Cooperative Assembly of Magic Number ${\mathbf{C}}_{60}$-Au Complexes

We report the assembly of magic number $({\mathrm{C}}_{60}{)}_m\mathrm{\text{−}}(\mathrm{Au}{)}_n$ complexes on the Au(111) surface. These complexes have a unique structure consisting of a single atomic layer Au island wrapped by a self-selected number (seven, ten, or twelve) of ${\mathrm{C}}_{60}$ molecules. The smallest structure consisting of 7 ${\mathrm{C}}_{60}$ molecules and 19 Au atoms, stable up to 400 K, has a preferred orientation on the surface. We propose a globalized metal-organic coordination mechanism for the stability of the $({\mathrm{C}}_{60}{)}_m\mathrm{\text{−}}(\mathrm{Au}{)}_n$ complexes.

Figure 1

(a) STM image ($25\mathrm{nm}\times 40\mathrm{nm}$) obtained using $-1.8\mathrm{V}$ sample bias and 0.03 nA tunnel current showing ${\mathrm{C}}_{60}$ molecules aggregating around Au islands at the elbow site at 110 K. (b) $({\mathrm{C}}_{60}{)}_7$ clusters with a uniform azimuthal orientation formed at the fcc region next to the bulged elbow site upon temperature rise to RT. The images in (a) and (b) are not from the same location of the sample. (c) Blue curve: height profile across a $({\mathrm{C}}_{60}{)}_7$ cluster. Red curve: height profile across a larger, ${\mathrm{C}}_{60}$-lined Au island.

Figure 2

(a) and (b) Ball model showing the positions of the seven ${\mathrm{C}}_{60}$ molecules. Dark purple spheres are the Au atom in the top-most layer of the substrate. Red spheres are top layer Au atoms in direct contact with a hexagonal face of the ${\mathrm{C}}_{60}$. Yellow spheres represent the single atomic layer Au island consisting of 19 Au atoms (c) $({\mathrm{C}}_{60}{)}_{10}\mathrm{\text{−}}{\mathrm{Au}}_{35}$ cluster. Inset is an STM image of such a cluster containing 10 ${\mathrm{C}}_{60}$ molecules. The two “bright” molecules are sitting side-by-side on top of the gold island. (d) $({\mathrm{C}}_{60}{)}_{12}\mathrm{\text{−}}{\mathrm{Au}}_{49}$ cluster. Inset shows an STM image of such a cluster.

Figure 3

Different types of $({\mathrm{C}}_{60}{)}_m\mathrm{\text{−}}{\mathrm{Au}}_n$ complexes. A: $({\mathrm{C}}_{60}{)}_7$ cluster with an extra molecule. B: $({\mathrm{C}}_{60}{)}_7$ cluster with a missing molecule. C: $({\mathrm{C}}_{60}{)}_{10}$ cluster with four additional molecules. D: $({\mathrm{C}}_{60}{)}_7$ cluster with extra five molecules. E: A relatively large irregular Au island with its step edges decorated by ${\mathrm{C}}_{60}$ molecules. F: Seven ${\mathrm{C}}_{60}$ molecules forming a closed cage around a Au island with no molecule sitting on top of the island.

Figure 4

Self-refining towards the stable $({\mathrm{C}}_{60}{)}_7\mathrm{\text{−}}{\mathrm{Au}}_{19}$ cluster. The three clusters are followed continuously as the sample temperature is slowly raised. The whole sequence of image collection takes $\sim 6\mathrm{h}$. These six images are from a collection of more than 100 images.