Pressure-Driven One-Dimensional Superlattices in Monolayer Crystals on a Vicinal Surface

A 1D superlattice can be imposed on monolayer materials by the periodic atomic steps of a vicinal crystalline surface. By means of the rotational anisotropy of second harmonic generation, we demonstrate that the periodic modulation of monolayer WS₂ by the diamond (230) surface gives rise to an orientation-dependent breaking of crystal symmetry, a fundamental prerequisite for generation of a one-dimensional superlattice from a two-dimensional lattice, when subjected to external pressure. These observations contrast with the case of monolayer WS₂ on the diamond (100) surface, which largely retains its 3-fold rotational symmetry when pressure is applied. Vicinal surfaces offer a potentially versatile approach to the nanoscale periodic in-plane modulation of layered crystals and engineering their electronic and optical functionality.