Carbon Monoxide Stripe Motion Driven by Correlated Lateral Hopping in a 1.4 × 1.4 Monolayer Phase on Cu(111).

We report an ultra-high-vacuum low-temperature (4.6 K) scanning tunneling microscopy study of the molecular structure and dynamics of a carbon monoxide (CO) monolayer adsorbed at 20 K on Cu(111). We observe the well-known 1.4 × 1.4 phase of CO/Cu(111) for the first time in real-space imaging. At 4.6 K, the hexagonal symmetry of the monolayer is locally broken by the formation of stripes made of single and double CO rows of different apparent heights. Using density functional theory calculations, we assign the high rows to CO molecules adsorbed mostly at off-center top sites and the low rows to bridge sites. Groups of three or four very high molecules appear randomly and are assigned to nearest-neighbor, titled top site molecules. We observe simultaneous hopping of a few CO molecules between adjacent top and bridge sites, which produces the apparent motion of the stripe pattern.