distribution and precipitation that occurs in pressure vessel steels and associated model alloys during irradiation. The three-dimensional atom probe is able to experimentally determine the elemental identities of the atoms and their spatial coordinates with near atomic resolution so that their distribution within small volumes of the specimen can be reconstructed and analyzed. This technique together with conventional atom probe field ion microscopy has been applied to many different types of pressure vessel steels and model alloys and has revealed and characterized several different nanostructural transformations. These radiation induced or enhanced processes lead to the formation of copper-nickel-manganese-silicon-enriched precipitates, and solute segregation to dislocations, dislocation loops, nanovoids and boundaries.
On the Effect of Neutron Flux and Composition on Hardening of Reactor Pressure Vessel Steels and Model Alloys
Authors: Odette G. R. , Lucas G. E. , Klingensmith D. 
Published: April 2011

ABSTRACTSingle variable experiments on a set of reactor pressure vessel and model alloys with a range of controlled compositions show a systematic effect of neutron flux (ϕ) on hardening in the intermediate fluence (ϕt) regime. The data suggest that high ϕ and enhanced recombination by vacancy trapping by solutes delays the onset of radiation-enhanced precipitation hardening.
Ion Beam Enhanced Formation and Luminescence of Si Nanoclusters from a-SiOx
Authors: Sun Yohan , Seo Se-Young , Shin Jung H. , Kim T. G. , Whang C. N. , Song J. H. 
Published: April 2011

ABSTRACTThe effect of ion beams on the formation of Si nanoclusters from a-SiOx films and their luminescence properties is investigated. a-SiOx films with Si content ranging from 33 to 50 at. % were deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) of SiH4 and O2. Prior to anneal, some samples were implanted with 380 keV Si to a dose ranging from 5.7 × 1014 cm-2 to 5.7 × 1016 cm-2. All films were rapid thermal annealed under flowing Ar environment, and hydrogenated after anneals to passivate defects and to enhance the luminescence of Si nanoclusters. For films with Si content less than 40 at. %, ion beam slightly reduces the photoluminescence (PL) intensity and induces a slight blueshift of the luminescence. For films with Si content greater than 40 at. %, ion beam greatly increases the PL intensity. Based on the effect of the ion beams dose and the ion specie, we propose that ion beams damage greatly promotes nucleation of small Si clusters from the a-SiOx matrix.
Ion-implantation Generated Nanovoids in Si and MgO Monitored by High Resolution Positron Beam Analysis
Authors: Eijt S.W.H. , Falub C.V. , van Veen A. , Schut H. , Mijnarends P.E. , van Huis M.A. , Fedorov A.V. 
Published: April 2011

ABSTRACTThe formation of nanovoids in Si(100) and MgO(100) by 3He ion implantation has been studied. Contrary to Si in which the voids are generally almost spherical, in MgO nearly perfectly rectangular nanosize voids are created. Recently, the 2D-ACAR setup at the Delft Positron Research Center has been coupled to the intense reactor-based variable-energy positron beam POSH. This allows a new method of monitoring thin layers containing nanovoids or defects by depth-selective high-resolution positron beam analysis. The 2D-ACAR spectra of Si with a buried layer of nanocavities reveal the presence of two additional components, the first related to para-positronium (p-Ps) formation in the nanovoids, and a second one most likely related to unsaturated Si-bonds at the internal surface of the voids. The positronium is present in excited kinetic states with an average energy of 0.3 eV. Refilling of the cavities by means of low dose 3He implantation (1×1014 cm-2) followed by annealing reduces the formation of Ps and the width of the Ps peak in the ACAR spectrum. This width reduction is due to collisions of Ps with He atoms in the voids. In MgO, p-Ps formed with an initial energy of ∼3 eV shows a final average energy of 1.6 eV at annihilation due to collisions with the cavity walls. Possibilities of this new, non-destructive method of monitoring the sizes of cavities and the evolution of nanovoid layers will be discussed.
Atomistic models of triple junctions and the origin of topological changes in microstructural evolution
Authors: Satta Alessandra , Colombo Luciano , Cleri Fabrizio 
Published: April 2011

ABSTRACTTriple junctions are crucial elements in microstructural evolution: for example, their mobility can be rate-limiting if lower than that of grain boundaries. However, very little is known about their atomic-level structure and properties. We studied the atomic structure of multiple-twin triple junctions in silicon, formed by the convergence of two {111} and one {221} symmetric-tilt grain boundaries. Molecular dynamics simulations with the Stillinger-Weber potential and constant-traction border conditions were performed on several triple junction configurations, obtained by different combinations of the three grain boundaries. All the configurations have a positive excess line energy, a measurable volume contraction and display regions of opposite, tensile and compressive, residual stress. Moreover, we tried to elucidate the role of triple junctions as being the seeds of theonlymicroscopic events that can lead to topological changes in the microstructure. Such events, usually dubbedT1andT2in mesoscopic models, correspond to grain switching (in the Ashby-Verrall sense) and grain-disappearance events, respectively. We present preliminary results for the atomic-scale modelling of both classes of topological events and discuss the connection between atomistic and mesoscopic modelling of microstructural evolution.
From the Electronic Structure to the Macroscopic Behavior: A Multi-scale Analysis of Plasticity in Intermetallic Compounds
Authors: Fähnle Manfred , Kohlhammer Susanne , Bester Gabriel 
Published: April 2011

ABSTRACTThe influence of crystal interfaces related to stacking faults on the properties of >110< superdislocations and hence on the temperature dependences of the yield stress in intermetallic compounds is investigated. This is achieved by a combination of the ab-initio density functional electron theory (which describes the electronic scale) with the generalized Peierls-Nabarro model (which describes the atomistic scale). For Pt3Al and doped Al3Ti our data do not support the hypothesis that the strong increase of the yield stress with decreasing T at low T results from sessile SISF-bound dislocation dissociations. Alternative explanations are suggested. For Ni3Al our results do not rule out the idea that Kear-Wilsdorf locks are responsible for the experimentally observed anomalous temperature dependence of the yield stress.
Simulation of the Rheology of Semisolid Alloys by Using a Two-phase Flow Approach
Authors: Ludwig A. , Wu M. , Hofmeister T. 
Published: April 2011

ABSTRACTSemisolid alloys exhibit a shear rate history dependent flow behavior. The increasing interest on numerical modeling of thixo-casting processes makes it quite important to understand the flow behavior of semisolids. Its apparent viscosity is the key parameter for the numerical models. In this paper a two phase approach is used to investigate the rheology of semisolid alloys. It is assumed that both, liquid and solid phase, can be regarded as inter-penetrating continua with its own viscosity. Thus, each phase is thought to behave as a Newtonian fluid. The simulation results show that the rheology of the two-phase flow is determined by the interaction between the solid and the liquid, i.e. the momentum exchange between the two phases. Non-Newtonian flow behavior of the solid-liquid mixture is predicted although both phases are considered as Newtonian fluids.
Critical Beha vior of a Depinning Dislocation
Authors: Zapperi Stefano , Zaiser Michael 
Published: April 2011

ABSTRACTThe dynamics of dislocations at yield can be understood within the framew ork of the depinning transition of elastic manifolds in random media. Close to the threshold stress for their long-range motion, the geometry and dynamics of dislocations are characterized by a set of critical exponents. We consider a single flexible dislocation gliding through a random stress field, taking in to account long-range self stresses, and estimate the critical stress where depinning takes place. Simulations of a discretized lattice model confirm the analytical estimate and yield numerical values of the critical exponents which are in agreement with theoretical predictions for an elastic string mo ving on a plane.
Simulation of a Grain Boundary in Zirconia
Authors: Finnis Michael W. , Paxton Anthony T. 
Published: April 2011

AbstractTetragonal zirconia, (t′–ZrO2) a ferroelastic material, readily forms domains with domain boundaries on {011}. For example, by compressing a single crystal along [100] the formation and movement of such domain walls has been demonstrated experimentally. We have made atomistic simulations of a domain wall with a self-consistent tight-binding model which cor- rectly reproduces both the high temperature tetragonal to cubic phase transition exhibited by zirconia, and its low temperature monoclinic phase. We analyse the results of our simulation, in particular the width of the domain wall, in terms of a Landau–Ginzburg theory in which the order parameter measures the degree of tetragonality of the lattice
Interface Reactions in LiNbO3 Based Optoelectronics Devices
Authors: Nagata Hirotoshi , Miyama Yasuyuki , Higuma Kaoru , Hashimoto Yoshihiro , Yamamoto Futoshi , Yamane Yuuji , Yatsuki Miki 
Published: April 2011

AbstractWe present secondary ion mass spectrometry (SIMS) study results on interfaces of LiNbO3 based optoelectronic devices, which have been performed in order to examine the cause of device failures. The devices are widely used in current high-speed optical fiber communication systems, and such investigation from a materials-viewpoint is important to improve the device quality. Especially, the device long-term stability is strongly affected by alkali-contaminants diffused into the SiO2 buffer layer of device, and here we confirmed that an adoption of common Si3N4 passivation is effective in preventing the process-induced contamination without any influence to device performance.
Effect of Substrate Surface Structure and Deposition Conditions on the Microstructure of Tin Dioxide Thin Films Synthesized by Femtosecond Pulsed Laser Deposition
Authors: Dominguez J. E. , Fu L. , Van Rompay P. A. , Zhang Z. Y. , Nees J. A. , Pronko P. P. , Pan X. Q. 
Published: April 2011

AbstractTin oxide films were deposited on sapphire and silicon substrates using reactive femtosecond pulsed laser deposition at temperatures ranging from room temperature to 700°C. The effect of electrical discharge and background oxygen pressure on the thin film microstructure was studied. The microstructure of the films was characterized by transmission electron microscopy and x-ray diffraction. SnO2 films fabricated consist of different textures in microstructures that depend on the deposition conditions and substrate surface structures. For instance, films deposited on the (1012) sapphire (R-cut) are amorphous if deposited at room temperature, whereas films deposited at 700°C were epitaxial, single crystalline. Discharge and oxygen pressure had a strong effect on the ion/neutral ratio of the ablated plasma plume of SnO2.
Al Doped Ta2O5 Thin Films for Microelectronic Applications
Authors: Joshi P. C , Cole M. W. , Hubbard C. W. , Ngo E. 
Published: April 2011

AbstractIn this paper, we report on the fabrication and characterization of pure and Al doped Ta2O5 thin films fabricated by metalorganic solution deposition (MOSD) technique. The pure and Aldoped Ta2O5 thin films were fabricated by spin-coating technique using room temperature processed carboxylate-alkoxide precursor solution. The structure of the films was analyzed by xray diffraction (XRD). The surface and cross-sectional morphology of the films were examined by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The electrical measurements were conducted on films in MIM configuration using Pt as the top and bottom electrode. The effects of Al concentration and the post-deposition annealing temperature on the structural, dielectric, and insulating properties were analyzed. The effects of the applied bias and the measurement temperature on the dielectric and insulating properties were also analyzed to establish the stability and reliability of Al doped Ta2O5 thin films.
Electrical Properties of Doped Tin Dioxide Thin Films Deposited Using Femtosecond Pulsed Laser Ablation.
Authors: Dominguez J. E. , Fu L. , Pan X. Q. 
Published: April 2011

AbstractTin dioxide thin films are widely used as chemical sensors. The mechanism for gas sensitivity depends on the chemisorption characteristics of the oxide surface and on the electronic characteristics of thefilm. Chemical doping and the film microstructure can influence the electronic properties. In this paper tin dioxide thin films doped with rare earth and transition metals were deposited on the (1012 -oriented sapphire substrates by femtosecond pulsed laser deposition. The resulting films were single crystalline with a thickness of about 15 nm and 30 nm. The response of the films to reducing gases was measured in a gas reactor at high temperature. The electrical transport properties of the films were determined by Hall effect measurements within the gas reactor. The valence and ionic radius of dopants have strong influence on the mobility and concentration of electrical carriers (i.e. electrons) and thus affect the response of the thin films to reducing gases. A model correlating the dopant characteristics to the electrical properties was developed.
Photochemical Reduction and Oxidation Reactions on Barium Titanate Surfaces
Authors: Giocondi Jennifer L. , Rohrer Gregory S. 
Published: April 2011

AbstractThe influence of the ferroelectric domain structure of BaTiO3 on the photochemical reactions that occur on its surface has been examined using atomic force microscopy. Both the photochemical reduction of aqueous silver cations and the oxidation of steric acid thin films were studied. During reduction, silver selectively deposits on the surface in patterns determined by the ferroelectric domain structure. Based on the analysis of domain polarization in single crystals, we find that the photochemical reduction reaction occurs preferentially on the positive ends of the dipoles. The most likely explanation for this phenomenon is that when the static dipolar field is oriented with the positive end of the dipole on the surface, photogenerated electrons are driven to the solid-liquid interface where they reduce metal cations. The oxidation of steric acid films, on the other hand, is not spatially selective. During oxidation, the films dissipate uniformly as they are converted to CO2 and H2O. In this case, we conclude that the oxidation occurs indirectly. Photogenerated holes create hydroxyl radicals which can migrate on the surface before reacting with the steric acid molecules.