Abstract

We have used scanning tunneling microscopy (STM) to investigate defects in Ag- and Sb-bearing galena from Zacatecas, Mexico. Large-area scans produced images of topographic features that formed during cleavage. Pits occur that are from 10 to 300 nm in diameter and >30 nm deep and are surrounded by what appear to be crystal fragments. These pits are interpreted as the remains of diaphorite inclusions that were plucked during cleavage.

Most of our atomic-resolution images have 0.42-nm periodicities, corresponding to the distance between comer and face-centered atoms in the galena structure. This periodicity indicates that only half the atoms are resolved in the images. Defects in surface structure consist of atoms that are laterally displaced from their ideal positions, resulting in kinking of atomic rows that parallel [110]. These defects are unlike any reported in previous STM studies of galena, suggesting that they are unique to the Ag- and Sb-bearing samples. A possible explanation for these local disruptions of the structure is strain caused by grouped substitution of Ag and Sb for Pb.

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