Growth of Dome-Shaped Carbon Nanoislands on Ir(111): The Intermediate between Carbidic Clusters and Quasi-Free-Standing Graphene

By combining high-resolution photoelectron spectroscopy and ab initio calculations, we show that carbon nanoislands formed during the growth of a long-range ordered graphene layer on Ir(111) assume a peculiar domelike shape. The understanding of the unusual growth mechanism of these C clusters, which represent an intermediate phase between the strongly coupled carbidic carbon and a quasi-free-standing graphene layer, can provide information for a rational design of graphenelike systems at the nanoscale.

Figure 1

C $1s$ (left) ($h\nu =400\mathrm{eV}$) and Ir $4f_{7/2}$ (right) ($h\nu =130\mathrm{eV}$) core level spectra and top and side views of the calculated structural models of (a) clean Ir(111) and (b) the graphene layer on Ir(111). The moiré corrugation of the graphene layer is displayed in red with different brightnesses. Low energy electron diffraction patterns are also shown.

Figure 2

C $1s$ (left) and Ir $4f_{7/2}$ (right) spectra after annealing at different temperatures of the Ir(111) surface saturated with ${\mathrm{C}}_2{\mathrm{H}}_4$ at 300 K. The spectra were measured at 300 K. The different components represent inequivalent C and Ir atoms, as explained in the text.

Figure 3

Calculated structural models of the C clusters formed by $n$ honeycomb rings with (a) $n=1$, (b) $n=3$, (c) $n=7$, and (d) $n=19$. ${\mathrm{Ir}}_i$ ($i=1,\dots ,6$) and ${\mathrm{C}}_j$ ($j=1,\dots ,4$) represent different Ir and C local configurations, respectively, as explained in the text. The distance of the central C atoms from the Ir substrate as well as the orientation of the cluster with respect to the $[10\overline{1}]$ direction of Ir(111) are also shown.

Figure 4

Evolution of the binding energy/atom as a function of the ratio of C atoms at the periphery $N_P$ and the total number $N_T$ in each C cluster.