Abstract
The computer-image simulation technique was used to address the interpretation of one-dimensional high-resolution transmission electron microscopy (1-d hrtem) images of sheet silicates and their intergrowths. Simulated images as functions of focus and small variations in specimen orientation were calculated for kaolinite, lizardite, chlorite, vermiculite, muscovite, and phlogopite and for intergrown illite/smectite, phlogopite/chlorite, lizardite/chlorite, and brucite/chlorite.
The simulations showed that compositional periodicities resulting from interlayer cation ordering and structural information pertaining to layer sequence and approximate layer thickness can be inferred from simple 1-d hrtem images of the basal planes of sheet silicates. However, dilferent specific imaging conditions were required to image compositional periodicities and structural information properly. Compositional periodicities were best reflected in overfocused images; structural information was conveyed accurately only in images obtained near the Scherzer focus.
The simulated images varied strongly with specimen orientation and microscope focus. They showed that, in many cases, ambiguities may be present in the interpretation of experimental 1-d hrtem images. The ambiguities, however, can be eliminated by an appropriate choice of imaging conditions (specimen orientation and focus). In materials where it is difficult to control these parameters accurately, such as clays and other finegrained specimens, intuitive interpretations of 1-d hrtem images may be in error.
