The effect of elevated temperatures on excitonic emission and degradation processes of WS₂ monolayers

Abstract

Controlled heating experiments in an inert environment have been performed on WS2 monolayers, in order to clarify the conflicting reports on the high-temperature photoluminescent response of 2D TMDs. We find...

Dynamic Growth/Etching Model for the Synthesis of Two-Dimensional Transition Metal Dichalcogenides via Chemical Vapour Deposition

“…That oxygen plays important role in the etching process is experimentally evident from the study by Yamamoto et al: While no etching takes place in 2D MoS 2 under Ar/H 2 atmosphere at 350 °C, etching is observed under Ar/O 2 atmosphere already at temperatures around 300 °C [44]. However, we observe such an etching effect in 2D WS 2 under completely inert Ar atmosphere at temperatures above 300 °C [48] [and SI 1 (Fig. S1)].…”

“…Hence, it is more likely to extend pre-existing defects (a certain number of intrinsic defects is always present) in the basal plane of 2D TMDCs, than to create new ones. This is supported by experiments giving evidence for grain boundaries and induced vacancies to be the preferred sites for the release of built-in atoms [45][46][47][48] [and SI 1 (Fig. S1)] and by studies showing the creation of defect clusters in form of triangular pits in 2D TMDCs [10,[42][43][44][45][46]48].…”

“…This is supported by experiments giving evidence for grain boundaries and induced vacancies to be the preferred sites for the release of built-in atoms [45][46][47][48] [and SI 1 (Fig. S1)] and by studies showing the creation of defect clusters in form of triangular pits in 2D TMDCs [10,[42][43][44][45][46]48]. The latter mechanism is often referred to as anisotropic (oxidative) etching.…”

“…Firstly, we start with 2D TMDC flakes heated up to temperatures significantly lower than their typical CVD temperatures (> 650 °C) and at or close to ambient pressure. In this case, it is experimentally observed that the flakes begin to degrade and finally decompose completely [10,[42][43][44][45][46][47][48][49] [and see SI 1 (Fig. S1)].…”

“…3. Because degradation of 2D TMDCs is also facilitated by increased temperatures [10,[42][43][44][45][46][47][48][49][50][51] [and see SI 1 (Fig. S1)], a dynamic process between growth and etching during a CVD process must obviously exists.…”