Large‐Area 2D Layered MoTe₂ by Physical Vapor Deposition and Solid‐Phase Crystallization in a Tellurium‐Free Atmosphere

Abstract

Molybdenum ditelluride (MoTe2) has attracted considerable interest for nanoelectronic, optoelectronic, spintronic, and valleytronic applications because of its modest band gap, high fieldeffect mobility, large spin-orbit-coupling splitting, and tunable 1T′/2H phases. However, synthesizing large-area, high-quality MoTe2 remains challenging. The complicated design of gasphase reactant transport and reaction for chemical vapor deposition or tellurization is nontrivial because of the weak bonding energy between Mo and Te. Here, we report a new method for depositing MoTe2 that entails using physical vapor deposition followed by a post-annealing process in a Te-free atmosphere. Both Mo and Te were physically deposited onto the substrate by sputtering a MoTe2 target. A composite SiO2 capping layer was designed to prevent Te sublimation during the post-annealing process. The post-annealing process facilitated 1T′-to-2H phase transition and solid-phase crystallization, leading to the formation of high-crystallinity few-layer 2H-MoTe2 with a field-effect mobility of ~10 cm 2 /(V•s), the highest among all nonexfoliated 2H-MoTe2 currently reported. Furthermore, 2H-MoS2 and Td-WTe2 can be deposited using similar methods. Requiring no transfer or chemical reaction of metal and chalcogen reactants in the gas phase, the proposed method is potentially a general yet simple approach for depositing a wide variety of large-area, high-quality, two-dimensional layered structures.

Selective phase growth and precise-layer control in MoTe2

“…For example, the peak associated with the E 1g -mode is unresolved due to the higher background. The subdued intensities are due to the transparency of the sapphire substrate to laser light 31 , which is in line with the previous observations for a 2.1 nm MoTe 2 film obtained on sapphire by physical vapour deposition 36 .…”

Reversible Electrochemical Phase Change in Monolayer to Bulk-like MoTe2 by Ionic Liquid Gating

“…Figure 5 shows a series of Raman maps highlighting the presence of a Te metal film next to a MoTe2 flake. Representative spectra from the Raman maps are plotted in Figure 5e displaying the characteristic Te metal peaks 28,29 at ~120 cm -1 and ~140 cm -1 as well as the 2H E2g MoTe2 and Silicon peaks. Because the p++ Si electrode is used as a universal contact, electrically connecting every flake on the substrate, we hypothesize that the Te metal film plates out of the ionic liquid and that the Te atoms potentially come from all MoTe2 flakes on the substrate and not solely from the flake in the image.…”

Strategies on Phase Control in Transition Metal Dichalcogenides

“…Currently, although many methods have been tried in the fabrication of TMDs, the CVD method is the one that is widely employed for high quality TMDs . The formation of a stable phase in TMDs is closely related with synthesis conditions, such as temperature, precursor type, ratio of precursors, and the growth procedure.…”