Discussion of Electron Induced Atomic Number Contrast

In this paper, atomic number (Z) contrast from electron induced images is revisited. Z contrast obtained with a scanning electron microscope (SEM) is generally associated with the collection of backscattered electrons (BSEs) and is considered to exhibit a monotonic increase in BSE signal with Z [1]. However, there is no monotonic relationship of the backscattering coefficient, η, with Z at electron energy E < 5 keV [2-5]. This is clearly illustrated in FIG. 1 which plots η as a function of Z for E < 5 keV using data from reference [2].