Ordered Vacancy Network Induced by the Growth of Epitaxial Graphene on Pt(111)

We have studied large areas of $(\sqrt{3}\times \sqrt{3})R30°$ graphene commensurate with a Pt(111) substrate. A combination of experimental techniques with ab initio density functional theory indicates that this structure is related to a reconstruction at the Pt surface, consisting of an ordered vacancy network formed in the outermost Pt layer and a graphene layer covalently bound to the Pt substrate. The formation of this reconstruction is enhanced if low temperatures and polycyclic aromatic hydrocarbons are used as molecular precursors for epitaxial growth of the graphene layers.

Figure 1

Constant-current STM images showing islands with the $(\sqrt{3}\times \sqrt{3})R30°$ structure. Scanned area of panels are (a) $52\times 41{\mathrm{nm}}^2$, (b) $12\times 12{\mathrm{nm}}^2$, and (c) $3.2\times 1.3{\mathrm{nm}}^2$. Bias voltages range from 20 to 100 mV and tunnel currents from 0.1 to 4 nA. The arrow indicates the $[11\overline{2}]$ surface direction. The image (a) was recorded for a partially covered surface, where the growth process was stopped before saturation. Panels (a) and (b) show the $(\sqrt{3}\times \sqrt{3})R30°$ superstructure coexisting with a Moiré region.

Figure 2

Top view (left) and side view (right) of the structural model derived from DFT calculations for the $(\sqrt{3}\times \sqrt{3})R30°$ reconstruction. Smaller sizes on the spheres represent deeper atoms. The side view is slightly tilted for a better visualization of the vacancy channels and interaction between C (black) and surface Pt [gray (yellow)] atoms.

Figure 3

STM image ($V=0.1\mathrm{V}$) for the $(\sqrt{3}\times \sqrt{3})R30°$ experimental (left) and DFT best-fit simulation (right). A schematic atomic model has been overlaid. Both images are merged in the central part.

Figure 4

C $1s$ core level spectra of graphene grown on Pt(111) recorded with 400 eV of photon energy. Upper spectrum using ethylene decomposition (red line), lower spectrum using polycyclic molecular precursors and experimental conditions in which the $(\sqrt{3}\times \sqrt{3})R30°$ phase coexists with Moiré regions on the surface (black line). Dashed lines correspond to the best-fit components.