Transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), and tungsten diselenide (WSe2) are of interest due to their intriguing properties including the transition from indirect gap to direct gap as the material is thinned to a single atomic layer. Layered TMDs also allows for the possibility of bandgap tuning. These properties lead to interest in applications involving hydrogen reduction, supercapacitors, batteries and solar cells.1 Few layer TMD stacks such as MoS2 have shown high stability for cycling and also a lower barrier to lithium intercalation through larger interlayer spacing as compared with bulk MoS2.2 Current methods of TMD fabrication involve exfoliation or vaporization of WO3 and Se powder, which limits industrial scalability. This work is focused on development of a metal-organic chemical vapor deposition process that can controllably produce highly-crystalline, atomically thin TMDs on large area substrates. Growth of controlled monolayer MoS2 and WSe2 was carried out using a metal organic chemical vapor deposition (MOCVD) process. Tungsten hexacarbonyl (W(CO)6) and dimethylselenium (DMSe) served as the tungsten and selenium precursors, respectively for WSe2 and Mo(CO)6 for the molybdenum source during MoS2 synthesis. Use of MOCVD precursors provides independent control of the transition metal and chalcogenide independently. Process variables including temperature (500-950°C), pressure (100-700 Torr), and chalcogenide:metal, were correlated with grain size, growth rate, and nucleation density to identify optimal parameters for atomically controlled synthesis of MoS2 and WSe2. WSe2 growth was carried out to understand growth of TMDs via MOCVD on sapphire. Increased growth pressure from 100-700 Torr can result in decreased growth rate and nucleation density, leading to a &gt;50X increase in grain size. Characterization of these samples via Raman and photoluminescence spectroscopy verified that high quality, monolayer WSe2 is readily achievable. Additional characterization to verify quality, grain size, and nucleation density of the synthesis on various substrates. Modification of growth parameters including reduced temperatures allows for control of film morphology from lateral to vertical growth. This allows for the ability to tailor the growth to achieve increased surface area and edge sites which is important for increased hydrogen evolution reactions (HERs) and enhanced catalysis.

Synthesis of 2D materials for energy applications

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.