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Nitrogen Vacancy Complexes in Nitrogen Irradiated Metals

Published online by Cambridge University Press:  15 February 2011

A.Van Veen
Affiliation:
Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, NL 2629JB, Delft.
K. T. Westerduin
Affiliation:
Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, NL 2629JB, Delft.
H. Schut
Affiliation:
Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, NL 2629JB, Delft.
E. J. E. Melker
Affiliation:
Materials Science, Delft University of Technology, Rotterdamseweg 137, NL 2628AL, Delft.
B. J. Thijsse
Affiliation:
Materials Science, Delft University of Technology, Rotterdamseweg 137, NL 2628AL, Delft.
B. Nielsen
Affiliation:
Brookhaven National Laboratory, Upton, N.Y. 11973–5000.
P. Asoka Kumar
Affiliation:
Brookhaven National Laboratory, Upton, N.Y. 11973–5000.
V. J. Ghosh
Affiliation:
Brookhaven National Laboratory, Upton, N.Y. 11973–5000.
K. G. Lynn
Affiliation:
Brookhaven National Laboratory, Upton, N.Y. 11973–5000.
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Abstract

Gas 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.

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Type
Research Article
Copyright
Copyright © Materials Research Society 1997

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