Role of Heterointerface in Lithium-Induced Phase Transition in T_d-WTe₂ Nanoflakes

Abstract

A new polytype of WTe 2 with a bandgap has been recently discovered through the intercalation of lithium into the van der Waals gaps of T d -WTe 2 . Here, we report the effects of reduced thicknesses and heterointerfaces on the intercalation-induced phase transition in WTe 2 . Using in situ Raman spectroscopy during the electrochemical lithiation of WTe 2 flakes as a function of flake thickness, we observe that additional electrochemical energy is required for the phase transition of WTe 2 from the T d phase to the new lithiated T d ′ phase, going from 0.8 V of the applied electrochemical voltage for a thick flake to 0.5 V and 0.3 V for 7-and 5layered samples, respectively. We ascribe this suppression of the phase transition to the interfacial interaction between the nanoflake and SiO 2 /Si substrate, which plays an increasing role as the sample thickness is reduced. The suppressed kinetics of the phase transition can be mitigated by placing the WTe 2 flake on a hexagonal boron nitride (hBN) flake, which facilitates the release of the in-plane strain induced by the phase transition. Our study underscores the significance of interfacial effects in modulating phase transitions in two-dimensional (2D) materials, suggesting heterogeneous transition pathways, as well as interfacial engineering to control these phase transitions.

Lithiation Induced Phases in 1T′-MoTe2 Nanoflakes

“…The intercalation of lithium (Li) ions has emerged as a highly effective method for inducing structural transformations in 2D TMDs, giving rise to phases characterized by distinctive optical and electronic properties. , Numerous studies have focused on the phase transition from a semiconducting 2H phase to a metallic 1T (or 1T′) phase in MoS 2 and WS 2 induced by the intercalation of Li ions. ,, Few reports explored the effects of Li intercalation in other TMDs, such as Mo- and W- ditellurides. A new polytype of T d -WTe 2 , driven by lithiation, was recently discovered, exhibiting a unique crystal structure ( T d ′) with a bandgap opening of 0.14 eV. , For MoTe 2 , lithiation studies are sparse. When 2H-MoTe 2 nanoflakes were immersed in n -butyllithium solution at 110 °C, the transition from the 2H phase to the 1T′ phase was observed only in the top and bottom layers of the nanoflakes .…”