Tuning the electronic structure of transition metal dichalcogenidemonolayers via dipole engineering through molecular adsorbates

过渡金属二硫族化合物（TMDC）的个别层，如MoS2或MoSe2，由于其迷人的电子和光学性质而受到广泛的研究。微纳米光电子学的可能应用包括场效应晶体管、热电发电机或光电探测器。由于这些材料的准二维结构，沉积在晶体衬底上的TMDC层的几乎所有原子都与衬底直接接触，从而使TMDC的光电性能对表面缺陷和吸附高度敏感。虽然近年来二维TMDCs的合成取得了很大的进展，并且许多这些化合物现在已经高质量地商业化了，但是一种基于界面的策略来控制表面电子结构的调整还没有实现。这是这个项目的起点。该项目是基于这样一个假设，即TMDCs的光电性能可以通过吸附有机π系统和调谐在这种方式形成的界面上的偶极子来定制。作为π-系统，我们使用了含氟金属酞菁和卟啉，它们允许与TMDCs的界面特性可调，如界面偶极子，能级位置和电荷转移。通过对酞菁的化学修饰，如氟化程度或金属中心，可以微调这些特性。基于光电发射的技术用于确定横向平均的电子界面性质。利用空间分辨拉曼显微镜、荧光显微镜和扫描隧道显微镜，研究了界面上能级排列和偶极子对TMDCs光学性质的影响，并澄清了它们以缺陷形式出现的局部偏差。电输运测量提供了有关吸附剂对各层电性能影响的信息。

Individual layers of transition metal dichalcogenides (TMDC) such as MoS2 or MoSe2 are subject to intense research efforts in view of their fascinating electronic and optical properties. Possible applications in micro- and nano-optoelectronics include field-effect transistors, thermoelectric power generators, or photodetectors. As a consequence of the quasi two-dimensional structure of these materials, nearly all atoms of a TMDC layer which is deposited onto a crystalline substrate, are in direct contact with the substrate, rendering the optoelectronic properties of TMDCs highly sensitive to surface defects and adsorbates. While the synthesis of two-dimensional TMDCs has made great progress in recent years and many of these compounds are now commercially available in high quality, an interface-inspired strategy for the controlled adjustment of the electronic structure at the surface is not yet available. This is the starting point for this project. The project is based on the hypothesis that the optoelectronic properties of TMDCs can be tailored via the adsorption of organic π-systems and tuning of the dipole at the interface formed in this way. As π-systems, we utilize fluorinated metal phthalocyanines and and porphyrins, which allow for tunable interface properties with the TMDCs, such as the interface dipole, the position of the energy levels and charge transfer. Through chemical modifications of the phthalocyanines like the degree of fluorination or the metal center, these properties can be fine-tuned. Photoemission-based techniques are used to determine the laterally averaged, electronic interface properties. Using spatially resolved Raman, fluorescence and scanning tunneling microscopy, the effects of energy level alignment and dipoles at the interfaces on the optical properties of the TMDCs are investigated, and their local deviations in the form of defects are clarified. Electrical transport measurements provide information about the effects of the adsorbates on the electrical properties of the layers.