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On the application of the weak-beam technique to the determination of the sizes of small point-defect clusters in ion-irradiated copper.

Description: We have made an analysis of the conditions necessary for the successful use of the weak-beam technique for identifying and characterizing small point-defect clusters in ion-irradiated copper. The visibility of small defects was found to depend only weakly on the magnitude of the beam-convergence. In general, the image sizes of small clusters were found to be most sensitive to the magnitude of Sa with the image sizes of some individual defects changing by large amounts with changes as small as 0.025 nm{sup {minus}1}. The most reliable information on the true defect size is likely to be obtained by taking a series of 5-9 micrographs with a systematic variation of deviation parameter from 0.2-0.3 nm{sup {minus}1}. This procedure allows size information to be obtained down to a resolution limit of about 0.5 nm for defects situated throughout a foil thickness of 60 nm. The technique has been applied to the determination of changes in the sizes of small defects produced by a low-temperature in-situ irradiation and annealing experiment.
Date: October 30, 1998
Creator: Jenkins, M. L.
Partner: UNT Libraries Government Documents Department

In-situ observations of point-defect precipitation at dislocations in electron-irradiated silver

Description: In-situ weak-beam observations of the development of electron irradiation damage at dislocations in silver are described. Dislocations constrict and promote in their vicinity the formation of stacking-fault tetrahedra. The possibility that these are of interstitial nature is discussed.
Date: September 1, 1986
Creator: Jenkins, M.L.; Hardy, G.J. & Kirk, M.A.
Partner: UNT Libraries Government Documents Department

Collapse of defect cascades to dislocation loops during self-ion irradiations of Fe, Ni and Cu at 30, 300 and 600/sup 0/K

Description: The formation of dislocation loops by self-ion irradiations of Fe, Ni and Cu has been studied in situ in the ANL High-Voltage Electron Microscope as functions of ion dose and irradiation temperature. At low doses (less than or equal to 10/sup 12/ ions/cm/sup 2/) at room temperature individual cascades were observed to collapse to vacancy dislocation loops in Cu with high probability, in Ni with lower probability, and in Fe with zero probability. Cascade collapse was observed at low doses at 30/sup 0/K in Cu and Ni, but at rates less than their respective rates at room temperature. A loop formation rate for Ni at 600/sup 0/K is also reported. At higher doses (>10/sup 13/ ions/cm/sup 2/) where overlap of cascades becomes significant, loops were first observed in Fe and with a supra-linear build-up with dose. Also at higher doses a decrease in loop production rate in Cu and Ni was observed due to loop coalescence. The materials and temperature dependence of cascade collapse probabilities are suggested to be related to thermal spike mechanisms during the cascade formation lifetime.
Date: February 1, 1986
Creator: Kirk, M.A.; Robertson, I.M.; Vetrano, J.S.; Jenkins, M.L. & Funk, L.L.
Partner: UNT Libraries Government Documents Department

Collapse of defect cascades to dislocation loops in Cu/sub 3/Au

Description: TEM and ordered Cu/sub 3/Au were employed to measure the probability of dislocation loop formation as functions of irradiating ion mass (Ar/sup +/, Cu/sup +/ and Kr/sup +/), energy (50 and 100 keV), and irradiation temperature (30 and 300/sup 0/K). Disordered zones were produced at every defect cascade site and imaged in dark-field superlattice reflections. Dislocation loops were imaged in fundamental reflections in the same sample areas to produce an accurate measurement of the probability of the collapse of each cascade to a dislocation loop, within a large set (approx.200) of defect cascades for each irradiation condition. The size distributions of dislocation loops and disordered zones were also measured. Defect cascades collapse to dislocation loops with significant probability (approx.0.5) even at 30/sup 0/K. Other observations include an increasing collapse probability with increasing cascade energy density (increasing ion mass) and with increasing sample irradiation temperature. However, no additional collapse was observed upon annealing from 30 to 300/sup 0/K, and no increase in collapse probability was observed upon increasing the bombarding ion energy from 50 to 100 keV. Disordered zone sizes also increased with increasing ion mass and with increasing sample irradiation temperature (30 to 300/sup 0/K).
Date: February 1, 1986
Creator: Black, T.J.; Jenkins, M.L.; English, C.A. & Kirk, M.A.
Partner: UNT Libraries Government Documents Department

In-situ observations of the development of heavy-ion damage in semiconductors

Description: In-situ observations on ion-beam induced amorphisation of GaAs, GaP and Si are reported. Direct-impact amorphisation was found to occur in GaAs irradiated with 100-keV Xe/sup +/ ions to low doses at low temperature (approx. 40K) in contrast to previous room temperature irradiations. In GaP and in silicon, where heavy projectiles do cause direct impact amorphisation at room temperature, the evolution of the damage structure with ion-dose was studied. The defect yield both in GaP irradiated with 100-keV Kr/sup +/ ions and in Si irradiated with 100-keV Xe/sup +/ ions was found to decrease monotonically with increasing dose over the dose range 10/sup 15/ to 10/sup 17/ ions m/sup -2/.
Date: January 1, 1985
Creator: Jenkins, M.L.; Chandler, T.J.; Robertson, I.M. & Kirk, M.A.
Partner: UNT Libraries Government Documents Department

On the determination of loop nature in the TEM

Description: The two direct methods available for determining the nature of small clusters, were studied. Experiments in heavy-ion irradiated Ag and Cu, including comparisons with Black-White contrast analysis (B-W), forced us to conclude that use of the 2-1/2D technique for analysis of faulted loops is impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to study the clusters produced by RT heavy-ion irradiation of Cu. In-situ irradiations were performed in Argonne HVEM-Tandem Facility using 40 and 80 keV Kr{sup +} ions. Nearly all the analysable first-layer loops were vacancy in nature. Some deeper cluster 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 analyzed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.
Date: January 1, 1997
Creator: Jenkins, M.L.; Fukushima, H. & Kirk, M.A.
Partner: UNT Libraries Government Documents Department

Collapse of defect cascades to dislocation loops

Description: We review a number of experiments that we have recently performed to investigate the collapse of defect cascades to dislocation loops. This important ion and neutron irradiation phenomenon has been studied with in situ ion bombardment in the Argonne National Laboratory High Voltage Electron Microscope-Ion Accelerator Facility at temperatures of 30 and 300/sup 0/K in Cu/sub 3/Au, Cu, and Fe, and 30, 300 and 600/sup 0/K in Ni. These experiments have demonstrated that individual defect cascades collapse to dislocation loops athermally at 30/sup 0/K in some materials (Ni, Cu and Cu/sub 3/Au), while in another material (Fe) only overlapped cascades produced dislocation loops. A slight sensitivity to the irradiation temperature is demonstrated in Cu/sub 3/Au and Fe, and a strong dependence on the irradiation temperature is seen in Ni. This phenomenon of cascade collapse to dislocation loops in metals at 30/sup 0/K provides an understanding for previous neutron irradiation data. The more detailed dependencies of the collapse probability on material, temperature, bombarding ion dose, ion energy and ion mass contribute much information to a thermal spike model of the collision cascade which we will describe.
Date: April 1, 1986
Creator: Kirk, M.A.; Robertson, I.M.; Jenkins, M.L.; English, C.A.; Black, T.J. & Vetrano, J.S.
Partner: UNT Libraries Government Documents Department

Contributions of inelastically scattered electrons to defect images.

Description: We have made measurements of the contribution of inelastically scattered electrons to images of dislocations in Ni{sub 3}Ga and nanometer-sized defects in ion-irradiated Au under weak-beam dark-field diffraction conditions [1]. The purpose is to determine the conditions for data acquisition required to eventually make detailed and quantitative comparisons to simulations of images for various defect models, thus determining defect structure, composition, and local strain field. Such image simulations usually consider only elastically scattered electrons, and thus it is important to understand and possibly eliminate the contribution of inelastically scattered electrons to the experimental images for quantitative comparisons with image simulations. Experimental data have been acquired with either JEOL 2010F or 3000F microscopes, both equipped with Gatan Imaging Filter electron spectrometers. Samples examined in the 2010F were Au, ion-irradiated to low dose (10{sup 11}Kr ions at 1 MeV energy) to form individual defects (1-10nm sized Frank dislocation loops and partial stacking fault tetrahedra). Samples examined in the 3000F were Ni{sub 3}Ga with long dislocation defects. Imaging conditions included weak-beam dark-field with deviation parameter generally > 0.2 nm{sup -1}. Energy filter slit width was set to 10 eV and centered on the zero loss peak in both instruments to obtain images produced by elastically scattered electrons. In the Au experiment an energy window was also set to image the 10-40 eV loss range to investigate the contribution to the defect images of plasmon-loss electrons. Electron intensity in defect images and backgrounds was measured by summing pixel values in appropriately sized rectangles using Digital Micrograph (Gatan) software.
Date: March 5, 2002
Creator: Kirk, M. A.; Twesten, R.; Martin, S. P.; Hetherington, C. J. D. & Jenkins, M. L.
Partner: UNT Libraries Government Documents Department

The interaction of HVEM-generated point-defects with dissociated dislocations

Description: This paper describes experiments we have performed to investigate the mechanisms of interaction of IIVEM-generated point-defects with dissociated dislocations in a series of austenitic Fe-Ni-Cr alloys and review earlier work in Cu-Al alloys and in Ag. In the Fe-Ni-Cr alloys interstitial climb was observed only at favorable sites such as pre-existing jogs, while vacancies clustered near dislocations to form stacking-fault tetrahedra. These observations are similar to those in Ag; the complex climb mechanisms seen in Cu-Al alloys were not found. The differences between materials is believed to be due to differences in the case of interstitial pipe diffusion. 28 refs., 9 figs.
Date: May 1, 1991
Creator: King, S.L.; Jenkins, M.L. (Oxford Univ. (UK). Dept. of Materials); Kirk, M.A. (Argonne National Lab., IL (USA)) & English, C.A. (AEA Thermal Reactor Services, Harwell (UK). Materials and Chemistry)
Partner: UNT Libraries Government Documents Department

The interaction of point defects with line dislocations in HVEM (high voltage electron microscope) irradiated Fe-Ni-Cr alloys

Description: This paper presents results of a study of the interaction of point defects produced by high voltage electron microscope (HVEM) irradiation with pre-existing dislocations in austenitic Fe-15% 25%Ni-17%Cr alloys, aimed at the determination of the mechanisms of climb of dissociated dislocations. Dislocations were initially characterized at sub-threshold voltages (here 200kV) using the weak-beam technique. These dislocations were then irradiated with 1MeV electrons in the Argonne HVEM before being returned to a lower voltage microscope for post-irradiation characterization. Interstitial climb was seen only at particularly favorable sites, such as pre-existing jogs, whilst vacancies clustered near dislocations, forming stacking fault tetrahedra (SFT). Partial separations were also observed to have decreased after irradiation. The post-irradiation configuration was found to depend strongly on both dislocation character and pre-irradiation dislocation configuration. These results, and their relevance to the void swelling problem, are discussed. 52 refs., 8 figs.
Date: May 1, 1990
Creator: King, S.L.; Jenkins, M.L. (Oxford Univ. (UK). Dept. of Materials); Kirk, M.A. (Argonne National Lab., IL (USA)) & English, C.A. (UKAEA Harwell Lab. (UK). Materials Development Div.)
Partner: UNT Libraries Government Documents Department

Weak-beam imaging of dissociated dislocations in HVEM-irradiated Fe-Ni-Cr alloys

Description: We report here on studies by weak-beam electron microscopy of the evolution of microstructures at and near preexisting line dislocations in a number of Fe-Ni-Cr alloys under electronirradiation in a high-voltage electron microscope (HVEM). The detailed observations are discussed in terms of dislocation climb mechanisms in these materials and a model based on interstitial pipe diffusion.
Date: June 1, 1992
Creator: King, S.L.; Jenkins, M.L.; Kirk, M.A. (Oxford Univ. (United Kingdom). Dept. of Materials) & English, C.A. (AEA Reactor Services, Harwell (United Kingdom). Harwell Lab.)
Partner: UNT Libraries Government Documents Department