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?:abstract
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A deep grasp of the interfacial properties between organic molecules and h-BN is an essential issue towards the full implementation of these two building blocks in the next-generation electronic devices. Here, we report on the geometric and electronic features of C60evaporated on a single layer of hexagonal-boron nitride (h-BN) grown on the Rh(110) surface using scanning tunneling microscopy (STM) and spectroscopy (STS) under ultrahigh vacuum (UHV). Two different molecular assemblies of C60on the h-BN/Rh(110) surface were observed. The first STM combined study at room temperature (RT) and at low temperatures (40 K) of the molecular orientation of C60on a 2D layered material is presented. Intramolecular resolution images have allowed to demonstrate the existence of a phase transition of C60over the h-BN/Rh(110) surface similar to that found on bulk solid C60. At RT molecules exhibit random orientations, while at 40 K such rotational disorder vanishes and they adopt a common orientation over the h-BN/Rh(110) surface. The decrease of the thermal energy allows the recognition between C60molecules, which makes them to become equally oriented in the configuration at which the van der Waals intermolecular interactions are optimized. Bias dependent submolecular features obtained by means of high resolution STM images have been interpreted as the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO). Besides, STS data evidenced that fullerenes are electronically decoupled from the substrate, with a negligible charge transfer effect if any. Finally, the very early stages of multilayer growth were also investigated.
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