Abstract
The formation of molecular secondary ions released from a Coronene film under irradiation with a 20-keV C60+ ion beam is investigated using combined time-of-flight Secondary Ion and Neutral Mass Spectrometry (ToF-SIMS/SNMS). More specifically, the charge state distribution of intact sputtered coronene molecules M is investigated by comparing the yield of molecular ions M+ with that of their neutral counterparts M0, with the latter being post-ionized after their ejection from the surface using single photon ionization in a pulsed vacuum-ultraviolet laser beam. A quantitative determination of the molecular ionization probability from such experiments requires precise information regarding the post-ionization efficiency as well as the laser induced photofragmentation of the sputtered neutral molecules, which is obtained from the laser intensity dependence of the measured ToF spectra. In order to assess the role of internal excitation encompassed during the sputter ejection process, the results obtained for sputtered molecules are compared with those obtained for thermally evaporated coronene molecules. As a result, we find an ionization probability of sputtered intact coronene molecules of the order of 10−3, which confirms previous data obtained in a similar experiment using a fundamentally different post-ionization scheme.
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