Revisiting Dynamical Theory To Elucidate Friedel's Law Breaking in Low-Energy Electron Diffraction as Strong Evidence of Unidirectional Growth of Monolayer 2H MoS2

Abstract

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-V) 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.