| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Wednesday Sessions |
| Session PS+EM-WeM |
| Session: | Plasma Processing of Materials for Energy |
| Presenter: | Souvik Bhattacharya, Case Western Reserve University |
| Authors: | T. Liu, Case Western Reserve University X. Liu, Case Western Reserve University S. Bhattacharya, Case Western Reserve University Z. Ye, Texas Tech University R. He, Texas Tech University X.P.A. Gao, Case Western Reserve University R. Akolkar, Case Western Reserve University R.M. Sankaran, Case Western Reserve University |
| Correspondent: | Click to Email |
There has been recent interest in growing layered materials such as molybdenum disulfide (MoS2) over large areas for electronic and energy applications. One such approach is chemical vapor deposition (CVD) in which vapor precursors are thermally decomposed to nucleate a thin film at the surface of a substrate. A plasma may also be employed to assist in decomposition of the precursor molecule through gas-phase excitation, for example in plasma-enhanced CVD (PECVD) or plasma-enhanced atomic layer deposition (PEALD). Here, we report a plasma-assisted approach which is fundamentally different than these deposition techniques which we term plasma-enhanced chemical film conversion (PECFC). Precursor films are first prepared as a thin film on a substrate from liquids and subsequently converted by a combination of heating and plasma treatment. The process is additive, in that the precursor is only present where it is desired and there is little materials wastage, and substrate-independent, by circumventing the need for adsorption, allowing direct growth on application-specific substrates.
In this talk, we will present results for the synthesis of MoS2 films and their application as electrocatalysts for the hydrogen evolution reaction (HER). A single-molecule precursor, ammonium tetrathiomolybdate (ATM), was first dispersed in solution with linear polyethylenimine (L-PEI) and spin-coated to produce a well-defined thin film less than 50 nm thick. The precursor film was then treated by an atmospheric-pressure dielectric barrier discharge (DBD) in a background of argon and hydrogen gas (80:20) at 500 oC. Conversion to crystalline MoS2 was confirmed by X-ray diffraction and micro Raman spectroscopy. Atomic force microscopy was performed to study possible nucleation and growth mechanisms by varying the growth temperature and treatment time. The chemical composition was analyzed by X-ray photoelectron spectroscopy which showed an ideal stoichiometric ratio of 1:2 Mo:S.
A potential application of MoS2 films is HER because it is composed of earth abundant elements and has been shown to be highly active through its edge sites. We carried out a systematic study of the origin of HER activity in our films, both after initial conversion and after several other post-synthesis treatments . The investigation showed that our initially-converted films have tensile strain leading to intrinsic activity that is comparable to previously reported sulfur vacancy generation by post-synthesis plasma treatment steps. In our case, the strain is induced in the initial fabrication step, providing a simpler and more scalable process to produce efficient HER electrocatalysts.