Profiling multilayer structures with monoenergetic positrons

Abstract

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