Terahertz Self-Mixing Reflection Interferometry and studies of adsorption/desorption at graphene surfaces

• Applicants: Professor Dr. Wolfgang Elsäßer; Professor Ralf Riedel
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 409301819

The terahertz (THz) region of the optical spectrum has actually developed into a spotlight of interests with a huge variety of applications in e.g. security technology, quality control in pharmaceutical and plastics industry, and spectroscopic sensing, in parallel with the occurrence of new materials with unprecedented novel performances, as, e.g. metamaterials and nanoscale materials. Here, the actual research proposal sets in, unifying these two fields between physics and physical chemistry/materials science by applying THz techniques for the investigations of the unique electronic properties of graphene and exploiting these novel functional materials performances towards adsorption/desorption processes. The key contribution of this DFG proposal is the combination of the recently developed THz Self Mixing Reflection Interferometry (SMRI) technique - established by the SCO group- which combines both CW terahertz radiation generation and phase-sensitive detection simultaneously in one photoconductive antenna (PCA) thus representing actually the world-wide most compact set-up for THz sensing with gas adsorption/desorption studies of graphene surfaces. Only by combining the joint expertise and experience in the field of THz spectroscopy and materials science, the ambitious goals of the proposal will be successfully realized.The main goals of the proposal arei) the improvement of the SMRI technique and ii) its exploitation towards studies of adsorption/desorption processes at 2D-surfaces, here graphene as the most intensively studied representative in the literature. Graphene is extremely sensitive to gas species due to its large surface area and its specific electronic properties, down to the detection limit of individual gas molecules. The SMRI technique will be applied to gain new insight into the adsorption/desorption and charge transfer processes at the graphene surface when interacting with selected gas species (NO2, NH3 and CO). These studies will be supported by ellipsometry and other surface specific spectroscopic techniques (XPS, EELS, SEM/TEM, AFM/STM and Raman) prior and after an adsorption/desorption process. Emphasis is given to the kinetics of adsorption/desorption processes and the binding energies of the molecules. The detailed knowledge of the changes during an adsorption/desorption process, sampled by the SMRI technique together with a comparison with model considerations, will result in a more profound understanding of the adsorption and desorption mechanisms enabling an improved gas sensing concept, thus paving the road for the realization of extremely compact and highly selective THz "finger print" gas sensors, superior to the current graphene-based gas sensors.

• DFG Programme: Research Grants