Two-beam diffracting conditions are used during the study of dislocations in a FCC metal structure. Which reflections should give zero contrast for the case of a Under what conditions might a phase...

Two-beam diffracting conditions are used during the study of dislocations in a FCC metal structure. Which reflections should give zero contrast for the case of a

Under what conditions might a phase contrast, lattice image be expected to mirror the atomic positions in the unit cell of a crystal? What are the problems associated with making such an assumption?