Transmission electron microtomography without the "missing wedge" for quantitative structural analysis

A three-dimensional (3D) visualization and structural analysis of a rod-shaped specimen of a zirconia/polymer nanocomposite material were carried out by transmission electron microtomography (TEMT) with particular emphasis on complete rotation of the specimen (tilt angular range: ±90°). In order to achieve such an ideal experimental condition for the TEMT, improvements in the specimen as well as the sample holder were made. A rod-shaped specimen was necessary in order to obtain a high transmission of the specimen upon tilting to large angles. The image resolution of the reconstructed tomogram was isotropic, in sharp contrast to the anisotropic image resolution of the conventional TEMT with a limited angular range (the "missing wedge" problem). A volume fraction of zirconia, φ, evaluated from the 3D reconstruction was in quantitative agreement with the known composition of the nanocomposite. A series of 3D reconstructions was made from the tilt series with complete rotation by limiting the maximum tilt angle, α, from which a couple of structural parameters, the volume fraction and surface area per unit volume, Σ, of the zirconia, were evaluated as a function of α. It was confirmed from actual experimental data that both φ and Σ slightly decreased with the increasing α and reached constant values at around α = 80 °, suggesting that the specimen may have to be tilted to ±80° for truly quantitative measurements.