Relationship between the c(4 x 2) and the (root 3 x root 3)R30 degrees phases in alkanethiol self-assembled monolayers on Au(111)

Transformation between the two well-known phases of alkanethiol monolayers on Au(111), c(4 x 2) and (root 3 x root 3)R30 degrees, has been studied using scanning tunneling microscopy in ultra-high vacuum. Among the many versions of the c(4 x 2) phases observed, one particular structure where a lateral shift of adsorbate by as much as 0.17 nm within the unit cell is found. This lateral shift along the [11 (2) over bar] direction corresponds to the movement of one adsorbed unit, towards its nearest neighbour from one hollow site to another (fcc to hcp, or hcp to fcc).