The Observation of Thick Specimens by High Voltage Electron Microscopy. II. Experiment with Molybdenite Films at 50-1200 kV.

Abstract

The maximum usable thickness of specimens, below which dislocation images were observable by transmission, was studied experimentally in the region 50–500 kV in the previous work [Japan J. appl. Phys. 6 (1967), 557]. The present work is a continuation of the previous one. The maximum usable thickness was determined by comparing the quality of images. The experimental result turned out to be 1.5, 2.5, 4.0, 5.0 and 6.0 µm at 100, 200, 500, 1000 and 1200 kV, respectively. These values are approximately proportional to β 2 =( v / c ) 2 , although the value at 1200 kV is a little too high. The factors limiting the observation of thick specimens, i.e. image intensity, resolution and contrast, are discussed. It is not yet clear whether the above result is common to other materials or is valid in the higher voltage region.