| AVS 65th International Symposium & Exhibition | |
| Applied Surface Science Division | Tuesday Sessions |
| Session AS-TuA |
| Session: | The Impact of Modeling (Ion, Electron) and Data Analysis on Applied Surface Science, a Celebration of the Career of Barbara Garrison |
| Presenter: | Lars Breuer, Universität Duisburg-Essen, Germany |
| Authors: | L. Breuer, Universität Duisburg-Essen, Germany A. Wucher, Universität Duisburg-Essen, Germany N. Winograd, The Pennsylvania State University |
| Correspondent: | Click to Email |
The implementation of cluster ion sources in secondary ion mass spectrometry (SIMS) opened the field to molecular imaging and depth profiling of organic materials. In the last years the trend to larger projectiles continued and led to gas cluster ion beams (GCIB) with projectiles consisting of thousands of atoms. The use of these projectiles not only reduces the chemical damage produced by the projectile impact and therefor preserves the molecular information, but also significantly increases the sputter yield of organic material. For the measured signal in a ToF-SIMS experiment the secondary ion yield is of greater interest. Here describes the probability that an intact quasi-molecular ion of species i is formed during the sputtering process. As for inorganics especially metals a long list of values for ionization probabilities has been reported in the literature only very little is known about ionization probabilities of organic molecules in particular under GCIB bombardment.
The knowledge of ionization probabilities and sputter yields is of great general importance. Not only is the process of ion formation not fully understood yet, but also can manipulating the ionization probability increase the sensitivity of the experiment. Possible approaches for such manipulations are changes is projectile size, kinetic energy and chemistry. The important question here is: “How much headroom is left to produce more secondary ions?”
To answer this question a measurement of the ion fraction in the flux of sputtered material is necessary. Such a measurement requires the direct comparison of the sputtered intact secondary (quasi-) molecular ion and its neutral counterparts. To perform such a measurement post-ionization without severe photo-fragmentation has to be performed. In our measurements we used a strong-field post-ionization scheme due to its universality and low fragmentation. In the past our lab performed this kind of measurements on material sputtered under C60 bombardment [1,2] which has been extended to the bombardment with GCIB in this study. As a result, we will compare ionization probabilities of sputtered molecular species under GCIB and C60 bombardment.
[1] Popczun, N.J., Breuer, L., Wucher, A. and Winograd, N., J. Am. Soc. Mass Spectrom. (2017) 28: 1182.
[2] Popczun, N.J., Breuer, L., Wucher, A. and Winograd, N., J. Phys. Chem. C 2017 121 (16), 8931-8937.