Nitrogen diffusion parameters in ion-implanted tungsten single crystals

Abstract

Diffusion of nitrogen implanted in single-crystal tungsten was studied in the temperature range 700–820° C. Measurements were carried out using a method of nondestructive determination of diffusivities (developed by the authors) from the dynamics of variation in the surface impurity concentration. The initial distribution and diffusion profiles for various annealing times were determined by secondary ion mass spectrometry. The relative surface concentration of nitrogen was measured by Auger electron spectroscopy. Several fluxes of impurity atoms in the surface region of ion-doped tungsten were experimentally detected to exist. Under the assumption that the fluxes interact with each other, the temperature dependences of the nitrogen diffusivities in the flux associated with dislocations generated by ion implantation and in the flux associated with the bulk diffusion mechanism were determined. Nitrogen diffusion is characterized by a rather low activation energy, namely, 0.15 and 0.75 eV for dislocation and bulk mechanisms, respectively.