Pits were produced by etching the (111) surfaces of single crystals for 10 to 50s at 280 to 300K using the Marukawa solution (FeCl3-6H2O-HCl-HBr). Electron microscopic observations of replicas revealed that spiral terraces often occurred at the apices of the etch pits that formed at screw dislocation sites. When the etching time was increased from 10 to 50s at 280K, concentric and closed terraces developed on the side faces, and several turns of a spiral terrace (clockwise or anti-clockwise) appeared at the apices. A similar morphological change was more apparent after etching for 10s, upon increasing the etching temperature from 280 to 300K. The spiral terraces tended to occupy somewhat wider regions as the etching time and temperature were increased. It was proposed that the formation of terraces originated from a bunching of steps that was caused by their retarded motion which, in turn, resulted from the adsorption of inhibitors at the steps.

S.Sugawara: Japanese Journal of Applied Physics, 1995, 34[1-10], 5729-31