Using atomic force microscopy to image the surface of the powdered catalyst KMn8O16

Atomic force microscopy (AFM) was used to determine the atomic configuration and topography of the surface of KMn8O16, a powdered form of alpha-manganese dioxide (alpha-MnO2) containing K ions, By depositing the powder on mica, we were able for the first time to use AFM to image the surface of the powder. We took three types of images: low-resolution, wide-scan (5 x 5 mu m(2) region); high-resolution (500 x 500 nm(2) region); and atomic-scale (10 x 10 and 2 x 2 nm(2) regions). The low-resolution imaging showed that the powder has needle-like crystallites. The high-resolution imaging showed that the surface of the powder has a ''faceted'' structure, The atomic-scale imaging revealed that the facet plane has a hill-and-valley structure with a height difference of 0.2-0.3 nm along the crystal C axis, Furthermore, the surfaces of the hills were (110) surfaces, and those of the valleys were surfaces formed by the removal of O-Mn-O units from these (110) surfaces, Atomic-scale imaging of a hill shows a periodic structure that corresponds to the configuration of surface hydroxyl species and bridging oxygen atoms of the (110) plane, The close agreement that we found when we superimposed the atomic-scale images and the bulk structure projection indicates that there is no reconstruction on the (110) surface of powdered KMn8O16. (C) 1996 Academic Press, Inc.