IMAGING THE INTERNAL ATOMIC-STRUCTURE OF LAYER SILICATES USING THE ATOMIC-FORCE MICROSCOPE

Use of the atomic force microscope (AFM) need not be restricted to the uppermost surface. A high tracking force on the cantilever tip can be used to remove atoms that comprise the upper surface layer and thus r eveal a material's near-surface internal structure. This technique was used to study the 1:1 layer silicate lizardite, Mg3Si2O5(OH)(4). Forc es of up to 325 nN on the cantilever tip rapidly remove both the oxyge n and silicon atoms of the sheet of tetrahedra to reveal the hydroxyl groups and oxygen atoms that form a central plane common to both the s heets of tetrahedra and octahedra of the 1:1 layer structure. Similar results were obtained with two other layered silicates, muscovite and clinochlore. The large hexagonal rings of the sheets of tetrahedra app ear to be a key factor in the layer-by-layer removal by providing an o pening for the initiation of the process. The large rings also allow a ccess of ambient H2O molecules, which could dissociate to H+ and OH- a nd satisfy the bonds broken by the removal of the surface atoms.