Raman Spectroscopy Used to Characterize Reactions with Transition Metal Dichalcogenides

Undergraduate #47
Discipline: Chemistry and Chemical Sciences
Subcategory: Materials Science

Erin Grills - Pennsylvania State University
Co-Author(s): Timothy Walther, Anna Domask, and Suzanne Mohney, Pennsylvanian State University

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Transition metal dichalcogenides (TMDs) have a two dimensional layered crystal structure with weak van der Waals bonds between layers, allowing for them to be exfoliated into thin layers with novel properties. Treatment and processing of these thin layers are being investigated to lower contact resistance and create heterostructure for use in devices such as transistors. This study characterized how TMDs change with different treatments that induce reactions. A wet chemical treatment of WSe2 with ammonium sulfide solution was hypothesized to substitute the surface selenium layer with sulfur atoms. With this chemical treatment, the WSe2 samples were submerged in 24% ammonium sulfide solution. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize any substitution of atoms. Thus far, no results confirming the substitution of surface Se atoms with S atoms have been collected. The second treatment investigated the effects of metallization of MoS2 on a sapphire substrate. Silver was deposited in 15 nm and 100 nm thicknesses, and samples were annealed at 200˚C, 300˚C, and 400˚C. Raman was done from the backside, through the sapphire substrate, of the metalized samples due to the Raman opacity of the metallic overlay on the topside. The change in Raman response was determined, which indicated different reaction products that formed at each annealing temperature. Backside Raman proved to be a viable technique used to characterize reactions between MoS2 and silver, as well as reactions between other TMDs with different metalized surfaces.

Funder Acknowledgement(s): National Science Foundation

Faculty Advisor: Suzanne Mohney,