Speaker
Description
Defects can strongly influence the electronic, optical and mechanical properties of 2D materials. However, their stability and distribution under different conditions of temperature, pressure and strain are not well characterized from an atomistic perspective.
We have investigated the structural and electronic properties, as well as the thermodynamic stability of point defects (vacancies and adatoms) in semiconductor monolayer transition metal dichalcogenides (TMDC) $MX_{2}$ with M = Mo/W
and X = S/Se, through density-functional theory (DFT) simulations with hybrid exchange correlation functional, as implemented in the all-electron package FHI-aims. We show quantitatively that in rich X conditions an X adatom is most favorable while, in a poor X environment, an X mono-vacancy is most favorable. Interestingly, an interplay between adatom and divacancies takes place as temperature increases.
Through the development of a novel method to compute tip-enhanced Raman spectroscopy images that combines time dependent density functional theory and density functional perturbation theory to obtain realistic local fields, we computed the local vibrational fingerprints of these defects. We expect this data to be fundamental for the characterization of defect structures in these systems in the near future, and to aid electronic structure engineering that also exploits nuclear vibrational modes and electron-phonon coupling in these systems.
Finally, in order to gauge the importance of vibrational entropy on the engineering of gap states in the 2D monolayers, we compare the formation energies of point defects and adsorbed organic molecules at various thermodynamic conditions. We perform ab initio-based random structure searches for flexible molecules on surfaces, in order to efficiently navigate the conformational space. With a handle on the stability of these systems, we study the origin and temperature-dependence of singly occupied gap states induced by molecular anchoring at defects on semiconductor TMDCs.
Addresses
(a) Present address: Yusuf Hamied, Department of Chemistry, University of Cambridge, Cambridge, UK
(b) Also at: MPI for the Structure and Dynamics of Matter, Hamburg, Germany
| Abstract Number (department-wise) | SG 12 |
|---|---|
| Department | Scheffler Group |
