The (001) surface of a white-tin crystal was etched with a HCl-NH₄NO₃-CuSO₄ solution (288 K) in order to form etch-hillocks at dislocation sites, and their shape and growth rate were investigated by replica electron microscopy. The hillocks took the shape of a square pyramid surrounded with lateral surfaces of {011} planes and often showed traces of Cu precipitates on their apices. Their height and width increased with etching time at rates of 5.2×10⁻⁹ and 9.4×10⁻⁹ m/s, respectively.
Moreover, etch patterns of some surfaces belonging to the [100] and [11\bar1] zones were observed by optical microscopy. The dissolved thickness of their surfaces was measured by two-beam interferometry. In the [100] zone, flattened pyramidal hillocks formed only on the surfaces which were inclined gently to a (001) surface relative to the inclination of a (011) surface; no hillock formed on the surfaces belonging to the [11\bar1] zone. On the other hand, the dissolution rates of the surfaces showed a minimum value of 1.9×10⁻⁹ m/s on a (011) surface, and their rates increased in both zones as the angular distance from a (011) surface increased. A maximum dissolution rate of 5.2×10⁻⁹ m/s was obtained on a (001) surface.
These results indicate that surface orientation as well as the two conditions of dissolution rate proposed by Batterman must be satisfied for the stable growth of etch-hillocks on the surface of white-tin crystal.

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