Field-assisted photodesorption of He, Ne, Ar, Kr and CO ions from W

The electric field dependence of the photodesorption yield of several noble gases from a tungsten surface was studied. Above a threshold field the desorption rate of ions increased until the field reached a characteristic value, which corresponds closely to the “best image field” observed for the respective gas in field ion microscopy. At still higher fields, the rate of photodesorption decreased rapidly. The intensity of the desorption signal increased in the order Kr ⪡ Ar < Ne ≈ He. Much less influence of field strength was found with a strongly chemisorbed species, CO