C60 chain phases on ZnPc/Ag(111) surfaces: Supramolecular organization driven by competing interactions

Abstract

Serpentine chain C60 phases were observed in scanning tunneling microscopy (STM) images of C60 layers on zinc phthalocyanine (ZnPc) or pentacene covered Ag(111) and Au(111) surfaces. This low-density, quasi-one-dimensional organization contrasts starkly with the close-packed hexagonal phases observed for C60 layers on bare metal substrates. STM was employed to perform a detailed investigation of these chain structures for C60/ZnPc/Ag(111) heterolayers. Motivated by the similarity of these chain phases, and the chain and stripe organization occurring in dipole-fluid systems, we investigated a model based on competing van der Waals attractions and electrostatic repulsions between C60 molecules as an explanation for the driving force behind these monolayer phases. Density functional theory (DFT) calculations revealed significant charge transfer to C60 from the Ag(111) substrate, through the intervening ZnPc layer, inducing electrostatic interactions between C60 molecules. Molecular dynamics simulations performed with attractive van der Waals interactions plus repulsive dipole-dipole interactions reproduced the C60 chain phases with dipole magnitudes consistent with DFT calculations.

Multiscale modelling of structure formation of C$_{60}$ on insulating CaF$_2$ substrates

“…Another possible explanation could be the effect of polarizability of the C 60 molecule. It was previously shown that it can have a significant impact on the growth of C 60 films on ZnPc/AG(111), where chain phases were observed [68]. Considering that the top fluoride layer of CaF 2 (111) is negatively charged, it can be suspected that polarizability may play a role in this diffusion process as well.…”

“…Because the coarse-grained representation has lost the rotational degrees of freedom of the C 60 molecules, it is usually assumed to be a good approximation for temperatures well above 260 K. At this temperature, crystalline C 60 undergoes a structural phase transition from a plastic crystal, in which orientations are disordered (at high temperatures), to a phase in which the molecular orientations align (at low temperatures) [54][55][56][57][58][59]. While the coarse-grained representation was therefore mostly used for studies at high temperatures -like the predictions of a stable liquid phase of C 60 [60][61][62][63][64] or the examination of C 60 /C 70 mixtures [65,66] -the simplicity of the potential occasionally motivates its use at lower temperatures [36,44,[67][68][69][70]. A comparative study between coarse-grained and atomistic versions of this potential was previously done for C 60 in bulk [48].…”

Resolving Site-Specific Energy Levels of Small-Molecule Donor-Acceptor Heterostructures Close to Metal Contacts

“…In this study, emphasis is therefore put on metallophthalocyanines (MPc) in combination with C 60 molecules. Whereas such systems have been analyzed quite in detail by means of various ensemble averaging techniques [ 10 , 11 , 17 , 18 , 19 ], the study of blends of molecules, by STM is rather scarce and has been mainly addressed from the growth point of view [ 20 , 21 , 22 ]. Here, we perform an in-depth spectroscopic study by high-resolution LT-STM of a ZnPc/C 60 heterostructure in contact with a silver substrate.…”