Correlations in a one-dimensional lattice fluid on Si(111)5×2-Au

The Si(111)5×2 Au surface forms a chain structure with a quarter-filled lattice fluid of additional Si atoms on top of the chains. The pair distribution function g(r) of these extra atoms is determined from an extensive set of scanning tunneling microscopy data covering (∼4500 adatoms) and is used to estimate the adatom-adatom interactions. A small probability of simultaneous occupation of nearest-neighbor sites reflects a repulsion of 220 meV (3.6k_BT). Persistent oscillations in g(r) are fit by a periodic potential of amplitude 1.2 meV (0.02k_BT), which might arise from an incipient charge density wave. The interchain correlations are very small. A good fit is obtained by a repulsive energy between interchain nearest neighbors of less than 12 meV (0.2k_BT), demonstrating the one-dimensional character of the lattice fluid. In addition to providing microscopic data on a one-dimensional lattice fluid the results help explain the limits of data storage density due to interactions between adjacent bits.