Paper SS2+EM+TF-FrM10
Potassium Induced Long Range Superstructure on C₆₀/Ag (111) Surface

Friday, October 19, 2007, 11:00 am, Room 611

Various long range superstructures were observed for potassium (K) doped C₆₀ monolayer on Ag (111) by scanning tunnelling microscopy (STM). Pristine C₆₀ monolayer exhibits a bright-dim contrast in the most stable (2√3×2√3)-R30 phase, whereas the molecular contrast is uniform in other metastable phases (denoted as R12 or R48 phases). Upon K doping, K segregate into compact islands at room temperature and the bright-dim contrast in the R30 phase is eliminated. Furthermore, ordered quasi-hexagonal patterns with periodicities of ~7 nm to ~40 nm appear. The ordered superstructures show distinct characteristics in each C₆₀ phase. Close inspection reveals that the super lattices are not exactly hexagonal but exhibit uni-directional distortion. Therefore, the finding is perplexing as it cannot be explained by, e.g., Morie patterns. We propose that the superstructures are due to overlaying an orthorhombic one-dimensional polymerized KC₆₀ phase over the hexagonal silver lattice. This is supported by high-resolution STM images showing the signature of [2+2] covalent bond formation.