OP: Surface- and Coherence-Enhanced Raman Sensing on MoS2 Heterogeneous Catalysts

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry and the Ceramics Program in the Division of Materials Research, Professor Zhang at Baylor University and Professors Sokolov and Voronine at Texas A&M University are applying various Raman techniques to monitor hydrodesulfurization reactions on a semiconductor substrate. Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products. Understanding how it happens on a catalytic substrate will help to improve oil refining efficiency and reduce environmental impacts. Traditional plasmonic Raman techniques are used to study these reactions on noble metals (gold, silver, and copper). Although these noble metals are important, the ability to study reactions on non-metallic catalytic substrates is needed. Professors Zhang, Sokolov and Voronine are using the most advanced state-of-the-art Raman spectroscopic techniques to examine reactions on non-metallic substrates, such as molybdenum disulfide (MoS2). The methods they are developing have the potential to lead to broad applications in many areas other than oil refinery studies. For example, the developed techniques could be used to monitor pollutants in environmental analysis or decipher DNA sequences. Three professors are also actively involved in many outreach activities by bringing the exciting world of nanoplamonics research to undergraduate students and to the general public through the programs such as the "Physics Day" event on campus, annual scanning tunneling microscopy (STM) training sessions, and the Research Experiences for Undergraduates (REU) program. Professor Zhang at Baylor University, Professors Sokolov and Voronine at Texas A&M University are advancing molecular-level chemical identification of molecules on non-traditional Raman scattering materials, such as MoS2, an important material for heterogeneous catalysis, using a combination of the most advanced Raman spectroscopies. They are working on three subprojects a) to examine the origin of Surface-Enhanced Raman Spectroscopy (SERS) on the two-dimensional (2D) semiconductor; b) to achieve unprecedented Raman signal enhancement on the 2D materials via a combination of the surface enhancement of SERS and the coherence enhancement of Femtosecond Adaptive Spectroscopic Technique for Coherent Anti-Stokes Raman Scattering (FAST CARS); and c) to identify the chemical composition of reagents, intermediates, and products with submonolayer sensitivity and nanoscale spatial resolution using Tip-Enhanced Raman Spectroscopy (TERS). Their work focuses on the molecular-level approach to understanding the chemical and physical nature of the Raman signal enhancement in non-metallic nanostructures. The expected outcomes of their research include better understanding of the structure-function relationships in semiconductors for new designs of advanced materials with improved functionalities.