A theoretical study was made of positron states and annihilation characteristics at clean alkali metal surfaces. Positron surface states and positron work functions were calculated for the (100), (110), and (111) surfaces by using the modified superposed-atom method to account for discrete-lattice effects. The results were compared with those obtained for transition-metal surfaces. Stable positron surface states were found in all cases, with the Li states lying about 0.5eV below the bulk positron band, and with other alkali metals having positron surface states which were a few hundredths of an eV below the bulk bands. Results for the positronium activation energy and positronium work function were also presented. The surface and bulk lifetimes, and the probabilities that a positron trapped in a surface state would annihilate with core-level electrons were also calculated.

Positron States and Annihilation Characteristics at the (100), (110) and (111) Surfaces of Alkali Metals N.G.Fazleev, J.L.Fry, A.H.Weiss: Physical Review B, 1998, 57[19], 12506-19