The Contrast of Electron Microscope Images of Thick Crystalline Object. Experiment with an Al-Mg-Si Alloy at 50-100 kV.

Abstract

The deterioration of the quality of electron microscope images with the increase of specimen thickness was studied at 50, 80 and 100 kV. The specimen used was an Al-Mg-Si alloy which has linear-precipitates along directions in the aluminium matrix. The images of the precipitates became invisible at 0.9, 1.4 and 1.7 µm at 50, 80 and 100 kV, respectively. The width of the images increased with the specimen thickness. However, the increase was much smaller than that calculated by use of the current formula of the chromatic aberration. The images became invisible due to the decrease of contrast. These results are explained by a detailed treatment of the chromatic aberration.