Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2023 / Paper 1 / Section A(i) / 1 / iv

A coarse fringe in a high-resolution transmission electron microscopy image need not directly identify the lattice spacing of a new phase. Check whether overlapping crystals, a particle and its substrate, or differently oriented domains can produce the corresponding moiré fringe. Compare the underlying reciprocal-space peaks and their difference, use the particle boundary to constrain how many periods are actually sampled, and examine neighbouring or differently oriented regions. For the closest pair here, fitting a periodicity from less than one complete period is particularly unreliable. Distinguishing lattice contrast from a beat envelope prevents misidentifying a phase or over-interpreting local strain.