Unravelling the multilayer growth of the fullerene C60 in real time

Abstract

Molecular semiconductors are increasingly used in devices, but understanding of elementary nanoscopic processes in molecular film growth is in its infancy. Here we use real-time in situ specular and diffuse X-ray scattering in combination with kinetic Monte Carlo simulations to study C60 nucleation and multilayer growth. We determine a self-consistent set of energy parameters describing both intra- and interlayer diffusion processes in C60 growth. This approach yields an effective Ehrlich–Schwoebel barrier of EES=110 meV, diffusion barrier of ED=540 meV and binding energy of EB=130 meV. Analysing the particle-resolved dynamics, we find that the lateral diffusion is similar to colloids, but characterized by an atom-like Schwoebel barrier. Our results contribute to a fundamental understanding of molecular growth processes in a system, which forms an important intermediate case between atoms and colloids.

Particle-resolved dynamics during multilayer growth ofC60

“…First steps towards unravelling C 60 multilayer growth have been taken in Ref. 13 where we developed, together with experiments, a KMC model capable of describing various real-space data. Application-wise, C 60 is a key component to semiconductor devices such as transistors 6,24 and solar cells 25 because of its high electron yield and photophysical properties 26,27 .…”

“…These studies include even subtle phenomena such as concerted gliding of islands 41 or direction-resolved step-edge diffusion 42,43 . In our recent study we have obtained, together with real-time experiments 13 , a consistent set of energybarrier parameters for KMC simulations which describe measurable morphological quantities such as island density and layer coverage as functions of time. Interestingly, these energy parameters reflect again the intermediate role of C 60 between atoms and colloids: While the step-edge diffusion barrier is close to what one expects for atoms, the binding energy stemming from attractive interactions is much smaller, reflecting indirectly the much shorter range of attraction.…”

“…It is therefore crucial to understand on a microscopic (molecular) level the entire process of formation of such organic-molecule structures from growth towards the final equilibrium state. From the experimental side, information on the morphology of the organic component is obtained e.g., via atomic force-9,10 and scanning electron microscopy 11 , Raman scattering 12 , X-ray scattering 13,14 and electron microscopy 15,16 . In particular, real-time X-ray scattering can be used to monitor the film formation in situ and thus gives important information about the system's behavior on its way towards thermal equilibrium.…”

Arrays of Pentacene Single Crystals by Stencil Evaporation

“…27 The precise understanding and quantification of this growth behavior requires specialized modeling tools such as kinetic Monte-Carlo simulations that combine all of the microscopic events described above. 28,29 This is left to further work. For large apertures of a = 10 µm, this diffusion-driven growth is not observed.…”

Morphology Change of C60 Islands on Organic Crystals Observed by Atomic Force Microscopy

“…This confirms that the molecule/molecule interaction is favoured whereas the molecule/substrate interaction is minimized upon shape modification, which is in agreement with the "Volmer-Weber" type of growth. Assuming that the interaction energy between two C 60 molecules is E i ∼ 130 meV 50 and neglecting their interactions with the BNL substrate, we estimate the cohesion energy (E C ) of the island before and after it undergoes the shape-modification process by summing the interactions energies of all C 60 with their nearest neighbours in or out of plane. The cohesion energies of the triangular and hexagonal islands are estimated to 484 meV/molecule and 495 meV/molecule, respectively.…”