Ultra-high-resolution electron microscopy of amorphous materials at 120 kv

Thin films of amorphous carbon, germanium and silicon have been examined by high-resolution transmission electron microscopy at 120 kV using bright-field axial illumination. Despite an interpretable resolution extending beyond the first diffraction ring of these materials, and contrast transfer to generally better than 0-25 nm, it was demonstrated that useful structural information could not be obtained from foils of around 10 nm in thickness. However, with much thinner foils, it was shown that images could be obtained which should be interpretable in terms of structure models in that phase randomization tests indicated the presence of meaningful information. For specimens of carbon and germanium of thicknesses probably less than 1 nm, both image resolution and detail visibility fell to levels lower than would be anticipated for the contrast transfer behaviour of the microscope and the projected potential values to be expected for these materials. The general problems of imago interpretation in terms of model structures for amorphous materials are further discussed with particular reference to overlap effects and the weak-phase-object approximation.