A molecular dynamics study of the effect of pentacene polymorphs on C60 surface adsorption and diffusional properties and the tendency to form nanowires

Abstract

Using atomic-scale molecular dynamics and energy minimisation techniques with semi-empirical molecular mechanics 3 potential energy functions, we consider the adsorption of a C60 molecule on pentacene in the known thin film and bulk phases and a series of hypothetical, variably angled, pentacene structures. The thin film phase has a more energetically isotropic surface than the bulk, and exhibits diffusion coefficients that are twice as high, potentially leading to preferable characteristics for ordered film growth. For the variably angled pentacene structures, where the long axis is parallel to the substrate, a relationship was discovered between the angle that the pentacene short axis makes with the surface normal (controlled by the underlying substrate) and the adsorption characteristics of C60. There is a transition of the dominant energy minima from between the pentacene rows at low values of ϕ1 to within the rows at high values of ϕ1, where ϕ1 is the angle the bottom pentacene short axis makes with the surface normal. This shift implies that the likelihood of forming C60 nanowires on pentacene is greater at extreme values of ϕ1 for which there would be a clear preference for C60 to be located between a row or within a row, rather than at intermediate values of ϕ1, where there is no clear preference.