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

随着超材料和纳米材料等具有前所未有的新性能的新材料的出现，光谱的太赫兹(THz)区域实际上已经发展成为人们关注的焦点，在安全技术、制药和塑料工业的质量控制以及光谱传感等方面有着广泛的应用。在这里，实际的研究方案开始了，通过应用太赫兹技术研究石墨烯独特的电子性质，将物理学和物理化学/材料科学这两个领域统一起来，并将这些新型功能材料的性能用于吸附/解吸过程。DFG建议的主要贡献是结合了最近开发的THz自混合反射干涉(SMRI)技术-由SCO小组建立-该技术在一个光导天线(PCA)中同时结合了连续太赫兹辐射产生和相敏检测，从而实际上代表了世界上最紧凑的太赫兹传感装置与石墨烯表面的气体吸附/解吸研究。只有将太赫兹光谱学和材料科学领域的专业知识和经验结合起来，才能成功地实现该提案的宏伟目标。该提案的主要目标是)改进SMRI技术和开发其在2D表面上的吸附/解吸过程的研究，其中石墨烯是文献中研究最深入的代表。石墨烯对气体物种极其敏感，因为它的大表面积和特殊的电子性质，一直到单个气体分子的检测极限。SMRI技术将被用来对石墨烯表面与特定气体物种(NO2、NH3和CO)相互作用时的吸附/脱附和电荷转移过程有新的认识。这些研究将得到椭偏仪和其他表面特定光谱技术(XPS、EELS、扫描电子显微镜/电子显微镜、AFM/STM和拉曼)在吸附/解吸过程前后的支持。重点讨论了吸附/脱附过程的动力学和分子的结合能。对吸附/解吸过程中变化的详细了解，通过SMRI技术采样，并与模型考虑因素进行比较，将导致对吸附和解吸机理的更深刻理解，从而实现改进的气体传感概念，从而为实现极其紧凑和高选择性的太赫兹“指纹”气体传感器铺平道路，优于目前基于石墨烯的气体传感器。

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.