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

Outline: 2. MoS2 monolayer (1) Build structure 1. Download and install Virtual NanoLab 2. MoS2 monolayer (1) Build structure (2) Optimize the structure (3) Change your unit cell (4) Simulate your structure (5) Analyze your results 3. IV curve for MoS2 nanoribbon

Installation http://quantumwise.com/free-trial 1. TRIAL LICENSE

2. DOWNLOAD 3. Installation

Manual for installation http://www.quantumwise.com/documents/manuals/latest/InstallationGuide /InstallationGuide.pdf

2. Simulation on MoS2 monolayer (1) Build your own structure. ① Jobs command window ② The jobs you have already finished ③ The jobs you are going to analyze ④ Analysis window

Find your crystal Unit cell of 3D MoS2

Drag to select right 3 atoms, Press Delete.

Press Ctrl + R: Stretch the unit cell ● Increasing the separation between neighboring layers Press Ctrl + R: (Make the unit cell in the central window)

Center the atoms in the central simulation box The unit cell of 2D MoS2 monolayer

Important! Change your lattice type back into Hexagonal ●Unit cell: the simulation box composes the whole structure. ●Hexagonal: the simulation box repeats infinitely in Hexagonal route.

(2) Optimize your structure Go to Script Generator

Due to 2D nature in A,B direction K-point Sampling nA=9 nB=9 nC=1, Due to 2D nature in A,B direction Spin: Unpolarized (No energy level separation) Polarized (The energy level separation in valence band)

Do not constrain cell Save your Job

Run it!

(3) Change your unit cell ● Changing unit cell is for better later simulation and results display. ● Changing unit cell do not means changing the lattice structure. Drag your structure into Builder

Change the supercell (Coordinate vector) ●Make it into rectangular coordinate Swap Axes ●Make it more transparent appearance

Center your atoms in the simulation box Press Ctrl + R:

Important! Change your lattice type into Simple orthorhombic ● Simple orthorhombic is for rectangular box.

(4) Simulate your structure Go to Script Generator Add your items. ● Physical properties you are interested.

K-point Sampling nA=1 nB=9 nC=9, Due to 2D nature in B, C direction

K space route: G, Y, Z, G ● G(0,0,0) ● Y(0,1,0) ● Z(0,0,1) ● Do not add X(1,0,0) due to 2D nature in B,C direction

(5) See your simulation results!

Band structure for monolayer MoS2 Density of states for monolayer MoS2

Chemical potential for monolayer MoS2 Electron density for monolayer MoS2

Effective mass

Effective mass Direction: [0, 1, 0]: zigzag [0, 0, 1]: armchair Relative band index: 0: Electrons -1: Holes Drag your nc file into Effective Mass Box

3. IV curve for MoS2 nanoribbon Repeat unit cell 5×9 ● Make it into nanoribbon Add electrodes

Device structure Go to Script Generator

Choose: New Calculator Transmission Spectrum 1st New Calculator: K-points 1×1×50 Bias voltage: 0.01V

Increase Maximum steps to 1000 ● Assure Converging

Set the boundary condition: Periodic Dirichlet: The electric potential continues at the boundary Neumann: The electric field continues at the boundary

For the 2ND New Calculator, set the same parameters but different electrode voltage: 0.02V Save and Run!

See your results Your results in Window 3 See your results

Drag your nc file into I-V Curve box

Your results: ● Transmission Spectrum ● Current vs. Voltage Calculated by non-equilibrium Greens function (NEGF)

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 2602