Theoretical background for HRTEM

HRTEM images closely depend not only on some optical factors in the imaging process by the electron lens, but also on a scattering process of the electrons 

Let us begin with a simple case where a central beam and one diffracted beam pass through the objective aperture of an electron microscope. Both beams starting from a site in the bottom surface of a thin specimen meet again at the image plane to form an image. With their contributions at the site X[ on the image plane, and the amplitude and intensity of the resultant 

A phase difference arises between Woixi) and x ) mainly because of the difference in the path length. As a result, interference fringes (a lattice image) appear in the image. The image contrast is called phase contrast since it owes its origin to the phase difference. For a very thin specimen with an incident beam of unit amplitude, 7q = 1 7g, 

Let us consider the imaging mechanism of a lattice image using Fig. 1.1(a) 

Secondly, these spots become new sources so that the electrons starting here 

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