KINETIC ROUGHENING OF A TERRACE LEDGE

We study the motion of an isolated terrace ledge on a crystalline surf ace within the framework of the terrace-ledge-kink model. We argue tha t for length scales larger than the diffusion length the step roughnes s is governed by the Kardar-Parisi-Zhang (KPZ) equation that predicts a broadening as t1/3. For smaller length scales a variety of possibili ties are explored. Their occurrence depends sensitively on the rates f or the adsorption and desorption processes both on the terraces and at the ledge. The ledge could be unstable, developing a fractal, dendrit ic type of structure. If the ledge is stable, we obtain a crossover fr om a t1/6 (conserved dynamics, model B) to a t1/4 (nonconserved dynami cs, model A) and a t1/3 (KPZ) broadening.