Nuclear-resonance photon scattering study of multilayers adsorbed on Grafoil at 12 K

The nuclear-resonance photon scattering technique was used for studying the out-of-plane orientation of (Formula presented) molecules physisorbed on Grafoil at 12 K and coverages (Formula presented) to 3.7 monolayers. By monitoring the resonantly scattered intensity ratios from the 6324 keV level in (Formula presented) with the planes of the Grafoil adsorbing surface set parallel and perpendicular to the direction of the incident photon beam, the average out-of-plane tilt of (Formula presented) relative to the graphite planes was obtained. The behavior of the system reveals a striking similarity to that of the (Formula presented) system. Specifically, the tilt angles of the (Formula presented) molecules with respect to the graphite surface are practically the same despite its more involved character. It is shown that the occurrence of a pure four-sublattice pinwheel ordering can be ruled out. The possibility of explaining the measured intensity ratios at 12 K, by assuming partial dewetting of the (Formula presented) molecules (where the molecules in the first layer lay flat on the graphite surface while the overlayers consist of highly disordered bulk) is discussed in some detail.