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

We apply multiscale methods to describe the strained growth of multiple layers of C60 on a thin film of pentacene. We study this growth in the presence of a monolayer pentacene step to compare our simulations to recent experimental studies by Breuer and Witte of submonolayer growth in the presence of monolayer steps. The molecular-level details of this organic semiconductor interface have ramifications on the macroscale structural and electronic behavior of this system and allow us to describe several unexplained experimental observations for this system. The growth of a C60 thin film on a pentacene surface is complicated by the differing crystal habits of the two component species, leading to heteroepitactical growth. In order to probe this growth, we use three computational methods that offer different approaches to coarse-graining the system and differing degrees of computational efficiency. We present a new, efficient reaction-diffusion continuum model for 2D systems whose results compare well with mesoscale kinetic Monte Carlo (KMC) results for submonolayer growth. KMC extends our ability to simulate multiple layers but requires a library of predefined rates for event transitions. Coarse-grained molecular dynamics (CGMD) circumvents KMC's need for predefined lattices, allowing defects and grain boundaries to provide a more realistic thin film morphology. For multilayer growth, in this particularly suitable candidate for coarse-graining, CGMD is a preferable approach to KMC. Combining the results from these three methods, we show that the lattice strain induced by heteroepitactical growth promotes 3D growth and the creation of defects in the first monolayer. The CGMD results are consistent with experimental results on the same system by Conrad et al. and by Breuer and Witte in which C60 aggregates change from a 2D structure at low temperature to 3D clusters along the pentacene step edges at higher temperatures.

STRUCTURAL, ELECTRONIC, MAGNETIC, AND OPTICAL PROPERTIES OF 3d TRANSITION METAL ENDOHEDRAL M@Ge12H12(M=Sc–Ni) CLUSTERS

The fulerine- Ni @ Ge 12 H 12 structure, which composes of four pentagons and four rhombi and is like a fullerene, has a closed-shell electronic structure, the largest HOMO–LUMO energy gap, the highest vertical ionization potential, and the lowest vertical electron affinity. All of these properties are characteristic of a magic cluster, therefore, we strongly suggest fulerine- Ni @ Ge 12 H 12 should be a magic cluster and promising as building blocks in developing cluster-assembled nanomaterials. This can be interpreted by the weak interaction between Ni and the cage together with the transference of two electrons from the 4s orbital to the 3d orbital of Ni . The magnetic moment of fulerine- M @ Ge 12 H 12( M = Sc – Ni ) varies from 0 to 3 μB, implying they have potential applications in developing new nanomaterials with tunable magnetic properties. The calculated TDDFT optical properties of fulerine- M @ Ge 12 H 12( M = Sc – Ni ) can be tuned broadly in the ultraviolet–visible region. This is very important for optoelectronic applications.