| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS1-ThM |
| Session: | Advances in Surface Analysis |
| Presenter: | D.A. Brenes, The Pennsylvania State University |
| Authors: | D.A. Brenes, The Pennsylvania State University D.G. Willingham, The Pennsylvania State University Z. Postawa, Jagiellonian University, Poland N. Winograd, The Pennsylvania State University |
| Correspondent: | Click to Email |
The temperature dependence in the molecular desorption of coronene films stimulated by 20-keV Au1+, Au3+, and C60+ projectiles were experimentally investigated by means of strong field laser photoionization coupled with time-of-flight secondary neutral mass spectrometry (ToF-SNMS) at 300 K and 77 K. The sputtering dynamics of highly energetic ion beams with surfaces have always been assumed to be temperature independent. However, recent data indicate this might not be the case for high energy cluster ion beams.
At 300 K, the kinetic energy distributions of ion beam desorbed coronene neutral molecules are projectile independent. The molecular desorption events stimulated by either projectile are ejected with a most probable translational energy of approximately 0.1 eV and show negligible differences in the high-energy component of the distribution when comparing the projectiles. However, at 77 K the most probable translational energy of ejection is shifted to higher energies as a result of cluster ion bombardment. A most probable translational energy of 0.5 eV is observed when using cluster projectiles such as 20-keV C60+. Fragments created by the C60 cluster ion sputtering dynamics are detected as low mass fragments at 300 K and exhibit a Maxwell-Boltzmann distribution. This behavior is not evident at 77 K or induced by the other projectiles.
In addition, by comparing the molecular to fragment ion (M/F) signal ratio of well known polyaromatic hydrocarbon photofragments, coronene molecules ejected by 20-keV Au1+ exhibit internal energies of sufficient magnitude to reach high energy fragmentation pathways resulting in photodissociation. Similarly, those that were desorbed by 20-keV C60+ not only have lower internal energies but the M/F signal ratios are enhanced at 77 K. This investigation suggests the desorption of coronene molecules by C60 primary ions is dependent on temperature and neutral molecules are ejected with low internal energies under cryogenic conditions.