EVIDENCE FOR RENEUTRALIZATION OF FIELD IONS GENERATED BY ELECTRON-STIMULATED FIELD DESORPTION

The reneutralization process of field ions created by electron-stimula ted field desorption (ESFD) is investigated by a newly developed exper imental method called field ion pair spectroscopy (FIPS). In contrast to field-free electron-stimulated desorption very high cross sections sigma are reported in the presence of an extremely high external elect ric field for the ESFD of noble gases such as helium and neon. Cross s ections are in the range of sigma almost-equal-to 10(-16) cm2. Especia lly for neon a detailed investigation of the reneutralization process as a function of the applied electric field has been performed. The re sults show that at low field strength (F < 40 V/nm) the probability fo r reneutralization of Ne+ ions is significantly higher than at high fi elds (F > 40 V/nm). The experimental observations are discussed in ter ms of a two step Menzel-Gomer-Redhead desorption model. The high cross sections in the electric field are due to the very short field-depend ent escape times. The ions created by ESFD leave the reneutralization zone in front of the surface before reneutralization via electron tunn eling from the metal into the ion can occur. The time for escape was c alculated for an applied field strength to be only a few 10(-14) s.