QUANTITATIVE SIMULATION OF CONTRAST OF SUPPORT FILMS IN HIGH-RESOLUTION ELECTRON-MICROSCOPY

Based on the electron wave-optical theory of image formation, the phase contrast of a single atom, consisting of the complex scattering amplitude is compared with the amplitude contrast consisting of the squared terms of elastic and inelastic scattering amplitudes as a function of spherical aberration and defocus by use of Kirchhoff diffraction integral in Fraunhofer approximation. By using these wave functions, the variations of the phase contrast with focus in image of layers of tungsten atoms simulated with the aid of a computational algorithm in an on-line graphic computer system are compared with images of carbon atoms in which the amplitude contrast due to the plasmon loss is predominant. By means of high resolution electron micrographs taken with an instrumental spherical aberration constant Cs = 0.7mm and their light optical diffractograms to check the exact amount of defocusing, it is confirmed that the theoretical resolution limit of 0.22nm is obtained in clusters of tungsten atoms. For carbon films some of the peaks of phase contrast in a range of small under-focus merge into the background noise and tend to disappear depending on the amplitude contrast. © 1979.