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Secondary Ions Produced by Low‐energy Impact of He + and Ne + ions on van der Waals Thin Films
Author(s) -
Sato T.,
Shimizu A.,
Nakamura K.,
Hiraoka K.
Publication year - 1997
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/(sici)1097-0231(19970630)11:10<1139::aid-rcm946>3.0.co;2-1
Subject(s) - chemistry , ion , van der waals force , thin film , analytical chemistry (journal) , dissociation (chemistry) , reflectron , sputtering , silicon , molecule , atomic physics , ionization , time of flight mass spectrometry , nanotechnology , materials science , chromatography , physics , organic chemistry
Secondary ions produced by low‐energy He + and Ne + ion impact on van der Waals solid thin films deposited on a silicon substrate were measured as a function of film thickness using a reflectron‐type time‐of‐flight mass spectrometer. The intensities of secondary ions N + and N 3 + produced by 400 eV He + impact on an N 2 film were found to reach a plateau with deposition of a 5 monolayer (ML)‐thick sample. In contrast, the Ar + ion formed by 400 eV He + impact on an Ar film showed a gradual increase with increase of the film thickness from 1 to 20 ML. This observed marked difference is mainly due to the fact that a considerable amount of energy of the incident He + ions is dissipated by the bond dissociation of N 2 in the solid N 2 target whereas it is mainly dissipated via electronic excitation and momentum transfer in the impact on solid Ar. For a sample consisting of an Ar film deposited on a 30 ML‐thick N 2 film, the intensity of the N 2 + ion originating from the underlying N 2 film was found to be nearly independent of the Ar film thickness between 1 ML and 20 ML. It seems likely that the hot spike produced by He + impact in the Ar film vaporizes the N 2 molecules in the underlying N 2 film and that vaporized N 2 molecules are ionized by charge‐transfer reaction with the pre‐formed Ar + in the spike. © 1997 John Wiley & Sons, Ltd.