Microtomography

SUMMARY The study of the internal structure of objects is the main purpose of practically all microstructural investigations. At present there are several direct and indirect methods for the analysis of the internal microstructure of specimens. The most popular of them is scanning electron microscopy in which inferences on microstructure are made from the images of cleavage or microsection surfaces. The only non‐destructive possibility for obtaining information on the internal microstructure of a specimen is by eliminating the need to break it. Information on the internal structure of an object can in this case be obtained in the form of shadow images in transmission, for instance, by means of X‐radiation (X‐ray microscopy). Unfortunately the images obtained are two‐dimensional projections and fail to give an adequate idea of the spatial microstructure. A three‐dimensional reconstruction from two‐dimensional projections constitutes the subject of computerized tomography (Herman, 1980). At present the main works in tomography are oriented for medical applications (New et al. , 1974; Hounsfield, 1973; Wood et al. , 1979). An elaborate mathematical apparatus for reproducing a three‐dimensional structure from projections enables similar methods to be used also in other fields, from the astronomy (Bracewell, 1979) to the transmission electron microscopy (Negeri, 1982). Most commercial X‐ray tomography systems permit of reconstructing objects more than 0·1 m in size with a spatial resolution to within fractions of a centimetre. In transmission electron microscopy the size of reconstructed objects is of an order of 1 μm with the spatial resolution of reconstruction to some units of nanometres. The reconstruction of the internal structure of the millimetre and micron size range specimens is the subject of the present work. Three‐dimensional reconstruction of specimens in the millimetre size range with a spatial resolution to within some micrometres proves necessary in the numerous fields of science and technology, such as materials science, defect studies (particularly for semiconductor devices and integrated circuits), biology, geology, physics, etc.