Natural science is now extensively developed thanks to electron microscopy, but around 1950, only thin specimens were used because of the low accelerating voltages. The behavior of crystalline materials is very sensitive to specimen thickness, and thus in Japan a practical 500 kV electron microscope was constructed in 1965 for thicker specimens. It was shown that simultaneous reflection increases with increasing accelerating voltage, so that the maximum observable specimen thickness increases almost linearly up to 500 kV. Since simultaneous reflection becomes prominent above 1,500 kV, the in-situ observation of various phenomena representative of most bulk materials has been carried out with an ultra-high voltage electron microscope, whose accelerating voltages can reach 3,000 kV. Thus, even the characteristics of high-Z materials have been clarified in detail, and new applications, such as foreign atom implantation and the formation of non-equilibrium phases, have also been developed. The present account deals mainly with the importance of 3,000 kV electron microscopes, as applied to the new research fields of materials science.


(Contributed by Hiroshi FUJITA, M.J.A.)