bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation between Structural and Optical Properties of Si Nanocrystals in SiO2: Model for the Visible Light Emission
Authors: López M. , Garrido B. , González O. , García C. , Pérez-Rodríguez A. , Morante J.R. , Bonafos C. , Carrada M. , Rodríguez R.J. , Montserrat J. 
Published: April 2011

AbstractThe correlation between the structural and optical properties of Si nanocrystals embedded in SiO2 is the key factor to understand their emission mechanism. However, there is a great difficulty in imaging Si nanocrystals in SiO2 and measuring their size distribution because of the lack of contrast in electron microscopy. We have used here a new method for imaging Si nanocrystals by using high resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Regarding the optical properties, the band-gap energies and photoluminescence have been measured by direct and independent methods. The results have allowed experimental determination, for the first time in this material, of the experimental Stokes shift between absorption and emission as a function of crystallite size. The experimental band-gap versus size correlates well with the most accurate theoretical predictions. Moreover, the photoluminescence energy emission versus crystallite size shows a parallel behaviour to that of band-gap energy. Consequently, the experimental Stokes shift is independent of nanocrystal size and is found to be 0.26±0.03 eV. This value is almost twice the energy of the Si-O vibration (0.134 eV). These results suggest that the dominant emission of Si nanocrystals passivated with SiO2 is a fundamental transition spatially located at the Si-SiO2 interface and with the assistance of a local Si-O vibration.
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.
Interactions of Point Defects and Impurities With Open Volume Defects in Silicon
Authors: Williams J.S. , Ridgway M.C. , Conway M.J. , Wong-Leung J. , Williams B.C. , Petravic M. , Fortuna F. , Ruault M.-O. , Bernas H. 
Published: April 2011

AbstractIon implantation can produce open volume defects in silicon by one of two methods, either by H or He implantation followed by annealing to create a band of nanocavities and also by direct implantation to reasonably high doses, which results in a vacancy excess region at depths less than about half the projected ion range. This paper reviews three interesting aspects of open volume defects. In the first case, the very efficient gettering of fast diffusing metals to nanocavities formed by H-implantation is illustrated. In addition, the non-equilibrium behaviour of Cu3Si precipitation and dissolution at cavities is examined. The second example treats the interaction of irradiation-induced defects with nanocavities, particularly preferential amorphisation at open volume defects and subsequent cavity shrinkage. The final example illustrates the coalescence of excess vacancies into small voids on annealing and the use of gettering of Au to detect such open volume defects.
MeV Ion Implantation Doping of Diamond.
Authors: Prawer S. , Jamieson D.N. , Nugent K.W. , Walker R. , Uzan-Saguy C. , Kalish R. 
Published: April 2011

AbstractDiamond-based semiconductor devices offer the promise of operation at high temperatures and under extreme radiation conditions. An essential step in the drive towards operational diamond-based electronic devices is the ability to controllably and reproducibly dope the diamond. Ion implantation is the method of choice for such doping because it offers precise control of the dopant concentration and spatially selective doping is achievable using standard masking techniques. However, compared to silicon, the doping of diamond is complicated by the tendency of the diamond to relax to graphite upon thermal annealing. Furthermore, even if graphitization can be avoided, the compensation of dopants by residual defects has proved in the past to be a limiting factor in obtaining very high mobility material. In this paper, we present a scheme for the effective doping of diamond using MeV ion-implantation. For MeV ion- implantation the doped layer is deeply buried under a cap of undamaged diamond, and so the scheme includes a method using pulsed laser irradiation for making electrical contact to the buried layer. We show that a boron doped layer fabricated by the MeV implantation scheme has, after suitable annealing and removal of these compensating/trapping defects, very high mobility and low compensation ratio. In fact, its electrical properties are quite similar to those of natural boron-doped type IIb diamond.
Synthesis of Continuous SmSi2 Layers on Si by Samarium Ion Implantation Using A Metal Vapor Vacuum Arc Ion Source
Authors: Cheng X.Q. , Zhu H.N. , Liu B.X. 
Published: April 2011

AbstractSamarium ion implantation was conducted to synthesize Sm-disilicide films on silicon wafers, using a metal vapor vacuum arc ion source and the continuous SmSi2 films were directly obtained with neither external heating during implantation nor post-annealing. Diffraction and surface morphology analysis confirmed the formed Sm-disilicilde films were of a fine crystalline structure under appropriate experimental conditions. Besides, the formation mechanism of the SmSi2phase is also discussed in terms of the temperature rise caused by ion beam heating and the effect of ion dose on the properties of the SmSi2films.
Load-Displacement Behavior During Sharp Indentation of Viscous-Elastic-Plastic Materials
Authors: Oyen-Tiesma Michelle , Toivola Yvete A. , Cook Robert F. 
Published: April 2011

ABSTRACTA constitutive equation is developed for geometrically-similar sharp indentation of a material capable of elastic, viscous, and plastic deformation. The equation is based on a series of elements consisting of a quadratic (reversible) spring, a quadratic (time-dependent, reversible) dashpot, and a quadratic (time-independent, irreversible) slider—essentially modifying a model for an elastic-perfectly plastic material by incorporating a creeping component. Load-displacement solutions to the constitutive equation are obtained for load-controlled indentation during constant loading-rate testing. A characteristic of the responses is the appearance of a forward-displacing “nose” during unloading of load-controlled systems (e.g., magnetic-coil-driven “nanoindentation” systems). Even in the absence of this nose, and the associated initial negative unloading tangent, load-displacement traces (and hence inferred modulus and hardness values) are significantly perturbed on the addition of the viscous component. The viscous-elastic-plastic (VEP) model shows promise for obtaining material properties (elastic modulus, hardness, time-dependence) of time-dependent materials during indentation experiments.
Sub-Micrometer Spatially Resolved Measurements of Mechanical Properties and Correlation to Microstructure and Composition
Authors: Kunert M. , Baretzky B. , Baker S. P. , Mittemeijer E. J. 
Published: April 2011

ABSTRACTThe variations of hardness, composition, and microstructure within a carbon implanted region – about 350 nm thick – of a Ti-6Al-4V alloy were measured using nanoindentation, Auger electron spectroscopy and transmission electron microscopy, respectively. Correlations among hardness, composition, and microstructure were made with a spatial resolution of about ±20 nm. The variation in hardness within the implanted regions was quantitatively explained as due to the formation of an almost continuous TiC layer and precipitate hardening. The problems that may arise in measuring and correlating spatial variations in such a complex material on this scale are outlined and a successful method to solve them is proposed. The need for highly spatially resolved measurement techniques is emphasized.
Three-Dimensional Contact Mechanics Studies of Zdol Hard Disk Lubricants
Authors: Lucas Barry N. , Hay Jack C. 
Published: April 2011

ABSTRACTThis paper reports the results of a study of the dynamic 3-dimensional response between a diamond point probe and a commercial hard-disk overcoat/lubricant system. The specific overcoat was CNx with a thickness of 50 Å. The lubricant layer was ZDOL with nominal thicknesses of 11 Å and 24 Å in unbonded and bonded conditions. The experiments were conducted with a constant lateral displacement oscillation in the z, x & y direction of 1 nm at a frequency of 125 Hz. Results of this study show that the bonded lubricant layer increases the lateral force required to maintain a constant lateral displacement oscillation compared to both the unlubricated CNx coating and the CNx coating with the unbonded lubricant.
Mechanical Properties of As-Grown and Ion-Beam-Modified GaN Films
Authors: Kucheyev S.O. , Bradby J.E. , Williams J.S. , Swain M.V. , Toth M. , Phillips M.R. , Jagadish C. 
Published: April 2011

ABSTRACTThe deformation behavior of as-grown and ion-beam-modified wurtzite GaN films is studied by a nanoindentation with a spherical indenter. Atomic force microscopy (AFM) and cathodoluminescence are used to characterize the deformation mode. No systematic dependence of the mechanical properties on the film thickness ( at least for thicknesses from 1.8 to 4 μm) as well as on doping type is observed. Results strongly suggest that (i) slip is the major contributor to the plastic deformatio of crystalline GaN and (ii) slip nucleation (rater than a phae transformation) is responsible for “pop-in” events observed during loading. Indentation with an ∼ 4.2 μm radius spherical indenter at maximum loads up to 900 mN does not produce any cracking visible by AFM in crystalline GaN. Instead, under such loads, indentation results in a pronounced elevation of the material around the impression. Implantation disorder dramatically changes the deformation behaviour of GaN. In particular, implanation-produced defects in crystalline GaN syppress (i) “pop-in” events during loading, (ii) slip bands observed by AFM, and (iii) the plastic component of deformation. GaN amorphized by in bombardment exhibits plastic flow even for very low loads. The values of hardness and elastic modulus of amorphous GaN are dramatically reduced compared to those of as-grown GaN.
Adhesion Quantification of Post-CMP Copper to Amorphous SiN Passivation by NanoIndentation
Authors: Vella J. B. , Smith S. M. , Volinsky A. A. , Adhihetty I. S. 
Published: April 2011

ABSTRACTIn this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reliably and repeatably produce these delaminations a TiW (10wt% Ti) superlayer was sputter deposited on to the test structures.[2,3] Mechanical properties, including elastic modulus and hardness of SiN, electrodeposited copper, and TiW measured by nanoindentation are also reported here.
Nanoindentation of Poly (Methyl Methacrylate)
Authors: Adams Michael J. , Gorman David M. , Johnson Simon A. 
Published: April 2011

ABSTRACTFor the indentation of an elastic-plastic homogeneous half-space with a pyramidal indenter, the load theoretically increases with the square of the total penetration depth. Experimental data are presented in the current paper that demonstrate the validity of this relationship for an organic polymer and a Berkovich indenter, provided that appropriate account is taken of the tip defect and viscoplasticity. It is also shown that a simple analytical solution exists for the ratio of the contact depth to the total penetration depth. These findings assist in identifying procedures for obtaining the rate-dependent mechanical properties of thin polymer coatings or polymeric materials with depth-dependent mechanical properties.
Fundamental Aspects of Friction and Wear Contacts in <100> Surfaces
Authors: Gerberich William W. , Tymiak Natalia I. , Kramer Donald E. 
Published: April 2011

ABSTRACTUnexpected friction and wear transitions occur in transition metals associated with dislocation emission, dislocation storage, and oxide break-through phenomena. Both normal nanoindentation and nanoscratch evaluations of conical diamond tips driven into tungsten {100} single crystal surfaces have been conducted. In terms of initiating plasticity undert the contact, this represents a high Peierl's barrier for dislocation motion in transition metals. Both quasi-equilibrium and kinetic aspects are reported along with current but speculative ideas on multiple friction and wear transitions. Preliminary results show that yielding under contacts can produce a 250 nm displacement excursion. Ramifications are seen in terms of friction coefficients which can double during the near-instantaneous yield excursion but then continue to triple from about 0.05 to 0.15 in the pile-up phase in front of the sliding contact. Implications of how nanotribological issues such as adhesion connect through this mesoscale activity to macroscopic friction and wear are discussed.
Deformation Mechanisms in Ferritic/martensitic Steels Irradiated in HFIR
Authors: Hashimoto Naoyuki , Zinkle Steven J. , Klueh Ronald L. , Rowcliffe Arthur F. , Shiba Kiyoyuki 
Published: April 2011

ABSTRACTA reduced activation ferritic/martensitic steel, F82H (IEA heat), developed for fusion energy applications was irradiated at 300 and 500°C to 5 dpa in the High Flux Isotope Reactor (HFIR). Changes in yield strength, deformation mode, and strain-hardening capacity were seen, with the magnitude of the changes dependent on irradiation temperature. Irradiation at 300°C led to a significant loss of strain-hardening capacity with a large change in yield strength. There was a tendency for a reduction in strain rate to cause a decrease in yield strength and elongation. Irradiation at 500°C had little effect on strength, but a reduction in strain rate caused a decrease in ductility. In order to determine the contributions of different microstructural features to strength and to deformation mode, transmission electron microscopy (TEM) specimens were prepared from the gage sections of the tested (strained) flat tensile specimens and examined; fracture surfaces were examined by scanning electron microscopy (SEM). The fracture surfaces showed a martensitic mixed quasi-cleavage and ductile-dimple fracture in the center at both irradiation temperatures. The microstructure in the necked region irradiated at 300°C showed defect free bands, which may be dislocation channels. This suggests that dislocation channeling could be the dominant deformation mechanism in martensitic steels irradiated at 300°C, resulting in the loss of strain-hardening capacity.
Radiation-Induced Phase Instabilities and Their Effects on Hardening and Solute Segregation in Precipitation-Strengthened Alloy 718
Authors: Thomas Larry E. , Sencer Bulent Hakan , Bruemmer Stephen M. 
Published: April 2011

ABSTRACTA classic example of radiation-induced phase instability and degraded mechanical properties occurs in γ′-γ″-strengthened alloy 718. During irradiation with neutrons or protons at ∼ 30 to 288°C, the Ni 3Nb γ″ particles disappear after low doses. The γ′ (present only in the matrix) also disappears after <0.6 dpa at 30 to 55°C, but at 288°C it persists to higher doses and eventually reprecipitates as new γ′ with changed composition. Hardness of the alloy is unaffected by disappearance of the γ″, but decreases appreciably at 288°C as the original γ′ particles dissolve. Fine-probe compositional measurements in a TEM showed that the softening coincides with solute redistribution and reprecipitation rather than with the phase disappearance. Compositional changes at grain boundaries included leveling of the thermally segregated Mo as well as strong Ni enrichment and loss of Nb after high doses. The complex phase stability and solute redistribution behavior reflects mainly ballistic mixing at 30-70°C irradiation temperatures and the influence of significant thermal diffusivities at the higher temperatures.
Effects of Proton Irradiation in Zeolite-Y
Authors: Gu Binxi , Wang Lumin , Wang Shixin , Zhao Donggao. , Rotberg Victor H. , Ewing Rodney C. 
Published: April 2011

ABSTRACTRadiation effects on zeolite-NaY have been investigated by irradiation with a 500 keV H+ beam. The crystalline-to-amorphous transition occurs at a total dose equivalent to an ionizing energy deposition of 3×1010Gy and a displacement damage level of 0.05 dpa. The ion exchange capacity of the irradiated zeolite-NaY with 10 mN SrCl2 or 10 mN AgNO3 solutions varies with the extent of the damage to the crystalline structure. After 25 hours of exchange, the Sr concentration in the amorphous region is nearly zero. This result shows that radiation-induced amorphization can cause a significant loss in ion exchange capacity. The data also suggest that the radiation damage by proton radiation in zeolite-NaY is through both ionizing and displacement processes. The result from Ag-exchange reaction with the irradiated zeolite suggests that higher radiation dose is required to block the penetration of Ag into the supercages. The Ag concentration (∼3 at.%) in the fully damaged region suggests that the cations in the small cages are still exchangeable even when amorphization has been achieved.
Microstructure of Swift Heavy Ion Irradiated SiC, Si3N4 and AlN
Authors: Zinkle S.J. , Jones J.W. , Skuratov V.A. 
Published: April 2011

ABSTRACTCross-section transmission electron microscopy was used to investigate the microstructure of single crystal silicon carbide and polycrystalline silicon nitride and aluminum nitride following room temperature irradiation with either 245 MeV Kr or 710 MeV Bi ions. The fluences ranged from 1×1012/cm2 (single track regime) to 1×1013/cm2. Ion track formation was observed in the Bi ion-irradiated Si3N4 specimen in regions where the electronic stopping power exceeded a critical value of ∼15 keV/nm (depths <24 μm). Ion track formation was not observed at any depth in 245 MeV Kr ion-irradiated Si3N4, in which the maximum electronic stopping power was 14.5 keV/nm. There was no evidence for track formation in either SiC or AlN irradiated with 710 MeV Bi ions, which indicates that the threshold electronic stopping power for track formation in these two ceramics is >34 keV/nm. The high resistance of SiC and AlN to track formation may be due to their high thermal conductivity, but further study is needed to quantitatively evaluate the suitability of the various track formation models.
Direct Comparison between Modeling and Experiment: an α-Fe Ion Implantation Study
Authors: Marian Jaime , Wirth Brian D. , Perlado J. Manuel , de la Rubia T. Diaz , Schäublin Robin , Lodi Dario , Hernández Mercedes , de Diego Gonzalo , Briceño Dolores G. , Stoller Roger E. 
Published: April 2011

ABSTRACTAdvances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusión Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline α-Fe samples have been irradiated with 150 keV Fe- ions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.
Atomistic Simulation of Dislocation-Defect Interactions in Cu
Authors: Wirth B. D. , Bulatov V. V. , de la Rubia T. Diaz 
Published: April 2011

ABSTRACTThe mechanisms of dislocation-defect interactions are of practical importance for developing quantitative structure-property relationships, mechanistic understanding of plastic flow localization and predictive models of mechanical behavior in metals under irradiation. In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. Thus, the resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present a comprehensive molecular dynamics simulation study that characterizes the interaction and fate of moving dislocations with stacking fault tetrahedra in Cu using an EAM interatomic potential. This work is intended to produce atomistic input into dislocation dynamics simulations of plastic flow localization in irradiated materials.