All-atom molecular dynamics simulation techniques were used to study the diffusional behavior of small numbers of C60 molecules on the surface of crystalline pentacene as a probe of molecular-level interactions between C60 and pentacene (table 32). The ultimate molecular probe of the pentacene surface, a single C60 ad-molecule, exhibited an anisotropic diffusion pattern that involved lingering in energetically preferred sites in the [1¯10] direction intercepting the (0, 1/2, 0) point in the unit cell. An Arrhenius analysis of these diffusion data gave:

D(cm2/s) = 2 x 10-3exp[-0.1(eV)/kT]

The surface diffusion of one C60 molecule on pentacene was significantly more rapid (by 1 to 2 orders of magnitude) than for the case where even one additional C60 admolecule was present. This implied that the C60-C60 cohesion interaction was stronger than the C60-pentacene adhesion interaction. Simulations involving up to four C60 molecules reinforced the suggestion that C60 preferred to de-wet a pentacene surface and showed a preference for forming small 3D nuclei.

A Computational Study of Surface Diffusion of C60 on Pentacene. Cantrell, R., Clancy, P.: Surface Science, 2008, 602[22], 3499-505