How to obtain a thickness-independent image in a STEM

"Z" contrast is independent of thickness only for extremely thin specimens (3 nm of carbon). Following Egerton [Ultramicroscopy 10 (1983) 293], we propose a new method of imaging which is really independent of thickness and which provides absolute values. It consists of a mixing of the unscattered, the annular darkfield and the inelastic signal. Two-dimensional histograms are used to determine the relative efficiency factors of the different images. Thus, in addition to the obtaining of lambda i/lambda e images, the method allows the calculations of the ratios of the detection factors, of the primary beam intensity image and the production of image free of beam fluctuations. An example of such a treatment is given for a biological specimen with knife-marks.