A molecular dynamics study of the effect of pentacene polymorphs on C₆₀surface 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 C 60 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 C 60 . There is a transition of the dominant energy minima from between the pentacene rows at low values of w 1 to within the rows at high values of w 1 , where w 1 is the angle the bottom pentacene short axis makes with the surface normal. This shift implies that the likelihood of forming C 60 nanowires on pentacene is greater at extreme values of w 1 for which there would be a clear preference for C 60 to be located between a row or within a row, rather than at intermediate values of w 1 , where there is no clear preference.

Multiscale Simulation and Modeling of Multilayer Heteroepitactic Growth of C60 on Pentacene

“…In the second, Hoffman investigated how environmental conditions of a CO molecule on a Pd (100) surface (e.g., different adsorption site geometries) determined which of the two lattices (CO or Pd) it adopted . Unlike Hoffman’s method, our algorithm did not require the two dissimilar lattices to match at the periodic boundary conditions, which effectively changes the lattice parameters.…”

“…During submonolayer growth (<50% coverage), the growth mechanism is dominated by the nucleation and growth of C 60 clusters on the pentacene surface. We focused on obtaining results for the “thin film” phase of pentacene due to its known higher surface diffusion rate compared to that of bulk phase pentacene . Snapshots for the thin film phase pentacene KMC simulation are shown in the SI and have been verified against prior work .…”

“…This follows Volmer–Weber growth, which is characterized by the formation of discrete islands on a surface. On the basis of their calculations and our previous work on submonolayer growth, we anticipate that growing C 60 on pentacene is also likely to follow this mode.…”

“…For KMC, we can anticipate issues in terms of both the effort required to generate all the needed energy barriers and, of more concern, whether an on-lattice approach can capture the transition from the triclinic structure of pentacene to the FCC-dominated C 60 . Our earlier work suggested that a multilayer KMC approach can be constructed, but results were only shown for submonolayer growth, and new computational issues will arise as we consider a multilayer growth process, as will be described here.…”

Computationally Derived Rules for Persistence of C60 Nanowires on Recumbent Pentacene Bilayers

“…We have been studying the structural properties of all-organic heterojunctions, in particular, C 60 /pentacene, − motivated by their potential as prototypical planar p–n junctions. − However, this system, like many small-molecule organic semiconductor systems, shows a tendency for C 60 to dewet pentacene surfaces in upright-standing polymorphs (namely, the thin film and bulk phases), leading to undesirable three-dimensional growth rather than a more ordered, and hence higher mobility, layer-by-layer growth. ,, Two-dimensional growth is preferred based on a rubric that links increased structural order to higher electron and hole mobilities. Dewetting occurs due to the consequences of the stronger C 60 –C 60 interactions in comparison to those for C 60 /pentacene, exemplifying the balance of forces that drives the preferred morphology of thin film growth in many such small-molecule organic semiconductor systems.…”