We present the results of a comparative study of Cl adsorption on Ag(111) by He+ISS and other methods, as well as a study of the He+neutralization rate. Workfunction and time of flight spectroscopy measurements show that Cl adsorption occurs rapidly in the 0-1.2 L range, and thereafter saturates. He+ISS illustrates the appearance of Cl at low exposures, but the signal remains very weak until about 1.5 L, when the Cl to Ag ISS peak ratio increases strongly. Measurements of He+neutralization indicate an increase in neutralization in the initial stages of adsorption, and then a decrease at exposures above 1.5 L, which we relate to AgCl island formation. The enhanced neutralization in the submonolayer chemisorption range explains the low ISS signal corresponding to Cl. We associate the increase to a lower neutralization on AgCl. The efficiency of Cl detection is thus environment dependent.
Casagrande, M., Lacombe, S., Guillemot, L., & Esaulov, V. A. (2000). On low energy ion scattering spectroscopy and chlorine adsorption on silver. Surface Science, 445(1). https://doi.org/10.1016/S0039-6028(99)01063-8