High-angle annular dark-field microscopy of franckeite

Franckeite (~FeSn₃Pb₅Sb₂S₁₄) is a sulfosalt mineral with a modulated structure. Its complex composition and composite layered structure, lack of a well-defined unit cell, incommensurate character, and poor crystal quality have made its structure difficult to study by standard X-ray and electron diffraction methods. Imaging by high-angle, annular, dark-field (HAADF) scanning transmission electron microscopy provides a way of mapping compositional distributions close to an atomic scale. By comparing the structure as viewed by standard high-resolution transmission electron microscopy with the compositional information provided by the HAADF technique, it was possible to test and confirm the assumption that layers consisting of multiple sheets of SnS₂ and PbS are stacked along the a axis with a 1.73 nm repeat. -from Authors