On the electron microscopy of biological specimens

Abstract

Calculations are presented for the elastic and inelastic image profiles for the transmission electron microscopy of amorphous (biological) materials, corresponding to objective lens defocus values, 0 to -2000 nm for an incident electron energy of 100 keV, used in the electron microscopy of biological specimens. These calculations are relevant to image analysis procedures which neglect the contribution of the inelastic electron scattering to the image intensity for these large underfocus values. For small defocus values, 0 to -200 nm, the inelastic contribution can be described as an unstructured background in the electron micrograph. However, corresponding to the larger underfocus values, -500 to -2000 nm, the elastic image resolution is inferior to that of the inelastic image. The inelastic image resolution is less dependent on the objective defocus value than the elastic image resolution, and in dark-field microscopy at defocus values -500 to -2000 nm, the inelastic image is of primary importance. In bright-field microscopy the dominance of the high-resolution elastic component is evident only for small underfocus values, but at the larger underfocus values the inelastic image is relevant.