Graphene Grown from Flat and Bowl Shaped Polycyclic Aromatic Hydrocarbons on Cu(111)

Abstract

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X‐ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400–450 °C), disordered defective graphene (500 °C–550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X‐ray photoelectron spectra of PIC and CR derived samples grown at 350–550 °C exhibit a characteristic C−Cu low binding energy component. Preparation at ≥600 °C eliminates this C−Cu species and only C−C bonded carbon remains.

On-Surface Hydrogenation of Buckybowls: From Curved Aromatic Molecules to Planar Non-Kekulé Aromatic Hydrocarbons

“…The fact that the intensity of carbon (C – ions) is not significantly decreased (Table S5) shows that the disappearance of PIC-derived signals after annealing to 624 K is due to nonspecific C–C coupling and fragmentation rather than desorption. These processes yield randomly linked carbon aggregates and ultimately (at higher temperatures) graphene …”

“…PAHs may exist in planar non-Kekulé diradicaloid structures, − but also in nonplanar species, such as helicenes or buckybowls. − That means a closed-shell structure is being pushed to the limit of dissociation of one π bond to generate an open-shell structure with two weakly coupled unpaired electrons within the molecule. Hence, the hydrogenated products were evaluated for potential planar non-Kekulé diradicaloid structures by theoretical means.…”

“…These processes yield randomly linked carbon aggregates and ultimately (at higher temperatures) graphene. 56 STM images of PIC/Cu(100) acquired after annealing to 490 K show that the PIC has been transformed into planar entities (Figure 6). As in the case of pristine PIC, these species appear with 5-lobes, but with a larger distance between two of them.…”