Revisiting Dynamical Theory To Elucidate Friedel’s Law Breaking in Low-Energy Electron Diffraction as Strong Evidence of Unidirectional Growth of Monolayer 2H MoS ₂

Unidirectional growth of monolayer molybdenum disulfide (MoS₂) holds immense promise for next-generation 2D electronics, yet robust and facile characterization techniques to verify its single-crystal characteristics at the wafer scale remain elusive. Although 3-fold symmetric low-energy electron diffraction (LEED) patterns have been presented as evidence of such growth, their fundamental origin and precise link to MoS₂ orientation have not been clearly understood. Here, we revisit dynamical theory to elucidate Friedel's law breaking in LEED, providing a comprehensive understanding of energy-dependent LEED intensities that uniquely confirm unidirectional growth of the monolayer 2H MoS₂. By systematically acquiring LEED intensity-voltage (<i>I</i>-<i>V</i>) curves, we reveal that the distinct intensity asymmetries observed in symmetry-related diffraction spots directly reflect the non-centrosymmetric characteristic of the MoS₂ monolayer, amplified by dynamical scattering. This approach allows an unambiguous determination of the monolayer orientation, addressing a critical gap in the qualitative interpretation of LEED.