JUN YAN UNIVERSITY OF MASSACHUSETTS AMHERST

1. SCIENCE OF TWO DIMENSIONAL MATERIALS JUN YAN UNIVERSITY OF MASSACHUSETTS AMHERST 2015 SUMMER INSTITUE ON NANOSCIENCE

2. A reminder of oleic acid molecule Non-polar end of oleic acid molecule: hydrophobic 1.97 nm Polar end of oleic acid molecule: hydrophilic Water molecules in a tray. Water molecule (polar)

3. From nano to sub-nano 1.97 nm

4. From nano to sub-nano 120º 120º 120º Benzene molecule: a very thin and flat disk! The thickness is less than 1 nm – sub-nano!

5. Graphene!

6. Graphene is a single atomic sheet of graphite Layered structure of graphite Carbon atomic layers slide with respect to each other under shear force during writing 0.335nm Writing makes graphene: a single atomic layer of graphite!

7. 100μm 100μm How do we make graphene? graphite Scotch tape Silicon chip

8. 2010: Nobel award over flake of carbon Andre Geim Konstantin Novoselov

9. How to make large size graphene? Chemical vapor deposition: breaking the methane (CH4) apart at high temperature! ~1000 Cº Samsung, Korea

10. Flexible touch screen Tensile strain 18.7% Graphene for flexible touch screen Corrosion resistant Electrical conductive and mechanically flexible and robust In salt water 3.5% NaCl

11. Exercise: how much graphene do we need to cover the empire state building with graphene touch screen?

12. 100μm 100μm See graphene By atomic force microscope By optical microscope By eye

13. How to see the carbon atoms in graphene? TEM image of graphene Transmission electron microscope

14. ‘Seeing’ the carbon atoms of graphene Scanning tunneling microscope STM images Brian LeRoy U. Arizona Joe Strocio NIST

15. Exercise: how much graphene do we need to cover the surface of the empire state building?

16. Exercise: how much graphene do we need to cover the surface of the empire state building? 1st task: find the density of carbon atoms, i.e. number of carbon atoms per unit area Observation: periodicity! (property of a crystal)

17. Exercise: how much graphene do we need to cover the surface of the empire state building? Let’s start from one hexagon: How many carbon atoms are there in each hexagon? What is the area of each hexagon? Next the empire state building: Height: 381 m; length: 129.2 m; width: 57 m What is its surface area (excluding the bottom surface)?

18. Exercise: how much graphene do we need to cover the surface of the empire state building? How many carbon atoms do we need? = Consider carbon atoms with 6 protons and 6 neutrons (1 mol) carbon atoms weigh 12 gram The amount of graphene we need is:

19. 2D materials beyond graphene: Boron nitride Graphene Boron atom Carbon atom Nitrogen atom yes yes 2D? no yes Conducts electricity?

20. 2D materials beyond graphene: Boron nitride Graphene Boron atom Carbon atom Nitrogen atom yes yes 2D? no yes Conducts electricity? Very different properties!

21. Another 2D materials: MoS2 Dry lubricant Also a 2D material, each unit has three atomic layers, with molybdenum sandwiched by sulfur atoms.

22. Another 2D materials: MoS2 Sample produced by the ‘scotch tape method’ Electrical property? Occurs in nature Single layer MoS2 Between graphene and boron nitride. Multi-layer MoS2 Si/SiO2 substrate

23. The 2D zoo Lasagna

24. The 2D zoo Atomic lasagna

25. Having fun with 2D materials Moire patterns as can be seen in STM measurements. Electrical measurement of graphene on boron nitride. Light emission diode made from MoS2-WSe2 atomic stacks. B. Leroy, Arizona C. Dean, Columbia X. Duan, UCLA

26. Thank you!