Mon, 10/21/2019 - 4:10pm to 5:00pm
DeMeritt 240
Material Science Seminar
Liping Yu, University of Maine

Understanding adsorbate bonding on solid surfaces and strain-induced electronic effects in 2D materials

The molecular-level description of the chemical bond between a solid surface and an atom or a molecule is the fundamental basis for understanding a broad range of scientific problems in heterogeneous catalysis, sensing, semiconductor device fabrication, fuel cells, anticorrosion, and tribology. Despite many decades of theoretical and experimental research in this area, what key physical factors and how they operate together in controlling the surface-adsorbate bonding strength remain elusive. Particularly, the actuating mechanisms for adsorbate bonding at different sites on inhomogeneous surfaces, which often contain defects, edges, kinks and corners, is far from being well understood on a predictive quantitative basis. In this talk, I will present a quantifiable model for understanding surface-adsorbate interactions from first principles calculations coupled with quantitative bonding analysis. The model will be demonstrated from the case study of the hydrogen adsorption on MoS2surfaces with various adsorption sites. Remarkably, we find that the energy levels of unoccupied antibonding surface-adsorbate states, which are often tacitly considered to have no effects on surface bonding, play a critical role in determining the trends in variations of surface adsorption energies. The role of vacancy-vacancy interaction in hydrogen bonding will be discussed. The resulting guidelines will also be presented for understanding and optimizing catalyst performance and designing new heterogeneous catalysts. If time allows, I will also talk about another topic, which is related to the interesting bending effects and auxetic effects predicted in some single-layer 2D transition metal dichalcogenide materials.