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Experiments on both single-crystal graphite and highly oriented pyrolytic graphite indicate that for 60Ͻ T Ͻ 300 K, C 60 forms single-layer islands of close-packed molecules at low coverages. Low-energy electrondiffraction measurements on the single crystal indicate that there is almost no preferred orientation of the C 60 lattice relative to the graphite lattice, producing continuous diffraction rings. A slight preference for the C 60 lattice oriented at 30°relative to the graphite lattice is explained as originating in the preference for the C 60 islands to nucleate and align at step edges, observed with scanning tunneling microscopy and low-energy electron microscopy. The energetics of this C 60 layer were investigated using the Novaco-McTague theory of epitaxial orientation, which found several minimum-energy angles near the experimental C 60 -C 60 spacing, inconsistent with the experiment and suggesting an extremely small C 60 -graphite corrugation. The thermal expansion of this "floating solid" C 60 lattice for 60Ͻ T Ͻ 120 K was compared to theoretical models using previously formulated C 60 -C 60 pair potentials. The calculated values, assuming perfect two-dimensional layers of spherical C 60 , are significantly smaller than the measured values, suggesting that additional thermal excitations, such as those involving molecular orientations, are present in this temperature range.

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We report on the growth of Pb thin films deposited either on the Al-rich fivefold surface of the icosahedral AlCu-Fe quasicrystal or on the (111) surface of fcc Al. On the quasicrystalline substrate, the diffusion length of Pb adatoms is short due to heterogeneous nucleation that enforces a quasiperiodic structure in the monolayer. On the Al(111) substrate, the mobility of Pb adatoms is high and the interaction with the substrate is flatter, leading to the formation of a (√31×√31)R8.95° higher-order commensurate structure. This moiré structure propagates up to the highest coverages investigated. Disciplines Condensed Matter Physics | Metallurgy CommentsThis article is from Physical Review B 79 (2009) We report on the growth of Pb thin films deposited either on the Al-rich fivefold surface of the icosahedral Al-Cu-Fe quasicrystal or on the ͑111͒ surface of fcc Al. On the quasicrystalline substrate, the diffusion length of Pb adatoms is short due to heterogeneous nucleation that enforces a quasiperiodic structure in the monolayer. On the Al͑111͒ substrate, the mobility of Pb adatoms is high and the interaction with the substrate is flatter, leading to the formation of a ͑ͱ31ϫ ͱ 31͒R8.95°higher-order commensurate structure. This moiré structure propagates up to the highest coverages investigated.