INVESTIGATIONS OF MICAS USING ADVANCED TRANSMISSION ELECTRON MICROSCOPY

Abstract

After a long history of development and improvement, recent transmission electron microscopes (TEMs) with various analytical functions have become important in material science and engineering. These functions include not only obtaining magnified images of specimens, but also electron-diffraction patterns, chemical analyses, and chemical-state analyses with spacial resolution far greater than other methodologies. It is impossible to cover all of these functions considering page limitations and, more importantly, considering the author’s knowledge and ability even for topics limited to studies of mica. This chapter focuses on the investigations of mica using high-resolution transmission electron microscopy (HRTEM). HRTEM is generally defined as a technique to obtain information about atomic structures in crystals from TEM images formed by phase contrast at high magnifications. Although HRTEM is just one of many functions in TEMs, several examples in sections below demonstrate that HRTEM often plays a decisive role in determining the local atomic arrangements in mica. An early study of mica by HRTEM was reported by Buseck and Iijima (1974). They clearly observed three dark lines representing a mica layer (the lines correspond to the two tetrahedral sheets and one octahedral sheet) and that cleavage was formed at the interlayer. During a quarter century after this pioneering work, many HRTEM studies for mica and related phyllosilicates have been reported (for instance, see the references in Baronnet 1992). These included many studies of mica, e.g., polytypism, transformations, defects and interface research. In the following section, recent HRTEM and related techniques are briefly reviewed. Next, two topics of HRTEM investigation, polytype and defect analyses are presented based on studies, mainly by the author and his colleagues. ### Transmission electron microscopy After the invention of TEM by E.E. Ruska in 1932, this apparatus was improved rapidly in response to requests from many fields of science. In the 1950s, lattice fringes in …