Abstract
ANY mechanism for producing Archimedes spirals on flat surfaces is interesting because of the great importance attached to these shapes in studies of crystal growth. When spiral figures appear on etched crystal surfaces, they are usually interpreted as dissolution structures related to screw dislocations. Spiral shapes on some electrolytically etched metal surfaces are not easily explained in this way, however, because they cross grain boundaries and are spiral troughs rather than the spiral terraces predicted from the screw dislocation mechanism1–3. It has been suggested that these spiral figures on metals, which are noted to form only in very special circumstances, may be the formation of a new phase, perhaps an oxide of a salt1–3. The chemistry at the etching surfaces is very complex, and the spirals remain a problem.
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