Change of wandering pattern with anisotropy in step kinetics

We study the effect of anisotropy in step kinetics on the wandering instabi lity of an isolated step. With the asymmetry of the step kinetics, a straig ht step becomes unstable for long wavelength fluctuations and wanders when the step velocity exceeds a critical value. Near the threshold of the insta bility, an isotropic step obeys the Kuramoto-Sivashinsky equation, H-T = - H-XX - H-XXXX + (H-X(2)/2), and shows a chaotic pattern. A step with anisot ropic kinetics obeys the Benney equation, H-T = - H-XX - delta H-XXX - H-XX XX + (H-X(2)/2), and the wandering pattern changes: when the anisotropy is strong, delta much greater than 1, the step shows a regular pattern. Near t he threshold of the instability, the anisotropy effect becomes strong while that of the step stiffness becomes weak. (C) 1999 Elsevier Science B.V. Al l rights reserved.