The effect of the H:C ratio on the sputtering of molecular solids by fullerenes

Abstract

AbstractThe understanding of the process by which molecular solids are sputtered by keV clusters such as C60 is of great importance if cluster SIMS is to be routinely used to depth profile a wide range of molecular materials. Computer simulations of the impact of a C60 cluster on a molecular solid show that an impact crater is produced. At the edges of the crater, a reaction zone is created which contains fragmented and cross‐linked molecules. It has been shown previously that this ‘reaction zone’ can be extensive for a molecular material like fullerite, and yet, for benzene it appears to be smaller. It is well known that fullerite cross‐links through cycloaddition under compression in which the normal sp2 bonding in the fullerene molecules takes on a tetragonal sp3 pattern when two molecules are forced together creating a strong cross‐link between them. It is this process which leads to such an extensive reaction zone after impact. The presence of hydrogen in other molecular systems could resist this process. The purpose of the investigation reported here is to observe the nature of the reaction zone for different molecular systems with varying hydrogen content and different initial coordination. Molecular dynamics simulations of molecular solids of octane, octatetraene, benzene and fullerite struck by 15 keV C60 were performed. Octane is initially four‐fold coordinated, whilst the other molecular solids are all three‐fold coordinated. The reaction zone of the crater formed by the impact was measured and it was concluded that the H:C ratio influences the nature of the reaction zone, whereas the initial coordination has only a secondary effect on the reaction zone. Copyright © 2010 John Wiley & Sons, Ltd.