Effects of Molecular Orientation and Size in Sputtering of Model Organic Crystals

Abstract

Using coarse-grained molecular dynamics simulations, we investigate the interaction of kiloelectronvolt C60, Au3, and Au projectiles with model polyethylene-like crystalline targets (hexacontane: C60H122). Two different orientations of hexacontane molecules were examined: horizontal and vertical. We observe strong structural effects related to the molecular orientation of the target on the sputtering yields. The simulations show that the sputtered mass increases dramatically when going from vertical to horizontal hydrocarbon chains (∼4−8 times, depending on the projectile). With the latter system, large chunks of organic material including many molecules are emitted (beyond 14 kDa). The observed differences are rationalized in terms of energy deposition, pressure wave development, and crater formation, in relation to the specific structure of the samples. This pronounced influence of the target structure might have implications for the mass spectrometric analysis of liquid-crystal-type materials and biological samples, including cells and tissues, where bilayered phospholipid membranes are a major constituent of the sample.