Muscovite surface structure imaged by fluid contact mode AFM

Abstract

The surface structure of muscovite was imaged using an atomic force microscope (AFM) in contact mode in water. The following three types of AFM images were observed: (1) those showing clearly the arrangement of hexagonal rings of SiO4 tetrahedra; (2) those showing a hexagonal array of bright spots separated by a distance of about 5.3 A; and (3) those changing gradually from image (2) to image (1). Image (1) successfully provides information on the tetrahedral tilt and basal surface corrugation that are particularly characteristic of dioctahedral micas. The mean unit cell dimensions for the muscovite surface measured from Image (1) were slightly longer than those of the bulk structure, due to the rehydration of the tetrahedral sheet and/or surface relaxation. Image (2) was made by varying the scan angles, even on the same surface in which Image (1) was obtained. Image (3) has information on a single plane rather than on two or more planes involving steps, kinks and so on. Therefore, what is depicted in Images (2) and (3) is not the arrangement of interlayer K ions but the basal plane of the tetrahedral sheet. Some structural relaxation of the tetrahedral sheet surface was also observed. Gradual expansion and contraction of hexagonal rings were randomly found on the muscovite surface. The surface relaxation results from a tetrahedral rotation and/or tilting after cleaving, since significant variations of both distances and bond angles between adjacent SiO4 tetrahedra on the surface were found.