Influence of weak atomic bonding on the height of growth spiral steps on cadmium iodide crystals

Abstract

Step heights of growth spirals on CdI2 crystals, unambiguously measured for the first time by STM, do not turn out to be integral multiples of the unit cell height, as normally expected, unless enhanced by a constant value of 0.31nm. The discrepancy primarily arises from the weak van der Waals bonding between the neighbouring molecular sandwiches I–Cd–I constituting the structure and from the dangling bonds existing at the edge of a growth step and at the crystal surface. The result is significant for problems of surface physics and surface chemistry.