Chemisorptive electron emission versus sticking probability - art. no. 045407

The chemisorption of N2O on thin Cs films has been studied by monitoring th e time evolution of the sticking probability as well as the kinetics of the low-energy electron emission. By combining the data sets, two time domains become distinguishable: the initial chemisorption stage is characterized b y a high sticking probability (0.1 < S < 1) and by a rather weak low-energy electron emission. The opposite is the case within the late stage where th e chemisorption saturates, a very intense electron emission is accompanied by the negligibly low sticking probability of less than 0.01. Such evident anticoincidence between the exoemission and the chemisorption excludes the model of surface harpooning as the elementary process responsible for the e lectron emission in the late chemisorption stage. A long-term emission deca y has also been observed after turning off the flux of chemisorbing molecul es. A model is proposed that attributes both, the late chemisorptive and th e nonchemisorptive electron emission to the relaxation of a narrow state or iginated from an oxygen vacancy in the Cs oxide layer terminating the surfa ce. The presence of such a state has been confirmed by the metastable de-ex citation spectroscopy [MDS, He*(2(1)S)].