VIRTUAL NANOLAB BY QUANTUMWISE Presentation by: Sheng Yu Supervisor: Prof. Qiliang Li

Strain engineering monolayer MoS2 by crystal Al2O3

Outline ● Create Al2O3/MoS2 interface structure A. Create MoS2 monolayer B. Create Al2O3 C. Merge to Al2O3/MoS2 interface structure ● Optimization the Al2O3/MoS2 interface structure ● Simulation on the structure under La=Lb=9.5Å A. Total Energy B. Bandstructure ● Calculation of the strain strength A. Investigate Total Energy vs. La=Lb B. Find La=Lb with minimum total energy C. Calculate Strain = (La-Lao)/Lao. Lao is lattice parameter of original MoS2 monolayer

● Create Al2O3/MoS2 monolayer structure ① Jobs command window ② The jobs you have already finished ③ The jobs you are going to analyze ④ Analysis window

● Create Al2O3/MoS2 monolayer structure A. Create MoS2 monolayer Drag MoS2.py into Builder Find material resources at: http://www.crystallography.net/index.php

● Create Al2O3/MoS2 monolayer structure A. Create MoS2 monolayer Fit the unit cell Drag to select right 3 atoms, Press Delete.

● Create Al2O3/MoS2 monolayer structure A. Create MoS2 monolayer Change the lattice type to hexagonal La=Lb=3.1604Å

● Create Al2O3/MoS2 monolayer structure B. Create Al2O3 Drag Al2O3.cif into Builder

La=Lb=4.785Å Al2O3 has hexagonal lattice type with parameter of La=4.785Å MoS2 also has hexagonal lattice type with parameter of Lb=3.1604Å The lattice parameter ratio is La/Lb= 1.514 Therefore I suggest a quasi-superlattice structure with 2 unit cells of Al2O3 and 3 unit cells of MoS2.

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure Repeat unit cell of Al2O3 by 2 × 2 × 1 La=Lb=9.57Å

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure Repeat unit cell of MoS2 by 3 × 3 × 1 La=Lb=9.481Å

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure We set La=Lb=9.5Å for both Al2O3 and MoS2

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure We set La=Lb=9.5Å for both Al2O3 and MoS2

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure Merge Al2O3 and MoS2 together

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure Increase the Lc of unit cell to 35Å Move MoS2 to make more space between MoS2/Al2O3

● Create Al2O3/MoS2 monolayer structure C. Merge to Al2O3/MoS2 interface structure Center the atoms in the unit cell Change the lattice type back to hexagonal

● Optimization Go to script Generator Optimization

● Optimization Set the method to GGA Do not constrain the unit cell

● Optimization Save your program by your directory Go to Job Manager After optimization, the separation between Al2O3 and MoS2 is 3.13Å

Simulation of the structure In running the program Drag your optimized structure to Script Generator

Simulation of the structure Choose Bandstructure and Total Energy under Analysis Set the basic parameters of Bandstrucuture

Simulation of the structure Save and run

● Calculate the strain strength A. Investigate Total Energy vs. La=Lb Drag your optimized structure to Builder Change La=Lb=9.51Å

● Calculate the strain strength A. Investigate Total Energy vs. La=Lb In the Script Generator, choose Bandstructure and Total Energy. Save and run!

● Calculate the strain strength A. Investigate Total Energy vs. La=Lb Set La=Lb=9.49Å In the Script Generator, choose Bandstructure and Total Energy. Save and run!

● Calculate the strain strength B. Find La=Lb with minimum total energy C. Calculate strain induced by interface Compare the total energy of 3 structures, we find the structure with Lc=9.50Å has the minimum total energy. Therefore the strain effect of Al2O3 on MoS2 monolayer is: (Lc/3 – Lb)/Lb = 0.198%

Display the bandstructure of Al2O3/MoS2 system.

Transmission spectrum of perfect sheets of graphene and MoS2: http://www.quantumwise.com/publications/tutorials/mini-tutorials/167 Opening a band gap in silicene and bilayer graphene with an electric field: http://www.quantumwise.com/publications/tutorials/mini-tutorials/209 Effective mass of electrons in silicon: http://www.quantumwise.com/publications/tutorials/mini-tutorials/135 Sheng Yu Email: syu12@gmu.edu Phone number: 7036470780 Engineering Building 3702