Influence of charge transfer doping on the morphologies of C${}_{60}$ islands on hydrogenated diamond C(100)-($2\times 1$)

The adsorption and island formation of C${}_{60}$ fullerenes on the hydrogenated C(100)-($2\times 1$):H diamond surface is studied using high-resolution noncontact atomic force microscopy in ultrahigh vacuum. At room temperature, C${}_{60}$ fullerene molecules assemble into monolayer islands, exhibiting a hexagonally close-packed internal structure. Dewetting is observed when raising the substrate temperature above approximately 505 K, resulting in two-layer high islands. In contrast to the monolayer islands, these double-layer islands form extended wetting layers. This peculiar behavior is explained by an increased molecule-substrate binding energy in the case of double-layer islands, which originates from charge transfer doping. Only upon further increasing the substrate temperature to approximately 615 K, the wetting layer desorbs, corresponding to a binding energy of the charge transfer-stabilized film of 1.7 eV.

Figure 1

(a) Electronic levels of diamond (left) and C${}_{60}$ (right), illustrating the electron transfer from the diamond valence band maximum (VBM) to the lower unoccupied molecular orbital (LUMO) in C${}_{60}$. (b) Spacial charge separation after electron transfer from diamond to C${}_{60}$ results in a distance of 10.2 Å as calculated in Ref. 10.

Figure 2

Topography NC-AFM image showing C${}_{60}$ fullerene islands on C(100)-($2\times 1$):H. (a) Overview of the as-deposited structure at RT after depositing 0.07 ML of C${}_{60}$. (b) Height profile as indicated by the dashed line in (a), revealing a height of approximately 0.9 nm corresponding to a single layer of C${}_{60}$.

Figure 3

(a) Topography NC-AFM image showing the C${}_{60}$ orientation in relation to the C(100)-($2\times 1$):H surface directions, which are pointed out by the dotted/solid pair of arrows in the lower left corner. The island consists of two domains rotated by ${30}^{\circ }$, as indicated by the dotted and the solid arrows. (b) Drift-corrected topography NC-AFM image showing individual C${}_{60}$ fullerenes aligning in a nearly hexagonal close-packed arrangement. (c) Model of the two domains.

Figure 4

Topography NC-AFM images showing a C${}_{60}$ fullerene island on C(100)-($2\times 1$):H after annealing. (a) Island formed after annealing a sample covered with 0.07 ML C${}_{60}$ to approximately 505 K. (b) High-resolution image revealing the hexagonally packed inner structure. (c) Line profile as indicated in (a) revealing an island height of approximately 1.9 nm, corresponding to two layers of C${}_{60}$.