Electron Spectroscopic Imaging and Diffraction in TEM

Abstract

Energy-filtering electron microscopy at 80 keV (ZEISS EM902) offers the combination of electron spectroscopic imaging (ESI) and diffraction (ESD) and electron energy-loss spectroscopy (EELS). For details the reader is referred to a description of the different modes, applications of ESI to biological and crystalline specimens and of ESD. The very important mode of elemental mapping with the difference of ESI below and beyond an edge will not be discussed in this review.The ESI mode increases scattering contrast of stained and unstained biological sections and avoids chromatic aberration by zero-loss filtering. Filtering at ΔE=250 eV below the C edge increases the (structure-sensitive) contrast by non-carbon atoms of unstained sections (Fig.1). Phase contrast is also increased but inelastically scattered electrons show a faint phase contrast which can be explained by treating partial inelastic waves with different q as incoherent. Bragg contrast of crystalline specimens is enhanced due to avoiding chromatic aberration and a blurring by the spectrum of excitation errors of inelastically scattered electrons (Fig.2).