Electrochemical etching

Abstract

The formation of two-dimensional negative nuclei (“Hohlkeime”) during the etching of edge dislocation emergence points has been appreciated as an atomistic process. Experimentally, by means of double-pulse potentiostatic method, {0001}-faces of zinc single crystals have been etched electrochemically according to a new “droplet” technique (in 1 N ZnSO 4 water solution). In this way the emergence points of screw and edge dislocations have been distinguished, the former being developed by deep pyramidal etch pits whereas the latter created flat-bottomed pits. By the electrochemical etching we observed ivariably 〈11 2 0〉 pit orientation (and, perhaps, in connection with this the appearance of non-symmetrical etch pits on the emergence points of screw dislocations with the Burgers vector 1 3 〈11 2 3〉). In contrast, the chemical etchant of Rosenbaum and Saffren (alcoholic HCl solution) created 〈10 1 0〉 oriented pits. Anyway, our experiments showed that the addition of SO 2− 4 to this etchant in concentrations exceeding 1:4 changes the azimuthal orientation of the chemically produced etch pits in 〈11 2 0〉 and it was concluded that the SO 2− 4 selective adsorption changes significantly the polar diagram of the lateral dissolution rate.