1. Techniques of synthesizing mono-layer Molybdenum Sulfide (MoS 2 ) Wu Kam Lam

2. What is Molybdenum Sulfide? A member of transition metal dichalcogenide (TMD) Layered structure similar to graphite. Normally appear in bulk form. Indirect band gap of 1.2eV S Mo Bulk MoS 2 Atomic structure

3. Attractiveness of Mono-layer MoS 2 2-Dimensional (2D) material with 0.8nm thickness Direct band gap of 1.8eV (no band gap in graphene) Application on electronics and photonic devices Consume 100,000 times less energy than silicon transistor in off state. Synthesis of wafer scale mono-layer MoS 2 is still challenging. Mono-layer MoS 2 Schematic of MoS 2 FET

4. Synthesis Techniques Top – down approach Mechanical Exfoliation Chemical intercalation Bottom – up approach Chemical Vapor deposition

5. Mechanical Exfoliation

6. Optical image SEM imageAFM image

7. Chemical intercalation LiPF 6 electrolyte

8. Suspension of layered MoS 2 in solvent Thin film from vacuum filtration of suspension Suspension of layered MoS 2 in water

9. Chemical Vapor deposition Gas Exhaust Gas Inlet(Ar) Quartz tube Furnace MoO3 S

11. Raman Characterization Raman shift: 19cm -1

12. Question?