Large-area synthesis of high-quality monolayer 1T’-WTe ₂ flakes

Abstract

Large-area growth of monolayer films of the transition metal dichalcogenides is of the utmost importance in this rapidly advancing research area. The mechanical exfoliation method offers high quality monolayer material but it is a problematic approach when applied to materials that are not air stable. One important example is 1T’-WTe2, which in multilayer form is reported to possess a large non saturating magnetoresistance, pressure induced superconductivity, and a weak antilocalization effect, but electrical data for the monolayer is yet to be reported due to its rapid degradation in air. Here we report a reliable and reproducible large-area growth process for obtaining many monolayer 1T’-WTe2 flakes. We confirmed the composition and structure of monolayer 1T’-WTe2 flakes using x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Raman spectroscopy and aberration corrected transmission electron microscopy. We studied the time dependent degradation of monolayer 1T’-WTe2 under ambient conditions, and we used first-principles calculations to identify reaction with oxygen as the degradation mechanism. Finally we investigated the electrical properties of monolayer 1T’-WTe2 and found metallic conduction at low temperature along with a weak antilocalization effect that is evidence for strong spin–orbit coupling.

Synthesis of tungsten ditelluride thin films and highly crystalline nanobelts from pre-deposited reactants

“…There has been some work on the bottom-up growth of nanoscale WTe 2 ; however, large-area and reproducible synthesis remains an open challenge [34,35]. Table 1 gives an overview of a range of publications that synthesised WTe 2 on the nanoscale.…”

“…Table 1 gives an overview of a range of publications that synthesised WTe 2 on the nanoscale. Chemical vapour deposition (CVD) growth of WTe 2 has achieved single-crystal monolayers with lateral dimensions on the order of tens to hundreds of micrometres from Te, WO 3 and WCl 6 precursors [34,35,40]. Despite requiring high growth temperatures, 650-800 °C, CVD growth remains the most promising method for highquality monolayer synthesis.…”

A Review of the Characteristics, Synthesis, and Thermodynamics of Type-II Weyl Semimetal WTe2

“…Furthermore, Naylor et al presented an accessible CVD method to fabricate monolayer 1T’-WTe 2 flakes, and the surface coverage of this method was around 20%. They also suggested that the degradation of WTe 2 could be averted by reducing the handling time and introducing few-layer graphene onto the substrate instantly after the reaction to passivate the WTe 2 [ 44 ]. There are two stacking sequences in the bilayer WTe 2 , and low-temperature transport measurements indicate a semimetal–insulator transition, as mentioned [ 45 ].…”

Raman spectrum of layered jacutingaite (Pt2HgSe3) crystals—Experimental and theoretical study

“…In the group of materials that can be exfoliated into monolayers and that have been predicted to be QSHI are the 1T ′ polytypes of some transition metal dichalcogenides, with scanning tunneling microscopy work detecting edge states for WTe 2 , MoS 2 , and WSe 2 . From these, MoS 2 and WSe 2 are unstable and tend to convert to the 2H phase, whereas WTe 2 quickly oxidizes in air . These issues make clear the urgency for the search and characterization of new stable materials with convenient structures to be applied as QSHIs and 3D topological insulators.…”