NCAFM2023 Programme Booklet

Tuesday 1500 -1520

UNRAVELING THE PRECISE STRUCTURE OF MAGIC CARBON CLUSTERS USING NONREACTIVE AND REACTIVE AFM PROBES

Mengxi Liu*, Xiaohui Qiu

1 National Center for Nanoscience and Technology, 100190 China Email: liumx@nanoctr.cn

Magic-sized carbon clusters with uniform size and identical geometric symmetry are usually observed in chemical vapor deposition growth of graphene on transition metal surface. Such uniform carbon clusters are believed to play a key role in graphene growth. However, there is still debate regarding whether these clusters act as nucleation sites or obstacles. Despite a significant number of STM results and DFT calculations, the precise structure of these clusters remains unclear. We employed temperature programmed growth method to prepare graphene on Ir(111), and observed a large number of magic carbon clusters coexisting with graphene domains. High-resolution STM images indicate that the clusters formed on Ir(111) is similar to those observed on Rh(111), Ru(0001) and Re(0001). Constant-height nc-AFM images reveal that the central part of the cluster is a carbon atom, which is in controversy with the previous works that assigned the central moiety as a carbon ring. Combined with constant-current nc-AFM imaging, we tentatively assign the magic-sized carbon cluster as C19 and determine its precise atomic registration with respect to the Ir(111) surface. As a comparison, the nc-AFM images obtained with a reactive metal tip demonstrate strong attraction at the location of carbon atoms. The force spectroscopy shows prominent energy dissipation, revealing the chemical bonding between Ir tip apex and carbon atom with a corresponding short-range force of ~1.5 nN. We also derive the vertical stiffness of the magic cluster after a stable chemical bond is formed between the tip and the carbon cluster. By combining passivated tip and chemically active tip, as well as constant-height and constant-current mode, we are able to elucidate the precise atomic structure and adsorbed configurations of non-planer nanostructures, providing the possibility to explore their chemical reactivity and mechanical properties.

Fig. 1 (a) Large-scale STM image of the magic-sized carbon clusters (labeled by white dotted circles) coexisting with graphene on Ir(111). Image size: 16×16 nm 2 . (b) Schematic illustrations of the nc-AFM imaging mode and the corresponding experimental images of the carbon cluster.

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