C 60 thin film growth on graphite: Coexistence of spherical and fractal-dendritic islands

Abstract

The initial growth stage of C(60) thin film on graphite substrate has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The C(60) layer grows in a quasi-layer-by-layer mode and forms round, monolayer high islands on the graphite surface. The islands are confined by terraces on the graphite surface and the mobility of C(60) fullerenes across steps is low in all layers. The second and all subsequent layers adopt a fractal-dendritic shape, which was confirmed by calculating the fractal dimension (D=1.74 prior to island coalescence) and is in agreement with a diffusion limited aggregation. The profound differences between the growth of C(60) layers on graphite (first layer) and on C(60) surfaces (second and higher layers) are caused by the restriction of the C(60) mobility on the highly corrugated fullerene surfaces. The orientation of the fractal islands follows the hexagonal symmetry of the densely packed (111) surface of the fullerene lattice, which introduces a bias in the direction of molecule movement. The differences in surface topography on the nanoscale determine the mode of film growth in this van der Waals bonded system.

Probing the interaction at the C60–SiC nanomesh interface

“…As such, a chemical reaction is unlikely to occur at the C 60 -nanomesh interface (more details can be found in later discussion), in contrast to C 60 on clean Si(1 1 1) or Si(1 0 0), where the Si dangling bonds usually induce the formation of covalent bonds between C 60 and Si substrates [25]. At the interfaces of C 60 on HOPG and C 60 on Ag (1 1 1), there are no interfacial chemical reactions [13,14], similar to the C 60 -nanomesh interface. For comparison, the growth behaviors of C 60 on Ag(1 1 1) and HOPG are also studied.…”

“…The interface between C 60 molecules and planar highly oriented pyrolitic graphite (HOPG) is dominated by van der Waals forces [12,13], as revealed by the relative low desorption temperature (237-257°C) of C 60 molecules from HOPG. On metal surfaces such as Au(1 1 1) and Ag(1 1 1), the desorption of C 60 occurs at a higher temperature of approximately 500°C, indicating a stronger C 60 -metal interface interaction [14,15]; such C 60 -metal interaction can even reconstruct the metal surface as is the case for Ag(1 0 0) [16][17][18] Ni(1 1 0) [19], and Cu(1 1 1) [20].…”

Floating two-dimensional solid monolayer ofC60on graphite

“…The eventual consensus of these studies is that at room temperature, C 60 grows in a layer-by-layer mode, 7,9,11,12,15 and before the first layer completes, subsequent layers can form dendritic islands that have fractal character. 8,14,16 Since we will later make some comparison to rare gases adsorbed on graphite, it is worth noting that rare-gas adsorption experiments, which typically see the near completion of each layer sequentially, 17 are typically performed in equilibrium with the gas, whereas the C 60 adsorption experiments are typically non-equilibrium experiments. This difference may affect the nature of the growth.…”

van der Waals interactions mediating the cohesion of fullerenes on graphene

“…As a rule, the islands are hexagonally shaped with edge angles of 120 • , which is an expected kind of behavior, since it has been already observed in the first layer of C 60 on highly oriented pyrolitic graphite. 21 The profile analysis of the islands gives an apparent height of 8.8(±0.3)Å and interestingly does not show medium-scale corrugation that could be expected due to the underlying 6 × 6 superperiodicity (resulting in a quasi-6 × 6 corrugation of the SLG in the STM topography 9 ). These findings are consistent with the recent observation made by Cho et al.…”