STM investigation of galena surfaces in air

The scanning tunnelling microscope has been used to resolve the surface microstructure of natural galena (PbS), cleaved in air. Large atomically flat (001) planes with single and multiple atom layer steps are common. Cubic (100) facets and dislocations are observed. Surfaces exposed to air for several days have also been imaged and results are compared with oxide depth measurements by XPS. We present evidence for discontinuous oxide layers on these air-exposed surfaces, which may have some implications in the flotation chemistry of minerals of this type.