Crossover in the scaling behavior of ion-sputtered Pd(001)

We investigate morphological evolution of Ar+ ion sputtered Pd(001) by in situ real-time x-ray reflectivity and grazing incidence small angle x-ray scattering (GISAXS) experiments. Surface roughness W, and its dynamic scaling behavior show a definite crossover across a crossover time t(c). Before t(c), growth exponent beta, varies from 0.20 to 0.49 depending on substrate temperature, T. After t(c), beta drops to similar to 0.1, irrespective to substrate temperature. Satellite peaks in GISAXS indicating laterally ordered structure develop as the growth time approaches t(c), which become clear with further sputtering. We think that the crossover behavior near t(c) indicates the reduction of non-linear effect and the scaling behavior would follow the Edwards-Wilkinson model.