VIRTUAL NANOLAB BY QUANTUMWISE Presentation by Sheng Yu

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

Outline: 1. Download and install Virtual Nano. Lab 2. Mo. S 2 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 Mo. S 2 nanoribbon

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

2. DOWNLOAD 3. Installation

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

2. Simulation on Mo. S 2 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 3 D Mo. S 2

Drag to select right 3 atoms, Press Delete.

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 2 D Mo. S 2 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

K-point Sampling n. A=9 n. B=9 n. C=1, Due to 2 D 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 n. A=1 n. B=9 n. C=9, Due to 2 D 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 2 D nature in B, C direction

(5) See your simulation results!

Band structure for monolayer Mo. S 2 Density of states for monolayer Mo. S 2

Chemical potential for monolayer Mo. S 2 Electron density for monolayer Mo. S 2

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 Mo. S 2 nanoribbon Repeat unit cell 5× 9 ● Make it into nanoribbon Add electrodes

Device structure Go to Script Generator

Choose: 1. New Calculator 2. Transmission Spectrum 3. New Calculator 4. Transmission Spectrum 1 st New Calculator: K-points 1× 1× 50 Bias voltage: 0. 01 V

Increase Maximum steps to 1000 ● Assure Converging

Set the boundary condition: 1. Periodic 2. Dirichlet: The electric potential continues at the boundary 3. Neumann: The electric field continues at the boundary

For the 2 ND New Calculator, set the same parameters but different electrode voltage: 0. 02 V 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 Mo. S 2: 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: syu 12@gmu. edu Phone number: 7036470780 Engineering Building 2602