The Role of Excitons in Electron- and Photon-Stimulated Desorption of Alkali Halides: An Energy and Spin-state Resolved Study of KI(100)

Low-energy (5 ˆ 30 eV) electron- and ultraviolet (5 ˆ 6.4 eV) photon-stimulated desorption of KI(100) single crystals yields I 2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the ((3/2)-exciton long wavelenght edge. Exciton decay at the surface directly produces I 2P3/2 and 2P1/2 with hyperthermal velocity and in competition with self-trapping. Spin memory of the (ˆexciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides.