The imaging of amorphous specimens in a tilted-beam electron microscope

Abstract

The transfer function of an electron microscope used in the tilted-beam interference mode is investigated. It is shown that tilting in the presence of spherical aberration introduces terms into the real part of the transfer function having the forms associated in the axial mode with overfocusing and axial astigmatism. The effect of the phase part of the transfer function can be seen as a combination of shift and blurring of the image. Attempts to improve the transfer function by use of the microscope stigmator can at best restore it to its axial (untilted) form. The implications for the tilted-beam 'lattice imaging' of amorphous semiconductors are discussed. The results explain recent experimental data on noncrystalline materials.