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Abstract:
The reneutralization process of field ions created by electron-stimulated field desorption (ESFD) is investigated by a newly developed experimental method called field ion pair spectroscopy (FIPS). In contrast to field-free electron-stimulated desorption very high cross sections σ are reported in the presence of an extremely high external electric field for the ESFD of noble gases such as helium and neon. Cross sections are in the range of σ ≈ 10-16 cm2. Especially for neon a detailed investigation of the reneutralization process as a function of the applied electric field has been performed. The results show that at low field strength (F < 40 V/nm) the probability for reneutralization of Ne+ ions is significantly higher than at high fields (F > 40 V/nm). The experimental observations are discussed in terms of a two step Menzel-Gomer-Redhead desorption model. The high cross sections in the electric field are due to the very short field-dependent escape times. The ions created by ESFD leave the reneutralization zone in front of the surface before reneutralization via electron tunneling from the metal into the ion can occur. The time for escape was calculated for an applied field strength to be only a few 10-14 s.
