Project title: Adsorbate Engineering in Two-dimensional Semiconductors

Supervisor: Dr Johannes Lischner and Dr Arash A. Mostofi

Project description: 

Monolayer transition metal dichalcogenides (TMDCs) are a recently discovered class of 2D semiconducting material that exhibit significant potential for emerging and future functional device technologies. Defects in modern day devices are frequently used to control functional properties, but little is known about the effects of surface adsorbates (such as atoms or molecules) on the electronic properties of TMDCs or how to use them as a route to defect engineering in these materials.

This project aims to study the defect properties of TMDCs using a multi-scale method which takes into account both local chemistry around the adsorbate and long-range screening effects in the 2D semiconductor. The bound quantum states associated with shallow defects extend over tens of nanometres or more because of weak dielectric screening in 2D materials. The long-range screened potential is difficult to fully capture with conventional electronic structure calculations based on density-functional theory because of the very large supercells required. This project combines ab initio calculations with large-scale tight-binding models, to quantify the long-range effects of adsorbates on the electronic structure of TMDCs. Our numerical predictions can be directly compared to scanning tunneling experiments.