Honors College Thesis


Investigation of MoS2 with Ambient Pressure X-ray Photoelectron Spectroscopy Public Deposited

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  • Molybdenum disulfide (MoS2) has potential applications as a low-cost catalyst for the hydrogen evolution reaction (HER). Defects on MoS2, such as edge sites and sulfur vacancies, are known to be the major active sites for HER. Controlling the formation of these defects allows for the enhancement in reactivity of MoS2 and other 2D materials. In this study, we have characterized the surface reactivity of bulk MoS2 samples using ambient pressure X-ray photoelectron spectroscopy (APXPS). Samples were exposed to 1 mbar of H2O vapor at temperatures ranging from 300-600 K. The APXPS Mo 3d, S 2p, and O 1s core levels for the as exfoliated surface showed no significant changes under all reaction temperatures due to the inert nature of the pristine MoS2 surface. To improve surface reactivity and activate the basal plane of MoS2 we have utilized Ar+ sputtering to form well controlled defect densities at the surface. The APXPS Mo 3d, S 2p, and O 1s core levels for the defective MoSx (x = 1.6, 1.2) surface showed the formation of MoO3 and MoOS at temperatures of 400 K and above. We have found that surface reactivity of MoS2 is strongly dependent on temperature and defect densities.
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  • Acquisition of the Ambient-Pressure X-ray Photoelectron Spectroscopy/Ambient-Pressure Scanning Tunneling Microscopy system was supported by the National Science Foundation-Major Research Instrumentation program (grant DMR-1429765), the M. J. Murdock Charitable Trust, Oregon BEST, Oregon Nanoscience and Microtechnologies Institute, and Oregon State University.
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