PHOTON-STIMULATED EJECTION OF ATOMS FROM ALKALI-HALIDE NANOCRYSTALS

Interband excitation of single alkali-halide nanocrystals, in the form of mass-selected M(n+/-1)X(n)+/-beams (M = K,Cs and X = Br,I), by ultraviolet radiation leads exclusively to halogen-atom emission with large cross section. The final state is a midgap (F-center) state. A pathway consisting of direct ejection of a photoneutralized surface atom is derived from a band picture using the computed energetics of the (3,3,3) nanocrystal M14X13+. This mechanism is contrasted with photon-stimulated desorption from crystal surfaces, and related to formation of surface defect states and metallized overlayers.