Molecular orientations and interfacial structure of C60 on Pt(111)

Abstract

Molecular orientations and assembled structures of C(60) molecules on Pt(111) have been characterized by low-temperature scanning tunneling microscopy for coverage between 0.1 ML and 1.5 ML. At room temperature, C(60) molecules preferentially decorate the steps and nucleate into single layer islands (SLIs) with hexagonal close-packed structures upon increasing coverage. C(60) islands comprise two differently oriented C(60)∕Pt(111)-(√13 × √13) R13.9° phases, in which five types of molecular orientation of C(60) carbon cage configurations are clearly identified by the high-resolution scanning tunneling microscopy image. Further annealing treatment leads to more uniform molecular orientation without apparent aggregation of C(60) SLIs. As coverage increases above 1 ML, domains corresponding to (2√3 × 2√3) R30° superstructure appear. To explain the above transformation, an interfacial reconstruction model is proposed according to the detailed study of the molecular adsorption structures in different domains.

C60on the Pt(111) surface: Structural tuning of electronic properties

“…4 As Table III exhibits, DFT and LEED agree closely, the two phases have almost identical local adsorption structures, and they show a strong covalent C-Pt bond character. 14 These results agree with the model proposed in a recent scanning tunneling microscopy study, 12 while providing much more information and reliability. In this structure, C 60 sits on top of the Pt vacancy with hexagon down and forms six C-Pt covalent bonds with the six Pt atoms surrounding the vacancy.…”

“…It has moreover been observed that annealing at 500 K cannot partially change the √ 13 phase to the 2 √ 3 phase, while such changes may occur at even higher temperatures. 12 Based on the determined geometric structures, we further study the electronic structures of C 60 in these two phases by DFT calculations. To understand the effects of C 60 -C 60 and Pt-C 60 interactions, Figs.…”

“…Such reconstructions are expected to be the rule rather than the exception in C 60 adsorption on metals. 7 Similar structures for C 60 on Pt(111) were proposed based on scanning tunneling microscopy observations, 12 but have not been confirmed by any direct method.…”

“…At each site, different rotations of C 60 around the surface normal were considered, with a hexagonal face pointing down to suit the observed symmetry. 12 …”

“…4 On Pt(111), C 60 forms two distinct phases, labeled ( √ 13 × √ 13)R13.9 • and (2 √ 3 × 2 √ 3)R30 • (hereafter referred to as the √ 13 and 2 √ 3 phases, respectively; note that 2 √ 3 = √ 12 is just 4% smaller than √ 13, so the 2 √ 3 phase is slightly compressed relative to the √ 13 phase; in terms of unit-cell areas and thus density, the compression is 1 -12/13 ∼ 8%). 12,13 These two phases have different intermolecular orientations and distances, as will be demonstrated in the following. Therefore, one may expect the two phases to exhibit different electronic properties.…”