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Abstract The layer stacking order in 2D materials strongly affects functional properties and holds promise for next-generation electronic devices. In bulk, octahedral MoTe₂possesses two stacking arrangements, the ferroelectric Weyl semimetal T_dphase and the higher-order topological insulator 1T′ phase. However, in thin flakes of MoTe₂, it is unclear if the layer stacking follows the T_d, 1T′, or an alternative stacking sequence. Here, we use atomic-resolution scanning transmission electron microscopy to directly visualize the MoTe₂layer stacking. In thin flakes, we observe highly disordered stacking, with nanoscale 1T′ and T_ddomains, as well as alternative stacking arrangements not found in the bulk. We attribute these findings to intrinsic confinement effects on the MoTe₂stacking-dependent free energy. Our results are important for the understanding of exotic physics displayed in MoTe₂flakes. More broadly, this work suggestsc-axis confinement as a method to influence layer stacking in other 2D materials. 

Abstract The phase transitions of two-dimensional (2D) materials are key to the operation of many devices with applications including energy storage and low power electronics. Nanoscale confinement in the form of reduced thickness can modulate the phase transitions of 2D materials both in their thermodynamics and kinetics. Here, using in situ Raman spectroscopy we demonstrate that reducing the thickness of MoS 2 below five layers slows the kinetics of the phase transition from 2H- to 1T′-MoS 2 induced by the electrochemical intercalation of lithium. We observe that the growth rate of 1T′ domains is suppressed in thin MoS 2 supported by SiO 2 , and attribute this growth suppression to increased interfacial effects as the thickness is reduced below 5 nm. The suppressed kinetics can be reversed by placing MoS 2 on a 2D hexagonal boron nitride ( h BN) support, which readily facilitates the release of strain induced by the phase transition. Additionally, we show that the irreversible conversion of intercalated 1T′-MoS 2 into Li 2 S and Mo is also thickness-dependent and the stability of 1T′-MoS 2 is significantly increased below five layers, requiring a much higher applied electrochemical potential to break down 1T′-MoS 2 into Li 2 S and Mo nanoclusters.