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

## TL;DR

This paper explains how breaking Friedel’s law in LEED patterns confirms unidirectional growth of monolayer MoS2, offering a new way to verify its crystal orientation.

## Contribution

The study provides a novel understanding of LEED intensity asymmetries as evidence of non-centrosymmetric monolayer MoS2 growth.

## Key findings

- LEED intensity asymmetries reflect the non-centrosymmetric nature of monolayer MoS2.
- Dynamical scattering amplifies these asymmetries, enabling precise orientation determination.
- This method fills a critical gap in the qualitative interpretation of LEED for monolayer characterization.

## 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.