Abstract

We report on a new time-of-flight (TOF) spectrometer designed to investigate sputtering phenomena induced by swift heavy ions in the electronic stopping regime. In this experiment, particular emphasis is put on the detection of secondary ions along with their emitted neutral counterparts in order to examine the ionization efficiency of the sputtered material. For the detection of neutral species, the system is equipped with a pulsed VUV laser for post-ionization of sputtered neutral atoms and molecules via single photon ionization at a wavelength of 157nm (corresponding to 7.9eV photon energy). For alignment purposes and in order to facilitate comparison to nuclear sputtering conditions, the system also includes a 5keV Ar+ ion beam directed to the same sample area. The instrument has been added to the M1-branch beam line at the German accelerator facility in Darmstadt (GSI) and was tested with 4.8MeV/u Au26+ ions impinging onto various samples including metals, salts and organic films. It is found that secondary ion and neutral spectra obtained under both bombardment conditions can be acquired in an interleaved manner throughout a single accelerator pulse cycle, thus making efficient use of valuable beam time. In addition, the keV ion beam can be intermittently switched to dc mode between subsequent data acquisition windows and accelerator pulses in order to ensure reproducible surface conditions. For the case of a dynamically sputter cleaned metal surface, comparison of secondary ion and neutral signals obtained under otherwise identical instrumental conditions reveals a nearly identical ionization probability of atoms emitted under electronic and nuclear sputtering conditions.

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