Variable-energy (0–25 keV) positron stopping and annihilation behavior is studied in a multilayer structure, which has subsequent (∼3000-Å-thick) ZnS and ${\mathrm{Al}}_2$${\mathrm{O}}_3$ layers on a glass substrate. Direct information on positron slowing-down properties is obtained. The positron implantation profile is shown to possess the shape of a derivative of a Gaussian function, in contrast to the more commonly used exponential profile. The mean positron penetration depth varies with incident positron energy E (in keV) as z¯=[4.0(3) μg/${\mathrm{cm}}^2$](E${)}^{1.62\left(5\right)\mathrm{}}$. The feasibility of the present technique for depth profiling of heterogeneous samples is considered. The accuracy of determining the positions of the interfaces is typically less than 100 Å in the present system. The mobility of positrons in ZnS and ${\mathrm{Al}}_2$${\mathrm{O}}_3$ layers is observed to be very low. This corresponds to positron trapping into structural defects with a relatively high concentration.

• Received 25 September 1986

DOI:https://doi.org/10.1103/PhysRevB.35.4606