We have studied smoothing kinetics of Rh(111) surfaces during low temperature annealing using in-situ real-time reflection high energy electron diffraction and scanning tunneling microscopy. The initial surface features were produced by low temperature homoepitaxial growth of Rh (111). Two types of surfaces were studied, surfaces with two-dimensional (2D) islands at submonolayer coverages, and those with 3D multilayered features. 2D islands coarsen rapidly at the onset of the anneal.3D features are more stable initially. Their annealing process exhibits a distinct transition from an initial slow coarsening, characterized by a nearly linear growth of lateral size, to a rapid flattening. The activation energy for the transition is approx 0.6 eV. The observed behavior indicates that the smoothing kinetics in the low temperature regime is limited by adatom detachment from the step-edges, and that the fast process for the 3D features is made possible by the formation of a network of "chain-like" structures which provide new pathways for diffusion thus overcoming the slow detachment kinetics. These effects determine the low temperature stability of the non-equilibrium epitaxial morphologies.
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