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Browsing by Author "Grabowski, Kenneth"

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    X‐ray diffraction analysis of concentration and residual stress gradients in nitrogen‐implanted niobium and molybdenum
    Rao, Satish I.; He, Baoping; Houska, Charles R.; Grabowski, Kenneth (American Institute of Physics, 1991-06-15)
    Large biaxial residual strains are developed after a 5-at.% implantation of N into Nb and Mo. The results indicate that the dominant source of internal strain arises from N located in interstitial sites. For Nb implanted at liquid-nitrogen temperature, the N atoms are located in octahedral sites. However, the data allow for some clustering as di- or tri-interstitials at the highest concentration (approximately 5 at. % N). Radiation damage is present as small vacancy and interstitial loops. Since vacancies and self-interstitials are present in nearly equal concentrations, the overall bulk dilatation cancels. However, because of their small size, a lesser core expansion has been included as a correction to the overall residual strain. Although one can obtain an estimate of the N distribution from TRIM, a more accurate description must include the distribution of knock-on energy. The latter has an important influence on the redistribution of N relative to that predicted by TRIM. Both host lattices (Nb and Mo) behave like "rigid containers" in directions parallel to the free surface and give a magnified elastic response normal to the free surface.
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    X‐ray diffuse scattering from a nitrogen‐implanted niobium film
    Rao, Satish I.; Houska, Charles R.; Grabowski, Kenneth; Ice, Gene E.; Sparks, C. J. (American Institute of Physics, 1991-06-15)
    A 2500-angstrom niobium single-crystal film was deposited onto a sapphire substrate and subsequently implanted with nitrogen to an average concentration of 0.5 at. %. Synchrotron radiation was used to measure the difference between the implanted and an unimplanted film to isolate the diffuse scattering from the implanted film near two Bragg reflections. This diffuse intensity arises mainly from elastic displacement fields about radiation-damage-related loops located on (211) planes. A small contribution of the scattering is calculated from the displacements about single interstitial nitrogen in octahedral sites. The Burgers vector of the loops is along the [111BAR] direction and makes an angle of 62-degrees with the loop plane giving a dominant shear component. Vacancy loops have a radius approximately 5 angstrom while interstitials are somewhat larger ranging from 10 to 15 angstrom. The number of vacancies and interstitials are nearly the same.