The next generation of 2D semiconductor materials doesn't like what it sees when it looks in the mirror. Current synthesizing approaches to make single-layer nanosheets of semiconducting material for atomically thin electronics develop a peculiar "mirror twin" defect when the material is deposited on single-crystal substrates like sapphire. The synthesized nanosheet contains grain boundaries that act as a mirror, with the arrangement of atoms on each side organized in reflected opposition to one another.
