Aperiodic incommensurate phase of a C60 monolayer on Ag(100)
Journal
Physical Review B - Condensed Matter and Materials Physics
Journal Volume
68
Journal Issue
24
Pages
245414-1 - 245414-12
Date Issued
2003
Author(s)
Hsu, C.-L.
Abstract
Detailed combined scanning tunneling microscopy and low-energy electron diffraction measurements reveal that the structure of a C60 monolayer on Ag(100) is not the previously accepted commensurate c(6 × 4) phase but rather an incommensurate (111) close-packed phase. The film exhibits a characteristic molecular contrast pattern with merely short-range order, and room-temperature fluctuations of the contrast show that a thermal equilibrium state is reached. The nature of this controversial bright-dim C60 contrast is clarified as a topographic feature due to C60-induced reconstruction underneath the dim C60 molecules. Due to interactions between the incommensurate C60 adlayer and the reconstructed substrate, the (111) phase is distorted laterally, forming a novel “tetramer” configuration of specific contrast order. The spatial distribution of these tetramers is aperiodic; this has crucial implications for the peculiar short-range contrast order observed experimentally. A lattice gas model with anisotropic nearest-neighbor interactions and a configuration energy of the tetramer is developed. Quantitative agreements between observation and modeling are achieved with reasonable phenomenological parameters derived within experimental constraints. © 2003 The American Physical Society.
SDGs
Type
journal article