Fig. 4: Numerical validation for dual-layer pop-out metrology.

a The radial average of Thon rings from a dual-layer specimen (simulated) and the radial average of the sum of contrast transfer functions (CTFs) from the defocus values of both layers. Both layers are 25 nm in thickness, and they are 180 nm apart; the defocus applied on the exit wave is 500 nm. Hence the centre of mass of both layers from the image plane is 512.5 nm and 717.5 nm. b A dual-layer 3D model is simulated, and the pop-out reconstruction is generated using the prior that the thickness of the top layer is known. c A dual-layer 3D model is simulated (total dose 20,000 e Å⁻²), and the pop-out reconstruction is generated using the amplitude ratio between the additive CTFs fitted for the top and bottom layers. This reconstruction shows that the additive CTF model can also provide relative layer thickness information as well as with depth information. The resolution voxel size (r.v.) indicates the corresponding reconstruction resolution.