Secondary Ions Produced by Low-energy Impact of He+ and Ne+ ions on van der Waals Thin Films
✍ Scribed by T. Sato; A. Shimizu; K. Nakamura; K. Hiraoka
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 187 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0951-4198
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✦ Synopsis
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.