Electrostatic ordering of the lanthanum endoatom in La@C ₈₂ adsorbed on metal surfaces

An investigation of the dynamic behavior of the endohedral La atom in La@C ₈₂ adsorbed on Ag(111) or Cu(111) using the normal-incidence x-ray standing wavefield (NIXSW) technique is presented. For the surface-normal (111) reflection, NIXSW demonstrates different La absorption profiles between the La@C ₈₂ monolayer and multilayer. Analysis of the profiles reveals significant La ordering in the monolayer; the degree of ordering increases as the film is cooled. First-principles calculations provide a description of the endohedral metal atom-cage bonding and the fullerene-surface interaction. Combined, these effects give rise to preferential binding sites for the endoatom resulting from electrostatic interactions within the adsorbed fullerene.