Temperature-dependent self-assemblies of C-60 on (1x2)-pt(110): A STM/DFT investigation

Thermal self-assembly of C-60 on (1 x 2)-Pt(110) following room-temperature deposition has been studied by means of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. Two distinct C-60 chemisorption phases have been identified and characterized as a function of the annealing temperature. After a thermal treatment at 700 K, islands of a C-60 quasi-hexagonal lattice form. These islands are characterized by the highest surface density so far reported for a two-dimensional surface-supported fullerene phase (the surface area per molecule is 87.0 angstrom(2)), with intermolecular nearest-neighbor distances equal to 9.6 +/- 0.1 angstrom. Embedded nanowires of fullerene dumbbell dimers (with an intermolecular distance equal to 9.2 +/- 0.1 A) occasionally nucleate within this high-density phase following a "molecular zip" mechanism. Highly site selective chemisorption driven by the particularly strong overlayer-substrate bonding is proposed to be responsible for the first reported example of surface-templated chemical bond formation between fullerene molecules. After annealing at 850 K, an oblique C-60 chemisorption phase forms. This is characterized by a tetramolecular basis associated to each lattice point of the two-dimensional superstructure and by a peculiar bright-dim contrast in STM images acquired at positive sample bias values. The combination of high-resolution STM images with LEED data and DFT calculations leads to the conclusion that the (1 x 2) substrate reconstruction is lifted at the fullerene-platinum interface and also provides a detailed description of the molecular bonding sites and orientations found within the phase. It is proposed that the main factor ruling the interconversion of chemisorption phases is the variation of substrate atom mobility as a function of temperature.