Nanoscale understanding and chemical functionalization of phosphorene and 2D InSe semiconductors

Phosphorene and InSe are recently discovered 2D semiconductors which possess a number of important and unique properties, such as high charge carrier mobilities, direct band gaps, and high optical absorptions, making them attractive materials for applications in electronic and light harvesting devices. Because of the atomically thin nature of 2D materials, their surface chemistry has tremendous influence on their properties. The high reactivity and air-instability of phosphorene and 2D InSe significantly complicates their studying and therefore their surface chemistry remains largely unexplored. In the proposed work, methods for phosphorene and InSe fabrication in ultra-high vacuum (UHV) conditions will be developed, which will allow to perform detailed nanoscale studies of their defects and surface chemistry using scanning tunneling microscopy and spectroscopy (STM and STS). Subsequent functionalization of their surfaces with various molecules (organic semiconductors, boranes, metal complexes) will allow for the formation of Type II heterojunctions, required for light harvesting devices, controlled n- and p-type doping schemes for electronic and optical applications, passivation against ambient degradation. STM, STS as well as tip-enhanced fluorescent (TEF) and Raman spectroscopies (TERS) will be used to perform molecular-resolution structural and optical characterization of the obtained heterojunctions, providing information about molecular arrangement, chemical interactions, charge distribution, defects and energy transfer. The obtained knowledge and functionalization approaches will further be applied for the solution-exfoliated phosphorene and InSe, together with the proposed non-covalent functionalization schemes based on carbenes and nitrenes. Ultimately, the new surface chemistry that will be developed for phosphorene and InSe through the proposed work will enable tailoring of their properties towards applications in optoelectronic devices such as FET, photodetectors, and light-harvesting devices.