Chalcogen Incorporation Process during High-Vacuum Conversion of Bulk Mo Oxides to Mo Dichalcogenides

Abstract

The optical, electronic, catalytic, and mechanical properties of transition-metal dichalcogenide (TMD) bulk crystals and monolayers have been examined extensively. TMD materials can be prepared through exfoliation, deposition from elemental and molecular precursors, and chemical conversion of corresponding transition metal oxides. Nevertheless, approaches for largescale synthesis of high-quality TMD crystals are needed to ensure the continued utilization of these materials within optoelectronic and energy conversion applications. Moreover, studies examining the principal stages of TMD nucleation and growth are comparatively rare and require further attention. We report a method for the conversion of bulk MoO 3 to MoX 2 (X = S, Se) under high-vacuum conditions and use this approach to isolate and examine intermediates formed during the chalcogenation process. Micron-scale Mo sub-oxide deposits are readily converted to MoS 2 when exposed to an atmosphere of S at 40 Torr and 300 °C. Notably, we show through elemental mapping of the cross-section of a partially converted single deposit that MoS 2 is present at higher concentrations nearest the deposit−substrate interface. We also note the formation of either distinct or alloyed TMD phases depending on whether a stepwise or concurrent chalcogenation, respectively, is performed. Our results provide an effective route toward conversion of transition metal oxides to bulk TMDs and provide insights into the mechanism of this scalable conversion process.

Inherent Resistance of Seed-Mediated Grown MoSe2 Monolayers to Defect Formation

“…Notably, we observe the presence of approximately 50 nm-sized particles (∼2 nm in thickness) near the i -MoSe 2 domains. As previously reported, ,, they are presumed to be Mo-containing nanoclusters (discussed in detail below), although no direct chemical information regarding these particles was obtained in our X-ray photoelectron spectroscopy (XPS) measurements (Figure d). The peaks observed primarily at 231.8 and 228.6 eV correspond to MoSe 2 (Mo 3d 3/2 4+ and Mo 3d 5/2 4+ , respectively), indicating that most of the i -MoSe 2 sample is composed of monolayer domains.…”

Morphotaxy of Layered van der Waals Materials

“…These examples indicate the importance of not only processing conditions but also the choice of the starting parent compound in determining the outcome of morphotaxial chalcogenization . Sadler and Kempa explored yet another way of accomplishing biphasic TMDCs by using multiple chalcogen sources in the high-vacuum conversion of bulk Mo oxides . Under a stepwise exposure to selenium and then sulfur at 40 Torr and 400 °C, Mo oxides converted into a biphasic mixture of MoSe 2 and MoS 2 , as evidenced by Raman spectroscopy.…”

“…Under a stepwise exposure to selenium and then sulfur at 40 Torr and 400 °C, Mo oxides converted into a biphasic mixture of MoSe 2 and MoS 2 , as evidenced by Raman spectroscopy. However, under concurrent exposure to both selenium and sulfur, Mo oxide converted to a more complicated structure, with a noticeable broadening of the A 1g peak and a shift from 242 to 264 cm –1 , indicative of an alloyed structure …”

“…However, under concurrent exposure to both selenium and sulfur, Mo oxide converted to a more complicated structure, with a noticeable broadening of the A 1g peak and a shift from 242 to 264 cm −1 , indicative of an alloyed structure. 106 Fundamental understanding of the processes involved in morphotaxial chalcogenization can also help guide the formation of heterostructures and patterned structures by promoting morphotaxy in desired locations. In particular, Afaneh et al utilized a 532 nm laser to locally pattern monolayers of WSe 2 and MoSe 2 into their respective sulfides in the presence of H 2 S. 107 In this case, the laser plays two roles; namely, local laser heating promotes the formation of selenium vacancies in the transition metal selenides in addition to assisting in the disassociation of H 2 S molecules such that free sulfur can then substitute into the vacancies.…”

A sustainable molybdenum oxysulphide-cobalt phosphate photocatalyst for effectual solar-driven water splitting

“…Owed to their enthralling electrical, optical, and catalytic properties, these nanomaterials are used to produce hydrogen and oxygen as alternative and sustainable green energy resources [20] . Different strategies, for instance, mechanical exfoliation [21] , solution-based chemical exfoliation [22] , chemical vapor deposition (CVD) [23] , hydro and solvothermal synthesis [24] , etc have been adopted to fabricate Molybdenum-oxy-sulphides (MoOxSy) and disulphide (MoS 2 ) photocatalysts. MoS 2 based nanomaterials are well-investigated for PEC-WS in comparison to MoOxSy photocatalysts.…”