Looking inside an endohedral fullerene: Inter- and intramolecular ordering of ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ on Cu(111)

The inter- and intramolecular ordering of the trimetallic nitride endohedral fullerene ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ with icosahedral cage symmetry $I_h$ on Cu(111) has been studied by scanning tunneling microscopy and synchrotron-based x-ray photoelectron diffraction (XPD). ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ is found to form ordered islands consisting of domains of equally oriented molecules. As for ${\text{C}}_{60}$ on the same substrate, the cage is facing with a hexagon toward the surface, which is however slightly tilted for ${\text{C}}_{80}$. The endohedral nitrogen atom remains at a position close to the geometrical center of the cage. Resonant XPD on the ${\text{M}}_{\text{V}}$ edge shows that the encaged ${\text{Dy}}_3\text{N}$ unit takes well-defined orientations with respect to the ${\text{C}}_{80}$ cage and the Cu(111) substrate.

Figure 1

Model of ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ adsorbed on Cu(111). Carbon atoms are shown in grayscale, while small white/gray filled circles correspond to endohedral nitrogen/dysprosium atoms.

Figure 2

(Color online) STM images of ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ on Cu(111). (a) Overview image showing the correlation between the overlayer structure and the local step edge direction. Arrows point to small patches of adsorbates, which adopt a superstructure different from the dominant $\sqrt{19}$ superstructure. (b) Intramolecular contrast resolved STM image of a $+23.4°$ island showing the formation of small domains of equally oriented molecules within an island. (c) Visualization of domains; colored (grayscale) STM image of the area shown in (b). (d) High-resolution STM image of two molecules, showing intramolecular contrast. Four protrusions per molecule can be identified. (e) Suggested models of ${\text{C}}_{80}$ cage orientation compatible with the symmetry of the intramolecular features from (d). Dashed lines correspond to the symmetry elements from (d). [Scanning parameters: (a) 80 pA, $-1.8\text{V}$ (B,C,D) 0.3 nA, $-0.1\text{V}$.]

Figure 3

Synchrotron radiation XPD $\left(h\nu =880\text{eV}\right)$ patterns of 1ML of ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ on Cu(111). (a) Experimental $\text{C}1s$-XPD. (b) Best-fit $\text{C}1s$-SSC. (c) Experimental $\text{N}1s$-XPD. (d) Best-fit $\text{N}1s$-SSC.

Figure 4

(Color online) rXPD of Dy-$MNN$ Auger lines. (a) Resonant enhancement of Auger lines (dotted lines) as a function of photon energy. The inset shows the corresponding x-ray absorption spectrum across the Dy ${\text{M}}_{\text{V}}$ edge $\left(3d\right)$. The dashed line designates the photon energy of 1291.5 eV. (b) Dy-$MNN$-rXPD of 1ML ${\text{Dy}}_3\text{N}@{\text{C}}_{80}$ $\left(I_h\right)$ on Cu(111), recorded at a photon energy of 1291.5 eV. (c) Best-fit SSC simulation (upper half, see text for details) and simulation based on disordered endohedral unit (lower half).