Selective phase growth and precise-layer control in MoTe2

Abstract

Minor structural changes in transition metal dichalcogenides can have dramatic effects on their electronic properties. This makes the quest for key parameters that enable a selective choice between the competing metallic and semiconducting phases in the 2D MoTe 2 system compelling. Herein, we report the optimal conditions at which the choice of the initial seed layer dictates the type of crystal structure of atomically-thin MoTe 2 films grown by chemical vapour deposition (CVD). When Mo metal is used as a seed layer, semiconducting 2H-MoTe 2 is the only product. Conversely, MoO 3 leads to the preferential growth of metallic 1T′-MoTe 2. The control over phase growth allows for simultaneous deposition of both 2H-MoTe 2 and 1T′-MoTe 2 phases on a single substrate during one CVD reaction. Furthermore, Rhodamine 6G dye can be detected using few-layered 1T′-MoTe 2 films down to 5 nM concentration, demonstrating surface enhanced Raman spectroscopy (SERS) with sensitivity several orders of magnitude higher than for bulk 1T′-MoTe 2 .

Chemical Vapor Deposition Mediated Phase Engineering for 2D Transition Metal Dichalcogenides: Strategies and Applications

“…Polymorphs of MoTe 2 have also been studied by Raman spectroscopy; 1T′ and 2H phases have been identified (Figure 6b). [ 43,44 ] The characteristic Raman peaks of 2H MoTe 2 corresponding to the E 1 2g , A 1g , and B 1 2g modes can be found at 174, 234, and 289 cm −1 , respectively. A reduced symmetry is exhibited by the 1T′ with peaks indexed as A g modes at 80, 108, 125, 163, and 265 cm −1 and a B g mode at 186 cm −1 , respectively.…”

“…Reproduced under the terms of the CC‐BY 4.0 license. [ 44 ] Copyright 2020, The Authors, published by Springer Nature. c) XPS analysis of Mo 3 d , S 2 s , and S 2 p core levels of samples annealed at different temperatures.…”

“…[ 32,56 ] Recently, Fraser et al also investigated the effect of transition metal precursors, Mo and MoO 2 , on tuning the phases of MoTe 2 . [ 44 ] Instead of the commonly used Te powder, FeTe 2 was used as the source of tellurium. The results revealed that Mo produces 2H phase, which has been hypothetically explained by the preference of the formation of the highly symmetric 2H phase from the highly symmetric crystalline Mo precursor.…”

“…On the contrary, MoO 2 produced 1T′ phase, probably because both present the lower monoclinic symmetry, based on a similar argument. [ 44 ] Stoichiometry/nonstoichiometry of the precursors is also an important factor leading to phase engineering. Tellurization of MoO 3 at all temperatures leads to 2H phase MoTe 2 deposition, while MoO 2.0–2.5 leads to temperature‐ and time‐dependent selection of 2H and 1T′ phases.…”

Toward understanding the phase-selective growth mechanism of films and geometrically-shaped flakes of 2D MoTe2

“…For example, Park et al 11 successfully synthesized centimeter-scale 2H-and 1T 0 -MoTe 2 lms by varying the Te partial pressure and quenching time, and Xu et al 12 reported the synthesis of the single crystals of 2H-and 1T 0 -MoTe 2 in a two-step CVD process, where the 2D MoO 2 single crystals were grown rst and were tellurized at different temperatures for growing different phases. Large area 2H-and 1T 0 -MoTe 2 lms have also been controllably synthesized by adjusting the substrate location and the cooling rate aer completion of the growth, 13 and by tellurizing the Mo metal lm and MoO 3 lms, 14 respectively. There are a few more reports [15][16][17][18] that also demonstrated the phase-controlled growth of large area 2H-and 1T 0 -MoTe 2 lms.…”