Roles of Surface/Volume Diffusion in the Growth Kinetics of Elementary Spiral Steps on Ice Basal Faces Grown from Water Vapor

We measured velocities V-step of lateral displacement of individual elementary steps on an ice basal face, for the first time, by advanced optical microscopy, under various bulk water vapor pressure p(H2O)(infinity). Distances L between adjacent spiral steps exhibited considerable variation under constant p(H2O)(infinity). Hence, we analyzed V-step as functions of L and p(H2O)(infinity). Then we found that (1) under a constant p(H2O)(infinity), V-step decreased with decreasing distances L when L <= 15 mu m and that V-step remained constant when L >= 15 mu m. We named V-step of L >= 15 mu m (isolated steps) V-step(int) and analyzed dependencies of V-step(int) on p(H2O)(infinity). Then we found that (2) the slope of the V-step(int) vs p(H2O)(infinity) plot gradually decreased with increasing p(H2O)(infinity). We proposed a model that took into account both the volume diffusion of water vapor molecules and the surface diffusion of water admolecules on a terrace. Our model could explain result (1) mainly by the competition of adjacent spiral steps for water admolecules diffusing on a terrace but could not explain the result (2) satisfactorily.