Fig. 6

a Relation between specimen thickness at contrast inversion and primary electron energy for PTB7 and PC₇₁BM derived from measurements and MC simulations using different scattering cross-sections. The inset in a shows a top-view SEM image of FIB-prepared TEM lamella with a constant thickness of about 184 nm. b–d HAADF–STEM cross-section images of the sample with stacked pure PC₇₁BM and PTB7 layers using a FIB-prepared lamella with a constant sample thickness taken at b 8 keV, c 16.5 keV, and d 30 keV. The grey line in a marks the electron energy (16.5 keV) at contrast inversion according to c and the derived lamella thickness. Images in b–d are post-processed according to the procedure described in  “Materials and methods” section