EP02.09.22 : Elucidating the Role of Seeding Promoters on MoSe2 Synthesis and its Impact on Optoelectronic Properties

5:00 PM–7:00 PM Apr 4, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E

Saujan Sivaram1 Berend Jonker1

1, US Naval Research Laboratory, Washington, District of Columbia, United States

Monolayer transition metal dichalcogenides (TMDs) are attractive building blocks for future optoelectronic and valleytronic applications due to their direct band gap and preferential valley filling in response to circularly polarized light. Despite this promise, few processes exist to synthesize single crystals of primarily monolayers over a large area. Chemical vapor deposition (CVD) using solid precursors is an attractive option to produce single crystals of TMDs at the research scale; however, selenide-based TMDs (i.e., MoSe2 and WSe2) are particularly difficult to synthesize. To promote lateral growth, organic molecules such as perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS) are frequently deposited onto the substrate prior to growth. The role of this organic semiconductor during synthesis and its subsequent effect on TMD properties is unclear. Its use also precludes the development of robust chemistry-structure relationships. In this work, we synthesize monolayer MoSe2 on SiO2 with and without PTAS and find significant differences in their growth behavior. We use a variety of post growth techniques such as PL, Raman, AFM, and XPS to understand the variations between the synthesized monolayers. Our results suggest that PTAS acts as a reservoir to increase the local concentration of Mo and Se precursors, thereby promoting MoSe2 growth. We explain the diminished PL in the PTAS-assisted MoSe2 as a consequence of the shorter nucleation time, which results in exposure to the deleterious effects of high temperature. This work is the first to address the morphological and optoelectronic differences in monolayer TMDs synthesized with and without seeding promoters. These findings serve as important steps towards the scalable growth of monolayer TMDs.