Ambient atomic force microscopy images of stilbite and their interpretation by molecular simulations

Atomic level AFM images of a cleaved (010) surface of stilbite, a natural zeolite, were obtained under ambient conditions. Two types of images were observed: one showing a surface which is close to bulk termination and the other showing a different atomic arrangement. The former gave surface lattice constants close to those of the bulk but within the surface unit cell the atomic arrangements differ from what is expected for the (010) surface. The latter showed periodicity in c direction 1.5 times that of bulk. Using a recently developed AFM simulator based on a molecular simulation technique, the bulk-terminated surface image was interpreted as the image of a surface partially covered with adsorbate. Reasons for the appearance of the nonbulk-terminated surface are examined.