High-Energy Electron Scattering in Thick Samples Evaluated by Bright-Field Transmission Electron Microscopy, Energy-Filtering Transmission Electron Microscopy, and Electron Tomography

Energy-filtering transmission electron microscopy (TEM) and bright-field TEM can be used to extract local sample thickness t and to generate two-dimensional sample thickness maps. Electron tomography can be used to accurately verify the local t. The relations of log-ratio of zero-loss filtered energy-filtering TEM beam intensity (I-Z(LP)) and unfiltered beam intensity (I-u) versus sample thickness t were measured for five values of collection angle in a microscope equipped with an energy filter. Furthermore, log-ratio of the incident (primary) beam intensity (I-p) and the transmitted beam I-tr versus t in bright-field TEM was measured utilizing a camera before the energy filter. The measurements were performed on a multilayer sample containing eight materials and thickness t up to 800 nm. Local thickness t was verified by electron tomography. The following results are reported: The maximum thickness t(max) yielding a linear relation of log-ratio, ln (I-u /I-ZLP) and ln (I-p/I-tr), versus t. Inelastic mean free path (lambda(in)) for five values of collection angle. Total mean free path (lambda(total))of electrons excluded by an angle-limiting aperture. lambda(in) and lambda(total) are evaluated for the eight materials with atomic number from approximate to 10 to 79. The results can be utilized as a guide for upper limit of t evaluation in energy-filtering TEM and bright-field TEM and for optimizing electron tomography experiments.