We quantitatively analyzed the contrast degradation and blur of 20-nm gold nanoparticles adsorbed on the top of amorphous silicon films of thicknesses of 0.54, 1.09, 1.63 and 2.2 μm in bright-field transmission electron microscope (TEM) images taken at accelerating voltages of 0.5, 1, 2 and 3 MeV. The thickness dependence of the transmission was well explained and consistent with our calculations. The blur function, derived by assuming that the TEM image of a thick specimen can be reproduced by convolving the TEM image of a very thin specimen with it, was found to be expressed by a two-dimensional Lorentzian function. Considering the two characteristics of the Lorentzian function, a sharp peak around the center and a long tail, we concluded that, for TEM observations of thick specimens, the image contrast is degraded predominantly by inelastic scattering and the image is blurred predominantly by multiple elastic scattering.
Keywords: blur function; contrast; transmission; ultra-high-voltage transmission electron microscope.