Polymorphism Control of Layered MoTe2 through Two-Dimensional Solid-Phase Crystallization

Abstract

Two-dimensional (2D) molybdenum ditelluride (MoTe 2 ) exhibits an intriguing polymorphic nature, showing stable semiconducting 2H and metallic 1T′ phases at room temperature. Polymorphism in MoTe 2 presents new opportunities in developing phase-change memory, high- performance transistors, and spintronic devices. However, it also poses challenges in synthesizing homogeneous MoTe 2 with a precisely controlled phase. Recently, a new yet simple method using sputtering and 2D solid-phase crystallization (SPC) is proposed for synthesizing high-quality and large-area MoTe 2 . This study investigates the polymorphism control of MoTe 2 synthesis using 2D SPC. The Te/Mo ratio and oxygen content in the as-sputtered films correlate strongly with the final phase and electrical properties of SPC MoTe 2 . Furthermore, the SPC thermal budget may be exploited for stabilizing a deterministic phase. The comprehensive experiments presented in this work demonstrate the versatile and precise controllability on the MoTe 2 phase by using the simple 2D SPC technique.

Amorphous-to-Crystal Transition in Quasi-Two-Dimensional MoS2: Implications for 2D Electronic Devices

“…Experimentally, we could not observe the a-MoS 2 to 1T′ phase transformation; however, the crystallization process can be observed in MoTe 2 , 24 where amorphous MoTe 2 first converts to the 1T′ phase and after long-term annealing above 600 °C gradually recrystallizes to 2H modification. Therefore, it can be assumed that the 1T′ phase appears to be an intermediate phase on the path between a-MoS 2 and 2H-MoS 2 .…”

“…In the latter approach, the formation of the layered crystalline phase via transformation from a 3D continuous amorphous phase avoids nonstoichiometric growth as has been very recently demonstrated for MoTe 2 . 24 In addition, deposition of amorphous chalcogenide thin films has been intensively investigated for many decades, and thus, this technology can be easily transferred to nanoscale applications as demonstrated, for instance, in phase-change materials. 25 Since there is very limited information about the physics of the amorphous-to-crystal (or 3D−2D) transformation in TMDCs, in this paper, we present a study of the amorphous and crystalline phases of MoS 2 , examined in terms of longrange and short-range orders.…”

cm2-Scale Synthesis of MoTe2 Thin Films with Large Grains and Layer Control

“…Because the A 1g and B 2g 1 modes are sensitive to layer number, we examined the A 1 g and B 2g 1 modes at various locations of the films across a 5–10 mm region, which confirmed thickness uniformity at the wafer scale (Figure S5, Supporting Information). Chemical analysis of the converted films using X-ray photoelectron spectroscopy shows a full conversion to MoTe 2 as evidenced by the peak shift of the Mo 3d peaks from MoO x to MoTe 2 (Figure b) . Energy-dispersive X-ray spectroscopy shows that the stoichiometry of our MoTe 2 films is identical to that of a flake exfoliated from bulk MoTe 2 grown by chemical vapor transport (Figure c, Methods).…”

“…Chemical analysis of the converted films using X-ray photoelectron spectroscopy shows a full conversion to MoTe2 as evidenced by the peak shift of the Mo 3d peaks from MoOx to MoTe2 (Figure 3b). 28 Energy dispersive x-ray spectroscopy shows that the stoichiometry of our MoTe2…”

“…However, mechanical exfoliation does not provide control over the thickness, size, or shape of the flakes, and the yield is low. Recent synthesis efforts have shown MoTe 2 monolayer flakes that are a few microns in size. , Large-area thin films of MoTe 2 have been demonstrated using molecular beam epitaxy, chemical vapor deposition, ,− and solution-phase synthesis, albeit for a limited range of thicknesses. Robust growth results of MoTe 2 thin films from monolayer to any arbitrary thickness with large grains have yet to be demonstrated.…”