The contrast of images formed by atomic focusers

The feasibility of the various modes for using atomic focusers to attain resolutions of 0.5 إ or better in TEM or STEM instruments, as proposed in a previous paper [Cowley, Spence and Smirnov, Ultramicroscopy 68 (1997) 135], has been confirmed in two ways. Firstly, theoretical expressions for the image contrast have been derived using a simple, justifiable, approximation for the transmission function of the focusers and show that components of the image intensity functions with the desired resolution exist. Secondly, computer simulations of the imaging for specimens consisting of pairs of gold atoms have demonstrated resolutions of 0.5 إ or better, with good contrast, for the modes involving the placing of the specimen at a Fourier image distance from a crystal multiple atomic focuser.