Session: 12-16-01: Multiscale Models and Experimental Techniques for Composite Materials and Structures Count

Paper Number: 111520

111520 - Photo Switchable Optical Property of Two-Dimensional Transition Metal Dichalcogenides 

For the last decade, transition metal dichalcogenides (TMDs) have received much attention for optoelectronic applications because of their band gap transition from indirect to direct as they decrease from multilayer to monolayer. Photochromic molecules switch between isomers with distinct energy levels when irradiated with ultraviolet (UV) or visible light. Going through the photochromic isomerization, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels shift.  Recent studies have experimented with the use of photochromic molecules to optically control the charge transport of two dimensional (2D) semiconductors.  In this work, a numerical study has been performed to test the possibility to control the optical property of 2D TMD monolayers with photochromic molecules. When the HOMO or LUMO energy levels are within the band gap of 2D TMD monolayers, the carriers (holes and electrons) will transport to the photochromic molecules, resulting in the reduction of excitons in the 2D TMD monolayers.  Through the photochromic isomerization, if the LUMO (HOMO) energy level of the photochromic molecules shifts below the conduction band minimum (above the valence band maximum) of the 2D TMD, the concentration of electron (hole) in the 2D TMD monolayers decreases and the optical response reduces due to the low exciton density in the 2D TMD.  The reduced optical response can be recovered by going through reverse isomerization. Therefore, shifting HOMO and LUMO energy levels into the band gap of 2D TMDs through isomerization is critical to realizing the photo-switchable optical property of 2D TMDs. To find viable pairs of a photochromic molecule and a 2D TMD monolayer, density functional theory calculations were employed.  Molybdenum diselenide (MoSe₂) and tungsten diselenide (WSe₂) monolayers were tested with various photochromic molecules including azobenzene, spiropyran, and diarylethenes (DAE 2 ethyl, DAE 5 ethyl, DAE 5 methyl) in open-chain and closed-chain forms.  The k-space electronic structures and density of states have been examined for the controllability of exciton density in the MoSe₂ and WSe₂ monolayers. It has been found that all the abovementioned DAEs with either MoSe₂ or WSe₂ monolayers would have controllable exciton density via irradiation with UV or visible light.  The WSe₂ monolayer with azobenzene would also have a controllable optical response through the transfer of holes.  The MoSe₂ monolayers with azobenzene or spiropyran do not exemplify photo-switchable behavior.  The systematic study presented in this work will provide the list of the photochromic molecule - TMD monolayer pairs, of which optical properties are photo-switchable. 

Presenting Author: Connor Cunningham University of St. Thomas

Presenting Author Biography: Connor Cunningham is an undergraduate student in the Department of Mechanical Engineering at the University of St. Thomas, St. Paul, MN.

Authors:

Connor Cunningham University of St. Thomas
Srajan Pillai University of St. Thomas
Jeong Ho You University of St. Thomas
Jaehoon Ji Purdue University
Jong Hyun Choi Purdue University