Kink-kink interactions and pre-roughening of vicinal surfaces

Thermal anisotropic roughening of vicinal surfaces is well known and well studied. Here, we consider the possibility that a separate pre-roughening transition might take place, prior to roughening. Within the framework of a terrace-step-kink model, we identify possible interaction mechanisms for promoting pre-roughening (PR) and the ensuing disordered flat (DOF) phase. In particular, the most likely to occur in real systems is a short-range repulsion between equally oriented parallel kinks. When this interaction is strong, PR shows up and the DOF phase is characterized by antiparallel order of kinks within a step. Next, we discuss the relevance of this scenario for real vicinals, in particular Ag(115), where high-accuracy scanning tunnelling microscopy data are available.