Higher order Laue zone effects in electron diffraction and their use in lattice parameter determination

By fitting small probe-forming lenses into a conventional electron microscope, we have been able to observe higher order Laue zone (h.o.l.z.) diffraction effects from high symmetry zone axes of a wide variety of materials. Cooling the specimen with liquid nitrogen both greatly reduces the contamination rate and increases the visibility of the h.o.l.z. lines. An interpretation of these lines is given in terms of the dispersion surface construction and conditions for the visibility of h.o.l.z. effects are deduced. A theory from which numerical solutions have been obtained is outlined. Using h.o.l.z. lines, we can deduce the microscope operating voltage or the lattice parameter of the specimen to approximately one part in a thousand; relative changes can be measured about five times more precisely. The spatial resolution of the technique is approximately 10 nm. Strain gradients within the illuminated area can produce fringe patterns.