bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Determination of Loop Nature in the Tem
Authors: Jenkins M. L. , Fukushima H. , Kirk M. A. 
Published: April 2011

AbstractWe have carried out systematic experiments to explore the range of applicability of the two direct methods which are available for the determination of the nature of small clusters. Experiments in heavy-ion irradiated silver and copper, including direct comparisons with the results of Black-White contrast analysis (B-W), forced us to the conclusion that use of the 21/2D technique for the analysis of faulted loops is effectively impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to investigate the nature of the clusters produced by room-temperature heavy-ion irradiation of copper. In-situ irradiations were performed in the Argonne HVEM-Tandem Facility using 40keV and 80keV Kr+ ions. Nearly all of the analysable first-layer loops were found to be vacancy in nature. Some deeper clusters were also certainly vacancy. There is no unequivocal evidence for interstitial loops under these conditions. The near impossibility of establishing that interstitial loops are not present is shown by the fact that a large fraction of loops - over 50% - could not be analysed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.
Microstructure of V-4Cr-4Ti Following Low Temperature Neutron Irradiation
Authors: Rice P. M. , Snead L. L. , Alexander D. J. , Zinkle S. J. 
Published: April 2011

AbstractThe V-4Cr-4Ti alloy displays excellent mechanical properties, including a ductile-to-brittle transition temperature (DBTT) below -200°C in the unirradiated condition. Specimens of this alloy were fission neutron-irradiated in the High Flux Beam Reactor (HFBR) at Brookhaven National Laboratory (BNL) to a dose of 0.4 dpa at temperatures from 100 to 275°C. Mechanical testing showed significant irradiation hardening in the alloy which increased with increasing irradiation temperature. Charpy impact testing also showed a dramatic increase in the DBTT on the order of 200 to 350°c. The mechanical property changes are correlated with preliminary results from the transmission electron microscopy (TEM) analysis of the defect microstructure resulting from the low-dose neutron irradiations. The TEM analysis of the irradiated material showed a nearly constant defect density of ∼1.6 × 1023 m−3, with an average defect diameter of slightly greater than 3 nm.
Modeling of Dislocation Loop Growth and Transient Enhanced Diffusion in Silicon for Amorphizing Implants
Authors: Gencer Alp H. , Dunham Scott T. 
Published: April 2011

AbstractIt has been observed that dislocation loops form and grow during annealing of silicon wafers implanted at doses above the amorphization threshold. Dislocation loops can act to store interstitials for prolonged periods of anneals, sustaining an interstitial super-saturation and thus causing substantial transient enhanced diffusion (TED). We have developed a comprehensive model which, in combination with a model and parameters for {311} defects from previous work, accounts for the formation and evolution of dislocation loops during ion implant annealing, as well as giving the correct TED behavior.
Nitrogen Vacancy Complexes in Nitrogen Irradiated Metals
Authors: Veen A.Van , Westerduin K. T. , Schut H. , Melker E. J. E. , Thijsse B. J. , Nielsen B. , Kumar P. Asoka , Ghosh V. J. , Lynn K. G. 
Published: April 2011

AbstractGas desorption and positron annihilation techniques have been employed to study the evolution of nitrogen associated defects in nitrogen irradiated metals: Fe, Ni, Mo and W. Nitrogen in these metals has a rather high affinity to vacancy type defects. The results obtained for low irradiation dose show that substitutional nitrogen (NV; with V=vacancy) is formed. The nitrogen vacancy complex dissociates at temperatures ranging from 350 K for Ni to 900K for Mo and 1100 K for W. At high doses defects are formed which can be characterized as nitrogen saturated vacancy clusters. These defects, as observed by helium probing, disappear during annealing for nickel at 800K, and for Mo at 1100 K. The direct observation of the desorbing nitrogen for nickel and molybdenum reveals a very fast desorption transient at the dissociation temperature of the clusters. This is the characteristic desorption transient of a small nitride cluster, e.g., by shrinkage with constant rate. For iron the nitrogen desorption is complicated because of a general background that continuously rises with temperature. With the positron beam technique depth information was obtained for defects in iron and the defect character could be established with the help of the information provided on annihilation with conduction and core electrons of the defect trapped positrons.
Irradiation-Induced Changes in the Mechanical Properties and Microstructures of Solution Annealed Austenitic Stainless Steel at Low to Intermediate Temperatures
Authors: Lucas G. E. 
Published: April 2011

AbstractThe evolution of the microstructure of solution annealed austenitic stainless steels irradiated by neutrons at temperatures less than 300°C is dominated by black spots and Frank loops. This leads to hardening and a degradation of ductility and work hardening accompanied by a loss of fracture toughness. Microscopic flow localization is attributed to the annihilation of loops by their interaction with moving dislocations. The resulting loss of work hardening can lead to flow localization on a macroscopic scale as well in the vicinity of notches, holes and cracks. The combination of macro and microscopic flow localization may have important implications to the failure modes available to structures and to irradiation-assisted stress corrosion cracking.
On the Composition and Structure of Nanoprecipitates in Irradiated Pressure Vessel Steels
Authors: Odette G. R. , Liu C. L. , Wirth B. D. 
Published: April 2011

AbstractNanoscale Cu rich precipitates (CRPs) are widely believed to be the dominant hardening feature resulting in severe embrittlement in irradiated reactor pressure vessel (RPV) steels. However, this view has recently been challenged by interpretations of atom probe field ion microscopy (APFIM) measurements that describe the dominant nanofeatures as dilute solute atmospheres (DSAs). The practical impact of these differing views is very significant. This work compares and contrasts the CRP versus DSA descriptions to a wide variety of pertinent data. Mechanical property trends as well as small angle neutron scattering (SANS) and field emission scanning transmission electron microscopy (FEGSTEM) measurements support the presence of CRPs. CRPs are also consistent with the fundamental thermodynamic and kinetic laws. However, standard theory cannot provide the atomic level resolution needed to fully understand the nanofeatures. Therefore, a new Lattice Monte Carlo (LMC) atomistic method is used to simulate the complex chemical structures of the CRPs. The LMC method unifies the SANS/FEGSTEM and APFIM data within a well founded physical framework.
Small Angle Neutron Scattering Modeling of Copper-Rich Precipitates in Steel
Authors: Spooner Stephen 
Published: April 2011

AbstractThe magnetic-to-nuclear scattering intensity ratio observed in the scattering from copper-rich precipitates in irradiated pressure vessel steels is much smaller than the value of 11.4 expected for a pure copper precipitate in iron. A model for precipitates in pressure vessel steels which matches the observed scattering typically incorporates manganese, nickel, silicon and other elements and it is assumed that the precipitate is non-magnetic. In the present work consideration is given to the effect of composition gradients and ferromagnetic penetration into the precipitate on the small angle scattering cross section for copper-rich clusters as distinquished from conventional precipitates. The calculation is an extension of a scattering model for micelles which consist of shells of varying scattering density. A discrepancy between recent SANS scattering experiments on pressure vessel stells was found to be related to applied magnetic field strength. The assumption of cluster structure and its relation to atom probe FIM findings as well as the effects of insufficient field for magnetic saturation is discussed.
Comparative Study on Intergranular Segregation of Sulfur and Phosphorus Induced During Neutron Irradiation And Thermal Ageing in Vanadium-20 WT.% Titanium Alloys
Authors: Bloomer T. E. , Lyu D. Y. , Kameda J. 
Published: April 2011

AbstractIntergranular impurity segregation induced during neutron irradiation (9.8 × 1024 n/mr at 438 °C) and thermal ageing has been studied in V-20 wt.% Ti alloys undoped, P doped and S doped all containing residual C and O. Neutron irradiation induced intergranular segregation and desegregation of S in undoped and S doped alloys, respectively. Thermal ageing resulted in a large increase in the S segregation in the undoped and S doped alloys. However, all unirradiated, aged and irradiated P doped alloys showed negligible S segregation. The vanadium alloys had smaller P segregation, compared to the S segregation in the undoped and S doped alloys. The irradiation and ageing enhanced the P segregation in a different fashion depending on the alloys. The grain boundary enrichment of C, O and Ti was reduced during the irradiation but promoted by the thermal ageing. The underlying mechanisms controlling intergranular impurity segregation caused by irradiation or thermal ageing are discussed in light of the impurity solubility change and dynamic interaction of defect and impurity fluxes.
Radiation-Induced Minor Element Segregation at Austenitic Stainless Steel Grain Boundaries
Authors: Simonen E. P. , Bruemmer S. M. 
Published: April 2011

AbstractMeasurement of minor element compositions at irradiated grain boundaries in austenitic stainless steels indicates that Si is the only element that significantly responds to radiation-induced segregation. Other minor elements, such as P or S, do not exhibit elevated grain boundary concentrations after irradiation. A rate theory evaluation of segregation is in accord with ioninduced Si enrichment, but reveals complexities in the interpretation of extrapolating behavior from ion-irradiation to neutron-irradiation behavior. The model calibrated to measured high-rate, ioninduced segregation greatly overestimates measured low-rate, neutron-irradiation segregation of Si.
Radiation-Induced Segregation of Metals At Moving SiO2-Amorphous Si Interfaces
Authors: Williams J. S. , Petravic M. , Conway M. , Short K. T. 
Published: April 2011

AbstractSecondary ion mass spectrometry and Rutherford backscattering/channeling analysis have been used to study the segregation of Au at moving Si-SiO2 interfaces during bombardment of Si with 15 keV O- ions. Essentially 100% of the Au is found to segregate at a bombardment temperature of 250°C, whereas only partial segregation occurs for room temperature bombardment. Up to 10 monolayers of Au can be segregated in disordered Si behind an SiO2 layer at 250°C. These results are discussed in terms of ion-assisted migration of Au in disordered Si and extremely low solubilities of Au in SiO2.
Threshold Irradiation Dose for Amorphization of Silicon Carbide
Authors: Snead L. L. , Zinkle S. J. 
Published: April 2011

AbstractThe amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electron and xenon irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface or strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be ∼0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1×10-3 dpa/s and with fission neutrons irradiated at 1×10-6 dpa/s irradiated to 1 5 dpa in the temperature range of ∼340 ±10K.
Hrtem of Extended Defects in Tl-2212 Thin Films
Authors: Newcomer P. P. , Venturini E. L. , Schöne H. , Doyle B. L. , Myers K. E. 
Published: April 2011

AbstractMany applications of high temperature superconductors, HTS, require the presence of lattice defects in the material structure to suppress the motion of magnetic vortices and enhance the critical current density, Jc. The microstructure of Tl2Ba2CaCu2O8-δ (T1–2212) thin films which have extended defects induced by high energy Au and Cu ion irradiation is studied using high resolution transmission electron microscopy, HRTEM, with slow scan digital imaging. In order to optimize the HTS properties and better analyze the consequent microstructural modification, the fluence is varied. At moderate fluences, resulting in ∼4% reduction of the superconducting transition, large enhancements of Jc, and vortex pinning potential are observed. The density and microstructure of isolated defects and surrounding structure will be discussed and compared to damage profiles calculated using the TRIM code. Correlation will be made between the HRTEM results and the changes in HTS properties.
Effects of Interstitial Clustering on Transient Enhanced Diffusion of Boron in Silicon
Authors: Solmi S. , Valmorri S. 
Published: April 2011

AbstractA simulation model for Boron diffusion which takes into account the aggregation of the excess interstitials in clusters, and subsequently, the dissolution of these defects, is proposed. The interstitial supersaturation and generation rate are determined according to the classical theory of nucleation and growth of particles, in analogy with the precipitation of a new phase in heavily doped silicon. The clusters are considered as precipitates formed by interstitial Si atoms. The B diffusion is modelled on the basis of the dopant-interstitial pair diffusion mechanism. The clusters dissolution during annealing maintains nearly constant, for a long period, the interstitial supersaturation and the related enhancement of the boron diffusion. This gives a good account of the diffusion results over a large range of experimental conditions. Furthermore, this approach describes most of the behavior of the transient enhanced diffusion (TED), like the temperature dependence of the level of the B diffusion enhancement, the dependence of the duration of the phenomenon on implanted dose, and the scarce dependence on the damage distribution in depth. The results of the simulations are compared with experimental data on the kinetics of interstitial cluster dissolution and of B TED.
Particle - Induced and Photo - Conductivities in Amorphous Si:H Under Proton Irradiation
Authors: Kishimoto N. , Amekura H. , Kono K. , Saito T. 
Published: April 2011

AbstractRadiation damage of amorphous Si (a- Si) under 17 MeV- proton bombardment has been studied, measuring particle- induced conductivity(PIC) and photoconductivity(PC). The in- situ measurements have been conducted to focus on the structural flexibility and the metastable nature, inherent in the amorphous structure. While the PC (with weak illumination) has a fast response and reversible nature, the PIC has a long time- constant ∼60 s, followed by a persistent conductivity for more than ∼103 s. Both the PIC and the PC remain fairly stable against further irradiation, comparing to crystalline Si (c-Si), but they decay in the higher fluence region. A large part of the decayed PC recovers after annealing at 450 K. The results of a- Si are compared with those of c- Si. It is suggested that, in the lower fluence region, a-Si is more resistant against proton irradiation than c- Si, relaxing the atomic displacements, and the excited conductivities gradually decay with accumulation of the dangling bonds.
1.8 MeV Electron Bombardment Induced Structural Changes on Graphite Surfaces Observed by Scanning Tunnelling Microscopy
Authors: Chen Y. J. , Wilson I. H. , Libin Lin , Xu J. B. 
Published: April 2011

AbstractHighly oriented pyrolitic graphite (HOPG) was irradiated with 1.8 MeV electrons at 45° and near grazing (86°) angles of incidence. For doses up to 1016 cm−2 the surface for the case of 45° incidence, observed by scanning tunnelling microscopy (STM), remained the same as the original sample showing only the usual periodic atomic corrugation. For near grazing incidence, at a dose of 5×10−2 cm−2, nm-hillocks are observed, some elongated along the direction of the beam incidence. These are attributed to the effects of single electron-carbon interactions in the top surface layers. At a dose of 5×1014 cm−2 (near grazing incidence) STM observations show an anomalously large (period 2.5 to 17 nm) superperiodicity superimposed on the normal 0.246 nm atomic spacing of graphite. This Moiré-like pattern suggests that the corrugations are electronic as well as topographic in origin. We propose that near grazing incidence electron irradiation causes a break-up of the surface layers into fragments, largely retaining the six-fold atomic rings, that rotate by a small angle resulting in the observed pattern by interaction with the deeper bulkstructure layers.
Ion Beam Injected Point Defects in Crystalline Silicon: Migration, Interaction and Trapping Phenomena
Authors: Priolo F. , Privitera V. , Coffa S. , Libertino S. 
Published: April 2011

AbstractOur recent work on the room temperature migration and trapping phenomena of ion beam generated point defects in crystalline Si is reviewed. It is shown that a small fraction (˜10−6) of the defects generated at the surface by a shallow implant is injected into the bulk. These defects undergo a long range trap-limited diffusion and interact with both impurities, dopants and preexisting defects along their path. In particular, these interactions result in dopant deactivation and/or partial annihilation of pre-existing vacancy-type defect markers. It is found that in highly pure, epitaxial Si layers, these effects extend to several microns from the surface, demonstrating a long range migration of point defects at room temperature. By a detailed analysis of the experimental evidences we have identified the Si self-interstitials as the major responsible for the observed phenomena. This allowed us to give a lower limit of 6 × 10−11 cm2/s for the room temperature diffusion coefficient of the Si self-interstitials. Room temperature trap-limited migration of vacancies is also detected as a broadening in the divacancy profile of as implanted samples. In this case the room temperature diffusion coefficient of vacancies has been found to be ≥3 × 10−12 cm2/s. These data are presented and their implications discussed.
A New Single-Crystal Adsorption Calorimeter for Determining Metal Adsorption and Adhesion Energies
Authors: Stuckless J. T. , Starr D. , Bald D. , Campbell Charles T. 
Published: April 2011

AbstractA microcalorimeter for measuring adsorption heats on clean single-crystal surfaces is described. The principle is similar to that pioneered by David King's group: A pulse of gas from a molecular beam adsorbs on an ultrathin single crystal's surface, causing a measurable transient heat input and temperature rise. Our novel heat detector is a 9 μm pyroelectric polymer ribbon, which is mechanically driven to make a gentle mechanical/thermal contact to the back of the singlecrystal sample during measurements. Advantages include use of thicker samples (>3 microns), sample preparation at very high temperatures, and measurements at 100 K. We have applied this to study the heats of adsorption of metals on clean, well-defined and single-crystalline oxide surfaces as a detailed function of coverage, from which we also extract the metal/oxide adhesion energy. We obtain pulse-to-pulse standard deviations of >2% for pulses containing >0.03 ML of Cu, and absolute accuracy within a few percent.
Micromechanical Deformation of Single-Crystal Alumina Surfaces
Authors: Zagrebelny Andrey V. , Nelson John C. , Carter C. Barry 
Published: April 2011

AbstractIn the present study, the micromechanical properties of single-crystal A12O3 have been tested using a micromechanical depth-sensing testing device. A series of microscratches are produced on the annealed {0001}, {1120} sapphire specimens of special geometry. The scratches were positioned in pre-selected crystallographic directions, determined with the backreflection Laue method X-ray diffraction method.The microscratch tracks were examined with transmission electron microscopy (TEM). The main emphasis in the analysis of deformation structure of sapphire has been placed on the correlation of irregularities observed on load-displacement curves to the extent of elastically deformed regions, nucleation of the dislocations on the surface, unique nature of the crack-dislocation networks associated the sapphire anisotropic deformation behavior.
Relating Polymer Indentation Behavior to Elastic Modulus Using Atomic Force Microscopy
Authors: Vanlandingham M. R. , Mcknight S. H. , Palmese G. R. , Eduljee R. F. , Gillespie J. W. , Mccullough R. L. 
Published: April 2011

AbstractThe atomic force microscope (AFM) has become a popular tool for characterizing surfaces of many different types of materials. In this paper, an AFM is used to probe the mechanical properties of polymer samples through examination of force curves produced during tip-sample contact and indentation. Three types of cantilever probes with spring constants estimated to be 1–5 N/m, 20–100 N/m, and 400–500 N/m respectively, were used to study different polymer samples with known modulus values ranging from 20 MPa to 3 GPa. A technique is developed that relates the measured sample response to elastic modulus, and illuminates the importance of the relative stiffnesses of the cantilever probe and the sample to the material response.
Deformation of Polymer Films by Bending Forces
Authors: Heermann D.W. , Linke A. , Pätzold G. , Hapke T. 
Published: April 2011

AbstractWe study the deformation of nano-scale polymer films which are subject to external bending forces by means of computer simulation. The polymer is represented by a generalized bead-spring-model, intended to reproduce characteristic features of n-alkanes. The film is loaded by the action of a prismatic blade which is pressed into the polymer bulk from above and a pair of columns which support the film from below. The interaction between blade and support columns and the polymer is modeled by the repulsive part of a Lennard-Jones potential. For different system sizes as well as for different chain lengths, this nano-scale experiment is simulated by molecular dynamics methods. Our results allow us to give a characterization of deformed states for such films. We resolve the kinetic and the dynamic stage of the deformation process in time and access the length scale between discrete particle and continuum mechanics behavior. For the chain lengths considered here, we find that the deformation process is dominated by shear.