EVIDENCE OF AGING EFFECTS IN SPUTTERED ZRN FILMS FROM POSITRON-ANNIHILATION

The lifetime of positrons in a lattice is strongly affected by structu ral defects even if the concentration of the latter is well beyond the limit of detection by classical methods. The lack of a repulsive cent er in a vacancy acts as a trap for the positron which then annihilates itself with reduced probability due to the lower electron density at this site. The existence of a component longer than the bulk annihilat ion thus reflects the presence of vacancies. The behavior of this long -lived component in ZrN films sputtered onto stainless steel substrate s was monitored over a period of 18 months. During this time, its valu e decreased steadily by a factor of 2-3 depending on the negative bias used during the sputtering. No significant changes in the color were observed during the measurements. A consistent explanation is the brea kup of polyvacancies or voids leading to a higher concentration of mon ovacancies. (C) 1997 American Vacuum Society.