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

光谱的太赫兹（THz）区域实际上已经发展成具有在例如安全技术、制药和塑料工业中的质量控制以及光谱感测中的各种各样的应用的关注的焦点，同时出现具有前所未有的新颖性能的新材料，例如超材料和纳米级材料。在这里，实际的研究建议是，通过应用太赫兹技术研究石墨烯独特的电子特性，并利用这些新型功能材料的吸附/脱附过程，将物理学和物理化学/材料科学这两个领域统一起来。该DFG提案的关键贡献是最近开发的THz自混合反射干涉（SMRI）技术的组合-由SCO小组建立-该技术在一个光电导天线（PCA）中同时结合了CW太赫兹辐射产生和相敏检测，因此实际上代表了世界范围内最紧凑的石墨烯表面气体吸附/脱附研究THz传感装置。只有将太赫兹光谱和材料科学领域的共同专业知识和经验结合起来，该提案的宏伟目标才能成功实现。该提案的主要目标是i）SMRI技术的改进和ii）将其开发用于二维表面的吸附/脱附过程的研究，其中石墨烯是文献中研究最深入的代表。石墨烯由于其大的表面积和其特定的电子性质而对气体种类极其敏感，低至单个气体分子的检测极限。SMRI技术将被应用于获得新的洞察吸附/脱附和电荷转移过程中的石墨烯表面时，与选定的气体物种（NO2，NH3和CO）相互作用。在吸附/脱附过程之前和之后，这些研究将得到椭圆光度法和其他表面特异性光谱技术（XPS、EELS、SEM/TEM、AFM/STM和拉曼）的支持。重点是吸附/脱附过程的动力学和分子的结合能。通过SMRI技术采样的吸附/解吸过程中的变化的详细知识以及与模型考虑的比较，将导致对吸附和解吸机制的更深刻的理解，从而实现改进的气体传感概念，从而为实现极其紧凑和高度选择性的THz“指纹”气体传感器铺平道路，上级于目前石墨烯基气体传感器。

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.