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

We measured velocities Vstep 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 PH2O∞. Distances L between adjacent spiral steps exhibited considerable variation under constant PH2O∞. Hence, we analyzed Vstep as functions of L and PH2O∞. Then we found that (1) under a constant PH2O∞, Vstep decreased with decreasing distances L when L ≤ 15 μm and that Vstep remained constant when L ≥ 15 μm. We named Vstep of L ≥ 15 μm (isolated steps) Vstepint and analyzed dependencies of Vstepint on PH2O∞. Then we found that (2) the slope of the Vstepint vs PH2O∞ plot gradually decreased with increasing PH2O∞. 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 e...