Selection Role of Metal Oxides into Transition Metal Dichalcogenide Monolayers by a Direct Selenization Process

Abstract

Direct reduction of metal oxides into a few transition metal dichalcogenide (TMDCs) monolayers has been recently explored as an alternative method for large area and uniform deposition. However, not many studies have addressed the characteristics and requirement of the metal oxides into TMDCs by the selenization/sulfurization processes, yielding a wide range of outstanding properties to poor electrical characteristics with nonuniform films. The large difference implies that the process is yet not fully understood. In particular, the selenization/sulfurization at low temperature leads to poor crystallinity films with poor electrical performance, hindering its practical development. A common approach to improve the quality of the selenized/sulfurized films is by further increasing the process temperature, thus requiring additional transfer in order to explore the electrical properties. Here, we show that by finely tuning the quality of the predeposited oxide the selenization/sulfurization temperature can be largely decreased, avoiding major substrate damage and allowing direct device fabrication. The direct relationship between the role of selecting different metal oxides prepared by e-beam evaporation and reactive sputtering and their oxygen deficiency/vacancy leading to quality influence of TMDCs was investigated in detail. Because of its outstanding physical properties, the formation of tungsten diselenide (WSe) from the reduction of tungsten oxide (WO ) was chosen as a model for proof of concept. By optimizing the process parameters and the selection of metal oxides, layered WSe films with controlled atomic thickness can be demonstrated. Interestingly, the domain size and electrical properties of the layered WSe films are highly affected by the quality of the metal oxides, for which the layered WSe film with small domains exhibits a metallic behavior and the layered WSe films with larger domains provides clear semiconducting behavior. Finally, an 8'' wafer scale-layered WSe film was demonstrated, giving a step forward in the development of 2D TMDC electronics in the industry.

Cation-Regulated Transformation for Continuous Two-Dimensional Tin Monosulfide

“…Another method commonly used for the synthesis of 2D chalcogenides is the sulfurization or selenization technique. In this process, a very thin metal oxide layer is formed by atomic layer deposition (ALD) ,, or sputtering, − and subsequently the surface of the metal oxides is exposed to a sulfur- or selenium-containing atmosphere to facilitate transformation into metal chalcogenides. ,− The common element in these conventional synthesis methods is that the synthesis is based on anion-controlled chemical reactions.…”

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

“…MoTe 2 , in particular, has shown promise for phase-change memory applications due to the small energy difference between the 2H and 1T′ phase with experimental demonstrations of the phase switching induced by strain, gating, , and heating . Despite the growing interest in the tellurides, large-scale synthesis of telluride thin films with precise layer control remains a challenge, although such synthesis has been demonstrated for sulfides and selenides. − …”

Atomic‐Level Customization of 4 in. Transition Metal Dichalcogenide Multilayer Alloys for Industrial Applications

“…However, position‐dependent formation of nucleation sites, ascribed to the nonuniform supplement of transition metal and chalcogen sources, leads to coexistence of flakes and films governed by Volmer–Weber and Stranski–Krastanov growth modes, which greatly impedes further material development in terms of scale‐up. Recently suggested synthetic routes, including direct chalcogenization of predeposited metal or metal oxide films, coevaporation of metal and chalcogen sources using a face‐to‐face metal precursor, and a metal organic CVD process, provide straightforward examples to fulfill this need; these are emerging candidates for a large‐area compatible approach. In parallel, we previously accomplished a major breakthrough in the synthesis of MoS 2 , a representative TMD material, involving direct synthesis of laterally connected MoS 2 onto a plastic substrate at low growth temperature and leading to roll‐to‐roll manufacturing of 50 cm long MoS 2 layers on inexpensive metal foils via well‐designed two‐step thermal decomposition of (NH 4 ) 2 MoS 4 as a single source precursor .…”