Kink-kink interactions and pre-roughening of vicinal surfaces

Thermal anisotropic roughening of vicinal surfaces is well known and well s tudied. Here, we consider the possibility that a separate pre-roughening tr ansition might take place, prior to roughening. Within the framework of a t errace-step-kink model, we identify possible interaction mechanisms for pro moting pre-roughening (PR) and the ensuing disordered flat (DOF) phase. In particular, the most likely to occur in real systems is a short-range repul sion between equally oriented parallel kinks. When this interaction is stro ng, 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 r eal vicinals, in particular Ag(115), where high-accuracy scanning tunnellin g microscopy data are available.