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SIMS21, Poland 2017 - Tingting Fu abstract

Tingting Fu oral presentation (FN1-Mon3-2-6)

Internal energy distribution of secondary ions under argon and bismuth cluster bombardments

Tingting Fu1,2, David Touboul2, Serge Della-Negra1, Alain Brunelle2

1 Institut de Physique Nucléaire, UMR8608, IN2P3-CNRS - Université Paris-Sud, Université Paris-Saclay, 15 rue Georges CLEMENCEAU, 91406 Oray, France
2 Institut de Chimie des Substances Naturelles, CNRS UPR 2301 - Université Paris-Sud, Université Paris-Saclay, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France

Despite the success in SIMS imaging [1], the routinely employed cluster ion beams (Binq+ and Aunq+) cause severe fragmentation of analytes, which has greatly limited the detection of intact biomacromolecules such as peptides and proteins. Promisingly, several studies of massive argon clusters have shown significant decrease of fragmentation and this is assumed due to a soft emission process [2, 3]. Therefore, to get a better understanding of the interaction between the target and massive argon projectiles, we propose to examine the energy imparted to the analytes, namely the internal energy distribution of secondary ions (SIs) under massive argon cluster bombardments and compare with that generated from bismuth cluster impacts.

Measurements were conducted with a series of substituent benzylpyridium salts and internal energy distributions calculated with the survival yield method proposed by De Pauw et al. [4]. Arn+ clusters with kinetic energies of 10 - 20 keV and cluster sizes ranging from 500 to 10000 were investigated. Meanwhile, Binq+ (n= 1 - 7, q = 1 - 2) clusters with 12.5 kV and 25 kV acceleration voltages were also examined, respectively.

Results show that internal energy of SIs formed under 20 keV Arn+ cluster impact decreases as the cluster size increases. A plot of the average internal energies versus the energy per atom (E/n) of the cluster beam reveals a rapid increase of internal energy from 1.56 eV to 2.21 eV where a plateau is reached at E/n = 10 eV. In addition, Arn+ clusters sharing the same E/n result in approximately the same internal energy distribution, regardless of energy and cluster size. This implies that E/n or velocity of the projectiles is the determining factor of energy transfer during bombardments. Whereas, all the examined bismuth clusters with 12.5 - 50 keV energies give similar internal energy distributions with an average internal energy around 2.40 eV. Thus, compared with small metal clusters, Arn+ cluster impact within certain E/n (~10 eV) tends to undergo a softer ionization process as a result of lower energy being imparted from projectiles to analytes. The impact patten of massive argon clusters is also under investigation.

[1] J. S. Fletcher, N. P. Lockyer, J. C. Vickerman, Mass Spectrom. Rev. 30 (1), 2011, 147-174.

[2] S. Ninomiya, Y. Nakata, K. Ichiki, T. Seki, T. Aoki, J. Matsuo, Nucl. Instrum. Methods Phys. Res. B 256 (1), 2007, 493-496.

[3] H. Gnaser, K. Ichiki, J. Matsuo, Rapid Commun. Mass Spectrom. 26 (1), 2012, 1-8.

[4] V. Gabelica, E. De Pauw, Mass Spectrom. Rev. 24 (4), 2005, 566-587.